Clover green manure productivity and weed suppression in an organic grain rotation

Abstract

AbstractGreen manure crops must produce high biomass to supply biological N, increase organic matter and control weeds. The objectives of our study were to assess above-ground biomass productivity and weed suppression of clover (Trifoliumspp.) green manures in an organic soybean [Glycine max(L.) Merr.]-winter wheat (Triticum aestivumL.)-corn (Zea maysL.) rotation in eastern Nebraska in three cycles (2011–12, 2012–13, 2013–14). Treatments were green manure species [red clover (T. pratenseL.) and white clover (T. repensL.)] undersown into winter wheat in March and green manure mowing regime (one late summer mowing or no mowing). We measured wheat productivity and grain protein at wheat harvest, and clover and weed above-ground biomass as dry matter (DM) at wheat harvest, 35 days after wheat harvest, in October and in April before clover termination. Winter wheat grain yields and grain protein were not affected by undersown clovers. DM was higher for red than for white clover at most sampling times. Red clover produced between 0.4 and 5.5 Mg ha−1in the fall and 0.4–5.2 Mg ha−1in the spring. White clover produced between 0.1 and 2.5 Mg ha−1in the fall and 0.2–3.1 Mg ha−1in the spring. Weed DM was lower under red clover than under white clover at most sampling times. In the spring, weed DM ranged from 0.0 to 0.6 Mg ha−1under red clover and from 0.0 to 3.1 Mg ha−1under white clover. Mowing did not consistently affect clover or weed DM. For organic growers in eastern Nebraska, red clover undersown into winter wheat can be a productive green manure with good weed suppression potential.