CLIMATE-BASED ESTIMATES OF FORAGE YIELDS IN THE PRAIRIE REGION OF WESTERN CANADA

A forage model (FORYLD) was used to estimate average potential (constraint-free) yields (B-y) and yields under rainfed conditions (B-ya) of alfalfa and wheatgrasses for the prairie region of Western Canada. Yield estimates were determined using 30-year climatic means (monthly values) and assumed available water-holding capacities (AWC) of soils ranging from 50 to 280 mm as inputs to the model. Calculations were made for 252 areas or zones known as Agroecological Resource Areas (ARAs) for the region. Estimates of B-y for alfalfa ranged from over 17.5 t/ha, in areas where three cuts of alfalfa were feasible if the crop were fully irrigated, to less than 10 t/ha in some northern ARAs where restricted length of the growing season limited potential to only one cut. For wheatgrasses B-y ranged from 15 to 17.5 t/ha in most areas where two cuts are possible. Estimates of B-ya for alfalfa, based on the predominant AWC for soils in each ARA, ranged from less than 2 t/ha in the driest portion of. the prairie region to more than 8 t/ha in the more humid areas. Yields of wheatgrasses were very similar to those of alfalfa in the driest zones but slightly more in some of the more humid regions. Effects of varying soil AWC on yield estimates are presented for the major soil groups of the prairies.