Allantoin-N concentration changes and analysis of the influencing factors on its changes during different manure composting

Allantoin is one of important nitrogenous compounds in manure. In this study, the simulation experiment of aerobic composting was adopted to explore concentration changes, degradation and relevant influencing factors of allantoin-N during six manure composting. The result showed that the allantoin-N concentration was markedly different among different manures. The various livestock and poultry excreted 1.92–11.14 g kg−1 allantoin-N which accounted for 9.98–32.27% of the total excreted nitrogen. The changing trend of the allantoin-N concentration firstly increased (for 0–14 days), then decreased (for 14–70 days) during different manure composting, and the allantoin-N concentration after composting was lower than the initial allantoin-N concentration in all manure composting. During allantoin degradation for 14–70 days of composting, the half-life of allantoin-N was 57.76 days in broiler manure, 46.21 days in layer-hen manure, 27.73 days in hog manure, 25.67 days in sow manure, 38.51 days in young pig manure and 15.75 days in dairy manure, and the sequence in the half-life was chicken manure > pig manure > dairy manure. Allantoin degradation conformed to first-order kinetics. Through the correlation analysis, hippuric acid, hydrolyzable nitrogen, amino acid–nitrogen, HUN fraction, NO3-–N and total hydrolyzable nitrogen could be closely related to allantoin-N transforming during composting. Humification could be the main influencing factor for reducing allantoin-N concentration during composting.