Variability in soil and crop productivity in the Northern Great Plains is related to the pedogenic development of the parent glacial deposits, climate, native vegetation, and topography. Anthropogenic field management over the past 100 years has contributed to additional field variability through tillage erosion, crop-fallow rotations, fertilizer management, livestock manure management and crop residue management. Field topography influences microclimate and the hydrological conditions within a landscape by the redistribution of water and soil thermal dynamics. Water movement from upper to lower slope and depression areas either by runoff or through subsoil will result in the physical redistribution of surface soil (erosion), translocation of soluble nutrients or accumulation of salts. The end result of this redistribution is drier warmer upper slopes, and wetter cooler lower slopes and depressions. This influences soil biological, chemical and physical processes that impact crop growth. Often, the lowest crop yields are measured on the upper slopes and the highest yields on the lower slopes. Upper slopes are prone to erosion, shallow surface horizons, higher carbonate levels, lower organic matter levels and lower available water. The lower slopes have deposits of eroded surface material, deeper surface horizons, greater depth to carbonates, higher organic matter levels and higher available water. However, spatial relationships between productivity and landscape position are not always consistent. Higher productivity does not always occur in lower slopes because yield reductions can occur as a result of planting delays, poor crop germination, poor soil aeration, poor drainage, poor root development, foliar and root diseases, compaction, nutrient deficiencies, weed competition, limited root development, stunted crop development, acidic soil and salinity. Precision farming provides an opportunity to utilize technology to manage the topographical and spatial variability. Elevation and positioning data collected from global positioning systems can be managed by means of geographic information systems. Landform segmentation provides a fundamental basis for subdividing fields into landscape management units based on topography. Field sensors such as crop yield monitors along with remote sensing, aerial photography, soil sampling and weed populations provide additional data layers needed for site specific management. Variable rate controllers provide the technology for fertilizer, manure, lime and herbicide applications. Ultimately, economics will determine the adoption of precision farming technology and practices.
