Phosphorus and potassium release during decomposition of roots and shoots of green manure crops

Decomposition rates of above- and underground biomass and the dynamics of the remaining phosphorus (P) and potassium (K) were studied in trials at the Estonian University of Life Sciences (58°23′N, 26°44′E) in Nordic conditions. The research focused on the decomposition of roots and leaves/shoots of green manure plants. In shoot residues of bird's-foot trefoil and white melilot, after 6 months 19% and 20%, respectively, of P remained. Red clover shoots decomposed the slowest, remaining 44% of P in the residue. In a year, legumes remained 20–22% of initial organic P and 11% in 2 years. Rapid release of K from legume shoot residue occurred in 6 months. The roots released K in a period lasting from 6 to 12 months. The roots retained 15–32% K over a year. White clover roots were the slowest in K release. Residue decomposition and P, K release were all influenced by weather conditions.