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Abstract: Availability of fresh water is one of the elementary conditions for life on Earth, however, water is a limited resource, which is now under an unprecedented pressure by global population growth, climate change and demand from several economic sectors such as tourism, industry, and agriculture. In particular, irrigated agriculture is one of the major water-consuming sectors. The aforementioned issues justify the need for a sustainable and rational use of water in irrigated crops, which motivates the implementation of new precise automatic irrigation technologies based on control theory. In this paper, we introduce the main concepts of control theory, how can it be applied to irrigation and a literature review of automatic irrigation control systems over the last decade. In addition, we present our latest developments in this field. In particular, we present some promising preliminary experimental results of four different control strategies applied to fruit trees in southern Spain to show the potential of the application of control techniques to irrigation. [Copyright &y& Elsevier]

Strawberry production requires the input of large amounts of water and its cultivation under plastic tunnels, relies entirely on water provided by irrigation during the production cycle. In these systems, water management is not easy, since soils are very poor and with low water holding capacity (sandy soils), and growers tend to use excessively and inadequately supplied water. This is especially tough at Huelva (the most important strawberry cropping area in Europe), where water is scarce and its use for irrigation is limited. Knowledge of water requirements of the main competitive strawberry cultivars of the region and their physiological and agronomical response to possible restrictions on water supply is required to keep its environmental sustainability. In this sense, no information pertaining to water requirements, crop-water use efficiency (WUE c ) and to the relative response to water shortage of the main strawberry cultivars currently growing in Huelva is available. Two experimental designs were carried out for the comparative evaluation of water requirements of seven strawberry cultivars ( Fragaria × ananassa Duch.) and of their physiological and growth response to water shortage (70% ETc). Main results showed that water consumption differs substantially among cultivars and these differences were associated with differences in the biomass partitioning into the harvest product (i.e. harvest index; HI) and in the transpiration efficiency of the standing biomass (TE v ) closely related to instantaneous water use efficiency ( A / T ). Cultivars were segregated on the basis of the relationship between both parameters, which integrate the differences among cultivars at the physiological (chlorophyll fluorescence, gas exchange, SPAD index, etc.) and at the growth response (fruit production, patterns of carbon allocation, LMA) levels in both water treatments. It is concluded that, in horticultural crops, such strawberry, greater leaf-level water use efficiency is not always an agronomical advantage in terms of water use. [ABSTRACT FROM AUTHOR]

Abstract: We applied two process-based models in a hedgerow olive orchard with the aim of understanding the limitations and mechanisms behind the control of transpiration in olive trees under drip irrigation. One model is based on the biophysics of water flow through the porous media of soil and xylem. The other is a hydromechanical model based on the observed dependence of stomatal aperture on whole-plant and epidermis water relations. The experiments were made in a hedgerow olive orchard (1667treesha−1) planted with 5-year-old ‘Arbequina’ trees. Measurements were made in control trees irrigated to replace 100% of the crop water needs, and in trees under regulated deficit irrigation (RDI) strategy, in which irrigation replaced ca. 30% of the control. Soil physical properties, root distribution, leaf area, sap flow, leaf osmotic pressure and key variables of leaf gas exchange and water status were measured and models were applied. Results show how in our orchard, with a shallow root distribution and very coarse soil, most of the limitation to transpiration was imposed by the hydraulics of the rhizosphere. The model shows how this limitation was related to the ratio of root to leaf area, and how this ratio can be managed by canopy pruning or by changing the number of drippers. Likewise, osmotic adjustment occurred similarly in both irrigation treatments, despite differences found on leaf water potential. Water stress largely affected plant hydraulic conductivity of RDI trees. A potential involvement of regulating signals, other than purely hydraulics, was evident in both treatments, although our data suggests that these signals were not regulated by the soil water status only. [Copyright &y& Elsevier]