Crop nitrogen recovery and soil nitrogen dynamics in a 10-year field experiment with biowaste compost

When fertilizing with compost, the fate of the nitrogen applied via compost (mineralization, plant uptake, leaching, soil accumulation) is relevant both from a plant-production and an environmental point of view. In a 10-year crop-rotation field experiment with biowaste-compost application rates of 9, 16, and 23 t ha(-1) y(-1) (f. m.), the N recovery by crops was 7%, 4%, and 3% of the total N applied via compost. Due to the high inherent fertility of the site, N recovery from mineral fertilizer was also low. In the minerally fertilized treatments, which received 25, 40, and 56 kg N ha(-1) y(-1) on average, N recovery from mineral fertilizer was 15%, 13%, and 11 %, respectively. Although total N loads in the compost treatments were much higher than the N loads applied with mineral fertilizer (89-225 kg N-tot ha(-1) y(-1) vs. 25-56 kg N-tot ha(-1) y(-1); both on a 10-year mean) and the N recovery was lower than in the treatments receiving mineral N fertilizer, soil NO3- -N contents measured three times a year (spring, post-harvest, autumn) showed no higher increase through compost fertilization than through mineral fertilization at the rates applied in the experiment. Soil contents of N-org and C-org in the plowed layer (0-30 cm depth) increased significantly with compost fertilization, while with mineral fertilization, N-org contents were not significantly higher. Taking into account the decrease in soil N-org contents in the unfertilized control during the 10 years of the experiment, 16 t compost (f. m.) ha(-1) y(-1) just sufficed to keep the N-org content of the soil at the initial level.