YIELD, NUTRIENT UPTAKE, NITROGEN FIXATION AND RELEASE BY SOYBEAN, PEA, AND LENTIL AND IMPACT ON FOLLOWING CROPS IN ROTATION IN SASKATCHEWAN, CANADA

As soybean acreage is expanding in western Canada, research is required to assess soybean production regarding the yield, nutrient uptake, N2 fixation, and the effects on following crops under local soil-climatic conditions. Through a two-year rotation study conducted at four sites in the Black and Dark Brown soil zones in Saskatchewan, Canada, this research aimed to estimate the grain and straw yield, nutrient uptake, and N2 fixation of three short-season soybean varieties in comparison to three pea and three lentil varieties, and the effects on the yield, nutrient uptake, and residue N recovery by following wheat and canola crops grown on the stubble of soybean, pea, or lentil. Soil nutrient supply rates and greenhouse gas emissions as influenced by soybean, pea, and lentil residues were also estimated in this research. Soybean produced similar or higher grain yield (2512 kg ha-1) and nutrient uptake (112 kg N ha-1 and 14 kg P ha-1), and had similar effects on soil macro- and micronutrient availability to the following crops in comparison to pea and lentil. Lentil generally had lower grain yield yet similar rotational effects across the sites. Compared to pea and lentil, soybean had significantly higher K, Ca, Mg, and S concentrations in the grain across the sites, and similar or larger removal of these nutrient elements, suggesting potential for additional depletion of these elements from the soil over the long-term when soybean is grown. At maturity, soybean, pea, and lentil fixed similar amount of N in the above-ground plant components (grain + straw), with the majority (67-85%) of fixed N retained in the grain of soybean (119 kg N ha-1), pea (160 kg N ha-1), and lentil (89 kg N ha-1). Nitrogen derived from fixation comprised over 60% of the total above-ground N of the pulse crops. Soybean, pea, and lentil stubbles demonstrated similar effects on greenhouse gas emissions and soil N and P supplies measured under both field and controlled conditions. Overall, this research suggests promising prospects for soybean production under the soil-climatic conditions in the northern Great Plains, with considerations for soil P and K depletion in the long term when soybean is grown, although similar short-term effects on yield and nutrition of following crops were observed from soybean, pea, and lentil grown under similar conditions