69 Water Saving Irrigation Strategies for Processing Tomato A. Battilani and D. Solimando F.L. Plauborg and M.N. Andersen Consorzio Bonifica CER University of Aarhus Italy Denmark C.R. Jensen L. Sandei University of Copenhagen SSICA Tomato and Vegetables Dept. Life Sciences Italy Denmark Keywords: partial rootzone drying, deficit irrigation, WUE, NUE Abstract A field experiment was carried out in Northern Italy (Po Valley), within the frame of the EU project SAFIR, to test the feasibility of partial root drying (PRD) management on processing tomato (2006) and to compare the PRD irrigation strategy with a regulated deficit irrigation management (RDI) (2007). PRD allowed remarkable water saving with respect to a full irrigated crop and RDI management. Water use efficiency (WUE) as well as yield and quality were assessed and compared. PRD is supposed to increase nitrogen use efficiency (NUE) as well because of improved root efficiency. Also this aspect was investigated. Furthermore, economical WUE and NUE were calculated considering the gross margin in order to evaluate the economic self-sustainability of the proposed fertigation strategies. INTRODUCTION Most of the world processing tomato acreage is located in areas of medium to severe level of drought proneness. Moreover, risk of water stress is becoming more and more frequent due to the rise of average temperature, reduction of rainfall and changes in its distribution. Although in the last 20 years tomato varieties have become more productive and tolerant to water stress, it remains that only tomatoes receiving regular water supplies can secure suitable profit to growers. Thus, strategies able to minimize irrigation when it has little influence on yield or product quality are essential for processing tomato. The aim of irrigation management is to control plant water status optimising crop production and quality while conserving water. Research in this area demonstrates that plant water status is jointly determined by the atmospheric and soil environment and by the plant physiology. Therefore plant water status can only be partly controlled by irrigation, especially by those strategies which focus only on a single factor (e.g evaporative demand or soil water content). Recent studies found tomato crop yield response to water (Ky), calculated on fresh matter basis, in the range 0.55-0.68 (Kirda et al., 2004; Gatta et al., 2007). These results indicate a tomato productivity behaviour which allows reduced water supply without harming the yield: there is still room to improve tomato water use efficiency (WUE) with a crop water and nutrients management focused on water saving (Battilani, 2006a). This is in accord with earlier findings that when exposed to mild soil water drying chemical and hydraulic signals inducing partial stomatal closure and increased root growth may optimize dry matter accumulation by maintaining CO 2 assimilation even when crop water use is reduced (Fulai et al., 2005). In recent years, the two main approaches for developing practical irrigation strategies to manipulate tomato aboveground vegetation and fruit growth, as well as fruit quality, have been deficit irrigation (DI) and regulated deficit of irrigation (RDI). Also a new irrigation management, developed in the last decade for grapevine and orchards, the partial rootzone drying (PRD) (Dry et al., 1996; Loveys et al., 1999), could be successfully applied to processing tomato. Deficit irrigation is aimed to restore less than full plant evapotranspiration (ET 0 ) Proc. XI th IS on the Processing Tomato Eds.: R. Pitblado and J. Routledge Acta Hort. 823, ISHS 2009