Progress 10/01/07 to 09/30/12
Outputs
OUTPUTS: Increasing the yield of grain crops in the future may depend on our ability to manipulate basic plant processes that determine yield, but any such manipulation will require a thorough understanding of the processes involved. Yield of all grain crops, including soybean, can be defined by its two components, the number of seeds per unit area and the average weight per seed (seed size). Environmentally induced yield fluctuations are generally the result of changes in seed number. It is well known that seed number is determined by the average level of photosynthesis during this critical period. Less is known about the effect of variation in photosynthesis during flowering and pod set. We found that short periods of reduced photosynthesis (4 to 9 days) during peak pod production had no effect on pod number. The soybean plant could not recover from reduced photosynthesis at the beginning of the pod set period that continued for more than 14 days. Seed number was reduced by reductions in photosynthesis that began as late as the beginning of seed fill (shortly before growth stage R6). The number of flowers produced by a soybean community is related to the number of nodes, but if the plant produces more flowers than needed (50% abortion is common in high yield environments), the number of nodes should not be related to the number of pods. We found, however, that there was a curvilinear relationship between nodes and pods m-2. Pods increased in conjunction with nodes at low node numbers, but at high node numbers, increasing nodes had no effect on pods. Low node numbers are often associated with early cultivars, late plantings, or low populations. The development a dynamic simulation of model of the pod set process at the whole plant - plant community level (based on our single-node model SOYPOD) continues. Most of the computer code has been written, but algorithms describing the assimilate supply that controls the continued growth of individual pods, the distribution of assimilate by node, and the intra-nodal interaction of the developing pods and the supply of assimilate are still under development. PARTICIPANTS: D.B. Egli, Professor. Principal investigator Marcy Rucker. Research analyst. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
We found that short periods of reduced photosynthesis (4 to 9 days) during peak pod production had no effect on pod number. The soybean plant could not recover from reduced photosynthesis at the beginning of the pod set period that continued for more than 14 days. Seed number was reduced by reductions in photosynthesis that began as late as the beginning of seed fill (shortly before growth stage R6). The number of flowers produced by a soybean community is related to the number of nodes, but if the plant produces more flowers than needed (50% abortion is common in high yield environments), the number of nodes should not be related to the number of pods. We found, however, that there was a curvilinear relationship between nodes and pods m-2. Pods increased in conjunction with nodes at low node numbers, but at high node numbers, increasing nodes had no effect on pods. Low node numbers are often associated with early cultivars, late plantings, or low populations. The development a dynamic simulation of model of the pod set process at the whole plant - plant community level (based on our single-node model SOYPOD) continues. Most of the computer code has been written, but algorithms describing the assimilate supply that controls the continued growth of individual pods, the distribution of assimilate by node, and the intra-nodal interaction of the developing pods and the supply of assimilate are still under development.
Publications
- Egli,D.B.(2012)Timing of fruit initiation and seed size in soybean.Journal of Crop Improvement 26:751-766.
- Egli,D.B.(2012)Relationship between the number of nodes and pods in soybean communities. Crop Science (In Press).
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Progress 01/01/11 to 12/31/11
Outputs
OUTPUTS: Increasing the yield of grain crops in the future will depend on our ability to manipulate basic plant processes that determine yield and any such manipulation will require a thorough understanding of the processes involved. Yield of all grain crops, including soybean, can be defined by its two components, the number of seeds per unit area and the average weight per seed (seed size). Environmentally induced yield fluctuations are generally a result of changes in seed number. Roughly 50% of the flowers on a soybean plant do not survive to produce mature pods containing developed seed, suggesting that the number of flowers never limits pod and seed number. Since the number of flowers on a soybean plant is partially determined by the number of nodes, the excess flower production implies that seed number and yield may not be closely related to the number of nodes. Some agronomists, however, feel that early plantings to increase nodes per plant are a key to high yields. We tested this hypothesis by varying the number of nodes per plant (using cultivars with a range in maturity) and per unit area (several plant populations) in a field experiment in 2009,2010, and 2011. The results from 2011 are yet available, but, in 2009 and 2010, the treatments created substantial variation in nodes m-2 (~600 to 1500, but there was no relationship between the number of nodes and seeds m-2 or yield. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Our tentative results are consistent with the belief that pod and seed number in soybean is determined by canopy photosynthesis during flowering and pod set, and the number of nodes and flowers are not important. Once we complete the analysis of the data from 2011, we will make our final conclusions. Our tentative results suggest that management practices to increase the number of nodes will not lead to higher yield.
Publications
- No publications reported this period
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Progress 01/01/10 to 12/31/10
Outputs
OUTPUTS: Increasing the yield of grain crops in the future will depend on our ability to manipulate basic plant processes that determine yield and any such manipulation will require a thorough understanding of the processes involved. Yield of all grain crops, including soybean, can be defined by its two components, the number of seeds per unit area and the average weight per seed (seed size). Environmentally induced yield fluctuations are generally a result of changes in seed number. Roughly 50% of the flowers on a soybean plant do not survive to produce mature pods containing developed seed, suggesting that the number of flowers never limits pod and seed number. Since the number of flowers on a soybean plant is partially determined by the number of nodes, the excess flower production implies that seed number and yield may not be closely related to the number of nodes. Some agronomists, however, feel that early plantings to increase nodes per plant are a key to high yields. We tested this hypothesis by varying the number of nodes per plant (using cultivars with a range in maturity) and per unit area (several plant populations) in a field experiment in 2009 and 2010. The results from 2010 are still being analyzed, but, in 2009, the treatments created substantial variation in nodes per square m (~600 to 1500) and per plant (18 to 31), but there was no relationship between the number of nodes and seeds per square m or yield. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Our tentative results suggest that management practices that extend the vegetative growth period and increase nodes per plant are not needed to produce high soybean yields. This conclusion is tentative pending analysis of the data from our 2010 experiment.
Publications
- No publications reported this period
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Progress 01/01/09 to 12/31/09
Outputs
OUTPUTS: Increasing the yield of grain crops in the future will depend on our ability to manipulate basic plant processes that determine yield and any such manipulation will require a thorough understanding of the processes involved. Yield of all grain crops, including soybean, can be defined by its two components, the number of seeds per unit area and the average weight per seed (seed size). Variation in yield must be caused by changes in either or both of these components, but environmentally induced yield fluctuations are generally a result of changes in seed number. It is well known that seed number is determined by the level of photosynthesis during flowering and pod set, but the exact period when seed number is sensitive to the supply of photosynthate is not well defined. We conducted field experiments in 2005 to 2008 to determine the effect of reducing photosynthesis (placing shade cloth over the crop) during flowering and pod set on seed number. We found that short periods of shade (4 to 9 days) during the peak pod production period had no effect on pod number. The soybean plant could not, however, recover from 14 days of shade at the beginning of the flowering and pod set period. These results can be explained by, first, the fact that individual soybean pods can tolerate assimilate starvation for substantial periods of time (perhaps as long as 8 days) without aborting, and, secondly, by the failure of the soybean plants to increase flower and pod production when the stress is relieved. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
We now know that the relatively short period of maximum pod production (less than half of the total period) in soybean does not make the plant more susceptible to environmental stress. It is clear that the soybean plant does not need a continuous high level of canopy photosynthesis (i.e., no cloudy days or dry periods) throughout the flowering and pod set period to produce high yields. Short periods of stress will not affect pod and seed numbers and therefore will not affect yield.
Publications
- Egli,D.B.(2010)SOYPOD: A model of fruit set in soybean. Agronomy Journal 102:39-47.
- Egli, D.B. (2010) Soybean reproductive sink size and short-term reductions in photosynthesis during flowering and pod set. Crop Science (In press).
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Progress 01/01/08 to 12/31/08
Outputs
OUTPUTS: Increasing the yield of grain crops in the future will depend upon our ability to manipulate the basic plant processes that determine yield. Any such manipulation will require a thorough understanding of the processes involved. Yield of all grain crops, including soybean can be defined by its components, the number of seeds per unit area and the average weight per seed (seed size). Variation in yield must be caused by changes in either or both of these components, but environmentally induced yield flucuations are generally a result of changes in seed number. It is well known that that seed number is determined by the level of photosynthesis during flowering and pod set, but the exact period when seed number is sensitive to the supply of photosynthate is not well defined. Experiments were conducted in 2007 and 2008 to define the critical period in the yield production process. Shade cloth was placed over soybean communites at various times to decrease the supply of assimilate to the developing pods. Results from the two years were very consistent and indicate that plants could not recover from shade stress after approximately growth stage R3(early in the flowering and pod set period). Pod and seed number were sensitive to the assimilate supply until early seed filling (just after the beginning of growth stage R6); shade applied after that time did not reduce pod and seed number. These results suggest that the critical period begins at approximately growth stage R3 and ends at the beginning of growth stage R6. Environmental conditions during this period have a large impact on the final yield. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
We have gained a better understanding of the processes involved in the determination of pod and seed number in soybean. This information will be helpful to plant breeders, agronomists, and crop modelers and will hopefully lead to greater production efficiences and higher yields for soybean producers.
Publications
- Sadras, V. and Egli, D.B. (2008). Seed size variation in grain crops: Allometric relationships between rate and duration of seed growth. Crop Science 48: 408-416.
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Progress 01/01/07 to 12/31/07
Outputs
OUTPUTS: Increasing the yield of grain crops in the future will depend on our ability to manipulate basic plant processes that determine yield and any such manipulation will require a thorough understanding of the processes involved. Yield of all grain crops, including soybean, can be defined by its two components, the number of seeds per unit area and the average weight per seed (seed size). Variation in yield must be caused by changes in either or both of these components, but environmentally induced yield fluctuations are generally a result of changes in seed number. It is well known that seed number is determined by the level of photosynthesis during flowering and pod set, but the exact period when seed number is sensitive to the supply of photosynthate is not well defined. We conducted a field experiment in 2007 to define this critical period in the yield production process. Shade cloth was removed from or placed over soybean communities at various times to increase or decrease
the supply of photosynthate to the developing pods. Preliminary results after one year suggest that pod and seed number was sensitive to assimilate supply until early seed filling (the beginning of growth stage R6.0); shade applied after that time did not reduce seed number. Plants could not recover from shade stress after approximately growth stage R3.0 (early in the flowering and pod set period) since shade removal after this growth stage resulted in lower seed numbers. These results suggest that the critical period for the determination of seed number begins at approximately growth stage R3.0 and ends at the beginning of growth stage R6.0. Additional experiments will be conducted to determine if this definition of the critical period is affected by environmental conditions (i.e., is consistent across years).
PARTICIPANTS: Dennis B. Egli Marcy Rucker
Impacts
It is difficult to evaluate the impact of this work after only one experiment, but our goal is to greatly improve our understanding of the processes by which the soybean plant determines how many seeds it will produce. Since seed number is a critical yield component, a better understanding of its regulation will be helpful to plant breeders, agronomists, and crop modelers and hopefully will lead to greater production efficiencies and higher yields for soybean producers.
Publications
- Egli, D.B., and Bruening, W.P. (2007). Accumulation of N and dry matter by soybean seeds with genetic differences in protein concentration. Crop Science. 47: 359-366.
- Egli, D.B., and Bruening, W.P. (2007). Nitrogen accumulation and redistribution in soybean genotypes with variation in seed protein concentration. Plant Soil 301: 165-172.
- Hyatt, J., Wendroth, O., Egli, D.B., and TeKrony, D.M. (2007). Soil compaction and soybean seedling emergence. Crop Science. 47: 2495-2503.
- Egli, D.B., and Lee, Chad. (2007). Record yields - What have we learned? Corn and Soybean Science Newsletter. 7 (1): 2-4.
- Egli, D.B. (2007). Will the dry May affect yield in 2007? Corn and Soybean Newsletter. 7(6):1-3.
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