Cover Crop Mixture Proportion and Starter Fertilizer Effects on Weed Competition and Yield in Organic Rotational No-till Maize Production.

Cereal and legume cover crop mixtures can be utilized in organic no-till maize production for fertility provision and weed suppression. In order to maximize maize yield without compromising the weed suppressive ability of the cover crop mulch, additional N fertility may be necessary. This study was conducted to evaluate weed competition and maize yield following varying cover crop mixture proportions of cereal rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth) receiving different starter fertilizer treatments. This experiment was employed at the USDA-ARS Beltsville Agricultural Research Center during the 2013 and 2014 maize growing seasons. Five cover crop mixture proportions of rye:vetch (100:0, 80:20, 60:40, 20:80, 0:100) were evaluated. Cover crops were terminated with a roller-crimper prior to maize establishment. Starter fertilizer treatments were applied at maize establishment to all cover crop mixture proportions and included broadcast poultry litter, subsurface banded pelleted poultry litter, and no added fertility. Cover crop mixture proportion affected cover crop biomass, with the lowest cover crop biomass observed with the 0:100 rye:vetch proportion in both years. Cover crop mixture proportion but not starter fertilizer treatment affected weed biomass.  The highest weed biomass was observed with the 0:100 rye:vetch proportion, while weed biomass tended to be similar among the other rye:vetch proportions. Cover crop mixture proportion affected maize yield in both years, with maize yield generally increasing as vetch proportion in the cover crop mixture increased. The lowest maize yield was observed where no vetch was included in the cover crop mixture.  Maize yield was similar among starter fertilizer treatments within each rye:vetch proportion, indicating that N release from cover crop mineralization had a larger effect on yield than starter fertilizer treatment at these environments. While the 0:100 rye:vetch proportion provided for high maize yield, weed suppression may be compromised by low levels of cover crop biomass and hairy vetch seed costs could be economically limiting to producers.  The 20:80 and 60:40 rye:vetch proportions may be more desirable selections for producers to achieve both weed suppression and high maize yield.