USE OF CROPSYST TO SIMULATE GROWTH, ETC AND N UPTAKE FOR THE DEVELOPMENT OF IRRIGATION AND N FERTILISER PROGRAMS IN INTENSIVE VEGETABLE CROP PRODUCTION

Combined systems of drip irrigation and fertigation that are automatically controlled by programmers are commonly used in intensive vegetable production. Such systems are regularly used in substrate-grown crops, and are being increasingly used with soil-grown crops. These systems provide growers with the technical capacity to “spoon-feed” both water and nutrients as required. Doing so would optimise the use of water and N, and minimise deleterious N losses to the environment. Crop simulation models provide a means to effectively use this technical capacity for precise irrigation and N management. The crop simulation model CropSyst was used to simulate crop evapotranspiration (ETc), growth and N uptake of pepper grown in soil. The crop was grown in simple plastic greenhouses, as is widely used for vegetable production in south-east Spain. The FAO radiation equation was used to simulate ETc. This equation was more accurate for the greenhouse conditions than (a) Penman-Monteith and (b) FAO-Pan, which are alternatives available in CropSyst. Crop N uptake was simulated using (i) crop growth estimated from radiation interception and transpiration, and (ii) curves of dry matter to N content that were determined empirically. Following calibration, validations were conducted in different crops. These simulation routines are being incorporated into a management-oriented program decision support system that will enable growers to evaluate and improve water and nitrogen management of vegetable crops grown in plastic greenhouses.