Yields and nutrient budgets under composts, raw dairy manure and mineral fertilizer

Composts made from rural and urban residues are increasingly available. Farmers wishing to use these materials need to know how they will perform as crop nutrient sources. The objectives of this field experiment were to evaluate compost as an N source, and to track the effects of compost application on NPK budgets. Four composts of various feedstocks, maturity, and nutrient content were compared to raw dairy manure (RDM) and conventional mineral fertilizer (CNV). A 3-year rotation of corn (Zea mays L.), bell pepper (Capsicum annum), and small grain was established, with all crops present every year. Treatments were applied on an N-equivalent basis, using a 40% availability factor for compost and 50% for RDM. Yields from compost-amended corn were comparable to RDM and CNV by the second year. Pepper, a less N-demanding crop, had no significant yield differences among treatments for the three years. The manure-based compost treatments had the highest P and K surplus after three years, showing that loading levels of these nutrients need consideration when using compost to satisfy crop N needs. Rotations can be designed to extract more P and K, but more practical for the long-term would be reducing compost additions and substituting an additional N source such as a legume.