ReviewIrrigation scheduling from stem diameter variations: A review
Section snippets
Towards precise irrigation scheduling
Fruit tree orchards are common in arid and semi-arid areas where water for irrigation is scarce. This, together with an increasing world population that has to be fed and with other water-using sectors competing for the limited water resources, makes the use of precise irrigation techniques in those orchards unavoidable. The response of the scientific community to this challenge has been to invest a substantial amount of research in the development of deficit irrigation approaches (Goodwin and
Fundamentals
There is a substantial amount of literature on the fundamentals of stem diameter variations (SDV). When transpiration (Ep) begins early in the morning, a tension is created in the xylem from the evaporative surface of the leaves to every organ of the plant. Part of the water stored in the plant tissues during the night is then lost, allowing the plant to respond rapidly to changes in atmospheric demand, without the need to rely on water uptake by the roots, which starts later (Hinckley and
SDV and water potential
Values of Ψstem are widely used to assess the plant water status, because of their reliability, low variability, and relatively good prediction of yield response to water stress (Shackel et al., 1997, Naor, 2006). In fact, Ψstem is considered to be more sensitive than other indicators such as stomatal conductance (gs) and net CO2 assimilation rate (A), at least for moderate water deficits (Goldhamer et al., 1999, Moriana and Fereres, 2002). Their measurements cannot, however, be easily
Difficulties for interpreting SDV records
Interpreting SDV records for irrigation scheduling is, in most cases, far from straightforward. In fact, expert supervision is usually required when using SDV records for irrigation scheduling. This is one limitation of SDV-derived indices for automating irrigation; another is that SDV does not depend solely on water stress, as we have just mentioned. Below, we detail to what extent plant characteristics and crop management affect the reliability of SDV records. Additional causes are mentioned
Irrigation scheduling from SDV records
The use of SDV records for irrigation scheduling was first proposed by Hendrickson and Veihmeyer (1941). A device which used the relationship between SDV and the water status of fruit trees to control irrigation was patented by the French Institut National de la Recherche Agronomique (INRA) in 1984 (Huguet et al., 1992). Huguet (1985), Li et al. (1989), Schoch et al. (1989), Li and Huguet (1990), Pelloux et al. (1990), and Huguet et al. (1992) used SDV records for irrigation scheduling. Garnier
Conclusions
SDV measurements have great potential for scheduling irrigation in commercial orchards of grapevines and fruit trees, although several factors can easily affect the usefulness of the SDV-derived indices when the method is not properly used. First, robust and reliable LVDT sensors and related equipment for data collection and transmission, suitable for operating in the field for the whole irrigation season, are available on the market. In most cases, however, little care is taken to prevent
Acknowledgements
Drs. A. Moriana, D. Intrigliolo, and A. Torrecillas clarified some of our doubts on how to handle SDV records, and sent us valuable comments and suggestions. Dr. A. Diaz-Espejo helped us with ecophysiological concepts, and Dr. E. Chacón with mathematical aspects. The experiments made by the authors were funded by the Consejería de Innovación, Ciencia y Empresas of the Junta de Andalucía (research projects C03-056 and ECOSAT), and by the EU research project ref. STREP 023120. We thank the
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