WATER USE OF FRUIT TREE ORCHARDS - CSIRfred.csir.co.za/extra/project/fruittrees/...1770ScientificArticle.pdf · WATER-USE OF FRUIT TREE ORCHARDS S ... 2University of Pretoria Deliverable

WATER-USE OF FRUIT TREE ORCHARDS

SCIENTIFIC ARTICLE

PREPARED BY:

Mark Gush 1, Michael Mengistu 1, Walter Mahohoma 2 and Nicolette Taylor 2 1CSIR, 2University of Pretoria

Deliverable submitted to the Water Research Commiss ion – Project K5/1770

November 2009

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SUMMARY

This report covers the drafting, presentation and publication of scientific

articles linked to the project in order to meet the requirements of project

deliverable 9, namely: Scientific articles covering interim field work

measurement results.

The 14th SANCIAHS Symposium, held between 21 to 23 September 2009 and

hosted by the University of KwaZulu-Natal in Pietermaritzburg, provided an

ideal opportunity to disseminate some of the interim results from this project.

Following the acceptance of an abstract submitted by the project team

(Mengistu et al., 2009), a poster was drafted and presented to symposium

delegates on the evening of Day 1. The poster was well received and

following evaluation by a panel of judges was subsequently selected as “Best

Poster” at the symposium, for which a prize to the principal author (Michael

Mengistu) was awarded. An extended abstract aligned with the poster was

also drafted and appears in the proceedings of the symposium. An image of

the poster as well as the extended abstract, are appended below.

A further abstract for an upcoming conference (Combined Congress) to be

held between 18-21 January 2010 at the University of the Free State in

Bloemfontein, was submitted by Walter Mahohoma (a University of Pretoria

PhD student on the project team), and has been accepted for oral

presentation. The abstract is appended below.

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TABLE OF CONTENTS PAGE

SUMMARY .......................................................................................................I

TABLE OF CONTENTS .................................. ................................................II

1. APPENDIX 1: SANCIAHS POSTER........................ ...............................1

2. APPENDIX 2: SANCIAHS PAPER ......................... ................................2

3. APPENDIX 3: COMBINED CONGRESS ABSTRACT............. .............12

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1. APPENDIX 1: SANCIAHS POSTER

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2. APPENDIX 2: SANCIAHS PAPER

Water use of fruit tree orchards: Comparing apples with oranges M.G. Mengistu 1*, M.B. Gush 1, N.J. Taylor 2, E. Etissa 2, A.D. Clulow 1, C. Jarmain 1 1CSIR – Natural Resources and the Environment, c/o Agrometeorology, UKZN, Private Bag X01, Scottsville, 3209, South Africa 2Department of Plant Production and Soil Science, University of Pretoria, Pretoria, 0002, South Africa E-mail: [email protected] Abstract The water use of ‘Cripps Pink’ apples and ‘Delta’ Valencia oranges was estimated for different seasons in 2008 and 2009. Heat pulse velocity (HPV) systems were used to monitor sap flow rates from the apple and orange trees. Total evaporation was estimated using the surface renewal (SR) and eddy covariance (EC) methods. Total evaporation and transpiration from the apple and orange trees ranged from 0 to 2 mm day-1 in winter and 3 to 8 mm day-1 in summer depending on the available energy at the orchard surface. The water use of the apple trees was close to 0 mm day-1 in winter as they lose their leaves compared to the evergreen orange trees with an average water use between 1 and 2 mm day-1. Significant variation in the seasonal water use of the apple trees is observed in contrast to the oranges which are more consistent. Keywords: Eddy covariance, sap flow, surface renewal, total evaporation, fruit tree 1. Introduction There is an urgent need to improve the management of irrigation water and water use of fruit trees worldwide and especially in water scarce countries such as South Africa, with mean annual rainfall less than the world’s average. Currently, there is a lack of comprehensive information on the water use of fruit trees that can be used for on-farm water management and water resources planning. Existing models in South Africa cannot confidently simulate water use of fruit trees for different climate, soil, water and management conditions. In addition, water use estimated from soil based measurements is very challenging due to the complexity of fruit tree orchards. The use of field measured sap flow rates and total evaporation can provide accurate estimates of water use of fruit trees. Total evaporation can be estimated using micrometeorological methods such as eddy covariance and the surface renewal techniques, while heat pulse velocity (HPV) systems can be used to monitor sap flow rates from different species of trees to estimate transpiration. The aim of this study was to estimate and compare the seasonal water use of ‘Cripps Pink’ apples and ‘Delta’ Valencia oranges from measurements of total evaporation (EC and SR methods) and transpiration using the HRM method. 2. Theory The eddy covariance (EC) method provides a direct measure of the vertical turbulent flux of a scalar entity of interest sF across the mean horizontal stream lines (Swinbank, 1951) providing fast response sensors (10 Hz) for the wind vector and scalar entity of interest are

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available (Meyers and Baldocchi, 2005). For a sufficiently long averaging period of time over horizontally homogeneous surface, the flux is expressed as:

's'wF as ρ= (1) where aρ is the density of air, w is the vertical wind speed and s is the concentration of the scalar of interest. The primes in Equation (1) indicate fluctuation from a temporal average (i.e., ww'w −= ; ss's −= ) and the over bar represents a time average. The vertical wind component is responsible for the flux across a plane above a horizontal surface. Based on Equation (1), the sensible heat flux (H) can be expressed as:

'T'wcH spaρ= (2)

where pc is the specific heat capacity of air, 'w denotes the fluctuation from the mean of the

vertical wind speed, and 'Ts is the fluctuation of air temperature from the mean. The

averaging period of the instantaneous fluctuations, of 'w and 's should be long enough (30 to 60 minutes) to capture all of the eddy motions that contribute to the flux (Meyers and Baldocchi, 2005). The surface renewal (SR) method is based on the idea that an air parcel near a surface is renewed by an air parcel from above. This method is relatively new, attractive and simple (Paw U et al., 1995; Snyder et al., 1996; Spano et al., 1997a, b, 2000; Drexler et al., 2004). The SR method for estimating fluxes from canopies involves high frequency air temperature measurements (typically 2 to 10 Hz) using fine wire thermocouples. Sensible heat flux (H) is estimated as (Snyder et al., 1996):

za

cH pa ταρ= (3)

where α is a weighting factor (a correction factor for unequal heating or cooling of the air parcel), a is amplitude, τ inverse ramp frequency, and z the measurement height. The weighting factor α , depends on the measurement height, canopy structure, thermocouple size, and the time lag used in the air temperature structure function (Snyder et al., 1996; Duce et al., 1998; Spano et al., 1997a, b, 2000; Paw U et al., 2005). Generally, α = 0.5 for coniferous forest, orchards, and maize canopies for measurements taken at canopy height (Paw U et al., 1995). Latent energy flux density Eλ may be estimated indirectly as a residual of the shortened energy balance using sensible heat flux density H , measured net irradiance nR , and soil heat

flux density G as:

HGRE n −−=λ (4) Heat pulse velocity (HPV) systems can be used to monitor sap flow rates from different species of trees to estimate transpiration. The heat ratio method (HRM) is used in this study to estimate transpiration as an HPV system. The HRM is a temperature measurement method which uses a short pulse of heat as a tracer to measure sap flow in xylem tissue (Burgess et al., 2001). The magnitude and direction of water flux is then calculated by measuring the ratio of heat transported to two symmetrically placed temperature sensors (thermocouples) above and below the heater probe. 3. Materials and methods 3.1 Site description of the orchards

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The apple orchard study was carried out at Nooitgedacht Farm, about 40 km north of Ceres, South Africa (33o12’ S, 19o20’ E, elevation 1089 m) over 11-year old micro-spray irrigated ‘Pink Lady’ (Cripps Pink Variety) apple trees. The study was conducted on a 134 m by 172 m north-south oriented plot. The average height of the trees was 5 m. The spacing between trees was 1.5 m and the spacing between rows was 4m. The fetch distance from the prevailing N-W winds was 110 m. The orange orchard site was at Moosrivier Farm (Schoeman Boerdery), about 16km north of Groblersdal, South Africa (25° 02’ 32.69” S and 29° 22’ 09.76” E, elevation 900 m) over 10-year old drip irrigated Delta Valencia Orange trees. The study was conducted within a 592 m by 597 m north-south oriented circular plot. The average height of the trees was 5 m. The spacing between trees and rows were 2.75 m and 5.75 m respectively. The fetch distance was 300 m from the prevailing N winds. 3.2 Instrumentation and methodology Air temperature was measured using two unshielded type-E fine-wire thermocouples (75-µm diameter) placed at heights of 6.4 and 7.5 m above the ground surface for the apple orchards. The fine-wire thermocouples were at 5.2 and 7.2 m (July, 2008) and 5.8 and 7.0 m above the ground surface (January, 2009). An RM Young three-dimensional ultrasonic anemometer (Model 81000, R.M. Young, Traverse city, Michigan, USA), was set up to measure sensible heat flux density at 8.0 m. All sensors were mounted on a lattice mast located in the middle of the plots, and were connected to a CR3000 datalogger (Campbell Scientific Inc., Logan, Utah, USA). Air temperature data were sampled at a frequency of 10 Hz and then lagged by 0.4 s and 0.8 s. The second, third and fifth air temperature structure function values required by the Van Atta (1977) approach were then formed after lagging the air temperature data. The data were then averaged and stored every two minutes in the datalogger. All eddy covariance data were also sampled at a frequency of 10 Hz and data were processed online in the datalogger and averaged every thirty-minute. Half-hourly EC sensible heat flux values were plotted against SR estimates computed using Equation (3) to determine α by forcing the linear regression through the origin. The weighting factor α is 0.5 for tall canopies such as coniferous forest, orchards, and maize canopies for measurements taken at canopy height (Paw U et al., 1995). In this study, α value of 0.5 was used to correct the SR sensible heat flux. Energy balance measurements for the apple orchards were conducted from 12 to 16 May (2008) and 3 to 18 December (2008). For the orange orchards, energy balance measurements were conducted from 29 July to 4 August (2008) and 27 January to 4 February (2009). Net irradiance was measured using two net radiometers (Model 240-110 NR-Lite, Kipp & Zonen, Delft, The Netherlands) above the trees and between the rows placed at 6.4 m from the ground surface. Four soil heat flux plates (model HFT-S, REBS) were used to measure soil heat flux density at a depth of 80 mm under the trees and between the rows and a system of four parallel-thermocouples at depths of 20 and 60 mm were used to calculate the heat stored above the plates. Volumetric soil water content was measured using a time domain reflectometer (CS616, Campbell Scientific). The sensors were connected to a CR23X datalogger and measurements were every ten seconds and averages obtained every ten minutes. The heat ratio method (HRM) of the HPV technique (Burgess et al., 2001) was used to measure sap flow rates. Sap flow monitoring systems were installed in four trees at each orchard site, using thermocouple (type-T) pairs and heater probes inserted to different depths within the sapwood to determine radial variations in sap flow. A CR10X data logger connected to two AM16/32 multiplexers (Campbell Scientific, Logan, UT) was programmed to initiate the heat pulses and record hourly data from the respective thermocouple pairs. Cellular phone modems connected to the loggers allowed remote downloading of data as well as uploading of programmes to the logger. Sap flow rates were monitored continuously from 16 May 2008 (apples) and 31 August 2008 for the oranges. Raw heat pulse velocity data are converted to total daily sap flow (in litres and millimetres). Measurements of sapwood area, moisture content and density, as well as the width of wounded (non-functional) xylem around the thermocouples are required to do this. These sapwood measurements are usually taken at the conclusion of the experiment due to the destructive sampling required. In this case wood

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cores of adjacent trees were taken to confirm bark thickness, sapwood depth, sapwood moisture content and wood density. It was however not possible to confirm wounding widths in the apple trees, as this would have necessitated removal of the HPV probes and damage to the trees, which would have disrupted measurements. A certain wound width was therefore assumed and used in the calculation of tree water-use values. These assumed wound widths will be confirmed once the HPV probes are removed from the apple trees at a later stage. For the orange trees, however, measurements of all the above variables, including wounding widths, were taken following the removal of some of the probes. 4. Results and discussion 4.1 Energy balance measurements The diurnal variation in H estimates using the SR and EC methods, net irradiance (Rn), and soil heat flux density (G) are shown in Figures 1 and 2 for different seasons in 2008 and 2009. Sensible heat flux estimates varied with time throughout the day and from day to day following the trend of fluctuation of the net irradiance. The energy balance components varied from season to season for both orchards, with summer being a season with the highest magnitude of the energy fluxes (Figures 1b and 2b). Latent energy flux (W m-2) was estimated as a residual of the shortened energy balance using Equation 4. Total evaporation is calculated by converting the latent energy flux (W m-2) to mm s-1 and then to daily water use (mm day-1) using the latent heat of vaporization (2.54 M J Kg-1).

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(a)

-100

0

100

200

300

400

500

134 135 136 137

Day of year (2008)

En

ergy

flu

x (W

m-2

)Rn GH_EC H_SR (6.4 m)H_SR (7.5 m)

(b)

-1000

100200300400500600700800900

337 337.5 338 338.5 339 339.5 340Day of year (2008)

En

ergy

flu

x (W

m-2

)

Rn G H_SR (6.4 m) H_SR (7.5 m)

Figure 1. Diurnal variations of half-hourly estimates of sensible heat flux densities from the apple orchard using surface renewal H_SR (at 6.4 and 7.5 m above the soil surface using time lag r = 0.8 s), eddy covariance H_EC at 8.0 m, net irradiance (Rn), and soil heat flux (G): a) Spring 2008; b) Summer 2008

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(a)

-100

0

100

200

300

400

500

212 212.5 213 213.5 214 214.5 215

Day of year (2008)

En

ergy

flu

x (W

m-2

)Rn G H_EC H_SR (5.2 m) H_SR (7.2 m)

(b)

-100

0

100

200

300

400

500

600

700

800

31 32 33 34

Day of year (2009)

Ene

rgy

flux

(W

m-2

)

Rn G H_SR (5.8 m)

Figure 2. Diurnal variations of half-hourly estimates of sensible heat flux densities from the orange orchard using surface renewal H_SR (at 5.2, 5.8, and 7.2 m above the soil surface using time lag r = 0.8 s), eddy covariance H_EC at 8.0 m, net irradiance (Rn), and soil heat flux density (G): a) Winter 2008; b) Summer 2009.

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4.2 Water use of the apple and orange orchards Total evaporation from the apple orchard was in the range of 0.5 to 2.5 mm day-1 in May 2008 (Figure 3a) and 5.0 to 8.0 mm day-1 in summer (Figure 3b). Transpiration from the apple trees ranged from 4.0 to 7.0 mm day-1 in summer. Total evaporation from the orange orchard ranged from 1.5 to 3.0 mm day-1 in winter (Figure 4a) and 2 to 5 mm day-1 in summer (Figure 4b), while transpiration ranged from 1.0 to 2.5 mm day-1 in winter and 1.5 to 3 mm day-1 in summer. Transpiration from the apple trees was close to 0 mm day-1 in winter as they lose their leaves compared to the evergreen orange trees which were actively transpiring through the winter (Figure 5).

(a)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

13/05/2008 14/05/2008 15/05/2008 16/05/2008

Day of year (2008)

Tot

al e

vap

orat

ion

(m

m)

EC (8.0 m) SR (6.4 m) SR (7.5 m)

(b)

0.0

1.0

2.0

3.0

4.0

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6.0

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8.0

09/12/08 10/12/08 11/12/08 12/12/08

Day of year (2008)

Tot

al e

vap

orat

ion

(mm

)

SR (6.4 m) SR (7.5 m) HPV transpiration

Figure 3. Daily HPV transpiration and total evaporation estimates (mm) from the apple trees using the eddy covariance (EC) at 8.0 m and the surface renewal (SR) at 6.4 and 7.5 m above the soil surface for time lag r = 0.8 s: a) Spring 2008; b) Summer 2008. Average canopy height of the apple trees was 5.0 m.

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(a)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

31/07/2008 01/08/2008 02/08/2008 03/08/2008

Day of year (2008)

Tot

al e

vap

orat

ion

(m

m)

EC SR (5.2 m) SR (7.2 m) HPV transpiration

(b)

0.0

1.0

2.0

3.0

4.0

5.0

30/01/09 31/01/09 01/02/09 02/02/09

Day of year (2009)

Tot

al e

vap

orat

ion

(m

m)

SR (5.8 m) HPV transpiration

Figure 4. Daily HPV transpiration and total evaporation estimates (mm) from the orange trees using the eddy covariance (EC) at 8.0 m and the surface renewal (SR) at 5.2, 5.8 and 7.2 m above the soil surface for time lag r = 0.8 s: a) Winter 2008; b) Summer 2009. Average canopy height of the orange trees was 5.0 m.

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0.0

1.02.0

3.04.0

5.0

6.07.0

8.0

01-J

un-0

8

02-J

ul-0

8

02-A

ug-0

8

02-S

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ct-0

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ov-0

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an-0

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ar-0

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ay-0

9

08-J

un-0

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Day of Year (2008/2009)

Tra

nspi

rati

on (

mm

day

-1)

Apples Oranges

Figure 5. Daily transpiration from the apple and orange trees using the HRM method for different seasons in 2008 and 2009. 5. Conclusions The water use of ‘Cripps Pink’ apples and ‘Delta’ Valencia oranges was estimated for different seasons from measurements of total evaporation using the EC and SR methods and transpiration using the HRM method. Sap flow and total evaporation fluctuated from day to day depending on the available energy at the orchard surface. In terms of water-use fluctuations observed in the deciduous apple trees at Ceres, day to day variation in the middle of the growing season was primarily driven by prevailing climatic conditions (i.e. responses to changing evaporative demands). However, leaf area changes at the start (increase) and end (decrease) of the growing season appeared to exert the most influence on the broadly seasonal water-use trends. This is in contrast to the evergreen orange trees which were more consistent in the long-term but also responded to daily changes in evaporative demand. Responses in water-use to changing phenological stages within these fruit tree species needs to be investigated further.

Acknowledgements Funding for this research from the Water Research Commission (South Africa) is gratefully acknowledged. We thank Mr Arno Marais (farm manager, Ceres) and Mr Jaco Burger (estate engineer, Groblersdal) for assistance, information and access to the study orchards. Technical support and assistance during the setting of the experiments from Mr Eric Prinsloo and Mr Vivek Naiken (CSIR) is also acknowledged.

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References Burgess, S.S.O., Adams, M.A., Turner, N.C., Beverly, C.R., Ong, C.K., Khan, A.A.H., Bleby,

T.M., 2001. An improved heat pulse method to measure low and reverse rates of sap flow in woody plants, Tree Physiol. 21, 589-598.

Drexler, J.Z., Snyder, R.L., Spano, D., Paw U, K.T., 2004. A review of models and micrometeorological methods used to estimate wetland evapotranspiration. Hydrol. Process. 18, 2071-2101.

Duce, P., Spano D., Snyder, R.L., 1998. Effect of different fine-wire thermocouple design on high frequency temperature measurement. In: AMS 23rd Conf. on Agricultural and Forest Meteorology. Albuquerque, NM, Nov. 2-6, pp. 146-147.

Meyers, T.P., Baldocchi, D.D., 2005. Current micrometeorological flux methodologies with applications in agriculture. In: Hatfield, J.L., Baker, J.M. (Eds), Micrometeorology in Agricultural Systems Agronomy Monograph no. 47. pp. 381-396.

Paw U, K.T., Qui, J., Su, H.B., Watanabe, T., Brunnet, Y., 1995. Surface renewal analysis: a new method to obtain scalar fluxes. Agric. For. Meteorol. 74, 119-137.

Paw U, K.T., Snyder, R.L., Spano, D., Su, H.B., 2005. Surface renewal estimates of scalar exchange. In: Hatfield, J.L., Baker, J.M. (Eds), Micrometeorology in Agricultural Systems Agronomy Monograph no. 47. pp. 455-483.

Snyder, R.L., Spano, D., Paw U, K.T., 1996. Surface renewal analysis for sensible heat and latent heat flux density. Boundary-Layer Meteorol. 77, 249-266.

Spano, D., Duce, P., Snyder, R.L., Paw U, K.T., 1997a. Surface renewal estimates of evapotranspiration: tall canopies. Acta Hort. 449, 63-68.

Spano, D., Snyder, R.L., Duce, P., Paw U, K.T., 1997b. Surface renewal analysis for sensible heat flux density using structure functions. Agric. For. Meteorol. 86, 259-271.

Spano, D., Snyder, R.L., Duce, P., Paw U, K.T., 2000. Estimating sensible and latent heat flux densities from grape vine canopies using surface renewal. Agric. For. Meteorol. 104, 171-183.

Swinbank, W.C., 1951. Measurement of vertical transfer of heat and water vapour by eddies in the lower atmosphere. J. Meteorol. 8, 135-145.

Van Atta, C.W., 1977. Effect of coherent structures on structure functions of temperature in the atmospheric boundary layer. Arch. Mech. 29, 161-171.

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3. APPENDIX 3: COMBINED CONGRESS ABSTRACT

ESTIMATING WATER USE OF ‘VALENCIA’ ORANGE TREES UND ER

DRIP IRRIGATION USING SAP FLOW MEASUREMENTS

W Mahohoma1, M Gush2, M Mengistu2 N Taylor1, JG Annandale1 and R Stirzaker3 , 2University of Pretoria

1Department of Plant Production and Soil Science, University of Pretoria, Pretoria 0002, 2CSIR – Natural Resources and the Environment c/o Agrometeorology, UKZN,

Scottsville, 3209 3CSIRO Land and Water, P.O. Box 1666, ACT 2601, Australia

Email: [email protected]

Introduction Precise water use estimation of irrigated fruit trees is important for irrigation planning and scheduling for sound management of already strained water resources. Sap flow measurements have been considered useful and accurate for directly estimating transpiration (i.e. water-use) of fruit trees. Materials and Methods Transpiration of ‘Valencia’ orange trees was estimated from sap flow measurements conducted on four trees using the Heat Ratio Method described by Burgess et al. (2001). Measured transpiration was correlated against Penman-Monteith reference evapotranspiration (ETo) calculated according to Allen et al. (1998) using weather variables measured by an on-site automatic weather station. Soil water contents (using ECH2O probes and time domain reflectometry), soil temperatures (copper constantan thermocouples) and soil solution electrical conductivities (EC meter and electrodes) were also measured. Changes in tree and orchard canopy structure (i.e. tree size and shape) and optical properties (i.e. leaf area index and photosynthetically active radiation interception) were quantified over time. Irrigation applications (timing and amounts) were determined using wetting front detectors, soil water sensors and in-line irrigation monitoring. Results and discussion Observed sap flow rates in the trees appeared to be more strongly correlated with seasonal changes in evaporative demand than tree growth, due to the evergreen nature of these trees which experience flushes of growth. Variation in daily citrus tree transpiration did not appear to be solely determined by atmospheric demand, as increases in ETo between July and early November were not met by similar increases in water use, and during this period there were declines in the calculated crop factor. However, when atmospheric demand subsequently declined between March and July similar declines in transpiration rates were observed. Conclusions Under seasonally low evaporative conditions citrus responds to atmospheric demand but when atmospheric demand becomes too high the roots cannot supply enough water to meet these demands. The major component of the total evapotranspiration within the orchard is transpiration. References: Allen, R.G., Pereira, L.S., Raes, D. and Smith, M., 2004. Crop evapotranspiration: Guidelines for computing crop water requirements. FAO Irrigation and Drainage Paper 56. pp 300. Burgess SSO, Adams MA, Turner NC, Beverly CR, Ong CK, Khan AAH and Bleby TM 2001 An improved heat pulse method to measure low and reverse rates of sap flow in woody plants. Tree Physiology, 21: 589-598. Key words: fruit tree water use, sap flow, heat pulse velocity, evapotranspiration, soil water.