Maximising nitrogen value while minimising pollution

摘要

In the first of a new series of occasional articles based on the guidelines contained in the MAFF Codes of Good Agricultural Practice, ADAS Pollution adviser Alan Brewer looks at the timing of slurry applications. Applying slurry in late winter or early spring makes the optimum use of its nitrogen content because this is as close as possible to the time when maximum crop growth occurs. The yield response of summer applications to grassland can be very variable depending on soil and weather conditions. Therefore spreading in July and August is likely to be less effective, while applications in autumn or early winter considerably reduce the value of spring nitrogen. Nitrogen lost as ammonia to the atmosphere is greater from high dry matter slurries left on the soil surface. Rapid incorporation or injection will reduce these losses. There is little leaching of phosphate or potash if they are spread at the recommended rates. Phosphate and potash which is not taken up by crops is absorbed by the soil Inorganic fertiliser rates should always be adjusted to take account of the nutrients in applied slurry.