Agricultural perspectives on the 2015-2018 Western Cape drought, South Africa : characteristics and spatial variability in the core wheat growing regions

Between 2015 and 2018, the Western Cape Province of South Africa experienced a multi-year severe drought, which negatively impacted major economic sectors. The province serves as an important producer of wheat in South Africa among other agricultural commodities. This study aims to analyze the 2015-2018 drought and its impacts on wheat production in the winter rainfall region of the Western Cape, South Africa. The central focus is to place the drought in both a historical and future context while emphasising the differences between the two core wheat growing regions. We present an analysis of the drought, as well as climate trends computed from weather data sets (1988–2018) from six weather stations across the two core wheat-growing. We first present a meteorological drought analysis of mean annual and seasonal rainfall and temperatures, subsequently providing an agricultural lens by computing Standardised Precipitation and Evapotranspiration Index (SPEI) accumulated over 12- and 36-month timescales, self-calibrated Palmer Drought Severity Index (sc-PDSI), changes to the start and end of the rainfall season, and their effects on wheat yields. Trend analysis was conducted to determine if drought observations form part of the longer-term trends in the region. Finally, we show how the drought varied spatially across the two regions. Results show that between 1988 and 2018, the wheat growing areas of the Western Cape experienced persistent drought with high spatial-temporal variability. The 2015-2018 drought, however, was the most severe experienced in the 30-year study period at five of the six stations. These results are consistent with conditions that can be expected under future climate change. Moreover, results can be useful for the development of early warning systems since they place the drought in the context of past drought conditions.The Agriculture Research Council's Professional Development Programhttps://www.elsevier.com/locate/agrformethj2022Geography, Geoinformatics and Meteorolog

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

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 lateseason 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. Keywords: cultivar canopy cover transpiration reduction xylem water potentia

Climate change in the western cape of South Africa: Trends, projections and implications for chill unit accumulation

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The effect of temperature and developmental stage on carbon dioxide exchange of attached 'royal gala', 'fuji' and 'cripps' pink' apple fruits

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The effect of time of scoring on yield, fruit and shoot growth and reproductive bud development on 'royal gala', 'fuji' and 'cripps' pink' apple trees

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Photosynthetic capacity and diurnal gas exchange of 'Brookfield Gala' apple leaves under three irrigation systems

Water and nutrient application using three irrigation systems, namely daily drip irrigation, pulsing drip irrigation and micro irrigation were studied with respect to photosynthetic efficiency, water use efficiency and leaf water relations in 'Brookfield Gala' apple trees during 2004/5 and 2005/6 in the Western Cape Province, South Africa. The amount of water used per irrigation strategy was 5254 m3 ha-1 yr-1 and 5661 m 3 ha-1 yr-1 for the micro irrigation; 3429 m3 ha-1 yr-1 and 39260 m3 ha -1 yr-1 for the daily drip and 3429 m3 ha -1 yr-1 and 4047 m3 ha-1 yr -1 for the pulsing drip for 2004/5 and 2005/6 seasons respectively. Trees were budded on either M793 or M7 rootstocks and planted in blocks using a split-plot experimental design with irrigation as the main effect and rootstock as the sub-plot. Maximum light-saturated net CO2 assimilation rate (Amax) was consistently higher under pulsing drip irrigation (this system applies water several times during the day creating an even shorter frequency cycle than the normal daily drip) compared to micro irrigation (applies water once to twice a week and uses sprinklers that spray water in a circle resulting in wetting a continuous strip within the drip row) but, occasionally, significantly higher than daily drip irrigation (applies water on a daily basis creating a shorter cycle compared to micro sprinkler system). The maximum rate of electron transport (Jmax) showed similar trends to Amax during 2004/5, but not during 2005/6. Amax peaked during midmorning (10h00) with a steady decline thereafter in all treatments, but with significantly lower rates under micro irrigation. Stomatal conductance (gs) declined steadily throughout the morning, with higher g s under the drip based systems compared to the micro system. The implications are that, irrigation application should be given early in the morning to sustain stomatal conductance and maximise CO2 assimilation rates during the period between 08h00 to 12h00. Results indicate higher photosynthetic capacity and water use efficiency under both drip-based irrigation systems compared to micro irrigation. Differences in photosynthetic capacity were related to both stomatal and non-stomatal responses.Articl

Response to elevated CO2 from a natural spring in a C4-dominated grassland depends on seasonal phenology

A South African C4-dominated grassland was exposed to twice-ambient atmospheric CO2 concentration using gas emitted by a natural CO2 spring and distributed over a 7m × 7m plot. A similar control plot was established 20m away at near-ambient CO2 concentrations. Photosynthetic CO2 response curves were performed on three C4 and one C3 grass species under both treatments, in spring (post-fire), mid-summer and autumn. Photosynthetic efficiency of the post-fire dominants, Alloteropsis semialata subsp. eckloniana (C3) and Andropogon appendiculatus (C4) was significantly enhanced in high CO2 only during the early season, when photosynthetic capacity was high. Thereafter, photosynthetic capacity decreased with advancing season in both species, and positive responses to high CO2 were lost or reduced. In the mid- to late-season dominant Themeda triandra (C4), photosynthetic capacity was maintained in elevated CO2 during the mid- to late-season, while decreasing in ambient CO2 relative to high CO2. Eragrostis racemosa (C4), a slow grower, showed no significant responses to high CO2 during the late season. CO2-responsiveness in the field generally followed the seasonal phenologies of each species, being greatest during the most active growth period.Articl

Peel color and blemishes in 'Granny Smith' apples in relation to canopy light environment

The dark green apple cultivar, Granny Smith (GS), makes up 25% of the South African apple industry. However, production of GS is becoming unprofitable as a result of a high incidence of sunburn, red blush, and pale green fruit that decreases the proportion of Class 1 fruit that is suitable for export to more lucrative markets. This study was conducted to investigate the relationship between canopy position and external fruit quality with the ultimate aim to devise pruning and training strategies to maximize export yield. During early fruit development [26 days after full bloom (DAFB)], chlorophyll concentrations were the highest in fruit from higher light environments. Good green color at harvest relied on exposure of fruit to high irradiance at this stage because 50% shading between 14 and 56 DAFB significantly decreased dark green color at harvest. Exposed fruit from the northern side of east-west rows received the highest irradiance throughout the season [53% of full sun photosynthetic photon flux (PPF)] and had the highest fruit surface temperature (on average 5°C above ambient). A high proportion of exposed fruit from either side of the row developed red blush. Only 22% to 39% of exposed fruit from the outer canopy did not develop sunburn or red blush. Partially shaded fruit from the southern side of east-west rows received '5% of full sunlight and had the highest chlorophyll concentrations and darkest green color at harvest. Deeply shaded inner canopy fruit received '2% of full sunlight, had low chlorophyll concentrations, and were lighter green in color. The 10% darkest green fruit received moderately high irradiance (25% to 45% of full sun PPF) during early fruit development (until '80 DAFB) but became progressively shaded (3% of full sun PPF) during the latter half of the season. Fruit that developed sunburn and the lightest green fruit were exposed to high (1300 mmol m-2 s-1) and extremely low (50 mmol m-2 s-1) light, respectively, throughout their development. In conclusion, maximum chlorophyll synthesis and dark green color require an open canopy during the first half of fruit development, whereas shading is necessary during the latter half of fruit development to avoid the occurrence of sunburn, red blush, and photothermal destruction of chlorophyll. GS may benefit significantly from the installation of shade netting if combined with rigorous pruning and vigor control.Articl

Exploring farmers' perceptions and lessons learned from the 2015–2018 drought in the Western Cape, South Africa

DATA AVAILABILITY : The authors do not have permission to share data.The agricultural sector is one of the most vulnerable sectors to the impacts of climate change. Between 2015 and 2018, the Western Cape Province of South Africa experienced a multi-year severe drought. Projections show that the Western Cape is likely to experience hotter and drier conditions, with more frequent droughts. Without appropriate adaptation actions, climate change is likely to increasingly constrain agricultural activities in the province. Commercial farmers represent a considerable population of decision-makers, which are fundamental to climate change adaptation. Understanding farmers' perceptions is important to develop effective policy, support structures, and communications. This study aimed to understand wheat farmers' and apple producers' perceptions of climate change and adaptation in the Western Cape, South Africa, and establish whether the recent drought offered lessons for adaptation. Study methods included the use of an online questionnaire as well as several in-depth interviews with farmers and producers. Results showed that most farmers and producers agree that climate change is real and is caused by human activities. Most farmers and producers in the region are already actively (or intend to start) preparing for climate change (69%). In response to climate change, apple producers view on-farm water management (such as irrigation management and water recycling) as the most important strategy. Wheat farmers strategies are focused on crop management (including cultivar selection and conservation agriculture). Many farmers and producers further agreed that they had learnt from the past 2015–2018 drought. Notably, results showed that farmers and producers who rely a great deal on weather forecasts were more likely to feel that their farm's response was effective. Furthermore, it was found that farmers and producers who felt they learned from the drought were also more likely to be actively preparing for climate risks. It is recommended that investments into climate change adaptation focus on research and development, particularly with regard to cultivar development, irrigation management, tailored weather forecasting, and localised risk assessments. Policy should prioritise the more vulnerable farmers and producers while focusing on integrated risk reduction measures which account for multiple stressors.The Agricultural Research Council's Professional Development Program (ARC-PDP).https://www.elsevier.com/locate/jrurstud2024-09-18hj2023Geography, Geoinformatics and Meteorolog

Ecological and ecophysiological patterns in a pre-altiplano shrubland of the Andean Cordillera in northern Chile

We report on community structural, ecophysiological, phenological, and morphological measurements made on woody plant species in the high elevation pre-altiplano zone on the western slopes of the Andean Cordillera of northern Chile. Notwithstanding extreme conditions of low rainfall, high atmospheric vapour demand and diurnal temperature fluctuation, a diversity of habitats (associated with drainage and slope aspect), appreciable local plant species richness (28 woody perennial plant species in a small area), and an array of adaptive morphological ecophysiological and phenological traits are present among woody species in these shrublands. Family diversity was low with four families accounted for 82% of the species. A range of gas exchange and watering use efficiency strategies was present ranging from highly efficient CAM species with a carbon isotope discrimination (Δ) of 3.7-7.5‰ through C 3 species with varying stomatal and gas exchange characteristics with a Δ of 14.4 to 19.8‰. Drought-deciduous small-leaved amphistomatic species from arid slopes generally had high stomatal conductance and high carbon assimilation rates during the rainy season. These drought deciduous species were largely leafless and, with one exception had low water potentials, during the dry season. Wash and less xeric site species commonly had broader evergreen to semi-evergreen leaves, higher dry season water potentials, and relatively consistent and moderate rates of gas exchange throughout the year. For all species, intrinsic water use efficiency (as estimated from the inverse of ci:ca ratio) correlated positively with mean leaf width (broader leaves had a lower higher intrinsic WUE) and dry season water potential. The charismatic high altitude tree, Polylepis rugulosa (Roaceae), had a population structure that suggests highly episodic establishment of seedlings, likely in sequences of wet years. Little of the area of these significant shrublands is currently protected. It would be desirable to add areas of pre-altiplano shrublands to adjacent national parks to ensure the persistence of these important communities.Articl