Stress Coefficients for Soil Water Balance Combined with Water Stress Indicators for Irrigation Scheduling of Woody Crops

Abstract

There are several causes for the failure of empirical models to estimate soil water depletion and to calculate irrigation depths, and the problem is particularly critical in tall, uneven, deficit irrigated (DI) crops in Mediterranean climates. Locally measured indicators that quantify water status are useful for addressing those causes and providing feed-back information for improving the adequacy of simple models. Because of their high aerodynamic resistance, the canopy conductance of woody crops is an important factor in determining evapotranspiration (ET), and accurate stress coefficient (Ks) values are needed to quantify the impact of stomatal closure on ET. A brief overview of basic general principles for irrigation scheduling is presented with emphasis on DI applications that require Ks modelling. The limitations of existing technology related to scheduling of woody crops are discussed, including the shortcomings of plant-based approaches. In relation to soil water deficit and/or predawn leaf water potential, several woody crop Ks functions are presented in a secondary analysis. Whenever the total and readily available water data were available, a simple Ks model was tested. The ultimate aim of this discussion is to illustrate the central concept: that a combination of simple ET models and water stress indicators is required for scheduling irrigation of deep-rooted woody crops.

Plant Water Status Indicators for Irrigation Scheduling Associated with Iso- and Anisohydric Behavior: Vine and Plum Trees

“…We consider that this example illustrates anisohydric behavior, due to the fact that differences in Ψst at noon were much higher than at pre-dawn, the main criteria we considered. Transpiration rates and Kc values as well as the relationship between RTr and Ψ pd (Ks function) were already presented and discussed in comparison with three other vineyards, mostly rainfed [1,56], where the vineyard described here was the one suffering more stress in spite of being irrigated, with the Ks function (Ks = 1.0011 exp −1.829 Ψ pd , r 2 = 0.73) distinct from other functions obtained for the rainfed situations (lower Ks for the same Ψ pd ). In parallel with this Ks function for grapevines, a Ks function from Ψ st for the plum orchard of Experiment 2 will be presented below.…”

“…The use of water stress indicators to schedule irrigation requires the selection of which variables should be used as well as their threshold values for different objectives concerning marketable yields (when to irrigate). Finally, the coordinated use of these approaches or steps can lead to a self-learning process, as proposed by Ferreira [1]. The use of soil water content (θ s ) can directly serve both purposes (when and how much), and is considered the ideal variable in low continuous crops though it presents several challenging difficulties when applied to woody crops.…”

“…Any excess application loses the benefit of the regulated deficit applied and any sub-application can lead to severe losses in yield or quality. Indeed, if water stress indicators, such as those based on plant water status, are used without estimating SWD, the exact amounts of water to be applied must be calculated from various tests that may result in an excessive or deficient amount of irrigation water, until the desired amount is found (trial and error [1,8]). …”

Monitoring Crop Evapotranspiration and Crop Coefficients over an Almond and Pistachio Orchard Throughout Remote Sensing

“…However, in order to determine optimal irrigation scheduling and to adopt such strategies efficiently, it is necessary to have reliable methods that provide information about the temporal and spatial variability of crop water requirements and, to understand the seasonal physiological responses to water stress. Therefore, the need for developing simple crop evapotranspiration (ET) modeling approaches with the inclusion of water stress indicators is required to quantify stress under deficit irrigation (DI) applications and for scheduling irrigation [10].…”

Evaluation of the Effect of Irrigation on Biometric Growth, Physiological Response, and Essential Oil of Mentha spicata (L.)

“…However, there is uncertainty in several aspects, including in the critical value of p. In order to illustrate the impact of changing this parameter to a lower value, typical of plants where water use is very sensitive to soil water depletion, p = 0.2 was taken, obtaining outputs (Figure 4b) very different, where stress effects on evapotranspiration are expected from DAT 25 (I 0 ) and 30 (I 50 ) onwards. Unfortunately, to our knowledge, there are no dedicated experimental studies to get this parameter for this crop regarding stress function studies [43], so the uncertainty remains. Figure 5 reveals biometric results for the three irrigation treatments (I 0 , I 50 and I 100 ).…”