Yield and quality of cotton fertilized with combined rates of nitrogen, potassium and boron

Abstract

The balanced nutritional management of cotton is fundamental to explore the yield potential, reduce costs and losses and ensure the quality fiber produced. So, the applied rates should explore the antagonistic and synergistic relationships that exist between the nutrients. Currently the use of N and K has been, in most Midwest crops, above the recommended rates, which in addition to increasing production costs, may be compromising the use efficiency of these nutrients as well as the absorption of boron. Since its deficiency is associated with soils with low level of organic matter, sandy, highly weathered or with very high pH, as most soils of the São Paulo state. The objective will be to evaluate the nutrition, yield and fiber quality of cotton submitted to different rates of nitrogen, potassium and boron. The experiment will be conducted in two production environments. The first one at the UNOESTE Experimental Farm, located in the city of Presidente Bernardes-SP, in a sandy texture dystrophic Ultisol and the second will be in Campos de Holambra region in a pivot irrigated system, in a Red Latosol with clay texture. The experiments will be conducted in the 2019/20 and 2020/21 seasons, using the medium cycle cultivar FM 954GLT in Holambra II and the late cultivar FM 985GLTP in the West of São Paulo region. The experimental design will be randomized blocks in factorial scheme 4x4 with four replications. The treatments will result from the combination of N rates (0, 70, 140 and 210 kg ha-1 N) and potassium (0, 70, 140 and 210 kg ha-1 K2O). Two experiments will be conducted at each place, one at a rate of 1.5 kg ha-1 of boron (at sowing) and another at a rate of 3 kg ha-1 of boron (50% at sowing and 50% at 25 DAE) The application of N (urea) and K (potassium chloride) will be performed in coverage (50% at 25 DAE and 50% at 45 DAE). The source of boron used will be ulexite (10% B). The sowing will happen in November. Plant height and number of nodes will be evaluated periodically (30, 60, 85 and 110 DAE), the leaf area index (LAI) will be evaluated at the same times mentioned above, using the Acupar LP80 equipment, the leaf sampling for diagnosis evaluation and enzyme evaluation (sucrose phosphate synthase, sucrose synthase and acid invertase) will be evaluated on leaves collected at full flowering. The yield mapping will be evaluated in 4 plants per plot and will consist of stratified cotton harvest, node by node, aiming to quantify the positions of the fruit structures in P1, P2 and P3 + (position 3 or higher) that will be later grouped in thirds (lower, middle and upper third). At the physiological maturity of cotton will be determined the yield components of cotton (number of bolls and average weight of bolls). The yield will be estimated using this same sample. A sub-sample will be ginned for further determination of fiber yield and will be forwarded to the laboratory for evaluation of cotton fiber quality (fiber strength, fiber length, maturity and micronaire) using the HVI (High Volume Instrumentals) method. N, K and B leaching in the soil profile will be performed after cotton harvesting, with soil samples at depths of 0-10, 10-20, 20-40, 40-60 and 60-80 m. The data will be submitted to analysis of variance and regression and for significant effects the means compared by Tukey test (p <0.05), using the statistical program SISVAR (Ferreira, 2000), and the graphs plotted in the Sigma Plot® software. (AU)