N-MOBILIZATION AND N-IMMOBILIZATION OF CO MPOSTS WITH DIFFERENT INPUTMATERIAL, DEGREE OF DECOMPOSITION AND C N RATIO/

N-mobilization and N-immobilization of 42 composts from different comp ost plants of the district of Northrhine-Westfalia were investigated i n a pot experiment. The composts differed in the composition of the in put material (30 % plant residues/70 % biogarbage; 70 % plant residues /30 % biogarbage; 100 % plant residues), degree of decemposition (fres h compost [fc]; highly matured compost [hmc]) and C/N relation (13/1 t o 28/1). Following results were obtained: While with highly matured co mposts (hmc) the proportion of plant residues had no influence on yiel d formation of ryegrass, with fresh composts (fc) yield decreased with increasing proportions of plant residues. Although the application of hmc with a proportion of 30 % of plant residues resulted in a higher N uptake of the first crop as compared with fc with the same compositi on of the input material, total N uptake of both treatments was the sa me. Caused by N immobilization the application of fresh compost with 7 0 % and 100 % plant residues, respectively, resulted in a lower N upta ke of the first crop as compared with the control. These differences i n N uptake were eliminated in the treatments with hmc after the first cut and in the treatments with fc after the third cut. Highest N explo itation, with a maximum of 7 % of total N applied with compost, was re ached independent of the degree of decomposition in composts with a pr oportion of 30 % plant residues. Especially with fc N delivery was inc reased by an additional N supply. With fc a significant correlation ex isted between the C/N ratio and the hot water soluble N, respectively, and N uptake of ryegrass. This correlation was less pronounced with h mc.