Figure 3. Changes in the quality and the amount of energy reflected as a result of transforming native grassland into different kinds of agricultural land. Annual pattern of the Normalized Vegetation Difference Index (NDVI) for a native grassland, a wheat field, and double cropping wheat-soybean in the Argentinean Pampas. The NDVI is an index derived from the reflectance in the red and infrared bands measured by satellites which is strongly correlated with leaf area, biomass and primary production.