Yield and composition of soybean seed as a function of potassium supply

Summary

A reduction in K supply to soybean plants to deficiency levels during both vegetative and reproductive development resulted in reductions not only in yield, but also in oil and K concentrations in the seed and a concomittant increase in seed protein concentration. Correlations between mean fruit yield and oil, protein and K concentrations, over a wide range of K regimes, were 0.97, −0.94 and 0.98, respectively. When K supply was increased well above the level necessary to produce maximum yields,i.e. luxury consumption, there was no significant change in K concentration in the seed, indicating a high degree of control in the movement of K to the develo** seed under high K regimes. When the K supply to the plant was limiting, the rate of accumulation of oil and carbohydrate fractions, but not of seed protein, declined during the latter part of podfilling. This resulted in a fall in the C/N ratio in the non-structural seed components during this part of seed development. Depriving plants of K only during seed development had no effect on seed composition or yield, whereas resupplying K to deficient plants after anthesis resulted in almost the same seed composition and yield as that which occurred with control plants. Possible mechanisms whereby K deficiency influences soybean seed composition and yield are discussed in terms of movement of carbohydrate and nitrogen to the seed. We suggest that potassium-deficient soils are likely to produce crops with low yields and low seed oil levels; the crop may respond to K fertilizers as late as anthesis.