Response of pea to rhizobia inoculation and starter nitrogen in Alberta

The introduction of new semileafless cultivars has contributed to the rapid expansion of pea (Pisum sativum) on the Canadian prairies. To determine the response of four new semi-leafless cultivars to rhizobia inoculation and starter fertilizer N, 58 field trials were conducted from 1995 to 1998 over a wide geographic region of Alberta. However, due to possible cross-contamination in 1995 and 1996 between inoculated and uninoculated treatments, average inoculation responses were only determined for the 22 trials conducted in 1997 and 1998. Rhizobia inoculation increased seed yield in 9 of the 22 trials by an average of 14%. The frequency of an inoculation benefit was only slightly higher (45% vs. 38%) on land with no history of legumes (n = 11) than on land that had grown a legume crop (n = 8), but the magnitude of the inoculation benefit was appreciably greater (19 vs. 5%) on land with no history of legumes. A significant interaction of inoculation with pea cultivar was observedin 6 of 22 trials: Majoret pea was the most responsive cultivar to inoculation while Baroness pea was the least responsive. Application of N fertilizer (20, 40 or 60 kg N ha–1) increased pea yield in 24% of the 58 trials conducted by an average of 9%. When spring soil NO3-N to 30cm was less than 20 kg N ha–1, application of N fertilizer increased pea yield in 33% of the trials by an average of 11% (n = 12). The modest benefits of rhizobia inoculation or starter N fertilizer in most trials, despite appreciable deficits between spring soil NO3-N and accumulation of N by pea, was likely due to adequate nodulation of pea by indigenous rhizobia.