Measuring crop response to subsurface drainage with satellite remote sensing

This research focused on evaluating remote sensing and combine-yield monitor data as tools for assessing the effectiveness of subsurface drainage. Differences in crop response were studied between field areas with and without subsurface drainage, as well as between field areas possessing subsurface drainage at different spacings. The major characteristics including crop type, vegetation index, image date, soil type and drainage intensity were explored. Two vegetation indices (VIs), Normalized Difference Vegetation Index (NDVI) and Tasseled Cap Transformation (TCT), derived from Landsat 5 satellite images were utilized. Two study sites located in South-central Minnesota with seven silty-clay soil types and eight Landsat 5 images from 1991, 1995, and 2001 were used to assess the presence of subsurface draiange. April- June precipitation was 50% and 48% above average for 1991 and 2001 and 5% below average for 1995. The results showed that the differences in crop response between field areas with and without subsurface drainage were discernible using remote sensing. However, the degree of discernability between drained and undrained treatments using VIs was dependent crop year and soil texture. In wetter years, the fields had greater variations in VIs, especially for finer textured soils. Vegetation index values between field areas possessing varying subsurface drainage intensities were at times discernible on both fine and coarse-textured soil types. This may be caused by low precipitation during August, which led to greater deficit moisture stress on narrower spaced drainage treatments.