Manipulating nitrogen release from nitrogen-rich crop residues using organic wastes under field conditions

Following mineralization of N-rich crop residues, large amounts of mineral N can be released into the soil. Manipulating N mineralization of crop residues may be an option to reduce NO3- in soil. The potential to manipulate the N release from vegetable crop residues by using organic wastes was tested under field conditions. At the start of the experiment, cauliflower (Brassica oleracea L. var. botrytis L.) residues (similar to 73 Mg fresh matter ha(-1)) together with an immobilizer waste (similar to 5 Mg C ha(-1) of straw, green waste compost, sawdust, or paper sludge) were incorporated into a silt loam soil. After 154 d, a remineralizing waste (similar to 1 Mg C ha 1 of vinasse or dairy sludge) was incorporated. During the field experiment, the mineral N content in the soil was measured at regular time intervals, and net N release, NO3- leaching, and denitrification were simulated using a N mineralization-immobilization model coupled to a NO3- leaching model. Straw, green waste compost, and sawdust were able to immobilize between 54 and 68% of the N released by the cauliflower residues and reduced NO3- leaching by 56 to 68%. Paper sludge released an extra amount of N due to its low C/N ratio. No consistent remineralization of N could be found in any of the treatments, probably due to an unsuitable composition of the remineralizer wastes. Manipulating N release of N-rich crop residues by using organic wastes may be a suitable method to reduce NO3- leaching; however, stimulating remineralization of immobilized N by the start of the following spring may not be easy to achieve.