Nitrate leaching from arable and horticultural land

Arable crops in the UK make a large contribution to nitrate leaching by vir tue of the land area they cover (> 4.5 million ha). By contrast horticultur al crops occupy only a small area (< 0.2 million ha) but can leach very lar ge amounts of nitrogen. The application of nitrogen fertilizer to arable an d horticultural crops is very cost-effective, stimulating its use. MAFF's N itrate Research Programme for arable and horticultural crops aims to reduce nitrate leaching and maintain productive farming through Best Management P ractice. The Programme has led to the development and testing of methods to measure nitrate leaching, the identification of 'leaky' crops, soils and p ractices, and strategies to optimize the use of fertilizer nitrogen. Data h ave been used to construct and test models of nitrate leaching, which in tu rn have been used to evaluate the leakiness of potential rotations. Current best practice to minimize nitrate leaching requires measures to improve th e efficiency of nitrogen use by crops, combined with measures to protect so il nitrogen from leaching during the late autumn to spring drainage period. This involves consideration of many factors: an appropriate crop variety m ust be chosen; a green cover must be maintained for as much of the year as is practicable; crops should be drilled early; fertilizer requirements shou ld be calculated using a recommendation system and allowing for soil minera l nitrogen and any manures applied; fertilizers should be spread evenly wit h a properly calibrated spreader, perhaps using split applications; starter fertilizers and banding of fertilizers should be used where appropriate to reduce losses from vegetables; pest and disease infestation must be minimi zed; any irrigation must be applied carefully with scheduling. Research is now moving on to study whole farm systems and the interactions between loss es of nitrogen and other pollutants to the environment with the aim of mini mizing total environmental impact.