Nitrogen source‐sink relationship in cotton

Although attempts have been made in developing soil and plant analysis procedures for cotton (Goseipium hirsutum) , N nutrition is not completely understood. To the present it has not been possible to predict when the maximum N utilization efficiency could be achieved. By exposing cotton plants to a 15N enriched solution for 5 periods of 30 days each in a temperature controled greenhouse, the accumulation and redistribution of N within the plant was followed in order to define the main N sources and sinks for each period. The main N source within the cotton plant after the first square stage was the leaves. Stems and burs acted as temporary storage organs remobilizing N to the seeds late in the growing season, while the roots were fairly neutral. Dry matter accumulation during the reproductive stage was not related to N redistribution in the plant, except for bolls. So at this stage, dry matter accumulation was not a important component in the N source‐sink relationship within the cotton plant.