chapter  1
15 Pages

Simple Spreadsheet Method for Scheduling Irrigation

WithEric W. Harmsen

A simple spreadsheet method for scheduling irrigation is presented. The water balance method used is based on the methodology of the United Nations Food and Agriculture Organization. Soil moisture is depleted from the soil profile by evapotranspiration. By maintaining the soil moisture content between the field capacity and the threshold moisture content, water stress can be avoided and 100% of the potential yield can be achieved, ignoring reductions in yield due to other factors such as fertility, disease, and salinity. The method provides an estimate of the crop stress factor, from which the relative seasonal yield can be estimated for many crops. Several graphs are provided in the spreadsheet, which help the user evaluate their real-time water management. In addition to estimates of the relative yield, the spreadsheet also provides an estimate of the lost irrigation (i.e., irrigation lost to surface runoff or deep percolation). Two examples are provided for the bell peppers located on the southern coast of Puerto Rico.