water balance components estimating in farm scale using simulation model swap

abstarct precise knowledge of all components of water balance is essential to optimize water use in irrigated agriculture. however, water balance components are difficult to measure in required time intervals because their measuring is time consuming and costly. unsaturated zone simulator models are useful tools for predicting the effects of agricultural management on crop water use and can be used to optimize agricultural practices such as agricultural water use. this research has been done on wheat irrigated farms in neyshabur plain, that is one of important plains in khorasan razavi province. swap agro-hydrological model, was used for simulation of water balance components and crop growth in three wheat fields: farob roman, hajiabad and soleimani. input data for model was a combination meteorological and field data. retc software package was employed to evaluate and calibrate the soil hydraulic parameters, used. simulation period was selected from october 2008 until early june 2009, in accordance with the wheat growing season. sensitivity analysis to soil hydraulic parameters showed that the model is more sensitive to and coefficients. also, acoording to presented statistical parameters, the results showed that swap is able to simulate water flow in soil, truly. mean r2 coefficient value was 0.62, mean error was between -0.1 to -2.28 and relative error was fluctuated between -0.33 and -12.69. therefore, calibrated swap model can be used as an instrumental tool for calculating all components of water balance in field scale, with time and cost saving.