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

Producers in the semiarid Canadian prairies have begun to extend and diversify their cropping systems. These newer cropping systems are often considered to be more sustainable. We examine the agronomic, environmental, and economic effects of reducing summerfallow use and including grain lentil (Lens culinaris Medikus) in rotation with spring wheat (Triticum aestivum L.). Data from a long-term crop rotation experiment conducted on a medium texture soil at Swift Current, Saskatchewan were analyzed. Four cropping systems were evaluated over the 1979 to 1997 period; namely, fallow-wheat (F-W), fallow-wheat-wheat (F-W-W), continuous wheat (W), and wheat-lentil (W-L). Nitrate leaching below the 120 cm rooting depth of wheat was lower under continuously cropped systems than under fallow-based rotations, and was lowest overall 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 extracted about 1.5 cm less water than wheat. On average, wheat yield was unaffected by inclusion of lentil in the rotation; however, grain protein content was higher in 11 of 18 years. The incidence of leaf spotting diseases in wheat was lowest for wheat grown after lentil and highest for wheat grown on fallow. Soil quality (soil organic carbon, mineralizable N and C, light fraction organic C, and water stable aggregates) increased with cropping intensity 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 for the continuous compared to fallow-based rotations, including lentil in the rotation lowered 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 confirm 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.