HI l x f IIHHIIHIHllliHIWWIWIIHUHIIHIIHIWHHHI (1)010 Illllllllllllllllllllllllllllllnllll|||l|lllllllllll|lllll 31293 00911693 This is to certify that the thesis entitled ROOT AND SHOOT RESPONSES OF (Zea mays L.) AND LEUCAENA LEUCOCEPHALA TO SUBSOIL ALUMINUM TOXICITY AND pH VARIATIONS USING CALCIUM SULPHATE AND CALCIUM CARBONATE presented by Bernard Mdoka Mtonga i has been accepted towards fulfillment of the requirements for Masters Crop & Soil Sci. degree in éflfitflfl 5%; Major professor Date September 23, 1991 0-7639 MS U is an Affirmative Action/Equal Opportunity Institution I N LIBRARY Michigan State University \ :4 PLACE IN RETURN BOX to remove this checkout from your record. TO AVOID FINES return on or before due due. r————_——_—_—_—_—__——j DATE DUE DATE DUE DATE DUE _l ll____ 'l:jL__J- fiijl‘j | l ROOT AND SHOOT RESPONSES OF CORN (Zea mays L.) AND LEUCAENA LEUCOCEPHALA TO SUBSOIL ALUMINUM TOXICITY AND pH VARIATIONS USING CALCIUM SULPHATE AND CALCIUM CARBONATE BY Bernard Mdoka Mtonga A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Crop and Soil Sciences 1991 ABSTRACT ROOT AND SHOOT RESPONSES OF CORN (Zea mays L.) AND LEUCAENA LEUCOCEPHALA TO SUBSOIL ALUMINUM TOXICITY AND pH VARIATIONS USING CALCIUM SULPHATE AND CALCIUM CARBONATE By Bernard M. Mtonga Soil acidity and aluminum toxicity are known to affect root growth with subsequent decreases in plant yield. However, little is known about the effects of soil acidity and aluminum toxicity on the growth of corn (Zea mays L. Var Great lakes 450) and Leucaena Ieucocephala. This study, using two sources of Ca, was designed to investigate the chemical, biological and physical responses of both corn and Leucaena to soil acidity and aluminum toxicity. This was achieved by measuring their effects on the growth of corn and Leucaena roots and shoots. Leucaena and corn treatments were established in the greenhouse. In both treatment types, natural acidic soil was used as a control treatment. Bernard Mtonga Data collected included weekly measurements of plant heights, and at harvest shoot and root dry weight, and root length and diameter. The data indicate that corn is more responsive to soil acidity than Leucaena. Both shoot and root dry weights were significantly different in corn in response to liming but not in Leucaena. However most of this difference in corn was due to the smaller root diameter range (0.00-0.55mm). Liming did not significantly cause any differences in the growth rate and maximum heights of both corn and Leucaena. There were no significant difference in shoot to root ratios in corn or Leucaena, but there was a trend for liming to decrease the ratio in Leucaena. Overall dry weight data showed an increase in total dry weight in corn when the soil was treated with either CaSO4 or 03003. Liming Leucaena showed that calcium sulphate is more effective in increasing total dry weight than calcium carbonate. Soil data indicated that of the two liming sources, calcium carbonate had a more negative effect on root weight that shoot weight. The water and KCI extracted pH's decreased after cropping. Both liming sources were effective in reducing the aluminum level from an initial content of 2.95 milliequivalents (meq) to less than 1 meq with calcium carbonate being more effective than calcium sulphate. Coefficients of variation ranged from 5 to 40%. Root growth was greatest when the subsoil was treated with calcium sulphate. Dedicated to Judith and Emmanuel for their encouraging companionship. ACKNOWLEDGEMENTS I wish to humbly express my heartfelt and sincere appreciation to my major Professor, Dr. B. G. Ellis for his excellent guidance and patience throughout my entire academic stay at Michigan State University. His outstanding wisdom, counsel and under- standing in directing my research and course work cannot be equaHed. Furthermore, I would like to particularly thank all the other members of my Guidance Committee, Dr. A. J. Smucker, Dr. E. Foster and Dr. M. Gold for their valuable advice and willingness to direct my research studies. The diverse nature of my committee. was a valuable contribution to my studies. I also greatly appreciate the valuable technical assistance that Rosamond Soanes provided in my data collection and processing. Special thanks to my wife Judith and my son Emmanuel for providing an encouraging friendship and company as l pursued my studies. I will remain eternally grateful to my mother, brothers and sisters for their patience to allow me to complete my advanced studies at Michigan State University. Special appreciation is extended to my Sponsors for the adequate financial support they provided through the Zambian Government. Finally, glory to God in the highest for His Grace to success- fully see me through my studies. To Him be the glory forever and ever, AMEN. iv TABLE OF CONTENTS Bade LIST OF TABLES ........................................................................................... v ii LIST OF FIGURES .......................................................................................... vi ii INTRODUCTION .............................................................................................. 1 CHAPTER 1: UTERATURE REVIEW .................................................... 3 Liming and Aluminum Toxicity ....................................................... 3 Alleviation of Al toxicity by Calcium Sulphate .......... 4 Response of Com to Ca addition and Al Toxicity ............................................................................. 6 Response of Leucaena to Ca addition and Al Toxicity ......................................................................... 1 0 Literature cited ..................................................................................... 1 3 CHAPTER 2: ROOT AND SHOOT RESPONSES OF CORN AND LEUCAENA LEUCOCEPHALA TO SUBSOIL ALUMINUM TOXICITY AND pH VARIATIONS USING CALCIUM SULPHATE AND CALCIUM CARBONATE ...................................................................... 1 8 Introduction ............................................................................................ 1 8 Materials and Methods ........................................................................ 2 0 Results .................................................................................................... 23 Discussion ................................................................................................ 4 5 Literature cited ..................................................................................... 5 4 CHAPTER 3: SUMMARY AND CONCLUSIONS ......................................... 5 7 LIST OF TABLES CHAPTER 2 Table 1: Table 2: Table 3: Table 4: Table 5: Table 6: Table 7: Table 8: Plant tissue dry weight and root to shoot ratios of corn and Leucaena as affected by lime andgypsum ...................................................................... 24 Root length and density of corn and Leucaena as affected by lime and gypsum ............................. 31 Root surface area of corn and Leucaena as affected by lime and gypsum ............................. 36 Root volume of corn and Leucaena as affected by lime and gypsum ............................. 39 Pre-plant top and subsoil data .......................................... 43 Pre-plant and post-harvest subsoil characteristics data ................................................... 4 3 Post-harvest top and subsoil characteristic analysis data .................................................................. 4 4 Predicted speciation of AI as affected by subsoil pH and CaSO4 ............................................ 4 9 CHAPTER 2 Figure Figure Figure Figure Figure Figure Figure Figure Figure la: 1b: 10: 2a: 2b: 3a: 3b: 4a: 4b: LIST OF FIGURES Effects of CaSO4 and CaCOg on the plant height of corn ................................................................. 2 6 Effects of CaSO4 and CaCO3 on the plant height of Leucaena ........................................... 27 Effects of CaSO4 and CaC03 on the maximum plant heights of corn and Leucaena ...................... 28 Effects of CaSO4 and Ca003 on the percent distribution of root length of corn ....................... 32 Effects of CaSO4 and CaCO3 on the percent distribution of root length of Leucaena ............. 33 Effects of CaSO4 and CaCO3 on the percent distribution of surface area of corn .................... 37 Effects of CaSO4 and CaCOa on the percent surface area distribution of Leucaena ................ 38 Effects of CaSO4 and CaCO3 on the percent root volume distribution of corn ........................... 40 Effects of CaSO4 and CaCO3 on the percent root volume distribution of Leucaena ................ 41 INTRODUCTION It is well known that soil is the natural matrix for plant root growth as well as the primary natural agricultural resource. Any unfavorable soil condition may place a stress on plant growth and yield. The vast majority of soils of the tropics, including the cultivated soils, are acid. This study was developed to focus on tropical soils because of the serious nature of soil acidity and liming problems in the tropics. The well established practice of liming temperate-region soils to neutrality has not been effective in most of the highly weathered soils of the tropics. More often than not, liming to pH 7 has caused more harm than good, especially since most of tropical crops are well adapted to acid soil conditions. Such crops do not respond to liming in the same manner as temperate zone crops. Poor crop growth in acid soils can also be directly correlated with aluminum (Al) saturation (Sanchez, 1976). It is well known that pH per se has little direct effect on plant growth, except at pH values below 4.2, where the hydrogen ion (H+) concentration may stop or even reverse cation uptake by roots (Black, 1967). Accord- ing to Jackson (1967), Al toxicity, calcium (Ca) and/or magnesium (Mg) deficiency are some of the major factors responsible for acid soil infertility. Aluminum tends to accumulate in the roots and impede the uptake and translocation of Ca and phosphorus (P) to the 1 tops (Foy, 1974). Thus Al toxicity may produce or accentuate Ca and P deficiencies. It is admittedly true that many studies have been done on the effect of various adverse soil factors on the performance of many crops. But little if any has been done to investigate the response of Leucaena leucocephala and corn to soil acidity and Al toxicity using Ca materials. Thus, the main purpose of this study was to investi- gate the primary effects of soil acidity and Al toxicity on the growth of corn and Leucaena Ieucocephala which are important for alley cropping in tropical Africa. CHAPTER 1 LITERATURE REVIEW Of the two environments for plant growth, the soil is more complicated than the atmosphere (Russell, 1977). Between the two parts of the plant, the root and the shoot, the root, which grows below the soil surface, seems more complex than the shoot. Any chemical, physical and biological stress in the environment of the soil may inhibit or reduce root growth and plant productivity. Soil acidity and Al toxicity are two adverse environmental conditions which reduce the growth and dynamics of root systems of both agronomic crops and tree species. LIMING AND ALUMINUM TOXICITY. The purpose of liming is primarily to neutralize exchangeable AI which is normally accomplished by raising the soil pH to 5.5. The factors which need to be considered include the amount of lime needed to decrease the percent saturation to a desired level at which the particular crop and variety will grow, the quality of lime and the placement method (Sanchez, 1976). Much effort has been devoted to finding the best methods for estimating lime needs in the tropics. Kamprath (1970) and Reeve and Summer (1970) 3 suggested that lime recommendations be based on the amount of exchangeable Al in the topsoil. This would be achieved by multiplying the milliequivalents (meq) of Al by 1.5 to give the meq of Ca needed to be applied as lime. This implies that for every meq of exchangeable Al present, 1.5 meq of Ca or 1.65 tons/ha of CaCOs-equivalent should be added. In soils with high organic matter, the factor has to be raised to 2 or 3 because of the presence of exchangeable W". This method has been used very successfully in Brazil and other parts of the tropics since 1965. Alleviation of Aluminum Toxicity by Calcium Sulphate. According to Noble et al., 1988, the alleviation of Al toxicity by CaSO4 is partly due to an increase in the formation of less phytotoxic AISO4+ species. They found that the magnitude of al- leviation of Al toxicity by CaSO4 was smaller at pH 4.8 than at pH 4.2. They suggested that this pH dependency is due to lesser formation of AISO4+ at pH 4.8 than pH 4.2, together with an increase in formation of AI(OH)2+ at pH 4.8. Addition of Ca amelio- rates acid soil infertility factors by the fact that this treatment mechanistically results in the precipitation, complexation, polymerization or chelation of Al thereby reducing the levels of phytotoxic AI in solution (Hoyt and Turner, 1975; Hue et al., 1986). However not all acid soils restrict plant growth through Al toxicity. Adams and Moore (1983) clearly demonstrated that certain acid subsoils suffered from Ca deficiency rather than Al toxicity. The ameliorating effect of Ca on Al toxicity can be attributed to either a reduction in the activity of phytotoxic AI species, through an increase in the ionic strength of the solution or a direct physiological effect of the added Ca on the root surface (Alva et al., 1986; Clarkson and Sanderson, 1971; Rhue and Grogan, 1977). Furthermore, the associated carrier anion, which depends on the source of Ca applied, may result in the formation of less phytotoxic species. Such an effect has been demonstrated for 8042‘ when Ca was applied as CaSO4 (Kinraide and Parker, 1987). The relationship between tap root length of soybean and the activity of AISO4+ has been reported to be relatively poor. This observation adequately supports the lesser phytotoxicity of AISO4+ species and strongly suggests the need to modify solution Al indices to account for the 8042’ complexation of Al in a form that is less phytotoxic. Since increasing activity of AISO4+ was obtained by an increase in CaSO4, there was a confounding effect of improved root length at the higher CaSO4 additions due to Ca alleviation of Al toxicity (Noble et al., 1988). Thus, increasing Ca in the root environment has been reported to play a physiological role in alleviation of Al toxicity. Response of Corn to Liming and Aluminum Toxicity According to Sanchez (1976), corn is sensitive to 40 to 60 percent Al saturation. Although liming to zero Al saturation might be beneficial, lowering the Al saturation level to 20 percent could be more economical. When extremely acid Oxisols have their topsoil limed to pH 5.5, most of the root development of corn occurs in the topsoil. The high subsoil Al saturation prevents deeper root penetration. For this reason, Gonzalez and Kamprath (1973) compared incorporating lime at two depths, 0 to 15 cm and O to 30 cm in an Oxisol using a rototiller. They found that deeper applications produced higher yields. Root studies showed that higher yields were associated with deeper root development in the O to 30 cm layer which also diminished water stress during short term water deficits. The feasibility of deep lime incorporation in the field depends largely on soil structural properties and available equipment. Prior to 1950, literature from tropical soil regions is full of reports citing the lack of response of crops when tropical soils are limed to near neutrality. This has created the general idea that liming does not work in the tropics (Richardson, 1951). Kamprath (1971) reviewed the reasons for the lack of positive lime responses when highly leached soils are limed to neutrality. He found that overliming caused yield reduction, soil structure deterioration, and decreased availability of P, boron (B), zinc (Zn) and manganese (Mn). The review indicated that liming to neutrality promotes the formation of smaller aggregates, thus reducing infiltration rates and making some Oxisols and Ultisols more susceptible to erosion (Peele, 1936; Schuffelen and Middleburg 1954; Ghani et al., 1955). Furthermore, overliming induces P deficiency in soils with high P fixation capacity. The bulk of the evidence suggests that highly weathered soils should not be limed to pH values greater than 5.5 since beyond that level yield decreases can occur. However, overliming oxides and oxide-coated layer silicate systems with little pH-dependent charge produces no yield decreases (McLean, 1971). Corn management, especially in the trapics, should be aimed at determining the minimum level of lime needed, selecting species and varieties more tolerant to Al, and following practices that promote deeper root development in the acid subsoils. Mahilum et al., (1970), studied the residual effects of liming in Hawaii and found that after 5 years, a rate of 2 tons lime/ha kept the Al level at about 1 meq (from an original value of 3 meq), even though most of the Ca was leached to lower levels. Apparently Al ions did not readily reoccupy the exchange sites even when Ca leached to lower depths such that after 5 years, the residual effect of liming at the rate of 5 tons/ha had completely disappeared. In sharp contrast, De Freitas and Van Raij (1975) obtained a positive corn response to lime in a sandy Oxisol of Brazil, that response was still apparent 6 years after lime application. They observed increasing yield responses with time and attributed them to the dissolution of the coarser lime particles. According to Rhue (1979), some plants have the ability to accumulate enormous amounts of Al in their foliage without evidence of injury or toxicity. In a review article on the effects of Al on plant growth, Jackson (1967) concluded that correlations between Al contents in the foliage of crop plants and Al toxicity are more the exception than the rule. He stated that toxic effects of AI may result from excess Al in the growth medium (soil) with little or no change in Al content in the foliage. Jackson further reported that in some situations the Al contents in the foliage of crop plants were either unaffected or actually increased with the addition of lime or P. Various mechanisms have been proposed to explain the differential Al tolerance of plant species. Mussel and Staples (1979) suggested that plants that are able to maintain sizeable concentrations of Al within their tissues while at the same time maintaining adequate P levels, must possess a mechanism whereby Al is prevented from precipitating with P at physiological pH's. Varietal differences in Al tolerance have also been reported in corn (Clark, 1974). As a species, corn is fairly tolerant of Al. Using nutrient solutions containing a range in Al concentrations, Foy and Brown (1964) showed that com was more tolerant to Al than barley. Of six species tested, corn gave the least response to lime when grown on acid soil which had an initial pH value of 4.6. In field studies, Kamprath (1970) observed that liming consistently increased the growth of corn only when the Al saturation was greater than 70%. In another study, Clark and Brown (1974) have shown differences in Al tolerance within and among different varieties of corn. They reported marked differences among inbred lines in their ability to take up P from acid, Bladen soil (pH 4.3). Using a Ca variable to control the degree of Al toxicity showed that a wide range in tolerance to Al exists among corn inbreds. Roots of one inbred (ND408) showed symptoms of severe Al toxicity at all levels of stress (swelling, stunting and discoloration), while those of another inbred (Va 17) were fairly tolerant even at the lowest level of Ca (Mussel and Staples, 1979). They further reported that the response of corn to Ca in the presence of 0.25 mM Al is not a direct response to Ca per se, but is a response to the ameliorating effect of Ca on Al toxicity. Genetic control of Al tolerance in corn has also been suggested in which the hypothesis of a multiple series of factors controlling tolerance in corn has been obtained from two composites, one of temperate and the other of tropical origin. The study indicated that rapid progress could be made in developing Al tolerant corn populations in only one or two cycles of selection starting with the original composites (Mussel and Staples, 1979). 10 Response of Leucaena to Ca Addition and Al Toxicity. While the humid tropics are viewed as areas of high potential productivity, production on many humid tropical soils is constrained by many factorssuch as low nutrient reserves, Al toxicity, high P fixation, soil acidity, steep slopes, low cation exchange capacity and shallow organic soils. These limitations adversely affect the performance of both trees and agronomic crops that are grown in an intercropping system. Climatic characteristics often limit tree growth. Moisture stress, seasonal temperature fluctuations, poor soil drainage and infiltration, soil acidity and soil infertility also limit tree and agronomic crop growth. Establishment of Leucaena Ieucocephala is often nutritionally constrained by low P levels in tropical soils (Benge, 1982). But its principal limitations are that it prefers a tropical lowland area, requires a reasonable mineral balance (Ahmad and N9, 1981) and specific rhizobia in the soil (Halliday, 1981; Sanginga, et al., 1988; Trinick, 1980). Low fertility diminishes its performance. Furthermore, Sanginga, et al., (1988), reported that most tropical soils are deficient in P such that fertilization with P becomes necessary for Leucaena growth. Leucaena Ieucocephala needs P for vigorous growth and N fixation (Benge, 1982; Hu and Chang, 1981; National Academy of Sciences,1977). In another study, Melo et al., (1987), showed that shoot height, shoot dry weight and nutrient accumulation were increased significantly in the Al-intolerant cultivar when inoculated with the mycorhizal fungus Glomus ll leptotichum. They also found non significant difference between seedlings given Al treatments. Leucaena is reported to have grown poorly on acid soils. However among the genetic introductions, variety K-636 showed the best growth at one site (llTA Annual Report, 1986). According to Fox et al., (1985), growth of Leucaena on an acidic Oxisol increased with increasing lime until a pH in excess of 7 was attained. The beneficial effects of liming on Leucaena growth were linear from pH 4.8 to 7.0. Liming the Oxisol depressed Al concentration in the pH range 4.8 to 5.5 and Mn in the pH range 4.8 to 5.7. They found that liming did not change solution Ca until pH 5.7 was reached, after which solution Ca contents of saturation extracts increased exponentially with increasing pH. They sug- gested that improved Ca nutrition may have been responsible for increased growth of Leucaena that was associated with increasing soil pH in the range 6 to 7 and beyond. Although Al toxicity rather than Mn toxicity was believed to be a major factor causing infertility of the Ultisol from one site, the Leucaena growth response curve was substantially the same as on the manginiferous Oxisol, including increased production with increasing pH in the range 5.8 to 7.1. These data suggest that Mn toxicity, Al toxicity, and at least one other factor including Ca deficiency, all inter- acting at the low pH, were responsible for growth responses asso- ciated with liming. Furthermore, they argue that an important factor in liming soils of the humid tropics is the small quantity of lime required to effect pH changes at low end of the lime curve and the relatively 12 large quantity of lime required to effect a change in Ca concentration. This is due to the fact that mineral soils with variable charge colloids are poorly buffered when soil pH is <5.3 (Fox, 1981). Relatively little lime was required to increase the pH of the Oxisol to 5.5, a pH at which Al toxicity is unlikely. Starting at a pH at which net charge of the soil is zero, an increase in pH of variable-charge soils is accompanied by an increase in effective cation exchange capacity (ECEC). In another study Juo and Uzu (1977), observed that Ca deficiency is a real possibility even for plants that have low Ca requirements if the plants are growing at a pH where liming produces little change in Ca concentration. Root dynamics studies have shown that Leucaena is generally deep rooted having both deep penetration and horizontal extension thereby exhibiting best root development both in the topsoil and subsoil (Hairiah and Van Noordwijk, 1986). In addition, Kang et al., (1985), have shown that com and Leucaena have different root feeding zones, with Leucaena extracting moisture from deeper soil layers. Prunings added as mulch substantially increased moisture retention in the topsoil. This is why maize is often grown in alley cropping system intercropped with Leucaena Ieucocephala. LITERATURE CITED Almad, N. and N9, F.S.P. 1981. Growth of Leucaena Ieucocephala in relation to soil pH, nutrient levels and rhizobia concentration. Leucaena Research Reports 2:5-10. Alva, A.K., C.J. Asher and 0.6. Edwards. 1986. The role of calcium in alleviating aluminum toxicity. Aust. J. Agric. Res. 37:373-382. Benge, MD. 1982. The miracle tree: Reality or myth? In: Leucaena Research in the Asian-Pacific Region. IDRC pp 95-98. Ottawa. Ontario. Canada. Black, C. A. 1967. Soil plant relationships, 2nd ed. Wiley, N.Y. Clark, RB, and J.C. Brown. 1974. lntraspecific differences in Al tolerance in corn. Comm. Soil Science Plant Anal. 5: 213-227. Clarkson, D.T., and J. Sanderson. 1971. Inhibition of the uptake and long-distance transport of calcium by aluminum and other polyvalent cations. J. Exp. Bot. 22:837-851. De Freitas, L. M. M., and B. Van Raij. 1975. Residual effects of liming a sandy clay loam Latosol. pp. 300-307. In E. Bornemisza and A. Alvarado (eds), Soil management in Tropical America. North Carolina State University. Raleigh. 13 14 Fox, R.L. 1981. Soils with variable charge: Agronomic and fertility aspects. pp.195-224. In B.K.G. Theng (ed) Soilswith variable charge.New Zealand Society of Soil Science, Soil Bureau, DSlR, Lower Hutt, N.Z. Fox, R.L., Yost, R.S., Saidy, NA, and RT. Kang. 1985. Nutritional Complexities with pH Variables in Humid Tropical Soils. Soil Sci. Soc. of Ame. J. 49: 1475-1480. Foy, 0.0., and J.C. Brown. 1964. Toxic factors in acid soils. ll. Differential Aluminum tolerance of plant species. Soil Sci. Soc. Amer. Proc. 28: 27-32. Foy, CD. 1974. Effects of aluminum on plant growth. pp. 601- 642. In E.W. Carson (Ed), The plant root and its environment. University Press of Virginia, Charlottesville. Ghani, M.O., K.A. Hassan, and M.F.A. Kahn. 1955. Effects of liming on aggregation, non-capillary pore space and permeability of laterite soils. Soil Sci. 80: 469-478. Hairiah, K. and M. Van Noordwijk. 1986. Root studies on a Tropical ultisol in relation to nitrogen management. Report of field work at llTA's high rainfall sub-station at Onne (Port Harcourt, Nigeria) in 1985. CODEN; IBBRAH (7-86) pp. 75-91. Halliday, J. 1981. Nitrogen fixation by Leucaena in acid soils. Leucaena Research Reports 2: 71-73. Hoyt, PB, and R.G. Turner. 1975. Effects of organic materials added to very acid soils on pH, Aluminum, exchangeable NH4, and crop yields. Soil Sci. 119:227-237. Hu Ta-Wei and Chang, W. E. 1981. Growth and nutrient levels of Leucaena Ieucocephala: Response to lime and phosphorus on acid soil. Leucaena Research Reports 2: 48-49. 15 llTA (International Institute Of Tropical Agriculture, 1986. Farming Systems Program Annual Report, 1985. lbadan Nigeria. 119-120. Jackson, WA 1967. Physiological effects of soil acidity. In Soil acidity and Liming (R.W. Pearson and F. Adams eds) Am. Soc. Agron. NO. 12243-124. Juo, A.S.R., and FD. Uzu. 1977. Liming and nutrient interactions in two Ultisols from southern Nigeria. Plant Soil 47:419-430. Kamprath, E.J. 1970. Exchangeable Aluminum as a criterion for liming leached mineral soils. Soil Sci. Soc. of Amer. Proc. 34:252- 254. Kamprath, E.J. 1971. Potentially detrimental effects of liming highly weathered soils to neutrality. Proc. Soil Crop Sci. Soc. Fla. 31:200-203. Kamprath, E.J. 1973. Soil acidity and Liming. pp126-128. In P.A Sanchez (ed.), "A Review of Soils Research in Tropical America." North Carolina Agr. Exp. Sta. Tech. Bull. 219. Kang, B.T., Grimme, H., and Lawson, TL 1985. Alley cropping sequentially cropped maize and cowpea with Leucaena on a sandy soil in southern Nigeria. Plant Soil 85: 267- 277. Kang, B.T.,Wilson, G, F. and Lawson, TL 1986. Alley cropping: A stable alternative to shifting cultivation. llTA. lbadan, Nigeria. 8- 21. May. Kinraide, TB, and DR. Parker. 1987. Non-phytotoxicity of the aluminum sulfate ion, AISO4+. Physiol. Planta. 71:207-212. 16 Mahilum, B. C., R. L. Fox, and J. A. Silva. 1970. Residual effects of liming volcanic ash soils in the tropics. Soil Sci. 109:102-109. McLean, EC. 1971. Potentially beneficial effects of liming: chemical and physical. Proc. Soil Crop Sci. Fla. 31: 189-199. Melo, I.S., Silveria, A. P. D. DA; Maluf, A. M. 1987. Effect of aluminum and Glomus leptotichum on the development of cultivars of Leucaena Ieucocephala tolerant and intolerant of aluminum. Superior agric. 44: 1365-1380. Mussel, H., and RC. Staples. 1979. Stress Physiology in crop plants. John Wiley and Sons, Inc. Wiley-lnterscience Publication. New York. pp. 61-106. ‘ National Academy of Sciences. 1977. Leucaena: Promising forage and tree crop for the tropics. Washington, DC. USA. NAS. pp115. Noble, A.D., M.E. Summer, and AK. Alva. 1988. The pH dependency of Aluminum phytotoxicity alleviation by calcium sulfate. Soil Sci. J. 53:1398-1402. Peele, TC. 1936. The effects of calcium on the erodibility of soils. Soil Sci. Soc. Amer. Proc. 1: 47-58. Rhue, RD, and 0.0 Grogan. 1977. Screening corn for aluminum tolerance using different Ca and Mg concentrations. Agron. J. 69:755-760. Rhue, RD. 1979. Differential Aluminum Tolerance in Crop Plants. Contribution from the Department of Agronomy, Cornell University, Ithaca, New York as Agronomy Paper N0. 1212. In Mussel, H., and RC. Staples. 1979. Stress Physiology in crop plants. John Wiley and Sons, Inc. Wiley-lnterscience Publication. New York. pp. 62-80. 17 Richardson, H. L. 1951. Soil acidity and Liming with tropical crops. World Crops 3: 339-340. Russell, RS. 1977. Plant Root System: Their function and interaction with the soil. Mc Graw-Hill Book Co. (UK) pp. 1. Sanchez, PA. 1976. Properties and management of soils in the tropics. John Wiley and Sons, Inc. NY. pp 224 - 253. Sanchez, P.A., Palm, C.A., Davey, C.B., Szcott, LT, and Russell, CE. 1985. Tree crops as soil improvers in the humid tropics? In: Cannel, M.G.R. and Jackson, J.E. Attributes of trees as crop plants. Institute of Terrestrial Ecology, Huntington, England. Sanginga, N., Mulongoyi, K., and Ayanaba, A. 1988. Response of Leucaena/Rhizobia symbiosis to mineral nutrients in southwestern Nigeria. Plant and Soil 112: 121-127. Schuffelen, A. C. and H. A. Middleburg. 1954. Structural deterioration of lateritic soils through liming. Trans. Fifth Int. Congr. Soil Sci. 22158-165. Trinick, M.J. 1980. Relationships among the fast growing rhizobia of Lab/ab purpureus, Leucaena Ieucocephala, Mimosa spp., Acacia farnesiana and Sesbania grandiflora and their affinities with other rhizobial groups. J. Appl. Bacteriol. 49:39-53. CHAPTER 2 ROOT AND SHOOT RESPONSES OF CORN (Zea mays L.) AND LEUCAENA LEUCOCEPHALA TO SUBSOIL ALUMINUM TOXICITY AND pH VARIATIONS USING CALCIUM SULPHATE AND CALCIUM CARBONATE. INTRODUCTION Aluminum (Al) toxicity and soil acidity are serious causes of poor plant growth and low yields due to the fact that they impair proper root growth and development. This problem is more common in the tropics than temperate regions (Sanchez, 1976) and the subsoil is the primary zone of soil acidity and Al toxicity. In normal circumstances, lime should be applied to the subsoil for effective reduction of Al toxicity and soil infertility due to soil acidity. But physically incorporating lime in subsoils is difficult. On the other hand CaSO4 is sufficiently soluble to allow the movement of significant quantities of Ca and 804 into the subsoil with water, when CaSO4 is applied to the top soil. 18 19 Previous studies have recorded that inhibition of root growth is one of the first observable symptoms of Al toxicity in plants (Scott et al., 1991). But a differential response exists between AI- tolerant germplasm and AI-sensitive germplasm. Briggs et al., (1989) have shown in wheat that Al-tolerant germplasm had greater root weight index than Al-sensitive germplasm in response to pH change. The objective of this study was to investigate the response of a grain crop (corn) and a N fixing multipurpose leguminous tree (Leucaena) to soil acidity and Al toxicity. The sources of Ca used were CaSO4 and CaCO3. The primary idea was to see the difference and effectiveness of these materials in neutralizing soil acidity and Al toxicity. Soil chemistry data, shoot and root dynamics were the major focus of interest to evaluate their effectiveness and response of corn and Leucaena to variation in soil pH and Al. MATERIALS AND METHODS This study was conducted in the greenhouse due to logistical considerations because naturally acidic soils were not located near Michigan State University Campus. The soil, with initial average topsoil and subsoil pH values (1N KCI 1:1 soil to solution) of 4.6 and 3.9, respectively was collected from Kellogg Biological Station. The soil was air-dried for 5-6 days, screened and thor- oughly mixed. Initial water and KCI measurements of pH, KCI extracted exchangeable Al, Ca, and P contents were done on the soil before planting using the methods of analysis outlined in the Agronomy Procedure N0.9 Part 2 (Page et al., 1982). The subsoil weight per container was 4,000 9 while the top soil weight was 4,200 g per container. The sub-soils were prepared for planting by adding either 43.35 g of CaSO4.2H20 or 9.63 g of Ca003 to the subsoil in separate cans. Each can was 15.5 cm in diameter and 17.5 cm high. In order to ensure even distribution of the chemicals, the soil was spread on a flat plastic onto which either of the substances were evenly distributed and mixed about 50 times. The bottom can was then packed half full with the subsoil after which 450 ml of de-ionized water was added. After filling the can completely with the subsoil an additional 840 ml of distilled water was added. Then a can with bottom removed was placed above the container and sealed on top of it. Potassium 20 21 phosphate (KH2P04) was added and mixed to the topsoil as a source of K and P at the rate of 1.04 g per can. After almost filling the top can with surface soil, more distilled water was added to bring the soil to field capacity. The seeds were then sown into the surface soil after which the rest of the topsoil was added to the top can. The procedure was similar for establishing Leucaena seedlings. The soil packing procedure aimed at reaching a field capacity of 18% moisture and a bulk density of 1.4 g/cm3. Leuceana Ieucocephala seeds were germinated in petri dishes in the dark and then transplanted after 3 days. Two seedlings were initially transplanted and then thinned to 1 seedling per can after 2 weeks. Corn (Zea mays L. var: Great Lakes 450) was directly seeded. Four seeds were sown after which the seedlings were thinned to 2 seedlings per can 2 weeks after planting. The cans were placed on a bench in a randomized complete block design (RCBD), with four replications. The treatments were: 1. Corn planted in untreated soil. 2. Leucaena Ieucocephala transplanted into untreated soil. 3. Corn planted in soil to which CaSO4 was added to the subsofl. 4. Leucaena Leucocephala transplanted into soil to which CaSO4 was added to the subsoil. 5. Corn planted in soil with the subsoil limed with Ca003. 6. Leucaena Ieucocephala planted in soil with the subsoil limed with CaC03. 22 Every day throughout the growing period, the soil was returned to field capacity by adding appropriate amounts of distilled water. Plant heights were measured weekly. Nitrogen was applied to corn twice during the growing period using NH4NO3 solution at the rate of 109 of N per container. Corn was harvested after 9 weeks (the plants had just tas- selled). The harvested plants were immediately weighed then dried and reweighed to determine shoot fresh and dry matter content. The roots were harvested from the top and subsoils separately then removed from the soil by washing with the hydropneumatic elutriation system (Smucker et al., 1982) after which they were stained and stored in the cooler at 4°C in readiness for processing with the Robotic camera system (Smucker, 1989) which was used to take video images of the roots. Root length and diameter were determined by computer image processing (Smucker et al., 1987). This procedure was repeated for Leucaena plant shoots and roots which were harvested 15 weeks after planting. Further data analysis was done with LOTUS 123 and MSTAT C. Post harvest measurements of soil pH, Al, Ca and P contents were also determined for the soil after harvesting. RESULTS From the results of shoot and root dynamics obtained in this study, it is obvious that corn responded more to lime and gypsum additions than did Leucaena. Leucaena may be more Al-tolerant than corn because it evolved in tropical areas. Responses of Plant Tissue Dry Weights and Root to Shoot Ratios to Lime and Gypsum Addition. Table 1 shows that root and shoot dry weights of corn were significantly increased by both CaSO4 and CaC03. But with Leu- caena, plant tissue dry matter (roots and shoots) was not significantly increased by application of CaSO4 or Ca003 but both sources did increase the shoot weights. In general, CaSO4 caused higher plant root dry weights in both corn and Leucaena than did CaCO3. The root to shoot ratios of corn and Leucaena were not significantly affected by CaSO4 or CaCO3 application. But there was a trend of decrease in root to shoot ratios with CaSO4 or CaCO3 additions in Leucaena. The plants had an increased shoot dry weight than root weight when either CaSO4 or CaCO3 was added. However, the decrease in the ratios was not significant. 23 24 Table 1. Plant tissue dry weight and root to shoot ratios of corn and Leucaena as affected by lime and gypsum. TREATMENTS Plant tissue dry weight Roots Shoots Rootzshoot ratio' Total dry wgt grams Corn. Control 0.65 45.2 0.014 45.9 03604 1.33 54.3 0.024 56.6 Ca003 1.08 54.7 0.018 55.8 LSDo.05 0.37 4.41 n.s. 4.7 Leucaena. Control 1.02 4.51 0.23 5.53 08504 1.21 6.03 0.20 7.27 06003 0.87 5.25 0.16 6.15 LS130.05 n.s. n.s. n.s. n.s. * Subsoil Root to Shoot ratios. 25 Furthermore, the results indicate that addition of CaSO4 0r CaC03 increased the growth rates of corn (Figure 1a) and Leucaena (Figure 1b) as well as the maximum plant heights attained by both corn and Leucaena after 9 and 15 weeks of growth respectively (Figure 1c). Of the two sources of Ca, CaSO4 generally gave higher values in both corn and Leucaena in terms of root and shoot dry weights, root to shoot ratios and the total dry matter content of the plants. PLANT HEIGHT (cm) 26 100 80" 60-1 401 20- —0— Control —"— C3304 +Cam3 .1 u TIME (WEEKS) 10 Figure 1a: Effects of 0380:, and 03003 on the plant height of 00m. PLANT HEIGHT (cm) 27 40 30-1 20"I 10-1 —‘3— Control —*—CaSO4 —'—CaCO3 5 1O 15 TIME (WEEKS) Figure 10: Effects of 06304 and 06003 on the plant height of Leucaena. 20 28 CORNDMYLD I LEUC. DMYLD \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\a III/IIIIIIIIIIII[I’ll/IIIIIIII/lII \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\L I’ll/IIII’ll!I’ll/IIIIIIIIIIIIIIII \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\. III/IIIIIIIIII’ll/IIIIIIIIIIIIIIII \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\. 'lr"""'ri'""'r"1rirlr""""r' 4 4 44|44444444 44 4 444444 4444 \\\\\\\\\\\\\\\\\\\\\\\\\\\ IIIIIIIIIIIIIIIIIIIIIIIII 4444 \\\\ I” \; I’k A L ’4 1 1 \\\\\\\\\\\\\\\\\\\\\\\\\\\\A III’ll/IIIIIIIIIIIIIIII’IIII \\\\\\\\\\\\\\\\\\\\\\\\\\\\L IIIII/I’llIIIIIIIIII’IIIIIII \\\\\\\\\\\\\\\\\\\\\\\\\\\\L IIII/IIIIIIIIIIIIII’ll/I’ll, \\\\\\\\\\\\\\\\\\\\\\\\\\\\L III/IIIIIIIIIII[III/IIIIIIII 100 80'- 60-1 u o 4. A59 From: .536 . o o 2 C6304 Effects of CaSO4 and 03003 on the maximum plant heights of 00m and Leucaena. Figure 10 29 Responses of Root Length and Density to Lime and Gypsum. Root length and density responses of corn and Leucaena to CaCO3 and CaSO4 addition are tabulated in Table 2. Root length results are similar to those of plant tissue dry matter. The root densities of corn or Leucaena were not increased by additions of CaCOg or CaSO4. Total root length is significantly increased in corn when CaCO3 or CaSO4 is added. However, adding CaSO4 or CaCO3 to the subsoil did not cause significant increases in root length of Leucaena. The significant increase in root length of corn in response to Ca003 and CaSO4, is primarily and significantly contributed by the smallest diameter range of root sizes (0- 0.25mm) which account for 74.9 to 81.6% of the total root length (Figure 2a). Furthermore, the figure shows that the medium diameter range of root size (0.25-0.55mm), contributes 15.4 to 20.5% of the total root length of corn whereas 2.2 to 4.6% of the total root length of corn is contributed by the largest diameter range sizes (0.55-0.90mm). In Leucaena, 42.5 to 46.2% of the observed differences in total root length is due to the smallest diameter root range sizes. The medium sized roots contained 46.5 to 48.1% of the total root length while the largest roots contribute only 7.2 to 9.9% of the total root length of Leucaena (Figure 2b). It is clear from this study that in both corn and Leucaena, the total root length is principally that of the small roots. But the medium sized roots contribute more towards the total root length in Leucaena than in corn. In both corn 30 and Leucaena, the largest roots gave insignificant contributions towards the total root length. 31 Table 2. Root length and density of corn and Leucaena as affected by lime and gypsum. Root length diameter classes Total Root (Millimeters) root length density TREATMENTS 0025 0.25-0.55 0.55-0.90 (cm) (g/cm3) Corn. (cm) Control 59.2 15.7 1.8 76.7 0.17 03504 123.8 34.0 7.2 165.0 0.13 Caoo3 132.3 24.9 4.9 162.2 0.14 LSDo.05 53.9 12.2 3.2 65.5 n.s. Leucaena. Control 32.6 34.7 5.1 72.4 0.12 08504 24.9 30.4 5.8 61.2 0.20 Ca(303 33.5 33.5 5.2 72.2 0.11 LSD0.05 n.s. n.s. n.s. n.s. n.s. 32 Control T -- -- -- \\\\\\\\\ _ 11111111: -K\\\\\\\\ an”... \Iuc. ”a .. n // / /.N.H.IH/I ./. .... . ... I..............p.......n. n /M./. ”r r // /// ///.//.,. O/J/Ur/oul/zz// ///U////ly /// //II//.l./I./ ././/// /////////.t// ././/..l./ // / III/IIIIIIIIIIIIIIIIIIIIII/IIIIIIII/II \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ IIIIIll/IIIIII/IIIIIIIIIIll/IIIIIIIIII V\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ yr’ff”’,rr’rff’frfrfffrfffffrrfrfrr 100- 80-1 20" u d 0 o 6 4 .3 20.25355 282$ 58 0-0.25mm 0.25-0.55mm 0.55-0.90mm Effects of C3304 and 06003 on the percent dstribution of root length of 00m. Figure 2a 33 Control 100 - 90 80' 70" q q q 1 q H 0 o O 6 5 4 36V 29595.90 502m.— boom - 0 3 u o 2 10'1 1 1 o 0.25-0.55mm 0.55-0.90mm 0-0.25mm Figure 20: Effects of C6304 and CaCO30n the percent distribution of root length of Leucaena. 34 Responses of Root Surface Area to Lime and Gypsum Additions. Table 3 indicates that the total root surface area of corn is significantly increased when CaCOg or CaSO4 is added, with CaSO4 giving the highest increase. The total root surface area of corn is almost equally contributed by the smallest and medium sized roots which account for 45 to 55% and 33 to 42% of the total root surface area, respectively. The largest roots contribute only 8 to 17% 0f the total root surface area (Figure 3a). Notably, CaSO4 caused a decrease in the individual root diameter sizes as well as total root surface area in Leucaena but the differences were not significant. There are more medium sized roots in Leucaena than in corn. They contribute 60 to 64% of the total root surface area of Leucaena. The smallest and largest roots are responsible for 17 to 20% and 17 to 23% 0f the total root surface area of Leucaena, respectively (Figure 3b). Reported in Table 4 is the response of total root volume of both corn and Leucaena to Ca003 or CaSO4 addition. The increase in root volume of corn and Leucaena in response to CaCO3 or CaSO4 addition is non-significant. However, the medium sized roots contributed 54 to 66% of the total root volume in corn (Figure 4a) and 64 to 70% in Leucaena (Figure 4b). In com, the smallest and largest roots are responsible for 14 to 21% and 16 to 30% of the total root volume, respectively. The contribution (4.1 to 5%) of the smaller roots of Leucaena towards the total root volume is almost negligible compared to that of larger roots which caused 25 to 35 32% increase in root volume of the total volume (Figure 4b). 36 Table 3. Root surface area of corn and Leucaena as affected by lime and gypsum. Root length diameter classes (Millimeters) TREATMENTS Total root 0-0.25 0.25-0.55 0.55-0.90 surface area cm2 Corn. Control 23.2 19 .7 4.08 47.0 08504 48.6 42.7 16.4 107.8 03003 51.9 31.4 11.2 94.5 LSDo.05 21.17 15.39 7.39 37.35 Leucaena. Contro' 12.8 43.6 11.7 68.1 C4504 9.8 38.2 13.3 61.3 03003 13.2 42.1 11.9 67.1 L300.05 n.s. n.s. n.s. n.s. 37 E Control LLLLLLLLLLLLLLLLLLLLLLLLLL LL;L.. 100 q 80 u o 4 u 0 5 3L 20.59590 boom 20- 0.25-0.55mm O.55-O.90mm 0-0.25mm Effects of CaSOAand CaCO30n the percent of root volume of 00m. Figure 4a 411 100 i -- Control 80' " I CaSO4 ' CaCO3 3 cf: 60- .— .3. (E 1 o , m 2 3 9 40- I— ........... 8 r: 20- " 0-0.25mm 0.25-0.55mm 0.55-0.90mm Figure 40: Effects 0103804 and CaCO3 0n the percent distribution of root volume of Leucaena 42 Pre-plant and Post-harvest Subsoil pH and Al Content in Response to Ca Addition. Results of the initial site, pre-plant and post-harvest soil analyses of top and subsoil pH, exchangeable Al and Ca, and extractable P are presented in Tables 5, 6, and 7. The initial pH in water and KCI of the subsoil were 4.97 and 3.91 respectively (Table 5). Pre-plant Al concentration levels range from 3.99 to 6.75 cmol per Kg (cmol (P+) Kg'1). For the control and CaSO4 treatments, the Al was reduced to about half the original values after plant growth. With both corn and Leucaena, there were no significant changes in P and Ca contents with plant growth and soil treatment. The post- harvest subsoil levels of Ca were relatively lower than expected (Table 6). A comparison of post harvest top and subsoil pH is given in Table 7. The soil analysis data shows that with both corn and Leucaena, there is a decrease in subsoil pH (H20 and KCI) after plant growth. In both crops, CaSO4 incorporation into the subsoil and the control resulted in a pH drop in the subsoil; whereas CaCO3 increased the subsoil KCI pH. Of the two sources of Ca, CaCO3 was more effective in reducing the Al level from an initial content of 6-7 to <0.2 cmol (P+) Kg'I. 43 Table 5. Pre-plant top and subsoil data. pH(H20) pH(KCl) TOPSOIL 5.62 4.61 SUBSOIL 4.97 3.91 Table 6. Pre-plant and post-harvest subsoil characteristics analysis data. Ex. Al (CEO) Ex. P(Conc.) Ex.Ca (Conc.) cmol(P+)Kg'1 ppm ppm (Pre) (Post) (Post) (Post) Corn. Control 5.91 3.65 56.25 286.0 08504 6.75 2.99 55.25 295.5 C6003 6.27 0.12 56.25 267.0 LS 00.05 n.s. 0.59 n.s. 32.87 Leucaena. Control 7.31 2.48 62.33 276.5 08504 6.27 2.48 59.33 324.0 93003 3.99 0.10 59.00 267.0 LSDo.05 n.s. 1.14 n.s. 45.18 Table 7: Post-harvest top and subsoil characteristics analysis data.’ TOP-SOIL . sue SOIL leH20) pHIKCII leH20) pHIKCI) Corn. Control 4.90 3.73 5.25 3.75 08504 4.50 3.70 4.43 3.78 C3003 4.80 3.70 5.88 4.80 LSDo.05 0.14 n.s. 0.46 0.17 Leucaena. Comm. 4.93 3.80 5.55 3.80 C3504 4.90 3.80 4.43 3.80 06003 4.85 3.85 5.80 4.93 LSD0.05 n.s. n.s. 0.32 0.09 * Ca treatments were applied to the subsoil only. DISCUSSION Plant Growth Changes Following Addition of CaSO4 and CaC03. According to Scott et al., (1991), the greatest effect of Al is on root growth. Therefore it is common to see a decreased root to shoot ratio with decreasing Al. In the absence of reduced photosynthesis, this would imply that a smaller proportion of the assimilated carbon is translocated to the roots, resulting in accumulations of carbon within the shoot. This is in agreement with the root to shoot ratios obtained in this study. But, of the two sources of Ca, CaSO4 caused a greater change in root to shoot ratio than did 03003 with the greatest effect seen in corn (Table 1). Since corn responded more to Al alleviation than Leucaena, it is likely that com is more Al-sensitive than Leucaena. Furthermore, in other studies, it has been shown that Al affects the concentrations of organic acids in a variety of plant species, and could play a role in detoxification of Al in the cytoplasm (Suhayda and Haung., 1986). They suggest that if accumulation of organic acids permits detoxification of Al ions by chelation, then concentrations should be higher in the Al-tolerant than Al- sensitive germplasm. In this study, this effect could be assumed to 45 46 explain differences between Al-tolerant Leucaena and Al-sensitive com. This is because when the plants were exposed to toxic levels of Al, the rate of photosynthesis in the primary leaves may have increased on a dry weight basis while the rate of translocation from primary leaves may have declined as Hoddinott and Richter (1987) have reported for beans (Phaseolus vulgaris). Thus, the photosynthetically fixed carbon must have been diverted into a metabolite pool other than starch. This shift in patterns of carbon allocation could represent an energetic cost of Al toxicity or metabolic cost of Al-tolerance mechanism which may require carbon skeletons for their action. For example, chelation of Al by carboxylic acids in the cytoplasm or rhizosphere have been postulated as tolerance mechanisms, and roots of Al-tolerant cultivars often have higher concentrations of carboxylic acids than Al-sensitive cultivars under conditions of Al-stress (Taylor, 1988). The effects of Al on the function of root cap and primary root meristem have been previously reported (Bennet et al., 1985; and Bennet et al., 1987) where the action of Al is considered to be primarily directed at the morphologically distinctive activities of the peripheral cap cells (Bennet and Breen, 1991). They argue that since the cells are not mitotically active, Al-induced changes in root growth rates are directed through naturally occurring regulators present in the cap. This concept is also supported by the studies of Bennet et al., (1987). Other studies have shown a regenerative capacity in primary roots which may permit their recovery from Al. Such results revealed the reactivation of 47 physiological mechanisms during recovery. They also provide information not only on how plant roots may recover from the unfavorable conditions associated with Al, but also indicate some of the cellular interrelationships within the root apex which are involved in regulating root growth responses (Bennet and Breen,, 1989) This is also likely to explain the plant growth changes observed in this study. Predicted Speciation of Al as Affected by Subsoil Lime and Gypsum Additions. The addition of lime to very acid subsoils is expected to reduce the Al3+ activity in the soil solution by increasing soil pH. This effect can be quantified by the use of thermodynamic constants and known soil chemical conditions. The speciation program called Minequal (Allison, et al., 1990) was used for this purpose to predict treatment effects on the activity of Al3+ under the experimental conditions of this study (Table 8). The addition of lime increased the subsoil pH to 5.8 in water and 4.8 in KCI. The pH in KCI was used for purposes of speciation since this more nearly approximates the ionic strength expected at field capacity where lime was applied. The predicted speciation given in Table 8 shows that the concentration of Al3+ decreased from 5.32x10'3 to 6.12x10“6 moles per liter as the pH was increased from 3.91 to 4.8. Other species of AI (Al(OH)2+ and Al(OH)3) became appreciable as the pH increased and accounted for 39% of 48 the Al in solution as compared to 7% at pH 3.91. It should also be noted that the total Al in solution decreased by nearly 1000 fold as soil pH changed from 3.91 to 4.8. 49 TABLE 8: Predicted speciation of Al as affected by subsoil pH and 03304. CaSO4 SPECIES CONTROL (No re-disol. of AI(OH)3) AI(OH)3 + CaSO4 Moles/Liter pH 3.91 Al3+ 5.32x10'3 (92.8%) 2.84x10'3 (51.6%) 9.65X10'3 (66.6%) AISO4+ 2.18X10'4 (3.8%) 2.01X10'3 (36.6%) 3.80X10'3 (26.2%) AISO42' 2.75X10'6 (<1%) 5.60x10'4 (10.2%) 7.84X10‘4 (5.4%) pH 4.2 Al3+ 4.16X10'4 (82.6%) 1.63x10'4 (39.2%) 8.32X10'4 (42.7%) Also4+ 4.54X10'5 (9.1%) 1.77X10'4 (42.5%) 7.93X10'4 (40.8%) Also42- 9.43X10'7(<1%) 6.49X10‘5 (15.6%) 2.66X10'4 (13.7%) pH 4.4 AI3+ 9.88x10'5 (77.1%) 7.63X10'5 (38%) 2.01X10'4 (38.7%) AISO4+ 1.22X10'5 (9.5%) 8.44x10'5 (42%) 2.16x10'4 (41.7%) AISO42' 2.71X10‘7 (<1%) 3.14x10’5 (15.7%) 7.9x10‘5 (15.2%) pH 4.6 Al3+ 2.45X10' 5(70.2%) 7.41x10'5 (36.9%) 4.99x10'5 (36.8%) AISO4+ 3.11X10'6(8.9%) 8.2X10'5 (40.9%) 5.56X10'5 (40.9%) 7.06x10‘8 (<1%) 3.06X10'5 (15.3%) 2.08X10‘5 (15.3%) 50 The addition of gypsum produced a pH in water of 4.43 (Table 7) by the end of the growing season. Since the subsoil should still contain gypsum, this is likely to be the ionic strength that would exist at field capacity. Therefore, a series of pH runs were made with increasing pH's from 3.91 to 4.6 to examine the change in Al3+ with increasing pH and in the presence of saturated CaSO4. The speciation was also accomplished assuming that gibbsite did not redisociate at a rate sufficiently rapid to react with all of the sulphate and also assuming that equilibrium was reached in which the gibbsite finally reached equilibrium with the solution. In a practical situation where gypsum is added to soils, the reaction with Al3+ would be expected to be very rapid but the redisolution of gibbsite would be expected to take from a few months to several years depending upon the crystallinity of the gibbsite. The addition of gypsum had significantly reduced the Al3+ in solution at all pH's that were examined If gibbsite rapidly dissociates, the addition of gypsum causes the formation of AI(SO4)+ without lowering Al3+ for a given pH. But in practice where excess gypsum is applied, gibbsite is expected to dissolve much more slowly than gibbsite. Under these conditions the Al3+ content of the soil solution is reduced at any pH with the formation of AI(SO4)+ complexes. The reduction from pH 3.91 without gypsum to 4.6 with gypsum was seven fold. The use of gypsum, therefore, offers a practical method of modifying the environment of acid subsoils without the expense of deep tillage. This is particularly important since many of the areas in the tropics have no opportunity of deep tillage. 51 The Role of 08504 and C8003 in Tropical Soils The application of lime to temperate acid soils is commonly aimed at raising the pH to near neutrality in the belief that effects such as low base status, Al toxicity, and P fixation will be eliminated or at least favorably affected (Reeve and Summer., 1970). But two earlier surveys (Adams and Pearson, 1967; Fisher, 1969) have indicated that it is unnecessary to lime to pH 6.5 or above while several other authors had already reported depressed yields as a result of heavy lime applications (Pierre and Browning, 1935, Hourigan et al., 1961; Shoop et al., 1961; Reeve and Summer, 1970). Liming to neutrality has proved almost always ineffective in the tropics. It is better to apply sufficient lime to alleviate AI toxicity than attaining near neutrality soil status. Lime and gypsum are two fundamental and cheaply available sources of Ca in the tropics. The cost of these materials may vary depending upon transportation costs. Hence their utilization in this study. A detailed and comprehensive representative of the acidity status of tropical soils such as Oxisols, Ultisols, Alfisols, and Inceptisols profiles are documented by Sanchez, (1976). Oxisols usually have a high percentage of Al saturation throughout their profiles (Guerrero, 1971). Some Ultisols also have high Al saturation, particularly in the subsoil. The Al status of other Inceptisols and Entisols is quite variable. Most vertisols, Mollisols and Aridsols are essentially 100 percent base saturated while most Spodosols and Histosols are acid. Some organic soils have high exchangeable hydrogen contents (Sanchez, 1976). This state of 52 tropical soils requires the use of cheap Ca materials to improve the status of soils for better plant growth and higher yields. This study showed that both 08804 and 08003 alleviate Al toxicity when applied to the subsoil (Table 6). To find lime sources of sufficient fineness and purity is a major practical problem in the tropics. The selection of sources must take into account the Ca and Mg contents of the liming material and the Ca and Mg status of the soil. Fineness is crucial for faster reaction. A good grade of fineness is more than 60 mesh; 8 better grade, 100 mesh (Sanchez, 1976). Subsoil application of Ca was undertaken in this study to exploit the beneficial effects of deep incorporation. When extremely acid Oxisols have their topsoil limed to pH 5.5, most of the root development of corn occurs in the topsoil. The high subsoil Al saturation prevents deeper root penetration. This was also observed in this study in both corn and Leucaena. Of the total root length of corn in the subsoil, most of it was contributed by the smallest root sizes (Figure 2a) which was also true for Leucaena (Figure 2b). In the tropics, Al toxicity is the most common cause of acid soil infertility. This can be corrected by CaSO4 and 08003 addition to precipitate the exchangeable Al as Aluminum Hydroxide (A(OH)3) and other Al complexes. 08 and Mg deficiencies are also important causes of acid soil infertility. Tropical crops differ widely in their ability to tolerate acid soil infertility conditions. Important varietal differences also exist in corn (Sanchez, 1976). The results obtained in this study support the hypothesis that CaSO4 53 and 08003 may play an important role in alleviating Al toxicity in tropical acid soils. LITERATURE CITED Adams, F., and R.W. Pearson. 1967. Crop responses to lime in the United states and Puerto Rico. Soil acidity and liming. Agr. 12:161- 206. Allison, J.D., D.S. Brown, and K.J. Novo-Gradac. 1990. Ninteqaz/Prodefa2, A geographical assessment model for environmental systems: Version 3.0 Users manual. Environmental Research Laboratory. USEPA. Athens, Georgia. Bennet, R.J. and 0M. Breen. 1989. Towards understanding root growth responses to environmental signals: the effect of Al on maize. S. Afr. J. Sci. 85:9-12. Bennet, R.J. and 0M. Breen. 1991. The recovery of roots of Zea mays L. from various Al treatments: Towards elucidating the regulatory processes that underlie root growth control. Envir. Exp. Bot. 31:153-163. Bennet, R.J., Breen, OM, and M.V. Fey. 1985. The primary site of Al injury in root of Zea mays L. S. Afr. J. Pl. Soil 2: 8-17. Bonnet, R.J., Breen, CM, and M.V. Fey. 1987. The effects of Al on root cap function and root development in Zea mays L. Envir. Exp. Bot 27: 91-104. Briggs, K.G., Taylor, G.J., Sturges, l., and J. Hoddinott. 1989. Differential AI-tolerance of high-yielding, early-maturing Cana— dian wheat cultivars and germplasm. Can. J. Plant Sci. 69:61-69. 54 55 Fisher, TR 1969. Crop yields in relation to soil pH as modified by liming acid soils. Research Bulletin 947. Univ. of Missouri- Columbia College of Agr. Exp. Sta. Guerrero, R. 1971. Soils of the Colombian Llanos Orientals. Composition and classification of selected soil properties. Ph.D. Thesis, North Carolina State University, Raleigh. Hoddinott, J., and C. Richter. 1987. The influence of Al on photo- synthesis and translocation in french bean. J. Plant Nutr. 10:443- 454. Hourigan, W.R., R.E. Franklin, E.O. McLean and LR. Bhumla. 1961. Growth and 08 uptake by plants as affected by rate of liming. Soil Sci. Soc. Amer. Proc. 7: 491-494. Page, A.L., .R.H. Miller and DR. Keeney. 1982. Methods of soil analysis. Agronomy N0. 9 Part 2 2nd Edition. Chemical and microbiological properties. ASA, SSSA. Pierre, W.H., and GM Browning. 1935.The temporary and injurious effect of excessive liming of acid soils and the relation to the phosphate nutrition of plants. J. Amer. Soc. Agron. 27:742-759. Reeve, R.G., and ME. Sumner. 1970. Lime requirements of Natal Oxisols based on exchangeable Aluminum. Soil Sci. Soc. Amer. Proc. 34:595-598. Sanchez, RA. 1976. Properties and management of soils in the tropics. John Wiley and Sons, Inc. NY. pp 224 - 253. Scott, R., J, Hoddinott, G. J. Taylor and K. Briggs, 1991. The influence of Aluminum on growth, carbohydrates and organic acid content of an Al-sensitive cultivar of wheat. Can. J. Bot. 69:711- 716. 56 Shoop, G.J., 0.R. Brooks, R.E. Brazer, and CW Thomas. 1961. Differential responses of grasses and legumes to liming and phosphorus fertilization. Agron. J. 53:111-123. Smucker, A.J.M., A.L. McBurncy and A.K. Srivastava.1982. Quantitative separation of roots from compacted soil profile by the hydropneumatic elutriation system. Agron. J. 74:500-503. Smucker, A.J.M., J.C. Ferguson, W. Debruyn, R.K. Belford, and J.T. Ritchie. 1987. Image analysis of video-recorded root systems. In: ASA Special Publication 50:67-80. ASA Madison, WI. Smucker, A.J.M.,1989. Operation manual for staining, preparation and video recording of washed root systems by the Robotic camera method. Suhayda, 0.6., and A. Haug. 1986. Organic acids reduce Al toxicity in maize root membranes. Physiol. Plant. 68:189-195. Taylor, G.J. 1988. The physiology of Al tolerance. In Metal ions in biological systems. Vol. 24. Edited by H. Sigel. Marcel Dekker, New York. pp. 165-260. CHAPTER 3 SUMMARY AND CONCLUSIONS Lime and gypsum incorporation caused a significant increase in total root length and shoot dry weight in corn. Leucaena was less responsive to lime and gypsum than corn clue to the fact that Leucaena is more Al-tolerant than corn. Calcium carbonate was generally less effective as a source of Ca. The study of soil acidity and Al toxicity on young plants of corn and Leucaena roots and shoots has great importance as far as the future life of the plants is concerned. The seedling stage is the beginning of the develop- mental stages of growth which will have a sequential influence on the final yield. 1 The fact that both corn and Leucaena are able to successfully grow in acidic soils is an important conclusion to draw from this study. Both species are grown in the tropics with an ever- increasing demand and use in alley cropping systems. This study was focussed on the response of corn and Leucaena when 08 is added to the subsoil using two affordable sources of Ca. The study offers sufficient support to justify the use of corn and Leucaena in an intercropping system in the acidic regions of the world as long 57 58 as Ca incorporation is included for better Al alleviation and yield results. TRTE UNIV. LIBRR RIES lllllllllllllllllllIlllllllllllllll 3009116934 MICHIGAN s lllllllllllllillll 3129