Crop Coefficients and Transpiration of a Super Intensive Arbequina Olive Orchard using the Dual Kc Approach and the Kcb Computation with the Fraction of Ground Cover and Height

Teresa Paço,Francisco Santos,José Silvestre,Luis Pereira,Paula Paredes

doi:10.3390/w11020383

Abstract

The SIMDualKc model was used to simulate crop water requirements for a super high density olive orchard in the region of Alentejo, Portugal. This model uses the dual crop coefficient approach to estimate and partitioning the actual crop evapotranspiration (ETc act) and therefore to perform the soil water balance. The model was calibrated with 2011 tree transpiration using trunk sap flow measurements and was validated using similar data from 2012 and tested with 2013 data. Low root mean square errors (RMSE < 0.53 mm·d−1) and acceptable modelling efficiency indicators (EF > 0.25) were obtained. Further validation was performed comparing modelled ETc act with eddy covariance measurements. These indicators support the appropriateness of using SIMDualKc to guide irrigation management. The basal crop coefficient (Kcb) curves obtained with SIMDualKc for those 3 years were compared with the Kcb values computed with the Allen and Pereira approach (A&P approach) where Kcb is estimated from the fraction of ground cover and plant height considering an adjustment factor for crop stomatal control (Fr). Fr values were obtained through a trial and error procedure through comparing the Kcb estimated with this approach and with SIMDualKc. The Kcb curves obtained by both methods resulted highly correlated, which indicates that the A&P approach may be used in the irrigation management practice to estimate crop water requirements. Results of performing the soil water balance with SIMDualKc have shown that soil evaporation is a large fraction of ETc act, varying between 41% and 45% for the 3 years under study. Irrigation, applied with a drip system, represented 39 to 56% of ETc act, which shows the great importance of irrigation to achieve the water requirements of super intensive olive orchards. Nevertheless, the analysis has shown that the irrigation management adopted at the orchard produces a water deficit larger than desirable, with a ratio of ETc act to non-stressed crop evapotranspiration (ETc) varying from 70% to 94% during the mid-season, when that ratio for a eustress irrigation management could be around 90%.

Highlights

Olive orchards consist of the dominant permanent crops in Portugal, covering approximately50% of the total area with tree crops, namely in Alentejo, southern Portugal, where olives are mainly cropped for oil production
Information on crop evapotranspiration can be obtained through using various field measurements techniques [14], those involving direct measurements of ET are generally expensive, labour consuming, require appropriate skills of users and are more appropriate for research, that is, for example, measurements of soil water content [15,16], sap-flow [17,18,19] and eddy covariance [18,19,20], which are applied in this study
The dynamics of both Tc act and transpiration derived from sap-flow measurements (TSF) are coherently described for all three years but fitting is less good for 2012 due to the heavy frost and subsequent pruning that occurred by that winter

Summary

Introduction

Olive orchards consist of the dominant permanent crops in Portugal, covering approximately50% of the total area with tree crops, namely in Alentejo, southern Portugal, where olives are mainly cropped for oil production. Super high density olive orchards, with more than 1500 trees ha , known as hedgerow olive orchards, are growing fast due to their high yield and economic productivity [1,2,3]. They have higher water requirements than less intensive orchards [1]; it is necessary to improve related knowledge about crop evapotranspiration to support appropriate irrigation management and scheduling [4,5].

Methods

Results

Conclusion