A Soil Conservation Package for Irrigated Rotations In Southern Alberta.

An irrigated rotation study with potatoes (Solanum tuberosum L.), sugar beet (Beta vulgaris L.), dry beans (Phaseolus vulgaris L.) and soft wheat (Triticum aestivum L.) was initiated in 2000 to examine the impact of conventional and conservation rotations on crop yield and quality and soil properties. The conservation rotations were built as a package which included: (1) reduced tillage where possible; (2) fall-seeded cover crops; (3) feedlot manure compost addition; and (4) where beans occurred in the rotation, solid-seeded narrow-row (20 cm) beans vs. conventional wide-row (60 cm) beans. Rotations varied in length from 3 to 6 yr with the longest rotation containing 2 yr of timothy (Phleum pratense L.). The 2011 growing season marks 12 yr (4 cycles of the shortest and 2 cycles of the longest rotations). Potatoes were the most responsive crop to soil conservation practices with increased tuber yield and reduced disease pressure (Verticilium wilt) especially in the shorter 3-yr rotation (potatoes-beans-wheat). Bean yields on the conservation rotations (narrow-row) were about 9.5% lower over 10 yr (2000-09) than the conventional wide-row beans. Sugar beet and wheat yields were less responsive to management practices than potatoes and beans. Most soil parameters pointed to beneficial effects of conservation management (e.g. increased soil organic carbon, microbial activity, and available water). For example, soil organic carbon increased by 11% on the 3-yr conservation rotation compared to a decrease of 10.4% on the 3-yr conventional rotation in the first 9 yr. This was mainly attributed to compost addition (42 Mg ha^-1 every third year) but also to direct seeding of the bean and wheat crops and cover cropping with fall rye after potatoes and before beans. The 3- and 4-yr conservation rotations averaged >25% higher than their conventional counterparts for microbial biomass C in bulk soil. The soil conservation package reduced overall erosion risk and promoted soil quality for irrigated soil.