A SIMPLE WEB-BASED METHOD FOR SCHEDULING IRRIGATION IN PUERTO RICO.

Abstract

There is antidotal evidence that many farmers in Puerto Rico do not employ scientific methods for scheduling irrigation for their crops. Instead, the pump is turned on for an arbitrary amount of time without knowing whether the amount of water applied is too much or too little. Over application of water can lead to the waste of water, energy, chemicals and money, and also may lead to the contamination of ground and surface waters. Under-application of irrigation can lead to reduced crop yields and a loss of revenue to the grower. There are various approaches for scheduling irrigation. One approach is to supplement rainfall with enough irrigation so that the cumulative rainfall and irrigation, over a specific period of time (e.g., one day, one week, one season), matches the estimated potential evapotranspiration, which is equivalent to the crop water requirement. Potential evapotranspiration (ETc) can be estimated by the product of a crop coefficient (Kc) and the reference evapotranspiration (ETo). Traditionally, potential evapotranspiration is derived from pan evaporation data or meteorological data from weather stations. Another approach involves monitoring the soil moisture and applying irrigation sufficient to maintain the soil moisture content within a predetermined range. In this paper we present an approach based on applying irrigation to the crop to meet the crop water requirements (i.e., potential evapotranspiration), but instead of using pan evaporation or meteorological data, we use a remote sensing technique. The advantage of the method is tha t reference evapotranspiration can be estimated at a 1 km resolution for the entire island each day. If the relatively simple approach presented in this paper is used it can potentially lead to increased efficiency of water and energy use, and help to reduce crop water stress and losses in crop yields. Potential crop evapotranspiration is estimated by using the simple relation