Oxidation/reduction (redox) potential (ORP) may be considered a "master chemical variable" affecting numerous soil reactions and the soil plant relationships. A 10 months experiment was conducted under controlled-conditions to continuously monitor and characterize the soil redox potential regime in irrigated soils and study its variations as affected by plant growth and irrigation water quality. The studied parameters, involved the effects of plant growth (P, Alfalfa) vs. bare-soil (C) and effluent (E) vs. fresh water (F) irrigation giving, in factorial design, the treatments PE, PF, CE and CF. Continuous monitoring of ORP enabled to discover three types of temporal redox cycles: daily, irrigation-dependent and harvest-dependent cycles. The "Daily cycles", driven by diurnal temperature changes were observed in all treatments and were characterized by moderate redox changes. The "Irrigation-dependent cycles" were driven by the 48-hour irrigation regime and were observed only in the plant treatments. Significant ORP decreases reaching values of pe=-5 and indicating reduced conditions, were measured immediately after irrigation and were followed by gradual increase of the ORP due to drying and reoxidation of the soil. The "Harvest-dependent cycles" affected the pattern of the irrigation cycles. They were characterized by extremely low ORP minima in the irrigation cycles after the harvests events, and high ORP minima in the irrigation cycles before harvest events. This study sheds light on the redox regime in irrigated soils and the effects of environmental factors and agro-technical treatments on it. It clearly shows that rhizosphere and plant root activity may strongly modulate ORP in the immediate environment of plant roots even in aerated soils, causing repeated intermittent periods of low ORP that may induce hypoxia or anoxia situations in the roots and affect element concentrations and availability in the soil.