Lack of soil disturbance in no-tillage changes some of the most important basic soil properties. Short-term changes have been well documented by previous research, but little is known about long-term changes. This study was to determine the effects of 20 yr of continuous corn (Zea mays L.) under no-tillage (NT) and conventional moldboard plow tillage (CT) with 0, 84, 168, and 336 kg N ha−1 on soil properties and grain yields and, to the extent possible, compare 20-yr results with previously published 5- and 10-yr results. Soil organic C and N; extractable P; exchangeable Ca, Mg, and K; and pH were significantly higher with NT than CT in the 0- to 5-cm depth. Below the 5-cm depth, Mehlich III P; pH; and exchangeable Ca, Mg, and K were higher with CT than NT. Organic C and N increased with increasing N rates. Conversely, pH and exchangeable Ca and Mg declined with high N rates. Bulk density was not significantly different among NT, CT, and bluegrass sod (Poa pratensis L.), but increased with depth. Comparisons of 1989 results with those obtained in 1975 and 1980 revealed that the soil's organic C was restored to the level of the bluegrass sod following a decline of 19% with CT and 9% with NT between 1970 and 1975. Grain yields, which declined along with organic C, have not recovered. Changes in organic matter content, with their many ramifications, are probably the most important long-term effects of tillage differences on basic soil properties.
Contribution of the Kentucky Agric. Exp. Stn. Journal Paper no. 93-3-85.