Effect of long-term compost application on yield and soil fertility

In a field trial run for 20 years the long-term effects of compost application on yield and soil fertility were studied. Compost was applied in amounts of 40-45 t/ha (dry matter) every third year for a period of 12 years, followed by an amount of 15 t/ha every year for the last 8 years. Compost application caused higher yields for all crops and increasing nitrogen mineralisation in the course of time. In the loamy soil without additional mineral fertilizing 16 % of the applied compost-N were found in the yield of the first rotation. In the last rotation this percentage rose to 40 %. The efficiency of compost-N was slightly lowered when mineral N-fertilizer was given additionally. Compost application accumulates organic matter and nutrients in the soil, improves soil structure and raises pH-values. In order to maintain the organic matter content of the soil about 7 t of compost (dry matter) are sufficient on condition that straw and leaf of beats have been removed.