Amounts of nitrogen and carbon returned to soil depending on green manure and the effect on winter wheat yield

The trials were carried out during the 2006-08 growing seasons at the Department of Field Crop Husbandry in the Estonian University of Life Sciences. A field experiment was conducted to investigate the effect of green manure treatments on the yield and yield quality of winter wheat. The total phytomass of leguminous green manures ploughed into soil in 2007 varied from 10.3 Mg ha-1 with the birdʹs foot trefoil to 13.9 Mg ha-1 with the white sweet clover. The root mass of legumes comprised 37-54% of the total biomass. The amount of carbon applied into the soil with the green material and roots of legumes varied from 4.43 Mg ha-1 to 5.98 Mg ha-1. The amounts of nitrogen were up to 274 kg of N ha-1. The highest wheat yields were attained in treatments with lucerne and red clover as preceding crops. Compared to the N0 treatment, the extra yield reached 3.26 Mg ha-1 with green manures. Both green manures and mineral fertilizers enhanced the quality of the winter wheat yield, but the results did not vary among different green manures.