Impact of long-term summerfallow practices in southern Alberta
Crop rotations with a high frequency of fallow remain the dominant practice in the semiarid northern Great Plains. The use of tillage to control weeds during fallow increases soils exposure to wind erosion. A long-term summerfallow management study was initiated on a clay loam soil at Lethbridge in 1955. Between 1977 and 1991 fallow treatments of tillage alone, herbicide alone and combinations of tillage and herbicide were compared. During this most recent 15-year period, average spring wheat (Triticum Aestivum L.) and barley (Hordeum Vulgare L.) yields were similar regardless of fallow treatment, with a 3.1 bu/acre difference between highest and lowest yielding treatments for wheat, and a 4.1 bu/acre difference for barley. Summerfallow managed using summer herbicides, followed by fall blade, resulted in the highest grain and grain N yields for wheat and barley, and highest soil nitrate-N concentration. Herbicides alone maintained the highest amount of crop residue cover and plant-available water at seeding. Surface (0-4 ft) and profile (0-10 ft) nitrate-N concentrations were highest for one-way disc, 70-100% higher than the lowest treatment, herbicide alone. While the herbicide alone treatment had the highest percentage of wind erodible aggregates in the spring, its maintenance of crop residue cover provided the best protection to wind erosion. The maintenance of surface residues becomes critical to erosion protection in the absence of tillage, particularly in years of low residue cover. Producers using a cereal-fallow rotation are encouraged to consider herbicides alone or herbicide-tillage combinations for summerfallow as the best means of ensuring adequate erosion protection and optimizing grain yield potential.
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