The use of sap flow measurements for scheduling irrigation in olive, apple and Asian pear trees and in grapevines

Abstract

We evaluated three approaches for scheduling irrigation in wine grape vineyards and in olive, apple and Asian pear tree orchards, based on sap flow measurements and models of plant transpiration. In the first approach, we analysed how the shape of the sap-flow profile changed in response to root-zone soil water conditions and potential evaporative demand. The second approach was based on a transpiration ratio, as defined from the actual daily water use of a target plant divided by the potential daily water use of similar-sized plants under non-limiting soil water conditions ("well-irrigated" plants). Values of the actual plant water use were always determined from measured sap flow. Two independent methods were assessed for the calculation of potential plant water use; either sap flow was measured in well-irrigated plants or we used a leaf-area based model of plant transpiration. On some occasions water stress was found to modify the shape of the sap velocity profile. However, most of the time the velocity profile was found to be an insensitive indicator for triggering irrigation. The transpiration ratio method, using measured sap flow in well-irrigated plants, was more useful for irrigation scheduling, at least for the two species (i.e. olive and grape) that were investigated here. Nonetheless, realization of such an approach in a commercial orchard may not be practical due to problems associated with irrigation management e.g. excessive vegetative growth may occur on the reference plants over time. Besides, irrigating the orchard to maintain non-limiting soil water conditions is not always the best option for water and nutrient management. The alternative transpiration ratio method based on a leaf-area based model of plant water use, yielded the best results. Modelled transpiration rates always provided reliable information not only for well-irrigated plants, but also for deficit-irrigated plants. This result lends support to the use of the method for irrigation scheduling of vineyard and orchard trees. However, the use of models does require detailed microclimate data as well as a userfriendly technique to quantify plant leaf area. From a practical viewpoint the method should encompass the spatial variability of the soil and plants within the orchard. Accurate quantification of these factors is a cornerstone of precision horticulture and such inforPlant Soil (2008) 305:91-104 mation would help to minimise risks associated with insufficient as well as excessive irrigation applications.

Coffee crop coefficient for precision irrigation based on leaf area index

“…It is interesting to note that the present results is substantiated by those obtained previously with different plant species such as grapefruit in Israel (Cohen, 1991) (Pereira et al, 2006;Fernández et al, 2008), and Tahiti acid lime in Brazil (Pereira and Villa Nova, 2009). Such results with very distinctive crops show that ET LA becomes independent of plant size and tend to merge in a unique linear relationship of ETo.…”

“…Consequently, the most likely value for the linear regression coefficient is 2.88 -1 = 0.347. Therefore, Kc = 0.347 L, as proposed by Villa Nova et al (2002), is theoretically sound for orchard and isolated trees (Pereira et al, 2006;Fernández et al, 2008). However, for coffee plantations such linear model for Kc is limited to L ≤ 3 as shown in figure 2.…”

“…Micrometeorological changes due to the canopy growth are discussed to support such inference. As recommended elsewhere (Pereira et al, 2006;Fernández et al, 2008) in order to become an operational tool in real-time precision irrigation schemes it is necessary an easy way to estimate plant leaf area. Simple empirical relationships between plant leaf area and planting rate or canopy volume interpreted to substantiate the discussion and to define thresholds.…”

Plant-Based Methods for Irrigation Scheduling of Woody Crops

“…For the correct use of terms, units and symbols related to sap flow, the papers by Edwards et al [91] and Lemeur et al [92] are recommended. Sap flow-related measurements are widely used in research for in situ determinations of plant water consumption and transpiration dynamics (Figure 7), and their potential for irrigation scheduling has been assessed by Nadezhdina [93], Fernández et al [94,95] and Jones [30], among others. Devices to schedule irrigation automatically from sap flow measurements have been designed and tested in fruit tree orchards [96,97], and comparisons with other methods to monitor plant water stress and to schedule irrigation have been made for a variety of crops, including apple [93], grapes [98], lemon [99], plum [100] and olive [101,102], among other species.…”

Evaluation of evapotranspiration models for estimating daily reference evapotranspiration in arid and semiarid environments

“…For example, Moriana et al (2003) showed that a decrease in olive productivity was observed when irrigation application approached that of maximum crop water requirement (ET c ). Thus, ET o models can help to choose an appropriate deficit irrigation approach by combining ET o information with the crop performance and soil water content (Fernandez et al 2001(Fernandez et al , 2008. Therefore, irrigation can be carried out according to recommendations based on ET o and crop coefficients, with adjustments according to crop water status assessments such as leaf water potential measurements, plant stem diameter, and sap flow measurements.…”