5 research outputs found
Measurement and modelling of water use by high yielding apple orchards and orchards of different age groups in the winter rainfall areas of South Africa
Apple production for the export market is in South Africa entirely dependent on
irrigation. In recent years, high performing orchards yielding up to 120 t of fruit ha-1
are becoming common in a country where the average yield is between 60 and 80 t
ha-1. This raises important questions regarding the sustainability of the exceptionally
high yields given the limited availability of water for irrigation. Moreover, there is also
no accurate quantitative information published on water use by apple orchards of
different age groups and this compromises efficient irrigation scheduling. The aim of
this study was to quantify water use by high yielding apple orchards and orchards of
different age groups. Data were collected in four commercial orchards, two planted to
non-bearing âCrippsâ Pinkâ and âGolden Deliciousâ apples and another two highyielding
full-bearing orchards of these cultivars. Transpiration in the full-bearing
orchards was measured using the heat pulse velocity sap flow method. Granier probes
were used on the young non-bearing trees. Orchard evapotranspiration (ET) was
measured using eddy covariance systems during selected periods. Ancillary data
which included the orchard microclimate, stomatal resistance, soil water content and
soil evaporation were also collected. The full-bearing âGolden Deliciousâ orchard (22-
year-old) had the highest seasonal transpiration of 785 mm, followed by the fullbearing
âCrippsâ Pinkâ (9-year-old) which transpired 587 mm. The non-bearing
âCrippsâ Pinkâ (3-year-old) transpired 272 mm compared to 198 mm for the nonbearing
âGolden Deliciousâ (2-year-old). The data were used to validate a dual source
ET model based on the Shuttleworth-Wallace method. Transpiration of full-bearing
orchards was accurately predicted by the model with the RMSE of 0.55 mm d-1 for
âCrippsâ Pinkâ and 0.70 mm d-1 for the âGolden Deliciousâ orchards. Improvements to
the substrate evaporation sub-model are required to account for various orchard
floor management practices.The research reported here formed part of a bigger project entitled âQuantifying water
use by high performing apple orchards in the winter rainfall areas of South Africaâ project no WRC K5/2398.The Water Research Commission (WRC),
with additional funding from Hortgro Science, through the South African Apple and Pear
Producers Association (SAAPPA) in South Africa.http://www.actahort.orgam2017Plant Production and Soil Scienc
Estimating the water requirements of high yielding and young apple orchards in the winter rainfall areas of South Africa using a dual source evapotranspiration model
Exceptionally high yielding (>100âŻt haâ1) apple orchards (Malus domestica Borkh.) are becoming common in South Africa and elsewhere in the world. However, no accurate quantitative information currently exists on the water requirements of these orchards. Information is also sparse on the water use of young apple orchards. This paucity of data may cause inaccurate irrigation scheduling and water allocation decisions, leading to inefficient use of often limited water resources. The aim of this study was therefore to investigate the dynamics of water use in eight apple orchards in South Africa planted to Golden Delicious and the red cultivars i.e. Crippsâ Pink, Crippsâ Red and Rosy Glow in order to understand how canopy cover and crop load influence orchard water use. Four of the orchards were young (3â4 years after planting) and non-bearing, while the other four were mature high yielding orchards. Transpiration was monitored using sap flow sensors while orchard evapotranspiration (ET) was measured during selected periods using eddy covariance systems. Scaling up of ET to seasonal water use was done using a modified Shuttleworth and Wallace model that incorporated variable canopy and soil surface resistances. This model provided reasonable estimates in both mature and young orchards. The average yield in the two mature âCrippsâ Pinkâ was âŒ110âŻt haâ1 compared to âŒ88âŻt haâ1 in the âGolden Deliciousâ orchards. However, average transpiration (Oct-Jun) was âŒ638âŻmm for the âCrippsâ Pinkâ and âŒ778âŻmm in the âGolden Deliciousâ orchards. The peak leaf area index was âŒ2.6 and ⌠3.3 for the mature âCrippsâ Pink and âGolden Deliciousâ orchards. So, canopy cover rather than crop load was the main driver of orchard water use. Transpiration by the young orchards ranged from 130 to 270âŻmm. The predicted seasonal total ET varied from âŒ900 to 1100âŻmm in the mature orchards and it was âŒ500âŻmm in the young orchards. Orchard floor evaporation accounted for âŒ18 to 36% of ET in mature orchards depending on canopy cover and this increased to more than 60% in young orchards.The Water Research Commission of South Africa (Project no WRC K5 2398//4), the South African Apples and Pears Producers Association and the South African Parliamentary Grant to the CSIR on Water Security (Project number ECHS043).http://www.elsevier.com/locate/agwat2019-09-30hj2018Plant Production and Soil Scienc