Water and salt management of irrigated open fields using drainage water of aquaponics

抄録

In aquaponics, water is used multiple times between aquaculture and hydroponics facilities, so it is a food production technology that effectively uses water resources. In this study, we reused aquaponics drainage water to irrigate open fields. Open culture experiments were conducted in Mexico, and numerical experiments were also run to assess the risk of salt accumulation in an open field. In these open culture experiments, 18 mm of water was used in irrigation once a day. Electric conductivity (EC_w) was around 4 dS/m. The soil water and salinity in the root zone were monitored by capacitance sensors. After 120 days, we found sufficient condition in soil moisture for crops no remarkable increase in salinity and at the monitoring points. The numerical experiments were conducted under conditions where the amounts of irrigation were 9 and 18 mm/d, the frequency was once a day, the EC_w in the irrigation water was 4 and 8 dS/m, and evapotranspiration of 6.4 mm/d was measured on June 19, 2019, and then continued for 30 days. Moreover, we also simulated irrigation of the water at an EC_w of 4 dS/m at an irrigation rate of 0.375 mm/h for 24 hours (total amount, 9 mm/d) under the same climate conditions of other cases. From these simulations, although salts accumulated at the edge of the wet zone formed by irrigation, we could observe that the saline concentration in the root zone was well maintained without any increase. We concluded that it is possible to use aquaponics drainage water of 4 dS/m as irrigation water for open culture if a sufficient amount of water is prepared or the scheduling of irrigation was planned effective for mitigating salt accumulation.