Nitrogen Release from Leaves and Prunings of Different Tree Species Used as Green Manures

Abstract

ABSTRACT A pot trial and an incubation trial were carried out simultaneously in a greenhouse to determine the effect of N, lignin and polyphenol contents of leaves and prunings of various decidious trees (Alnus incarta (L.) Moench, Alnus glutinosa (L.) Gaertn., Salix viminalis L., Populus trichocarpa Hook x Populus deltoides Marsh.) and white clover (Trifolium repens L.), added to soil as green manures, on N mineralization and crop production. Mixing residues of different quality was considered as a way to improve synchrony between N release and crop demand for N. Material with “lower quality” (high C:N ratio, lignin and polyphenol level) decreased yield and N utilization efficiency. The lignin content exerted a much greater influence on N mineralization than did phenolics. The best predictor of N utilization efficiency was the (lignin+phenol):N ratio but significant relationships were also found with the C:N, lignin:N and phenol:N ratios and initial lignin content. A mixture of white clover with grey alder leaves and prunings gave practically the same barley yield and net N mineralization as white clover alone. The mixing of low and high quality residues could thus be a way of increasing yield and at the same time enhance organic matter build up.