Optimal seeding rate for organic production of field pea in the northern Great Plains

Abstract

Seeding rates have not been established for organic production of field pea in the northern Great Plains and producers must rely upon a recommended target stand of 88 plants m-2 for conventional production of this crop. This seeding rate may not be suitable as the two systems differ in the use of inputs and in pest management. The objective of this study was to determine an optimal seeding rate for organic production of field pea considering a number of agronomic factors and profitability. Field sites were established using a randomized complete block design with increasing seeding rates, summerfallow and green manure treatments. Seed yield increased up to 1725 kg ha-1 with increasing seeding rate. Weed biomass decreased with increasing seeding rate by up to 68%. Post-harvest soil phosphorus levels and soil water storage did not change consistently between treatments. Post-harvest soil inorganic nitrogen (N), however, was higher for the summerfallow and green manure treatments than for the seeding rate treatments. Field pea reached a maximum economic return at a seeding rate of 200 seeds m-2 and an actual plant density of 120 plants m-2. Organic farmers should increase the seeding rate of field pea to increase returns and provide better weed suppression. Key words: Pea (field), organic, seeding rate, weed suppression, profit, soil N