Fallow is used to increase soil moisture under rainfed conditions, but its effectiveness is dependent on climate and soil conditions of each region. Simulations were performed to evaluate fallow at 5 locations in east Azarbaijan (Ahar, Maragheh, Minab, Sarab and Tabriz) using 23 years weather data. Results indicated that at the end of seasonal fallow (SF: form September to March) 79-140 mm water is stored, which is 50 to 60 % of precipitation. Soil evaporation was the most important loss that

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... sulted in 40 to 50 % loss of precipitation. Contribution of runoff and deep drainage was relatively low and similar (between 1 to 10 %) in water loss. In yearly fallow (YF: form September to September) soil moisture stored was between 67 and 104 mm which consisted 16 to 31 % of total precipitation. Comparison of SF and YF indicated that YF does not have any advantage with respect to soil moisture storage, but resulted in considerable moisture losses via runoff and deep drainage. And hence soil erosion and nutrients leaching. Simulation results also showed that application of straw mulch (0.5 to 2 t/ha) does not have any advantage in SF or YF.