Influence of rates and timing of biowaste compost application on rye yield and soil nitrate levels

Beneficial use of biowaste compost depends on identifying an application strategy that optimizes crop yield and minimizes nitrate leaching, soil compaction and labor. The effects of applying the same total quantity of biowaste compost in different doses and in different intervals were assessed in a randomized 5–year field trial with permanent rye. Biowaste compost (from source-separated organic household waste and yard trimmings) was applied either at 20 t ha–1 (fresh matter) annually, or at 40 t ha–1 every second year, or at 60 t ha–1 every third year, or at 60 t ha–1 in two consecutive years, or at a single dose of 70 t ha–1. The application of 40 t ha–1 in 2-year-intervals resulted in slightly higher rye yields than the other treatments. However, the differences between the treatments were not statistically significant. In the treatment receiving 20 t ha–1 annually, yields increased after 4 years for the first time. The baking quality of the rye was good in all treatments. The treatments receiving 20–40 t ha–1 per single application showed smaller amplitudes in the soil nitrate-nitrogen levels in autumn than the treatments receiving 60 t ha–1. Nevertheless, nitrate-nitrogen levels (0–90 cm) in autumn were at maximum 49 kg ha–1 higher in these treatments than in the untreated control. Based on yield and soil nitrate-N contents, no justification was found to legislate a reduction in the amount of a single application to as low as 20 t ha–1.