Soil application of water hyacinth biochar as a source of nutrient- and carbon-rich biomass may be an effective ploy to eradicate this invasive aquatic weed. Incubation trial was conducted to assess effects of water hyacinth biochar addition on some sandy soil biochemical and biological properties and potential carbon sequestration at different application rates and methods. Results demonstrated that pyrolysis of water hyacinth at temperature of 300 °C and 30 min furnace residence time produced biochar with coveted physicochemical properties. Field emission scanning electronic microscopy (FE-SEM) images obtained for water hyacinth biochar showed major macroscopic changes caused by substantial changes in pore structure, surface area and surface morphology due to insufficient carbonization. Soil biochemical and microbiological characteristics after incubation exposed obvious significant improvements at all rates compared to control and varied markedly between addition of biochar as incorporation and broadcasting. Among different treatments, biochar addition as incorporation at the rate of 3% resulted in higher significant increases in most tested soil parameters. Water hyacinth biochar provided nitrogen and carbon immediately via SOC, DOC and DON in treated sandy soils providing energy for microbial biomass compared to control and this reflected by increases in soil values of C-MIC N-MIC and P-MIC. In addition, water hyacinth biocharring would greatly improve sandy soil carbon sequestration at high application rates. It could be concluded that water hyacinth transformation into biochar represents a sustainable strategy for managing these weeds and thus become a valuable organic source for sandy soils and will boost carbon sequestration.

The current research aims to study the impacts of adding corncob biochar to a sandy soil irrigated with drainage water on wheat productivity, heavy metals fate, and some soil properties that reflect healthy soil conditions. This research consists of two separate experiments under field (lysimeters) and pot incubation conditions conducted on sandy soil irrigated with drainage water and treated with corncob biochar at the rate of 0.0, 1, 2, and 3% as mixing or mulching. Results specified that drainage water electrical conductivity value (5.89 dS m⁻¹) lies under the degree of restriction on use of “Severe”, indicating that nonstop irrigation with such drainage water may cause a severe salinity problem in soil in the long run. A comparison of heavy metal concentrations of biochar-treated soils with the control showed that total heavy metals had accumulated significantly in the topsoil layer. Most of the available heavy metal concentrations in all soil leachate fractions were below the method detection limits. Mean concentrations of Ni, Cd, and Pb in wheat crops were far below the concentrations considered phytotoxic to wheat plants. More than 90% of the Ni, Cd, and Pb contained in the drainage water of the Al-Moheet drain were significantly present (p ≤ 0.05) and adsorbed by biochar in the top 20 cm of soil lysimeters, indicating the high biochar adsorptive capacity of heavy metals. Total counts of bacteria and fungi gradually and significantly increased over the soil incubation time despite irrigation with contaminated drainage water. Soil resistance index (SRI) values for microbial biomass were positive throughout the experiment and increased significantly as the application rate of corncob biochar increased. These results indicated the high feasibility of using corncob biochar at a rate of 3% to temporarily improve the health of sandy soil despite irrigation with drainage water.

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.

Soils must receive maximum protection to assure sustainable agriculture and quality food production. Heavy metals tend to accumulate in the soil rather than decompose and at a certain limit of their content, toxic consequences for living organisms occur. This research was conducted to survey the contamination status of Cd, Cr, Ni, and Pb and microbial activity in soils affected by long-term sugarcane monoculture in Upper Egypt. The rise of diacetate fluorescein hydrolysis (FDA) ranged from 86.25 to 201.25 mg kg-1 soil·h-1 in sugarcane monoculture fields, while the increase under crop rotation fields showed higher and significant values ranged from 207.25 to 266.67 mg kg-1 soil·h-1. In this study, generally soil microbial biomass and enzymatic activity was usually and significantly higher under crop rotation than sugarcane monoculture. The highest potential ecological risks were found in soils under long-term irrigated sugarcane monoculture, while being moderate for crop rotation. Under both sugarcane monoculture and crop rotation farming systems, cadmium Cd was observed to be the urgency pollutant with the highest degree of contamination even though Cd had the lowest average concentration (Cd 27.03 mg kg-1) in sugarcane monoculture fields, and Cd (10.46 mg kg-1) in crop rotation. In view of the impacts of these potentially toxic elements of cadmium (Cd), chromium (Cr), nickel (Ni) and lead (Pb), on the ecological system and public health, the introduction of new management practices in sugarcane monoculture fields are essential to protect the environment and to achieve future sustainability in sugarcane production in Upper Egypt.