Developing and testing a model for open field horticultural crops to enable use of a 'just-in-time' fertilization management

Today more than ever, increased crop production depends on judicious use of resources. In addition, issues such as climate change, climatic variability and environmental sequestration have become ever important. The objective of this study is to provide user-friendly ways for farmers to control the amount of nitrogen fertilizer in a very precise manner, in order to avoid overuse of fertilizer, which is not only harmful to the environment, but also a major production cost factor. This should however, be realized without suffering from production or quality losses. This is especially so in the case of intensive open field horticultural crops, where abundant to extreme use of fertilizers is very widespread. As such, cauliflower has been chosen as the research object in this study. Taking into account that in the future, governments will undertake action by the means of fines, it is in the interest of the horticultural farmer to be able to handle these issues in a sustainable manner. An experimental site was set up, allowing real time follow-up of all fertilization and irrigation inputs and outputs. Four different nitrogen application rates and four fertilization treatments, from broadcasting to fertigation, resulted in a four by four completely randomized factorial design, replicated in two blocks. The fertilization rates were set in a way that luxury nitrogen availability as well as restricted availability was present in the experiment. Drainage water per plot was being retained so that the water volume could be sampled during growth and measured regularly for nitrogen content. Destructive growth analysis of plant biomass, both leaves and curd, was carried out on a fortnightly basis. At harvest time, about 83 days after planting, plants were sampled commercially (i.e. with leaf crown) and non-commercially (i.e. the whole plant). Both the curd and leaves were analyzed for fresh weight, dry weight and nitrogen content. Furthermore, leaf soil coverage and specific leaf area index were measured. Additionally, root growth and root length density were extensively analyzed. Gathered data resulted in a crop growth model for growth estimation of a cauliflower crop and its nitrogen content, depending on its application rate. Parallel with this crop growth model, a soil mineralization-water model has been developed through intensive root growth measurements to provide an accurate projection of the volume of soil where uptake is taking place, influencing soil-N-sequestr