Grass and legume cover crop effects on dry matter and nitrogen accumulation

Careful cover crop management during the spring growth period may allow farmers to maximize dry matter (DM) yield and N accumulation for the subsequent crop. A 2-yr study was conducted to determine the effect of grass and legume cover crops on spring DM production and N accumulation. Each year, cover crops were planted in late August and late September on a loamy, mixed, mesic Humaquept in the Fraser River Delta. Wheat (Triticum aestivum L.), rye (Secale cereale L.), and ryegrass (Lolium multiflorum L.) were planted in monoculture and in mixtures with crimson clover (Trifolium incarnatum L.). Other treatments included pure stand of crimson clover and wheat-hairy vetch (Vicia villosa Roth.) mixture. Cover crop biomass was sampled three times in 1995 and four times in 1996 during the spring growth period. Dry matter accumulation of early planted cover crops increased by 26 to 269% during the spring growth period, ranging between 0.6 Mg ha(-1) for clover and 10 Mg ha(-1) for wheat, wheat-clover, and wheat-vetch treatments. Late-planted cover crops produced between 15 and 75% lower DM yield compared with early planted cover crops. Nitrogen accumulation increased by 3 to 74 kg ha(-1) for early planted crops and by 3 to 47 kg ha(-1) for late-planted crops. Nitrogen accumulation at final spring sampling ranged from 44 to 144 kg ha(-1) for early planted crops and from 10 to 99 kg ha(-1) for late-planted crops. The low C/N ratio of wheat-vetch treatment compared with wheat monoculture at final sampling indicated the potential for vetch to increase the N content of the mixture.