OE?“ , UNIVERSITY} ROOT ‘ e, w 7 x T. . 2mm“, .D m , . 7 ~ , ,» C x «2‘, .. . , l , . , _: , C m m V , V .rA_gquw 3wy§g_ ,5. 5", V. , ‘. J111111111111111011111 L 1mm . 1293 301005 7465 Michigan State " * University This is to certify that the thesis entitled PLANT COMPETITION, ROOT GROWTH AND ETHY LEN E EVOLUTION . presented by Stanley J. Kays has been accepted towards fulfillment of the requirements for W\\“ degree in WflWM/L K‘Ap‘ kWAAWQ W WW: cWQW [Md Maje:roeSSpf Date WW, \Q) [\qu 0-7639 (D ' ' .—- ...._.—.__. I m—qw-fi— _~_ ..-_- _-,. _ ABSTRACT PLANT COMPETITION, ROOT GROWTH AND ETHYLENE EVOLUTION By Stanley J. Kays The effect of increasing population pressure on the variation between individuals within homogenous communities of tomato plants, Lycopersicon esculentum Mill., was studied. Plant populations of 5 x 5, 10 x 10, 20 x 20 inches between plants were used. Population increases resulted in a decreas— ing number of fruit per plant and clusters with fruit per plant. As the population of plants increased, the variation between plants within a stand became progressively larger. The number of fruit per plant and the weight of fruit per plant appeared to be more sensitive to population pressure than the total plant weight or number of clusters with fruit per plant. The variation in number and weight of fruit per plant and the number of clusters with fruit per plant gener— ally increased relative to the lowest or most stable popula— tion upon approach of final harvest. increased plant density also results in a higher mortality rate among members of a population. Increased plant population appeared to result in both beneficial factors (e.g. decreasing number of clusters with fruit per plant) and detrimental factors (e.g. increased plant to plant variation) in relation to obtaining the highest percent of ripe fruit using a once-over harvest technique. Stanley J. Kays If the total yield is fixed, one can predict that if other factors do not become limiting, the point of balance between increasing variation between members of a population and de- creasing number of clusters will give the highest potential yield of ripe fruit/acre. Three plant populations of tomato (5 x 5, 10 x 10 and 20 x 20 inches) were studied from the standpoint of changing water needs, alterations in the composition of their soil gas phase and changes in soil compaction. Increased populations of plants required progressively more water per unit area of land. Distinct changes in the soil gas phase also occurred with increased plant population, date of measurement and depth in the soil. A typical inverse relationship between CO2 and 02 concentrations occurred with increasing soil depth. Both CO2 and 02 decreased with increased population. An inverse relationship between CO2 and 0 occurred in the 2 early part of the growing season, while a positive correla- tion was noted in the latter part. The 0 concentration in— 2 creased progressively during the growing season. The concen- tration of ethylene in the soil gas phase increased during the growing season, however, no significant population or depth effects were noted. There were no significant differ— ences in soil compaction with increased plant population, however, a progressive consolidation with time was noted. Increases in population density of tomatoes results in both changes in requirements for production and distinct altera- tions in the plant communities environment. Stanley J. Kays Bean roots (Vicia faba, L., variety Broad Windsor) were enclosed in glass chambers where their axial growth was re- stricted by a hard plastic barrier. A perforated hard plastic tube enclosed the root to prevent curvature. Upon contacting the barrier, the level of ethylene evolution increased to as much as 6 times that of controls and was maintained for up to 30 hours after initiation, however, with a gradual decline. Removal of the barrier resulted in a decrease in ethylene evolution to near that of controls. Exogenous application of ethylene at very low concentrations stimulated growth in length while higher concentrations inhibited length growth. Exogenous ethylene also resulted in an increase in radial diameter. Ethylene found in the soils gas phase reached near physiologically significant concentrations late in the fall. Water from irrigation resulted in a temporary depression in the ethylene concentration in the soil gas phase. The re— sults indicate that ethylene evolution by bean roots acts as an endogenous growth regulator in response to high mechanical resistance. A technique was developed utilizing an electron micro— probe x—ray analyser for the measurement of small changes in bulk density around plant roots or other below ground plant organs. The effective diameter (root diameter + the distance of deformation) of Vicia faba, L., variety Broad Windsor was approximately 6 times the original diameter of the root. The Stanley J. Kays potential for overlapping areas of deformation between neigh- bor roots was calculated from existing root density data for single plants and is substantial. PLANT COMPETITION, ROOT GROWTH AND ETHYLENE EVOLUTION By '. LA“ 5' - Stanley Jf Kays A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Horticulture 1971 ACKNOWLEDGMENTS The author wishes to express his appreciation to Drs. C. W. Nicklow and D. H. Simons for their help and guidance throughout this study and to Drs. D. Penner, A. L. Kenworthy, R. C. Herner, B. G. Ellis and J. D. Downes for their valuable suggestions concerning this research. Appreciation is also expressed to Drs. A. A. De Hertogh and D. R. Dilley for the use of their laboratory facilities. ii ACKNOWLEDGMENTS The author wishes to express his appreciation to Drs. C. W. Nicklow and D. H. Simons for their help and guidance throughout this study and to Drs. D. Penner, A. L. Kenworthy, R. C. Herner, B. G. Ellis and J. D. Downes for their valuable suggestions concerning this research. Appreciation is also expressed to Drs. A. A. De Hertogh and D. R. Dilley for the use of their laboratory facilities. ii Guidance Committee: Sections I, II, III and IV are segments of related thesis research information condensed into for- mats suited and intended for publication in the Proceedings of the American Society for Horticultural Science (sections I and II), Planta (section III) and Soil Science Journal (section IV). TABLE OF CONTENTS Page Number Section I "Plant Competition: Influence of density on the individual within the community" Introduction . . . . . . . . 1 Materials and Methods . . . . . . . 3 Results . . . . . . . . . . . A Discussion 5 Section II "Plant Competition: Influence of density on community phenomena" Introduction . . . . . . . . . . 28 Materials and Methods . . . . . . . . . 29 Results . . . . . . . . . . . 31 Discussion . . . . . . . . . . . . 33 Section III "Ethylene in Relation to the Response of Roots to Physical Impedance" Introduction . . . . . . . . . . 57 Materials and Methods . . . . . . . . . 58 Results . . . . . . . . . . . . . 62 Discussion . . . . . . . . . . . . 71 Section IV "A Sensitive Technique for Measuring Root Mediated Soil Deformations and Their Potential for Overlap Between Neighboring Roots" Introduction . . . . . . . . . . 75 Materials and Methods . . . . . . . . . 76 Results . . . . . . . . . . . 80 Discussion . . . . . . . . . . . . 80 Appendices . . . . . . . . . . . . . 89 LIST OF TABLES Page Number Section III Table 1A Change in ethylene concentration in soil gas phase during the grow— ing season . . . . . . . . . 7O lB Percent change in ethylene con- centration in the soil gas phase after irrigation (1/2 in.) . . . 70 Appendix Table 1 Harvest data for the number of fruit/ plant, number of clusters with fruit/ plant, fruit weight/plant and total plant weight . . . . . . . . 89 Table 2 Soil gas atmosphere data for C02, 02 and ethylene . . . . . . . . 90 Table 3A Soil probe resistance (gm) . . . 91 3B Ethylene concentration in the soils gas phase after irrigation . . . 91 30 Total fruit yield (tons/acre) . . 91 Section I Figure Figure Figure Figure Figure Figure Figure Figure Figure 0\ \1 CD LIST OF FIGURES Page The change in number of fruit per plant and number of clusters with fruit per plant with increasing plant population . The change in coefficient of vari— ation for the number of fruit per plant and the weight of fruit per plant with increasing plant popula— tion The change in coefficient of vari— ation for plant weight and number of clusters with fruit per plant with increasing plant population The change in coefficient of vari— ation for the number of fruit per plant with time for 3 populations and the percent change in coeffi— cient of variation over the lowest population The change in coefficient of vari— ation for the number of clusters with fruit per plant with time for 3 populations and the percent change in coefficient of variation over the lowest population The change in coefficient of vari— ation for the fruit weight per plant with time for 3 populations and the percent change in coefficient of variation over the lowest popula— tion The change in number of deaths per 100 plants with increasing popula- tion The change in coefficient of vari— ation for the number of plants re— maining of the original population with time for 3 plant populations A hypothetical curve for the optimum time of once—over harvest . . . vi Number 10 12 1A 16 18 20 2A Page Number Section II Figure l The affect of increasing plant population on total yield in tons of fruit per acre . 3A Figure 2 The cumulative inches of water (rain and irrigation) per plot for each population during the growing sea— son . 36 Figure 3 The inches of water required per plot with increasing population during the 1969 and 1970 growing seasons . . . 38 Figure Aa The increase in soil compaction for all populations during the growing season . . A0 Figure Ab The change in soil compaction for plots devoid of plants, with and without irrigation,during the growing season . . AO Figure 5 The change in concentration of CO and O in the soils gas phase witg increasing plant population . A2 Figure 6 The change in concentration of CO and O with increasing depth in tge soil, with and without plants . . . AA Figure 7 The increase in concentration of ethylene in the soils gas phase with time during the growing season . . A6 Figure 8 The change in concentration of CO and O in the soils gas phase during the gPowing season . . . . A8 Section III Figure 1a Apparatus for the measurement of endogenous ethylene evolution . . . 59 Figure 1b Apparatus for exogenous application of ethylene . . . 59 Figure 1c Apparatus for measurement of soil gas atmosphere . . . . 59 Figure 2 The increase in rate of ethylene evolution from Vicia faba, L. roots upon contacting a physical barrier . 6A Figure 3 The effect of exogenous concentra— tions of ethylene on the increase in length of Vicia faba, L. roots after A8 hours . . . . . . . 66 Page Number Section III Figure The effect of exogenous concentra— tions of ethylene on the increase in diameter of Vicia faba, L. roots after A8 hours . . . . . . 68 Section IV Figure 1 Apparatus for the embedding of sam— ples . . . . 78 Figure 2 Line profile analysis run perpen- dicularly to the vertical root, showing the distribution of Si and Ca . . . . . . . . . . . . 81 Figure 3 Change in voids ratio with distance from the root . . . . . . . . 83 viii SECTION I Plant Competition: Influence of density on the individual within the community Introduction Much of the data available on plant populations con— cerns the influence of plant density on the community, generally measured as yield per unit area of land (10,1A,15). With increasing population pressures it becomes desirable, however, to study the effect of density on individuals with— in the community, since total yield is a function of col— lective individual behaviors. This provides the potential for a greater understanding of controlling relationships in plant populations and may facilitate prediction of the problems arising with intensive cropping. Plants display a high morphological "plasticity", re— sponding in shape and size to the prevailing environmental conditions (5). ”Early competition with neighboring plants immediately results‘in a reduction of growth rate and the reduction increases with increasing intensity of competition (1). The timing of competition, relative to the morphologi— cal development of the plant, is important both to the physical aspects of the "plasticity" of response and in some cases, total yield per acre (A). In cereals, if com— petition is delayed until after florescence, a greater number of inflorescences are produced per plant and upon the onset of competition there is both competition between neighboring plants and between inflorescences within the same plant. This results in a decrease in the number and size of seeds per inflorescence. If, however, competition occurs before flowering, flower formation and flower number are a function of the stress and consequently there is not a decrease in seed size or number per inflorescence. There— fore, maximum yield is not only a function of the stress between plants in a community but also the competition within individuals of that community (A). Withfiincreasing‘population pressure, homogenous com— munities move progressively toward a skewed distribution for size of the members of the community and generally the shift is toward an increasing proportion of smaller plants (7,9,13). For some crops (e.g. Egg gays) the shape of the height distribution curve of the population moves to the right with the shorter plants having a higher growth rate in length resulting in a net equalization of height (8). Density or distance to the nearest neighbor also re— sults in changes in the mortality rate (3,6,7). The high— est plant mortality rate corresponds with the highest plant densities. The purpose of this paper is to describe some of the responses of the individual within a community and their possible implications in production problems. the onset of competition there is both competition between neighboring plants and between inflorescences within the same plant. This results in a decrease in the number and size of seeds per inflorescence. If, however, competition occurs before flowering, flower formation and flower number are a function of the stress and consequently there is not a decrease in seed size or number per inflorescence. There- fore, maximum yield is not only a function of the stress between plants in a community but also the competition within individuals of that community (A). With increasing population pressure, homogenous com— munities move progressively toward a skewed distribution for size of the members of the community and generally the shift is toward an increasing proportion of smaller plants (7,9,13). For some crops (e.g. £92 gays) the shape of the height distribution curve of the population moves to the right with the shorter plants having a higher growth rate in length resulting in a net equalization of height (8). Density or distance to the nearest neighbor also re— sults in changes in the mortality rate (3,6,7). The high: est plant mortality rate corresponds with the highest plant densities. The purpose of this paper is to describe some of the responses of the individual within a community and their possible implications in production problems. the onset of competition there is both competition between neighboring plants and between inflorescences within the same plant. This results in a decrease in the number and size of seeds per inflorescence. If, however, competition occurs before flowering, flower formation and flower number are a function of the stress and consequently there is not a decrease in seed size or number per inflorescence. There— fore, maximum yield is not only a function of the stress between plants in a community but also the competition within individuals of that community (A). Wgsgmigsraasaggspopulation pressure, homogenous com- munities move progressively toward a skewed distribution for size of the members of the community and generally the shift is toward an increasing proportion of smaller plants (7,9,13). For some crops (e.g. gsa gays) the shape of the height distribution curve of the population moves to the right with the shorter plants having a higher growth rate in length resulting in a net equalization of height (8). Density or distance to the nearest neighbor also re— sults in changes in the mortality rate (3,6,7). The high— est plant mortality rate corresponds with the highest plant densities. The purpose of this paper is to describe some of the responses of the individual within a community and their possible implications in production problems. the onset of competition there is both competition between neighboring plants and between inflorescences within the same plant. This results in a decrease in the number and size of seeds per inflorescence. If, however, competition occurs before flowering, flower formation and flower number are a function of the stress and consequently there is not a decrease in seed size or number per inflorescence. There— fore, maximum yield is not only a function of the stress between plants in a community but also the competition within individuals of that community (A). Wgsgmigsraasaggspopulation pressure, homogenous com- munities move progressively toward a skewed distribution for size of the members of the community and generally the shift is toward an increasing proportion of smaller plants (7,9,13). For some crops (e.g. gsa gays) the shape of the height distribution curve of the population moves to the right with the shorter plants having a higher growth rate in length resulting in a net equalization of height (8). Density or distance to the nearest neighbor also re- sults in changes in the mortality rate (3,6,7). -IEEIEE§P_ est plant mortality rate corresponds with the highest plant densities. The purpose of this paper is to describe some of the responses of the individual within a community and their possible implications in production problems. Materials and Methods Populations of direct seeded tomatoes, variety Heinz 1783, were studied utilizing spacings of 20 x 20 in., 10 x 10 in. and 5 x 5 in. The statistical design was a split plot with three replications. The plots were 8 x 8 feet square with guard rows around the edges. Fertilizer appli— cations were made according to soil test results (M.S.U. Soil Testing Laboratory) for the production of tomatoes and a pre—emergence herbicide, diphenamid, at the rate of 5 pounds/acre was applied. Accurate spacing was obtained by using a dibble board with the appropriate spacing. At the cotyledon stage, extra plants at a single space were pinched off, leaving a 100% stand. The plots were irrigated individually upon reaching A5% of the available soil moisture. Soil water status was measured with individually calibrated Bouycous soil moisture blocks placed in the center of the pOpulations at depths of 8 and 16 inches. Irrigation (l/A in.) was applied using a calibrated hand hose as a light spray for the necessary length of time. Three harvest dates at approximately 30 day intervals were used. A once over harvest was utilized for total yield. The following data was taken: total weight of fruit in each class, plant weight, number of clusters with fruit, number of fruit per plant and number of plants remaining of the original population. Results As anticipated from previous work (2,11,12) both the number of clusters with fruit per plant and the number of fruit per plant were reduced with increasing population pressure (Fig. 1). However, looking at the progressive changes in variation or skewness of the populations yields additional information is obtained concerning the behavior of individuals, relative to their neighbors, within a given population. With increasing density of plants, the varia- tion in number of fruit per plant and the weight of fruit per plant between members in a population increases (Fig. 2). There was a small increase in coefficient of variation be- tween the low and medium populations but a dramatic rise was noted for the most intensively competing population. The variation in weight of the individual plants and the number of clusters with fruit per plant increased progressively, in a near linear fashion, with increasing plant density (Fig. 3). As growth progressed toward final harvest, the varia— tion between plants in the highest population continued to increase up to harvest with regard to the number of fruit per plant (Fig. A). However, the variation decreased within the lower populations as they approach harvest. This may be demonstrated by the percent increase in coefficient of variation over the lowest or most stable population with time. The most intensively competing stands continued to increase in variation compared with the variation of the lowest plant population. All populations tended to stabi- lize with respect to the variation in the number of clusters with fruit per plant as final harvest approached (Fig. 5). However, relative to the lowest population, the variation within the highest density of plants became progressively larger with time. As with number of fruit per plant, the variation in weight of fruit per plant was amplified with increasing population or decreasing area per plant (Fig. 6) while the variation within the lower populations tended to stabilize near harvest. The mortality rate, expressed as deaths per hundred plants, increased with increasing plant population (Fig. 7). The variation in number of live plants left in a stand also increased with increasing population and with time (Fig. 8). While there was a continual increase in the variation of the number of live plants at the highest plant density, the lower populations were little affected (Fig. 8). Discussion The variability between individual plants was much greater at higher densities of plants than at lower densi- ties. With this, the mortality rate also rose with in- creased population thus giving an overall effect of in- creased diversity. The rapid rise in variation between plants at the highest population with respect to the number Fig. 1.——The change in number of fruit per plant and number of clusters with fruit per plant with increasing plant population. The significance probability of the F statistic for population was 0.002 for the number of fruit per plant and 0.0005 for the number of clusters per plant. mun . cwsnns 200 300 400 AREA PLANT 100 25 0 w 0 0 0 I20 100 8 4 2 p21: >5... :23 23539 3 53.5: 2.3 5.3.. >55. 1.0.02 .35» (50. IN.) Fig. 2.——The change in coefficient of variation for the number of fruit per plant and the weight of fruit per plant with increasing plant population. The significance probability for the F statistic for population was 0.002 for the number of fruit per plant and 0.0005 for the weight of fruit per plant. COEFFICIENT OF VARIATION a O 25 WEIGHT or FRUIT I PLANT NO. or mun I PLANT 100 zoo AREA] PLANT (so. IN.) 10 Fig. 3.--The change in coefficient of variation for plant weight and the number of clusters with fruit per plant with increasing plant populations. The significance probability for the F statistic for population was 0.0005 for the number of clusters per plant and 0.0005 for the plant weight. COEFFICIENT OF VARIATION 11 100 so PLANT WEIGHT 60 NO. or CLUSTERS 40 WITH FRUIT ‘ s \ \ \ ‘ \ \ O m 0 25 100 200 300 400 AREA / PLANT (so. IN.) 12 Fig. A.——The change in coefficient of variation for the number of fruit per plant with time for three popula- tions and the percent change in coefficient of variation over the lowest population. The significance probability for the F statistic for population was 0.002 and 0.0005 for date. The standard deviations for the coefficients of variation are plotted on the figure. (————represents the % increase in coefficient of variation over the lowest population.) 13 100 5X5 w m x 5 x w u m [LI / / / / / / / / / / / / w m 20:320.. 39 .26 .>.u z. 3352. N 1:0 20- h(.l¢> b0 Eu-U-uquU - 2OX2O 0 9/29 3/30 DAT E 12 Fig. A.—-The change in coefficient of variation for the number of fruit per plant with time for three popula— tions and the percent change in coefficient of variation over the lowest population. The significance probability for the F statistic for population was 0.002 and 0.0005 for date. The standard deviations for the coefficients of variation are plotted on the figure. (——-—represents the % increase in coefficient of variation over the lowest population.) 13 100 5X5 m m x s x m u m ILII / / / / / / / / / / w m 20:320. 39 .26 .>.u z. 3352. o\o 1:0 ZO.h(—l<> NO #2203300 ~ 0 IOX‘IO . 2OX2O 9/29 8/30 DAT E 12 Fig. A.—-The change in coefficient of variation for the number of fruit per plant with time for three popula— tions and the percent change in coefficient of variation over the lowest population. The significance probability for the F statistic for population was 0.002 and 0.0005 for date. The standard deviations for the coefficients of variation are plotted on the figure. (-———represents the % increase in coefficient of variation over the lowest population.) 13 100 5X5 0 0 0 m s m n m x x o o o 9 w 5 2 .I 2 2 LI ~0 n V / I / x .1 x z I / . / I / I / I / / I / I / . . m fl » a D / / / / / / // / / / / / / / / / / / / / / // / 9 2 U m w m o 20.n(a3t2 30a uu>0 .>.u Z. uu 50 #2225qu0 1A Fig. 5.—-The change in coefficient of variation for the number of clusters with fruit per plant with time for three populations and the percent change in coefficient of variation over the lowest population. The significance probability for the F statistic for population and date were 0.0005. The standard deviations for the coefficients of variation are plotted on the figure. o m m m 5 mm 5 X X X n w n m w n n A P r I / 9 /M / / / / / / / / / / / / / / / / // / / / .I/JV O E 3 T 5 l m m w w m I I I 2955.9. 33 ~25 .>.u 2. 333.... .X. ‘60 ZO-b<.¢(> sO bluaflquU 16 Fig. 6.——The change in coefficient of variation for the fruit weight per plant with time for three populations and the percent change in coefficient of variation over the lowest population. The significance probability for the F statistic for population and date were 0.0005. The standard deviations for the coefficients of variation are plotted on the figure. (————represents the % increase in coefficient of variation over the lowest population.) 17 5X5 5X5 )3 IOXIO 20x20 w m 20.5.5.9. 33 ¢u>o .>.u z. 3.33:. ..\o .3... 2035.; .0 522.33 0 IOXIO a 20x 20 9 2 I 9 18 Fig. 7.—-The change in number of deaths per 100 plants with increasing population. The standard deviation for each population is plotted on the figure. l9 o 5 $24.... on. \ 2.53 .02 35:2. 300 400 200 AREA PLANT 100 25 (SO. IN.) 20 Fig. 8.——The change in coefficient of variation for the number of plants remaining of the original population with time for three plant populations. The standard deviations for the coefficients of variation are plotted on the figure. 21 m IOXIO 20:32.9. 120.030 2.» no 02.2.52: £25.. zo...<.¢<> no 520530 «a 20X 20 9/23 8/20 DATE 22 of fruit per plant and the weight of fruit per plant may have been partially due to the dependence of these param- eters on the number of clusters per plant. Therefore, any diversity in number of clusters would have an additional effect on the variation for the number and weight of fruit per plant since normally one cluster has more than one fruit. Consequently, anything that would decrease the number of fruit per cluster, while not affecting cluster number per plant, would force downward the variation be— tween plants under intensive competitive stress. From this it can be seen that number of fruit per plant and weight of fruit per plant were much more sensitive to intensive popu— lation pressure than the number of clusters per plant and plant weight. The critical question is: what effect do these param— eters have on the uniformity of harvest when utilizing a once over harvest technique? Because of the increase in variation between plants at higher and higher populations, it would seem that increased population works, from this standpoint, against uniformity. However, at the same time, the effect of increased plant density on the average number of clusters with fruit per plant may force a decrease in the potential for diversity and by doing so increase the potential for uniformity. Consequently, increasing popula— tion has both a positive (decreasing number of clusters with fruit per plant) and negative (increased coefficient of vari— ation) effect on the diversity of the members in the stand. 23 One may increase yields per acre for a given variety by more efficient utilization of the land area and/or more efficient utilization of the plants. If the potential yield (total tons of fruit per acre) for a given population of plants is considered fixed (Fig. 9), then any factor that decreases the distance between a and b (without affect~ ing total yield or by affecting it less than the increase in benefit from decreasing the distance between a and b allows) will increase the tons of ripe fruit per acre. Population increases appear to do this (2), although land use efficiency also increases, mainly by decreasing the number of clusters per plant with fruit and subsequently the potential spread in harvest. However, any factor that forces the distance between a and b wider will have the opposite effect. As noted in the results, population in- creases also may increase the percent variation between plants which would tend to force the curve lower and wider; therefore, few tons of ripe fruit per acre. If the total yield is fixed, one could predict that, if other factors do not become limiting (e.g. depression of total yield), the point of balance between increased variation between members of a population and decreasing number of clusters will give the highest efficiency of plant use and consequently the highest potential yield/acre of ripe fruit. 2A Fig. 9.—-A hypothetical curve for the optimum time of once—over harvest. 25 100 43.0» “.0 :2: E... x In” HARVEST DATE curly 10. 26 Literature Cited Black, J. N. 1957. Seed size as a factor in the growth of subterranean clover (Trifolium subterraneum L.) under spaced and sward conditions. Aust. J. Agri. Res. 335—351. Bryan, H. H., J. W. Strobel and J. D. Dalton. 1967. Effects of plant population, fertilizer rates on tomato yields on Rockdale soil. Proc. Fla. St. Hort. Soc. 80: lA8—150. Clements, F. E., J. E. Weaver and H. C. Hanson. 1929. Plant Competition. Carnegie Inst. of Washington, Publ. 398. Donald, C. M. 195A. Competition among pasture plants. II. The influence of density on flowering and seed pro- duction in annual pasture plants. Aust. J. Agri. Res. 5:585—597. Donald, C. M. 1963. Competition among crop and pasture plants. In "Adv. in Agron.". 1511-118. Acad. Press, N.Y. Goodall, D. W. 1960. Quantitative effects of intraspe- cific competition: an experiment with marigolds. Bull. Res. Council Israel. 8Dzl8l—19A. Harper, J. L. 1961. Approaches to the study of plant competition. In "Mechanisms in Biological Competition". Symp. Soc. Expt. Biol. 15:1—39. Hozumi, K., H. Koyama and T. Kira. 1955. Intraspecific competition among higher plants. IV. A preliminary account on the interaction between adjacent individuals. J. Inst. Polytech. Osaka City Univ. Ser. D. 6:121—130. Koyama, H., and T. J. Kira. 1956. Intraspecific com— petition among higher plants. VIII. Frequency distri- bution of individual plant weight as affected by the interaction between plants. J. Inst. Polytech. Osaka City Univ. Ser. D. 7:73—9A. Moore, J. N., A. A. Kattan and J. W. Fleming. 1958. Effect of supplemental irrigation, spacing, and ferti— lization on yield and quality of processing tomatoes. Proc. Amer. Soc. Hort. Sci. 71:356—368. 11. 12. 13. 1A. 15. 27 Odland, M. L. l9A9. Interrelation of spacing, vari— ety and interplanting on yield and fruit size of tomato. Proc. Amer. Soc. Hort. Sci. 53:393-A01. Reeve, E., W. A. Robbins, W. S. Taylor and J. F. Kelley. 1962. Cultural and nitrogen fertilization in relation to tomato fruit set and yield. Proc. Plant Sci. Symp. (Campbell Soup Co.), pp. 129—1A7. Stern, W. R. 1960. Thesis, Dept. Agron., Univ. of Adelaide, Adelaide, Australia. Vittum, M. T., and W. T. Tapley. 1953. Spacing and fertility level studies with a determinate type tomato. Proc. Amer. Soc. Hort. Sci. 61:339—3A2. and . 1957. Spacing and fertility level studies with a paste—type tomato. Proc. Amer. Soc. Hort. Sci. 69:323—326. SECTION II Plant Competition: Influence of density on community phenomena Introduction Rising costs and labor shortages have forced changes in culture to achieve a high yield for machine harvest. One of these changes has been the use of higher plant pOpu— lations (19,20). The typical response of tomato to in— creased plant population is an increase in total and early yield/acre (3,16,21,2A,25,29,30), a decrease in fruit size (2A,25,29,30) and a decrease in number of fruits/plant (18, 29,30). Competition begins earlier in the growing season as the planthensity increases (6). The intensity of competition increases as the season progresses and may, in some crops (e.g. Lolium rigidum), result in the complete cessation of growth. Consequently, the yield at extremely low plant den— sities tends to approach, with time, the yield at extremely high densities (5). The yield of vegetative dry matter/unit area often reaches a relatively constant level (1), however, the total yield of reproductive parts may be depressed at high densi- ties (13). A considerable range of densities appear to give near-maximal yields (3,16) but this varies from year to year (21). 28 29 Several less pronounced community induced phenomena that under certain conditions may critically influence plant growth and subsequent yield, have been ivestigated. Materials and Methods Populations of direct seeded tomatoes, varieties New Yorker and Heinz 1783, were studied in 1969 and 1970, re- spectively. Spacings of 20 x 20 in., 10 x 10 in., and 5 x 5 in. were utilized. The statistical design was completely randomized with 3 replications in 1969 and a split plot with 3 replications in 1970. The main plots were for date of har— vest with plant population within. The plots were 8 x 8 feet square with guard rows around the edges. Fertilizer application was made according to soil test results (M.S.U. Soil Testing Laboratory) for the production of tomatoes and a pre—emergence herbicide, diphenamid, at the rate of 5 pounds/acre was applied. Since soil gas composition, com— paction and water utilization data were to be taken, to avoid compacting or disturbing the soil, hand seeding and all subsequent thinning and weeding were done from a temporary overhead platform. Accurate spacing was obtained by using a dibble board with the appropriate spacing. At the cotyledon stage, any extra plants were pinched off, leaving a 100% stand. Water Use: Individually calibrated Bouycous soil moisture blocks were placed in the center of each population 30 at 8 and 16 in. depth prior to planting. Soil moisture was measured on alternate days and individual plots were irri— gated when the soil contained A5% of the available water. Irrigation (l/A in.) was applied using a calibrated hand hose as a light spray for the necessary length of time. Any run off from rain or irrigation was prevented by a 3 in. dike around the edge of the individual plots. Soil Compaction: Compaction of the upper 2 in. of soil was measured using a polished point probe (1/8 in. diameter x 2 1/2 in., 22° point angle) attached to a Hunter Spring mechanical force gauge giving a measure of resistance in grams. The probe was polished to decrease skin friction and a uniform entry rate was maintained. One hour prior to measurement, each plot was irrigated with 1/2 in. of water to eliminate differences in resistance due to differences in percent soil moisture. Fifteen measurements were taken per plot per date. The measurements were taken at random in the population and equidistant between two neighboring plants. Soil Gas: Glass tubes (5, 9 and 17 in.), sealed at the apex with a serum vial stopper and open but covered with a fine copper grid at the base, were placed in each plot. A smaller glass tube was placed through the serum vile cap at the top and extended down to 2 cm from the copper grid. This second tube was also sealed with a serum vile cap. The soil gas phase at the depth of the open end was allowed to equilibrate with the gas in the tube. The second, internal, 31 tube was used to take the bulk of the sample as close to the open end as possible. Three sampling tubes per plot were placed in the soil, one each at A, 8 and 16 in. depth, using a soil core sampler. The tops were covered with aluminum foil to minimize any sun mediated effects. Gas samples (10 ml.) were taken with a syringe and subsamples were analysed by gas chromatography within 30 minutes of sampling. O2 and 002 were determined on the same 5 ml. samples with a thermal conductivity detector while 2 ml. samples were used for ethylene with a flame ionization detector. Harvest: A once over harvest was utilized for total yield. Results As noted in previous studies (3,16,21,2A,25,29,30), total yield increased with increasing plant population (i.e. decreasing area per plant) (Fig. 1). Although the total yields were considerably higher in 1970 as compared with 1969, the yield response to plant population was similar each year. The water requirement also increased with increasing plant populations (Fig. 2). The greatest requirement for irrigation corresponded with periods of low rainfall. Part of the variation in total water requirement between years was due to a A2% increase in rainfall in 1970. Consequently, 32 the differences in water requirement between populations in a year of high rainfall (1970) were less pronounced than during the 1969 growing season. The increasing populations of plants responded with the same trend each year with re— spect to their water requirements (Fig. 3). This is demon— strated by the similarity in shape of the curves for the two years and the linearity of the difference in water re- quirements between years. Consequently, although the total rainfall and total irrigation varied considerably with year, the populations of plants responded similarly in their need for additional water. The soil in the upper 2 inches, became more compacted with time (Fig. AA). Plant population did not appear to have a significant effect. However, this was confounded by the requirement of greater amounts of water by higher plant populations. Irrigated soil, devoid of plants, was more compacted than soil not irrigated (Fig. AB). There— fore, the population effect could be substantially masked by the increasing amount of water applied with increased populations. The levels of soil O2 and CO2 in the soil gas phase significantly decreased with decreasing area per plant or increasing plant population per acre (Fig. 5). The com— plexity of the relation of population to its soil atmos— phere, however, is suggested by the absence of the 1:1 reciprocal relationship normally noted between oxygen and carbon dioxide in biological systems. Ethylene levels in 33 the soil gas phase were not significantly affected by the number of plants per unit area of soil. Soil 02 decreased with increasing soil depth while CO increased with increas— 2 ing soil depth (Fig. 6). The fact that there was a typical reciprocal relationship between the two gases with depth adds credibility to the population effect noted previously. Also, the levels of soil 02 were higher and CO lower in 2 soil without plants than in soil with growing plants. Ethylene in the soils gas phase tended to be pocketed and highly random, consequently no significant depth effect was noted. The concentration of ethylene in the soil in— creased during the growing season (Fig. 7). The response of oxygen and carbon dioxide with time suggested the inter— action of several controlling factors (Fig. 8). An inverse relationship existed during the first part of the growing season, however, this reversed to a direct relationship in the latter part of the season. Discussion The results obtained in this study indicate a definite increase in water requirement with increasing density of plants. Karper (1A) demonstrated the relationship between rainfall and optimum plant density over a 10 year period. For one genotype (Kafir) the optimum density in a wet season was 10 times that of a dry season. The optimum plant densi— ty has also been increased with increased irrigation (l2). 3A Fig. 1.——The effect of increasing plant population on total yield in tons of fruit per acre. The significance probability for the F statistic was 0.001 for both popula— tion and year. TONS or FRUIT/ACRE 35 \ ‘0 40 20 I969 o 25 100 200 300 400 AREA / PLANT (so. IN.) 36 Fig. 2.——The cumulative inches of water (rain and irrigation) per plot for each population during the growing season. The significance probability of the F statistic for water use was 0.05 in both 1969 and 1970. 37 uh825“ duthOFruZut O... muzgpmaul £20 >flh2u lubur‘Oflhu-‘un O... muzspmaul .nsO 9128 DATE 8/20 z/To A2 Fig. 5.—-The change in concentration of CO2 and O2 in the soils gas phase with increasing plant population. The significance probability of the F statistic for population was 0.0005 for both CO2 and O2. ole 02 19.6 18.2 hsd .05 Ind .05 25 100 A3 zoo AREA/ PLANT (50. IN.) 300 400 AA Fig. 6.-—The change in concentration of C02 and 02 with increasing depth in the soil, with and without plants. The significance probability of the F statistic for depth was 0.0005 for both CO2 and O2. 20.0 I9.5 10.5 A5 5.0 4.0 / ”C02 with I plants a 8 N10 02 without plants C02 without , “ plants 7 P o, with z I plan" 2.0 ------'V ‘5 Ind .05 co, 4 0 16 EOIL DEPTH (in) A6 Fig. 7.—-The increase in concentration of ethylene in the soils gas phase with time during the growing season. The significance probability for the F statistic for date was 0.0005. ETHYLENE (ppb) A7 hsd .05 10 7/ 29 9/2 DATE 9/29 A8 Fig. 8.——The change in concentration of CO2 and O2 in the soils gas phase during the growing season. The signifi— cance probability of the F statistic for date was 0.0005 for CO2 and 0.003 for O2. A9 IRA z: 6.0 I Ind 95 199 02 4.0 ,CO2 / N N \ // 2,135 ‘8 \k / .\ °\° \ / \ / l/ ‘\ 2.0 \ / \ / \ / \ / \ / 10.0 '5 d oh z]: 9 9]: DATE 9,29 50 Carolus, et a1. (5) found the growth of tomatoes to be both a function of available soil water and degree of atmospheric stress. The greater the leaf area the plant develops before extensive plant to plant competition, the greater was the root system and the less likely was the plant to suffer from drought (17). Consequently, as the water requirement of a population increases the potential for stress also in- creases. This relative to the decreasing number of fruit per plant and the relationship of water stress to the occur- rence of blossonend rot of tomato accentuates the need for increased control over the water requirements at high plant populations. The effect of increasing plant density on soil com— paction presents a complex problem. Wollny (31) attributed the lower percent decrease in soil volume with increasing population to the additional protection from rain drops afforded by the increased canopy. The results reported herein support this well—known effect of water on compac— tion. Since the soil tends to consolidate in volume with time, a beneficial effect of an earlier connecting matrix of roots under high populations might also be expected. However, at the same time the effect of root pressure on the consolidation of soil into aggregates is well—documented (A,26), and with an increase in root volume per unit volume of soil with population (23), localized increases in den- sity would be anticipated. The results obtained for popula- tion in this study were confounded with water application 51 increasing with population, consequently the population ef- fect may have been masked. The fact that water has a defi— nite effect on compaction and that no apparent effect was realized even though the total amount of water applied in— creased with population supports this possibility. Changes in soil aeration mediate an array of diverse biological and chemical responses. Morphogenic alterations, nutrient availability, pH, redox potential and resistance to disease are but a few that have the potential to reduce yields or cause total crop failure (10). It is important to note that because of the soil's di— versity and dynamic state of flux many important factors (e.g. water status, gas diffusion rates, partitioning co- efficients, physical conditions, etc.) are in constant interplay and are of critical importance in the determina- tion of the quantity and quality of the soils atmosphere at a given instant. It is generally accepted that 02 deficiency is of greater importance than CO toxicity (10). Flooding 2 of tomatoes results in a rapid inhibition of respiration and metabolism in the entire plant and inhibition of the TCA cycle in the roots (8). Anaerobic metabolism may result in two moles of CO2 and ethanol for every mole of glucose metabolized (10). Fulton, et a1. (7), in fact, found an accumulation of ethanol in xylem exudate shortly after flood- ing tomatoes.' Evidence of Patrick, et a1. (22), indicated the degree of sensitivity of tomatoes in relation to root oxy- gen. 21% oxygen was needed to obtain maximum growth. 52 CO2 is fixed and is generally stimulatory to roots at low levels (11,27,33) although some plants (e.g. pea, bean and sunflower) have been reported to be inhibited by 1.0 to 1.5% CO2 (28). Stemmit (27) noted both an increase in IA root and shoot growth with absorption of C 0 from solu- 2 tion compared to plants given insufficient carbon dioxide levels. Consequently, soil CO2 levels were not independent of shoot growth and high root fixation may, in some cases, result in increased production. Therefore, it is not sur— prising that CO2 fixation by roots would shift 02 and CO2 away from a 1:1 ratio in the soil. CO2 and 02 responded in an inverse relationship with depth in the soil. Also, areas with plants were higher in CO2 and lower in 02 than those without plants. The in— creased utilization of oxygen with population may be ac— counted for by the increased mass of metabolically active roots. This is also supported by the difference in concen- tration of these gases between soil with and without plants. The response of C02 and 02 concentration to date, may be indicative of the interaction of at least two control systems. If one considers the increased aeration and de— creased water content in the soil with time (resulting in a decreased 002 concentration) interacting with increased respiration due to increasing root mass with time, a curve with depression then recovery would be anticipated. The sensitivity of plants to low levels of ethylene has been known for some time (32). Recent work (9.15) has 53 indicated that ethylene is a natural growth hormone in grow— ing plants and has several important biological functions. Roots and hypocotyls give off low levels of ethylene during growth. The absence of a population effect, however, would indicate that the ethylene produced by roots does not signif— icantly effect the soil atmosphere. Water has been shown to have a definite, at least transitory, effect on 5011's ethyl— ene concentration (15); however, it is doubtful that this alone could account for the increase with time. 10. 11. 5A Literature Cited Aspinall, D., and F. L. Milthorpe. 1959. An analysis of competition between barley and white persicaria. I. The effects on growth. Ann. Appl. Biol. A7:157—l72. Bradley, G. A. and B. B. Rhodes. 1969. Vegetable fertilization may need changing with once— over harvest. Ark. Farm. Res. 18:7. Bryan, H. H., I. W. Strobel and J. D. Dalton. 1967. Effects of plant populations, fertilizer rates on to— mato yields on Rockdale soil. Proc. Fla. St. Hort. Soc. 80:1A9—150. Burger, H. 1926. Die physikalische Bodenunterschung inbesondere die Methoden zur Bestimmung der Luftkapazi— tat. Proc. Ath Intern. Conf. Soil Sci. (Rome). 2:150— 163. Carolus, R. L., A. E. Erickson, E. H. Kidder, and R. Z. Wheaton. 1965. The interaction of climate and soil moisture on water use, growth, and development of toma— toes. Mich. State Univ. Agri. Expt. Sta. Quart. Bull. A7(A):5A2-557. Donald, C. M. 1951. Competition among pasture plants. I. Intra—specific competition among annual pasture plants. Aust. J. Agri. Res. 2:355—376. Fulton, J. M., and A. E. Erickson. 196A. Relation be- tween soil aeration and ethyl alcohol accumulation in xylem exudate of tomatoes. Soil Sci. Soc. Amer. Proc. 28:610—61A. Fulton, J. M. A. E. Erickson, and N. E. Tolbert. 196A. Distribution of Cl” among metabolites of flooded and aerobically grown tomato plants. Agron. J. 56: 527— 529. Goeschl, J. D., L. Rappaport, and H. K. Pratt. 1966. Ethylene as a factor regulating the growth of pea epi— cotyls subjected to physical stress. Plant Physiol. Alz877-88A. Grable, A. R. 1966. Soil Aeration and Plant Growth. Adv. in Agron. 18:57—101. (A. G. Norman, ed.) Acad. Press, N.Y. Grable, A. R., and R. E. Danielson. 1965. Influence of 002 on growth of corn and soybean seedlings. Soil. Sci. Soc. Amer. Proc. 29:233-238. 12. 13. 1A. 15. 16. l7. l8. 19. 20. 21. 22. 23. 2A. 55 Grimes, D. W., and J. T. Musich. 1960. Effect of plant spacing, fertility, and irrigation managements on grain sorghum production. Agron. J. 52:6A7-650. Holliday, R. 1960. Plant Population and Crop Yield. Part 1. Field Crop Abstr. 13:15A-167. Karper, R. E. 1929. The contrast in response of Kafir to Milo to variations in spacing. J. Amer. Soc. Agron. 21:3AA—354. Kays, S. J., D. Simons and C. Nicklow. 1971. In prepa— ration. Laughton, A. 1967. Report Hort. Res. Inst. Ont. pp- 35—37. Milthorpe, F. L. 1956. In ”Growth of Leaves". (F. L. Milthorpe ed.), p. 1A1. Butterworth, London. Moore, J. N., A. A. Kattan and J. W. Fleming. 1958. Effect of supplemental irrigation, spacing, and fertil- ity on yield and quality of processing tomatoes. Proc. Amer. Soc. Hort. Sci. 71:356-368. Nicklow, C. W., and M. E. Austin. 1965. Cost of me— chanical tomato harvesting vs. hand harvesting. The Canning Trade. 88:13,6—7. Nicklow, C. W., and J. D. Downes. 1971. Influence of nitrogen, potassium and plant population on the maturity of field seeded tomatoes for once—over harvest. Proc. Amer. Soc. Hort. Sci. 96:A6-A9. Odland, M. L. l9A9. Interrelation of spacing, variety and interplanting on yield and fruit size of tomato. Proc. Amer. Soc. Hort. Sci. 53:393—A01. Patrick, W. H., and M. B. Sturgis. 1955. Concentration and movement of oxygen as related to absorption of ammon— ium and nitrate nitrogen by rice. Soil Sci. Soc. Amer. Proc. 19:59—62. Pavylychenko, T. K. 19A2. Root systems of certain forage crops in relation to management of agricultural soils. Natl. Res. Counc. Canada, Publ. No. 1088. Reeve, E., W. A. Robbins, W. S. Taylor and J. F. Kelley. 1962. Cultural and nitrogen fertilization in relation to tomato fruit set and yield. Proc. Plant Sci. Symp. (Campbell Soup Company), pp. l29—1A7. 25. 26. 27. 28. 29. 30. 31. 32. 33. 56 Reeve, E., and W. A. Schmidt. 1962. Influence of plant spacing on canning tomato yields. Proc. Amer. Soc. Hort. Sci. 59:38A—388. Rostovzeva, O. S., and M. I. Avaeva. 1935. The role of perennial grasses in the formation of stable soil structure. Pedology. Nos. 5 and 6:797—81A. Stemmet, M. C., J. A. DeBruyn and P. B. Zeeman. 1962. The uptake of carbon dioxide by plant roots. Plant and Soil. 17:357—36A. Stolwijk, J. A. J., and K. V. Thimann. 1957. On the uptake of carbon dioxide and bicarbonate by roots, and its influence on growth. Plant Physiol. 32:513—520. Vittum, M. T., and W. T. Tapley. 1953. Spacing and fertility level studies with a determinate type tomato. Proc. Amer. Soc. Hort. Sci. 61:339—3A2. and . 1957. Spacing and fertility level studies with a paste—type tomato. Proc. Amer. Soc. Hort. Sci. 69:323-326. Wollny, E. 1877. Der Einfluss der Pflanzendecke und Beschattung auf die physikalischen Eigenschaften und die Fruchtvarkeit des Bodens. Berlin. Zimmerman, P. W., and A. E. Hitchcock. 1933. Initia— tion and stimulation of adventitious roots caused by unsaturated hydrocarbon gases. Contrib. Boyce Thompson Inst. 5(3)!35l-369- Grinfel'd, E. G. 195A. (Nutrition of plants with CO assimulated through the roots.) Doklady Akad. Nauk. SSSR. 97:919—992. SECTION III Ethylene in Relation to the Response of Roots to Physical Impedance Introduction It has been proposed that certain auxin effects on plant growth and development are mediated through their stimulation of ethylene synthesis (Zimmerman and Wilcoxon, 1935; Hall and Morgan, 196A). The possibility of a natural regulatory role of ethylene in roots is suggested by the similarity in response of roots to exogenous application of ethylene, auxin and mechanical resistance. Each has been shown to decrease the rate of elongation (Richards and Mac— Dougal, 190A; Ekdahd, 1953; and Eavis, 1965), increase radial expansion (Richards and MacDougal, 190A; Ekdahd, 1953; and Eavis, 1965), and induce the formation of root hairs and/ or lateral roots (Zimmerman and Wilcoxon, 1935; Eavis, 1965; Hitchcock and Zimmerman, l9A0; and Zimmerman and Hitchcock, 1933). The evolution of ethylene has been noted in diseased, senescing, wounded and pharmacologically induced tissues (review by Burg, 1962). The work of Goeschl et a1. (1966 and 1967) demonstrated that ethylene does act as a natural growth regulator in intact healthy plants. The following paper deals with the ethylene control of root growth in response to mechanical impedance in the soil. 57 58 Materials and Methods Seeds of the test plant, Vgsga fasa, L., variety Broad Windsor were imbibed in aerated water for 8 hours, planted in trays containing 15 cm of moist vermiculite, and grown in continuous dark for either A8 or 72 hours. All opera— tions were at 18°C. Ethylene Evolution: The apparatus used for measure— ment of ethylene evolution (Fig. 1A) consisted of a hollow glass tube (2.1 cm ID X 15 cm length) covered with black electrical tape to exclude light. Gas tight seals were made at the ends of the tube with soft neoprene stoppers. A hard plastic tube (2.3 cm in length with an ID slightly larger than the diameter of the root) was inserted in the base of the upper stopper perpendicular with the plastic barrier. This was used to simulate the radial restriction presented by the soil. The tube was perforated to insure adequate ventilation of the root. The adjustable hard plastic bar— rier was placed at the base of the tube or 3 cm below it in the case of unobstructed controls. Background measurements were made on identical apparatus, however, a glass plug was placed in the root hole in the neoprene stopper. A small piece of moist filter paper was placed around the glass just under the upper neoprene stopper. Seedlings with roots 2.2 to 2.A cm long were carefully removed from the vermiculite and placed through a hole in the upper stopper and into the plastic tube. The stopper with seedling was then inserted 59 Fig. lA.--Apparatus for measurement of endogenous ethylene evolution: 1) air inlet and exhaust, 2) moist vermiculite, 3) wire restrainer, A) seedling, 5) neoprene seal, 6) root, 7) moist filter paper, 8) perforated plas— tic tube, 9) plastic barrier, 10) glass rod for raising and lowering barrier, and 11) basal neoprene seal. Fig. lB.--Apparatus for exogenous application of ethylene: 1) air inlet and exhaust, 2) moist vermiculite, 3) seedlings, A) neoprene seal, 5) roots, and 6) moist filter paper. Fig. lC.--Apparatus for measurement of soil gas at— mosphere: 1) serum cap, 2) glass tubing, 3) Copper grid, and A) open basal end. 6O 3 C1\ 4 Q 11 61 into the glass tube and secured with wire taped to the glass tube. This was necessary to prevent the root from simply lifting the seed out of the vermiculite when it contacts the obstruction. A polystyrene pot was then taped around the seedling and upper portion of the glass tube. Moist ver— miculite was placed around the seedling. The plants were allowed to equilibrate 1 hour before measurements were taken. A flow rate of l ml./min. was selected since relatively low gas exchange rates are characteristic of the soil. AV 10 m1./min. capillary was placed at the exhaust to minimize any back diffusion of ethylene from the surrounding air. The air stream had ethylene removed with a potassium permanganate scrubber and was humidified before entering the chamber. Two ml. gas samples were collected by closing the ex— haust and withdrawing at the same rate as the air was enter— ing. Ethylene concentrations were determined by flame ionization gas chromatography using an alumina column. CO2 and 02 concentrations were periodically monitored and did not deviate substantially from the norm. Ethylene Treatment: Three plants with roots 2.0 to 2.5 cm long were placed with their roots through holes in a neoprene stopper and inserted in a glass jar (A.5 cm ID X 10 cm deep) containing moist filter paper (Fig. 1B). The jars were painted on the outside to exclude light. Poly— styrene pots were then fitted around the top and filled with moist vermiculite covering the seedlings. Air flow into the 62 jar was 30 ml./min. Ethylene was applied by the method of Pratt et a1. (1960), in a concentration range from 0 to 1236 ppb. Four replications per concentration were used for each experiment. After A8 hours, the roots were cut off at the lower surface of the neoprene stopper and shadow graphed for measurement. Measurements of diameter were made with an optical stage micrometer and a 10X stereomicroscope. Soil Ethylene Levels: Glass tubes (Fig. 10) were placed vertically in a field (devoid of plants) at soil depths of A, 8 and 16 inches. The surface end of the tube was sealed with a serum vile stopper and the lower end covered with a copper screen. Samples were removed through a second smaller tube, also serum stoppered, to obtain the gas from as near the soil surface at the appropriate depth as possible. The samples were chromatogramed within 20 minutes after removal. The possibility of ethylene evolution from the serum vile stop— pers was tested and found not to be a factor. The plot had 1/2 inch of irrigation just prior to the first measurement. Results Upon reaching a physical obstruction, ethylene produc— tion by roots increased to as much as 6 times that of con- trols (Fig. 2). This increase normally started within 1 hour of contacting the obstruction. The rate of increase in ethylene evolution appeared to be partially related to the rate of root growth into the impeding zone; however, 63 the maximum rate of evolution was similar, irrespective of the rate of increase. Upon removal of the obstruction, the rate of ethylene production decreased to near that of con— trols. If the physical barrier is not removed, the high level of ethylene evolution was maintained for up to 30 hours after its initiation; however, during this time there was a gradual decline of about 25%. Exogenous application of ethylene at very low concen— trations stimulated growth in length (Fig. 3). Stimulation occurred at two distinct ethylene levels and may indicate a dual effect of ethylene on root growth. The second stimula— tion was less pronounced and consequently not conclusive. Ethylene also resulted in an increase in radial en— largement of the root (Fig. A) reaching 20% above the control in 1236 ppb ethylene. The rate of increase in diameter was greatest at low levels (100 ppb) but occurred over the con- centration range tested. The most pronounced increase in diameter occurred 20 mm from the tip, however, the swelling at 10 mm and 30 mm was substantial. Ethylene found in the soil gas phase reached near physio- logically significant levels (Table lA) late in the fall (10/1/70). The concentrations were pocketed and increased during the growing season (Kays and Nicklow, 1971). On the plots measured, which were devoid of higher plants, there was no apparent depth effect for ethylene as typically noted for O and CO 2 tion or rain results in a temporary depression of the level 2 (Kristensen and Enoch, 196A). Water from irriga— of ethylene in the soils gas phase (Table 1B). 6A Fig. 2.——The increase in rate of ethylene evolution from Vicia faba, L. roots upon contacting a physical bar— rier. 65 an on I .0523 . ‘ 12,050» 50.30.. D .5: at... on —‘ ‘| “' 00» 000 000 can MOP/'5’! [1d ) NOILII'IOAI TNTTAIILa 66 Fig. 3.——The effect of exogenous concentrations of ethylene on the increase in length of Vicia faba, L. roots after A8 hours. Each point represents an average of 36 roots. 67 00".. 000.. Jog—.200 00¢ 3...... 20.52.2323 .2325 000 00¢ 00“ (was) 'IOIINOD IIAO HLONJ'I NI BONVHD 68 Fig. A.-—The effect of exogenous concentrations of ethylene on the increase in diameter of Vicia faba, L roots after A8 hours. Each point represents an average of 36 roots. 69 TI * a E E E E E E F 8 8 ° 5 0 n. t. 0. N. -. 0. 0: N 0 3 N d a N a N N a - .- —' I'll“) IEHWVIC NI ISVEUDNI 1200 1000 000 400 200 ETHYLEN E I PPb) ' distance from root Np 70 Table lA.-—Change in ethylene concentration in soil gas phase during the growing season.* Concentration of Ethylene (ppb) Date *(average of 3 soil depths of A, and 16 inches) 8/1 Not Detectable 9/2 8.67 i 2.16 lO/l 15.67 i 2.61 Table lB.-—Percent change in the ethylene concentration in the soil gas phase after irrigation (1/2 in.). Days From Time % Decrease From The Irrigation First Measurement 0 0 3 66.6 11 A5.0 71 Discussion Roots and underground shoots deform the soil by tensile failure, shear failure without compression and shear failure with compression (Barley and Greacen, 1967). The radial force exerted by a root is substantial. Measurements up to 6.1 bar have been made for Vgsga fasa (Pfeffer, 1893). Small changes in root diameter can mediate a substantial increase in shear failure potential in a soil or ped of high mechani— cal impedance thus enhancing the root's chances of overcom— ing the restriction. Resistance to radial expansion also greatly increases the longitudinal force potential. Conse- quently, radial and longitudinal resistances are closely related to radial and longitudinal expansion and subsequent growth. The results indicate that axial mechanical resistance mediates an increase in ethylene evolution from roots and this in turn results in radial expansion. An increased force potential could result in a resumption of elongation and/or an increase in elongation. The physiological changes in size and shape of the root are closely tied to the nature of the resistance and the root's potential to mediate shear failure. It should be noted that Radin and Loomis (1969) using cultured radish roots found the opposite effect on radial expansion. However, the swelling response was appar- ent when ethylene was applied to excised roots (Chadwick and Burg, 1967). 72 As with the response of hypocotyls to physical stress (Goeschl et al., 1969), the area of ethylene evolution ap- pears to be localized. This is indicated by the uniform level of evolution of control roots even though their total weight and mass increases with time. The root swelling response occurred after the increase in rate of ethylene evolution. If the roots were not grown through tubes, upon reaching the barrier, they bent rapidly without a detectable increase in ethylene production or noticeable change in diameter. One might anticipate that a certain minimum resistance must be present before high levels of ethylene are produced. Goeschl et a1. (1967) found the level of ethylene evolution from hypocotyls to be a function of resistance rather than total load. Ethylene in the soil atmosphere has in the past been largely neglected. The fact that it can be found and in significant amounts opens a series of new questions and problems. As indicated by Table 1B, transient water changes appear to cause fluctuations in the ethylene level in the soil atmosphere, possibly reflecting the high partitioning coefficient of ethylene into water. Since the soil where the samples were taken was devoid of plants, the increase in ethylene concentrations during the growing period cannot be ascribed to increasing number of plant roots. Consequently, one might anticipate the role of soil micro-organisms and organic matter to be of considerable interest and importance. 73 Literature Cited Barley, K. P., Greacen, E. L.: Mechanical resistance as a soil factor influencing the growth of roots and under— ground shoots. Adv. of Agron. l9, l—AO, ed. A. G. Norman. Acad. Press, N.Y. (1967). Burg, S. P.: The physiology of ethylene formation. Ann. Rev. Plant Physiol. 13, 265-302 (1962). Chadwick, A. V., Burg, S. P.: An explanation of the inhi— bition of root growth caused by indole-3—acetic acid. Plant Physiol. A2, A15-A20 (1967). Eavis, B. W.: Soil physical conditions and root growth. Ph.D. Thesis, Univ. of Reading (1965). Ekdahd, 1.: Studies on the growth and the osmotic condi- tions of root hairs. Symbolae Botan. Upsalienses. 11 (6), 1—83 (1953). Goeschl, J. D., Pratt, H. K., Bonner, B. A.: An effect of light on the production of ethylene and the growth of the plumular portion of etiolated pea seedlings. Plant Physiol. A2, 1077-1080 (1967). Rappaport, L., Pratt, H. K.: Ethylene as a factor regulating the growth of pea epicotyls subjected to physical stress. Plant Physiol. A1, 877-88A (1966). Hall, W. C., Morgan, P. W.: Regulateurs naturels de la croissance vegetale. 727—7A5, ed. J. P. Nitsch. Centre National de la Recherche Scientifique, Paris (196A). Hitchcock, A. E., Zimmerman, P. W.: Effects obtained with mixtures of root inducing and other substances. Contrib. Boyce Thompson Inst. 11, lA3—l60 (19A0). Kays, S. J., Nicklow, C. W.: In preparation (1971). Kristensen, K. J., Enoch, H.: Soil air composition and oxygen diffusion rate in soil columns at different heights above a water table. Trans. 8th Intern. Congr. Soil Sci. (Bucharest). 2, 159-170 (196A). Pfeffer, W.: Druck und arbeitsleistung durch wachsende pflanzen. Abhandlungen der koniglich sachsischen gesellschaft der wissenschaften. 33, 235-A7A (1893). 7A Pratt, H. K., Workman, M., Martin, F. W., Lyons, J. M.: Simple method for continuous treatment of plant material with metered traces of ethylene or other gases. Plant Physiol. 38, 262—267 (1960). Radin, J. W., Loomis, R. S.: Ethylene and carbon dioxide in the growth and development of cultured radish roots. Plant Physiol. AA, l58A—1589 (1969). Richards, H. M., MacDougal, D. T.: The influence of carbon monoxide and other gases upon plants. Bull. Torrey Botanical Club. 31, 57—66 (190A). Zimmerman, P. W., Hitchcock, A. E.: Initiation and stimula— tion of adventitious roots caused by unsaturated hydro- carbon gases. Contrib. Boyce Thompson Inst. 5, 351—359 (1933)- Wilcoxon, F.: Several chemical growth substances which cause initiation of roots and other responses in plants. Contrib. Boyce Thompson Inst. 7, 209-229 (1935). SECTION IV A Sensitive Technique for Measuring Root Mediated Soil Deformations and Their Potential for Overlap Between Neighboring Roots Introduction Roots, hypocotyls and other below ground plant parts alter existing structure of the soil that is in close proximity with the organ (5). Shear failure with compres— sion and shear failure without compression are the primary means of channel formation by plant roots (3). The degree of soil consolidation is a function of both the properties of the soil and the plant root. Furthermore, the soil ex— erts a pronounced influence on root growth (9). Root growth can be restricted in cemented or indurated horizons (12). Soil strength appears to be a primary factor in the pene— tration and growth of roots into the soil (A). Where the soil strength is sufficiently high, crop yields may in turn be significantly depressed (1,10). Several methods of measuring density changes in simu— lated soil systems have been developed (7,11). Greacen's technique (11) has the greatest precision and consists of a photographic determination based on the relationship between film density and bulk density of the medium. Although the technique appears reasonably accurate for a large diameter deforming penetrometer (in this instance a 3 mm steel probe), the optical properties of soils would present substantial accuracy problems when measuring the effect of small roots. 75 76 The objective of this study was to develop a technique for measuring small changes in bulk density around plant roots or other below ground plant organs and determine the effective root diameter. Materials and Methods Vlsga fasa, L., variety Broad Windsor, seeds were im— bibed for 8 hours in aerated distilled water and planted singly in 50 ml. plastic beakers containing washed sand of either 18.27 H or A9.09 u average diameter. The perforated bases of the beakers were covered with filter paper before sand was added. A seed was placed at A0 ml. level, covered with sand and then wetted from the base with distilled water. The seeds were grown in the dark at 18°C for 96 hours. At this time the seedling was fixed in situ for 2A hours with 5% gluteraldehyde, also taken up from the base of the beaker. The beakers with seedlings were dried at 60°C for A8 hours and vacuum impregnated (Fig. l) with methacrylate (30% ethyl and 70% butyl) with 2% benzoyl peroxide catalyst. The ~beaker was placed under a particle vacuum (717 mm. Hg) and lowered slowly to a point where the methacrylate in a con— tainer below moved up into the beaker with seedling from the base by capillary action. Methacrylate was utilized as the embedding medium because of its viscosity properties, sim- ilar to water, which minimized structural alterations due to front movement during embedding. After the methacrylate 77 front reached the surface of the sand the entire container was slowly lowered into the beaker of methacrylate to a point 1 cm from the top. The vacuum was released and the container placed in a nitrogen gas atmosphere and dried at 60°C for A8 hours. The embedded samples were cut vertically, parallel to the main root, using a diamond circular saw, and ground to the center of the root with silicon carbide grinding paper. The samples were polished with a progressive series of silicon carbide grinding paper (grits 120 through 600). The polished sample was carbon coated. Point scans using an EMXS—M electron microprobe x-ray analyserl were run for Si and Ca. Ca scans were used to give the exact location of the root edge. Data was collected with a strip chart recorder. Six to 8 scans were made for each density measurement. The scans were made at set intervals of approximately 1/2 the average diameter of the media parti— cles progressing down the root. Knowing the probe scan speed and the chart speed, the distance of any point, on the print out, from the root could be calculated. The ratio of the solids to the voids was measured at 1/2 peak height. Measurements were made for 1 mm distances, however, 250 or 500 u distances can also be made. 1Applied Research Laboratories 78 Fig. l.—-Apparatus for the embedding of samples: a) glass rod for lowering sample, b) vacuum barostat, and 0) line to vacuum pump. 79 80 Results A single scan for both Si and Ca is presented in Fig. 2. Calculating the voids ratio at 1/2 peak height, the ratio of solids to voids is plotted vs the distance from the root (mm) in Fig. 3. The density increased out to about 5 mm in fine sand in comparison with a distance of about 6 mm in coarse sand. Therefore, the effective diameter (root radius + distance of deformation x 2) increased approxi— mately 6 times. Discussion The results indicate that the effective root diameter (root radius + distance of deformation x 2) is increased to approximately 6 times the diameter of the root in coarse sand. Greacen (11) reported a A fold increase in effective diameter with a steel probe which, unlike plant roots, ex- hibits no radial increase from swelling or secondary growth. The question that arises is: under high populations of plants or other areas with substantial root densities, do the effective diameters of neighboring roots overlap? If one afssumes that roots of rye exhibit the same percent increase in effective diameter as Vasga fasa, L., then the effective diameter, based on previous measurements of the average root diameter (.23 mm) (2), can be calculated. Substituting the effective diameter for d in the following equation for the average distance between roots, 81 Fig. 2.——Line profile analysis run perpendicularly to a vertical root, showing the distribution of Si and Ca. 82 a.) _1 J4 I. oo _ 83 Fig. 3.——Change in voids ratio with distance from the root. VOIDS RATIO 8A 1.80 1.60 1.40 1.20 fine «and 1.00 7 ‘ “ / \ / o o \ / / \ . / coarse sand \ / / 0 \ ‘ - -' t' I o o .50 0 0M 1 2 3 4 5 6 7 8 DISTANCE PROM ROOT (mm) 85 d = l/(LV1T >1/2 (1) where d represents the average distance between roots and Lv is the root density (cm-2), and solving for density, a 2 is obtained. Therefore any density of 2 value of 33.A cm- roots greater than 33.A cm- could have overlapping effec- tive diameters or areas of deformation. A comparison of this value with actual measurements of root density for rye 2 2 and/or wheat (Andrews, 53 cm" (2), Pavlychenko, 53 cm- 2 (8)) indicates that a single rye or (1A), Dittmer, 50 cm- wheat plant exhibits approximately twice the density of roots required to have their areas of deformation overlap. Although this provides an excellent indication that roots have the potential for their areas of deformation to overlap, there are several considerations that must be kept in mind. (A). This method assumes that the root system is perfectly symmetrical. Work of Melhuish (13) and Barley and Sedgley (6) indicates that this is not the case. Since estimates were calculated under an ideal situation or per- fect root distribution, then any move away from a perfect distribution would tend to increase the significance of the overlap potential. (B). The estimate assumes the same relative percent deformation regardless of the root diameter and particle size distribution. The results in Fig. 3 indi— cate, as one would anticipate, that particle size is of importance in relation to the distance of deformation. (0). It neglects, at present, changes in bulk density, vertical and radial resistances, and plasticity and elastic- ity changes in the soil. 86 The magnitude of the difference in estimates of essen— tial and actual root density, indicates the potential for overlap of physical deformations of roots. The physical and biological factors which determine if this competition for space by the roots actually results in a changed size and shape of the root system remain to be tested. 10. ll. 12. 87 Literature Cited Adams, E. P., Blake, G. R., Martin, W. P., and Boelter, D. H. 1960. Influences of soil compaction on crop growth and development. 7th Intern. Cong. Soil Sci. 607-613. Andrews, R. E., and Newman, E. I. 1969. Resistance to water flow in soil and plant. III. Evidence from ex- periments with wheat. New Phytol. 68:1051—1058. Barley, K. P. 1963. Influence of soil strength on growth of roots. Soil Sci. 96:175-180. Barley, K. P., Farrell, D. A., and Greacen, E. L. 1965. The influence of soil strength on the penetration of a loam by plant roots. Aust. J. Soil Res. 3:69-79. Barley, K. P., and Greacen, E. L. 1967. Mechanical resistance as a soil factor influencing the growth of roots and underground shoots. Adv. in Agron. 19:1—A0. Barley, K. P., and Sedgley, R. H. 1961. The blockage of soil pores by plant roots. Aust. J. Sci. 23:297— 298. Day, P. R. 19A8. Experiments in the use of the micro— scope for the study of soil structure. Soil Sci. Soc. Amer. Proc. l3:A3—A9. Dittmer, H. J. 1938. A quantitative study of the sub— terranean members of three field grasses. Amer. J. Bot. 25:65A—657. Eavis, B. W. 1965. Soil physical conditions and root growth. Ph.D. Thesis, Univ. of Reading. Flocker, W. J., Timm, H., and Vomocil, J. A. 1960. Effect of soil compaction on tomato and potato yield. Agron. J. 52:3A5—3A9. Greacen, E. L., Farrell, D. A., and Forrest, J. A. 1967. Measurement of density patterns in soil. J. Agri. Engng. Res. 12:311—313. Lutz, J. F. 1952. Mechanical impedance and plant growth. In "Soil Physical Conditions and Plant Growth". Amer. Soc. Agron. Monograph. Vol. 2. Acad. Press, Inc. N.Y. pp. A3—71. 13. 1A. 88 Melhuish, F. M. 1968. A precise technique for measure— ment of roots and root distribution in soils. Ann. Bot. 32:15—22. Pavlychenko, T. K. l9A2. Root systems of certain forage crops in relation to management of agricultural soils. Publs. Natu. Res. Coun. Canada. No. 1088. APPENDICES 89 Appendix Table l.—-Harvest data for the number of fruit/ plant, number of clusters with fruit/ plant, fruit weight/plant and total plant weight. X X“ X X6 X l 2 3 5 7 l l l 0 0 0 0.20 l l 2 7.2 3.6 O.AA 0.62 1 l 3 8.7 A.A 0.60 0.76 1 2 l 0 0 0 0.67 l 2 2 35.3 16.0 0.97 3.07 1 2 3 3A.6 16.2 2.A0 2.83 l 3 l 0 0 0 1.67 l 3 2 61.0 28.2 2.A3 5.83 l 3 3 110.6 53.0 8.03 10.95 2 1 1 0 0 0 0.25 2 1 2 11.2 6.2 0.26 1.08 2 l 3 7.A 3.8 0.53 0.19 2 2 l 0 0 0 0.18 2 2 2 22.9 15.1 0.75 2.25 2 2 3 36.3 16.7 2.50 3.32 2 3 1 0 0 0 1.17 2 3 2 96.3 32.8 3.72 6.59 2 3 3 125.7 5A.3 8.29 12.10 3 l l 0 0 0 0.30 3 l 2 11.6 6.1 O.A5 0.89 3 l 3 10.3 A.6 0.59 0.19 3 2 1 0 0 0 0.8A 3 2 2 1A.9 7.3 0.72 1.01 3 2 3 29.3 12.A 1.87 2.A8 3 3 l 0 0 0 1.19 3 3 2 A3.7 22.3 2.01 3.20 3 3 3 109.A A7.l 7.53 9.83 X = Replication X = Plant population: 1 5 x 5 inches 2 = 10 x 10 inches 3 = 20 x 20 inches X3 = Date: 1 = 7/29 2 = 8/30 3 = 9/20 X“ = Number of fruit per plant X5 = Number of clusters with fruit per plant X6 = Fruit weight per plant (in pounds) X7 = Total plant weight (plant + fruit) (in pounds) 90 Appendix Table 2.——Soil gas atmosphere data for CO 0 and ethylene. 2 2 X1 X2 X3 X“ X5 X6 X7 X8 X9 X10 X11 X12 1 l l 1.98 2.6A A.l3 16 75 15.89 16.75 0 0 0 1 2 l 1.10 3.A1 3.03 20 19 l5.A6 16.32 0 0 0 1 3 l 2.68 2.81 3.A7 16 18 17.18 17.18 0 0 0 2 l l 2.35 3.38 5.5A 19 76 18.28 16.30 0 0 0 2 2 l 2.11 5.00 6.36 20 75 17.78 18.28 0 0 0 2 3 1 A.95 5 20 5.15 16 30 16.30 17.29 0 0 O 3 l l 3.81 6 22 5.05 20 25 19.76 17.78 0 0 0 3 2 l 1.A8 5.05 2.11 20 75 19.76 19.76 0 0 0 3 3 1 2.79 5.3A 5.00 18 77 17.78 18.28 0 0 0 A 1 1 1.81 2.60 2.55 21 2A 19.76 18.28 0 0 0 A 2 l 1.96 2.16 2.01 19 76 20.25 19.27 0 O 0 A 3 l 1.91 1.52 2.31 20 75 21.2A 18.77 0 0 0 l 1 2 0.32 O.AA 0.57 19 28 18.81 19 28 12 05 21 l 2 2 0.3A 0.92 1.3A 19 30 18 38 18 38 00 00 00 l 3 2 0.3A 0.51 0.67 19 28 19 28 18 81 02 07 07 2 l 2 0.65 0.65 1.03 18 81 19 28 18 81 05 06 16 2 2 2 0.A8 0 67 0.88 19 30 16 5A 18 38 05 02 00 2 3 2 0.26 0 33 0.75 18 95 18 55 18 1A 11 1A 10 3 l 2 0.21 O.A6 0.86 19 76 19 76 19 35 12 11 20 3 2 2 0.75 1.76 2.00 19 28 18 3A 19 28 09 10 O7 3 3 2 O.A7 0.59 1.03 19 28 18 81 19 28 03 10 10 A l 2 0.72 0.50 0.8A 19 35 19 76 19 35 10 08 16 A 2 2 0.37 0.95 0.90 19 35 2O 16 18 96 08 12 11 A 3 2 0.92 0.A2 0.92 19 76 19 76 19 35 00 07 06 l 1 3 3.55 A.95 A.79 18 66 18 22 18 AA 12 13 2A 1 2 3 3.21 A.A2 A.63 20 88 18 66 18 66 11 21 30 l 3 3 1.87 3.A1 A.95 19 55 19 55 18 22 18 23 19 2 1 3 2.5A A.A2 5.09 19 11 18 66 18 66 A9 15 12 2 2 3 5.22 5.22 5.A2 18 66 18 66 18 66 2A 166 1A 2 3 3 3.21 5.02 5.35 18 66 18 66 18 66 12 12 22 3 l 3 3.88 5.69 5.A2 18 66 18 66 18 66 ll 20 ll 3 2 3 2.01 3.Al 5.09 19 99 19 ll 19 99 10 06 ll 3 3 3 1.3A 3 28 6.09 19 99 19 55 19 11 06 10 06 A l 3 3.28 2.27 2.3A 19 55 19 55 19 11 16 10 12 A 2 3 2.21 1.87 3.21 19 99 19 55 18 66 16 2A 20 A 3 3 2.7A 3.29 A.01 19 55 19 55 18 22 21 09 13 X1 = Plant population: 20 x 20 inches X6 = CO at 16 in. l: 2 = 10 x 10 inches X _ o 2 t u . 3 = 5 x 5 inches 7 _ 2 a 1n. A = without plants X = O at 8 in. X = Replication 8 2 2 X9 = 02 at 16 in. X = Date: 1 = 7/29 CO as % _ . 3 2 = 9/2 O22as % X10 — C2HA at A 1n. X _ C0 3 5 9/29 C2HA as ppb Xll = 02H” at 6 1n. u ” 2 at l“- xl2 = 02H,l at 8 in. X = CO at 8 in. 2 91 Appendix Table 3.—-a) Soil probe resistance (gm); b) Ethylene concentration in the soils gas phase after irrigation; 0) total fruit yield (tons/acre). ID 100 O X1 X2 X3 XA X1 X2 X3 X” X1 X2 X3 XA l 1 1 A22 0 l l 1 58.5 1 l l 58.10 1 2 1 A78 6 l 2 1 62.2 1 l 2 80.89 1 3 1 A68 0 l 3 1 52.1 1 2 l AA.80 2 1 1 A39.0 2 l 1 100.6 1 2 2 75.23 2 2 1 A82 0 2 2 1 20.1 1 3 1 17.93 2 3 l A2A 0 2 3 1 29.3 1 3 2 A0.3A 3 l 1 A01 0 3 l l A2.1 2 l 1 53.22 3 2 l 395 3 3 2 l A1.l 2 l 2 75.38 3 3 1 A52 0 3 3 1 5.9 2 2 l A6.80 1 1 2 589 0 l l 2 20.7 2 2 2 67.00 1 2 2 5A2 0 l 2 2 20.7 2 3 l 23.33 1 3 2 5A6 0 l 3 2 1A.l 2 3 2 Al.6A 2 1 2 570 0 2 l 2 12.5 3 l 1 55.22 2 2 2 623 0 2 2 2 7.1 3 l 2 76.A1 2 3 2 696 0 2 3 2 21.8 3 2 l A6.39 3 l 2 502 0 3 l 2 15.8 3 2 2 A7.99 3 2 2 A89.0 3 2 2 18.5 3 3 l 25.06 3 3 2 537 0 3 3 2 10-9 3 3 2 37-80 l l 3 609 3 1 1 3 A2.7 l 2 3 678 6 l 2 3 22.2 1 3 3 592 o 1 3 3 39.8 2 1 3 636 6 2 l 3 lA.2 2 2 3 587 3 2 2 3 A3.8 2 3 3 576 6 2 3 3 29.0 3 l 3 A57 3 3 l 3 15.9 3 2 3 513 0 3 2 3 9.7 3 3 3 588 O 3 3 3 9.1 A: X = Date: 1 = 0 X = Pla t o ulation' 1 = 20 x 20 inches 3 2 = 3 days 1 n p p . = 10 x 10 inches 3 = 11 days . X = C H — water data 3 = 5 x 5 inches A 2 A ( b) X2 = Replication 0' pp X3 — Date. 5 ; gégg X1 = Replication 3 = 9/28 X2 = Plant population: XA = Soil probe data 1 = X 5 in. 2 = 10 x 10 in. B: 3 = 20 x 20 in. X1 = Depth: 1 a 16 inches X3 _ Date. ; ; I976 2 — 8 inches _ . = A inches X“ — Total y1eld 3 X2 = Replication S \f HICH GQN STRTE UNIV. LIBRRRI i u MHI 31293010057465