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L122 .x. pr. ... .2; HUHJIJ.HII..V..CV¢ I..v1. ..I . g . .. .rfio. tvfllto nfla. .1. 2 l2. IllllllilHIillilllHllllllllllHllIllilllllllllllllllillllli 3 1293 0157064 This is to certify that the dissertation entitled Field Specific Nitrogen Fertilizer Requirement for Sugarbeet (Beta Vulgaris L.) Grown on a Misteguay Silty Clay Soil in Michigan presented by Gladis M. Zinati has been accepted towards fulfillment of the requirements for Ph.D. degree in Crop_and Soil Sciences Owe. 9W Major professor Date 98/201 1997 MSU is an Affirmative Action /Equal Opportunity Institution 0- 12771 LIBRARY Mlohlgen State Unlverelty ‘ PLACE IN RETURN BOX to remove this checkout from your record. TO AVOID FINES return on or bdore date due. DATE DUE DATE DUE DATE DUE L ll IL I L l -L_J__J Ll II II I MSU Is An Afflnnetlve Aotlm/Equel Opportunity lnetltwon W FIELD SPECIFIC NITROGEN FERTILIZER REQUIREMENT FOR SUGARBEET (BETA VULGARIS L.) GROWN ON A MISTEGUAY SILTY CLAY SOIL IN MICHIGAN By Gladis M. Zinati A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Crop and Soil Sciences Department 1997 Copyright by Gladis M. Zinati 1997 ABSTRACT FIELD SPECIFIC NITROGEN FERTILIZER REQUIREMENT FOR SUGARBEET (BETA VULGARIS L.) GROWN ON A MISTEGUAY SILTY CLAY SOIL IN MICHIGAN By Gladis M. Zinati Optimum and economic sugarbeet production without polluting the environment requires an accurate estimate of the fertilizer N required. The main goal of this study was to develop a model that predicts N fertilizer needs by rain-fed sugarbeet grown on a Misteguay silty clay (fine, illitic (calcareous), mesic, Aeric Endoaquent) soil. In the development of the model temporal and spatial distribution of 1’N in the soil and temporal pattern of N uptake were measured. Long term aerobic laboratory incubation studies were conducted to measure cumulative net N mineralization and hence to predict cumulative net N mineralization in the field. Models predicting daily soil-water balance, daily N leached and daily uptake were developed. Root yields and quality parameters as afl'ected by N fertilizer rates were evaluated. Nitrogen fertilizer efliciency was determined. Mineral N concentration was highest in the 30 cm depth afier l-week after application. At the point of application, atom % l’N excess declined with time at all depths. Ten cm lateral movement of the tracer 1’N from point of injection was detected at 75 cm and 120 cm deep at 4-weeks after application. Nitrogen uptake and 1’N uptake by sugarbeet from various depths followed a typical S-shaped pattern. Percent N derived from the tracer as well as N uptake by sugarbeet were recovered from all depths but most efi‘ectively from the top 30 cm depth. Data from the cumulative net N mineralization (Na) in laboratory incubation was fitted to linear and exponential models. Rates of mineralization in both models were adjusted for field air temperatures and values of NIn were corrected to soil moisture (W). Predicted cumulative net N mineralizations in the field were 92.9 and 120 kg ha" for 1993 and 1994 growing seasons, respectively. Estimated amounts of mineral N leached were 6.9 kg ha" for 1993 and 35.7 kg ha" for 1994. Both models predicted the field curmlative net N mineralized (M) well in both years. Root yield and recoverable sugar per hectare increased significantly as N rates increased reaching a maximum at 134 kg N ha". Recoverable sucrose per megagram, % sucrose and clear juice purity (CJP) decreased with increased N rates applied in both seasons. Nitrogen fertilizer needs model took the form: N; = [Nup(opt) - e,,' (N, + Nmm)]/ef. Nap (opt) was higher (217 kg ha'l) in 1994 than that in 1994 (178 kg ha'l). e". was 0.83 in 1993 whereas 0.65 in 1994. e; was 0.62 in 1993 and 0.82 in 1994. N,...-,. was 43.9 and 55.3 kg ha" in 1993 and 1994, respectively. This work suggests that for optimum returns N fertilizer requirement for sugarbeet, N], is 103 kg ha'1 in moderate weather years and 126 kg ha’1 in wet or humid years. DEDICATION Since I was a little girl I always had the feeling that I will discover something very important and precious. Years passed, I grew up and that feeling never left me. I did not know what I will discover but I kept looking. I traveled thousands miles. I left my home country, Lebanon, in 1990 to pursue a PhD. degree in Crop and Soil Sciences at Michigan State University. Evidently, I found that I was not only working towards the degree but also searching for what I should discover. Finally, I found the most precious, priceless treasure I was looking for. I found THE TRUTH I AM WHO I AM Dear Lord, I dedicate this piece of work to YOU- ALMIGHTY. For there is no one in this universe would give me what you give me and accept me as I am. YOU are with me fi'om the beginning of my life, YOU protect me and nurture me with YOUR Love and Kindness. YOU never leave me even when I leave YOU. YOU love me unconditionally, bless me with Knowledge, Wisdom, Health, Wealth and Protection. YOU are so gentle and never force yourself on me, but YOU let me know YOU, taste YOU and accept YOU with my own free will. My Lord, my heavenly Father, I thank YOU for teaching me Forgiveness, Love, Patience, Obedience, Joy and above all Trusting in YOU. YOU give me eyes to see and ears to hear THE TRUTH. YOU let me understand who I am and why I am here on earth. Thank YOU for always BEING with me, surrounding me with YOUR Holy Angels and for my Guardian Angel Leelayo who all minister to me. My God, finding YOU is a treasure. May YOU Lord continue with me to submit myself to YOU completely with all my mind and all my heart. To be YOUR “Follower” is what I am aiming for. It is a title that I would be proud to carry and be known for. With proud, Lord I dedicate this work to YOU and hope it will be a doorway to Eternity. ACKNOWLEDGMENT “Tomorrow is the first day of the rest of your life, what do you want to do?”, Dr. Christenson said to me one day. These words had deep meaning and were the turning point in my life. I am indebted to you, Dr. Donald Christenson, my advisor and committee member, for your mentoring, patience, moral and financial support, time and input you showed during the years I worked with you. I am thankful for my committee members: Dr. Boyd Ellis, Dr. Darryl Wamcke and Dr. Irvin Widders for their time, effort and interest throughout the completion of my dissertation. My gratitude to Dr. Dave Harris who was the raw model for patience, kindness and simplicity. Thank you for the unlimited hours of analytical and technical support and for training me to use the mass spectrophotometer for this project. I am also thankful to Dr. Joe Ritchie for helping me on the water balance model that was an integral part of the project. I am grateful to Dr. Dave Douches and Dr. Ken Sink for giving me the wonderful opportunity to learn the plant cellular and molecular techniques that were taught in their course. Special thanks to Mr. Calvin Bricker, Mr. Lee Siler and Mr. Rick Schmenk for the hundreds of hours of technical support in the field, barn and laboratory. The completion of this dissertation would not have been possible without the financial support provided by: 0 Michigan Sugar Company. 0 Monitor Sugar Company. 0 Doctoral Dissertation Completion Fellowship from the Graduate School, Deans Oflice of Agriculture, Department of Crop and Soil Sciences and Ofice of International Students and Scholars, Michigan State University. 0 W. B. and Candace Thoman Fellowship, Michigan State University. 0 My Family; Graduate School and Office of International Students and Scholars, Michigan State University for Emergency Funding. I owe special thanks to my parents, brothers and sisters for their, love, kindness, sincerity, encouragement, moral and financial support. I also owe special thanks to all fiiends who stood by me in good and bad times, to the wonderful people in my life, especially Rabi Mohtar for his sincere friendship and encouragement; Ahmed Mitkis for his emotional and moral support, inspiration, for challenging me and being my mirror; and Carlos Garcia Salazar for his unconditional fi-iendship; moral and spiritual support. vii TABLE OF CONTENTS LIST OF TABLES ......................................................................................................... xi LIST OF FIGURES ...................................................................................................... xiii CHAPTER] GENERAL INTRODUCTION ........................................................................................ 1 Introduction ................................................................................................................. 1 List of References ........................................................................................................ 5 CHAPTER 2 TEMPORAL AND SPATIAL DISTRIBUTION OF 1’N TRACER AND TEMPORAL PATTERN or l’N UPTAKE BY SUGARBEET FROM VARIOUS DEPTHS ....................................................................................................... 6 Introduction ................................................................................................................. 6 Materials and Methods ............................................................................................... 10 Study Site ............................................................................................................... 10 Cultural Practices .................................................................................................... 10 Temporal and Spatial Distribution of 1’N in Soil ....................................................... 10 Temporal Pattern of N Uptake by Sugarbeet ........................................................... 12 Plant and Soil Processing and Analysis .................................................................... 12 Soil preparation and analysis ................................................................................ 12 Plant processing and analysis ................................................................................ 14 Results and Discussion ............................................................................................... 15 Temporal and Spatial Distribution of 1’N in Soil ....................................................... 15 Temporal Pattern of N Uptake by Sugarbeet ........................................................... 16 Summary .................................................................................................................... 25 List of References ....................................................................................................... 26 CHAPTER 3 ESTIMATION OF CUMULATIVE NET N MINERALIZATION IN THE FIELD FROM A LABORATORY INCUBATION STUDY ............................................................ 28 Introduction ............................................................................................................... 28 Nitrogen Mineralization Potential (No) ..................................................................... 33 viii Nitrogen Mineralization Rate (k) ............................................................................. 36 Soil N Losses .......................................................................................................... 40 Nitrogen Mineralization Prediction Models .............................................................. 41 Materials and Methods ............................................................................................... 47 Field Experiment ..................................................................................................... 47 Water Balance Model .............................................................................................. 48 Long-Term Aerobic Incubation Experiment ............................................................. 48 N Mineralization Models ......................................................................................... 49 Prediction of N Mineralized in the Field ................................................................... 50 Prediction of Soil Mineral N Losses ......................................................................... 51 Prediction of Atom % 15N in Mineral N ................................................................... 54 Results and Discussion ............................................................................................... 55 Incubation Experiment ............................................................................................ 55 Field Experiment ..................................................................................................... 55 Prediction of Field Cumulative Net N Mineralization ............................................... 68 Prediction of Leached Soil Mineral N ...................................................................... 7O Prediction of Atom % 15N in Mineral N ................................................................... 71 Summary .................................................................................................................... 76 List of References ....................................................................................................... 80 CHAPTER 4 PREDICTIN G NITROGEN FERTILIZER NEEDS FOR SUGARBEET GROWN ON MISTEGUAY SILTY CLAY SOIL IN MICHIGAN ............................... 89 Introduction ............................................................................................................... 89 Nitrogen Recovery Efliciency (NRE) ....................................................................... 90 Models for Estimating N Fertilizer Requirement ...................................................... 93 Materials and Methods ............................................................................................... 95 Root Yield and Quality ............................................................................................ 95 Nitrogen Uptake (N...) ....................................................................................................... 96 Modeling N Fertilizer Needs ............................................................................................. 96 Soil mineral N (Nina and N.) ................................................................................. 97 Predicted field N mineralization ( N.) .................................................................. 97 Plant N uptake at optimum N rate ( Nup(opt)) ....................................................... 97 Fraction of mineral N recovered by plant (e...) ...................................................... 98 Nitrogen fertilizer efliciency (er) ........................................................................... 98 Prediction of N fertilizer rate (Np) ........................................................................ 99 Results and Discussion ............................................................................................... 99 Root Yield and Quality .......................................................................................... 100 Model Variables Determinations ............................................................................ 100 Soil mineral N (Nm and N.) .............................................................................. 100 Predicted field N mineralization (N1) ................................................................... 101 Plant N uptake at optimum N rate (Nap) ............................................................. 101 Fraction of mineral N recovered by plant (em) ..................................................... 109 N recovery efficiency (Cf) ................................................................................... 109 ix Prediction of N fertilizer rate (Nr) ....................................................................... 109 Summary .................................................................................................................. 113 List of References .................................................................................................... 117 CHAPTER 5 SUMMARY AND CONCLUSIONS ........................................................................... 120 Temporal and Spatial Distribution of 1’N in Soil ....................................................... 121 Temporal Pattern of N uptake by Sugarbeet ............................................................. 121 Estimation of Cumulative Net N Mineralization in the Field from a laboratory Incubation Study .............................................................................................. 122 Predicting Nitrogen Fertilizer Needs on Sugarbeet Grown on Misteguay 8th Clay Soil in Michigan ............................................................................................... 124 LIST OF TABLES CHAPTER2 Table 1 - Mineral N concentration (mg kg") at 30, 75 and 120 cm deep on soil samples taken at 1-, 4- and 12-weeks after application on a Misteguay silty clay soil ................................................................................................. 15 CHAPTER 3 Table 1- Predicted field cumulative net N mineralization values afier adjustment for air temperature and soil moisture (W) using linear and exponential models at Q10 2 and 2.2 in 1993 ................................................................................ 69 Table 2 - Predicted field cumulative net N mineralization values afier adjustment for air temperature and soil moisture (W) using linear and exponential models at Q10 2 and 2.2 in 1994 ................................................................................ 69 Table 3 - Predicted soil mineral N leached from 0-45 cm deep during the 1993 and 1994 growing seasons using 2 approaches of estimation ......................... 71 Table 4 - Predicted gross N immobilization rates for 1993 incubation experiment ........ 75 CHAPTER 4 Table l - Root yield, N uptake, recoverable sugar per hectare (RWSH), recoverable sugar per ton (RWST), sucrose and clear juice purity (CJP) of sugarbeet as affected by nitrogen rate on a Misteguay silty clay soil, 1993 ........................................................................................................... 102 Table 2 — Root yield, N uptake, recoverable sugar per hectare (RWSH), recoverable sugar per ton (RWST), sucrose and clear juice purity (CJP) of sugarbeet as affected by nitrogen rate on a Misteguay silty clay soil, 1994 ........................................................................................................... 102 Table 3 - Mass of soil mineral N at 0-45 cm deep in check plots of a Misteguay silty clay soil in 1993 and 1994 growing seasons ......................................... 103 Table 4. Equations and coefficients of determination (r2 or R2) of linear and exponential models of cumulative net N mineralization predicted on check plots of a Misteguay silty clay soil in an aerobic incubation experiment in 1993 ............................................................................................................. 103 Table 5. Predicted and measured model parametrs'l’, Nu, , N. , N., N.., (opt), N;, e. and eat Q10 of 2.0 for 1993 and 1994 growing seasons .............. 104 xii LIST OF FIGURES CHAPTER2 Figure 1 - Schematic diagram of a microplot containing four sugarbeet plants and holes with and without l’N tracer applied in 1991 ........................................... 11 Figure 2 - Schematic diagram of a microplot containing one sugarbeet plant and four holes with 15N tracer applied in 1991 ...................................................... 13 Figure 3 - Atom percent l’N excess in mineral N at the 30 cm depth, 1, 4 and 12 weeks after 15N application on a Misteguay silty clay soil in 1991 ..................... 17 Figure 4 - Atom percent l’N excess in mineral N at the 75 cm depth, 1, 4 and 12 weeks after 15N application on a Misteguay silty clay soil in 1991 ..................... 18 Figure 5 - Atom percent l’N excess in mineral N at the 120 cm depth, 1, 4 and 12 weeks after 1’N application on a Misteguay silty clay soil in 1991 ........... 19 Figure 6 - N uptake by sugarbeet grown on a Misteguay silty clay soil in 1991 ....... 20 Figure 7 - Tracer l’N uptake by sugarbeet grown on a Misteguay silty clay soil in 1991 .............................................................................................................. 21 Figure 8 ~Percent N derived from tracer l’N applied at various depths on a Misteguay silty clay soil in 1991 .............................................................................. 23 Figure 9 - Percent N uptake by sugarbeet from various depths on a Misteguay silty clay soil in 1991 ............................................................................................ 24 CHAPTER 3 Figure 1 - A linear fit of cumulative net N mineralization of laboratory incubated Misteguay silty clay soil samples with time in 1993 ................................ 56 Figure 2 - An exponential fit of cumulative net N mineralization of laboratory incubated Misteguay silty clay soil samples with time in 1994 ................................. 57 xiii Figure 3 - Rainfall during the interval between samplings on a Misteguay silty clay soil during the 1993 growing season ............................................................. 58 Figure 4 - Volumetric moisture content of Misteguay silty clay soil during the 1993 growing season. The vertical line at each data point represents the standard error of the mean .................................................................................. 60 Figure 5 - Rainfall during the interval between samplings on a Misteguay silty clay soil during the 1994 growing season ............................................................. 61 Figure 6 - Volumetric moisture content of Misteguay silty clay soil during the 1994 growing season. The vertical line at each data point represents the standard error of the mean ................................................................................... 62 Figure 7 - Soil mineral N of unfertilized Misteguay silty clay soil during the 1993 growing season. The vertical line at each data point represents the standard error of the mean ................................................................................... 63 Figure 8 - Soil mineral N of unfertilized Misteguay silty clay soil during the 1994 growing season. The vertical line at each data point represents the standard error of the mean ................................................................................... 65 Figure 9 - Predicted cumulative N uptake by sugarbeet grown on unfertilized Misteguay silty clay soil in 1993 .............................................................................. 66 Figure 10 - Predicted cumulative N uptake by sugarbeet grown on unfertilized Misteguay silty clay soil in 1994 .......................................................... 67 Figure 11 - Predicted and measured atom % l’N in mineral N of unfertilized Misteguay silty clay soil samples incubated in 1993 .............................................. 73 Figure 12 - Gross and net N mineralization of unfertilized Misteguay silty clay soil incubated in 1993. ............................................................................... 74 CHAPTER 4 Figure 1 - Recoverable sugar as affected by N fertilizer rate applied in 1993 ........ 105 Figure 2 - Recoverable sugar as affected by N fertilizer rate appied in 1994 ......... 106 Figure 3 - N uptake by sugarbeet as affected by N fertilizer rate applied in 1993 .. 107 Figure 4 - N uptake as affected by N fertilizer rate applied in 1994 ....................... 108 Figure 5 - N recovery efficiency (e) as the slope of the regression line of N uptake as affected by N fertilizer rate applied in 1993 .......................................... 111 xiv Figure 6 - N recovery efliciency(ef) as the slope of the regression line of N uptake as affected by N fertilizer rate applied in 1994 ......................................... 112 Chapter 1 GENERAL INTRODUCTION Nitrogen is an essential constituent of proteins, amides, amino acids, coenzymes, nucleic acids, certain hormones and chlorophyll of plant cells. In sugarbeet (Beta vulgaris L.), N is important in sucrose synthesis and in many reactions involving the utilization of sucrose as an energy source for plant growth and cell maintenance. Insufficient N limits yield while excess N (higher than 180 kg ha“) reduces recoverable sugar by suppressing sucrose concentration and increasing impurities in the sugarbeet juice (Hills and Ulrich, 1971). Decreased root sucrose concentration with increased N application is generally attributed to the tops becoming the dominant photosynthate sink at the expense of the roots. Increased impurities may result from many factors but are generally associated with higher N uptake that increases the nonsucrose, soluble solids (Carter, 1985). Nitrogen taken up by sugarbeet during the season comes fi'om mineral N present in the spring, N mineralized during the growing season and fertilizer N. Determination of the amount of mineral N and N mineralized during the growing season is essential in designing fertilizer N recommendations which provide adequate but not excessive N. Mineral N can be assessed with routine extraction by M KCl. Estimation of mineralizable N is usually done by conducting a laboratory incubation under standard conditions. However, these types of studies are not readily applicable to routine soil testing for fertilizer recommendations. The manner in which N is mineralized during incubation may follow one of four patterns (Tabatabai and Al-Khafaji, 1980): i) immobilization of N during the initial period of incubation followed by mineralization in the later period; ii) a rate of release that decreases with time; iii) a steady linear release with time over the whole period of incubation, or iv) a rapid release during the first few days followed by a slower linear rate of release. Models describing the latter two patterns have received the most attention in the literature. Obviously, iii above is a linear (zero order) equation and can be fit with linear regression. This model gives a rate of release, but does not give a value understood to be mineralization potential. Addiscott (1983) and Tabatabai and Al-Khafaji (1980) found linear relationships N nrineralized and time. The latter authors reported an average Q10 of 3.0 for N mineralization of some major soil series in Iowa. However, Beauchamp et al. (1986) suggested that Tabatabai’s data showed some curvilinearity during the early stages of incubation. Stanford and Smith (1972) used a first order exponential equation to describe mineralization on a wide range of soils. They used a first-order exponential equation: N = N. (1- exp (-kt)) which estimated mineralizable N with respect to time, rate of mineralization (k) and N mineralizable potential No. Beauchamp et a1. (1986) modified this equation to take into account an “easily” mineralized N fraction (Ne) often seen during the incubation of air dried soil. The model took on the form N = [No - (No- Ne) exp (-kt)], where N, No, k and t are defined as before and Ne is the N fraction released during the first 7 days of incubation. This N released (Ne) is attributed to microbes killed as a result of drying the soil (Richter et al., 1982). However, Beauchamp et al. (1986) attributed Ne as an experimental artifact and not part of the true No. Consequently, they concluded that their model allowed for the existence of this fraction and thereby gave a better fit of the first order rate model with the experimental data. They firrther suggested that either their model be applied with air-drying pretreatment or freezing or field-moist pretreatments should be considered to provide better accuracy. Using a mass balance approach for evaluating N availability to crops requires measurement of losses as well as assessment of mineralization. Nitrogen may be lost from soil from soil through denitrification, NH3 volatilization, leaching and erosion (Stevenson, 1986). Armstrong et al. (1986) noted that denitrification and leaching may cause loss of NO3-N before it is taken up by the crop. Leaching is generally greatest during cool seasons when precipitation exceeds evaporation when downward movement in summer is restricted to periods of heavy rainfall. The magnitude of NO; leaching is diflicult to estimate and depends on a number of variables, including quantity of N03, amount and time of rainfall, infiltration and percolation rates, evapotranspiration, water holding capacity of the soil and presence of growing plants (Stevenson, 1986). Shaffer et al. (1991) developed a N leaching model that estimates the daily soil N potential for leaching. The model required initial mineral N present and daily estimates of water drained, N mineralization and N uptake by the plant. An accurate estimation of fertilizer N is required for optimum and economic argarbeet production without polluting the environment. This estimation requires prediction of N supply from soil organic matter as well as soil N losses. Models for predicting fertilizer N requirement for use in N recommendations for sugarbeet under Michigan conditions are not yet developed. This study examined field specific N fertilizer requirement for rain-fed sugarbeet grown on a Misteguay silty clay soil in Michigan. Specific objectives of this study were to: 1. deterrrfinethetemporalmrdthespafialdismbufionofappfiedl’Nferfifiza'm micmplots on a Misteguay silty clay soil. 2. determine the temporal uptake of N by sugarbeet from various depths. 3. determine the efficiency of fertilizer recovery using non-isotopic linear regression and isotopic methods. 4. predict cumulative net N mineralization in the field from a long term aerobic laboratory incubation study. 5. predict N fertilizer needs by sugarbeet grown under rain-fed conditions on a Misteguay silty clay soil in Michigan utilizing: a. daily soil-water balance b. daily soil N leached c. daily N uptake by sugarbeet d. daily net N mineralization. LIST OF REFERENCES Addiscott, T. M. 1983. Kinetics and temperature relationships of mineralization and nitrification in Rotharnstead soils with different cropping histories. J. Soil Sci. 34:343- 353. Armstrong, M. J., G. F. Milford, T. O. Pocock, P. I. last and W. Day. 1986. The dynamics of nitrogen uptake and its remobilization during the growth of sugar beet. J. Agric. Sci. Camb. 107:145-154. Beauchamp, E. G., W. D. Reynolds, D. Brasche—Villeneuve, K. Kirby. 1986. Nitrogen mineralization kinetics with different soil pretreatments and cropping history. Soil Sci. Soc. Am. J. 50: 1478-1483. Carter, J. N. 1985. Potassium and sodium uptake effects on sucrose concentration and quality of sugarbeet roots. J. Am. Soc. Sugar Beet Technol. 23:183-201. Hills, F. J. and A. Ulrich. 1971. Nitrogen nutrition. p. 111-135. In Johnson, R T., J. T. Alexander, G. E. Rush and G. R. Hawkes (ed.) Advances in sugarbeet production: Principles and practices. The Iowa State University Press. Ames, Iowa. Ritcher, J ., A Nuske, W. Habenicht and J. Bauer. 1982. Optimized N-mineralization parameters of loess soils from incubation experiments. Plant and Soil 68: 379-3 88. Salter, R M. and T. C. Green. 1933. Factors affecting the accumulation and loss of nitrogen and organic carbon in cropped soils. J. Am. Soc. Agron. 25: 622-630. Stanford, G. and S. J. Smith. 1972. Nitrogen mineralization potentials of soils. Soil Sci. Soc. Am Proc. 36:465-472. Stevenson, F. J. 1986. The nitrogen cycle in soil: Global and ecological aspects. p. 132-168. In Cycles of soil carbon, nitrogen, phosphorus, sulfur, micronutlients. John Wiley and Sons, New York. Tabatabai, M. A and A A Al-Khafaji. 1980. Comparison of nitrogen and sulfirr mineralization in soils. Soil Sci. Soc. Am. J. 44:1000-1006. Chapter 2 TEMPORAL AND SPATIAL DISTRIBUTION OF "N TRACER AND TEMPORAL PATTERN OF L"N UPTAKE BY SUGARBEET FROM VARIOUS DEPTHS Assessment of nitrogen fertilizer needs for sugarbeet requires a knowledge of the amount of N available from the soil profile and specially below the plow layer. Sander (1974) suggested that nitrate in the soil profile occurs primarily from unused or carryover N fertilizer. The amount of N released from the more stable organic matter complex in soils varies greatly from soil to soil depending on past cropping history, weather and other factors. Furthermore, the amount of NO3-N that accumulates will vary greatly depending on precipitation, irrigation practices and application methods. Armstrong et al. (1986) mentioned that the contributions of residual mineral N and mineralized N to the total N uptake by sugarbeet vary considerably with soil type and season. Kaiser and Heinemeyer (1993) found that the soil surface layer is the most biologically active site for agricultural ecosystem processes. Soil near the surface is exposed to the largest nutrient and energy inputs and undergoes larger diurnal and seasonal changes in temperature and moisture than the deeper underlying soil. These factors have a considerable influence on soil microorganisms. We further need to know the temporal distribution of this uptake since excessive N late in the season may be very detrimental to the final yield of sugar. Baldwin and Davis (1966) noted that excess N fertilizer applied would result in a lower sucrose content. Studies by Last and Haggard (1985) indicated that irrigated sugar beets had reduced amino-N concentrations which could be attributed to moist soil conditions that allowed N to be taken up and used for growth during summer. However, in unirrigated crops N was taken up later in the growing season and was stored in the root as amino nitrogen. Anderson et al. (1972), utilizing ”N, showed that sugarbeet took up more N from deeper soil layers if the surface soil N03 concentration was low. They also found out that sugarbeet could efl‘ectively use N03-N from depths greater than 135 cm. They indicated that N fertilization management must be optimized to maximize sucrose content as well as root biomass yield. Waem and Persson (1982) examined N uptake by oats grown on heavy clay soil in Uppsala, Sweden, using l’N labeled NO3-N that was placed on soil surface and at depths of 25,‘ 70 and 110 cm. Their results showed that the above ground portion of oat plants removed l’N labeled N from 25 cm deep one month after sowing, from 70 cm seven weeks after sowing and from 110 cm deep before harvest. About 80 percent of labeled nitrogen placed on the surface and at a 25 cm depth was recovered in the above ground portion of the plants at harvest. Sixty and 45 percent of nitrogen placed at a depth of 70 cm and 110 cm was recovered at harvest, respectively. As described by Linden (1981 and 1982), the utilization of mineral N in deeper layers in the soil profile depends on root depth which is closely connected with the soil structure in the horizons in question. Also when uptake has ceased, soil mineral N reserves usually were depleted down to one meter in loam and clay soils. He also reported that for winter wheat and sugarbeet, N has often been utilized down to 1.5m. Linden (1980) found that the largest concentrations of NILNOg were in the top soil (usually 5-20 kg ha'1 within 0-20 cm). In the subsoil there were generally small amounts of NH4N03 which didn’t vary appreciably with depth. Ventura and Yoshida (1978) found very little movement of 1’N labeled NIL-N from the site of placement. They concluded that the availability of N fi'om point-placed fertilizer was restricted mostly to the rice plants adjacent to the point of placement. Panda et al. (1988) studied the vertical and horizontal movement of N (100 kg ha") in flooded soils. They applied N as broadcast urea or urea supergranules placed near the rice transplants. The surface- broadcast N was found mostly in the top 5 cm of soil and there was a small vertical movement of N to 5-10 cm. With broadcast applications, the NH4- N concentration was 40-68 mg kg'1 soil in the top 0-5 cm of soil within the first 3-6 days, decreased at a faster rate fiom the 6'” to 12"I day and then at a slower rate up to the 32"" day. With point placement of l-g urea granules, the fertilizer N was found mostly at the 5-10 cm depth and within 2.5 cm horizontal distance from point of placement, compared with 5 cm for 2.5-g granules. Barber (1962) and Savant and De Datta (1979) reported that the transport of NFL in soil was a diffusion-controlled process. Reddy et al. (1980) reported that movement of NIL-N was along a concentration gradient, but the diffusion coefficient was very low compared with nitrate. This might explain the slight upward and downward or lateral movement of N fi'om point-placed urea supergranules. Any latter movement was proportional to the amount applied. The disappearance of NIL-N from the region of placement might be attributed mainly to plant uptake but might also be due to diffusion, convection and fixation by clay minerals (Savant et al., 1982). Owing to the limited mobility of N fi'om point-placed urea supergranules, it would be necessary to ensure uniformity of placement for the benefit of the rice crop. Savant and De Datta (1980) studied the in-situ distribution patterns of NIL-N and 1’N uptake by wetland rice in a dry season. Two-gram urea supergranules were placed at 5-, 10-, and 15-cm' soil depths in wetland rice plots. The ammonium concentration gradients near placement sites showed that the NIL movement was slow and in general, downward > lateral > upward fiom deep placement sites of urea supergranules in a wetland Maahas clay. Ammonium concentrations decreased with time largely due to plant uptake and the 1’N uptake followed the S-shaped pattern. Studying the distribution patterns of 1’N in the soil was accompanied by certain assumptions such as, the tagged N was uniformly mixed with soil and was distributed throughout the layer where the labeled N was applied. The work here is designed to measure the distribution after application at a confined spot. In addition, studying the temporal pattern of N uptake by sugarbeet would aid in knowing when, how much and at what rate the plants were absorbing N from soil. Therefore, the present experiments were designed to study the 1) the temporal and spatial distribution of 1’N tracer applied at difl'erent depths and 2) the temporal pattern of uptake of N by sugarbeet from various application depths. 10 MATERIALS AND METHODS Study Site Studies to determine the dynamics of applied 1"N fertilizer in soil and its uptake by sugarbeet were conducted in 1991 at the Saginaw Valley Bean and Beet Research F arm in Saginaw county, Michigan (43° 4’ N, 84° 6’ W). The soil is classified as a Misteguay silty clay (fine, illitic (calcareous), mesic, Aeric Endoaquent). Cultural Practices In both experiments, the soil was fall plowed to 22 cm depth in 1990. It was tilled once with a field cultivator to 7 cm deep in spring of 1991. Ammonium nitrate (34-0-0) was surface broadcasted to plots at planting time at a rate of 90 kg ha". Sugarbeet (Mono-Hy-E-4) were planted in 71 cm rows on May 3"I of 1991 and thinned to 20 cm within row spacing. Temporal and Spatial Distribution of'5N in Soil Microplots 40.3 x 80.6 cm in size containing 4 sugarbeet plants were established. Seven holes were dug in each microplot using a soil probe of 2 cm diameter. These holes were spaced 10 cm around the two middle sugarbeet plants in each microplot. One month afier planting 10 ml solution of 7 mg of 1’N concentration, as an equimolar of K‘SNO3 and ("Naozsol (99.7% 1’N), was applied in each hole (Figure 1). The 1’N was applied at 30, 75 and 120 cm deep in a randomized complete block design with 4 replications. Subsoil was used to refill the holes upon l’N application. Soil samples with and without 1’N were collected from the south side of the microplot (Figure 1). ll .82 E 35% cocoa 2: Bones wee 55 8.2 v5 353 «89ng Sea wage—co 83828 a we cage 3852mm ._ earn 319.32 0 Zn. use—EB one—em— . 22 5?.» 83mm _ Eu 3 _ o m 0 v 8.2— wEEEam o n O N O u Z. >9 12 These samples were taken fiom 15-45, 60-90 and 105-135 cm depth on the 1‘, 4"I and 12"I week after application. The four adjacent plants in each microplot were harvested in the first week of October of 1991. Soil samples and sugarbeet plants were processed and analyzed as described in plant and soil processing and analysis procedures section. Temporal Pattern of N Uptake by Sugarbeet A second study was conducted to determine the temporal pattern of N uptake by sugarbeet. Ten ml of a solution containing 7 mg of N of an equimolar mixture of K'5N03 and (”NI-LhSO. as 1’N (99.7%) was placed in each of 4 holes dug in microplots containing 1 sugarbeet plant (Figure 2). These holes were spaced 10 cm from the sugarbeet plant. Labeled N, 1"N, was applied one week before each plant sampling. It was applied at the surface, 30, 60, 90, 120 and 150 cm depth in a randomized complete block design with 6 replications. The surface treatment had a metal fi'ame 20 cm x 20 cm installed to a depth of 12 cm. Plant samples were collected 3, 6, 9, 12, 15 and 18 weeks after planting. One plant per microplot per treatment was harvested. The collected plants were processed and analyzed as described below in the following section. Plant and Soil Processing and Analysis Soil samples and plant material were handled and analyzed similarly in all experiments of this chapter and the following studies. I Soil preparation and analysis Soil samples were air-dried, ground to pass through a 2 mm sieve. Ten grams of ground soil was shaken with 50 ml of M KCl (Keeney et a]. 1982) for 1 hour and filtered through a Whatman #5 filter paper. The extracts were split into two parts. One part was 13 .32 e 33% cocoa Z: 55 83: Sea 98 En 838mg one 568 83828 a mo Sewage agom .N 03w:— 339.32 _ E A: _ 0 Zr; :33 mag—om geom— 14 used to analyze for mineral N (NH. and N03) using an Flow Injection Analyzer (Prokopy, 1993). The other part of the extract was used to determine l’N atom °/o on a mass spectrometer. This was achieved by a difi‘using technique presented by Brooks et al. (1989). In this technique Davardas alloy was used to reduce NO3-N in the extracted sample to NIL-N and volatalize it by increasing the solution pH with M30. The ammonium was trapped on a Fe804 impregnated paper disc. At the end of the 7th day of difi‘usion the discs were dried at 65 °C and pelleted in tin capsules for analysis. Plant processing and analysis Sugarbeet plant samples were split into leaf, petiole and root. The leaves and petioles were washed in water, dried at 60 to 65 °C, weighed, ground to pass through a 0.5 mm screen. The fresh weight of each whole root was recorded. A root sub-sample was taken by cutting the whole root in half and scrapping approximately 50 g of beet tissue fi'om the exposed face of the sugarbeet. Root dry weight was calculated fi'om the wet and dry weights of the 50 g subsamples and the fresh weight of the root. Dried sub- samples were ground and saved for analysis. A ground plant sample containing 100 mg of N was pelleted in tin capsule for 15N atom % analysis. 15 RESULTS AND DISCUSSION Temporal and Spatial Distribution of 15N in Soil Mineral N concentration declined at all depths for the 1- and 12- weeks samplings (Table 1). At the 30 cm depth N declined from over 14 mg kg'l to less than 6 mg kg“1 between one and 4 weeks after application. There was no further decline at this depth by week 12. There was a similar decline at 75 cm ranging from 10 mg kg'1 to less than 2 mg kg" between 1- and 12-weeks afier application. The decline with time at 120 cm was less pronounced than at the other depths. Table 1. Mineral N concentration (mg kg") at 30, 75 and 120 cm deep on soil samples taken at 1-, 4- and 12-weeks after application on a Misteguay silty clay soil. Depth (cm) Sampling 30 75 120 1- week 14.22 9.85 6.47 4-weeks 4.28 6.24 4.45 lZ—weeks 5.49 1 .93 2.63 LSD (a: o_os) = 4.043 Atom percent excess one week after application was less in the 30 cm layer than in the lower depths (Figures 3-5). At point of application atom % l5N excess declined 16 with time at all depths (Figures 3-5). This could be attributed to several reactions involving N. Among these were mineralization-immobilization-turnover, leaching, denitrification, fixation in clay minerals and plant uptake. While there are no data to support any one of these pathways, it would seem that any of these mechanisms could play a major role in this decline. One of the objectives of this work was to determine lateral movement of tracer 1’N from point of injection with time. Ten cm lateral movement of "N from point of injection was detected at 75 and 120 cm deep at the 4-weeks afier application sampling (Figures 4 and 5). Temporal Pattern of N Uptake by Sugarbeet Nitrogen uptake curve followed the typical S-shaped pattern for plant grth when total N uptake by sugarbeet from various depths was plotted against time of sampling (Figure 6). The rate of N uptake increased markedly between 3 and 6 weeks after planting and held somewhat constant until 15 weeks after planting when uptake of N was ceased. Fifteen weeks after planting (3"I week of August 1991) marked the period when the sugarbeet began to direct energy to storage of sugar rather than vegetative growth. There was senescence of older leaves and leaf loss due to mechanical damage which might account for the small decline in total N between 15 and 18 weeks. Uptake of ”N was negligible at all depths up to 6 weeks after planting (Figure 7). After that point there was a general increase in the amount of 1’N uptake until the 12 weeks after planting at all depths. Nine weeks after application, the plants picked 1’N from the surface more significantly than deeper depths. Uptake of 1’N reached maximum by the 12'” week after application in the t0p 90 cm soil layer. Although there was a 17 3.83 2 98 v ._ Snow So cm 2: 3 Z 1558 5 335 Z: 3082. 89< .m onE .32 a =8 E0 Ea $525 8 consign 2: 3% 828m 9.83 2 LT 383 v In: 6.8379: z: 55 25 0.0 1 ON I 06. I O6 1 0.x od— [ros u; ssaoxg % mow 18 3.83 N_ 93 v ._ £83 :8 2. 05 “a Z 18%: E 33x0 2: «582. 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This decline could be due to the dry period between July 26 and August 16 (Christenson et al., 1991) and/or the roots were more active in exploring more soil volume at deeper layers than at the top 30 cm layer. In general, uptake from the surface applied 1’N was somewhat greater than for the other depths and there was no significant difl‘erence in the amount of tracer taken up fi'om depths greater than 30 cm after the 2" sampling. Uptake of 1’N by sugarbeet followed the typical S-shaped pattern. This is in agreement with the findings reported by Savant and de Datta (1980) on 1’N uptake by rice. Comparing the patterns total N uptake and 15N uptake we found that they were similar. Percent N derived from tracer l’N applied at various depths was shown in Figure 8. At 3 weeks after planting there was a higher amount derived from the surface with a negligible quantity from the 30 cm depth. From week 6 through week 15 there was a fairly constant amount derived from the surface applied tracer. The amount from the 30 cm depth increased from the 3 week level across weeks 6 through 12. In the last two samplings, there were negligible amount from 30 cm and below. Therefore, sugarbeet plants recovered lsN most effectively from the surface layer throughout the growing season and fi'om the top 30 cm layer between the 2ml and the 4"I samplings. Percent N taken up by sugarbeet from various depths was plotted against time of sampling (Figure 9). N uptake was primarily from the surface after 3 weeks of planting and fiom' the top 30 cm layer at 6 weeks after planting. This pattern continued till end of the season. However, 18 weeks afier planting N uptake was almost equal from each layer. 23 .53 a :8 >26 bum .3358qu a .8 33% 30.53 S 123% Z: .39: 88m 32.3 Z 8083 .w 05$..— méfia 5% £83 So 02- 60 OS- Eo oafi Eocen— Eo em. . Ifiodvnv sure! 3 o- 8.. H (%) 19021 .1. 1110.13 paAtJoq N 24 Scam... .583 508D Econ. 825mm £55 £2 38% .82 5 =8 baa bum >33me .8 23% «no.5? 89a 833mg 3 83% Z 838m 2: n €253 H a 235 m ,2 é - 8 _._ é T 2 1 0w 02 (%) amdn N 25 SUMMARY Results of temporal and spatial distribution of 1’N in soil experiment showed that soil mineral N was highest in the 30 cm depth after l-week afler application. It decreased with time at all depths except at 4-week sampling (Table 1). Ten cm lateral movement of the tracer 1’N from point of injection was detected at deeper depths at 4-weeks after application. Atom % l’N excess in soil declined at all depths with time (Figure 3-5). Results of temporal pattern of N uptake by sugarbeet experiment showed that the total N uptake and 1’N uptake followed a typical S-shaped pattern. Percent N derived from the tracer was recovered from all depths but most effectively from the top 30 cm depth. Percent N uptake by sugarbeet from various depths was mostly from the surface and 30 cm deep. Thus, these results suggest that while sugarbeet recover N from deeper depths, the N available in the top 30 cm is the most important in sugarbeet nutrition. These results, in part, agreed with Anderson et al. (1972) in that N was taken up by sugarbeet plants from deeper depths as 135 cm and with Kaiser and Heinemeyer (1993) in that the soil surface layer is the largest nutrient input to - sugarbeet. LIST OF REFERENCES Anderson, F. N., G. A. Peterson, and R A. Olson. 1972. Uptake patterns of 1’N tagged nitrate by sugar beets as related to soil nitrate level and time. J. Amer. Soc. Sugar Beet Techn. 17:42-48. Armstrong, M., A. Squire and G. Milford. 1986. The nitrogen nutrition of sugarbeet-an approach to better forecasting of nitrogen fertilizer requirement. British SugarBeet Review. 54(1):84-87. Baldwin, C. S., and J. F. Davis. 1966. Effect of time and rate of application of nitrogen and date of harvest on yield and sucrose content of sugar beets. Agron. J. 58:373- 376. Barber, S. A. 1962. A diffusion and mass-flow concept of soil nutrient availability. Soil Sci. 93:39-49. Brooks, P. D., J. ‘M. Stark, B. B. McInteer and J. Preston. 1989. Difi‘usion methods to prepare soil extracts for automated nitrogen-15 analysis. Soil Sci. Soc. Am. J. 53:1707-1711. Christenson, D. R, C. E. Bricker and L. F. Siler. 1991. Introduction and weather. p. 1-7. In 1991 Saginaw Valley Bean and Beet Research Report. Mich. Agric. Exp. Sta. Mich. state Univ. E. Lansing, MI. Kaiser, EA and O. Heinemeyer. 1993. Seasonal variations of soil microbial biomass carbon within the plough layer. Soil Biol. Biochem. 25: 1649-1655. Last, P. and K. Haggard. 1985. Current thoughts on nitrogen growth and quality. British Sugarbeet Review. 53(4):49-53. Linden, B. 1980. Mineral nitrogen in cultivated soils in the Swedish provinces of Halland and Uppland. Division of Soil Fertility, Dept. of Soil Sciences, Swedish University of Agricultural Sciences, Report No. 125, p. 50-53. Linden, B. 1981. Relationships between cultivation practices and the supply of mineral nitrogen in the soil. Royal Swedish Academy of Agriculture and Forestry, Report No. 5, p. 67-123. 26 27 Linden, B. 1982. Movement and distribution of ammonium and nitrate nitrogen in the soil. IV. Influence of N-application technique and precipitation. Studies in field trials. Division of Soil Fertility, Dept. of Soil Sciences, Swedish University of Agricultural Sciences, Report No. 145, p. 69-73. Panda, D. H. S. Sen and S. Patnaik. 1988. Spatial and temporal distribution of nitrogen in a puddled rice soil following application of urea-based fertilizers by different methods. Biol. Fertil. Soils. 6:89-92. Prokopy, W. R 1993. Quick Chem Method l2-lO7-04-1-F. Nitrate in 2M KCl soil extracts. Latchat Instruments. Milwaukee, WI 53218. 13p. Roddy, K. R, W. H. Jr. Patrick and R. E. Phillips. 1980. Evaluation of selected processes controlling nitrogen loss in a flooded soil. Soil Sci. Am. J. 44: 1241-1246. Sander, D. H. 1974. Nitrogen efficiency. Part I: The Central Plains. Fertilizer Solutions. 18:30-36. Savant, N. K. and S. D. De Datta. 1979. Nitrogen patterns from deep placement sites of urea in a wetland rice soil. Soil Sci. Soc. Am. J. 43: 131-134. Savant, N. K., S. D. De Datta and E. T. Craswell. 1982. Distribution patterns of ammonium and 1’N uptake by rice after deep placement of urea supergranules in wetland soil. Soil Sci. Soc. Am. J. 46:567-573. Ventura, W. and T. Yoshida. 1978. Distribution and uptake by rice plants of lsN-labeled ammonium applied in mudballs in paddy soils. Soil Sci. Plant Nutr. 24:473-479. Waern, P. and J. Persson. 1982. Nitrogen uptake by oats fi'om various depths in a heavy clay. Division of Soil Fertility, Dept. of Soil Sciences, Swedish University of Agricultural Sciences, Report No. 146. p.11. Chapter 3 ESTIMATION OF CUMULATIVE NET N NIINERALIZATION IN THE FIELD FROM A LABORATORY INCUBATION STUDY Nmogmfafiliwmgmisanhnponamwpeaofcropproducfionpracfices becauseoftherdafivdyhrgemnoumomequiredbprsmdeobflityindresofl. One of the first steps towards accurate N fertilizer recommendations is the ability to predict the quantity of N mineralized fi'om soil organic matter which may be available for plant uptake. MatusandRodriguez(l994)showedthatNmineralizedduringagrowingseasoncomesfiom soilorganicmatterandrecentorganicinputs. Twotennsneedtobedefirdenriner’alizationandNirnmobilization Nitrogen mineralization is defined as the transformation of organic N to NIL, NH; and N03 ions. The process is performed by heterotrophic soil organisms that utilize nitrogenous organic substances as an energy source. Nitrogen immobilization is defined as the transformation of inorganicN compounds(NH4,NH3,N03,N02)intotheorganicstate. Microorganismsand higherplantsassimilateinorganichytransformingittoorganichonstimentsoftheircells andtissues,thesoilbiomass. Thetwoprocessesworkhoppositedirecfionsbuildingupand breaking down organic matter, respectively. The difi‘erence between the two processes will be a net effect, net mineralization, or net innnobilizatim (Stevenson, 1985). 28 29 Brernner (1965) found that the reliability and reproducrbility ofmethods for measuring soil N mineralization determine their suitability for assessing the potential ability of soils to provide N for crop growth Control of water content during incubation was regarded as a major problem for soils having a wide range in water-holding capacities. Keeney and Bremner (1967) attained optimal water content byadding a constant level ofwater to the incubated soil samples. Stanford (1968) showed the existence of two general pools of organic N in soils. Thefirstpoolisdecomposedrelativelyeasilytlnoughmiaobialaction. Thesecondpool, however, is somewhat resistant to further rapid decomposition and contributes a small proportion of N mineralization during a short-term incubation or even within a cropping season Keeney and Brernner (1966), Hanaway and Ozus (1966) and Comforth (1968) found that both aerobic and anaerobic incubation gave values that con'elated highly with N uptake by corn in the greenhouse (r2 = 0.93 and 0.89, respectively). Similarly, Gasser and Kalernbasa (1976) found a very high correlation (r2 = 0.98) between N mineralized anaerobically (7 days, 40°C)andaerobically, andtheseindexescon’elatedequallywellwithNuptakebyryegrass(r2 = 0.93). Stanford (1982) reported that most of the earlier studies emphasized developing methods of soil N evaluation based on short-term incubation under controlled conditions and calibration with yield responses to field and greenhouse N. Westerrnan and Crothers (1980) found that using a buried polyethylene bag technique had potential for monitoring the soil N-mineralization process during the cropping season and for estimating N uptake by crops. Indigenous available N is derived mainly from mineralization of soil organic matter (Bieder’oeck et al., 1984). It has been fi'equently observed that N mineralization is lower in 30 fine-textured soils than in coarse-textured soils (Van Veen et al., 1985; Cartroux et al., 1975, Hassink, 1994). In addition, Bonde and Rosswall (1987); Bonde et al. (1988) and Clay and Clapp (1990) have reported increased N mineralization in soils supplied with fertilizer. When fertilizerNisaddedtosoil,itinteractswiththeindigenoussoileometimesincreasingthe mineralization of soil N, a phenomenon known as “priming effect” (Westerman and Kurtz, 1974, Domaar, 1975). Allison (1966), Azarn et al. (1991) and Jenkinson et al. (1985) also showedhpdemaimmBMusinghraeasingamoWsoffafilizaNmaeasedtheamoum ofaddedNimmobilizedinthesoil. AnincreaseintheamountofsoilNintheharvested crop has not always been evident. Coleman et al. (1983) showed that soil microbes play a key role inmineralization andirmnobifizafionprocessesbecauseofflreirabihtytosa'veasaswrcemd sink of soil nutrients and as a "driving force" of nutrient availability. Ammonium rather than NOgisflnNsomcepmfmedbynnamrgamgnsmthehmnobflimfionreacfionsinsofl (Gainey, 1936; Rice and Tiedje, 1989). Nielsen and Jensen (1986) postulated microbial immobilization as the main process explaining the disappearance of N soon after fertilizer application. Similarly, Messier et al. (1979) found that fertilizer N considered to be immobilized at the beginning of the growing seasonstartedtoremineralizelaterduringtheseason Alexanderetal. (1977) foundthatN immobilizationinsoilresultsfrom microbial assimilation ofNH4andN03 intoproteins, nucleic acids and other organic complexes contained within microbial cells. Only a small fi'action (< 15%) of the N immobilized in organic forms usually becomes available to plants from one growing season to the next (Stevenson, 1986). Stanford et al. (1974) showed that short term N mineralimtion may be heavily influenced by microbial biomass and recently incorporated residues relative to mineralimble 31 fi'actionsofsoilorganicN. ThepresenceofhighCeratioresiduealsoafl‘ectsthenet mineralization that occurs in short-term incubations (Chichester et al., 1975). Fredrickson et al. (1982) showed that crop residues with a wide C:N ratio, when mixed with the soil, immobilize inorganic N fi'om both fertilizer and soil sources. Studies by Wagger et al. (1985) showed that 15%ofwheat residueNand33% ofsorglmmresiduereremineralizedafieronecropping season Nanfinaafizafiondiflermcesmngflleseaopredduesnmybeamihnedtobofllflre C:Nratioandchemicalcompositionoftheseplantmaterials. Soiltextureandtheadditionof fertilizer N influenced the initial rate ofmineralimtion, particularly with wheat residue. Power and Doran (1988) indicated that N contained in crop residues can contribute a significant amountothothenextcropandresiduesfiomleguminouscropsoflencontribute substantially more than nonleguminous crops. The extent of decomposition of organic compoundsinsoilisgreaterwithhigherC mineralizationrateasreportedbyNyhan (1976) and Roper (1985) or with higher temperature (Pal et al., 1975; Kralova et al., 1980 and Donnelly et al., 1990). Norman et al. (1990) found that in soils where residues with low C:N ratios were appliedflrerewaslessNrecoveredfiomthesoilorganicfiactionatharvest. Thiswas accompanied by larger amounts of N mineralized fi'om residue. Kanamori and Yasuda (1979) investigated the mineralimtion and immobilization of tracer N (K"Nos) applied to soil togetherwithtwotypesoforganic matters. They comparedthe decomposition rates ofadded herbaceole organic matter (e.g. rice straw and peat moss) vs. those of woody organic matter (sawdust and bark) in an incubation experiment for three months at 30 °C. With C:N ratio of 56, 44, 268 and 579 the decomposition rates were 41, 5, 7 and 5% for rice straw, peat moss, softwood-sawdust and softwood-bark, respectively. The data showed that the peat moss and 32 barkwerehighlyresistanttotheactionofmicroorganisms. Irmnobilizationofoertilizer incubatedwith organicmatterwasquite slow. KirkhamandBartholomew (1954 and 1955) derived theoretical equations for following nutrient transformations in soil using tracer data. hunobiflnfionofNfiomahomogenoushlorgachpooluuowhichhbdethadbeen addedandmineralizationofNintothepoolwereused. Theauthorsmadethreeassumptionsin theirworkforfindhganalyficalsolufionstoflredifl‘erenfialequafions:(i)bothisotopesofNH4 andNogbdmveflwsmnemsoiHfiflmmbflizedhbdedhmrgachisnmwmmmdand (fii)ratesofnnmobflizafionmdnunaafimfionmemnstamdunngthehuavalbetwew successive measurements. The differential equation derived for calculation of gross immobilizationwasziAt = (AT,-AT2)[ln(ALt/ALz)/(ln(AT1/AT2)] whereiAtisthegross irmnobilinfionduringanintervalfime,AT1isflretotalamomnoflabeledandunlabeledNIL-N atstartofintervaltime,AT2isthetotalamountoflabeledandunlabeledNIL-Natendof irrtervalfimeALlisthelabeledNI-Is-Natstartofintervaltimeand AinsthelabeledNHs-Nat end of interval. Also, gross immobilization can be calculated as the difl‘erence of gross mineralizationfiomnetmineralization. The efl'ects of temperature and moisture factors on N mineralization and soil respirationhavebeenstudied simultaneouslyandseveralresearchersfoundthatthereare interactions betweenthesetwo factors (\Vddungetal, 1975;KowalenkoandCameron, 1976 andCassman ande 1980). However, Kladivko andKeeney (1987) indicated that soil N mineralization is not governed by temperature and moisture interactions. Ellert and Bettany (1992)mdicatedfluthunadizafiothhmmdividudgrowmgseasomnnybenmm sensitive tofluctuationsinmoistureandtemperaturethanitistothesizeofthemineralimblepool. 33 Gesteletal. (1993) concludedthatsoildryingandrewetting promotedtheturnover ofC daivedfiomaddedpMmataialmdflmtflfisinaeasethydmgwasmainlydmto enhanced turnover of microbial products. Smithetal.(1994)indicatedthatthedegreetowhichplantscanextractfixedNE dependedontheextenttowhichtheylowerNIrIaanchoncentrationsinthevicinityofthe roots. maddifiomtheirrewhsindicatedrdafivelyfitdefixedNILwasrdeasedusing conventional laboratory available N indexes. Further research needs to focus on quantifying the degree to which fixed NH4 is available under actual crop growth conditions. Such infonnationwouldhelpestablishwhetherfixechreditsneedtobeusedinconjunctionwith soil N tests. Nitrogen Mineral'uation Potential (N .) Stanford and Smith (1972) presented the concept of soil N mineralization potential, No. No is a definable soil characteristic which may be of value in estimating N supplying capacities of soils under specified environmental conditions. Moreover, No provided a common basis for evaluating various chemical and biological availability indexes under a broad range of soil conditions for making quantitative estimates of N mineralization in the field. Mineralization potential was estimated from the cumulative amounts of N mineralized under optimal conditions of soil water and temperature based on the assumption that N mineralization obeyed the first-order kinetics’ equation: log (No - N.) = log No -lrt/2.303. N. denotes the cumulative amount of N mineralized during a specified period of incubation, i, and k is the rate constant. 34 Gianello and Bremner (1986) and Smith and Stanford (1971) showed that soil organic nmuawasmtasgoodanieammofpotaifiaflyavaihbleNassomediarficalemwfion methods. CabreraandKissel(l988a) showedthatNmimralizationpotentialwasclosely rdatedtototalanninnoforgachmidcmsoflabtnofliastudiesslmwedmmch relationship (TabatabaiandAl-Khafaji, 1980). Carlyleetal. (1990) identified organicPasan usefill index of potentially mineralizable N for sandy soils. Simard and N'dayegamiye (1993) daunfimdflnNnfinaalimfionpotaififlmflmthamficalnwddstnpropalydesmbe fliedynamicsofdiemineralizafionprocessinZOmeadowsoflsfiomQuebec. Thecumulative mineralization curves inmostsoilswerechaiacterizedbyasigmoidalpattemandnear-linear releasewithtimeafterZOwk. ThetotalamountofmineralizableN andthepotential mineralization rate were very closely correlatedwiththetotalamountsof C orN(i’ >0.73;P <0.or). Studies showedthatsoileineralization potential wouldbeafl‘ectedbyclimatic factors suchasmoisturesupplyandtemperatme(CassmanandMunns, l980andMyersetal., 1982). Inaddition, El-Harriset al. (1983) showedthattherewerelarge difl‘erences inN mineralimtionpotentialandrateofmineraleroductionforfallvs.springsoilsamplinginthe Pacific Northwest. Difl‘erences in N mineralization potential due to tillage were greater in the springthaninthefall. CumulativeNmineralized,NmineralizationpotentialandrateofN nfinadizedmaeasedudmmsigmficmnmaeasemsoflthmferfifizaNappflcafionwas increased. CarterandRennie (1984) comparedtheefl‘ects of zero and conventional tillage systems on N transformations ofChemozemic soils in Western Canada The results suggested thatthedifl‘erencesintillagedidnotcausemarkedchangesinthesoilNcycle. 35 Tlnefl‘eaofsofldisuubmmewasalsostudiedmdhwasfoundflmmdisturbedsofl coresNowaslowerflnninundisuirbedcores.PotemiaflymhmhnbleNmaybe overestimatedbydrying and sievingthe samplesbefore incubation (CabreraandKissel, 1988b) orbythebiasintroducedintotheestimationoftheparametersasthetimeofincubation increases (Dendooven, 1990). Carnpbelletal. (1991) indicatedthattheproductofNoandkyieldedtheinitialpotential mteomeinaalimfionwlfidiwashigherforflmadfivatedflmnforthemidisturbed soil cores. The initial potential rate of N mineralization had been proposed as a criterion for the definition of soil organic matter quality. Moreover, Juma et al. (1984) conducted incubation studies on Saskatchewan soils to determine the suitable mathematical equation and its parameters descnbingthenetNmineralizationinsoil. Theyfoundthatthedatafittedtoeitherhyperbolic or first order equations. The kinetic parameters, potentially mineralizable (No) and time required for ‘/2 No to mineralize (7), were determined by non-linear least squares (NLLS) method. The hyperbolic No values ranged fi'om 51 to 429 ttg N g'1 soil while the Tvalues ranged fi'om 7.3 to 45.8 weeks. The No and 1: (net N mineralization rate constant) ofthe first order equation ranged from 35 to 255 [13 N g'l soil and 0.036 to 0.164 wit", respectively. BothequationsacairatelypredictedtheamomnofnetNmineralizedovera14week iriaibation However, the parameter estimates of potentially mineralizable N and mineralizable N half-life were dependent upon the model used. Determining the long-term mineralimtion capacity of soils is laborious, expensive and time-consuming (Stanford, 1982). The relative significance of N derived fiom the various mineralimble sources may well differ with short and long-term measurements. These 36 wnddaafiommylwlpmmlainwhyaflmnpmmrdafingshon-tmnNnfinaahnfimdatatoN uptakebyaparticularcroporasuccessionofcropsgrownondifl‘erentsoilsmideruniform conditionshavemetwithvaryingdegreesofsuccess. Nitrogen Mineralization Rate (It) Investigators used a variety of incubation techniques to estimate net nitrogen mineralizationandnetnitrificationratesinforest soil. Methodsdifl‘eredintheseways: 1) site of incubation, field versus laboratory, 2) pro-incubation treatment, sieving versus no sieving, and 3) length ofincubation. Each method offers advantages and disadvantages, but there was no reference method against which to measure mineralization rates (Adams et al., 1989; Eno, 1960; Nadelhofl‘er et al., 1983; Raison et al., 1987 and Vitousek and Matson, 1985). Depletion of highly labile organic matter substrate, NHa accumulation and NH; volatilization all could potentially act to decrease measured mineralization rates with increasing incubation times (Kaiser and Heinemeyer, 1993). Studies showed that rate of N mineralization was dependent on cropping practices (Campbell and Souster 1982; El-Harlis et al., 1983) tillage intensity (El-Harris et al., 1983), crop residues (Smith and Sharpley, 1990) and fertilizer application (Janzen 1987). Soudi et al. (1990) conducted a study to determine the influence of soil depth on N mineralization rate and its relationship with total N and amino acid N contents for eight representative soils of the subaiid zone of Morocco. Nitrogen mineralization was evaluated in a 16 week laboratory incubation study. Individual samples were leached periodically to extract the mineralizedN. RemltssuggestedthatNmineralizationvaiied amongthesoils studiedandthe decrease of mineralization rate in a given soil was attributed to decreased biodegradability of 37 theorganiccompoundswithdepth ThedecreaseofaminoacidN(asparticacid, glycine, mmmlnsfidhn)wManwithdemhwasrdafivdygiwaflnnmedeaeaseoftotd N. msmiglnbeduetotrappingofannnoacidsincomplexorgamccompounds. These wnmuflswchasqmmnesmidphmobwaelessdewnmosablebybidogicdpmcemeswim increased depth. Soflmanicpotenfialhadasigrfificamefl‘eaonflierateofnetnfineralizafion Bothnet mmficafionmdmnificafionmesdechmdfiommopfinmmvaluenearfiddcapadtyasdn soil dried (Reichman et al., 1966; Campbell and Biederbeck,1972). The rate ofdermeasewas more rapid with nitrification than with ammonification. Amrnonification, unlike nitrification, confirmed at soil matric potentials below the permanent wilting point (Robinson, 1957). By implication therefore, soils with an increasingly greater initial soil matric potential (wetter) would show progressively smaller increases in mineralization rate upon wetting (Pilbearn et al., 1993). Fungi and bacteria play an important role in N transformations (Stevenson, 1986). An important factor determining the rate of N mineralization is the C:N ratio of the microbes as well as that of their substrate. When bacteria decompose organic matter, more inorganic N is released from the organic matter when the bacteria have a higher C:N ratio of 6 rather than 4 (De Rutier, 1993). In comparison of six grassland soils it was found that the C:N ratio of the microbial biomass was higher in sandy soils than in loams and clays and was positively correlated with the N mineralization rate per unit of microbial biomass N (Hassink et al., 1993). 38 PMMaiaIswaflddecayvfithdifl‘aanratesdepaflingonflidrC2Nrafioandhgmn content. Inflieearlystagesofdecomposifionmpideinaalizafionwasexpectedmcrop residueswithlowC:Nratioandlowlignincontent(Partonetal.,1987). Astimeofincubation increased,lower mineralization rateswereobservedahrnt, 1979). AttiwillandAdams(l993) reportedthatstudiesdoneonEuropeansoilsshowedthattherewasagenerallyslowerrateof mineralization under field conditions compared with laboratory conditions, and slower rates in forestsoilscomparedwithagriculturalsoils. Theseslowratesofmineralizationwereofien associatedwithalackofnitrification. Inadditionsoildisturbanceincreasedmineralization rates for a relatively short period. This was followed by a longer period in which net nfinaflinfiondeaeasedmmefimestodwpohnwhaemorgmuchashnnnbihzedforl-Z years. Mneralizationratesandsoilpoolsofinorganicheresimilartothosebeforethe disturbance. The fact that the competition for NIL by heterotrophic microorganisms ensured thamuificafiondepmdedmmemteofammomficafionwluchmmwasstronglymflumed bytheC2Nratiooftheorganicsubstrates. WhentheC2Nratioofagiiculturalcropresidues exceeded25:1therewouldbenonetminerahzationofNandNIL-Nwouldbehnmobilized. Grace et al. (1993) reported that increases in N mineralization associated with cultivation had been attributed to the destruction ofaggregates and exposure of organic materials previously inaccessible to microbial attack. The microbial biomass itself was identifiedasasignificantsourceofN. IncreasedsoilNog-Nduetocultivationmayalsobe due to higher potential for nitrification, lower rates ofN immobilization or less potential for N loss through denitiification. 39 Sevaalmwbafionsmdieshidicuedfliataflushofmhiaahnfionwouldbedetected following soil sieving (Hassink, 1992 and Nordrneyer and Ritcher, 1985). Piccolo et al. (1994) showedflnthighanaNnfinaafimfionmdmuificafimrmeswaemeaauedmhbomorymd insituinaibationsofsievedsoil, comparedwithinsituincubationofintactsoilcores. Rates calculated in seven-day incubations were higher than determined by longer incubations. Sieving mathreaseNnfinaahmfionmfl/mdeaeaseNhnmobihnfionwnmuedwithhnactmres. largesoflmoistureflucmafionsaeatedpotalfidproblammhnaprefingmeasuedna Nmina'alintionrates. Tubeorburied bagmethodswithintactcores minimizedsoil dishnbmeMmayafledfimsfonmfionmteahnflwcarbonmputscausedbysevaingof live roots might influence transformation rates. Methods that utilize sieved soil created artificial soil conditions but eliminated most carbon inputs fi'om fi’eshly severed roots. Because ratesofnethfinaalizafionmdnamuificafionmmmwmnwthodsvafiedwiddymdwae often near wo, incubations of sieved soil served as a better index ofN availability. The possibility still existed, however, that rates of net mineralization and nitrification were substantially altered by sieving. Changes could result fi'om either enhanced mineralintion of organic matter following sieving, or from reduced immobilization after the removal of roots and large, poorly decomposed organic matter fi'agments. Incubation studies by Beloso et al. (1993) showed that in a non-fertilized soil, N mineralization increased continuously from the beginning of the incubation. Nitrogen mineralization showed no signs of leveling ofl‘ at the end of the incubation although a decrease in N mineralization rate was detected after week 2 of incubation Ladd et al. (1994) showed that fertilizer N application didn’t impair soil mineralization activities, expressed in percentage 40 ofsoilorganicCandN. Carbonandeineralizationratesperunitofmicrob'mlbiomassC increased in the fertilized soils. Nitrogen fertilizer application increased the annual return of plunreéduesunhadmefl‘eaonpercmmgemhiaflimfionmes.1herenflmwggefledflm fliedeiomaschommmfafihzedsoflwasduespedficaflytohiaeasedratesof conversionofCfiom thebiomasspooltothenon-biomasspool. ShghandSingh(l994)foundthatfliehicreasemNnnnaalimfionmsuaw+fafihzer Wm97°bgefiaflmflwwnfloflmfafilizermdrefi¢readde®ummoismm level. Nitrogen mineralization was greatest during the wet period of the year. It increased exponmfiallywithmmemngeofS-23%soflmoismrecomauinlndiandrylmds. In wndusioawnibhwdmpruofsuawmidfafihwmhmweanunaflizafionmereaflfingma larger available N pool. This would increase the N supply even during the period when fertilizer application was not feasible due to low moisture in dryland farming conditions. Soil N Losses Soil N losses may include a) leaching of N03-N from the rooting zone and into the groundwater, b) denitrification when microbes uses Nos-N rather than oxygen and thaeby reduces N primarily to N20 or N2 gas into the atmosphere, c) volatilization of NI-L-N from fertilizers and manures, d) erosion of surface N (Meisinger and Randall, 1991). Denitrification and leaching may cause nitrate-N to be lost before it is taken up by the crop (Armstrong et al., 1986). These losses are a continuing concern for farmers and for society. The agricultural cormnmitymustreducetheselossesandberesponsrbleforthesoilandwaterresourcesand improve crop N-use eficiency and farm profitability. Shaffer et al. (1991) developed a N 41 leaching model that estimates the daily soil N potential for leaching. The model required daily water drained, daily N mineralization, daily N uptake by the plant and initial mineral N. FafilizerNreqmremanofacropdepmdsmpmtonfliemnamoannnaahzedfiom soilorganicheforeandduiinggrowth Anyatternpttopredictrequirernentbymodeling techniquesneedssomeformofmodel formineralization Sincemineralizedeaybeleached whainismuifiedhishnponmnflmflnmoddshmfldalsohwludemuificafimofNEandbe compatible with an appropriate leaching model (Addiscott, 1983). Measurements or estimates of other N losses such as denitrification, volatilization and erosion should be included in N needs predicting models whenever they apply. Nitrogen Mineralization Prediction Models The need for rapid and reliable methods of assessing soil N availability motivated most short-term incubation studies of soil N mineralization (Harmsen and Van Schreven, 1955, Brernner 1965). In early studies of long-term N mineralization capabilities of soils, samples were continuously incubated in bottles or flasks. In 1955, Stanford and Hanway proposed measurement of NO; production in soils by a method that permitted canying out series of incubations with a single set of soil samples. Stanford and Smith (1972) conducted a study to assess -term mineralization in 39 soils differing widely in chemical and physical properties. Cumulative netN mineralizationwas linearly related to the square root oftime (tn) throughout the 30 weeks of intermittent incubation with most of the soils tested. The quantity of soil N mineralized in a given time was dependent upon temperature, available water, rate of oxygen replenishment, pH, amount and nature of plant residues and level of other 42 nutrients. This work was further evaluated in relation to uptake of N by sudangrass in a greenhouse experiment using lsN labeled fertilizer. The findings showed that with a Qto of 2, the mineralimtion rate (It) didn’t difl’er significantly among soils between 5 to 35 °C. This indicates that the organic sources of mineralizable N were similar despite wide variations in origin and management history of the soils. Amounts of soil organic N mineralized during cropping plus the mineral N present initially in the soils correlated highly with amounts of soil N taken up by whole plants (Stanford et al., 1973). Stanford et al. (1974) demonstrated that Na could be reliably estimated from the amount of N mineralized during 2-week incubations following preliminary incubations of 1 to 2 weeks. In addition, the rate constant It was influenced markedly by temperature and soil water content. Miller and Johnson (1964) found that the optimum matric suction for N mineralization ranged from 0.15 to 0.5 bar. Stanford and Epstein (1974) studied the relationships between soil N mineralization, soil water content and matric suction on nine soils. Highest N mineralization rates occurred between a matric suction of 1/3 and 0.1 bar. Tabatabai and Al-Khafaji (1980) compared the N and S mineralization of 12 major soil series in Iowa. Field moist samples collected from 0-15 cm were incubated at 20 and 35 °C for 26 weeks. They found that cumulative amounts of N and S mineralized were linear with time of incubation. The rate of N mineralization, however, was greater than the rate of S mineralization and temperature had a marked efl‘ect on organic N and S mineralization in soils. The linear relationship obtained for cumulative N mineralized at 20 and 35 °C and time of incubation did not support the finding of Stanford and Smith (1972) 43 that cumulative N mineralization is related to t”. In addition, Addiscott (1983) showed that mineralization of soil organic N measured in laboratory incubation experiments on Rothamsted soils with contrasting histories could be expressed by the simple zero-order relationship N. = kt in which N, is the amount of N mineralized in time t. The approach in which No was evaluated with first-order kinetics, as proposed by Stanford and Smith (1972), could not be applied to these data. Hadas et al. (1986) conducted an incubation experiment on 38 difl‘erent soil samples collected from various places in Israel. The samples were incubated for 32 weeks at a constant temperature of 35 °C and a moisture content of water-holding capacity. The study was to evaluate the contribution of different soil layers of mineral N of the whole root zone and to relate the rate parameters obtained to various soil N factors. They found that the soil layers of 60-120 or 60-160 cm contributed about 30% of the N mineralized in the whole soil profile. In addition, the total N weighted with respect to soil layer depth was the best estimate of N mineralized in soil profiles. Bonde and Rosswall (1987) evaluatedthreemodelsto describetheldneticsomeineralizationduringincubation: (i)first- order, (ii) two-component (sum of two first-order models), and (iii) a simplified special case of the two-component model. The latter model offered the best description ofthe curves of accurrlrlated mineral N. Cabrera and Kissel (1988a) studied the N mineralized in disturbed and undisturbed soil samples. A double exponential model fitted disturbed samples; whereas, a single exponential model was required for undisturbed samples. For each soil, the amount of N mineralized in disturbed samples was larger than in undisturbed samples atanytime. 44 Cabrera and Kissel (1988b) dried ground samples of 3 soil series and incubated them at 35 °C for a total of 252 days to evaluate a method that predicts N mineralized from soil organic matter under field conditions. To predict N mineralized in the field, the rate constants of mineralization were adjusted for soil temperature. In addition, predicted amounts of N mineralized, N mineralization potentials and adjusted rate constants were further adjusted by soil water content. The water content factor used was similar to that proposed by Myers et al. (1982): W = (WC - AD)/(OWC - AD) where WC is soil water content, AD is water content of air-dry soil (calculated as 50% of the water content at - 1.5 MPa) and OWC is the optimum water content (assumed to be that at -0.02 MPa). However, this factor only accurately predicted the amount of N mineralized in 104 days in fallow plots and significantly overpredicted by 67 to 343% the amount of N mineralized in the field. Overprediction may be attributed to improper soil water content factor, drying, grinding and sieving of the samples before incubation. On the other hand, Campbell et al. (1984) developed a model that predicted the amount of net N mineralized during a growing season when soil was incubated in plastic bags placed in incubators or buried in the field. The basic equation used was: N. = No (1 - exp (-lit)) where N, is cumulative N mineralized, No is the potentially mineralizable N determined at an assumed optimum temperature of 35 °C and optimum moisture (-0.03 to -0.01 MPa), 1: is the rate constant at optimum moisture and temperature and t is time. Campbell et al. (1988) used the model to estimate net N mineralized in situ under cropped-dryland, cropped-irrigated and summer fallow conditions. Model output showed good agreement to field measurements especially for the first 45-60 days, but thereafter tended to underestimate the measured 45 data particularly under cropped-dryland conditions. The model was not dynamic since it didn’t allow for No to be replenished continuously by N derived fiom decomposition of fresh residues and rhizosphere microbial biomass. This might explain the underestimation. Other sources of possible discrepancy could be imprecision in measuring the mineralization of N and in estimating the parameters in the model. In addition, the model underestimated the amount of N mineralized whenever the soil became very dry and then rewetted by rainfall. This was because the latter process resulted in large flushes in mineral N in situ while in laboratory estimates of No and 1:, this effect was not adequately simulated. ElGharousetal. (1990) showedthatsingleexponentialandhyperbolicmodelscanbe usedtoestimateNoandkvalues. Onthesearidand semiaridMoroccan soilstheactive fi'action oftotal N ranged from 7 to 22% and 10 to 36% for the exponential and the hyperbolic models, respectively. Simard and N‘dayegamiye (1993) suggested that for accurate prediction of soil N availability,itwashnportarntoselectamodelthatwouldsinmlatethebehaviorofN mineralization for a wide range of soils. They conducted incubated studies on 20 meadow soils for 55.4 weeks at 20 °C. Results showed that the cmnulative mineralization curves in most soilswerecharacterizedbydefinitelagsorasigmoidal patternandnear-linearreleasewithtime afier20weeks. ThedatawerebestdescribedbytheGompertzequation: N..=N.,e"""’-N.e *,where,N..isthecumulativeamountofmineralizedN, tisthetime, kistherateconstant,N. is the amount ofpotential mineralizable organic N and h is a proportionality constant ofthe equation. 46 MatusandRodriguez(l994)developedamodelthatpredictedthereleaseoforoma mgeofsoflsmdifl’aanagiimhuralmneswithhrgevmiafiommfieshorgmncmpms weather conditions and soil types. The model avoided the use of the potentially mineralizable N of Stanford and Smith (1972). In addition, results showed that N mineralintion heavily depaidedonenvhomnanalfactorsmchassofltanpaanuemdmoisnuecoman. Theefl‘ect ofternperature on N mineralization is given by : K; (T.) = K; (To) “ exp (0.0616 * (I‘.- T), where K2 ('1‘.) is the constant decay rate K2 adjusted to the temperature T. (520 3?. Samoa: 3:535 b89583 .«o sowed—Sofia Z 8: gun—=83 .«o E 382598 2 5:333 me than 02 own 00m own com - 1 57 p e 8862.. lot 33 o cog ow weed u R 8 :83. -V ea - 3 e? u az .N edema (13)] But) uonazrlerourw N 19M GAIJBIIIIImQ 58 demuom mEBSm 82 2: 9.56 :8 >30 .33 .3303: a no mmE—QES c853 3:85 2: mats“. 525 .n 233m main—am no 039 vu e an 3 on Q vm N. hm 2 flow .Eom .m=< .m:< :3. 22. . 0:2. as: x $2 ‘ m H .. .H, , HH‘ [o2 (tun!) [WW8 59 Tluswasfoflowedby65mmbythe24mof1une.Thenthercwasadrierperiodof apploidmatelyonemonthwithlessthanlSmmofrain.BetweenJuly12andJuly29theplots receivedover50mmfollowedbyanothermonthlongdryperiodwithlessthanZOmmofrain. Tinsmnepanemwasrepeetedmdflia’ewasneaflymmofminbetwemAugust 12and August29followedbyneaflyamonthwithlessrain(August29toSeptemberé). Thenbythe 24'. of September there was approximately 55 mm of rain. Thistainfaflpafianmfluamedtherdafivemoisuimcommmflieaufacewmparedto thesubsoil(Figure4). Moismrecontentoffliesurfacewasequaltoorgreaterdunfliembsoil untilthefirstofJuly. Fromthenuntilthe29‘ofluly,thembsoilhadequalorgreaterwater comentthanthemrfacesoil. Dudngtherestofflieseasonmoisturecontentwassimilarinthe two horizons. The faster growing rate of sugarbeet crop and the wanner temperatures dried thenu'facesoildmingthemonthofluly. Evidentlytherainbetweenluly lZandAugust 12 kept the surface more moist, probably due to canopy closure during this period. Therainfaflpaflemwasmommifomml994udthshonerpedodsudthfitflerainfafl (Figure 5). This keptthesurfacemore moist relative tothesubsoilduringthewhole season. Themwasneveranextendedperiodwherethemrfacewasdfierflmthembsofl(Figure6). AswillbeseenlaterinthediswssiontheintensityofraineaflyinMayaswellasbetweenJune and mid July promoted greater leaching of N. Generally, [when the soil moisture content exceededthefieldcapacityitwoulddrytobelowfieldcapacityvfitlninho3days. MineralN wmamfionmflnmrfacehyawassigrfificandyhigherflmmthembsofldufinglummd eaflyAugustofthe1993growingseason(Figure7).InbothlayersminemlNincreaseduntil latelunethenitdeclineddramaticallyuntilendofJulyoreaflyAugustwhereitremainedfairly constar1tthcrestoftheseason.1heincreaseinsoiln1inetaleetweenMay l7andJune24 60 can .538 05 mo coho @8936 05 negate.— ufioq 8% some 3 on: .39? 2F .335.— =am£8 usage 85 magma—9. 882%.. 3%: 833 .338 358m 82 05 mats—o :8 >30 5:... >303: me 3350 2:368 05052.5 .v 953m 30> me than 8" ova can con ow~ o2 o3 o3 “ h u h T w n 2 .0 So we - an '0' If . Eonu..o..l.. . omo . . .. «a 23 . .8 am w=< .. . . u" .. 4 ha an: L1 mm 0 cm a m 0 flow .1 . . 5 25m .. . 11 one 2 m2 .. it . .. .. . . 1, 2.0 . am as .. ..... .. ...l. 233. I..........E.. . : ovd L. .. e S 3: 36 111911103 GMSlOW [tog amoumlo A .0800... magew v02 05 meta—0 :8 >20 >50 >308: 0 co 3:29:00 0003009 32005 05 meta—0 .305 .m oBmE 338$ no 0000 cm 0 mm a mm a 5 an 30m .30m .w:,,< ..m=< 3 >1: 2 >14 0.0.3. 003 >02 m >02 E3. . ., , ... . no \ION \:ov m \T00 flow -2: lofi ...... -ov~ (mm) “emu 62 .508 05 .«o 8.5 209.06 0.: 3:00.050. 052. 300 £000 00 0:: 30:02, 2:. .3010; €058 00005.30 00c0 $53800 2.00052 0000: 00:5 .0808 359% 002 05 macaw :8 >30 >50 >0=w0§2 .«0 E0280 003068 :8 050822, .0 0.35 000.» «0 >09 emu 8m ovu can con ofi R: o: 2: 02 w w w 0 w 0 fl 0 2.0 80 me .. am IT 8035:... #omo # mad .. a 0:2. mm =8< . . -r end an 003 . . . i- and w .flgm o: 0 s 0 o “N %—:H I o oooooooooo 41 ov.° on .aom a .w:< L, 3.0 . 0 R 002 > mm Q3 2 3.. m 02 one 111911103 anusyow nos omaumlo A 63 .8008 0.: Eu 880 808.08 0.: 0800080.. 88a 0000 £000 00 08— _00_t0> 2E. .8800». @303 82 05 98.6 :8 >06 >50 >338: 30580.8: mo Z .8088 =om .0 0.5me 30> mo >0Q can own ovm cum con 03 OS oi oi b b p h q q .4»- «+- O R :2 .. 2 h 08:. ...... ., vn 08;. .8910an .. 80NN-o..I.. --ov (1.1m 3%) N Imam HOS 64 was probably due to mineralization and nitrification of previous crop residues and to low N uptake by small sugarbeet plants. Mineralintion and nitrification of decomposed organic Maidwaemhmcedbywmnatempaauuegmcrusedmfivhyofmfiifyingorgmfiansand rainfall. 'I‘hedramaticdeclineinmineralNafierJunewasprobablyduetothehigherNuptake by sugarbeet plants relative to soil mineralization. ThepattemofsoilmineralNinl994gmwingseasonwassimilartothatofl993 atceptinflwfirstqmnerofflwseasonwhaeflwmmaalencamafioninflwmbwflwas greaterthanthatofthesmfacelayermgureS).Thiswasduetoheavyrainfallsof104mm (April 22 and May 27) and negligible to low N uptake by the small sugarbeet plants. Soil mineraleasleachedfi'omthesurfacelayertothesubsoillayerandperhapstothedeeper layers (Figure 8). Soil mineral N increased in both layers until early June, decreased dramaficaflyuntillulyllandremainedconstantunfiltheendoftheseason Thereasonsfor theincreaseofsoilnfineralNinl994werethesameasthosediscussedfor1993. However, thedeclineofsoilmineraleasduetohighNuptakebyplantsG'igures9and10)and leaching. During June 136 mm ofrain fell followed by 89 mm during the first 10 days ofJuly. In all likelihood this leached considerable amounts of mineral N. Measurements of leached soil mineraleerenottakenduringanyofthegrowingseasons. However,amodeltopredictthe daily mineral N leached from 0-45 cm depth for both growing seasons was developed. The estimatedamountofsoilmineralNleachedwasG92kgha"and35.7kgha"during1993and 1994 growing seasons, respectively. 65 .0008 05 08 .5000 E00003 05 0800080.. “Eon 300 £000 00 08. .0383 05. 88000 wage» 32 05 wctau :8 >03 >50 >852: 000580.80 00 Z .8088 mom .0 05me 000> mo >09 own com ova can ooN ow~ 02 o: 03 oo— “ L. + w w w w w “ 0 3 >5. mm 0:2. r. m I 11 1.! O“ S ...... .. . >0 0. ...... ..... .....w m 2 i: n l. .. >0 m. 0 80m . 0:: pm 2 an -- on m on flow a w=< : >1: + ..r .. a a ..NN _. < N. mN w=< 1. mm N 88 am .. .. . . \vm 00300 + , -- 8 am. a .. .. . 9.... so 3- 000+ .. .. -- mm ( as 02 A A 80W.NNI°on.-nu SEW.“ irov mv 66 .33 8 :00 .0 050E >06 >50. >0=w0E2 0005808: no 0263 00090?» >0 00—03: 2 0300383 0000805 0800m $865 .00 0>0D oi 02 02 on 8 ow on em 08:. 5 >02 .. ./ 00 0.2 1.11 00 300 \\ 4/ an amzws< L .CN row row I oo— cm— (1.911 8») amdn N 67 . .33 8 :8 >20 >50 >303: 000580.83 :0 3303 0009.090 >0 00.083 Z 0300—3830 3000605 .3 2&5 080% @3305 .«o m>0D 03 02 0: OS 00— cm 1 -. e. M .. mm 033 d m ...... L: 00 9 a i. 8 .n w. ...... 4 ow (v... Lu. om .aom mm .03< / L I oo— / 8 >3. om— 68 Prediction of Field Cumulative Net N Mineralization Prediction offield cumulative net N mineralization (M) required the adjustment ofN... inbothmodels. 'I’hiswasachievedbymodityingtherateofmineralintion (k) forboth models todailyfieldairternperaturesusingEq. [3.3]. NnrineralizedintheMSemlayerwas esfimatedbytomlnfineraleeiglnethhrespeamdepthsinuhrtoHadasaal. (1984). After correcting N. for soil moisture (W) using Eq. [3.4], M was fitted to Eq. [3.5] and [3.6] for linear and exponential functions, respectively. Soil N mineralization is governed by tanpaafinemdmoistmeefi‘edshagrowingseasondufingdwhgmdrewetfingcydes (Wildung et al., 1975; Kowalenko and Cameron, 1976; Cassman and Munns, 1980; Ellert and Bettany, 1992andGesteletal., 1993). Thisagreeswiththefindingsofthefieldexperimentof 1994,whereadjusfingfortemperammandmoisunefaaorincreasedeyamund 10 to 12kg ha'1 in both models at Q10 of2 or 2.2. However, that adjustment did not change N. in 1993 becausetherewerenomajordrymgandrewettingcyclesto influence soileineralizatiorL Valuesof Musingbothmodelsathoonand2.2areshowninTables l and2. The calmlatedmmulativenetNmineralizedinthefielddurhrgthegrowing seasonof1993 and 1994 was 93.5 kg ha" and 84.1 kg ha", respectively (Tables 1 and 2). Some uncertainty is expected due to imprecision in collecting and measuring soil mineral N, N uptake and calmlatingthemeasuredmineralizationofN. Thisuncertaintycouldalsoleadtosome imprecisioninestimatingtheparametersinboth modelsandinpredictingtheNmineralization inthefield. In 1993, the predicted cumulative net N mineralization (M) value (Table 1) was close to the calculated one (93.5 kg ha"). In 1994, adding the estimated amount of mineral N leached (35.7 kg ha") to the calculated cmnulative net N mineralized (84.1 kg ha") 69 Table 1. Predicted field cumulative net N mineralization values afier adjustment for air temperature and soil moisture (W) using linear and exponential models at Q10 2 and 2.2 in 1993. Linear Exponential Q10 -k,t+c W(k,t+c) No(l-exp(-k,t)) WNo(l-exp(-k,t))'l' kg h a'1 2.0 83.7 82.7 94.0 92.9 2.2 80.6 79.6 90.3 89.1 1‘ Calculated cumulative mineral N in the field was 93.5 kg ha" in 1993. Table 2. Predicted field cumulative net N mineralization values afler adjustment for air temperatmeandsoilmoisture(W)usinglinearandexponentialmodelsatQlo2and2.2in 1994. Linear Exponential Q10 k1t+c W(k,t+c) No(l-exp (-k,t)) WN°(l-exp (-k,t))T kg ha'1 2.0 96.0 107 108 120 2.2 92.5 103 104 116 1 Calculated cumulative mineral N in the field was 84.1 kg ha" in 1994. 70 hroughtthelattervalueclosetothepredietedvalueonzokgha" (Table 2). Thesemodels pndiaedthemmdafivenanfinaafizafionmdrefiddwdlwlfichisconmmCabmmd Kissd(l988b).1hemoddsusedbyd1emarfimwdaudmovaprediaedflleamoumN nfinaalizedinthefieldby67to343‘yo. Theposslblereasonsforbetterpredictionhereare: i) udngnmiflwflsamplesmflraflmdfiedgmuflmmplesmflnuwbafionsmdyfi)mdn soflmhaflmnusingmn—siwedmmacmeswhaemotsmmtranovedmdifi)usingconea adjustment for soil moisture. Prediction of Leached Soil Mineral N The constants a and k determined for 1991 N uptake were used in Eq. [3.9] to predict the daily N uptake in both seasons. Predicted armulative N uptake for both years were similar (Figures 9 and 10). Although sugarbeet were planted 25 days earlier in 1994 than in 1993 yet thetotalNuptakewasthesame(114kgha")inbothyears. In 1994, predicted mmulativeNmineralizationinthetieldwas3okgha" greaterthan the calculated value. A model to predict soil mineral N leaching was developed to test that difference. Using Eq. [3.8] for the first approach showed that the predicted amount of leached N was 10.0 and 16.1 kg ha'1 for 1993 and 1994 growing seasons, respectively. However, the second approach (Eq. [3.10]) showed that predicted amount of mineral N leached was 6.92 kg ha“1 and 35.7 kg ha" for 1993 and 1994 growing seasons, respectively. The two approaches yielded insignificant losses to leaching during the 1993 growing season. Results showed that usingthefirstapproachunderestimatedthesoilNleachedin 1994, whereasthesecond approach was comparable with the value found by calculating the difference between the predicted and the calculatedN mineralization in 1994 (Table 3). It is apparent that the second 71 approachismomcomprehmsivemdacwmtsformaijmsfonmfiommdfitmesflmt occluduringtheseason. 'I’hedrawbackofthefirstapproachisthatsoileasrneasm’edonly whmgreaedunssmmormmtalmdeomequmdyaudeNmndupduemrmnealindon especiallyatthebeginningoftheseasonwasnotaccormtedfor. MineralNinsoilsampleswas assmnedtobetheaveragesoileortheirfierval. preriodicandmorefiequentmeamrements ofsoileeredone,thetwoapproacheamighthavebeenmoresimilar. Table 3. Predicted soil mineral N leached from 0-45 cm deep during the 1993 and 1994 growing seasons using 2 approaches of estimation. Predicted N leached Approach 1993 1994 kg ha'1 Approach IT 10.05 16.1 Approach 21 6.92 35.7 1 Approach 1: using average mineral N concentration per interval, equation [3.8]. 1 Approach 2: using Shafl‘er’s et al. (1991) equation [3.10]. Prediction of Atom '/o ”N in Mineral N Predicted atom % 15N in mineral N at each sampling was determined using Eq. [3.12]. Curvesshowingmeasuredandpredicted atom% l’NinmineralNareshownirlFigure 11. Measured and predicted atom % 1’N in mineral N declined rapidly until the 20III day ofthe incubationandthendecreasedataconstant ratefortherestoftheincubationperiod. Predicted atom% ”NinnuneraleasaJmostdoublethemeamredvaluefiomthebegimungunfilthe 20‘I day of incubation. Reasons for overprediction might be attributed to i) added amount of 72 atom%”Nnotbeeingthoroughlymixedwithsoil,ii)preferentialfixationof”besoil microorganismsandiii)fixationofNI-It-Ninclays. Wugdidn’tappeartobetheeasesince theentiresoilsamplewasextracted. Ashortinwbationexperimerfiwasmnfor‘idaystotest whetherlabeledeasfixedbyclayminerals.Twosetsofsoflsampleswa'eusedacontrol withno”Naddedandasettreatedwith”N. Attheendoftheincubationeachsetwassplit intotwoandextractedwithKClorwater. Resultsshowedthatlabeledeasnotfixedinclay minerals. AhhoughwecouldnotacplaindledisaepmcyuptodayZO,wecouldesfinmted1e gross immobilimtionbetweenanytwo intervals oftimeusingEq. [3.13]. Thedeclinein immobilization rate was probably due to the easily decomposed substrates that were used by the microbes and not immobilized as much. Table 4 showed the predicted immobilization rate values. Gross rate ofminemlization is 25.8 % greater than net mineralimtion rate (Figure 12). Irmnobilizationratehadasmallefl‘ect oanudget ofthis soil. Irmrlobilizationrateatthe beginning ofincubation decreased to 1/10 ofinitial value bythe end ofthe incubation. 73 .89 E 33305 8388 :8 >20 3% >306: 35.2: mo 2 1:058 5 z: .x. :83 @8838 28 38:85 .: onE now—3:2: mo than omm can 03 com 02 OS on o p p _ q q d .lL L. N Imam II! N91 % mow 88:85 lnl 333‘ o 74 .33 E 3:535 :8 use acme man—mom: 33:95.2: mo egg—8058 Z 8: 98 $80 .2 9:55 5.53:2: mo 9an can 8m emu 8N ofl 02 an o w .r w a w m o gr 2 gages i om Z 82 38:85 / + on 4/ l e r on 5:333:va Z 305 36:85 l 8 (1.3 811) “ODWFIBJGUFW N 75 Table 4. Predicted gross N immobilization rates for 1993 incubation experiment. Predicted gross N immobilization Interval time *- 9“? 7‘“ - ------- 118 8" day“ ------ 5 0.828 8.5 0.604 15 1.744 27.5 2.093 42.5 1.667 60 1.761 80 2.019 g 105 1.552 140 1.223 180 0.991 236.5 1.685 301 1.051 76 SUMMARY NmogarfafifizerreconunardafiomformgarbeamquiresdlequmfifieafionofN nfinaalizedfiomsoflorgarficmaflerwhichmaybeavailableforplarfiuptake. This qlmnifieafimcmddbeaclflevedbypredicfingfiddwmdafiwnaNnfimfimfionbasedon laboratoryinalbationstudy. Along-termlaboratoryirmbationstudywasconductedin1993. haddifiomtwofiddarpaimanswerewnduaedmaMiQegmysoflmflwBeanmdBea Researcth Saginaw,in1993andl994. CmnulafivenetNmmemlizafionmm)datafiomd1emwbafionsmdywasfittedto linearandone—pool exponential models (Figures 1 and2). Nmincreasedwithtimeof inwbationwithoutlevelingofl‘attheendofdleirmbationpedod. ThisagreeswithBelosoet al. (1993). Rates ofmineraliattion (k) were 0.152 mg kg" day" and 0.00337 mg kg" day" for linearandexponentialmodels,respectively. Potentiallymineralizablenitrogen,N.,was73.1in thcexponentialmodel. Theexponentialmodeldidn’tallowforreplenislnnentofN. contiruously by N derived fiom decomposition of flesh residues and rhizosphere microbial biomass. letotdrainfaflwas368mmdufing¢el993growingseason1herainfaflpfltanof the1993groudngseasonshowedflmteachheavyrainfaflpaiodwasfoflowedbyafiglnone (Figure 3). Inl993,thesurfacesoil layer (0-22 cm) generally tended tobeequalorslightly wetterthanthesubsoillayer(22-45cm),exceptduringthemidseasonbetweenendof1ulyand earlyAugust(Pigure4). Duringthel994growingseasontotalrainfallwas$l4nnn The 77 rdnfaflpfltanwudNeachMolwawrainfiflpaiodswefoflowedbyafiglnomGigme 5).Theaufacesoflwasequalinmoisttuerehfivetod1atofaibsofl(Figme6). MnaalencamafioninthearrfacehyerwaslnghadmfllewbsofldufingJune andearlyAugustforthel993growingseason. InbothlayersthesoilmineralNincreaseduntil lateJunethendeclineddramaticallyuntilendofJulyand itleveledoffafierthatGigure7). InereasesinfieldmineralNdm-ingthel993and1994 earlyinthegrowingseasons waemuilnnedtomhwrdizafimandmuificafionofpreviousaopredrhresandmwa uptake by sugarbeet plants. Mineralization and nitrification of decomposed organic material wacmhncedbywamatanpemurQMeasemacfivityofmufiyMgorgmummdsofl moisturecontent. ThedranuticdeclineinmineralNafierJunewasmainlyduetothehigherN uptakebysugarbeetplantsrelafivetosoilmineralizafionandniuificafion Thepatternoffield soilmineralNin1994growingseasonwassimilarto1993exceptinthefirstquarterofthe season(Figure8)wheresoilmineraleaslostfiomthesurfacetothedeeperlayerszgure 8). Amodelwasdevelopedtopredicttheamormtoleostduringthegrowingseasonsbased on predicted field N mineraliution, predicted daily N uptake and water balance models. N leached during 1993 growing season was considered insignificant. However, losses of mineral Nfiomtherootingzoneeariyduringthe19945easonweremainlyduetohighrainfallevents druingAprilandJuly. Theestimatedleachedamountoffieldmineraleas35.7kgha“for thatyear. CumulativeNuptakeincheck plots of 1993 and 1994 growing seasons are shownin Figures9and10. 78 Theealaflatedaumlafivenethfinerafizeddufingflregmwingseasonwas935 kg ha"and84.1 kgha" for 1993 and 1994 growing seasons, respectively. Lackofprecisionin collectingsoilsamples,measuringsoilmineralNanddeterminationofNuptakeatharvestmay leadmmtaintymcalmhfingNnfinerdimfionmthefiddesfimfingflwpamnaasmboth modelsandinpredictingNmineralizationinthefield. ' Ratesofmhlaafizafioninfinearmdexponalfialmodelsweremodifiedtofiddau temperaturesatho of2and2.2 forbothyearsusingEq. [3.3]. Values owaerecorrected for soil moisture (W) using Eqs. [3.5] and [3.6] and were presented in Tables 1 and 2. The linearand exponential models predictedthefield clunulativenetNmineralized (M) in 1993. Thctwo models wereusedto testtheprediction of field wnmlativenetNmineralizedin 1994. AddingtheestimatedleaohedsoilmineralN(35.7kgha“)tothecalculatcdcrumrlativenetN mineralizedduringtheseason (84.1 kgha")broughtthelattervalueclosetothepredicted value (120 kg ha"). Linear and exponential models predicted the cumulative net N mineralimtion in the field from a long-term aerobic incubation of Misteguay silty clay soil equallywell. Predictedatom%"NinmineralNateachsamplingwasdeterminedusingEq. [3.12]. Measuredandpredictedatom%'NinmineralNdeclinedrapidlyatthebeginninguntilthe 20m day ofthe inalbationthendecreasedataconstant rate (Figurell). Predicted atom% l’N inmineraleasalmostdoublethemeasuredvaluefiomthebeginningoftheincubationuntil the 20‘ day. The overprediction during that period of incubation might be attributed to irmnobilizationof'5besoilmicroorganisms. Althoughwecannotexplainthediscrepancyup today20,sfiflwecanestinmteflregrossunmobifizafionbetwecnanytwohnervalsoffime 79 (Figure 12) using the modified equation by Kirkham and Barholomew (1945 and 1955). Gross rate of mineralization was 25.8 % greater than net mineralization rate. LIST OF REFERENCES Adams, M. A, P. J. Polglase, P. M. Attiwill and C. J. Weston 1989. In situ studies ofnitrogen mineralization and uptake in forest soils: some comments on methodology. Soil Biol. Biochem. 21 :423-429. Addiscott, T. M. 1983. Kinetics and temperature relationships of mineralization and nitrification in Rotharnsted soils with difl‘erent histories. J. Soil Sci. 34:343-353. Alexander, M. 1977. Introduction to soil microbiology, 2nd edition. John Wiley, New York Allison, F. E. 1966. The fate of nitrogen applied to soils. Advances in Agronomy. 18:219-258. Academic Press, London Attiwill, P. M. and M. A Adams. 1993. Tansley Review No.50. Nutrient cycling in forests. New Phytol. 124, 561-582. Amm, F., A Lodhi and M. Ashraf. 1991. Interaction of "N-labeled ammonium nitrogen with native soil during incubation and growth of maize (Zea mays L.). Soil Biol. Biochem 23:473-477. Beloso, M. C., M C. 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Xu,C.1991.Tillageandrowspacingefl‘ectsonthedevelopmentandgrowthofdrybean (Phaseolis vulgaris L.) and sugarbeet (Beta vulgaris L.) on a Parkhill loam soil. MS. Thesis, Michigan State University, E. Lansing Chapter 4 PREDICTIN G NITROGEN FERTILIZER NEEDS FOR SUGARBEET GROWN ON MISTEGUAY SILTY CLAY SOIL IN MICHIGAN Greater use of nitrogen fertilizer has been a major factor in increasing yields of arable crops. Nevertheless, there is concern within the sugar industry that too much N is currently being applied to the sugar beet (Beta vulgaris L.) crop because excessive N has deleterious effects on the quality which reduces the profitability for both the grower and the processor. In particular, beet given too much fertilizer N contains smaller concentrations of sugar and higher concentrations of or-amino N compounds, both of which decrease the efliciency of sucrose extraction. Mineral N taken up during the course of sugar beet growth comes from three main sources: that present in the soil in spring, soil organic N mineralized during the growing season and that applied as fertilizer. Denitrification and leaching may cause nitrate-N to be lost before it is taken up by the crop (Armstrong et al., 1986). Residual N, N mineralized from soil organic sources during the growing season and individual crop needs must be considered when predicting the N fertilizer required. Adams et al. (1983) mentioned that, as with any agricultural crop, an important cultural decision faced by the sugar beet producer is the appropriate rate of fertilizer application. 89 90 The question of appropriate fertilization rates had been extensively investigated by agronomists. The producer’s actual rate of application might reflect information obtained from soil test reports, extension agronomists and fertilizer suppliers as well as the producer’s own experiences and expectations concerning plant response and crop price. For sugar beets, a typical measure of fertilizer response is root yield. For some producers, root yield appears to be of primary concern, rather than recoverable sucrose, even though returns are ultimately based on recoverable sucrose production. The decision as to the economically appropriate fertilization rate should be keyed to the response of recoverable sucrose to fertilizer, not simply root yield. Halvorson and Hartman (1988) studied the effects of tillage systems on N requirements for optimum yield and quality of sugarbeet grown on a furrow-irrigated silty clay loam soil. They found that application of N significantly increased root yield as well as gross and recoverable sucrose yields, but reduced sucrose concentration of sugarbeet root and clear juice purity of all tillage treatments. They recommended that a N fertilizer rate of 112 kg ha'1 can be used for sugarbeet produced with reduced-tillage systems. Nitrogen Recovery Efiiciency (NRE) Westerman and Kurtz (1974) suggested that there were four methods to calculate fertilizer N recovery by crops. These were the i) difference method, ii) unlabeled regression (N uptake vs. N rates applied- Slope of the relationship between N uptake and applied N rates), iii) isotopic method (”N recovered in plants), iv) labeled regression (”N recovery in plants vs. N rates applied and where the intercept was considered theoretically as zero). 91 The most common method for determining fertilizer nitrogen recovery eficiency was the difference method. It was calculated as the difl‘erence in amount of fertilizer N taken up by the crop in fertilized and unfertilized plots divided by the amount of fertilizer N rate applied. Alternatively, if the experiment involved rates of N fertilizer, recovery might also be calculated by linear regression of N uptake by the crops with rate of applied N. This method might be vitiated by the priming effect, which results in increased uptake of N fi'om soil organic matter in fertilized plots, causing an over estimation of NRE (Hank and Bremner, 1976). Both of these methods were indirect and would not distinguish between fertilizer N and soil N. The assumption was that immobilization-mineralization and other N transformations during the course of the experiment were the same for both treated and control plots. Obviously this was an erroneous assumption and could account for gross differences between recovery calculated by nonisotopic and isotopic techniques (Westerrnan and Kurtz, 1974). In addition, Rao et al. ( 1991) reported that the increased availability of soil N in fertilized plots had been attributed to: (i) stimulation of microbial activity by addition of N fertilizer, (ii) nitrification of NI-L fertilizers, causing acid hydrolysis of soil organic substances, (iii) changes in the plant’s physiological processes induced by fertilizer N, (iv) osmotic efl‘ects and (v) increased root growth in fertilized plots. The isotopic dilution technique was used by many workers to determine NRE by direct measurement of l’N-labeled fertilizer taken up by the plant. This method was influenced by pool substitution of 15N for 1"N, which could result in erroneous NRE estimations. This substitution leaves less l5N available for plant uptake and so N recoveries 92 estimated by this method might be low and could result in erroneous NRE estimation when substitution is not accounted for quantitatively. Low and Piper (1957) studied the uptake of l’N-labeled ammonium sulfate and urea N in ryegrass grown under greenhouse conditions. They found that N uptake calculated by the difference method was greater than the amount calculated by the 15N tracer method. The difference method indicated that 37.5% of the applied N was taken up compared to 28% uptake calculated by the 1’N method. Terman and Brown (1968) stated that the commonly used difference method was oversimplified and didn’t effectively characterize the efficiency of applied N. In addition, they stated that labeling techniques offered no distinct advantage over nonisotopic techniques in most routine N efliciency studies if multiple rates were compared. Zamyatina et al. (1968) determined the eficiencies of fertilizer N use in small field plots by difl‘erence method were higher than those obtained by the 1’N method. Applications of fertilizer N in greenhouse and laboratory experiments had been reported to stimulate, depress or have no effect on the mineralization of soil N (Westerrnan and Kurtz, 1973). In 1974, the same authors used 4 methods to estimate the recovery of fertilizer N by Sudax (sorghum-sudangrass hybrid) grown under field conditions. They found that on average the difference method over-estimated recovery of urea and oxamide N in sudangrass by 30% when compared to the isotopic tracer method. Similarly, nonisotopic linear regression of total N in crops on rates of N over-estimated recovery of urea and oxamide N when compared to linear regressions of isotopically-labeled fertilizer N. Westerrnan and Kurtz (1974) concluded that recoveries by nonisotopic methods were more likely to coincide with recoveries from isotopic method when only 93 one harvest of the crop was considered and when N removed in the crop was small or when mineralizable N in the soil was low. In their opinion, a simpler and probably better method to determine the N recovery efliciency was from the difl'erence between the total N uptake on fertilized and unfertilized plots. Recoveries measured in this way were usually constant over a considerable range of N fertilizer rates although they vary substantially among sites and crops. Similarly, a pot study by Rao et al. (1991) to estimate the N-recovery efficiency by spring wheat showed that the NRE estimation by the isotopic method averaged 20% lower than the difference method, although the two estimations were strongly correlated (r’= 0.94). Models for Estimating N Fertilizer Requirement ThefertilizerNrequirement ofacrop dependsinpart ontheamountomeineralized from soil organic N before and during growth. Any attempt to predict the requirement by modeling techniques thus needs modeling of N mineralization. Since mineralized N may be leached when it is nitrified, it is important that the model should also include nitrification of ammonium ions and be compatible with an appropriate leaching model (Addiscott, 1983). One model developed in France for estimating the N fertilizer requirement of winter wheat ( Viaux 1980, Reemy and Viaux 1982) was : bY= (N..+M. +M,+M., +F) C where: Y is expected yield. b is total N per unit yield of grain, M., is mineral N in soil at the end of winter to the depth of soil to which the crop roots finally penetrate, M. is N mineralized fi'om the soil organic matter, Mr is N mineralized fi'om residues of a previous crop, M0 is N 94 mineralized from organic manures, F is fertilizer N to be applied and C is the emciency of utilization. Nitrogen balance systems for giving advice on fertilizer use had also been developed in the United States (Stanford 1973, 1982; Carter et al., 1976). Carter et al. (1976) developed a model where the inputs were the potential crop yield, profile mineral N at the start of the growing season and a recovery factor. Sugarbeet, a rainfed crop, is grown on a wide diversity of soils and management practices in Michigan. These practices include crop rotations of legumes, returning crop residues and application of animal manures. In Michigan, researchers reported the efl‘ect of crop rotation on increasing yields of sugarbeet (Cook et al., 1946; Robertson et al., 1965 and 1977; Christenson, 1989; Christenson et al., 1991). Optimum and economic sugarbeet production without polluting the environment requiresanaccurateestimationofthefertilizerNrequired. Inviewofthisconcern, itis necessary to have a prediction of N supply from soil organic matter for making fertilizer N recommendations for sugarbeet production. Models for predicting fertilizer N needs for sugarbeet under Michigan conditions are not develOped yet. The objective of this study was to develop a model to predict N fertilizer requirement forsugarbeetgrownonahfisteguaysiltyclaysoil. Thismodelwasbasedoaneaching,N uptake and N mineralization models that were developed and discussed in Chapter 3. 95 MATERIAIS AND METHODS This chapter will cover root yield, quality and estimation of each parameter that constitutes the prediction model for N fertilizer needs on mgarbeet. In 1993 and 1994 two field experiments were established at the Saginaw Valley Bean and Beet Research Farm, Saginaw County, Michigan (43° 4’ N, 84° 6’ W). Sugarbeet were planted after dry bean (Phaseolus vulgaris L.) on a Misteguay silty clay soil (fine, illitic (calcareous), mesic, Aeric Endoaquent) in both years. Nitrogen as NH4N03 was broadcast prior to sugarbeet planting in both years. Nitrogen rates were 0, 33, 67, 100, 134 and 168 kg N ha". The plot size was 3 x 21 m and the experiment was placed in a randomized complete block design. There were 6 replications in 1993 and 4 in 1994. At the end of each season four sugarbeet plants were harvested, processed and analyzed for total N using the processing and analysis procedures mentioned in Chapter 2. Root Yield and Quality Root yield was determined by harvesting two-10 m rows in 1993 and one-19 m row in 1994. Sugar quality was determined by selecting twenty average size beet roots from each plot for juice extraction. These beets were sliced and the juice extracted fiom the resulting pulp was immediately frozen. The frozen juice was analyzed for clear juice purity and sucrose concentration as described by Dexter et al. (1967) and Caruthers and Oldfield (1961), respectively. Recoverable sugar per hectare and per megagram were calculated using the 96 following equations based on the work of Dexter et al. (1967) and modified by Michigan Sugar Company (Dr. Zielke, personal communication)‘: RWST [(%s * 18.4 - 22)*(1-(60/(CJP-3.5)))]/0.4 [4.1] RWSH = RWST " RY [4.2] where RWST is the recoverable white sugar per megagram, %S is the percent sugar, CJP is the clear juice purity, RWSH is the recoverable white sugar per hectare and RY is the root yield (Mg ha"). Nitrogen Uptake (N .) Nitrogen uptake was estimated at harvest by removing 4 evenly spaced beet plants. The plants were divided into leaves, petioles and roots. They were processed as described in Chapter 2. Nitrogen was determined using a UN analyzer. Ground plant material (2-3 mg for leaf 5-6 mg for petiole and 8-11 mg for root tissue) was pelletized prior to analysis. Modeling N Fertilizer Needs The N fertilizer needs model consists of five independent variables and takes on the form: N! = [Nup(opt) ’ eM(Nt + Null» )Jlef [43} where: Nf is predicted fertilizer N rate (kg N ha"), M.,,(opt) is plant N uptake at an optimum N rate (kg ha"), e... is fiaction of mineral N recovered by plant, N. is predicted field net N mineralization (kg ha"), Nm is measured mineral N at the beginning of the ‘ Dr. Richard Zielke, Director of Research, Michigan Sugar Company, Carrollton, Michigan. 97 season (kg ha") and e; is fertilizer N eficiency. It was assumed that predicted net N mineralization in the field in check plots was the same as in the fertilized plots and the mineral N at the beginning of the season was also the same in treated and nontreated plots. Fraction of mineral N recovered by the plant (e,.) was also considered to be constant in treated and non-treated plots and accounted for any N not used by the crop such as the residual N at the end of the growing season (N ,) and leached N (M). Soil mineral N (N...-. and N) Soil samples from 0-22 and 22-45 cm deep were taken periodically during each growing season from the center of each check plot. They were processed and analyzed for mineral N (NIL and N03) using the methods and analysis described in Chapter 2. Mineral N at the beginning of growing season (M.,...) was used in N fertilizer needs prediction model and that at the end of the season (N,) was measured but not used in the model. Predicted field N mineralization (N,) Data from 1994 were used to test the prediction equations. Extensive details of results and conclusions on the cumulative N mineralization in the field were presented in Chapter 3. Plant N uptake at optimum N rate ( N,(opt) ) Four adjacent plants were harvested fiom each plot in October of 1993 and 1994. Plant samples were separated, into leaves, petioles and roots. They were processed (cleaning, 98 dryingandgrinding)usingfl1eprocessingpmcedmeouflinedinChapter2. Pelletscontaining ground plant material (2-3 mg for leaves, 5-6 mg for petioles and 8-11 mg for roots) were analyzedfortotalNonaC/Nanalyzer. Optimum N rate was determined from the first derivative of the equation of recoverable sugar per hectare versus applied N rate. Then, N uptake at the optimum N rate was determined from a plot of N uptake versus N rate. The values of N uptake at optimum N rate were then used in Eq. [4.3] to predict N fertilizer needs on sugarbeet for 1993 and 1994 growing seasons. Fraction of mineral N recovered by plant (e...) Based on Eq. [4.3] the fraction of mineral N recovered by plant, e,,., was determined using the following equation: e... =( Nup - (8f . Nf))/(M + NW") [4.4] N uptake fiom the check plots (Nap), fertilizer N rate (Me) in check plots, predicted cumulative N mineralization in the field (M) and soil mineral N at the beginning of the growing season (NM) were used to determine e,,.. Nitrogen fertilizer efficiency (Cf) Nitrogen fertilizer efficiency (e,) was determined by non-isotopic linear regression method in both years and isotopically in 1993. Using the non-isotopic method, e; was determined from the slope of the linear regression line of N uptake as a function of applied 99 fertilizer N rate. Isotopic determination was made in a separate experiment on the same soil. NRE (e,) was calculated using the equations suggested by Rennie and Rennie (1983): %Ndfi = atom % lsN excess in plant/atom % l’N excess in tracer [4.5 ] NRE = (%Ndft * plant total N )lrate of N fertilizer applied [4.6 ] Prediction of N fertilizer rate (N1) Using all the above mentioned parameters N fertilizer rate was predicted using the following equation: Nf = [Nup ( opt. N rate) - Nap ( 0 N rate ) ]/e, [4.7] RESULTS AND DISCUSSION The 1993 and 1994 growing seasons were different which affected yield of sugarbeet. The yield tended to be greater in 1994. However, the pattern of response to applied N was Similar in both years. The optimum N rate was 128 kg ha'1 for both years. Sugarbeet quality (percent sugar and recoverable sugar per Mg) declined with increasing N rate both years. The difl‘erent weather patterns for the two years played a significant role in the differences between the two years. However these factors did not affect clear juice purity (CJP) as it would be shown in the following sections of this chapter. 100 Root Yield and Quality In 1993 and 1994, root yield and recoverable sugar per hectare increased with increasing N rate reaching a maximum at 134 kg N ha" (Tables 1 and 2). Recoverable sucrose per megagram, % sucrose and CJP decreased with increasing N rates applied in both growing seasons. In addition, root yield, recoverable sugar and % sucrose tended to be higher in 1994 than 1993 at the same N fertilizer rates applied. However, CJP values tended to be similar for both seasons. The 1994 season was warmer and there was more rainfall (Christenson et al., 1994). Model Variables Determinations N; was predicted using Eqs. [4.3] or [4.7] and N, was predicted using equation [3.6] as shown in Chapter 3. N”. was measured and M.,, e; and e,,. were calculated using Eq. [4.4]. Nup (opt) was determined using equations in Figures 1 and 3 for 1993 and Figures 2 and 4 for 1994. e; was determined as the slope of the regression equations in Figures 5 and 6 for 1993 and 1994, respectively. In the following sections, results of each variable for both years will be presented in details. Soil mineral N (Na. and N.) Table 3 Showed the mass of mineral N in check plots at the beginning (NW-n) and at the end of the growing season (N,) for both years. N”, was less in the 1993 than in 1994. NM was used in Eq. [4.4] to calculate em and in turn in Eq. [4.3] to predict N fertilizer needs by sugarbeet, N;. The mass of N at the end of the season (N,) in 1993 was not difl‘erent from that of 1994. N, was measured but not used in the model. 101 Predicted field N mineralization av.) The cumulative net mineralization in the long-term aerobic incubation experiment, N.., was fitted to two models. Both models, N mineralization rates (k), N mineralization potential (No) as well as r2 or R2 are presented in Table 4. The regression curves are shown in Figures 1 and 2 of Chapter 3. Cumulative net mineralization (N,) in the field for 1993 and 1994 were predicted by correcting N. for temperature and soil moisture. N. for 1993 and 1994 at Qlo 2.0 were 92.9 kg ha'1 and 120 kg ha", respectively (Table 5). The 1994 N, tended to be greater than 1993. This was due to warmer air temperatures and moisture conditions during 1994 growing season (Christenson et al., 1994) that indirectly increased the microorganisms activities to mineralize the decomposed crop residues. PlantNuptake at optimum Nrote (N...) In 1993 and 1994, N uptake increased significantly as N rates increased reaching a maximum at 134 kg ha" (Tables 1 and 2). Maximum N uptake in the 1994 growing season was 30% more than in 1993. The optimum N rate was determined fiom the regression equation in Figures 1 and 2 for 1993 and 1994, respectively. N uptake at the optimum N rate was determined from the equation in Figures 3 and 4 for 1993 and 1994, respectively. N uptake at optimum N rate was 178 kg ha'1 and 217 kg ha’1 for 1993 and 1994 growing seasons, respectively (Table 5). These values were used in Eq. [4.3] to predict N fertilizer needs (Nf). 102 Table 1. Root yield, N uptake, recoverable sugar per hectare (RWSH), recoverable sugar per ton (RWST), sucrose and clear juice purity (CJP) of sugarbeet as affected by nitrogen rate on a Misteguay silty clay soil, 1993. Nitrogen Root Nitrogen Rate Yield Uptake RWSH RWST Sucrose CJP kg ha“ Mg ha" kg ha'l kg ha" kg Mg" ----«....- % -..- ...... 0 59.8 114 7500 125 17.3 94.2 33 61.6 124 7515 122 17.0 93.8 67. 65.8 141 7870 120 16.9 93.3 101 65.2 141 7810 120 16.7 93.7 134 69.5 189 8020 116 16.4 93.2 168 68.5 222 7780 114 16.0 93.4 LSDp e 0.05, 3.61 33.8 455 3.65 0.29 0.85 Table 2. Root yield, N uptake, recoverable sugar per hectare (RWSH), recoverable sugar per ton (RWST), sucrose and clear juice purity (CJP) of sugarbeet as affected by nitrogen rate on a Misteguay silty clay soil, 1994. Nitrogen Root Nitrogen Rate Yield Uptake RWSH RWST Sucrose CJP kg ha'1 Mg ha’1 kg ha'1 kg ha'1 kg Mg'l ----------- % ---------- 0 _ 68.5 114 9050 132 18.1 94.4 33 76.4 135 9940 130 17.8 94.5 67 79.5 176 10305 130 17.9 94.1 101 81.8 176 10420 128 17.8 93.6 134 85.3 236 10635 125 17.4 93.6 168 84.2 247 10500 125 17.5 93.4 LSD(p (0,05) 4.39 49.7 797 5.41 0.59 0.78 103 Table 3. Mass of soil mineral N at 0-45 cm deep 1n check plots of a Misteguay silty clay soil m 1993 and 1994 growing seasons T Year Season Mass ----.- kg ha'1 ..---- 1993 Beginning (Nara) 43.9 (2.4) End (N.) 35.8 (0.6) 1994 Beginning (Nan) 55.3 (2.0) End (N,) 23.2 (0.7) 1’ Numbers in parantheses are standard errors of the means. Means are average of 6 replications for 1993 and of 4 replications for 1994. Table 4. Equations and coefficients of determination (r2 or R2) of linear and exponential models of cumulative net N mineralization predicted on check plots of a Misteguay silty clay soil in an aerobic incubation experiment in 1993. Model Equation r2 or R2 Linear 0.152 t + 3.4 0.979 Exponential 73.1 (1 - exp ( - 0.00337 t) ) 0.988 104 Table 5. Predicted and measured model parametrs‘l’, N.., , N. , N. , Nu, (opt), N;, e... and e at Qto of 2.0 for 1993 and 1994 growing seasons. Year Nu, N; Nu, (Opt) Nf e... 6f kg ha'1 1993 114 92.9 178 103 0.83 0.62 1994 114 120 217 126 0.65 0.82 '1' N uptake in check plots (Nup ); predicted net mineralization (Nt ); plant N uptake at optimum N rate (N,p (opt)); predicted N rate (N; ); fraction of mineral N recovered by plant (e...) and N fertilizer efficiency (q). 105 .82 a 33% one sauce 2 .3 Boobs 3 came... ozeoscoom ._ been one we use Banana 2. 03 of o: 02 00— on ow ov on o . 82. _ — — — ~ u q — db- 1— ‘1’ p. p— cop coon cot. cows cog 5.5 u an ._ . 8358.0 - as: + «3 u a 1. 80m co; (Ipq 8x) refing olqeraAooog 106 .32 5 ocean as donate 2 3 88% a awe. osabscoom .N acme 9.2 use case cease z ow. o2 o3 ofi 2: 8 00 on em o _ b P _ _ q . . a 1)— cc -tl- - oovo m m w m... 9 08¢ my 00 m \YIIU GO Us 0 cox: Bk. ( / seed u we succeed - x28 + ”Se 1 » 89: 107 .82 a 33% as nuance z 3 Become a sesame 6 sea: 2 .m came fa z we use agape 2 ea 8: c: on. 2: 8 8 on em o .. a .. u a a a a o .. em - 02 l on 83 u an -. 8N ”demoed + used + e: n e 03 (Iraq 851) :3de N 108 o3 03 ov— I— p.- .vefl E woman 88 Snap—om Z .3 38% an 833: Z .v oeswfi as L fa use case cease 2 CS ow on 3.. on o h » a p < L Al 4- - u awed u am axeoooe + cameo + m: u a 8 8 (1.9!! 8)0 94min N O In v-It § emN 109 Fraction of mineral N recovered by plant (e...) The fraction of mineral N recovered by plant, e,., is calculated using Eq. [4.4]. Values of e... at Q10 2.0 for 1993 and 1994 growing seasons are Shown in Table 5. The fiaction of mineral N recovered by plant, e... , accounted for any soil mineral N not used by the crop during the growing season. This fraction was higher for 1993 than 1994. This could be either due to higher predicted values of field N mineralization or predicted N leached than should be. These values were used in Eq. [4.3] to predict N fertilizer needs by sugarbeet, Nf. N recovery efficiency (e) Using the non-isotopic linear regression method nitrogen fertilizer efficiency, (3; was determined as the slope of the regression line of N uptake as a function of applied fertilizer N rate (Figures 5 and 6). Nitrogen fertilizer efliciency, ef, tended to be lower in 1993 compared to 1994 (Table 5). This was due to higher rainfall and warmer air temperatures. These two factors increased soil N mineralization and plant growth rate. This suggests that e, is a moisture and temperature dependent parameter. Nitrogen fertilizer eficiency, ef, determined by non-isotopic linear regression method was 0.62 and 0.4 when determined by isotope N fertilizer in 1993. Prediction of N fertilizer rate (N) Equations [4.3] or [4.7] were used to predict N fertilizer rate. Predicted N fertilizer rate, N]; was 103 kg ha" in 1993 and 166 kg ha'1 in 1994 (Table 5). An increase in N fertilizer beyond the optimum rate would add to production costs. The excess N 110 would be either left in soil at end of season, exposed for denitrification and/or leaching. The model suggested that 103 kg N ha'1 is an optimum fertilizer N rate to be applied for optimum returns in moderate weather years and 126 kg N ha'1 in wet or humid years. 111 .82 a Base 28 donate 2 .3 v08»? mm 833: Z we 2.: 2.22022 2: mo 2.2m 2: 3 Q 2 65680 .0982 Z .m 83E one we use nuance z 2: a: o: as 2: 8 8 on om o a a a .. a a a a o t On N m -e 2: m a a 9 0 Dr 1T o2 meow m (o. 83 u a. .- com o sued + N2 .1. a can 112 .32 a 8:23 as nuance z .3 380% mm 8.8% Z .«o 2.: commmocmoe 65 mo 82m 2: we 13.65686 .0382 Z .0 652m Ca was can agree 2 of om: oi . o2 00— on 8 ov on o p — h _ «r— «r- «h- p q u q u q mac n a. bead + 2 T a 91 8 .— r— 8 N (van 831) para/10093 N 113 SUMMARY Excessive use of N has deleterious efl‘ects on the quality of the harvested beet which makes the crop less profitable for both growers and processors. Optimum and economic sugarbeet production without polluting the environment requires an accurate estimate of the fertilizer N required. In N balance models, N fertilizer requirement is efl‘ectively calculated as the demand of the crop for N less the sum of the inorganic N in the soil at beginning of the season and an estimate of the total amount mineralized during the growing season. Prediction of N supply from soil organic matter is necessary for evaluation of N fertilizer needs on rain-fed sugarbeet production in Michigan. Nitrogen supply of Misteguay silty clay soil from soil organic matter in Michigan was predicted. Results were presented in Chapter 3 and were used in a working model with seven independent variables and one dependent variable using Eq. [4.3]. The model predicted N fertilizer needs of sugarbeet. Initial soil mineral N, soil N processes and weather factors have a big influence on yield, N uptake by crops, crop quality, fraction of mineral N recovered by plants and on prediction of N fertilizer needs. In 1993 and 1994, root yield and recoverable sugar per hectare increased significantly as N rates increased and reaching a maximum at 134 kg N ha'1 (Tables 1 and 2). An increase in N rate from 134 to 168 kg N ha'1 didn’t increase the root yield and recoverable sugar per hectare significantly in both years (Tables 1 and 2). Recoverable sucrose per megagram, % sucrose and CJP decreased with increased rates applied in both growing seasons (Tables 1 and 2). In addition, the values of root yields, recoverable sugar 114 per hectare and per megagram and % sucrose tended to be higher in 1994 compared to those of 1993 at same N fertilizer rates applied. However, CJP values were Similar both years. The reasons behind this increase could be attributed to warmer temperatures, higher rainfall, increased soil microorganisms activities, more mineralization of soil organic residues and higher initial soil mineral N in 1994 growing season compared to that of 1993. Nitrogen fertilizer needs model consisted of seven independent variables and took on the form: Nf = [Nap - e... (N, + NM," we where Nf is predicted fertilizer N rate (kg N ha"), Nap is plant N uptake at an optimum N rate (kg ha"), e... is fraction of mineral N recovered by plant, N, is predicted field net N mineralization (kg ha"), N,,.,-,. is measured mineral N at the beginning of the season (kg ha' 1) and e, is N fertilizer efficiency. Table 3 showed the mass of soil mineral N in check plots at the beginning (NW-n) and at the end (N,) of the growing season for both years. NM," for 1993 growing season was lower than that of 1994 growing season at 0-45 cm deep. However, N, of 1993 growing season was higher than that of 1994 at same depth. Cumulative net mineralization in the field, N,, for 1993 and 1994 were predicted by modifying N... for temperature and soil moisture. N, for 1993 and 1994 at Q10 2.0 were 92.9 kg ha" and 120 kg ha", respectively (Table 5). N, was higher in 1994 than in 1993. This was due to warmer temperatures and more rainfall during the 1994 growing season that indirectly increased the microorganisms activities to mineralize the decomposed crop residues. 115 The optimum N rate was determined from the regression equation in Figures 1 and 2 and N uptake at the optimum N rate was determined fi'om the equation in Figures 3 and 4. N uptake at optimum N rate was 178 kg ha’l and 217 kg ha'1 for 1993 and 1994 growing seasons, respectively (Table 5). The fraction of mineral N recovered by plant (e,..) at Qto 2.0 for 1993 was 0.83 0.65 for 1994 (Table 5). em accounted for any soil mineral N not used during the growing season. In 1993 and 1994, N uptake increased significantly as N rates increased and they were maximum at 134 kg ha’1 (Tables 1 and 2). Maximum N uptake in 1994 growing season was 30% more than in 1993. Using the non-isotopic linear regression method nitrogen fertilizer efficiency, cf, was determined as the slope of the regression line of N uptake as a function of applied fertilizer N rate (Figures 5 and 6). e; was lower in 1993 as compared to that of 1994 (Table 5). This was due to more rainfall and warmer air temperatures that in turn increased soil N mineralization and plant growth rate. This suggests that ef is a moisture and temperature dependent parameter. Nitrogen fertilizer efficiency, ef, determined by non-isotopic linear regression method was 0.62 and 0.40 when determined by isotope N fertilizer in 1993. Equation [4.7] was used to predict required N fertilizer rate for optimum N uptake. waas 103 kg ha'1 in 1993 and 126 kg ha‘1 in 1994 (Table 5). With higher N fertilizer efficiency the plant N uptake was higher and hence the N fertilizer needed was greater in 1994 as compared to that of 1993. 116 Applying N fertilizer in excess of the optimum N rate would be costly and non- profitable. In addition, mineral N left in soil as residual mineral N after harvest and not taken up by plants would be lost as denitrification or leaching. The results suggest that 103 kg N ha'1 is an optimum fertilizer N rate to be applied for optimum returns in moderate weather years and 126 kg N ha’1 in wet or humid years. These recommendations are done under rain-fed sugarbeet grown on a Misteguay silty clay soil. The N fertilizer needs model predicted the fertilizer required for sugarbeet well. LIST OF REFERENCES Adams, R. M., P. J. Farris and A. D. Halvorson. 1983. Sugar beet N fertilization and economic optima: Recoverable sucrose vs. root yield. Agron. J. 75: 173-176. Addiscott, T. M. 1983. Kinetics and temperature relationships of mineralization and nitrification in Rotharnsted soils with difl‘ering histories. J. of Soil Science 34:343- 353. Armstrong, M. J., G. F. Milford, T. O. Pocock, P. J. Last and W. Day. 1986. The dynamics of nitrogen uptake and its remobilization during the growth of sugar beet. J. Agric. Sci. Camb. 107:145-154. Burghes, D. N., I. Huntley and J. McDonald.1982. Applying mathematics: A course in Mathematical Modeling. p. 113. Ellis Horwood Ltd. England. Carruthers, A. J. F . T. Oldfield. 1961. Methods for assessment of beet quality. Intern. Sugar J. 63:72-74. Carter, J. N., D. T. Westerrnann and M. E. Jensen. 1976. Sugar beet yield and quality as affected by nitrogen level. Agron. J. 68:49-55. Christenson, D. R. 1989. Sugar beet yield trends as affected by cropping system. J. Sugar Beet Res. 26:A5. Christenson, D. R., C. E. Bricker and R. S. Gallagher. 1991. Crop yields as affected by cropping system and rotation. Michigan State Univ. Agric. Exp. Sta. Res. Rep. 516. Christenson, D. R., P. E. Horny and D. Fleischmann. 1994. Introduction and weather. p. 1-6. In 1994 Saginaw Valley Bean and Beet Research Report. Mich. Agric. Exp. Sta. Mich. state Univ. E. Lansing, MI. Cook, R. L., C. E. Miller and L. S. Robertson. 1946. Sugar beets in seven Michigan systems of crop rotation. Proc. Am. Soc. Sugarbeet Tech. 4:73-87. 117 118 Dexter, S. T., M. G. Frakes and F. W. Snyder. 1967. A rapid and practical method for determining extractable white sugar as may be applied to the evaluation of agronomic practices and grower deliveries in the sugarbeet industry. J. Am. Soc. Sugar Beet Tech. 14:433-454. Greenwood, D. J. 1986. Prediction of nitrogen fertilizer needs of arable crops. Adv. Plant Nutr. 2: 1-61. Halvorson, A. D. and G. P. Hartman. 1988. Nitrogen needs of sugarbeet produced with reduced-tillage systems. Agron. J. 80:719-722. Hank, R D. and J. M. Bremner. 1976. Use of tracers for soil and fertilizer nitrogen research. Adv. Agron. 28:219-266. Keeney, D. R. and R. F. Follett. 1991. Managing nitrogen for groundwater quality and farm profitability: Overview and introduction. p. 1-7. In Follett, R. F., D. R. Keeney and R. M. Cruse (ed.) Managing nitrogen for groundwater quality and farm profitability. SSSA, Madison, WI. Low, A J. and F . J. Piper. 1957. Nitrogen, Sulphur and carbon uptake from some nitrogen fertilizers using 15N. 35S, and 13C as tracers. J. Agr. Sci. 49:56-59. MicroSofi Excel. 1995. User’s guide version 5.0. Microsoft Corporation. Seattle, Wa, USA Parr, J. F. 1973. Chemical and biological considerations for maximizing the efficiency of fertilizer nitrogen. J. Environ. Qua]. 2:75-84. Rao, A C. S., J. L. Smith, R. I. Papendick and J. F. Parr. 1991. Influence of added nitrogen interactions in estimating recovery efficiency of labeled nitrogen. Soil Sci. Soc. Am. J. 55:1616-1621. Reemy, J. C. and Ph Viaux. 1982. The use of nitrogen fertilizer in intensive wheat growing in France. Proc. Fert. Soc. 211:67-92. Rennie, R. J. and D. A. Rennie. 1983. Techniques for quantifying N2 fixation in association with nonlegumes under field and greenhouse conditions. Can. J. Microbiol. 29: 1022-1034. Robertson, L. S., R. L. Cook, C. D. Piper, R. H. Dowdy and J. F. Davis. 1965. Sugarbeet production as affected by crop sequence and fertility levels. J. Am. Soc. Sugarbeet Tech. 13:304-313. Robertson, L. S., R. L. Cook and J. F. Davis. 1977. The Ferden Farm Report. IV:Soil management for navy beans. Michigan State Univ. Agric. Exp. Res. Rep. 350. 119 Rogers, T. H. 1961. Recovery of applied N by crops. Proceedings of Southern Agriculture Workers 58th Annual Conf. pp. 86-87. Shafl‘er, M. J ., A. D. Halvorson and F. J. Pierce. 1991. Nitrate leaching and economic analysis package (NLEAP) Model description and application. p. 285-3 22. In Follett, R. F., D. R. Keeney and R. M. Cruse (ed.) Managing nitrogen for groundwater quality and farm profitability. SSSA, Madison, WI. Stanford, G. 1982. Assessment of soil nitrogen availability. p. 651-687. In Stevenson (ed) Nitrogen in agricultural soils. ASA Spec. Publ. 22. ASA, Madison, WI. Stanford, G. M., H. Frere and D. H. Schwaninger. 1973. Temperature coeflicient of soil nitrogen mineralization rate. Soil Sci. 115232-23. Terman, G. L. and M. A. Brown. 1968. Crop recovery of applied fertilizer N. Plant Soil 29:48-65. Viaux, P. 1980. Manure nitrogen on winter cereals. Perspectives Agric. 43:10-26. Westerman R L. and L. T. Kurtz. 1973. Priming effect of l’N-labeled fertilizers on soil nitrogen in field experiments. Soil Sci. Soc. Amer. Proc. 37:725-727. Westerman, R. L., and L. T. Kurtz. 1974. Isot0pic and non isotopic estimations of fertilizer Nitrogen uptake by Sudangrass in field experiments. Soil Sci. Soc. Amer. Proc. 38:107-109. Zamyatina, V. B., N. I. Borisova, N. M. Varyuskina, S. V. Burtzeva and L. I. Kirpaneva. 1968. Investigations on the balance and use of l’N—tagged fertilizer nitrogen by plants in soils. Int. Congr. Soil Sci, Trans. 9th. (Adelaide, Aust.) 11:513-521. Chapter 5 SUMMARY AND CONCLUSIONS Optimum and economic sugarbeet production without polluting the environment requires an accurate estimate of the fertilizer N required. This entails evaluating the amount of mineral N present in the soil at the beginning of the season and the amount of N released from soil organic matter during the growing season. It seemed that modeling would be the best approach since models to predict N fertilizer needs by rain-fed sugarbeet are not developed yet. The main goal of this study was to develop a model that predicts N fertilizer needs by sugarbeet grown in rain-fed system on a Misteguay silty clay soil. The field studies were located on the Saginaw Valley Bean and Beet Research Farm in Saginaw County, Michigan (43° 4’ N, 84° 6’ W). In the development of the model, temporal and spatial distribution of 1’N in the soil and temporal pattern of N uptake were measured. Long term aerobic laboratory incubation studies were conducted to measure cumulative net N mineralization and hence to predict cumulative net N mineralization in the field. Models predicting daily soil-water balance, daily N leached and daily N uptake were developed. Root yields and quality parameters as affected by N fertilizer rates were evaluated. 120 121 Nitrogen fertilizer efliciency was determined. The results were summarized as follows: Temporal and Spatial Distribution or "N in Soil 1. Mineral N concentration was highest in the 30 cm depth after l-week after application. Mineral N concentration decreased with time at all depths except at 4-weeks after application. The decline with time at 120 cm was less pronounced than at the other depths. At point of application, atom % l’N excess declined with time at all depths. One week after application, atom % l’N excess was less in the 30 cm layer than in the lower depths. Ten cm lateral movement of the tracer 15N from point of injection was detected at 75 cm and 120 cm deep at 4-weeks after application. Temporal Pattern of N uptake by Sugarbeet 1. Nitrogen uptake and 15N uptake by sugarbeet from various depths followed a typical S-shaped pattern. Fifleen weeks after planting (3"l week of August 1991) marked the period when sugarbeet began to direct energy to storage of sugar rather than vegetative growth. Percent N derived fiom the tracer was recovered from all depths but most effectively from the top 30 cm depth. Eventhough N was taken from depths to 120 cm, N was taken up mainly from the surface 30 cm. 122 Estimation of Cumulative Net N Mineralization in the Field from a Laboratory Incubation Study 1. Data fi'om the cumulative net N mineralization (Na) in laboratory incubation study was fitted to linear and exponential models. Rate of mineralization was 0.152 mg kg'1 day“l and coefficient of determination was 10.974 for linear fit. These parameters were 0.00337 mg kg" day'1 and 0.988 for exponential fit, respectively. The potential N mineralization (No) for Misteguay silty clay soil was 73.1. This was determined at Optimum temperature and moisture of 25 °C and -0.03 Mpa, respectively. Rainfall during the growing season was less (368 mm) in 1993 than in 1994 (514 mm). The rainfall pattern in 1993 influenced the relative moisture content in the surface (0-22 cm) compared to the subsoil (22-45 cm). Moisture content of the surface soil was equal or greater than the subsoil except during the month of July where the surface soil had equal or less water content than the subsoil. The rainfall pattern in~1994 was more uniform with shorter periods with little rainfall. The surface soil was more moist relative to the subsoil during the whole season of 1994. Mineral N concentration was significantly higher in the surface layer than in the subsoil during June and early August of 1993. In both layers, mineral N 10. ll. 12. 13. 14. 123 concanrafionmcreasedunfillateJunemldthendecfineddrmmficaflyunfilmdof Julywhereitremainedfairlyconstanttherestoftheseason. 'I'heincreaseinsoilmineralNduringthegrowing seasonofl993 wasdueto mineralization ofsoil organic matterwhereasthedecreasewasdue to higherN uptake by sugarbeet relative to N mineralization. 'I‘hepattemofsoilmineralNinthe1994growingseasonwassimilartothatof1993 in the exceptinthefirstquarterofthe seasonwheremineralNconcentrationwasgreater in the subsoil layer than in the surface layer. This was due to heavy rainfall (104 mm) during a Short period of time and negligible to low N uptake by small sugarbeet plants. ' Thereasonsbehindtheincrease ofsoilmineralNin 1994 growing seasonwerethe same as those in 1993. However, the decline was due to leaching in addition to high N uptake by plants relative to soil N mineralization. Predicted field cumulative net N mineralization (N,) based on long-term incubation of Misteguay silty clay soil took the following forms: N, = W (k, t) + c and N, = W No (1- exp (-k, t)) for linw and exponential models, respectively. No is potential mineralizable N, k, is the adjusted rate of mineralization to air temperature, W is soil moisture correction and c is constant. The calculated cumulative net N mineralization in the field was 93.5 and 84.1 kg ha'1 for 1993 and 1994 growing seasons, respectively. Using the N balance approach suggested by Shafl’er’s et al. (1991), predicted amounts of N leached during 1993 growing season was considered insignificant 15. l6. l7. 18. 124 (6.9 kg ha"). However,estimated N leached in 1994 growing season was 35.7 kg ha". The addition ofthe estimated leached amounts ofsoil mineral N (35.7 kg ha") in 1994 to the calculated cumulative net N mineralization (84.1 kg ha") brought the latter value close to the predicted value (120 kg ha"). Measuredandpredictedatom% l’NinrrrineralNdcrlinedrapidlyathebeginning untilthe20'“dayoftheincubationthendecreasedataconstant rate. Predicted atom % 1’N in mineral N was almost double the measured value from the beginning ofthe incubation until the 20'h day. The overprediction could be attributed to immobilization of 1’N by soil microorganisms that wasn’t accounted for in the measured value. Gross rate of mineralization was 25.8% greater than net N mineralization rate. Predicting Nitrogen Fertilizer Needs on Sugarbeet Grown on Misteguay Silty Clay Soil in Michigan 1. Root yield and recoverable sugar per hectare increased significantly as N rates increased and they were maximum at 134 kg N ha'1 in 1993 and 1994. Recoverable sucrose per megagram, % sucrose and clear juice purity (CJP) decreased with increased rates applied in both growing seasons. Nitrogen fertilizer needs model took the following form: Nf = [Nup(0Pt) - en (M + Natal/er where: N; is predicted fertilizer N rate (kg N ha"), M.,,(opt) is plant N uptake at an optimum N rate (kg ha"), e... is fraction of mineral N recovered by plant, N,is 125 predicted field net N mineralization (kg ha"), NM is measured mineral N at the beginning of the season (kg ha") and e, is N fertilizer efliciency. 4. Optimum N uptake by sugarbeet was 178 kg ha‘l and 217 kg ha‘1 for the 1993 and 1994 growing seasons, respectively. 5. Fraction of mineral N recovered by plant (e,,.) was 0.83 and 0.65 for 1993 and 1994 growing seasons, respectively. e,.. accounted for any soil mineral N not used by the plants during the growing seasons. 6. Using the exponential model and at Q10 of 2 predicted field net N mineralization (M) was 92.9 kg ha" and 120 kg ha" for 1993 and 1994, respectively. 7. The measured mineral N at the beginning of the season (NM) was less (43.9 kg ha") in 1993 than that in 1994 (55.3 kg ha"). 8. N fertilizer efficiency (ef) was 0.62 in 1993 whereas it was 0.82 in 1994. 9. Optimum fertilizer N rate recommended for rain-fed sugarbeet grown on a Misteguay silty clay soil was 103 kg N ha'1 in moderate weather years and 126 kg N ha'1 in wet or humid years. This work showed that fertilizer N requirement could be predicted in both dry and wet seasons if the appropriate adjustments were made to selected coeflientients. These adjustments included the modification of N mineralization rate It for air temperatures and correction of N... for soil moisture W. This model should be tested on other soils and crops. It requires weather, soil and plant data to predict the N fertilizer needed. However, we realize that this model like any 126 other model is used after the harvest. Would it be possible to use this model at the beginning rather than at the end of the season? This can be achieved only after conducting experiments to get average values for optimum N uptake by the crop and the N fertilizer efliciency on a particular soil. Then Eq. [4.7], N; = [Nw(opt) - N (no fertilizer)]lef, can be used to predict the required N fertilizer to be applied during the growing season. MICHIcaN srnre UNIV. LIBRRRIES WWW lllHllWWlllN "mm ll WIN“ "WWI 31293015706421