Yield and Agronomic Advantages of Pea Leaf Type Mixtures under Organic Management

Field pea (Pisum sativum L.) is an important organic crop due to its contribution to soil fertility and other rotational benefits. Leafed (wild-type) pea cultivars tend to be more weed suppressive, but their poor standing ability limits yield compared with semi-leafless cultivars. Crowing mixtures of leafed and semi-leafless cultivars may improve weed suppression and yield compared with monocultures of the same cultivars by altering canopy morphology. To test this hypothesis, replicated field experiments were conducted under weedy, organic conditions in Saskatchewan, Canada, in 2011 and 2012. Mixtures of a leafed and semi-leafless cultivar, CDC Sonata and CDC Dakota, were sown in ratios of 0:100, 25:75, 50:50, 75:25, and 100:0 leafed to semileafless pea, at target seeding rates of 88 and 132 plants m(-2). :Mixtures that included 50% or more semi-leafless pea had similar lodging resistance and weed biomass suppression to the agronomically superior semi-leafless cultivar grown alone. The strong competitive ability of the semi-leafless cultivar was unexpected based on previous accounts. The combined yield of the two cultivars grown in a 75% semi-leafless mixture exceeded the seed and biomass yield of either single cultivar by at least 18 and 12%, respectively. Yield enhancement was attributed to the leafed cultivar, whose seed yield increased by more than two and a half times in this mixture relative to its monoculture. Results suggest that breeding of leafed cultivars specifically for mixture with semi-leafless pea may be a future source of yield gains in organic and low-input systems.