Spatial and Seasonal Simulations of Irrigated Processing Tomato

Abstract

Crop simulation models are used to compare crop management techniques, allowing for multi-year and multi-location runs over minimum time intervals. In Southern Italy, where water- limited conditions are common, it is important to identify irrigation scenarios which allow for a more efficient transformation of water (and irrigation water) into commercial yield. In this research project, a spatial analysis of a long-term simulation was carried out with AEGIS/WIN, a GIS interface of the DSSAT crop simulation package. The case-study refers to a 1000 km² area, characterized by 481 soil samples collected over a regular grid. The processing tomato was simulated punctual-based using long-term weather data. The evaluated crop management scenarios were a) rainfed and b) 13 automatic irrigation levels based on soil CAW thresholds. Commercial yield, water and irrigation water use efficiencies (WUE and IRRWUE respectively), and NR were evaluated for each soil sample in order to select the optimum irrigation scenario. This choice was based on different criteria which were defined taking into account the objectives of different stakeholders involved in the tomato crop chain. All the above variables were visualised and mapped with GIS. According to the criteria, the results of the rainfed scenario were not useful, showing low values for fruit yield and negative net returns for WUE. An increase in the threshold of soil water content in order to start irrigation improved the fruit yield, its temporal stability and the WUE. The overall mean of the IRRWUE decreased for thresholds of CAW higher than 50%. Results showed that the optimum CAW threshold was on average 45% for the different criteria parameters. The selection of the optimum scenarios based on yield and profitability were affected by the hydrological properties of the soils. The option criterion based on WUE maximisation proved to be suitable from different points of view and matched the interests of several stakeholders. In this work, a methodological approach is proposed for the spatial and temporal evaluation of irrigation scenarios, developing a support decision system for different stakeholders in planning irrigation water distribution. Some relationships among the stakeholders are also discussed, based on simulated results.