Thirty-year tillage effects on crop yield and soil fertility indicators

Long-term studies are crucial for quantifying tillage effects on productivity and soil fertility. Moldboard plow, chisel plow, spring disk, ridge-tillage, and no-tillage systems were evaluated after 32 years of a corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] rotation and 27 years of continuous corn in central Iowa, U.S.A. Productivity was quantified using yield, while soil fertility status was evaluated by collecting four, 5-cm diameter soil cores to a depth of 0.9 m from each treatment, dividing them into four depth increments (0–15-, 15–30-, 30–60-, and 60–90-cm), analyzing them for bulk density (BD), NO3-N, NH4- N, electrical conductivity (EC), pH, Mehlich-3 extractable P, K, Ca, Mg and DTPA-extractable Cu, Fe, Mn, and Zn, and interpreting the data using Iowa State University (ISU) guidelines. Production costs for each tillage and cropping system were also computed. To account for genetic and agronomic changes during the 30-year study period, yields were examined for establishment, maintenance, and intensification/ recovery phases. Rotated corn yield averaged 8.6, 8.8, and 11.6 Mg ha-1 and soybean yield averaged 2.7, 3.2, and 3.4 Mg ha-1, respectively, for each of the phases. Continuous corn from 1988 to 2006 averaged 7.5 and 10.1 Mg ha-1 for the maintenance and intensification/recovery phases, respectively. Fixed plus variable machinery costs for corn ranged from 233 to 354 USD ha-1, while for soybean they ranged from 194 to 280 USD ha-1. Net returns to land, labor and management ranged from 233 to 269, 560 to 620, and 437 to 483 USD ha-1 for continuous corn, rotated corn, and rotated soybean, respectively. Based on 9- year (2003–2011) average grain prices and yields from this study, the corn–soybean rotation was twice as profitable as continuous corn. Soil-test P and K measurements, as well as calculated P and K removal, suggest that nutrient mining occurred during the course of this study. The soil-test data also indicate that further studies are needed regarding plant availability of subsoil K and its impact on fertilizer recommendations. Overall, we conclude that with good nutrient management and crop rotation, yield and soil fertility differences between no-tillage and more intensive tillage systems can be minimized and that no-till production can be profitable on glacial till derived soils