Crop yield response to water - Cra

ox 4 Sample calculation of E dz , E wz , and Tr cc .Assume an olive orchard with a tree ground cover, G, of 0.33; the average monthly ET o inApril is 3.5 mm/day; the emitters wet 7 percent of the ground (wz=0.07), and there are 7rainy days per month (F=7/30 = 0.23).a) Calculation of E from soil not wetted by emitters, E dz ,Using Equation 5 and 6, the average E dz for the month of April is:K s,e = 0.31 x (1-0.07) = 0.29E dz = 0. 29 x 3.5 = 1.01 mm/day or 30.4 mm/monthb) Calculation of E from wet spots E wzEquation 8 yields:E wz = 0.6 x 3.5 x 0.07 = 0.147 mm/day or 4.4 mm/monthc) Calculation of cover crop Tr cc ,If the olive orchard with 8 x 6 m tree spacing, has a cover crop that covers a strip 4 m wideevery tree row (f cc = 4/8), and is fairly dense and kept cut about 5-8 cm height, the wateruse of the cover crop would be estimated as:Tr cc = 0.45 x 3.5 mm/day x 0.5 = 0.79 mm/day or 23.6 mm for the month of AprilCalculation of E wzHere, as a first approximation, E wz is calculated as(7) E wz = 0.6 ET o wzWhere 0.6 is an empirical factor described above and wz is the fraction of the soil surface thatis kept wet by the emitters.Calculation of transpiration from the cover crop, Tr ccOrchards with cover crops have higher ET rates than orchards that are clean cultivated. Thewater-use rate of cover crops in orchards is difficult to measure and has not been thoroughlyinvestigated. Either cover crops are planted in strips of variable width between tree rowsor, sometimes, weeds are allowed to grow in these areas and are controlled periodically bycutting or with herbicides. Cover crops are shaded at least part of the day, and it is difficultto measure their ET independently of the other ET c components. The Tr cc will vary widely,depending on the cutting frequency, plant density, degree of shading by the tree canopies,and whether it has sufficient water available, i.e. whether the cover crop is fully wetted by theirrigation applications. Thus, the estimation of Tr cc is site specific. The approach to calculate ituses a coefficient, K cc and the ET o as follows:Yield Response to Water of Fruit Trees and Vines 261