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

Determining factors driving sustainable performance through the application of lean management practices in horticultural primary production

Erasmus Mundus Inspire Projec

Uitdun norme vir inmaakpersekes om inkomste te optimaliseer.

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Historical and future impacts of warming on chill unit accumulation in the Western Cape.

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Erratum to: Nutrient composition and content of various biological active compounds of three South African-based commercial seaweed biostimulants (Journal of Applied Phycology, (2016), 28, 2, (1379-1386), 10.1007/s10811-015-0644-z)

The original version of this article unfortunately contains many mistakes. The corrections are given in the following list: 1. Table 1 contains errors and should be replaced with the table found in this article. 2. “Results” section (under “Mineral nutrient and alginate content”, paragraph 1), the following paragraph is the correct version after correcting Table 1 and therefore should replace the current version: Results from the mineral composition and alginate content of raw E. maxima fronds and stipes as harvested in Gansbaai and Kommetjie in October 2013 showed a tendency of higher levels in the fronds compared to the stipes for N and Mg, well as lower levels in kelp obtained from the Gansbaai compared to the Kommetjie area (Table 1). 3. “Results” section (paragraph 3, second sentence), the below paragraph should replace the current version: N and P concentrations were significantly higher in Afrikelp® and Basfoliar®Kelp compared to Kelpak® and substantially higher than naturally occurring levels. 4. “Discussion” section (paragraph 3, first and second sentences), the text should be corrected as: When mineral content was considered, the significantly higher P and N concentrations reported in Afrikelp® and Basfoliar®Kelp compared to those in Kelpak®, may indicate an additional permissible enrichment of these products, all produced from E maxima, as natural levels in the freshly milled seaweed prior to processing were found to be much lower (Tables 1, 2). Similarly, significantly higher P levels in Afrikelp® and Basfoliar®Kelp products were reported in this study, also as pertaining to free phosphate levels (Tables 1, 2 and 3). 5. “Discussion” section (paragraph 4, fourth sentence) the below paragraph should replace the current version: The seaweed used for Afrikelp® production grows in the warmer waters of Gansbaai (ca. 15.8 °C) compared to the seaweed harvested for Kelpak® production from Kommetjie (ca. 13.3 °C) (Lötze 2012) and could not have been the cause of this difference in alginic acid levels in the final product, as the alginate concentration in raw seaweed was higher in Gansbaai. (Table presented.)

Climate Change in the Western Cape of South Africa: Trends, Projections and Implications for Chill Unit Accumulation.

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Foliar application of calcium plus boron reduces the incidence of sunburn in ‘Golden Delicious’ apple

Losses of apple fruit due to sunburn damage under South African climatic conditions can reach up to 40% per annum for specific cultivars in certain years. Various approaches to reduce the incidence and severity of sunburn resulted in temporary effects but, at present, no single remedy is available to provide a significant and consistent reduction in sunburn damage on a commercial scale. ‘Golden Delicious’ apple trees that received both calcium (Ca) and boron (B) as foliar applications on a weekly basis, when applied from approx. 21-70 d after full bloom (DAFB), showed significantly less sunburn in two consecutive seasons (P = 0.0500 and P = 0.0247 respectively) than untreated control fruit, or treatments based on Ca alone. The minerals were applied as supplements of sugar-alcohol complexed with Ca and B, trading as Manni-Plex® Ca [10% (w/w) Ca] and Manni-Plex® B [3.3% (w/w) B], respectively. The mode of action by which the incidence of sunburn was reduced using combined sprays of Manni-Plex® Ca plus Manni-Plex® B remains to be elucidated

Nutrient composition and content of various biological active compounds of three South African-based commercial seaweed biostimulants

Positive results reported in commercial agriculture following the application of seaweed (kelp) products vary from root growth stimulation to increased disease resistance. The described impact of seaweed applications is mostly reliant on the specific species of seaweed used, the prevalent environmental growing conditions, together with the extraction and formulation protocol implemented in the production of the commercial extracts. These possible variables alone or in combination may lead to inconsistencies in efficacy between different commercial seaweed products, especially under field conditions. In this paper, we quantify selected active components in three different, but apparently similar, commercial seaweed products manufactured from Ecklonia maxima which could impact on biological activity, following application as evaluated for mung bean root growth. Significantly higher P and N concentrations were found both in Afrikelp and Basfoliar Kelp compared to Kelpak. These elevated mineral nutrient concentrations indicate possible enrichment of these products, as they exceed the natural nutrient element concentrations in the freshly milled E. maxima prior to formulation. Kelpak showed higher concentrations of Ca, Mg and K compared to Afrikelp and Basfoliar Kelp, but lower levels were reported to occur naturally in freshly minced seaweed from E. maxima. Concentrations of mannitol, uronic acid and neutral sugars together with alginic acid content were significantly higher in Kelpak than in Afrikelp and Basfoliar Kelp. Similarly, mung bean root growth stimulation was significantly higher in Kelpak than in Afrikelp and Basfoliar Kelp. This study showed that commercial seaweed products, manufactured from the same seaweed source such as E. maxima, and thus generally marketed as equivalent products, may vary significantly in product composition and thus in efficacy to induce specific plant responses following application, when manufactured by different companies. Distinct differences in harvesting and manufacturing protocols place an obligation on the end user to ensure that the composition of the product of choice is well aligned with the specific plant response required

Adjuvants and application date of calcium nitrate sprays effect Golden Delicious fruit calcium concentration.

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