The effects of pure and undersowing green manures on yields of succeeding spring cereals.

A field experiment was conducted in 2004-2006 to investigate the effect of green manure treatments on the yield of oats and spring barley. In the experiment, different green manure crops with undersowing and pure sowing were compared for amounts of N, C, and organic matter driven into soil and their effect on cereal yield. The spring barley field had a total of 41.7-62.4 kg N ha-1 and 1.75-2.81 Mg C ha-1 added to the soil with straw, weed, and roots, depending on the level of fertilisation; with red clover, and both common and hybrid lucerne undersowing, with barley straw and roots, the values were 3.45-3.96 Mg C ha-1 and 139.9-184.9 kg N ha-1. Pure sowings of these three leguminous green manure crops had total applications of 3.37-4.14 Mg C ha-1 and 219.7-236.8 kg N ha-1. The mixed and pure sowing of bird's-foot trefoil provided considerably less nitrogen and carbon to the soil with the biomass than with the other leguminous crops. Application of biomass with a high C/N ratio reduced the yield of the succeeding spring cereals. Of the green manures, the most effective were red clover and both common and hybrid lucerne, either as undersowing or as pure sowing. Undersowings with barley significantly increased the N supply for the succeeding crop without yield loss of the main crop compared with the unfertilised variant. Compared with ploughing-in of green manure in autumn, spring ploughing gave a 0.2-0.57 Mg ha-1 larger grain yield. [ABSTRACT FROM AUTHOR]