Browsing by Author "Dzikiti, S"

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    Contribution of understorey vegetation to evapotranspiration partitioning in apple orchards under Mediterranean climatic conditions in South Africa
    (Elsevier, 2021) Ntshidi, Z; Dzikiti, S; Mazvimavi, D
    Orchard evapotranspiration (ET) is a complex flux which has been the subject of many studies. It often includes transpiration from the trees, cover crops and weeds, evaporation from the soil, mulches and other orchard artefacts. In this study we investigated the contribution of the orchard floor evaporative fluxes to whole orchard ET focusing on the transpiration dynamics of understorey vegetation which is currently not well known. Data on the partitioning of ET into its constituent components were collected in apple (Malus Domestica Bork) orchards with varying fractional canopy cover. The study orchards were in the prime apple growing regions in South Africa. The orchards were planted to the Golden Delicious/Reinders and the red cultivars (i.e. Cripps’ Pink/ Royal Gala/Fuji). Tree transpiration was quantified using the heat ratio method and the thermal dissipation sap flow techniques. Understorey transpiration was measured at selected intervals using micro stem heat balance sap flow gauges calibrated against infrared gas analyser readings. Orchard ET was measured using an open path eddy covariance system while the microclimate, radiation interception, and soil evaporation were also monitored. Orchard floor evaporative fluxes accounted for as much as 80% of the measured ET in young orchards with dense understorey vegetation that covered most of the orchard floor.
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    Modelling water utilization patterns in apple orchards with varying canopy sizes and different growth stages in semi-arid environments
    (Elsevier, 2021) Dube, T; Mobe, N.T; Dzikiti, S
    Accurate estimates of orchard evapotranspiration (ET) and its components are important for precise irrigation scheduling, irrigation system designs, and optimal on-farm water allocation particularly in water-limited environments. Direct measurements of ET remain costly, laborious and sometimes difficult to apply over heterogeneous surfaces such as crop fields. Therefore, accurate crop water-use models are required for on-farm precise water resources management. In this study, we adopted and improved the Priestley-Taylor Jet Propulsion Laboratory (PT-JPL) model developed by Fisher et al 2008 to estimate crop water use across different apple plants. Specifically, the model was developed to quantify the partitioning of apple orchard water use into beneficial (tree transpiration) and non-beneficial water use (orchard floor evaporation) as influenced by tree canopy cover. Data were collected in twelve orchards spread across key apple producing regions in the Western Cape Province of South Africa over three growing seasons (2014/15, 2015/16, 2016/17). Model ET estimates were tested against ET data measured; using the eddy covariance method and transpiration measured based on sap flow monitoring techniques. The results showed that the original Fisher PT-JPL model performed poorly in ET estimation across all the orchards under study.
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    Water use of selected cover crop species commonly grown in South African fruit orchards and their response to drought stress
    (Elsevier, 2021) Mazvimavi, D; Ntshidi, Z; Dzikiti, S; Mkunyana, Y
    Cover crops are widely planted in orchards for a variety of reasons. These include suppressing soil erosion, nutrient cycling, phytosanitary purposes, general orchard aesthetics etc. However, there is need to balance these benefits against use of scarce resources such as water and nutrients. Currently no information exists on how different cover crop species use water in orchards and how they cope with drought stress. The aim of this study was therefore to compare the transpiration dynamics of various cover crop types in order to identify species with conservative water use rates. Studied species included: 1) two exotic legumes i.e. Lupine (Lupinus albus L.), and Common vetch (Vicia sativa), 2) three exotic grasses i.e. Tall fescue (Festuca arundinacea), Rye grass (Lolium perenne), and Kikuyu grass (Pennisetum clandestium) and; 3) grasses that are indigenous to sub-Saharan Africa i.e. African Lovegrass (Eragrostis capensis) and Rhodes grass (Chloris gayana). The crops were planted in pots under controlled greenhouse conditions. Transpiration rates were quantified using miniature stem heat balance sap flow gauges and by manual weighing. Drought stress was imposed by withholding irrigation at selected intervals and the responses were quantified through changes in the water relations of the plants. The study showed that exotic legumes had the highest daily water use which peaked at about 2.4 L per square metre of leaf area per day, followed by exotic grasses at 1.5–2.0 L/m2/d. The indigenous grasses used the least water ranging from 0.8 to 1.2 L/m2/d. The indigenous grasses largely displayed an isohydric response to drought stress by maintaining their leaf water status with increasing soil water deficit. The exotic species, on the other hand, showed risk taking behaviour (anisohydry) wherein both the transpiration and leaf water status decreased sharply as drought stress increased. Consequently, some exotic species failed to recover when stress was relieved. From a water use perspective, this study demonstrates that indigenous grass species are more appropriate as cover crops in South African orchards because of their low transpiration rates and the ability to cope with extended periods of water deficit. © 2021 Elsevier Ltd