Is No-Tillage Enough? A Field-Scale Watershed Assessment of Conservation Effects

No-tillage and contour strip cropping are two conservation practices recommended by the Natural Resources Conservation Service (NRCS). Our objective was to quantify the effects of those practices after imposing them on deep loess soils in two field-scale watersheds in western Iowa. Hydrology, soil fertility, and crop yield response were evaluated for a 9-yr period after converting both watersheds from conventional tillage, continuous corn (Zea mays L.) to a no-tillage corn - soybean [Glycine max (L.) Merr.] rotation or no-tillage contour strip-cropping with a 6-year corn, soybean, and alfalfa (Medicago sativa L.) rotation. Despite having three of the most intense rainfall events recorded during the 45-year research record for this site, no-tillage plus contour strip-cropping reduced runoff 20% for rainfall amounts of 35 to 80 mm d-1 (1.4 to 3.2 in d-1). No-tillage alone, however, resulted in increased runoff. After a 4-yr transition period, the diversified 6-yr rotation reduced N fertilizer requirements for corn by approximately 75% compared to the long-term average [178 kg N ha-1 (159 lb N ac-1)] for continuous corn. Improved genetics, coupled with the conservation practices and good agronomic management, increased corn yield by 2 Mg ha-1 (32 bu ac-1) compared to the long-term average. Average soybean [3.6 Mg ha-1 (54 bu ac-1) and 1st, 2nd, and 3rd year alfalfa yields [4.2, 7.5, and 7.5 Mg ha-1 (1.9, 3.3, and 3.3 tons ac-1), respectively] were typical for this region. Economic comparisons emphasize the impact of market price and importance of agronomic management. We conclude that implementing conservation practices that include diversified crop rotations plus very reduced or no-tillage operations can be profitable for land owners/operators and more environmentally sustainable for taxpayers supporting conservation for clean water and healthy soils.