ABSTRACT

Field studies to assess the effects of deficient, optimum and excessive rates of nitrogen (N) fertilization on uptake of N, P, K and other nutrients by cotton ('Deltapine 41') were conducted at St. Joseph, LA on a Commerce silt loam. Plots used in these experiments have been continuously cropped to cotton since 1987 and have received preplant applications of 0, 75 or 150 lbs N/A annually. By defoliation, uptake of all nutrients was greater in crops receiving 75 or 150 lbs N/A. With the exception of N, most of the increases in nutrient uptake could be attributed to increases in biomass induced by N fertilization. The concentrations of N in standing plant tissue and ground litter collected prior to defoliation averaged 1.4%, 1.7 % and 2.0% in plots receiving 0, 75 and 150 lbs N/A. Amounts of P, K, S, Ca, Mg and micronutrients assimilated into bolls, seeds or whole plants receiving an excessive rate of 150 lbs fertilizer N/A were similar to those in cotton receiving a near optimum rate of 75 lbs N/A. Harvesting resulted in the removal of 80 lbs N, 16 lbs P, 39 lbs K and 15 lbs S per acre from plots producing near optimum yields (3725) lbs seedcotton/A).