Vegetation Indices to Estimate Spray Application Rates of Crop Protection Products in Corn

Abstract

Spray deposition in corn crop is related to the vegetation indices. Spray deposition in corn crop is related to the spray application rate. Plant stand density has no influence on the spray deposition. Determination of the spray application rates (SAR) of crop protection products for different crops is subjective. The study aimed to develop an equation to estimate optimal spray application rates using a vegetation index (VI) and an expected relative spray deposition for summer corn crop. An experiment was performed in the crop year 2015 to 2016, and 2016 to 2017, with a plant density of 60,000 plants ha−1 with 0.45‐m row spacing, under the no‐tillage system, in the municipality of Chapadão do Sul. An active multispectral sensor (Crop Circle ACS‐470) was used to obtain the VI Red Edge, Normalized Difference Red Edge (NDRE), and Normalized Difference Vegetation Index (NDVI), using the red, red edge, and near‐infrared bands. The experiment consisted of plots subdivided in a 4 × 4 factorial scheme (four spray application rates and four phenological stages), with four replications for each treatment. The mass balance analysis measured leaf deposits. The relationship between vegetation index values and middle stratum deposits showed a quadratic trend. When the vegetation index values are increased, the spray application rate (from 40 to 100 L ha−1) needs to also increase to maintain the same spray deposition (from 50 to 100%) in the middle stratum of corn plants. The vegetative indices studied (VI Red Edge, NDRE, and NDVI) positively correlated to the spray deposition in the middle stratum of corn plants, which also depends on the SAR. Furthermore, the relationship between vegetation index and spray deposits need to be studied for other crops, plant architecture, and stand density.