| Nitrogen (N) nutrition is critical to the balance between vegetative and reproductive growth in cotton (Gossypium spp.) production. N deficiency reduces vegetative and reproductive growth and induces premature senescence potentially reducing yields. Conversely, excess N prolongs vegetative growth resulting in delayed crop maturity and sometimes reduced lint yields. Negative environmental effects may result from excessive N availability. Experiments were conducted to improve the understanding of N dynamics in an irrigated cotton cropping system and to characterize the regulation of genes involved in nitrate uptake and assimilation. This two-pronged approach should help optimize cotton N use efficiency and minimize negative environmental impacts. Acala (G. hirsutum L.) cotton was grown for three years 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 (G. barbadense L.) cotton was grown for two years on the Panoche clay loam only. Four N treatments were established in a randomized complete block design at each site year: 56, 112, 168, and 224 kg N ha -1. In selected treatments, microplots were established by applying 15N-labeled fertilizer. Maximum three year average Acala lint yields were 1842 and 1621 kg ha-1 in the 224 and 168 kg N ha -1 treatments on Panoche clay loam and Wasco sandy loam, respectively. Pima lint yields did not increase above the 112 kg N ha-1 treatment (1467 kg ha-1; 2-yr average). Fertilizer 15N recovery was not different between the soil types and N treatments and averaged 46% for Acala. Pima 15N fertilizer recovery averaged 48% and was not affected by N treatment. In all treatments, total 15N fertilizer recovered in soil and plants was at least 76%. Recovery of residue 15N was greater on the Wasco sandy loam than on the Panoche clay loam in the first and in the second crop after residue application. In cotton seedlings grown under controlled conditions temporal transcriptional regulation of a putative high-affinity nitrate transporter, nitrate reductase, nitrite reductase, and glutamine synthetase was observed in response to nitrate feeding. Nitrate concentration and N source also affected the expression of these genes. |
