Response of Irrigated Acala and Pima Cotton to Nitrogen Fertilization

Abstract

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 NO−3 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 11 900 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.