Submitted to: Electronic Journal of Integrative Biosciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 29, 2009
Publication Date: June 15, 2009
Citation: Karlen, D.L., Dinnes, D.L., Tomer, M.D., Meek, D.W., Cambardella, C.A., Moorman, T.B. 2009. Is No-Tillage Enough? A Field-Scale Watershed Assessment of Conservation Effects. Journal of Integrative Biosciences. 7(2):1-24. Interpretive Summary: Conservation has been an important part of American agriculture since 1935, but it is still difficult to quantify benefits of past and current practices. Following 40 years of conventional tillage, continuous corn production, we conducted a nine-year study comparing no-tillage corn-soybean and a no-tillage, six-year, contour strip-cropping rotation of corn-soybean-corn-alfalfa-alfalfa-alfalfa on two adjacent field-scale watersheds on deep-loess soils in western Iowa, USA. The six-year rotation decreased runoff by more than 50% despite having three of the most intensive rainfall events in the 40-year history of the research site. Using the late-spring soil nitrate test (LSNT) reduced fertilizer N applications to between 22 and 34% of the long-term rate (160 lb/acre). This study demonstrates the importance of combining diverse crop rotations with no-tillage practices to achieve the greatest conservation benefits. The information will be useful to producers, conservationists, and crop consultants who develop land use plans and to taxpayers who are supporting the conservation programs.
Technical Abstract: 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 nine-year period after converting both watersheds from conventional tillage, continuous corn (Zea mays L.) to a no-till corn – soybean [Glycine max (L.) Merr.] or no-till contour strip-cropping with a six-year corn, soybean, and alfalfa (Medicago sativa L.) rotation. Despite having three of the most intense rainfall events recorded for this site, no-till plus contour strip-cropping reduced runoff 20% for rainfall amounts of 35 to 80 mm d-1. No-tillage alone, however, resulted in increased runoff. After a four-year transition period, the diversified six-year rotation reduced nitrogen(N) fertilizer requirements for corn by approximately 75% compared to the long-term average (178 kg N ha-1) for continuous corn. Coupling the conservation practices with good agronomic management increased corn yield by 2 Mg ha-1 compared to the long-term average. Average soybean (3.6 Mg ha-1) and 1st, 2nd, and 3rd year alfalfa yields (4.2, 7.5, and 7.5 Mg ha-1, respectively) were also good. Economic comparisons demonstrate the impact of market price and stress the importance of good agronomic management. We conclude that implementing conservation practices that include diversified crop rotations plus very reduced or no-till operations can be profitable for land owners/operators and more environmentally sustainable for taxpayers supporting conservation for clean water and healthy soils.