Field and Modeling Study on Saving Mineral Fertilizers, Increasing Farm Income and Improving Soil Fertility Using Bio-Irrigation with Drainage Water from Fish Farms

The reuse of new and non-traditional sources of water for the purpose of irrigation is the primary goal of all countries that are located in dry areas and suffer from water scarcity, including Egypt in particular. This study was conducted to determine the appropriateness and quantify the benefits of using fish farm wastewater (DWFF), as an alternative to fresh irrigation water (IW), for the irrigation of barley. Two types of water quality were tested for the irrigation of barley, namely DWFF and IW, in addition to four levels of fertilization rates, 100% N, 80% N, 60% N, and 40% N, where 100% N represents 156 kg of nitrogen per hectare. The results showed a positive effect of increasing the nitrogen fertilization rate with irrigation water on the crop with the use of DWFF and IW for irrigating barley in two seasons: 2017/2018 and 2018/2019. The yield when using DWFF for the irrigation of barley was higher than the yield when using IW, which was in the range of 5.1% and 25.9% in 2017/2018 and between 9.8% and 33.3% in 2018/2019. This was due to the additional amount of dissolved biological nitrogen and other nutrients contained in DWFF. Notably, an additional amount of dissolved nitrogen is inherent in DWFF (12.81 kg nitrogen ha−1 in 2017/2018 and 12.43 kg nitrogen ha−1 in 2018/2019) and other elements, such as phosphorus and potassium, which are two macronutrients for crops. The SALTMED model was used to simulate soil moisture content, water application efficiency, nitrogen concentration in the soil layer in the effective root zone, N uptake, the dry matter of grown barley, and yield and water productivity for all treatments, with R2 values of 0.94, 0.89, 0.99, 0.916, 0.89, 0.915, and 0.919 respectively. The research concluded that the use of DWFF is an effective alternative to IW for irrigating barley. It also helped to achieve higher yields while applying lower amounts of IW and chemical fertilizers. There are also additional benefits, such as reducing the drainage to the drainage network and increasing the income of farmers.