Resource use of annual, cover crop, and perennial cropping systems, as well as the native grass system

The native vegetation of the Winnipeg Plains ecoregion is the tall-grass prairie, which is capable of using available resources from the onset of spring thaw until fall freeze-up. In contrast, the typical cropping system of this region currently is an annual cropping system, which takes advantage of available resources from mid-May to the end of August. As a result, there is potential for improving resource use efficiency throughout the maximum potential growing season by modeling the native grass system. The objective of this study was to determine the impact of perennializing the annual cropping system, either by using a perennial crop or by using a cover crop to extend the duration of resource use into the spring and fall (i.e., before the typical annual crop planting and after harvest), on resource use and the risk of nitrate pollution.;Differences in water use and soil moisture content among management systems were negligible as a result of the two wet growing seasons of 2004 and 2005. The risk of nitrate-nitrogen pollution by leaching was greatest in the fallow cropping systems, due to high levels of mineralization over the growing season. The presence of actively growing plants significantly reduced the risk of nitrate leaching and the native grass system was the least threatening, having the lowest levels of nitrate-nitrogen in the soil profile. The presence of the cover crop re-growth in the fall did not significantly enhance fall productivity compared to the weed growth of the annual cropping system. However, the perennial cropping system was more productive in the fall than the annual cropping system, and more productive in the spring than all other management systems. The lag time required for establishment of spring-planted crops was evident when compared to the perennial and native grass system indicating the advantage of early season resource use in perennial crops.;Under the conditions of this study, the cover crop did not provide an advantage, with respect to resource use, over the typical annual system. However, the perennialization of annual cropping systems by using a perennial crop can enhance productivity in the fall and spring periods and model after the native grass system. The risk of nitrate leaching was high for all management systems based on the amount of soil moisture. However, the native grass system maintained low levels of residual nitrate-nitrogen at freeze-up, making it the least susceptible to nitrate leaching.;Soil moisture, residual nitrate-nitrogen at freeze-up, and productivity were measured in management systems that were chosen to represent a typical annual cropping system [oats (Avena sativa L. var. ACS Assiniboia)], a cover crop cropping system [oats intercropped with berseem clover ( Trifolium alexandrinum L. var. Joe Burton) managed so that fall re-growth of the clover functioned as a fall cover crop], a perennial system [alfalfa (Medicago sativa L. var. OAC Minto) measuring both the year of establishment, yr 1, and the following year, yr 2], a chemical fallow cropping system, and a native grass system of established native grasses. Trials were conducted at Carman, Manitoba (Hochfeld fine sandy loam soil) and Glenlea, Manitoba (heavy clay soil on a combination of Dencross, Hoddinott, and Scanterbury soil series) in both 2004 and 2005.