Seasonal nitrogen concentration, uptake, and partitioning pattern of irrigated Acala and Pima cotton as influenced by nitrogen fertility level

A better understanding of plant nitrogen (N) dynamics in modern varieties of Acala (Gossypium hirsutum L.) and Pima (G. barbadense L.) cotton grown with prevailing management practices may help in the design of N management strategies that optimize N utilization and lint yields. The response of Acala cotton to different N fertility levels was evaluated on a Panoche clay loam (fine-loamy, mixed (calcareous), thermic Typic Torriorthents) and on a Wasco sandy loam (coarse-loamy, mixed, nonacid, thermic Typic Torriorthents). Nitrogen treatments of 56, 112, 168, and 224 kg N [ha.sup.-1] and check plots were established in 1998, 1999, and 2000. Plant shoots were collected and fractionated into different components at several growth stages for determination of N concentration. Both Acala and Pima tissue N concentrations were strongly affected by developmental stage and N treatment. Acala tissue N concentrations differed significantly between soil types. Maximum N uptake rates of both Pima and Acala occurred between early square and early bloom. Physiological N use efficiency averaged 11.4 kg lint [kg.sup.-1] plant N for Acala grown on the Panoche clay loam and 9.4 kg [kg.sup.-1] on the Wasco sandy loam, and 13.2 kg [kg.sup.-1] for Pima grown on Panoche day loam. Leaf N concentration as an in-season indicator of N status and estimates of seasonal soil N mineralization potential may be useful in optimizing cotton N management.