NITROGEN INTERACTIONS AND CROP UPTAKE FROM FRESH AND COMPOSTED N-15-LABELED POULTRY MANURE

15N‐labelled poultry excrement was obtained by feeding chickens with 15N‐labelled barley grain. The excrement produced was tested for uniformity of 15N‐labelling; only small variations in the 15N 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. Copyright © 1990, Wiley Blackwell. All rights reserved