Yield Advantage and Nitrogen Economy of Annual Crops Following Biennial Forage Legumes in the Cropping Systems.

Key words: Cropping system, crop rotation, Red Clover, Alsike Clover, annual crops, nitrogen

High root to shot ratio and nitrogen assimilating properties of forage legumes impart a basis for sustaining productivity and profitability of the cropping systems. In the Peace River region of Canada, the acreage under forage seed crops is declining in favour of annual crops, which can compromise the resiliency of the cropping systems. A crop rotation study involving various forages and annual crops was initiated in 2013 to evaluate the relative merits of various cropping sequences. The agronomic benefits of rotations integrating biennial forage legumes for seed production were evident in the succeeding plots of wheat. Replicated field research plots of wheat receiving no fertilizer following biennial stand of either red or alsike clover grown for seed produced significantly higher grain yields compared to rotations where wheat was preceded by annual crops such as peas, wheat, barley or canola. In the absence of a supplemental nitrogen application, wheat plots preceded by biennial stand of red clover produced yield increases of 31% (968 kg ha^-1) and  41% (1213 kg ha^-1) compared to wheat plots preceded by pea-barley and wheat-canola sequences respectively. Similarly, wheat plots preceded by biennial stand of alsike clover produced yield increases of 24% (760 kg ha^-1) and 35% (1004 kg ha^-1) compared to wheat plots preceded by pea-barley and wheat-canola sequences respectively. The biennial legume seed crops of red and alsike clovers replaced the nitrogen fertilizer requirement for succeeding wheat crop by at least 90 kg ha^-1.  Preliminary results of soil fertility indicators contributing to the cropping systems productivity will also be highlighted.