The use of vegetation index via remote sensing allows estimation of soybean application rate

Abstract

Currently, researchers have been looking for techniques to reduce the spray volume to guarantee a determined spray deposition at the lower third of the crop, reduce production costs, and increase the operational capacity of the applications. Is it possible to use vegetation indexes to estimate the spray application rate and deposition in soybean? This study aimed to develop an equation that indicates an adequate spray application rate (AR), based on the information of vegetation indices (VIs) and relative deposition (DEP) for the soybean crop. The experiment was carried out in the agricultural years 2016/17 and 2017/18, in the municipality of Chapadão do Sul - MS. Reflectance data were recorded by a Sequoia passive sensor, which allowed calculating the NDVI and VI NIR/G. The experiment evaluated four application rates (40, 70, 100, and 130 L ha−1) in a randomized complete block design, with three replications. The mass balance analysis measured the leaf spray deposition in the middle third of the plant. NDVI and VI NIR/G negatively correlated to spray deposition in the middle third of the soybean plant. The increase in the VIs values required higher application rates to maintain DEP. The AR of 100 L ha−1 was considered as the most adequate for soybean crop at all the phenological stages mapped. The 70 L ha−1 was considered as critical for being strongly influenced by the vegetation indices variability. According to the validation procedure, the spray application rate variation according to the NDVI is effective for maintaining the deposition in the medium stratum of the crop. Thus, the obtained result can contribute to the advancement in soy application technology, since it is simple and practical to use a multispectral sensor in the field, reducing subjectivity in the spray application rate recommendation.