Sorghum Growth and Nutrient Uptake in Relation to Soil Fertility: I. Dry Matter Accumulation Patterns, Yield, and N Content of Grain1

Abstract

AbstractAn understanding of the seasonal dry matter accumulation pattern of the sorghum [Sorghum bicolor (L.) Moench] plant under varying fertility levels is important for planning an efficient fertilization program. Field experiments were conducted to determine the effects of varying rates of N (0, 60, and 120 kg/ha) on the dry matter accumulation pattern, yield, and grain N content of a sorghum hybrid. Plant samples were collected at weekly intervals and partitioned into component parts for dry matter estimation.The rate of dry matter accumulation in fertilized plants was rapid early in the season and continued almost linearly until maturity (91 days after sowing), but in unfertilized plants it began to drop after 70 days. In general, dry matter weight of leaves and stems reached a maximum by the 56th and 70th days, respectively, and then remained almost constant. The subsequent increase in total dry weight was due to increased head weight. Accumulation rate in the heads of fertilized plants at 70 and 77 days was very high in comparison to that of unfertilized plants. Contributions of stem, leaves, and head to the total dry matter yield with N0P0 and N120P26 treatments were 41, 23, and 36%, and 32, 18, and 50%, respectively.Dry matter yield of whole plant, grain yield, and grain N content were higher with 60 kg N/ha than with no nitrogen by 26, 47.6, and 14.5% respectively. They were also higher (9.2, 8.8, and 10.9% respectively) with 120 N/ha. Dry matter and grain yields were higher with 26 kg P/ha than with no P by 25.6 and 46.2% respectively. N content of grain was unaffected by addition of P.