Plant mapping, yield and fiber quality of cotton cultivars in response to nitrogen and plant density

Abstract

Cotton cultivation in Brazilian subtropical regions, such as in Paranapanema-SP, has been an important agricultural activity in the composition of production systems. The limitation of these environments is the low temperatures at the end of the cycle, therefore the cropping window is shorter compared to the Brazilian Cerrado. Thus, cultivation techniques that promote the yield earliness are desirable, since the elongation of the cycle increases production costs. The hypothesis of the work is that the cultivation of cotton under lower plant densities combined with the moderate nitrogen rate may favor the boll set in the bottom of the canopy, mainly in cultivars that concentrate the production in this portion of the canopy. The objective of this study was to evaluate plant mapping, yield and fiber quality of cotton cultivars subjected to different nitrogen rates and plant densities. The experimental design used will be in randomized blocks in a 4x2 factorial scheme with four replications. Two experiments will be conducted, one with FM 906GLT and another FM 954GLT. The treatments will be the plant densities: 6, 7, 8 and 9 plants m-1 and N rates: 100 and 140 kg ha-1 (urea) applied in top dressing (50% at 30 DAE and 50% to 60 DAE). Shoot dry weight as well as the accumulation of nitrogen and the nitrogen leaf content will be quantified at 85 DAE; the leaf area index (LAI) will be measured at 30, 45, 60, 75 and 90 DAE. The positions of the fruit structures at P1, P2 and P3 + (position 3 or higher) will be quantified and later grouped into thirds (bottom, middle and top); as well as cotton yield and yield components (boll number, boll weight). The quality of the cotton fiber will be evaluated by the HVI method. The data will be submitted to analysis of variance and regression and for the significant effects the averages compared by the Tukey test (p <0.05), using the statistical software Sisvar.