Water use by drip-irrigated late-season peaches

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 irrigated 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 coefficient (Kc) was calculated using the measured water losses and grass reference evapotranspiration calculated using the CIMIS Penman equation. Kc 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 Kc 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.