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 −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 −1 plant N for Acala grown on the Panoche clay loam and 9.4 kg kg −1 on the Wasco sandy loam, and 13.2 kg kg −1 for Pima grown on Panoche clay 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.