Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 15, 2013
Publication Date: July 1, 2013
Citation: Karlen, D.L., Cambardella, C.A., Kovar, J.L., Colvin, T.S. 2013. Tillage and crop rotation effects on soil quality in two Iowa fields. Soil & Tillage Research. 133:54-64. Interpretive Summary: Tillage and crop rotation are two management practices that can affect long-term soil health. This study, which evaluated several soil quality indicators after using five different tillage practices for 31 years for either a corn-soybean rotation or continuous corn, showed that moldboard plowing was more detrimental to soil quality than the other tillage practices. This probably occurred because the number of tillage operations required to prepare a seedbed following moldboard plowing resulted in greater destruction of above- and below-ground crop residues. Based on our results, producers are encouraged to adopt tillage practices that are less aggressive than traditional moldboard plowing. The information will be useful not only for producers, but also crop consultants, extension personnel, and other researchers studying soil management practices.
Technical Abstract: Soil quality is affected by inherent (parent material, climate, and topography) and anthropogenic (tillage and crop rotation) factors. We evaluated effects of five tillage treatments on 23 potential soil quality indicators after 31 years in a corn (Zea mays L.)/soybean [Glycine max (L.) Merr.] rotation or 26 years of continuous corn in two adjacent fields located in central Iowa U.S.A. Within each field, samples were collected from two soil map unit (SMU) groups. Composite soil samples (n=158) from 0 to 5- and 5 to 15-cm depth increments were collected, analyzed, and evaluated by depth. The Soil Management Assessment Framework (SMAF) was used to compute indices for nine indicators and an overall soil quality index (SQI) for each tillage, crop rotation, and SMU. Among indicators used for SMAF analysis, water stable aggregation (WSA), total organic carbon (TOC), microbial biomass carbon (MBC), and potentially mineralizable nitrogen (PMN), values were all significantly lower at 0 to 5-cm and generally lower at 5 to 15-cm for the moldboard plow treatment, presumably reflecting greater physical breakup and oxidation of above- and below-ground plant residues. Bray-P was also significantly lower at both depth increments within both fields. Between SMUs, significant differences were found for WSA, Bray-P, TOC, and MBC at both depth increments and for both cropping systems. Except for WSA at the 0 to 5-cm depth, within Field 70 (continuous corn), measured values for all four of these indicators were lower for Clarion loam than for Webster silty clay loam (sicl) sites. SMAF scores for 0 to 5-cm samples were lowest for TOC and electrical conductivity (EC), averaging 0.62 and 0.63, respectively. Within the 5 to 15-cm increment, SMAF scores were lowest for MBC (average = 0.32) and TOC (average = 0.49). When combined into an overall SQI, both SMUs in both fields were functioning at 82 to 85% of their potential at 0 to 5-cm and at 75% of their potential at 5 to 15-cm. Overall, for both cropping systems, tillage (especially moldboard plowing) appears to have had the greatest long-term negative effect on soil quality indicators. Based on this assessment, we recommend that producers interested in long-term sustainability of their soil resources should strive to adopt less aggressive tillage practices.