In search of a sustainable cropping system for the semiarid Canadian prairies

Producers in the semiarid Canadian prairies have begun to extend and divers ify their cropping systems. These newer cropping systems are often consider ed to be more sustainable. We examine the agronomic, environmental, and eco nomic effects of reducing summer fallow use and including grain lentil (Len s culinaris Medikus) in rotation with spring wheat(Triticum aestivum L.). D ata from a long-term crop rotation experiment conducted on a medium texture soil at Swift Current, Saskatchewan were analyzed. Four cropping systems w ere evaluated over the 1979 to 1997 period; namely, fallow-wheat (F-W), fal low-wheat-wheat (F-W-W), continuous wheat (W), and wheat-lentil(W-l). Nitra te leaching below the 120 cm rooting depth of wheat was lower under continu ously cropped systems than under fellow-based rotations, and was lowest ove rall for W-L. Wheat, whether grown on fallow or stubble, used almost all of the available water in the 0-120 cm depth soil profile, but lentil extract ed about 1.5 cm less water than wheat. On average, wheat yield was unaffect ed by inclusion of lentil in the rotation; however, grain protein content w as higher in 11 of 18 years. The incidence of leaf spotting diseases in whe at was lowest for wheal grown after lentil and highest for wheat grown on F allow. Soil quality (soil organic carbon, mineralizable N and C, light frac tion organic C, and water stable aggregates) increased with cropping intens ity in the order of W-L greater than or equal to W > F-W-W > F-W. Although inputs of non-renewable energy and CO2 emissions were higher Ibr the contin uous compared to fallow-based rotations, including lentil in the rotation l owered the energy requirements for N fertilizer and provided an overall 19% , reduction in CO2 emissions. The economics favored the W-L system whenever lentil price was above $350 t(-1). The level of financial risk was lowest for F-W and F-W-W, intermediate for W-L. and highest for W. Our findings co nfirm the recent changes in land use practices being adopted by producers, and clearly show that extending and diversifying crop rotations by reducing fallow and including pulse crops in the rotation will improve the overall sustainability of agricultural production in this semiarid region. (C) 2001 by The Haworth Press, Inc. All rights reserved.