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.

Soil deterioration and yield decline are the main factors affecting the environmental sustainability of long-term irrigated sugarcane monoculture. This research was conducted to detect changes of soil physical, chemical and physicochemical quality parameters associated with intensive irrigated sugarcane monoculture with groundwater for long term. Sugarcane monoculture resulted in a severe impact on some soil physical indicators of soil quality as increased the soil bulk density and reduced soil clay content, decreased soil aggregate stability and the water content at the field capacity causing decreases in soil porosity and decline in soil fertility. Significant impacts on some soil chemical indicators of soil quality were also recorded as reduced soil organic matter content and increased soil pH and EC producing soil salinity. Fields under long-term irrigated sugarcane monoculture had low OM values ranged from 2.09 to 2.61% while areas under crop rotation had the highest OM values ranged from 2.62 to 3.39%. Fields under sugarcane monoculture system had higher pH, EC and SAR values ranged from 7.96 to 8.41, from 2.98 to 4.22 dS m -1 and from 7.75 to 11%, while fields under crop rotation system had the lowest pH, EC and SAR values ranged from 7.64 to 7.92, 1.41 to 2.42 dS m -1 and from 4.51 to 5.86%, respectively. From these results, it could be concluded that long term sugarcane monoculture has significantly deteriorated soil physical and chemical properties indicating the urgent demand for more sustainable management practices to preserve soil quality.

Pot experiments were conducted during two successive seasons of 2019 and 2020 at the Fac. of Agric., Minia Univ. to investigate effects of four application rates of compost (0, 1, 2 and 3%) (w/w) and six treatments of bio-fertilizers and/or mineral NPK fertilization (control, Azotobacter chroococcum + Bacillus circulans, Azotobacter chroococcum + Bacillus megaterium, mixture of bio., mixture of bio. + 75% NPK and 100% NPK) on vegetative criteria, accumulation of bioactive compounds (phenolic compounds and flavonoids) through improving plant's secondary metabolism and antimicrobial activity of methanolic and ethanolic extracts of Populus alba. All compost treatments significantly improved all transplant vegetative growth parameters such as plant height, diameter, aerial part fresh and dry weights, main root length and roots fresh and dry weights, as well as, total chlorophylls and NPK% as compared to control. Biofertilizers and/or mineral NPK fertilization treatments significantly increased all the previous traits, the mixture of three species of bacteria plus 75% NPK followed by mineral full dose of NPK treatments were the most effective than other used treatments. The highest values were obtained when Populus alba transplants were grown in sandy soil contained 3% compost plus inoculation with three species of bacteria plus 75% NPK or compost at 3% plus 100 % NPK and these two treatments give the highest values of phenolic compounds in the methanolic and ethanolic extracts. This research confirmed that poplar is a promising wooden tree to be grown on sandy soils for timber production in Egypt, woody products and bioactive compounds.