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Guidelines for improved nitrogen fertiliser recommendations for grassland and forage crops - NT1601

Current recommendations for application of N fertilizers, which are designed to prevent nutrient pollution from agriculture and leaching of nitrates into watercourses, do not consider precisely enough the N supply from the soil and other sources, or crop demand. This study will aim to produce new guidelines regarding N fertilizer applications by integrating predictive modelling with soil experiments, in order to define N fluxes in grassland soils in relation to plant demand and use, and removal by loss processes. The project will be composed of 10 objectives which are outlined as follows: 1. Specification of a soil mineral N flux model under different grassland management schemes. The system will include effects of previous fertilizer and manure inputs, grazing returns, soil type and yield potential, which will require development of a series of sub-models; 2. Use of the N flux model to define total N supply and temporal distribution of mineral N according to management, soil climate and weather, with regard to a range of target levels of production and nitrate leaching criteria. Fertilizer requirements will be defined for each target; 3. Use of the N flux model to derive mineral N profiles (defined quantities of nitrates and ammonium in the soil), specifying the supply/output balance for each month which corresponds to a range of economic and/or environmental targets; 4. Determination of soil N supply by measurement of soil mineral N, crop uptake and N status and growth responses on a number of intensively monitored sites. Relationships derived in the model will also be tested on these sites. In addition, regulation of soil mineral N will be examined by adjusting fertilizer inputs according to the balance between measured N and expected uptake, and their effects on yield and nitrates will be measured; 5. Relationships between site history, soil N supply, crop demand and crop responses will be examined on a wide range of sites so that a series of prototype N-efficient fertilizer strategies can be assembled. These will be applied and evaluated using both modelling and soil testing. Nitrate leaching risk will also be measured over winter using porous cups or spring mineral N measurements; 6. Further development of soil testing approaches for ease and effectiveness of use; 7. Examination of plant N status as a potential means of adjusting requirements; 8. Development of relationships between grass yield potential and drought stress (as estimated by water use models and use of previous experiments) and integration with N flux model; 9. Testing of the model using results of the study and comparison with effects of current fertilizer recommendations. Outputs tested will include economic optima, yield and nitrate leaching losses, while inputs will be based on a full range of detail from broad regional to soil N data. Discrepancies will be identified and resolved; and 10. Development of a prototype decision support system for multi-goal fertilizer recommendations with documentation and supporting scientific background, using various levels of detail in inputs to accommodate types of data likely to be available to users.
Time-Scale and Cost
From: 1995

To: 1998

Cost: £579,027
Contractor / Funded Organisations
Institute of Grassland and Environment Research (IGER)
Fields of Study
Fertilisers and Nitrate Pollution