Yield, nutrient removal, and quality of sorghum grain and biomass as influenced by nitrogen and phosphorus fertilization

Abstract

Field experiments were conducted during 1983 and 1984 at two locations using one conventional (ATx399 x RTx430) and two high energy sorghum hybrids (Sorghum bicolor L., Moench) to evaluate the effects of N and P applications on grain, biomass, and fermentable carbohydrate production. Genotype and N most influenced grain and biomass yields at both locations. Cultivars ATx399 x RTx430 and ATx623 x RTx430 produced more grain, but less biomass than ATx623 x Rio. Applied N increased grain yields at College Station more in 1984 than in 1983, indicating a decrease in soil N after one year of total dry matter removal. Less yield response to N was observed at Weslaco. Applied P had little effect on grain or biomass production at either location. Genotype affected nutrient concentrations and partitioning, with ATx399 x RTx430 exhibiting the greatest biomass and lowest grain nutrient concentrations. This cultivar removed the least nutrients in biomass and the most through grain. Nutrient concentrations and removals in ATx623 x Rio components were the reverse of the grain hybrid. When total crop N and P removals were considered, however, no genotypic differences were observed at either location. Total crop removals of K, Ca, Mg, Fe, and Zn at College Station and K and Mg at Weslaco were influenced by genotype, with ATx623 x Rio removing the greatest quantities. Applied N increased grain and biomass concentrations and uptake of most nutrients. Increased nutrient removals generally resulted more from increases in dry matter production than from changes in nutrient concentrations. Apparent N uptake efficiency was higher at College Station (41 to 53%) than at Weslaco (24 to 37%). Complete aboveground dry matter removal of high energy sorghums resulted in an additional removal of 100 to 180 kg K and 40 to 50 kg N/ha when compared with conventional sorghum produced for grain only. Genotype influenced stalk fermentable carbohydrate yields, with ATx623 x Rio producing substantially greater amounts than the other hybrids. Applied N decreased structural carbohydrates, while nonstructural carbohydrates remained unchanged. Stalk fermentable carbohydrate yields, however, increased linearly with N application because of higher biomass yields with applied N.