Crop yields and soil fertility as affected by dryland rotations in Southern Alberta

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Abstract
Six of 7 nonfertilized dryland crop rotations, consisting of combinations of fallow, wheat, alfalfa and grass, depleted several major plant nutrients in the soil in 20 yr. The average contents of organic matter, total N and exchangeable K were decreased by 14.5, 10.1 and 26.7%, respectively, in the 0- to 15-cm soil horizon and by 24.1, 13.3 and 25.7% in the 15- to 30-cm horizon. Total P content of the soils changed very little during 20 yr of cropping. The amount of NaHCO3-extractable P decreased by 38.3% in the 0- to 15-cm horizon of all soils except those in a manured fallow-wheat-wheat rotation, where a 30.6% increase occurred. Although soils were generally depleted, plant nutrients have not yet reached critically low levels, and crop yields are maintained at a fairly uniform level by using improved cereal varieties, timely tillage, good seedbed preparation, suitable seeding methods, and adequate in-crop weed control. Further depletion of plant nutrients from the soils will probably restrict crop production. Applications of adequate amounts of N, P and K fertilizers, as determined by soil tests and correlative field tests, must be made to these and similar soils to ensure continued productivity.