Carbon input to soil from oilseed and pulse crops on the Canadian prairies

Abstract

The dynamics of carbon (C) in soil is fundamentally affected by crop mix in diverse cropping systems, yet, little is known about C inputs from oilseed and pulse crops. This study determined carbon allocation coefficients in grain, straw, roots, and rhizodeposits for important oilseed and pulse crops in comparison with spring wheat ( Triticum aestivum L.) under low-water (rainfall only) and high-water (rainfall plus irrigation) conditions. Three oilseeds [canola ( Brassica napus L.), mustard ( Brassica juncea L.) and flax ( Linum usitatissimum L.)], and three pulses [chickpea ( Cicer arietinum L.), field pea ( Pisum sativum L.) and lentil ( Lens culinaris Medik.)], along with a wheat control were tested in Saskatchewan, Canada, in 2006 and 2007. Crops were grown in 15-cm diameter, 100-cm long metal lysimeters pushed into the field of medium-textured Aridic Haploboroll with the soil structure in lysimeters undisturbed. Root mass in the 0–100 cm depth was greater ( P < 0.01) under irrigation than that under rainfall for wheat (126% greater), flax (54% greater), and mustard (14% greater); there was no difference for dry pea; and was lower ( P < 0.01) under irrigation for chickpea (−16%) and lentil (−35%). Straw-to-root ratio averaged 4.90 under rainfall conditions and 6.22 under irrigation; the ratio differed among crop species only under rainfall conditions where the ratios for wheat (6.33), dry pea (5.35) and mustard (5.00) were greater than the ratios for canola, chickpea, and lentil. The relative C allocation coefficients in grain ( R g), straw ( R s), roots in the 0–100 cm depth ( R r), and rhizodeposits ( R e), expressed as estimated C input from each plant part in proportion to total C, varied among crop species. On average, the allocation coefficient for pulse crops ( R g: R s: R r: R e) was 0.24:0.46:0.18:0.12 under low-water, and 0.31:0.47:0.14:0.09 under high-water conditions. For oilseeds, the corresponding values were 0.17:0.58:0.15:0.10 for low-water, and 0.19:0.56:0.15:0.10 for high-water conditions. These C allocation coefficients in oilseeds and pulses should provide modellers with essential tools in quantifying C dynamics and soil C sequestration for agricultural systems involving broadleaved crop species.