The drying of the soil profile after planting seed 

Because the climate affect the rate of drying, it is necessary to get an estimate of the potential evapotranspiration rate that will occur in the future. Use past climate years to estimate the future climate. 

To predict how many days for the soil to dry  in the seed zone requiring a new irrigation,  run the soil evaporation model by Campbell

The model requires the potential evapotranspiration rate in mm/ day (25.4 mm/day= 1 inches/day)  and the soil parameters. The soil parameters determine the rate that water moves from the lower soil depth to the surface. The potential evapotranspiration controls the maximum rate that water evaporates from the surface. When the soil is near saturation, the soil evaporation rate is in stage one controlled by the atmospheric conditions. As the soil dry , the rate of soil evaporation becomes stage two, controlled by the soil conductivity characteristics.

Blow are a plot from the Campbell model for 1 hr and 72 hrs after irrigation stops with a potential evapotranspiration rate of 12 mm/day.

The plots below are for a clay soil after 1 hr and 168 ( 4 days) of soil evaporation at 12mm/day

As can be observed it takes 3 days for the sandy loam soil to dry to 20% moisture content  in the top 10 cm , where is takes 7 days for the clay soil to dry to 30 percent.