The benefit of using drainage water of fish farms for irrigation: field and modelling study using the SALTMED model

This study investigated the suitability and benefits of using drainage water of fish farms (DWFF), instead of canal fresh water (IW), for wheat irrigation. Two water qualities, DWFF and IW, and four levels of N-fertigation rates [100% N (192 kg N ha−1 season−1), 80% N, 60% N and 40% N] were tested. The results showed a positive impact when increasing N-fertigation rate on the yield using both DWFF and IW. However, the yield under DWFF was higher than the yield under the IW treatment by between 11 and 51% in 2014 and between 8 and 38% in 2015. This is due to the additional amount of dissolved biological nitrogen and other nutrients inherent in DWFF. The SALTMED model simulated reasonably well the soil moisture and nitrogen content of all soil layers as well as wheat dry matter, yield and water productivity for all treatments, with R2 of 0.99, 0.97 and 0.96, respectively. It was concluded that the use of drainage water of fish farms instead of fresh water for irrigation of wheat could help to achieve higher yields while using less irrigation water and less chemical fertilizers. Additional benefits are less drainage to the drainage network and higher income for farmers.