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Crop yield response to water - Cra

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The model Aqua<strong>Crop</strong> computes E for the two stages according <strong>to</strong> the equations:(3)E Stage I =(1-CC*)Ke x ET oE Stage II =Kr(1-CC*)Ke x ET oWhere, CC is canopy cover, (1-CC*) is the non-shaded, exposed soil from which evaporationtakes place, corrected with an advection coefficient; Ke x is a coefficient set at 1.1, and Kr is areduction coefficient, which is calculated as a function of the soil-<strong>water</strong> content of the uppersoil surface layers.Figure 9 shows a calculation of bare soil evaporation using the Aqua<strong>Crop</strong> model for a periodof 15 days after a thorough irrigation.figure 9 Evaporation from bare soil in midsummer calculated with the Aqua<strong>Crop</strong> model following60 mm irrigation.876E (mm)5432100 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16DayThe major complication in computing E from an orchard or vineyard is that the soil is partiallyand dynamically shaded by the crop canopy, and even if the surface is wet, E is limited by theincoming energy.The spatial variation of incoming energy within the orchard floor depends on tree spacing,canopy size and architecture and on the leaf area density. Some models have been developed<strong>to</strong> compute E under orchards and they can be used <strong>to</strong> compute E from soil that is wetted byeither rainfall or by full coverage irrigation.Yield Response <strong>to</strong> Water of Fruit Trees and Vines 259

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