Nitrogen interactions and crop uptake from fresh and composted 15 N‐labelled poultry manure

SUMMARY 15 N‐labelled poultry excrement was obtained by feeding chickens with 15 N‐labelled barley grain. The excrement produced was tested for uniformity of 15 N‐labelling; only small variations in the 15 N content were found, indicating uniform labelling. The excrement was mixed with straw to produce manures which were used in a pot experiment measuring uptake of labelled and unlabelled N by ryegrass from the mixture in both a fresh form and after a period of composting. Interactions of N pools differed between the two materials. Addition of composted manure to soil caused a larger uptake of unlabelled N by ryegrass, whereas fresh manure caused a smaller plant uptake of unlabelled N. The proportion of plant N coming from labelled N from fresh manure was 25.7% and from composted manure 3.8%. However, the contributions of the two manures to plant uptake of total N were 15.5% and 13.8%, respectively. The fresh manure, being a mixture of excrement and straw, is considered as a two‐component material, whereas composted manure is considered as a single component. It was concluded that the increase or decrease in the quantity of unlabelled, soil‐derived N in plants after manure addition was related to the amount of energy available in the different manures.