An understanding of seasonal nutrient accumulation patterns 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) and P (0 and 26 kg/ha) on the N, P, and K accumulation pattern by various plant parts of a sorghum [Sorghum bicolor (L.) Moench] hybrid. Plant samples were collected at weekly intervals, partitioned into plant parts, and analyzed for N, P, and K.
Nitrogen and P accumulation by whole plants increased almost linearly until maturity, but K accumulation was more rapid early in the season. A significant loss of K from the whole plant (and head) occurred during the last week. Nitrogen, P, and K accumulation rates were higher during the 35th to 42nd day and 70th to 91st day which coincided with the peak vegetative growth period and the grain-filling stage, respectively. In unfertilized plants relatively higher translocation of N and P from the vegetative parts to the developing grain occurred. Little K was translocated. A much smaller percentage of total K was found in the head and more K accumulated in the stem than N and P.
Application of 60 kg N/ha significantly increased N, P, and K yields of whole plant by 60.9, 49.4, and 19.1%, respectively. Further respective increases were 19.0, 18.9, and 12.3%, with 120 kg N/ha. Respective increases were 28.6, 49.0, and 17.1% with 26 kg P/ha over no phosphorus.