Nitrogen contribution of field pea in annual cropping systems .2. Total nitrogen benefit

The total nitrogen (N) benefit of field pea (Pisum sativum) to a succeeding non-legume crop was measured in a small plot experiment at Scott, Saskatchewan in the moist Dark Brown soil climatic zone, and in a small plot and landscape experiment near Melfort, Saskatchewan in the moist Black soil climatic zone from 1993 to 1995. The total N benefit was calculated as the difference in net N mineralized from soil plus N in the above-and below-ground crop residue between field pea and non-legume stubble-cropped plots over the growing season. Landscape slope position did not affect the total N benefit of field pea to a succeeding wheat crop, and preseeding tillage had an inconsistent effect on the total N benefit between years. The direct N benefit of field pea aboveground residue available to the succeeding crop in the landscape experiment was a minor component of the total N benefit, which averaged 25 kg N ha(-1). The total N benefit was equivalent to the N residual effect, defined as the amount of fertilizer N required for a non-legume crop grown on non-legume stubble to achieve the same yield as that of the non-legume crop on field pea stubble. This confirms that the N residual effect of field pea to the succeeding non-legume crop was due to the N contribution; any non-N contribution to the N residual effect was effectively excluded.