Keywords: Nitrogen, fertiliser, recommendations, prediction systems, economic optimum, efficiency, environment.
Attempting to optimise the use of nitrogen fertilisers has commanded the attention of many agronomists and others for at least the last hundred years. The complexity of the nitrogen cycle, which involves numerous soil nitrogen transformations and the effect of weather on these and on crop growth and hence nitrogen demand, make accurate prediction very difficult. In the past, farmers and growers tended to Ã¢â‚¬Å“err on the high sideÃ¢â‚¬Â with nitrogen applications to avoid the risk of yield loss, but they are now under pressure from all quarters not to do this because it might lead to excessive nitrate in the produce and in the soil at harvest. This paper considers the basis of nitrogen recommendations and also the main methods of predicting optimum levels of fertiliser nitrogen. The ADAS N – index system, which was developed from extensive trials data, has been an important step forward in quantifying nitrogen recommendations for all crops in the UK. Soil mineral nitrogen (SMN) measurement was used widely for recommendation purposes on the continent where winters were generally colder, more predictable and consequently effective mineralisation did not occur until early spring. In the UK, measurement of SMN is now becoming more widespread, not just for research purposes but also on commercial farms because a number of trials have shown that better fertiliser N recommendations can be made particularly where there are high soil N residues. There is a problem, however, in assessing the level of nitrogen mineralisation during the growing season unless numerous soil N measurements are taken. Also, most recommendation systems rely on an accurate prediction of crop yield and errors lead to an incorrect nitrogen recommendation. More recently, computer models have been developed to quantify the various nitrogen transformation processes.These were originally used to quantify changes in field trials but now are being developed as potential advisory tools.
G H MacKenzie, Consultant, Ellesmere, Shropshire, UK.
J-C Taureau, COMIFER Groupe Azote, Hydro Agri France, 106 rue des Trois Fontanot, 92000 Nanterre, France.
50 pages, 11 figures, 25 tables, 64 refs.