Row Configuration and Nitrogen Application for Barley–Pea Intercropping in Montana

Intercropping barley ( Hordeum vulgare L.) with Austrian winter pea ( Pisum sativum ssp. arvense L. Poir) may increase the use efficiencies of growth resources and reduce fertilizer N requirements. The objectives of this study were to determine (i) row configuration and (ii) fertilizer N effects on yield, protein content, and the land equivalent ratio (LER) of barley–pea intercropping systems. A 3‐yr barley–pea intercropping study was conducted at the Western and Central Agricultural Research Centers (WARC and CARC) of Montana State University from 2000 to 2002 with three row configurations (4 rows barley × 4 rows pea, 2 rows barley × 2 rows pea, and barley–pea mixed within rows) and three N application treatments (0, 67, and 134 kg N ha −1 ). Barley biomass production increased 41% at WARC and CARC, whereas pea biomass production decreased 34% at WARC and 46% at CARC with the row configuration changing from the 4 × 4 to the mixed configuration. The LER ranged from 1.05 to 1.24 on a biomass basis and from 1.05 to 1.26 on a protein basis, indicating a production advantage of intercropping. Barley is a more competitive component than pea. Separated row arrangements are advantageous where the desired outcome is a greater pea component in the harvested forage, but the mixed arrangement has a greater total biomass yield and LER. Fertilizer N increased total biomass yield and protein level in barley–pea intercrops, but high N rates could decrease the LER and result in toxic levels of nitrate in the forage.