Green manure as a nutrient source for succeeding crops.

The trials were carried out in the Estonian University of Life Sciences (58°23'N, 26°44'E), and studied to what extent green manure crops bind nutrients and the effect and stability of biologically fixed nitrogen (N). Our research covered more species than most of the earlier studies in the Nordic countries. Compared with biomass from unfertilized barley, legume undersowing, straws plus roots added up to 4 times more N, 2.8 times more phosphorus (P) and 2.5 times more potassium (K) returning to the soil. Red clover, hybrid lucerne and white melilot as pure sows produced the highest biomass, amounts of N, P, and K being up to 206, 24 and 144 kg/ha, respectively. The effect of additional N in soil was measured by weighing successive grain yields. In the first test year, 1 kg of N from green manure had the effect of producing 8.6 kg grain and this relation did not change even for higher N amounts. Green manure had a significant effect even in the third year after the green manure was ploughed into soil.