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`The impact of the Response Curve, used to assess nitrogen economic optimum, on nitrate leaching in sandland areas` - NT1210

The Nitrate Sensitive Areas and Nitrogen Vulnerable Zones schemes have been implemented to reduce nitrate loss from agricultural land to vulnerable drinking water supplies. One of the major successes of the NSA scheme has been to ensure that fertiliser inputs of nitrogen match MAFF recommendations (Lord, 1994), since research has shown that leaching losses increase rapidly once the economic optima area is exceeded. However, these fertiliser recommendations were based on the estimation of a crop`s nitrogen optimum using linear plus exponential models, where parameter r=0.99. Current work has indicated this approach may be unreliable for sandy soils. Fixing r to 0.99 appears to overestimate the N optimum, and the curve does not reliably follow the shape of the response. This has potential implications for the control of nitrate leaching since many of the greatest problems arise on sandy soils. Overestimation of N optimum by fixing r in the linear plus exponential model could significantly increase nitrate leaching. A number of models that estimate N optimum are currently being investigated, and improvements in fit have been shown to be possible. A large number of (mainly MAFF funded) experiments on sandy soils have appropriate yield, soil mineral nitrogen and leaching measurements which would allow a critical assessment of the economic and environmental impact of developing improved recommendations. The principal scientific objective is to quantify the impact on nitrate leaching from sandy soils by using different models for the assessment of yield response to N. The study will advance our understanding of the sensitivity of nitrate leaching to menthods of estimating optimum fertiliser N. The results have implications for other crops, notably potatoes where the optimum is particularly difficult to estimate precisely and nitrate losses can be very large.
Time-Scale and Cost
From: 1995

To: 1997

Cost: £19,080
Contractor / Funded Organisations
Fields of Study
Fertilisers and Nitrate Pollution