Response of irrigated Acala and Pima cotton to nitrogen fertilization: Growth, dry matter partitioning, and yield

Acala (Gossypium hirsutum L.) and Pima (G. barbadense L.) cotton growth, lint yield, and fiber quality responses to N in the San Joaquin Valley, CA were evaluated. Numerous reasons, including adaptation of N fertilization guidelines to modern production practices, recent increases in energy costs, and growing concerns about NOT contamination of ground water, led to the initiation of this study. Acala was grown for 3 yr on a Panoche clay loam [fine-loamy, mixed (calcareous), thermic Typic Torriorthents] and a Wasco sandy loam (coarse-loamy, mixed, nonacid, thermic Typic Torriorthents). Pima was grown for 2 yr on the Panoche clay loam. Four N treatments were established in a randomized complete block design: 56, 112, 168, and 224 kg N ha(-1). Three-year average aboveground dry matter production of Acala was 7800 and 12 600 kg ha(-1) on the Panoche clay loam and 8500 and 11900 kg ha(-1) on the Wasco sandy loam for the 56 and 168 kg N ha(-1) treatments respectively. The equivalent 2-yr averages for Pima were 7600 (56 kg N ha(-1)) and 10 800 kg ha(-1) (168 kg N ha(-1)). Linear increases in lint yield with increased N fertility level occurred for Acala on Panoche clay loam in every year. Maximum lint yield averaged over 3 yr was 1842 kg ha(-1) in the 224 kg N ha(-1) treatment. The response of Acala lint yield to N management on the Wasco sandy loam was smaller than on Panoche clay loam, with a maximum lint yield of 1666 kg ha(-1) (224 kg N ha(-1), 3-yr average). Pima lint yield responded to N management in a quadratic fashion with maximum yields in the 168 kg N ha(-1) treatment in both years (1638 kg ha(-1), 2-yr average). Acala gin turnouts were greater at the Panoche than at the Wasco site. Decreases in gin turnout with increasing N were significant on the Panoche clay loam (Acala and Pima) but not on the Wasco sandy loam (Acala). There was a generally positive relationship between increasing N fertilization and yield; however, efficient N management should include an assessment of available soil residual N, soil type, and yearly climatic conditions.