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Research has shown water application rates = 6 L s–1 ha–1 (38 gpm/acre) are more effective than lower rates in reducing fruit temperatures by evaporative cooling (EC). Applications at about 6.25 L s–1 ha–1 (40 gpm/acre) were sufficient to hold core temperatures close to the selected temperature range during a 40° C (104° F) day with clear skies and sunny conditions. Automated control of EC-based on-core temperatures worked well in this project. The management of EC systems should pulse water applications on and off so free water is continually evaporating, hydro-cooling is minimized, and water is conserved.

A long-term research project was initiated in 1983 on a 1.2 ha trickle-irrigated Vitis vinifera vineyard to address water management of White Riesling (WR), Chenin blanc (CB), and Cabernet Sauvignon (CS) grapes in central Washington. Six large drainage lysimeters, two per cultivar, were installed to monitor crop water use. Each lysimeter contained two vines. Vines were balance pruned and shoot-thinned to achieve an equivalent crop level of about 15 Mg/ha of grapes. Analyses showed that published crop coefficients (ET o ) for mature grapes greatly overestimate water use early and late in the season for Washington conditions although peak crop coefficients of about 0.8-0.9 were similar. Annual crop water use for all three cultivars ranged from 130 mm for one-year-old vines in 1985 to as much as 540 mm for mature vines in 1990. The average crop water use for small, young vines (1985–1986) was about 146 mm/yr, and from 1987–1990 for mature plants it was about 417 mm/yr for all three cultivars.

High frequency furrow irrigation can achieve tree growth and yield responses similar to trickle irrigation on sweet cherry trees. Daily surge flow furrow irrigations from 1982 through 1986 were scheduled based on daily pan evaporation. Application efficiencies were near 80% and soil erosion was minimal even though slopes were in excess of 3%. This technique is potentially a low cost alternative to solid-set microirrigation or sprinkle systems in widely-spaced perennial crops. The method is limited to lands normally suited to surface irrigation, but requires automation and careful system management.

‘Golden Delicious’ apples (Malus domestica Borkh.) from trickle-irrigated plots were more mature than sprinkle-irrigated apples. Trickle-irrigated apples were higher in yellow color, soluble solids, and pH. Titratable acidity and moisture were less in fresh and stored apples that were grown with trickle irrigation. Applesauce from trickle-irrigated apples was superior in consistency and developed less free liquor (weep) than sauce from sprinkle-irrigated apples. Drip losses were greater in frozen apple slices from sprinkle-irrigated apples. Canned or frozen apple slices were firmer when produced from apples that were sprinkle-irrigated. The color of apple products from trickle-irrigated apples was superior to the products from sprinkle-irrigated apples. These differences resulted from treatments where leaf water potential differed by only 1 to 2 bars, –14 and –12 bars with trickle and –12 and –11 bars with sprinklers in 1978 and 1979.

Cherry (Prunus avium L.) and prune (P. domestica L.) trees were trickle irrigated daily or weekly at 100%, 50%, and 15% of evaporation from a standard Class “A” pan, adjusted to the area of the tree canopy (Ec), for one full growing season. Soil moisture remained above the wilting point throughout the soil profile with 100% Ec but reached the wilting point except for a wetted zone near the emitters for 50% Ec and 15% Ec. Leaf water potential of shaded cherry leaves at midday averaged near -14 bars for 100% Ec, near -20 bars for 15% Ec, reaching as low as -28 bars for prunes in late July and August. Growth of fruit and vegetative parts was reduced by severe stress but the trees survived on 15% Ec. Prunes recovered to normal yield and growth by the second year after treatment. Peripheral branches of cherries died back during the year of treatment and in the following year. Cherries grew and fruited normally by the third year after treatment except for reduced bearing surface.