Yield and Uptake of Phosphorus by Wheat and Canola Grown after Two Years of Forage Legume and Annual Crops

Abstract

Annual legumes have been shown to enhance the growth and phosphorus (P) uptake by following rotational crops. However, there is lack of information on the effect of perennial forage legumes included in rotation for a short duration on yield and P uptake of crops like wheat ( <i> Triticum aestivum </i> L.) and canola ( <i> Brassica napus </i> L.) grown after the forage legume. A field study was conducted in four soil zones of Saskatchewan, Canada to assess: 1 ) the effect of two years of forage legume versus annual cereal, oilseed and grain legume on yield and P uptake of wheat and canola grown in the two subsequent years and 2 ) the effect of the complete four-year rotation on soil P dynamics and P balance. Four different crop sequences (alfalfa-alfalfa, red clover-red clover, barley-pea and barley-flax) employed over the first two years of crop rotation were compared as treatments followed by wheat and canola. Wheat grain yield was improved 32% - 60% by alfalfa ( <i> Medicago sativa </i> L.) and red clover ( <i> Trifolium pretense </i> L.) rotations at three of the four sites (P = 0.008, P = 0.001, P < 0.0001) compared to annual grains, while grain P uptake was enhanced 38% - 43% by red clover and alfalfa rotation at two sites (P = 0.013, P = 0.033). In the following year, positive yield benefits (55% - 64%) of having two years of alfalfa and red clover were observed at three sites. Four years of continuous cropping with a limited addition of fertilizer P resulted in a negative soil P balance and significant depletion of soil P fertility at all locations.