Forage yield and biological nitrogen fixation of pea-cereal intercrops for hay production

Intercropping forage pea (Pisum sativum L.) with barley (Hordeum vulgare L.) or oat (Avena sativa L.) is an alternative way of cropping to improve forage yield and quality for hay production compared to monocropping. A 2-year (2016-2017) field study was conducted at three sites in Saskatchewan, Canada, to evaluate forage production and biological nitrogen fixation (BNF) of pea-cereal intercrops in comparison to pea, barley, and oat monocrops with and without 60 kg N ha(-1) fertilization. Barley and oat were dominant (p < 0.001) in the intercrop by accounting for 65%-92% of the total dry matter (DM) yield. Compared to the pea monocrops, pea-cereal intercrops significantly increased forage DM yield at Melfort (52%-73%), Saskatoon (68%-118%), and Swift Current (25%-69%). At Melfort, nitrogen (N) fertilization increased total forage DM yield (p = 0.003) of monocrops and intercrops but it reduced N fixation by 22%-63% (p < 0.01). At Swift Current site, N fixation was reduced by 35%-65% (p = 0.019) when N fertilizer was applied. The total amount of N fixation varied from 18 kg N ha(-1) (Swift Current) to 59 kg N ha(-1) (Melfort), whereas the N transfer rate ranged from 17% (pea:oat) to 43% (pea:barley) in the intercrops. This study indicates that intercropping forage pea with forage barley or oat increased forage DM yield and N fixation. Effect of N fertilization on BNF was site specific, reducing N fixation of pea at two of three sites in the study.