Modelling the interaction of water and nitrogen

Abstract

The amount of useful plant material that a farmer collects from his field at the end of the season, is the integrated result of a large number of processes which interact during the plants' life cycle. In some cases, it may be obvious which growth factor is the major determinant of that final result. Especially in high intensity agriculture as practised in Western Europe, a state of 'potential growth' often exists where the available radiant energy during the growth period determines the yield. In situations where the growing conditions cannot be controlled, or only to a very limited extent, it is much more difficult to pinpoint the factors responsible for a particular yield. However such knowledge is of prime importance for people who are engaged in agricultural planning and development, because it forms the basis for any attempts to improve the situation. Especially in the developing world, where agricultural research has no long tradition, such knowledge is often lacking. Intuitive application of principles and knowledge obtained under completely different conditions in more developed countries, rarely leads to the expected improvements since the production system is not understood well enough. Many of the basic processes which govern production may be the same, but the environment may modify the rates of these processes to such an extent that their relative importance changes completely. In each situation, a systematic examination of processes is therefore necessary to asses which are critical. It is often difficult, if not impossible, to make such an analysis in the real world, since the environment is fluctuating and unpredictable. When the relevant processes can be studied separately, they may be combined in models which can be used for simulation experiments. The results obtained may serve as a basis for further experimentation.