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Studies of microbial and chemical factors affecting nitrogen release from crop residues - NT1523

Previous studies have demonstrated the importance of the biochemical and physical quality of crop residues on nitrogen mineralization. However, there is a need to understand how other features of the soil environment (e.g. soil organic matter (SOM) and soil microbial population) interact with quality to determine patterns of nitrogen mineralization. This study will investigate how the biochemical composition (quality) of crop residues interacts with key chemical parameters of the soil environment to control residue decomposition and subsequent mineralization of nitrogen. Effects of residue quality and soil environment on metabolic diversity and functional attributes of the soil microbial population will also be investigated in order to determine the value of these measurements as predictors of nitrogen release patterns and to help elucidate the microbial processes underlying nitrogen mineralization. The study will be composed of 3 specific objectives outlined as follows, together with ways in which they might be achieved: 1. Investigation of how the quality of previous residue inputs influences mineralization of nitrogen from subsequent additions, and the duration of any effects. Four residues of contrasting quality will be chosen and may include shoot and root tissues of sugar beet, Brussels sprouts and rye grass; wheat straw will also be included. Residues will be cut into small pieces and incorporated into sandy loam. After 2 and 4 months, soil will be analysed for mineral nitrogen and undecomposed residues. At each of these times, 15N-labelled shoot residues will be mixed into portions of the soil, and N mineralization from newly incorporated residues and pre-existing SOM, as well as residue decomposition, will be measured over the next 3 months; 2. Determination of how crop residue quality interacts with the quality of existing SOM to affect decomposition and nitrogen mineralization. 15N-labelled root and shoot residues of varying quality will be incorporated into soils with low and high SOM, which will be assessed firstly for SOM quality. N mineralization from crop residues and native SOM will then be measured over a period of 4 months; and 3. Investigation of the microbial mechanisms underlying results by examining the effects of treatments on conventional measures of microbial populations, and metabolic functioning and diversity of the microbial community. All samples will be analysed for microbial respiration, and microbial biomass carbon and nitrogen. The origin of biomass nitrogen will be determined and key treatments from the previous experiments will be selected for analysis of microbial diversity and enzyme activities. Data will be analysed statistically to reveal relationships between starting SOM content, nitrogen mineralization, decomposition and microbial parameters. Results of the study will be of value for improving existing methods for predicting mineralization of nitrogen from crop residues, which will assist in the development of new reduced input systems that use nitrogen from these potentially valuable resources more efficiently, reducing the risk of pollution.
Time-Scale and Cost
From: 1998

To: 1999

Cost: £60,415
Contractor / Funded Organisations
Horticulture Research International
Fields of Study
Fertilisers and Nitrate Pollution