A numerical simulation model has been developed, to compute vadoze zone soil moisture content profiles under transient field conditions by coupling soil moisture flow equation with a non linear root water uptake model. The model has been tested for the sensitivity of its non linear uptake parameter, for obtaining its optimal value. Computation takes into account a variable transpiration rate and a field measured initial moisture content. Rainfall, irrigation and evaporation have been treated as sources of non-uniform potential surface flux. Solutions to the computation have been obtained numerically by a fully implicit finite difference scheme, involving a non linear system of equations, which has been linearized using Picard’s iterations. Field crop data of maize (Zea mays), which is among the most important crops in India and several other countries in the world, has been used to evaluate the results of the simulation. Determining the water requirements of crops is important for improved scheduling of irrigation, which in turn requires accurate measurement of crop evapotranspiration (ET_c). As the first objective, daily and seasonal ETc of maize are computed using Lysimeter set up in an experimental field from May 2006 to September 2006 at Roorkee, India. The average daily ETc of maize varied from a range of 1.4 to 3.4 mm day^–1 in the early growing period to 8.3 mm day^–1 at peak that occurred 9 weeks after sowing (WAS) at the silking stage of maize, when leaf area index (LAI) was 4.54. Average daily ETc declined sharply to 2.57 mm day^–1 during late season stage of crop. The measured seasonal ET_c of maize was 495 mm. Development of computation based schedules of irrigation is the second objective of the study. Plant parameters like root depth and crop height have been continuously observed throughout the crop period. Top 0.3 m depth of root zone is considered to represent the soil moisture status governing the schedules of irrigation. Application of the computation technique to field conditions and comparison of the results with filed measured data shows very good agreement.