Effects of five non-agricultural organic wastes on soil composition, and on the yield and nitrogen recovery of Italian ryegrass

We studied the effects of five diverse non-agricultural organic wastes on soil composition, grass yield and grass nitrogen use in a 3-year field experiment. The applied wastes were distillery pot ale, dairy salt whey, abattoir blood and gut contents, composted green waste (two annual applications each), and paper-mill sludge (one annual application). With the exception of N immobilization in the paper-mill sludge treatment, the wastes had no unfavourable effects on the soil. In the 2-year treatments, grass dry matter yields from the abattoir and distillery wastes (26.3 t ha^-1) were larger than those from a NH₄NO₃ fertilizer treatment (24.3 t ha^-1) and from the dairy waste (20.4 t ha^-1) and composted waste (22.8 t ha^-1). Yield and N recovery were impaired markedly after the single application of paper-mill sludge, both in the year of application and in the following year. The results demonstrated clear differences in the ability of the applied wastes to provide crop-available N. We conclude that in order to improve prediction of both the benefits and risks from waste recycling to land, more information should be gathered on soil/waste/crop interactions.