Nitrogen Mineralization Variability at Field Using Vegetation Spectral Indexes.

Making nitrogen recommendations without knowing the N supply capability of a soil can lead to inefficient use of nitrogen. In humid regions, the supply of N from the soil is mainly dominated by in-season soil N mineralization. Spatial variability in N mineralization, even within a small field, represents a potential problem in estimating the quantity of N mineralized under field conditions. The techniques to determine soil N mineralization are time consuming and could be economically prohibitive for precision farming which requires quick estimates of soil nitrogen. Then, remote sensing techniques were used to detect the nitrogen mineralization spatial variability at field scale.  Many fields in the Central Western Pampas, Argentina, have soils with widely different physical and chemical properties, which may lead to variability in N mineralization. The aims of this study were 1) to explore the N mineralization variability within a field in the Central Western Pampas, and 2) to determine if N mineralization parameters were related to vegetation indices derived from spectral remote sensing. Soil and plant samples were taken  in a grid pattern  (5 rows and 10 columns) at start and final corn crop. A long-term aerobic incubation was carried out with these samples to measure potentially mineralizable N. The data of cumulative net N mineralized with time (Nt) were fit to Nt= N₀.(1-e^{-k t}), where t is time, N₀ is the N mineralization potential. An N balance study was conducted in the field at each of the grid sites for estimating the apparent N mineralized. Both measurements were related with spectral indexes (NVDI, REIP and TCARI) took at crop early stage (V₆ and V₁₀). These results are promising because they would allow estimating the spatial variability of N mineralization in early stages of crop.