Using sap flow data to assess variations in water use and water status of apple orchards of varying age groups in the Western Cape Province of South Africa

Authors

  • NT Mobe 1. Smart Places Cluster, Council for Scientific and Industrial Research (CSIR), Stellenbosch, South Africa; 2. Institute for Water Studies, Department of Earth Sciences, University of Western Cape, South Africa
  • S Dzikiti 1. Smart Places Cluster, Council for Scientific and Industrial Research (CSIR), Stellenbosch, South Africa; 2. Department of Horticultural Science, Stellenbosch University, Stellenbosch, South Africa; 3. Institute for Water Studies, Department of Earth Sciences, University of Western Cape, South Africa
  • T Volschenk Soil and Water Science Programme, ARC Infruitec-Nietvoorbij, Stellenbosch, South Africa
  • SF Zirebwa Department of Horticultural Science, Stellenbosch University, Stellenbosch, South Africa
  • Z Ntshidi 1. Smart Places Cluster, Council for Scientific and Industrial Research (CSIR), Stellenbosch, South Africa; 2. Institute for Water Studies, Department of Earth Sciences, University of Western Cape, South Africa
  • SJE Midgley Department of Horticultural Science, Stellenbosch University, Stellenbosch, South Africa
  • WJ Steyn 1. Department of Horticultural Science, Stellenbosch University, Stellenbosch, South Africa; 2. Hortgro, Paarl, South Africa
  • E Lötze Department of Horticultural Science, Stellenbosch University, Stellenbosch, South Africa
  • S Mpandeli Water Research Commission (WRC), Private Bag X03, Gezina 0031, South Africa
  • D Mazvimavi Institute for Water Studies, Department of Earth Sciences, University of Western Cape, South Africa

DOI:

https://doi.org/10.17159/wsa/2020.v46.i2.8236

Keywords:

cultivar, canopy cover, transpiration reduction, xylem water potential

Abstract

No accurate quantitative information currently exists on how water use of apple (Malus domestica) orchards varies from planting to full-bearing age, leading to poor irrigation and water allocation decision making. This study sought to address this knowledge gap by investigating how the water use and tree water status vary with canopy cover, cultivar, and climatic conditions in 12 orchards growing in prime apple-producing regions in South Africa. The orchards were planted to the Golden Delicious/Golden Delicious Reinders cultivars which are widely planted in South Africa and the Cripps’ Pink/Cripps’ Red/Rosy Glow which are high-value late-season cultivars. The performance of two transpiration reduction coefficients, one based on sap flow (Ksf) and the other based on soil water depletion (Ks) (FAO approach) were evaluated against the midday stem water potential (MSWP) in all the orchards. While canopy cover had a clear effect on the whole-tree sap flow rates, there were no significant differences in the transpiration per unit leaf area among the cultivars. The daily average sap flux density under unstressed conditions was highest (~284 cm3∙cm-2) in the medium canopy cover orchards (30–44% fractional cover), followed by the mature orchards (~226 cm3∙cm-2), and was lowest in the young orchards (~137 cm3∙cm-2). Canopy cover rather than growing season length had a greater effect on seasonal total water use. Peak daily orchard transpiration ranged from 1.7 mm for young Golden Delicious Reinders trees to 5.0 mm in mature Golden Delicious trees that were maintained with large canopies to reduce sunburn damage to the fruit. For the red cultivars, the peak daily transpiration ranged from 2.0 to 3.9 mm, and the mature trees were maintained with less dense canopies to facilitate the development of the red fruit colour. The less dense canopies on the red cultivars had water-saving benefits since the seasonal total transpiration was lower relative to the Golden Delicious cultivar. The sap flow derived stress coefficient was strongly correlated to the MSWP (R2 ~ 0.60–0.97) in all the orchards while Ks was not able to detect plant stress due to over-irrigation.

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Published

2020-04-29

How to Cite

NT Mobe, S Dzikiti, T Volschenk, SF Zirebwa, Z Ntshidi, SJE Midgley, WJ Steyn, E Lötze, S Mpandeli, & D Mazvimavi. (2020). Using sap flow data to assess variations in water use and water status of apple orchards of varying age groups in the Western Cape Province of South Africa . Water SA, 46(2 April). https://doi.org/10.17159/wsa/2020.v46.i2.8236

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Section

Research paper