Control of quality and N pollution in greenhouse lettuce production: A modelling study

One major challenge for making greenhouse winter lettuce cropping systems s ustainable is to produce high quality lettuces in terms of calibre and nitr ate content, while being friendly to the environment (i.e, limiting N pollu tion). The aim of the research is to design crop management programs that a chieve this objective. A simulation model of the cropping system's behaviour was built, to test th e effects of technical decisions on nitrogen pollution and lettuce quality. This model integrates three modules: (i) spatial breakdown module, designe d to account for the very uneven spread of environmental conditions in the greenhouse; (ii) soil behaviour module, using an available mechanistic mode l; (iii) crop behaviour module, simulating crop growth, crop's nitrogen dem and, effect of stress on lettuce weight and nitrate content of lettuce at h arvest. The models' parameters were set on the basis of bibliography or spe cific experiments, then model was validated by independent data. This model is first used to analyse the effects of irrigation and N fertili sation on lettuce quality and N pollution. The simulation results show that the system is highly sensitive to the amounts of water and nitrogen provid ed, and there is a strong interaction between these two command variables. Secondly, we use the model to explore several possibilities for managing N inputs and irrigation. The simulation results show that, using sprinkler fe rtigation technique could make it possible to keep a lower store of nitrate in the soil during the crop (which is valuable to limit pollution) and cou ld reduce the variations in the amounts of soil nitrate at harvest (which i s essential for lettuce quality in term of uniformity of weight and nitrate content of lettuce).