Impact of Sustainable Management Practices on an Irrigated Rotation Study in Southern Alberta.

Irrigated cropping offers a dual challenge of producing high value crops while maintaining soil quality. An irrigated rotation study was initiated in 2000 at Vauxhall, Alberta to examine the impact of conventional and sustainable rotations for potatoes, sugar beets, beans and soft wheat. The sustainable rotations were built around four specific management practices: direct seeding/reduced tillage, cover crops, feedlot manure compost application and where beans occurred in the rotation, solid-seeded narrow-row beans vs. conventional wide row beans. There was a total of six rotations: 3-yr conventional and sustainable; 4-yr conventional and sustainable; 5-yr sustainable; 6-yr sustainable (which included 2 yr of timothy); as well as continuous wheat. Responsiveness of crops to sustainable management ranked potatoes > beans > wheat > sugar beet. In the first cycle of the 4-yr rotations (2000-03), potatoes yielded 9% lower with sustainable compared to conventional management. However, in the second cycle (2004-07), they yielded 6% higher with sustainable management, denoting an increased response to sustainable management as the study progressed. The overall effect of sustainable management was to increase soil organic carbon (SOC) mass by 22% (29.2 vs. 24.0 Mg ha-1) in the 0-15 cm soil depth by fall 2005. On the sustainable rotations, compost application, greatly increased SOC mass while inclusion of 2 yr of timothy was less effective. The 3- and 4-yr sustainable rotations averaged 26-27% higher than their conventional counterparts for microbial biomass C in bulk soil. At the 0-100 cm depth, 31% of 294 sampling dates (across years and crops) showed a significantly higher percent available water under sustainable management while only 4% showed significantly higher available water under conventional management. Most crop and soil parameters pointed to beneficial effects of sustainable management practices for irrigated cropping in southern Alberta.