EFFECT OF SOIL DEPTH AND EROSION ON YIELD IN THE MISSISSIPPI BLACKLANDS

Farmer fields were used 4 consecutive year (1982-1985) to determine effects of soil depth and other parameters on soybean yield in the Mississippi Blackland Prairie. Grain yields were variable from year to year for specific sites as well as from site to site within a given year. Differences from site to site were due to variation in soil organic matter and rainfall distribution; whereas, differences within a site were influenced by organic matter, soil depth, and other parameters such as pH and available K which were related to depth. Soil depth was a much better predictor of yield at sites with low organic matter, especially when rainfall was also low. A regression model for depth vs. yield indicated that 10 mm of soil was worth an average of 0.006 Mg ha-1 of soybean grain within the 500- to 1500-mm depth but worth 0.06 Mg ha-1 within the 50- to 150-mm depth.