Evaluation of Annual Polycrop Mixtures for Soil Health, Grazing Capacity, and Economics

This study evaluated grazing a swathed whole-plant annual polycrop mixture (POLY) containing peas, hairy vetch, crimson clover, Italian ryegrass, sorghum, Winfred forage brassica, Hunter brassica, and Graza forage brassica compared to swathed whole-plant monocrop barley (BAR) for its effect on soil organic matter content and composition, grazing capacity, and system economics. The study was conducted over a two-year period at a 13.2 ha site near Lanigan, SK (Canada). Dry pregnant beef cows (70252 kg) were randomly allocated to 1 of 2 replicated (n=3) winter grazing systems consisting of BAR or POLY paddocks. Above-ground forage yield and forage utilization were lower in POLY than BAR (P < 0.01). In yr 2, botanical composition of the POLY was evaluated where weed species comprised 60.8 % (P < 0.01) of the above-ground POLY biomass. POLY forage had lower dry matter, total digestible nutrients, and neutral detergent fiber, and higher crude protein, acid detergent fiber, calcium, sulfur, and nitrate-nitrogen than BAR (P < 0.01), while phosphorus content was not different. Cows grazing the BAR had a higher final body weight (P=0.04), more grazing days (P < 0.01), positive average daily gain (P < 0.01), lower cost of crop production (P < 0.01), and lower cost cow-1 d-1 (P < 0.05) than the POLY. Soil samples were collected in Spring 2017, Spring 2018, and Fall 2018 at both upslope and downslope landscape positions to two depths (0-5 cm and 5-20 cm). When observing change in TOC from Spring 2017 to Fall 2018, in the upslope landscape position the POLY 5-20 cm sampling depth showed a TOC gain of 8.4 Mg ha-1 (P=0.03) compared to a loss of TOC in BAR. The root biomass was higher in the POLY (P < 0.05) than the BAR in the upslope landscape position, consistent with significant gains in TOC observed in the 5-20 cm depth of the POLY system upslope soils. Results from this study suggest that with proper management, there is the potential for the use of annual polycrop mixtures for extensive grazing in western Canada, with an opportunity for gains in soil organic carbon.