MICRO-IRRIGATION: ADVANCES IN SYSTEM DESIGN AND MANAGEMENT Water use by drip-irrigated late-season peaches Received: 16 October 2000 / Accepted: 8 January 2002 / Published online: 7 August 2003 Ó Springer-Verlag 2003 Abstract A 4-year experiment was conducted using a large weighing lysimeter to determine the crop coefficient and crop water use of a late-season peach cultivar (Prunus persica (L.) Batsch, cultivar O’Henry) irrigated with a surface drip system. Two trees were planted in a 2·4·2 m deep weighing lysimeter that was surface irri- gated with ten 2 L/h in-line drip emitters spaced evenly around the trees. Irrigation was applied in 12 mm applications after a 12 mm water loss threshold was exceeded as measured by the lysimeter. The crop coef- ficient (K c ) was calculated using the measured water losses and grass reference evapotranspiration calculated using the CIMIS Penman equation. K c was plotted against day of the year and linear, quadratic, and cubic regressions were fitted to the data. A three-segment linear and the cubic equation had the best fit to the data. The maximum K c determined for the linear fit in this experiment was 1.06 compared with a maximum of 0.92 recommended for use in California and 0.98 calculated using the FAO method. Average annual water use for the 4 years of the experiment was 1,034 mm. Mid-day canopy light interception was found to be well correlated with the crop coefficient determined using the lysimeter data. Introduction Accurate irrigation scheduling is needed to match the depth of application to the crop water requirement. Proper irrigation scheduling requires actual crop water use data in relation to the potential water use (evapo- transpiration) as a function of plant development. The data for the water requirements of deciduous fruit and nut crops as a function of growth varies widely depend- ing on climate, soil, and irrigation methods and man- agement. As a result, they are difficult to interpret and not necessarily useful for establishing baseline values. The relationship between crop water use and potential water use is often called the crop coefficient. These data are routinely collected for field crops using drainage and weighing lysimeters but seldom for tree crops because of the large lysimeters required and the need to collect data over several years. Water use data for perennial crops have often been collected in the past using soil water balances for short periods of time, which is not a very accurate method (Fereres and Goldhamer 1990). Various studies, using this method and weighing and drainage lysimeters, have produced widely varying crop coeffi- cients for mature trees (Miyamoto 1983; Worthington et al. 1984; Mitchell et al. 1991; Chalmers et al. 1992). A large weighing lysimeter was constructed specifically to quantify the water requirements for an irrigated late- season peach variety, and to develop a crop coefficient to describe the crop water use as a function of time for a mature tree. Additional studies correlated the crop coefficient of mature trees with mid-day canopy light interception. This paper reports on the measured crop water use and the resulting crop coefficient for a well watered, mature, late-season peach variety based on lysimeter measurements and light interception. Materials and methods An experiment was conducted using a 1.0 ha (120·87 m) plot containing a weighing lysimeter located at the University of Irrig Sci (2003) 22: 187–194 DOI 10.1007/s00271-003-0084-4 J. E. Ayars Æ R. S. Johnson Æ C. J. Phene T. J. Trout Æ D. A. Clark Æ R. M. Mead Communicated by P. Thorburn J. E. Ayars (&) Æ T. J. Trout Æ D. A. Clark Water Management Research Laboratory, USDA-ARS, Parlier, CA 93648, USA E-mail: jayars@fresno.ars.usda.gov Tel.: +1-559-5962875 Fax: +1-559-5962850 R. S. Johnson Kearney Agricultural Center, University of California, Parlier, California, USA C. J. Phene SDI, Clovis, California, USA R. M. Mead United Agri Products, PO Box 2357, Fresno, CA 93745, USA