Nitrogenous fertilizer recommendation model for cotton under mulch -drip irrigation

Nitrogen recommendation for cotton under the mulch-drip irrigation condition was explored based on the measurements using chlorophyll meter (SPAD-502). Field experiment was conducted at Wulanwusu Agricultural Meteorological Experiment Station, Shihezi, Xinjiang, China, during the 2006 cotton growing seasons. The adopted cotton variation was Xinluzao24. The results showed that leaf nitrogen contents and SPAD value varied markedly in different leaf position. Significant correlation was found between SPAD and leaf chlorophyll concentration, N concentration in leaf or N absorbed content. The leaf tip position of the reverse 4th leaf from the apex of the main stem is the best measuring position because of the small deviation of measurement value. There were significant linear correlation between SPAD value and the rate of applied nitrogenous fertilizer at budding peak stage, flowering stage, flowering peak stage and bolling stage. A significant correlation between SPAD value and the cotton yield was detected as well. The highest link yield was 4686.5 kg/ha, correspondingly, the optimal nitrogenous fertilizer rate was 293.1 kg/ha under the experimental management scenario. The most profitable N rate was 207.33 kg/ha and the economic yield was 4565.9 kg/ha. The critical SPAD value at the budding peak stage, flowering stage, flowering peak stage and bolling stage were 60.5, 60.0, 60.8 and 59.1 respectively. A statistic model was evaluated for N fertilizer recommendation in cotton cultivation under drip irrigation with film mulch, the recommended N fertilizer rate is 10.81, 8.46, 13.42, and 6.29 kg/ha at budding peak stage, flowering stage, flowering peak stage and bolling stage for unit change of SPAD value.