Modeling ‘yield-population’ relationships in soybean
Our objectives were to evaluate the seed yield of soybean, and Duncan's model with respect to relationship between seed yield and plant population, and analyze the response of soybean seed yield components to light enrichment initiated at different growth stages. Duncan coined the term crowding to include the effects of density and planting pattern. Duncan's model states that there is a linear relationship between natural logarithm of yield plant−1 and crowding. Results of the studies fitting Duncan's model to the data obtained from different soybean cultivars planted at different densities and planting patterns indicated that the model can predict the changes in yield with changing densities and planting pattern especially if the variability in the data is low.
In order to analyze the response of soybean seed yield components to non-destructive light enrichment initiated at different growth stages, light enrichment was imposed on the indeterminate soybean cultivar Evans by installing wire mesh fencing on either side of the center row to push the adjacent rows aside at different growth stages. Fences prevented plants in the neighboring rows from encroaching on the growing space of the center row plants. Pod number per plant and to a lesser extent seed size accounted for variation in seed yield. Light enrichment initiated at late vegetative or early flowering stages increased seed yield 217%, mainly by increasing pod number, while light enrichment beginning at early pod formation increased seed size 23%, resulting in a 115% increase in seed yield. Responses to light enrichment occurred proportionately across all node positions despite the differences in the time (15 to 20 days) of development of yield components at the different node positions. Although maximum seed size may be under genetic control in soybean plants, our results suggested seed size can still be modified by the environment with some internal control moderating the final size of most seeds in all pods. It indicates that plants are able to redistribute the available resources to components not yet determined, in an attempt to maintain or improve yield.