Impact of long-term compost amendments on soil fertility, soil organic matter fractions and nitrogen mineralization

Soil organic matter (SOM) is a major carbon (C) pool and can play a significant role in C mitigation measures. It is also a crucial factor for several soil physical properties and a major nutrient source for crops. To obtain an understanding of the changes that occur in the soil following long‐term annual compost application, the Soil Service of Belgium started a long‐term field trial in Boutersem, Belgium, in 1997. Here, 12 different treatments (fallow, unfertilized, mineral fertilized and nine compost treatments differing in intensity from 15 to 45 t ha‐1 and in application frequency from annual to every 3 years) were implemented in four repetitions. All compost‐amended treatments partially substituted the mineral nutrient requirements of the crop and had a positive influence on soil chemical and physical parameters. The continued application of compost also has important effects on the amount and distribution of SOM. To quantify this, soil samples from five treatments were divided into seven fractions differing in physical and biochemical protection levels of the associated SOM. Not only did the total amount of C in the amended soils increase significantly over the course of the experiment, it also increased specifically in the less‐protected SOM fractions. These results were combined with a 217‐day‐long incubation experiment to investigate the influence of long‐term compost fertilization, causing an altered SOM distribution, on soil respiration and nitrogen mineralization.