Articles
Measurement and modelling of water use by litchi (Litchi sinensis) orchards under subtropical conditions
Article number
1409_23
Pages
167 – 174
Language
English
Abstract
The Inkomati-Usuthu Water Management Area (IUWMA) in north-eastern South Africa is a major producer of subtropical fruit.
Water resources in this catchment are almost fully allocated.
Yet no current information on the water use of major irrigated tree crops such as litchi (Litchi sinensis) exists.
This study aimed to estimate the water use of a full-bearing litchi orchard from basal crop coefficients Kcb determined from readily available data according to Allen and Pereira (2009, AP). In this study leaf stomatal conductance was measured hourly from sunrise to sunset on selected days.
Tree transpiration was measured using the heat ratio sap flow method and the data were used to develop and test a dynamic Jarvis-type leaf conductance sub model that includes responses to vapour pressure deficit (VPD) and solar radiation.
The variable leaf conductance was used to replace the constant values in the AP method.
Whole tree transpiration (T) was modelled as T = Kcb × ETo, where ETo is the reference evapotranspiration.
The modelled stomatal conductance closely matched the measured values (R2~0.96). Modelled daily tree transpiration also closely matched the measured sap flow values (R2 ~0.74, RMSE ~±0.37 mm day‑1 and MAE ~±0.34 mm day‑1). The measured daily transpiration on a typical clear day peaked at approximately 332 L tree‑1 d‑1 with ETo ~7.16 mm day‑1. These results demonstrate that: 1) litchi leaf stomatal conductance can be accurately modelled using readily available weather data in a Jarvis-type model; 2) variable leaf conductances for litchi trees can improve the estimation of Kcb in the AP method, and; 3) mature individual litchi trees planted in low density orchards (~70 trees ha‑1) consume large volumes of water.
These data are essential for improving irrigation scheduling in litchi orchards under subtropical conditions.
Water resources in this catchment are almost fully allocated.
Yet no current information on the water use of major irrigated tree crops such as litchi (Litchi sinensis) exists.
This study aimed to estimate the water use of a full-bearing litchi orchard from basal crop coefficients Kcb determined from readily available data according to Allen and Pereira (2009, AP). In this study leaf stomatal conductance was measured hourly from sunrise to sunset on selected days.
Tree transpiration was measured using the heat ratio sap flow method and the data were used to develop and test a dynamic Jarvis-type leaf conductance sub model that includes responses to vapour pressure deficit (VPD) and solar radiation.
The variable leaf conductance was used to replace the constant values in the AP method.
Whole tree transpiration (T) was modelled as T = Kcb × ETo, where ETo is the reference evapotranspiration.
The modelled stomatal conductance closely matched the measured values (R2~0.96). Modelled daily tree transpiration also closely matched the measured sap flow values (R2 ~0.74, RMSE ~±0.37 mm day‑1 and MAE ~±0.34 mm day‑1). The measured daily transpiration on a typical clear day peaked at approximately 332 L tree‑1 d‑1 with ETo ~7.16 mm day‑1. These results demonstrate that: 1) litchi leaf stomatal conductance can be accurately modelled using readily available weather data in a Jarvis-type model; 2) variable leaf conductances for litchi trees can improve the estimation of Kcb in the AP method, and; 3) mature individual litchi trees planted in low density orchards (~70 trees ha‑1) consume large volumes of water.
These data are essential for improving irrigation scheduling in litchi orchards under subtropical conditions.
Authors
P. Dangare, G.P. Nel, T. Sawunyama, P.J.R. Cronje, S. Dzikiti
Keywords
Allen and Pereira method, basal crop coefficient, Jarvis model, stomatal conductance, transpiration
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