Soil moisture regimes under summerfallow, wheat and red fescue in the upper peace river region

Abstract

By use of the absorption block electrical resistance method an almost daily record of the soil-moisture content in fallowed land and under crops of spring wheat and red fescue was obtained over a 5-year period. Changes in soil moisture were collated with the growth and phenological stages of the crops. During the fallow year (spring break-up to winter freeze-up) 11.2 inches of water were lost by evaporation. This loss of moisture from fallow compared to 13.2 and 12.9 inches evapotranspired over the same period from fields where crops of spring wheat and established stands of fescue were grown. A feature of the study was the small amount of precipitation that was stored in the soil during the fallow period, which extends from the harvest of the crop preceding the fallow to the planting of the next crop some 20 months later. At Beaverlodge only 6% of the precipitation falling during this period was stored as compared with 12–21% elsewhere. When the ground was bare of residue as after the fallow year none of the winter precipitation was saved, while with wheat stubble only 5% was saved. Since the winter precipitation at Beaverlodge is about 6 inches or 1 3 of the annual, such loss is serious. Fescue sward proved superior to wheat stubble for with fescue 10% of the winter precipitation was stored. At the latitude of Beaverlodge the photoperiod effected a water economy. Thus, in selected seasons when water was not limiting it was found that only 11.1 inches of water were needed at Beaverlodge to produce 54 bushels per acre of wheat, while 15.9 inches were needed at Swift Current, 450 miles south, for 50 bushels per acre, and 18.1 inches were needed at Dickinson, North Dakota, 750 miles south for 36 bushels per acre. Wheat with its extensive root system withdrew moisture from at least a depth of 3 ft., while fescue did not withdraw it from much beyond 1 1 2 ft. Established fescue withdrew water more rapidly and thoroughly than wheat, particularly in the spring before wheat had a fully developed root system. If moisture was plentiful, wheat used it rapidly at all stages from jointing (4th leaf) to near maturity. Under the same conditions fescue was fairly constant in water uptake from soon after start of spring growth to reduction of growth in the fall. Hay harvest had little effect on water consumption.