Nitrogen contribution of field pea in annual cropping systems. 1. Nitrogen residual effect

The nitrogen (N) residual effect of field pea (Pisum sativum L.) to a succeeding non-legume crop was determined 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 N residual effect, defined as the amount of fertilizer N required for a non-legume crop grown on non-legume stubble to produce the same yield as that of the non-legume grown on field pea stubble, averaged 27 and 12 kg N ha−1 at Melfort and Scott, respectively, in the small plot experiment, and 28 kg N ha−1 in the landscape experiment. Landscape slope position and preseeding tillage did not have a significant or consistent effect on the magnitude of the N residual effect of field pea to the succeeding non-legume crop. The N residual effect, calculated using the difference (economic N rate) method, was presumably due solely to the N benefit, with no non-N benefit contribution. The non-N benefit was effectively marginalized when the crop sequence that included field pea was compared with a reference rotation that included a cereal and an oilseed crop. Based on field pea seed yields and the calculated N residual effect, the N credit (N fertilizer replacement value) of field pea to a succeeding non-legume crop in the moist Black soil climatic zone was 15 kg N ha−1 for every 1000 kg of seed. This is slightly higher than the current recommendation of 5 to 10 kg N ha−1 1000 kg−1 seed. Results from the small plot experiment at Scott indicate that current N credit recommendations for field pea are appropriate for the moist Dark Brown soil climatic zone.