Variation in Soil Properties and Crop Yields at Different Topographic Positions.

Topography is highly related to crop yields as it causes changes in physical and chemical properties of uphill and downhill soils which includes soil nutrients, organic matter, redistribution of soil particles and water availability due to both vertical and horizontal water redistribution. However, the influence of topography on crop yields has been reported on relatively small scale.  The objectives of our study was to determine the influence of topographic positions (shoulder, backslope, and deposition slope) on soil properties and crop yields on watershed scale. A field experiment was conducted at agricultural research site adjacent to Southern Illinois University’s tree improvement center located on west side of the City of Carbondale, IL. Experimental design consists of three basins per watershed, which were delineated in ESRI ArcMap (Version 10.2.2) using DEM and hydrology toolbox. Crop yields were monitored from 2012 to 2015. Soil samples were collected in fall 2015 after harvesting of corn from two depths 0-15 cm and 15-30 cm and analyzed for standard soil fertility parameters (pH, organic matter, total carbon %, total nitrogen %, Bray-P, Mehlich-3 P, and Mehlich-3 extractable elements) and soil moisture. Bulk density was also measured using core method. The collected data was analyzed using PROC GLIMMIX procedures of the SAS statistical software. Soybean and corn yields were significantly lower at the deposition position in 2014 and 2015, which might be due to higher soil moisture content. Soil pH, total N, total organic carbon, Bray I P and Mehlich-3 P, Na, Fe, S, Fe, Mn and Cu at depositional position was significantly higher compared to the  backslope position. Topography significantly affects crop yields and soil properties on watershed scale.