Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 3, 2013
Publication Date: June 3, 2013
Citation: Karlen, D.L., Kovar, J.L., Cambardella, C.A., Colvin, T.S. 2013. Thirty-year tillage effects on crop yield and soil fertility indicators. Soil & Tillage Research. 130:24-41. Interpretive Summary: Long-term evaluations of soil and crop production systems are essential for quantifying subtle effects of tillage and as a source of data for subsequent simulation modeling. This study examines 30 years of effects for five tillage systems used for a corn/soybean rotation or continuous corn production on glacial-till derived soils in central Iowa, USA. The results show that crop rotation increased corn grain yield by 17% compared to growing continuous corn. Applying fertilizer phosphorus(P) and potassium (K) at recommended rates was not adequate for this type of soil indicating that soil-test recommendations for Central Iowa need to be reevaluated. The study also showed that although yield levels were sometimes lower for no-tillage practices than for treatments with more intensive tillage, net returns for continuous corn, rotated corn, and rotated soybean were greater for the no-tillage treatment compared to moldboard plowing, chisel plowing, or disk tillage. This long-term management record and yield response to five tillage systems on glacial till soils in Central Iowa USA will be useful for producers, crop consultants, conservationists, modelers, and research scientists.
Technical Abstract: Long-term studies are crucial for quantifying tillage system effects on crop productivity and soil fertility status. We examined 30 years of data for five tillage systems evaluated on two glacial till soils in central Iowa, USA from 1975 through 2006. Moldboard plow, chisel plow, spring disk, ridge-tillage, and no-tillage systems were established in a randomized complete block design with four replicates and used for a corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] rotation for 32 years or continuous corn for 27 years. Crop yield response was used to evaluate productivity effects. Soil fertility status was evaluated primarily by collecting four, 5-cm diameter soil cores to a depth of 0.9 m from each plot following the 2005 growing season. Samples were divided into four depth increments (0 to 15-, 15 to 30-, 30 to 60-, and 60 to 90-cm), analyzed for several soil-test parameters, and interpreted in combination with a limited amount of plant analysis data. Production costs for each tillage and cropping system were computed using Iowa State University protocols. To account for genetic and agronomic changes occurring during the 30-year study period, crop yields were examined for an establishment phase, maintenance phase, and intensification/recovery phase. 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 1980 through 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 ranged from 1163 to 1200, 1374 to 1433, and 884 to 928 USD ha-1 for continuous corn, rotated corn, and rotated soybean, respectively. The soil analyses showed several statistically significant differences within the depth increments. 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 indicates 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 on these soils.