Once the soil outside the irrigated zone is fully depleted of available water, the root system essentially goes dormant in the dry soil. However, the root system remains ready to resume activity once the soil is rewetted. Thus, only in areas of marginal rainfall is the root system largely confined to the irrigated zone. It is in the irrigated zone where root density is the highest and water extraction capability the greatest. Monitoring soil moisture and proper scheduling are two keys to an effective irrigation program.
Water is applied to satisfy the crop's requirements.
The ET value is equivalent to the crop's water requirement in the field. Additional applied water may move beyond the reach of the crop's roots as deep percolation losses. However, this leaching may be necessary where salinity is a concern. Thus, knowledge of ET is essential for the most efficient irrigation scheduling. The Kc value changes during the course of the year and should be available through your local farm advisor's office.