EFFECT OF DIFFERENT IRRIGATION TECHNIQUES AND WATER QUALITIES ON YIELD, FRUIT QUALITY AND HEALTH RISKS OF TOMATO PLANTS

Abstract

The effects of different irrigation techniques and water qualities on tomato (Solanum lycopersicum L., hybrid 'Verdoun') yield, fruit quality and health risks were investigated under field conditions in Crete, Greece. Nine irrigation treatments were applied, including combinations of 3 water quantities: full irrigation (FI), regulated deficit irrigation (RDI) and partial root drying (PRD), 2 water qualities: fresh water (FW) and secondary treated municipal wastewater (WW), and 2 depths of application: surface (S) and subsurface (SS). WW was used after an on site treatment which included: a) heavy metal (As, Cd, Cr, Cu, Pb) addition, b) a sand filter, c) a special filter for heavy metal removal (HMR), and d) a UV treatment for reducing bacterial populations. The marketable, non-marketable and defective fruit yield was measured and fruit samples were analyzed for total soluble solids (TSS) and titratable acidity (TA). Samples of irrigation water, soil and fruit were analyzed for heavy metals, E. coli, total coliform and total bacterial populations. Commercial fruit yield was not significantly affected by the deficit irrigation regimes applied, although in absolute values it was 5-7% lower compared to the fully-irrigated treatment. This was mainly due to an increase of the non-commercial fruit (small-sized). Irrigation water use was reduced by 23% in RDI and PRD treatments, while water use efficiency for harvested yield was increased by 20%. Marketable yield was not affected by the quality of the irrigation water used. The UV treatment was efficient in removing E. coli from the WW, with no sample through the growing season detected as E. coli-positive. No E. coli populations were detected in the harvested fruit, while in soil, the percentage of E. coli-positive samples was similar in both FW and WW treatments, indicating soil contamination by exogenous factors. The combination of sand filter and HMR was efficient in removing heavy metals, resulting in no differentiation of soil heavy metal content between FW and WW treatments. In conclusion, the application of deficit irrigation practices can efficiently reduce water use with no significant effects on yield and quality of tomato plants, under the local conditions of Crete. Moreover, the possibility for the safe use of municipal wastewater for irrigating vegetable crops may further enhance the potential for fresh water saving in an area where fresh water availability for irrigation is limited.