Assessing long term effects of compost fertilization on soil fertility and nitrogen mineralization rate

Background: Fertilization with organic waste compost can close the nutrient cycles between urban and rural environments. However, its effect on yield and soil fertility must be investigated. Aim: This study investigated the long-term effect of compost on soil nutrient and potentially toxic elements (PTEs) concentration, nutrient budgets, and nitrogen (N) mineralization and efficiency. Methods: After 21 years of annual compost application (100/400 kg N ha–1 year–1 [100BC/400BC]) alone and combined with mineral fertilization, soil was analyzed for pH, organic carbon (SOC), nutrient (total N and P, Nmin, extractable CAL-P, CAL-K, and Mg), and PTE (Cu, Ni, Zn) concentrations. Yields were recorded and nutrient/PTE budgets and apparent netmineralization (ANM, only 2019) were calculated. Results:Nefficiency was the highest in maize and formineral fertilization. Compost application led to lower N efficiencies, but increased ANM, SOC, pH, and soil N, and surpluses of N, P, and all PTEs. Higher PTE concentrations were only found in 400BC for Cu. Nutrient budgets correlatedwith soil nutrient concentration. A surplus of 16.1 kg P ha–1 year–1 and 19.5 kgKha–1 year–1 resulted in 1mg kg–1 increase in CAL-P and CAL-K over 21 years. Conclusion: Compost application supplies nutrients to crops with a minor risk of soilaccumulation of PTEs. However, the nutrient stoichiometry provided by compost does not match crop offtakes causing imbalances. Synchronization of compost N mineralization and plant N demand does not match and limits the yield effect. In winter wheat only 65–70% of Nmineralization occurred during the growth period.