Response of pea to rhizobia inoculation and starter nitrogen in Alberta

The introduction of new semi-leafless cultivars has contributed to the rapi d expansion of pea (Pisum sativum) on the Canadian prairies. To determine t he response of four new semi-leafless cultivars to rhizobia inoculation and starter fertilizer N, 58 field trials were conducted from 1995 to 1998 ove r a wide geographic region of Alberta. However, due to possible cross-conta mination in 1995 and 1996 between inoculated and uninoculated treatments, a verage inoculation responses were only determined for the 22 trials conduct ed 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 o f the inoculation benefit was appreciably greater (19 vs. 5%) on land with no history of legumes. A significant interaction of inoculation with pea cu ltivar was observed in 6 of 22 trials: Majoret pea was the most responsive cultivar to inoculation while Baroness pea was the least responsive. Applic ation 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 30 em was less than 20 kg N ha(-1), application of N fertilizer increased p ea yield in 33% of the trials by an average of 11% (n = 12). The modest ben efits of rhizobia inoculation or starter N fertilizer in most trials, despi te appreciable deficits between spring soil NO3-N and accumulation of N by pea, was likely due to adequate nodulation of pea by indigenous rhizobia.