Abstract
Irrigation scheduling is often performed based on a soil water balance, where orchard evapotranspiration is estimated using the reference evapotranspiration (ETo) times the crop coefficient (Kc). This procedure, despite being widely spread, has some uncertainties. Because of this, plant and soil water status monitoring could be alternatively or complementarily used to schedule irrigation. The usefulness of capacitance probes was evaluated during several seasons in large irrigation districts where irrigation practices were changed over years from the ETo * Kc model to the analysis of soil water status trend. This area corresponds to drip irrigated orchards planted with citrus, peach, nectarine and persimmon. Around 25% less irrigation was applied with no substantial yield penalty when the information provided by capacitance probes was correctly applied for irrigation management. On the other hand, the usefulness of stem dendrometers for continuously monitoring plant water status was evaluated in a young plum experimental orchard. Over two years, irrigation was scheduled using exclusively trunk shrinkage via the signal intensity approach by means of a baseline equation previously obtained in the orchard. Results showed that it was not always possible to schedule irrigation based on the trunk shrinkage signal intensity due to the temporal changes in the reference values that occurred as trees aged. Overall, results obtained are discussed in terms of the possible extrapolation at field level of both capacitance probes and stem dendrometers. Advantages and drawbacks of each technique are analyzed and discussed.
Highlights
Irrigation scheduling is often performed based on a soil water balance, where orchard evapotranspiration is estimated using the reference evapotranspiration (ETo) times the crop coefficient (Kc), according to the procedure suggested by FAO (Allen et al, 1998)
The irrigation scheduling based on a soil water balance only provides information on the amount of water to apply to an orchard during a certain period
The irrigation scheduling approach with the capacitance probes was based on the following two main points: 1) the maintenance of soil water content (SWC) in the 10-50 cm depth in an optimum range between field capacity and an allowable soil water depletion that depends on the farmer strategy, crop species and phenological periods for each species, and 2) avoiding water percolation down to 70-80 cm in order to minimize water lost by drainage
Summary
Irrigation scheduling is often performed based on a soil water balance, where orchard evapotranspiration is estimated using the reference evapotranspiration (ETo) times the crop coefficient (Kc), according to the procedure suggested by FAO (Allen et al, 1998). Measurements of plant water status integrate both soil water available to the plants and the climatic conditions, and might provide for a better prediction of tree responses to water supply (Intrigliolo and Castel, 2006a). In this sense, stem water potential is the more commonly used parameter to estimate plant water status (Shackel et al, 1997).
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