Decomposition and nitrogen dynamics in vegetable crop residues with contrasting biochemical composition

Abstract

Abstract Aim To improve nitrogen (N) use efficiency in vegetable-growing systems, the characteristics of N-release from vegetable crop residues needs to be better understood. This study aimed to quantify the decomposition rate and the contribution of decomposition to mineral N supply from residues of commonly grown vegetable crops. Methods The rate of decomposition and N release from nine vegetable residues was quantified in a laboratory incubation with barley straw included for comparison. Dried and ground residue material was incorporated into soil at a rate of 1% w/w and incubated at 90% of field capacity for 118 days at 15°C. CO2 production and soil mineral N concentrations were determined periodically during the incubation. Results Decomposition of the vegetable residues was rapid, with 29–46% of residue-C respired as CO2 in the first week of incubation (vs 10% of barley straw C). The decomposition data fitted an exponential decay model with evidence of fast and slow pools of decomposable-C in all residues. The effect of residue addition to soil ranged from N immobilisation to net N mineralisation over the course of the incubation with the proportion of N released or immobilised linearly related to residue total N. Conclusions With residue total N and residue-soil contact time as input variables, a simple model provided good predictions of N release from vegetable crop residues under controlled conditions in the laboratory. It is important however, that our predicted residue N release rates be validated under field conditions before being used to guide N use decisions.