Nitrogen Partitioning and Dry Matter Allocation in Soybeans with Different Seed Protein Concentration

Physiological studies of soybean (Glycine max L. Merr.) genotypes with wide differences in seed protein concentration may permit detection of important yield-related processes. Crop growth analyses were performed in 1977 and 1980, at Gainesville, FL, on seven and eight near homozygouds eterminates oybean genotypes, respectively. In 1977, the relationships between yield, seed protein concentration, and the visual length of seed filling were also studied in 23 genotypes. The purpose of this work was to characterize N partitioning and dry matter allocation to seed, and their association with yield and other characteristics. Soybean genotypes with a range in seed protein concentration of approximately 0.38 to 0.50 kg/kg were used. Nitrogen partitioning to seeds was estimated as the change in Harvest Nitrogen Index (HNI), the ratio of seed N weight shoot N weight (disregarding fallen leaves) with time, from beginning linear seed growth until maturity. Nitrogen partitioning in high seed protein genotypes was positively associated with their higher seed N demanda nd faster or earlier vegetative N depletion. In both years, Harvest Index (HI) estimated as the ratio of seed dry weight to shoot dry weight (disregarding fallen leaves) increased linearly with lime in all genotypes from the beginning of linear seed growth until maturity (R8). The Dry Matter Allocation Coefficient (DMAC), an estimate of the rate of dry matter allocation to seed, is defined as the derivative of HI with respect to time, during the linear phase of HI increase. Thus, DMAC is a constant for each genotype-environment combination. Dry Matter Allocation Coefficient exhibited less variability than Seed GrowthR ate estimated on a land area basis (CV = 6.8 vs. 21.8%). In both years, DMAwCa s positively associated with seed protein conten~ and faster vegetative dry weight decline during seed filling, and negatively associated with seedfilling duration, and yield. Yield was positively associated with seed-filling duration (RS-R7), and negatively associated with seed protein concentration. Thus, in general, high seed protein genotypes exhibited faster N partitioning and dry matter allocation into seeds, shorter seed-filling duration, and lower yield.