Assessment of Drainage Tile Efficacy for Common Row Crops Using Vegetation Indices Measured with UAVs

Abstract:

Much of the Midwestern portion of the United States uses tile drainage systems to control soil moisture. The most common crops in this area are corn and soybeans, and the vigor of these crops is often assessed using UAVs to determine a vegetative index, most commonly the NDVI. In this research, 44 plots were planted with corn or soybeans at a field site in northern Missouri (USA). Each plot had either no tile drainage, tile drains placed at 20-foot spacing, or tile drains with 40-foot spacing. A UAV was used to collect multispectral data including green, red, red-edge and near-Infrared wavelengths, and these data were used to calculate five vegetation indices: NDVI, NDRE, GNDVI, CIG, and VARI. Comparison of these vegetative indices with tile drainage density revealed some unexpected patterns. For corn, bare patches in the plots seemed to have a greater influence on NDVI, NDRE, and VARI data than did tile spacing, while GNDVI and CIG data indicated higher vegetative vigor in plots with less drainage, perhaps due to drier soil conditions at the time of the survey. For soybeans, the effect of tile drainage was more pronounced, with higher vegetation indices observed in the plots with tile drainage than in the undrained plots. A comparison of indices between corn and soybeans revealed that soybeans generally had higher indices values than did corn. The exception to this pattern was NDRE data, which penetrate deeper into the canopy, and thus are better for monitoring mature corn plants.

The results of this research show that drainage tile efficacy can be a function of crop type and that different vegetative indices are useful for determining crop vigor versus bare soil patches for different crop types. Thus, calculating multiple indices and evaluating different indices for different crops may be helpful for producers in understanding total crop health over an area.