HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by Board, J. Search for Related Content PubMed Articles by Board, J. Agricola Articles by Board, J. Related Collections Soybean Other Cropping Systems Plant and Environment Interactions

CROP PHYSIOLOGY & METABOLISM

Reduced Lodging for Soybean in Low Plant Population is Related to Light Quality

Dep. of Agronomy, Louisiana Agric. Exp. Stn., LSU Agric. Ctr., Baton Rouge, LA 70803

Corresponding author (jboard{at}agctr.lsu.edu)

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION Light Quality and Quantity CONCLUSION REFERENCES

 
Lodging is a common production problem for soybean [Glycine max (L.) Merr.] in the southeastern USA. Reducing plant height by planting at a low optimal population (plant population sufficient to optimize yield) is a recognized practice for reducing lodging. Environmental factors responsible for reduced plant height in response to low optimal population have not been determined, however. Plant height for determinate soybean is determined mainly during the vegetative period (emergence to R1). Because light quality affects stem extension, our objective was to determine the roles of red/far red light ratios and blue light irradiance during the vegetative period on plant height. Determinate cultivar Deltapine 3606 (Maturity Group VI) was planted at an optimal planting date during 1995 and 1996 at low (80 000 plants ha^-1), medium (145 000 plants ha^-1), and high (390000 plants ha^-1) plant populations on a Commerce silt loam soil (fine-silty, mixed, nonacid, thermic, Aeric, Fluvaquents) near Baton Rouge, LA (30°N Lat). Experimental design was a randomized complete block in a split plot arrangement with four replications. Plant populations were main plots and split plots were staked (non lodging) and unstaked (prone to lodging) treatments. Increased lodging in staked vs. unstaked plots resulted in a 10% yield loss. Across unstaked plots, decreased lodging in low vs. high population was associated with a 25% reduction in plant height and a 29% increase in main stem thickness. These morphological changes were more closely related to differences in red/far red light ratios for low vs. higher plant populations rather than to changes in blue light irradiance.

Abbreviations: R/FR ratio, red/far red light ratio

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION Light Quality and Quantity CONCLUSION REFERENCES

 
BECAUSE OF HIGH VELOCITY WINDS and frequent heavy rainfall, lodging is a common production problem for soybean in the southeastern USA (Noor and Caviness, 1980; Mancuso and Caviness, 1991). Although some yield losses occur because of mechanical harvesting problems (Weber and Fehr, 1966), greatest reductions occur because of reduced pod production (Woods and Swearingin, 1977; Noor and Caviness, 1980). Yield losses were greatest when lodging occurred during the R4 to R6 period (stages according to Fehr and Caviness, 1977). Independent of harvest losses, lodging can reduce yield by as much as 22% (Noor and Caviness, 1980). Reduced plant height is recognized as an effective means of reducing or eliminating lodging (Cooper, 1981; Mancuso and Caviness, 1991). Wilcox and Sediyama (1981) reported that across a range of genotypes there was a 0.3 increase in lodging score (1 = erect; 5 = completely lodged) with each 10 cm increase in plant height.

Early studies recognized that lodging increased with plant population (Cooper, 1971). Nagata (1968) determined that decreased lodging with lower plant population was associated with reduced plant height and wider stem diameter. Possible environmental factors explaining short and thick main stems in sparse vs. dense stands are light quantity and quality. Independent of photosynthetic effects, both factors affect plant development and morphology through a process called photomorphogenesis (Kendrick and Kronenberg, 1986). For example, in conditions where photosynthetic capacity is similar, stem sections receiving greater quantities of white light have slower elongation rates (Garrison and Briggs, 1972). Light quality, specifically the ratio of red/far red light (R/FR) and blue light irradiance, also affect stem extension. As sunlight penetrates a canopy, not only is the level of light decreased, but the R/FR declines because of greater absorption of R vs. FR light by leaves (Holmes and Smith, 1977). Analysis of light quantity and R/FR changes determined that the latter had greater importance in affecting stem elongation (Smith and Morgan, 1981). Stem elongation effects of R/FR occur between neighboring plants before any mutual shading occurs (Ballare et al., 1990). Independent of R/FR, low levels of blue light (<6.3 W m^-2) can also stimulate stem extension (Wheeler et al., 1991).

Because light quality factors have been shown to affect stem extension and plant height and because plant height is related to lodging, the objective of this study was to determine if altered R/FR and/or differential blue light irradiance in sparse vs. dense plant populations were responsible for shorter plant height (and hence less lodging) in sparse populations.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION Light Quality and Quantity CONCLUSION REFERENCES

 
Determinate cultivar Deltapine 3606 (Maturity Group VI) was planted at the Ben Hur Research Farm near Baton Rouge, LA, (30°N Lat) on a Commerce silt loam soil. Seed were machine planted 23 May 1995 and 17 May 1996 on a 75-cm row width at high plant populations. Experimental plots were 10 contiguous rows with a 6.1-m row length. Within each plot, two adjacent rows with border rows were used for plot yield determination and three separated rows (each bordered) were used for sampling and light quantity and quality determinations. Prior to V3, plots were thinned to three plant populations: low (80 000 plants ha^-1), medium (145 000 plants ha^-1), and high (390 000 plants ha^-1). Plant populations were the averages of seven stand counts starting at two weeks after emergence and ending near R2. Stand counts were randomly taken by counting the number of plants occupying a 66-cm length of bordered row from interior portions of the plot and then multiplying by two to obtain plants per square meter. Weeds, diseases, and insects were controlled with recommended practices. Fertilizer was applied before planting at the rate of 0-0-67 kg ha^-1 (N-P-K) according to soil test recommendations. Rainfall was adequate for optimum crop growth throughout the duration of the study.

Experimental design was a randomized complete block in a split plot arrangement with four replications. Main plots were the low, medium, and high plant populations described above and split plots were staked plots in which lodging was minimized and unstaked plots in which natural lodging occurred. Data obtained for all plots were lodging score and plot yield (kg ha^-1) determined by combine harvest of two interior rows (6.5 m²) of each plot that had been end trimmed to 4.3 m and corrected to 130 g kg^-1 moisture. Lodging was based on a visual rating between one to five as follows: 1, almost all plants erect; 2, either all plants leaning slightly or a few plants down; 3, either all plants leaning moderately or 25 to 50% of the plants down; 4, either all plants leaning considerably or 50 to 80% of the plants down; and 5, all plants prostrate.

Assessments of light quantity and quality were obtained between emergence and R2, since this is the main stem elongation period for determinate soybean. Because no lodging occurred in staked and unstaked plots during the sampling period, data were obtained only for staked plants. Experimental design for these parameters was a randomized complete block in a split plot arrangement with four replications. Main plots were the three plant populations and the split plots were sampling dates. Light quantity within the canopy was assayed by the degree of intrarow mutual shading between plants as determined by light interception per plant. Greater mutual shading (i.e., greater interplant competition for light) is indicated by how much of the intercepted light is received by each plant in a particular population [i.e., light interception per plant (% per plant)]. Light interception per plant was determined by measuring photosynthetic photon flux density (µmol m^-2 s^-1) at soil level by placing a 1-m long LI-COR Line Quantum Sensor (LI-COR Inc., Lincoln, NE), connected to a LI-1000 data logger, diagonally between rows; measuring ambient photon flux density; using these values to determine light interception by the canopy; and then dividing this figure by plants per meter square. Light interception per plant was determined at 14, 21, 28, 35, 42, 49, and 56 d after emergence within 1 h of solar noon.

Experimental design for red/far red light ratios (R/FR) and blue light irradiance was a randomized complete block in a split plot arrangement with four replications. Recordings were done only for staked plantes. Main plots were staked plant populations and split plots were sampling dates at 14, 28, 42, and 56 d after emergence. Red (645 nm), far-red (735 nm), and blue (sum of irradiance between 400–500 nm) light irradiances were determined at 14, 28, 42, and 56 d after emergence with a LI-COR portable spectroradiometer (band width of 1 nm) equipped with a fiber optic probe. Wavelength selection for red and far red light was based on Kasperbauer (1987), who stated that these values approach the peaks for phytochrome action in green plants. Recordings were taken between 1300 and 1500 in the afternoon under the overcast conditions typical of the Gulf Coast Region of the USA. Although ambient light conditions varied between sampling dates, relative spectral quantum fluxes at 645 and 735 nm are only slightly affected by overcast vs. clear-sky conditions (Holmes and Smith, 1977). Preliminary recordings indicated a similar relationship occurred for soybean in our study. Thus, changes in ambient irradiance did not confound R/FR recordings. Blue light was recorded under the same overcast conditions as R/FR in order to obtain a more realistic appraisal (compared with clear-sky conditions) of prevailing conditions. The sampling date treatment factor affecting blue light levels was confounded by the degree of cloudiness throughout the study. Thus, blue light levels reported in this paper represent a monitoring of data rather than a measure of how sampling date affected this parameter.

Red/far red measurements were taken at the midpoint of plant height according to a method described in Kaul and Kasperbauer (1988). A single plant was removed and replaced with a wooden stake to support the fiber optic probe. The probe was oriented to measure incoming light parallel to the soil surface at north, south, east, and west positions. Ambient R/FR was also determined by placing the probe toward the sky at a position just above and parallel to the top of the canopy. This was done to verify that ambient R/FR did not change with the degree of overcast conditions. Analysis of variance was according to the SAS General Linear Model with mean separation according to LSD after demonstration of significant F test. Correlation coefficients for lodging vs. R/FR ratios and lodging vs. blue light were determined within sampling dates from the six population x year treatment combinations (low, medium, and high populations for 1995 and 1996).

Internode length and width were determined at the termination of main stem growth (R2) for Internodes 7 to 10 and again at R7 for Internodes 7 to 13 in all staked plots. Internode 1 started at the primary leaf node. Five plants per plot were randomly sampled and dried in a forced-air dryer at 60°C to a constant weight. After measuring plant height, Internodes 7 to 10 (7–13 at R7) were segmented and length and midpoint width measured. Experimental design for internode length and width at R2 and R7 was a randomized complete block with four replications and one factor (plant population). Mean separation was according to LSD after demonstration of significant F test.

	RESULTS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION Light Quality and Quantity CONCLUSION REFERENCES

 
Yield, Plant Height, and Lodging
Both year and lodging significantly (P < 0.05) affected yield (data not shown); however, all other main effects and interactions had no significant (P < 0.05) effect on yield. Across populations and staked/unstaked treatments, yield fell 10% from 4126 kg ha^-1 in 1995 to 3709 kg ha^-1 in 1996. Reduced yield in the second year was associated with greater lodging (3.4 in 1996 vs. 2.4 in 1995). Across populations and years, yield for unstaked plots was significantly (P < 0.05) less compared with staked plots (Table 1). Environmental variation for yield was low (C.V. = 7.4%). Associated with lower yield in the unstaked plots was greater lodging (2.9) compared with the staked plots (1.4). Lodging differences between staked and unstaked plots were established by R5 (Table 1), the stage at which lodging has greatest effect on depressing yield (Woods and Swearingin, 1977). Lodging was significantly (P < 0.05) affected by year (greater in the second year) and plant population. Significant (P < 0.05) interactions occurred for year x staked/unstaked and population x staked/unstaked. Because the year x population x staked/unstaked interaction was not significant (P < 0.05), population x staked/unstaked treatment combinations for lodging were averaged across years (Table 1).

Eighty-seven to 91% of final plant height was determined by R2 (56 d after emergence) (Fig. 1) . Although differences in plant height between the populations were apparent by three weeks after emergence, significant differences did not appear until 42 d after emergence. By R2, plant height was significantly greater in high vs. medium and in medium vs. low populations. Thus, most of the difference in plant height was created by Internodes 7 to 13, which were developing between 30 to 56 d after emergence (Fig. 1). When measured at R2, lengths for Internodes 7 to 10 were significantly (P < 0.05) less in low vs. medium and in medium vs. high populations (Table 2). At R7 all internodes at the top half of the main stem (7–13) showed a similar relationship.

View larger version (36K): [in this window] [in a new window]   Fig. 1. Main stem length during the vegetative period for soybean planted at low, medium, and high plant populations in 1995 and 1996, Baton Rouge, LA. Low population = 80 000 plants ha-1; medium population = 145 000 plants ha-1; high population = 390 000 plants ha-1. Population means within dates followed by different letters are significantly (P < 0.05) different according to LSD

View larger version (27K): [in this window] [in a new window]   Fig. 2. Red/far red light ratios (645/735 nm)received at the main stem for soybean planted at low, medium, and high plant populations and averaged across 1995 and 1996, Baton Rouge, LA. Low population = 80 000 plants ha-1; medium population = 145 000 plants ha-1; high population = 390 000 plants ha-1. Population means within dates followed by different letters are significantly (P < 0.05) different according to LSD

View larger version (28K): [in this window] [in a new window]   Fig. 3. Light interception per plant for soybean planted at low, medium, and high populations and averaged across 1995 and 1996, Baton Rouge, LA. Low population = 80 000 plants ha-1; medium population = 145 000 plants ha-1; high population = 390 000 plants ha-1. Population means within dates followed by different letters are significantly (P < 0.05) different according to LSD

View larger version (33K): [in this window] [in a new window]   Fig. 4. Blue light irradiance (400–500 nm) received at the main stem for soybean planted at low, medium, and high populations for 1995 and 1996, Baton Rouge, LA. Low population = 80 000 plants ha-1; medium population = 145 000 plants ha-1; high population = 390000 plants ha-1

	DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION Light Quality and Quantity CONCLUSION REFERENCES

Plant height and lodging declined with reduced plant population (Table 1), such that a 25-cm decrease in plant height from 103 cm in the high population to 77 cm in the low population decreased lodging from 3.6 to 2.0 among unstaked plots. This 0.64 unit lodging decrease with each 10-cm reduction in plant height was more than the 0.30 unit lodging decrease per 10-cm plant height reduction reported by Wilcox and Sediyama (1981). A possible explanation is that main stem thickness also increased with reduced plant population (Table 3), a second factor conducive to lodging resistance (Poehlmann and Sleper, 1995). Although stem thickness was not mentioned in the study by Wilcox and Sediyama (1981), research by Nagata (1968) indicated that main stem thickening in response to sparser plant populations occurred for determinate but not indeterminate cultivars. Determinate cultivars also showed greater reductions in lodging with decreased plant population compared with the indeterminate cultivar in Nagata's study. Greater lodging reduction with reduced plant population for determinate vs. indeterminate cultivars may result because reduced plant height and main stem thickening occur in determinates, whereas only reduced plant height may occur for indeterminates. Yields were similar across plant populations, even though plant density in the low population was 68% below recommended rates in Louisiana (Boquet, 1996). Thus, under optimal growing conditions such as occurred for this study, a viable means to avoid lodging is to plant at low populations.

Comparisons of internode lengths between high vs. low populations (Table 2) indicated that 85% of the plant height difference between the two populations was accounted for by Internodes 7 to 13. During the first 28 to 35 d after emergence, significant differences in plant height between populations did not occur (Fig. 1), although plants in the high population were always numerically taller than the medium or low populations. Significant differences started occurring afterwards and became more pronounced with time until final plant height was achieved shortly after R2 (56 d after emergence). Population differences in main stem width also were established by R2 (Table 3). Between R2 and maturity, significant (P < 0.05) thickening occurred for main stems in all plant populations. However, relative differences in main stem thickness between populations were similar compared to R2. Thus, sturdiness of the main stem to resist lodging for low vs. higher populations was established by 56 d after emergence.

	Light Quality and Quantity

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION Light Quality and Quantity CONCLUSION REFERENCES

 
Light interception per plant (Fig. 3) and blue light irradiance levels (Fig. 4) indicate that during most of the vegetative period interplant shading (i.e., light competition) was greater for the medium vs. low and high vs. medium populations. Except for the first sampling date (14 d after emergence), blue light irradiance was greatest in the low population, indicating greater canopy light penetration for this treatment. This was caused by less interplant shading within the low population as indicated by greater light interception per plant. Progressively lower levels of light interception per plant for the medium and high populations indicated greater levels of interplant shading as population was increased. As in similar studies (Holmes and Smith, 1977), less shading in the low population resulted in greater R/FR ratios compared with denser populations. Red/far red light ratios were usually greater for low vs. medium and medium vs. high populations until 56 d after emergence. Equilibration of R/FR occurred between populations as canopy closure was reached.

Thus, Internodes 7 to 13, the ones most responsible for plant height differences between populations, were being formed during a time when low vs. denser populations had higher levels of irradiance within the canopy, higher blue light irradiances, and greater R/FR ratios. It is unlikely that blue light differences within the canopy were responsible for plant height differences, since throughout the stem extension period, blue light for all plant populations was several times greater than the threshold level (6.3 W m^-2), at which stem extension is induced (Wheeler et al., 1991). This occurred, even though recordings were made in the middle of the afternoon under overcast conditions where irradiance was well below clear-sky conditions. Because ambient conditions prior to noon are usually less overcast compared with afternoons, it is unlikely that blue light level fell below the threshold level during morning periods. However, future studies may reveal that threshold levels for blue light effects on stem extension are higher than those reported by Wheeler et al. (1991). Blue light and lodging were significantly negatively correlated during the period (30–56 d emergence, Fig. 1) that accounted for most of the plant height differences between populations. Thus, the role of blue light in creating the lodging differences shown in this study cannot be dismissed.

A more likely possibility explaining differences in plant height and stem thickness between plant populations is altered R/FR induced by differences in interplant shading. Photomorphogenic responses in plants are influenced by R/FR ratios between 0 to 1.1 (Smith and Holmes, 1977), such as those found in the current study. Smith and Morgan (1981) cited several controlled-environment studies concluding that stem extension observed in natural shade was primarily induced by altered R/FR and that low light irradiances had little influence.

Results in the current study indicate that prior to and during the formation of Internodes 7 to 13, R/FR ratios were greater for low vs. medium and high populations; although these differences attenuated near the end of main stem development (Fig. 2). Associated with less internode extension, was internode thickening, another response adding to lodging resistance. In conclusion, greater R/FR ratios in low vs. denser populations during the vegetative period induced a photomorphogenic response resulting in shorter and thicker internodes on the top half of the main stem. These changes, in turn, were associated with increased resistance to lodging.

	CONCLUSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION Light Quality and Quantity CONCLUSION REFERENCES

 
Greater lodging resistance for soybean in low compared with denser populations was related to reduced internode extension and greater thickness for the top internodes (7–13) of the main stem. The most likely explanation for these morphological changes was greater R/FR ratios received at the main stems during the vegetative period for plants in low populations. This conclusion is based on the fact that R/FR differences between populations were within the range expected to cause photomorphogenic changes in stem extension; these R/FR changes occurred prior to and during the development of internodes that accounted for the differences in lodging resistance; blue light levels were correlated with but probably too large to have an effect on stem extension; and previous research indicated that differences in light quantity did not play a major role in phenomena such as observed in the current study. Results indicate lodging can be avoided by planting at a seeding rate that achieves optimum yield, while at the same time increasing R/FR during the vegetative period so as to create a short, thick main stem. Also, a possible means for identifying genetic resistance to lodging is main stem responses (internode extension and thickening) to low R/FR ratios.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION Light Quality and Quantity CONCLUSION REFERENCES

 
Approved for publication by the Director of the Louisiana Agric. Exp. Stn. as manuscript no. 00-09-0181.

Received for publication March 27, 2000.

	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION Light Quality and Quantity CONCLUSION REFERENCES

 

• Ballare, C.L., A.L. Scopel, and R.A. Sanchez. 1990. Far-red radiation reflected from adjacent leaves: an early signal of competition in plant canopies. Science 247:329–332.[Abstract/Free Full Text]
• Boquet, D.J. 1996. Row spacings and plant population density. In W. Morrison (ed.) Louisiana soybean handbook. Louisiana Coop. Ext. Serv., Baton Rouge, LA.
• Cooper, R.L. 1971. Influence of early lodging on yield of soybean. Agron. J. 63:449–450.[Abstract/Free Full Text]
• Cooper, R.L. 1981. Development of short-statured soybean cultivars. Crop Sci. 21:127–131.
• Garrison, R., and W.R. Briggs. 1972. Internodal growth in localized darkness. Bot. Gaz. (Chicago) 133:270–276.[ISI]
• Fehr, W.R., and C.E. Caviness. 1977. Stages of soybean develoment. Iowa Agric. Exp. Stn. Spec. Rep. 80.
• Holmes, M.G., and H. Smith. 1977. The function of phytochrome in the natural environment: II. The influence of vegetation canopies on the spectral energy distribution of natural daylight. Photochem. Photobiol. 25:539–545.
• Johnston, T.J., and J.W. Pendleton. 1968. Contribution of leaves at different canopy levels to seed production of upright and lodged soybeans. Crop Sci. 8:291–292.
• Kasperbauer, M.J. 1987. Far-red light reflection from green leaves and effects on phytochrome-mediated assimilate partitioning under field conditions. Plant Physiol. 85:350–354.[Abstract/Free Full Text]
• Kaul, K., and M.J. Kasperbauer. 1988. Row orientation effects on FR/R light ratio, growth and development of field-grown bush bean. Physiol Plant. 74:415–417.
• Kendrick, R.E., and G.H.M. Kronenberg. 1986. Photomorphogenesis in plants. Martinnus Nijhoff/Dr. W. Junk Publishers, Dordrecht, Netherlands.
• Mancuso, N., and C.E. Caviness. 1991. Association of selected plant traits with lodging of four determinate soybean cultivars. Crop Sci. 31:911–914.[Abstract/Free Full Text]
• Nagata, T. 1968. Studies on the significance of the indeterminate growth habit in breeding soybeans. V. On the varietal difference in lodging resistance in different planting rates. Japan. J. Breed. 18:235–240.
• Noor, R.B.M., and C.E. Caviness. 1980. Influence of induced lodging on pod distribution and seed yield in soybeans. Agron. J. 72:904–906.[Abstract/Free Full Text]
• Poehlman, J.M., and D.A. Sleper. 1995. Breeding objectives and techniques. p. 216–239. In Breeding field crops (4th ed.). Iowa State Univ. Press, Ames, IA.
• Smith, H., and M.G. Holmes. 1977. The function of phytochrome in the natural environment. III. Measurement and calculation of phytochrome photoequilibria. Photochem. Photobiol. 25:547–550.
• Smith, H., and D.C. Morgan. 1981. Characteristics of the visible radiation incident upon the surface of the earth. p. 3–20. In H. Smith (ed.) Plants and the daylight spectrum. Academic Press, London, UK.
• Weber, C.R., and W.R. Fehr. 1966. Seed yield losses from lodging combine harvesting in soybeans. Agron. J. 58:287–289.[Abstract/Free Full Text]
• Wheeler, R.M., C.L. Mackowiak, and J.C. Sager. 1991. Soybean stem growth under high-pressure sodium with supplemental blue lighting. Agron. J. 83:903–906.
• Wilcox, J.R., and T. Sediyama. 1981. Interrelationships among height, lodging and yield in determinate and indeterminate soybeans. Euphytica 30:323–326.
• Woods, S.J., and M.L. Swearingin. 1977. Influence of simulated early lodging upon soybean seed yield and its components. Agron. J. 69:239–242.[Abstract/Free Full Text]

This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by Board, J. Search for Related Content PubMed Articles by Board, J. Agricola Articles by Board, J. Related Collections Soybean Other Cropping Systems Plant and Environment Interactions