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Understanding the grassland nitrogen cycle in order to improve fertiliser recommendations(Previously NT0601) - NT1602

Grazed grassland swards have been shown to be significant sources of nitrate and other forms of N pollution. This study will aim to increase understanding of factors associated with grass swards and their management (sward age, presence of dung and urine and impact of soil organic matter in relation to soil microbial activity) that affect the N balance of the soil in order to predict their impact on nitrate and other losses and provide the means to make reductions via more efficient fertilizer use. The study will be composed of 3 objectives which are outlined as follows, together with ways in which they might be achieved: 1. Effects of sward age on nitrogen cycling processes and losses from grassland. Key nitrogen cycling processes will be examined in soils from grasslands of different ages in order to identify processes which are sensitive to sward age, together with mechanisms involved; 2. Influence of dung and urine patches on nitrate leaching from grassland. The fate of N excreted in the field will be studied in relation to how it is affected by environmental and soil conditions, while modelled estimates of areas affected by excreta under different grazing patterns will allow definition of effects. Spatial characteristics of excreta deposition will also define fertilizer requirements and will resolve difficulties associated with defining optimum fertilizer rate when this is applied as a uniform dressing over a spatially very variable system; and 3. Changes in N status and release in relation to changes in N and C status and associated soil microbial biomass activity. Since soil microbial biomass provides the means of all transformations and much of the transfer of N in soil systems, a range of grassland soils will be studied to assess soil microbial biomass and its role in controlling soil N balances/losses under different conditions. In addition, microbial biomass will be characterised, and controls over its activity will be examined as a way of understanding and manipulating the system in order to reduce losses. Results of the study will further understanding of flows, inputs and losses of N not only from grassland but also from other agricultural systems. The project will also be of relevance to investigations regarding denitrification and ammonia volatilisation as well as nitrate leaching.
Project Documents
• Final Report : Understanding the grassland nitrogen cycle in order to improve fertiliser recommendations(Previously NT0601)   (113k)
Time-Scale and Cost
From: 1995

To: 1998

Cost: £576,878
Contractor / Funded Organisations
Institute of Grassland and Environment Research (IGER)
Fields of Study
Fertilisers and Nitrate Pollution