Tertiary treated wastewater used for irrigation of processing tomatoes

The shortage of fresh water due to increasing uses and climate change has led to considering wastewater for crop irrigation. In Capitanata plain (southern Italy), tertiary treatment of municipal wastewater allows for 6 million m3 year-1 to be used for agricultural purposes. An open-field experiment was conducted in a private farm to compare the yield and quality of processing tomatoes irrigated with conventional water (CONV) and tertiary-treated wastewater (TWW) from a nearby public wastewater treatment plant. Irrigation water, soil, and crop samples were taken to assess the chemical-physical parameters, possible contaminants and microbiological indicators. Tomato hybrid “Taylor” was transplanted on 11 June 2021 and was harvested on 5 October 2021. Daily soil water balance and irrigation scheduling were calculated by a “cloud-based” Decision Support System (Bluleaf TM). Plant height, percentage of land cover, LAI, plant biomass, and fruit yield were collected biweekly. Seasonal water irrigation volume was about 7,210 m3 ha-1 (in 44 watering events). LAI behavior was similar in the two treatments during the first phase of the growing cycle, while it resulted higher in TWW during the fruit maturity stage. Total plant biomass at harvest was found to be greater in TWW than in CONV (125.9 vs. 92.5 t ha-1), as well as the commercial fruit yield (105.3 vs. 75.4 t ha-1). These positive effects on plant development and marketable fruit yield observed for the TWW treatment were likely due to the increased amounts of N, P and K supplied to the soil with the irrigation water. The heavy metals content were above the Italian thresholds for TWW reuse, and the irrigation treatments did not affect the microbial quality of the marketable yield.