Submitted to: Soil & Tillage Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/16/2002
Publication Date: 7/5/2004
Citation: Logsdon, S.D., Karlen, D.L. 2004. Bulk density as a soil quality indicator during conversion to no-tillage. Soil & Tillage Research. 78:143-149. Interpretive Summary: Soil compaction can reduce crop yields, and increase runoff and associated soil erosion into surface waters. This is why soil density is often included among the measurements to determine how good the soil is for crop growth and to maintain water quality. But how dense would the soil need to be to reduce crop growth or increase surface runoff? How large should the soil density sample be? What is the best season to measure soil density? For soils high in silt (flour-size particles), the critical density value should be increased because of large pores and cracks in the soil. These large pores and cracks permit roots and water to move through the soil even if the soil is dense. Larger samples related better to crop growth than did smaller samples. During 5 years of conversion from continuous corn and conventional tillage to 2 or 6 year rotations under no-tillage, the soil density was not affected by the change in management. The soil density depended more on the time of the sampling than on management practices. This information is important for farmers and extension to show them that conservation management changes will not harm their crop production.
Technical Abstract: Producers often identify soil compaction as a soil quality concern. Therefore, bulk density is usually included in the minimum data sets used to evaluate crop and soil management practices. The hypothesis of this study was that bulk density would be a useful soil quality indicator for comparing crop and soil management practices during conversion to conservation tillage and longer rotation management. Two watersheds were converted in 1996 from conventional tillage to no-tillage management, and a third watershed remained in ridge-tillage, continuous corn (Zea mays L.) since 1972. All three sites had originally been in continuous corn. One watershed was converted to a 2-year rotation, and the other to a 6-year rotation. We measured bulk density at three landscape positions: summit, side-slope, and toe-slope, for five years in three field-scale watersheds located on deep-loess soils in western Iowa, USA. We took bulk density and water content samples five times between September 1996 and May 2000 in 20-mm increments to a depth of 300 mm. To characterize the site, we determined organic C, and total N to a depth of 160 mm from the initial sampling. Neither bulk density nor water content showed any significant differences between the two watersheds being converted to no-tillage or between them and the ridge-till watershed. There also were no significant differences among landscape positions. Bulk densities and water contents showed some differences when analyzed between adjacent sampling dates, but had no overall or consistent trend. Our results suggest that using no-tillage or ridge-tillage on Hapludolls, Udorthents, or similar deep-loess soils will not result in decreased soil quality because of increasing bulk density.