Declining water availability in the American Southwest continues to generate interest in efficient subsurface drip irrigation (SDI) for cotton (Gossypium hirsutum L.) production. Fertigating urea ammonium nitrate (UAN) at low rates with high frequency is an important advantage of SDI. However, N fertilizer management guidelines specific to SDI cotton are lacking. A 3‐yr study was conducted on a Casa Grande sandy loam soil in Maricopa, AZ, to test a pre‐plant soil profile NO3 test algorithm and a canopy reflectance approach to manage in‐season N fertilizer for SDI cotton. Treatments included soil test‐based N management, reflectance‐based N management, and zero‐N at 100% evapotranspiration irrigation replacement. A second irrigation level of 70% evapotranspiration replacement included just the soil test‐based N and zero‐N treatments. The five treatments were replicated three times. Soil test–based N treatments received from 172 to 224 kg N ha−1, and reflectance‐based N amounts were 112 to 158 kg N ha−1. Nitrogen recovery efficiency (RE) of UAN‐N was high, with 24 fertigations during 6 wk between first square and mid bloom ranging from 58 to 93%. The isotope dilution method estimated similar RE in 2017. Residual post‐harvest soil NO3–N was notable only with 70% irrigation. Lint and seed yields were significantly reduced with the 70% irrigation treatment compared with 100% irrigation. The key result of this study is that reflectance‐based N management saved 17 to 112 kg N ha−1 without reducing lint yields compared with the soil test–based N treatment.

A standardized experiment was conducted during 2009 and 2010 at 20 location‐years across U.S. cotton (Gossypium hirsutum L.)‐producing states to compare the N use requirement of contemporary cotton cultivars based on their planting seed size. Treatments consisted of three cotton varieties with planting seed of different numbers of seed per kg and N rates of 0, 45, 90, and 134 kg ha–1. Soil at each trial location was sampled and tested for nitrate presence. High levels of soil nitrate (>91 N‐NO3– kg ha–1) were found in Arizona and western Texas, and soil nitrate in the range of 45 to 73 kg N‐NO3– ha–1 was found at locations in the central United States. Cotton lint yield responded to applied N at 11 of 20 locations. Considering only sites that responded to applied N, highest lint yields were achieved with 112 to 224 kg ha–1of applied plus pre‐plant residual soil NO3—translating to an optimal N requirement of 23 kg ha–1 per 218 kg bale of lint produced. Among the varieties tested those with medium‐sized seed produced higher yields in response to N than did larger and smaller seeded varieties. Varieties with larger seed had longer and stronger fibers, higher fiber length uniformity than small seeded varieties and decreased micronaire. Seed protein and oil increased and decreased slightly in response to increasing amounts of soil nitrate plus applied N, respectively.

No abstract

No abstract

Management of water and fertilizer N are important aspects of cotton production in the desert Southwest. GOSSYM, a cotton growth simulation model, has been used extensively to manage these inputs. Our objectives were to further validate GOSSYM by comparing model‐simulated and measured soil NO‐3‐N profiles, to evaluate GOSSYM's potential as a management tool under irrigated growing conditions in the desert part of the U.S. Cotton Belt, and to address questions about the way GOSSYM simulates NO‐3‐N movement through the soil profile in relation to irrigation water management (which in turn affects prediction of plant growth and development). We compared measured profiles of NO‐3‐N with GOSSYM‐simulated profiles. Soil profile samples were obtained from an existing N‐management field study, a split‐plot within a randomized complete block design. Mainplots were upland and pima cotton (G. hirsutum L. cv. DPL 5415 and G. barbadense L. cv. Pima S‐7, respectively). Subplots were a check (0 fertilizer N) and three other N‐management strategies. The cotton was grown on a Casa Grande sandy loam [fine‐loamy, mixed, hyperthermic Typic Natrargid (reclaimed)] near Maricopa, AZ, in 1994 and 1995. Fertilizer N rates ranged from 0 to 350 kg ha−1 in 1994 and 0 to 392 kg ha−1 in 1995. Soil samples taken to a depth of 120 cm in 30‐cm increments were analyzed for NO‐3‐N. Comparisons of simulated and actual NO‐3‐N profiles revealed tendencies in GOSSYM to overestimate NO‐3‐N leaching out of the effective rooting zone, resulting in simulated N stresses midseason. When GOSSYM simulated an N stress, between 50 and 75% of the simulated soil NO‐3‐N values were greater than the measured values, yet the simulated N stress still occurred. This indicates possible limitations in GOSSYM's ability to adequately predict N uptake by plants. The dynamic soil N portion of the model needs further refinement, particularly for cotton production under irrigated desert conditions.