Among crucial factors that control flooding events are extreme climate, urban growth, and mismanagement. Islands in the Nile River have experienced successive cycles of flooding and drying due to recent rainy years in the Nile Basin countries. This paper focuses on the impact of floods on the amounts of ammonium-N released, total concentrations of heavy metals, enzyme activities, and microbial biomass (C and N) in flood soils of 11 Nile River islands. Field moist soils and their airdried counterparts were collected from the outskirts of the island and incubated for 15 days at 30 °C to be analyzed. Results reflected that the amounts of released NH₄-N were higher in airdried than in wet soils. The average hydrolysis rates of the studied six enzyme substrates were correlated significantly with organic C, organic N, microbial bio-mass C and N in the field moist soils. The highest correlation coefficients (r) were with rates of hydrolysis of substrates of asparaginase, amidase, and β-glycosaminidase. A significant intercorrelation between rates of hydrolysis of the six studied enzyme substrates and r values which range from 0.81 to 0.98. At 10 mmol kg⁻¹ soil, Co⁺², Cd⁺², Pb⁺², Cu⁺², Cr⁺³, and Ni⁺² inhibited the release of NH₄-N. Arginine hydrolysis was inhibited by the six heavy metals at 5 mmol kg⁻¹ soil; the most effective inhibitors were Pb⁺², Ni⁺², and Cr⁺³. Due to the complex soil enzymatic and organic nitrogen hydrolase activities that occur during floods, fertile fields on the Nile River islands should not be fertilized before the summer flood seasons, which will prevent contamination of the Nile River water and loss of its island soil fertility.

Biofertilizers and biocontrol agents have been improved for several decades as microbiological tools that can provide beneficial outcomes in the growth and health of plants. Two field experiments were performed in the Scientific Farm of the Horticulture Department, Faculty of Agriculture, Minia University, Egypt during the winter of 2022/2023 using clay loam soil. Control plots were treated with the recommended rates of mineral fertilizer of NPK (100%) without inoculation, while other plots were inoculated with Egyptian isolates of effective microorganisms (EMs) (a mixture of Azotobacter chroococcum and Azospirillium brasilense) and strains of Bacillus spp.; the biofertilizers were applied to the soil through mixing with irrigation water. For mycorrhizae, Glomus mosseae and Glamus fasiculatum isolation stock cultures were combined to create the mycorrhizal inoculum. The results showed that biofertilizers with 75% NPK were the best. Biofertilizers changed the properties of soil, increased its content of beneficial microorganisms, increased the total good quality production of onion and potato and decreased the stress of chemical pesticides and mineral fertilizers on crop growth and productivity.

Dual use of water for fish and crop production could be a promising approach to improve irrigation under arid conditions. A watercress pot study was carried out to assess the effects of irrigation by catfish and tilapia aquaculture water on the sandy soil properties as well as the growth parameters of watercress with various combinations of artificial NPK fertilizers at El-Minia Governorate of Egypt (28°18′16″ N latitude and 30°34′38″ E longitude). Catfish aquaculture water had the greatest phytoplankton abundance at 83,762 units (×10⁴/L), while the minimum number of phytoplankton existed in tilapia aquaculture water, recorded at 14,873 units (×10⁴/L). There were significant average changes that varied from 120 to 237 (×10⁴ cfu/mL⁻¹) in total bacterial counts in tilapia and catfish waters. Watercress growth quality parameters closely paralleled at all NPK application rates, indicating that the highest quality plants were produced in pots receiving 25% of the recommended levels and irrigated with catfish aquaculture water. Nitrate concentrations of watercress plants were determined under pollution levels established by the European Commission for leafy and tuber vegetables. In conclusion, the use of microbial and phytoplankton-rich aquaculture water to irrigate vegetables and as fertilizer can maintain a balanced soil ecosystem.