Evaluation of cropland productivity in the Hebei Plain via graded multi-year MODIS-NDVI data

Moderate resolution imaging spectroradiometer sensor (MODIS) provides high-temporal, medium-spatial resolution science-quality global land cover data. Calculated normalized differential vegetation index (NDVI) from MODIS data is widely used for crop growth monitoring and yield forecasting. However, variations of NDVI values in the same season of each year lead to uncertainties and biases in forecasting cropland productivity. This study presented a method for evaluating cropland productivity and indirect monitoring of soil quality, using annual NDVI calculated from multi-year MODIS data in the Hebei Plain. Calibrated Landsat data with high spatial resolution were used to process geometric registration of the MODIS data. This was used to determine the exact region with continuous winter wheat cultivation for many years in the plain. Mean NDVI of winter wheat cultivated area from reviving to maturity stage was calculated for 2000~2008 and ranked into different levels in order to analyze for spatial variations in farmland productivity. The study showed that while high productivity croplands were mainly located in the piedmont of Mount Taihang, medium or low productivity croplands were in the central and eastern regions of the plain. Longitudinal change in NDVI was not regular, indicating that the method used was not affected by latitude difference. The distribution pattern was driven by variations in local land use types and cropland quality management. The study also analyzed the causes of biases in the coefficient of variation for the 9-year NDVI data. The analysis showed that the coefficient of variation was relatively high during the reviving and maturity stages of winter wheat, with also spatial differences. Combined geo-spatial and NDVI analysis was used to map cropland productivity at county level. The map showed spatial differences in productivity with huge potential croplands where low/medium productivity was located at. The study therefore laid the theory basis for land control and cropland quality management in Hebei Province, which could be vital for improving cropland quality at county level.