The release and plant uptake of nitrogen from some plant and animal manures

Summary Field and laboratory experiments were used to examine the efficiency of N uptake from various manure forms, and at different rates of application. In a field experiment, wheat was grown on soils with different amounts of ¹⁵N-labelled legume residues. The amount of N taken up by the crop was directly proportional to the amount applied, with a recovery of between 15% and 23% of the legume N. In a second field experiment, inorganic N was applied at rates varying from 0 to 120 kg N ha^-1 in the presence and absence of poultry manure. The uptake of N by barley was 11 kg ha^-1 greater in the manured plots when no inorganic N was applied, and 23 kg ha^-1 greater when N was applied at the top rate. N uptake in a pot experiment was again shown to be directly proportional to the rate of manure application, but the amount of N taken up was strongly related to the N content of the manure. An incubation experiment demonstrated that net N mineralisation reached a maximum where residue concentrations were 1,5%. The significance of added nitrogen interactions in the context of manure-N additions is discussed.