Development of a crop extension product in Argentina using MODIS data at 250m and NDVI thresholds estimated from phenological metrics

Agriculture is an economic activity of great importance in the Argentine Republic due to its extensive arable land, favourable climatic conditions and agricultural tradition. In order to plan and manage land use effectively, it is essential to know the location and extent of the areas dedicated to annual summer cropping in each agricultural season. In this study, a map of the areas dedicated to extensive annual summer cropping has been produced with a spatial resolution of 250 metres, covering a large area that includes 14 Argentine provinces. The methodology used was based on multi-temporal NDVI data from MODIS and field reference records of soybean and maize crops. NDVI temporal signatures of the crop growth cycle were analysed and NDVI thresholds for the phenological stages of ‘emergence’, ‘flowering’ and ‘physiological maturity’ were calculated. These thresholds were used to create decision rules to be applied to a series of NDVI images from the MOD13Q1 product (period 2000-2021) in order to map areas for annual agricultural use. The results showed the technical feasibility of identifying areas dedicated to the production of annual summer crops. One map was obtained for each agricultural campaign analysed. The maps showed an increase in the area dedicated to agriculture over the period 2000-2021. Comparing the area mapped by campaign with the areas estimated by the National Agriculture Agency, a very good agreement between the values was observed throughout the period. When the 2010-2021 maps were evaluated with the ground reference data, the overall accuracy was around 52-72%. The present maps are an unpublished product in the Argentine Republic, they show good validation values and can be very useful for subsequent studies.