Índices de vegetação e sua correlação com a produtividade da cultura da soja em área irrigada e de sequeiro

Abstract

Soybean is a prominent crop in Brazilian agriculture with great representation in the national economic scenario. In the state of Rio Grande do Sul, its yield has been increasing, mainly as a result of the use of technology in the field and the use of precision agriculture. Among the tools that contributed to the evolution of yield levels, the use of remote sensing stands out. The objective of this work was to map the spatial variability of the spectral response and the soybean yield, as well as to evaluate the correlation between the maps generated, from the calculation of the vegetation index: NDVI, NDMI, NDRE, in a irrigated and rainfed area. The study was developed in a rural property in the municipality of Cachoeira do Sul. Soybean yield was mapped by a mapping system built into the harvester. The mapping of vegetation index was carried out using the Crop Monitoring online platform. Maps of spatial variability of the studied vegetation indices were generated for different dates, throughout the crop cycle, cultivated in irrigated and rainfed systems. Yield data and vegetation index made up the database used in the statistical and geostatistical analyses. For data analysis and processing, was used the computational programs MapFilter, Statistica and QGIS. The NDVI, NDMI and NDRE vegetation index showed spatial variations in the studied areas, during the development cycle of the soybean crop, in irrigated cultivation and in rainfed cultivation. The highest mean values of the studied vegetation index were observed for the spectral response of the soybean crop under irrigated cultivation. The soybean yield showed spatial variability in irrigated and rainfed cultivation, in rainfed cultivation, the minimum observed value was 3,588 kg ha-1 , the maximum was 4,998 kg ha-1 and the average was 4,405 kg ha-1 . In the irrigated area, the minimum value observed was 3,960 kg ha-1 , a maximum of 5,398 kg ha-1 and an average of 4,636 kg ha-1 . All vegetation index studied showed a significant spatial correlation with the spatial variability in soybean yield, in irrigated and rainfed cultivation. In rainfed cultivation, the highest significant positive correlation value was observed between NDVI and soybean yield (0.57), occurring 43 days after sowing. For the NDMI and NDRE index, these values were 0.47 and 0.54 respectively, observed in 48 days after sowing. In irrigated cultivation, the highest values of significant correlation were also positive, with values 0.60, 0.48 and 0.63 observed, respectively, for the correlation of soybean yield with the NDVI, NDMI and NDRE indices, 128 days after sowing.