SOYBEAN YIELD RESPONSE TO TILLAGE, FRAGIPAN DEPTH, AND SLOPE LENGTH

Abstract

Soybean (Glycine max) yield from continuous no-till and conventional-till systems were measured for 14 yearson 12 pairs of 30.5-m long up-and-down-hill plots. The plots were located on shallow Loring (Typic Fragiudalf) silt loamsoil that was underlain by a restrictive fragipan. The no-till provided minimal erosion and the conventional-till providedexcessive erosion. After the first three years, no-till yields exceeded those from conventional-till for the remainder of thestudy. This report deals with soybean yields that were measured from sequential 7.6-m slope segments designated as A, B,C, and D from the top to the bottom of each plot. The average fragipan depths in the spring of 1985 were 42, 38, 37, and30 cm in the conventional-till plots and 46, 44, 35, and 30 cm for the no-till plots for each of these respective segments.The effective slope length for runoff travel distance on segments A through D were 7.6, 15.2, 22.8, and 30.5 m,respectively. Tillage, year, effective slope length, and fragipan depth significantly affected crop yield during the 1984 to1997 study period. Both increase in slope length and decrease in fragipan depth produced lower yield in both tillagesystems with greater yield reduction from the conventional-till practice. An exponential equation fitted to the differencesof no-till and conventional-till average yield reflected that no-till soybean yield exceeded conventional-till soybean yieldby about 70% after 14 years. Predicted erosion per unit area (RUSLE, version 1.06) within segments B, C, and D forconventional-till increased 54, 85, and 108%, respectively, as compared to that within segment A. The increase was only12.5% for no-till segments B, C, and D as compared to that within segment A. The estimated accumulated depth of soilloss from each slope segment A, B, C, and D for conventional-till represented a net decrease in fragipan depth of about 2,5, 8, and 10%, respectively, from 1984 to 1997. No-till produced no estimated significant changes to depth of fragipanduring the study period. The authors believe the data suggest that greater erosion from conventional-till on the lowerslope segments contributed to a decrease in soil productivity on these soils.