Do green manures as winter cover crops impact the weediness and crop yield in an organic crop rotation?

The effects of different winter cover crops and their combination with composted cattle manure on weeds and crop yields were investigated within a five-field crop rotation (barley undersown with red clover, red clover, winter wheat, pea, potato) in three organic cropping systems. The control system (Org 0) followed the rotation. In organic systems Org I and Org II the winter cover crops were used as follows: ryegrass (Lolium perenne L. in 2011/2012) and a mixture of winter oilseed-rape (Brassica napus ssp. oleifera var. biennis) and winter rye (Secale cereale L.) in 2012/2013 before pea; winter oilseed rape before potato and winter rye before barley. In Org II system composted cattle manure was also applied. In comparison with the control system, the winter cover crops, depending on plant species used, reduced the biomass and density of the weeds. In both years winter rye was a better suppressor of weeds than the other winter cover crops. Cover crops increased the yield of potato in rotation crops. When used together with composted cattle manure the cover crops caused significant yield increase in cereals.