Scheduling Irrigations On Drip-Irrigated Vegetable Crops Using Climate-Based Coefficients and Canopy Measurements

As in all regions of the country, the southwest U.S. has experienced a resurgence of home gardens to provide fresh vegetables for the domestic table and for sale at increasing numbers of local farmers markets. Concurrently, the increasing demand for water in this arid region by rapidly rising populations and urban development has forced many municipalities to either impose restrictions on outdoor water use or to provide incentives, including block-rate pricing structures, to encourage water conservation. If limited, or expensive domestic water is used to irrigate vegetable gardens, water conserving techniques such as drip irrigation and efficient irrigation scheduling must be implemented to minimize water-use while sustaining optimum yields and/or economic returns. This study was initiated to evaluate the yield/water relationships of drip irrigated chile pepper (Capsicum annuum), sweet corn (Zea mays), and tomato (Lycoperisicon esculentum) in an effort to formulate climate-based scheduling coefficients for developing efficient irrigation management strategies for these vegetable crops when grown in small plots in northwestern New Mexico. Three to four drip irrigation treatments per year, ranging from 0.50 to 1.05 of Penman-Monteith standardized reference evapotranspiration (ETrs) were imposed on each crop in alternating block or randomized block experiments from 2004 through 2009. Irrigation treatment factors (TF) were held constant while canopy area varied in the equation used to derive volumetric, per plant, treatment levels: I = (ETrs – EP) x TF x CA x 0.623; where; I = irrigation treatment (gals/plant), ETrs = reference ET in inches, EP = effective precipitation (60% of events > 0.2 inch) in inches, TF = treatment factor (ranged from 0.50 to 1.05 of ETrs), CA = canopy area (sq ft), and 0.623 = constant to convert inches/sq ft to gallons. Results varied slightly between years but overall, the optimum crop coefficients (Kc) suggested for scheduling drip irrigations on chile pepper, sweet corn, and tomato were 0.80, 0.85, and 0.70, respectively when used in a simplified equation: IR = (ETrs – EP) x Kc x D2 x 0.49: where; IR = irrigation required (gals/plant), ETrs = Penman-Monteith standardized reference ET for tall crops in inches, EP = effective precipitation in inches, Kc = crop coefficient, D = diameter of plant in feet, and 0.49 = constant to convert plant diameter to canopy area and inches per sq ft to gallons.