PRELIMINARY RESULTS FOR STANDARDIZATION OF NDVI USING SOIL NITRATES IN CORN GROWING

摘要

A convenient method for quick mapping of crop nitrogen (N) status over large areas is the use of unmanned aerial vehicles (UAV). Estimating plant nitrogen status by remote sensing can be a useful tool in the timely diagnosis of nitrogen deficiency or sufficiency within a field and, as a result, lead to the optimization of nitrogen fertilizer inputs. In a well-fertilized area, the Sufficiency Index (SI) values, i.e. the ratio of the Normalized Difference Vegetation Index (NDVI) divided by the NDVI value of the well-fertilized area (NDVI_(ref)), can be determined. This procedure is necessary for calibration of the remote sensing data. In Greece however, the small size of the field parcels limits the implementation of UAV's. Thus, a simple equation was derived for indirect determination of the NDVI_(ref) measurement in corn using soil nitrates as follows: Soil NO_3-N = 35.18 SI~(2.561), R~2 = 0.51 (1). The NDVI_(ref) then can be calculated by dividing the mean NDVI value measured by the field parcel using the remote sensor to the SI value measured by equation (1) according to the following equation NDVI_(ref)= NDVI/SI. Finally, a quadratic function has been determined in order to translate SI values to N fertilization of corn: SI = 0.655 + 0.002(N rate) - 0.000003(N rate)~2, R~2 = 0.60.