Quantifying the effects of soil erosion on crop productivity

The effects of soil erosion on yield and root development were determined for soybean (Glycine max (L.) Merr.) (1984) and corn (Zea mays L.) (1985) grown on Grenada silt loam (Glossic Fragiudalfs) in West Tennessee. Seven sites were selected in a cropped field where depth to the fragipan ranged from 0 to 107 cm below the soil surface. To verify the deep sites were relatively uneroded, selected physical and chemical properties of the 107 and 15 cm sites were compared to an area of Grenada silt loam in Crockett County, Tennessee with no history of cultivation. Across-the-site comparisons involving bulk density, soil color, exchangeable Na, and organic matter indicated that profile modification at the experimental sites had occurred as a result of soil erosion. Soils were sampled to either 90 or 120 cm depths in 15 cm increments at six points each within the row and 25 and 51 cm from the row; subsamples were composited by each depth increment. Four such samplings were made for each site. Roots were extracted and total root length was determined by the line-intercept method. Greater total root lengths were observed with increasing depth to the fragipan. Crop yields were correlated with total root length. Soybean yields ranged from 2.8 Mg ha^-1 on the 107 cm site to 0.5 Mg ha^-1 on the 0 cm site, whereas, corn yields ranged from 10.0 Mg ha^-1 to 5.5 Mg ha^-1 from the 107 cm site to the 0 cm site, respectively.