The effects of imposing tillage on long term no-till soils
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During the last two decades, an increasing number of producers have adopted a no-tillage or minimum tillage system because of the potential to reduce soil erosion, conserve soil moisture, improve soil structure and increase net economic returns. Some potential concerns related to elimination of tillage include stratification of nutrients near the soil surface and lack of herbicide options to control certain weeds. These concerns have lead some producers in Western Canada to consider applying one or more cycles of tillage to their no-till fields. Little information exists on the impact of imposing one or more tillage operations on a long term no-till soil. Therefore a study was conducted to examine the effect of tillage on soil conditions and crop growth at three long-term no-till sites, one in each of the Brown, Black, and Gray soil zones of Saskatchewan. The sites were previously managed as no-till for 10 years or more. In this study, the sites were subjected to a one year cycle of tillage at three levels of intensity involving spring cultivation only, fall + spring, and fall + spring + disc, and a no-till control. Soil cores were taken in the spring and fall after imposition of the tillage treatments. Total and particulate soil organic carbon, pH, EC, and mean weight diameter of the soil aggregates generally were not significantly affected by the tillage operations. However, there was a trend at all sites for tillage treatments to have lower mass of organic carbon in the 0-10 cm depth. Tillage tended to reduce the bulk density at the 5-10 cm depth and resulted in a small increase (~ 1oC) in spring soil temperature at the 5 cm depth. Tillage reduced phosphorus stratification to some extent, but there appeared to be no associated effect on crop P uptake. There were no wheat yield differences due to the tillage treatments at the Brown soil zone site while canola yield at the Black soil zone site showed some small yield increases in tilled treatments that may be attributed to nitrogen (N) mineralization. The canola grown at the Gray soil zone site experienced canola grain yield reductions of approximately 100 to 600 kg.ha-1 in tilled treatments compared to the no-till control. At this site, lower soil available N due to incorporation of large amounts of fresh straw and subsequent immobilization is believed to be a contributing factor. Overall, the imposition of one cycle of tillage on long-term no-till soils does not appear to have a major impact on soil properties or crop growth.
soil organic carbon
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