By Lize Reinecke, Amy Grundling & Adelene van Zyl
Fertigation is the process of nutrient application through irrigation where nutrients are introduced to the watering system used for irrigation. Fertigation can be applied either through a drip or a spray irrigation technique. It is used to regulate the amount and duration of fertilizer application, the dilution of the fertilizer in the water as well as the start and ending times of the fertigation process.
In the nursery industry fertigation has become increasingly popular due to the high efficiency rate. Most growers use injectors to mix concentrated fertilizer solution into the irrigation system. A large variety of injector are available to meet the different needs of any size nursery. Well-designed systems can be monitored at different stages in the process to ensure that the injectors work efficiently and that the plant receive the correct amount of nutrients.
The nutrient solutions are prepared in stock tanks from where it is injected into the irrigation water tanks. For fertilizer to mix with irrigation water, the fertilizer must be at a higher pressure than the irrigation water, that is why it is referred to the fertilizer being injected into the irrigation water.
Types of Fertigation
There are four categories into which fertigation can be placed: Continuous, Three Stage, Proportional and Quantitative Application. The choice will depend on crop response and the risk of excessive nutrient runoff.
Advantages and Disadvantages
The advantages of fertigation include the precise control of both the concentration and balance of nutrients, an equal distribution of fertilizer, increased penetration of fertilizer in soil, decrease in nitrogen loss and nutrient solutions can easily be customised for any plant growth stage or species. Disadvantages of fertigation include high levels of toxicity in the irrigation system which can damage nursery crops and the environment, frequent mixing and applying of liquid fertilizers increase labour cost, clogging of irrigation pipes and exposure to high levels of fertilizer may result into health problems.
Fertigation can be applied from a small nursery to large commercial farming. This method enables farmers to lower their input cost through precision farming and maximise their production. However, it is important that fertigation systems to be monitored and managed frequently to prevent any damage.
By Amy Grundling
Sunburn is a physiological disorder that occurs on fruit species, such as apples, due to excess exposure of sunlight . This disorder causes large crop losses of up to 50% of the total crop yield in the South African apple industry . Depending on the type of cultivar, the symptoms of sunburn can vary from dark brown spots to white patch discoloration. The affected areas also create an easy entrance point for pathogens, causing the internal quality of the fruit to decrease. This combination results in decreased quality making the fruit unmarketable. Therefore, it is necessary to understand the causes of sunburn and how its effect on apples can be mitigated.
Types of Sunburn
1. Sunburn Necrosis: creates a brown or black necrotic spot on the fruit surface. This type of damage occurs when the fruit surface temperature reaches 52 ± 1◦C for ten minutes and longer . The high temperature of the fruit surface causes the denature of proteins, which decreases the integrity of the membrane. Damage can occur between a few millimeters to numerous centimeters deep in the sub-epidermal tissue. These symptoms will be visible after one to four days after exposure.
2. Sunburn Browning: is the most common type of sunburn that affects attached apples that are exposed to the sun. This type of sunburn causes brown, yellow and bronze spots on the exposed surface of the apple. The discoloration is due to the decrease levels of chlorophylls and anthocyanins and increased levels of carotenoids and quercetin glycoside in the surface . Sunburn Browning is a result of high solar radiation that increases the fruit surface temperature to a specific minimum temperature. Unlike Sunburn Necrosis, Sunburn Browning do not cause damage in the sub-epidermal tissue.
3. Photo-oxidative Sunburn: occurs on apples that have grown under the shade and then suddenly becomes exposed to solar radiation . This type of sunburn creates white patches on the surface of the fruit. These symptoms occur due to the fruit that are not acclimated to high solar radiation. The sudden exposure to sunlight can take place after thinning and pruning. The induction factors of Photo-oxidative Sunburn are the production of reactive oxygen species (ROS) and solar radiation in viable range of wavelengths; contrasting to Sunburn Necrosis and Sunburn Browning which is influenced by the maximum fruit surface temperature.
Indirect Factors that Influence the Severity of Sunburn
There are also many indirect factors that influence the severity of sunburn on apples. These factors include climate, geographic locations, previous exposure, soil, cultivar and crop cover. Low relative humidity with high temperature increases the atmospheric water demand. This causes higher levels of water stress, which increases the sensitivity of apples for stress-induced disorders. Wind velocity have an impact on the temperature of the air surrounding the fruit. Increased air movement reduces the heat by convection cooling. The susceptibility of the cultivars to sunburn also play a great role. Different cultivars have different susceptibility to sunburn due to the following factors: solar absorptivity, interception of solar energy, temperature tolerance, photostability, tolerance to UV radiation and the ability to acclimate. Cultivar such as Granny Smith and Jonagold are highly susceptible. Moderate susceptible cultivars include Fuji, Golden Delicious and Braeburn. The least susceptible cultivars are Pink Lady, Idad and Topaz.
The geographic location influences the probability of sunburn due to the elevation and latitude that impacts the climate of a specific region, as well as factors that influence the intensity of solar radiation such as aspect. South Africa have a combination of subtropical, arid and mediterranean regions. These regions experience clear summer skies, high temperature and high evaporative demand. This causes high levels of sunburn in the apple industry. Orchard management also play an important role in sunburn. Sunburn is more likely to occur in high-density orchard, for example. The fruit will be more exposed to solar radiation due to less canopy cover. Training system with open pruning also increases sunlight interception.
How to Prevent Sunburn
There are three main techniques, namely climate-ameliorating, suppressants and chemical, that can be used to decrease sunburn damage. Climate-ameliorating entails technological techniques that changes the micro-climate surrounding the fruit . Evaporative cooling is used to mitigate heat stress, through overhead sprayers. Heat is reduced through the evaporation, which decreases the fruit surface temperature. However, evaporative cooling does not reduce the damage done by UV radiation . Therefore, Sunburn Browning damage does not decrease under this system. The calcium and magnesium carbonates that are deposited on the surface of the fruit by water can also have a negative impact on the fruit appearance. Another downside of the evaporative cooling system is the high cost of installations, intensive management and high-water requirement. Due to these factors the South African apple industry do not use this system.
In South Africa shade nets are more frequently used. High-density polyethylene (HDPE) nets are placed over the tree canopy. The shade net reduces solar radiation interception experienced by the apples which in turn decreases fruit surface temperatures. The colour and density percentage of the material determines the effectiveness of the shade net. The downside of shade nets is the reduction of colour development in the red cultivars. However, the protection shade nets provide against excessive solar radiation and hail outweighs the negative effects.
Suppressants, such as particle films and sunscreen, are materials that are sprayed on the fruit. Particle films are composed out of kaolin clay, hydrated magnesium silicate or calcium carbonate . These white inorganic products reflect solar radiation from the surface of the fruit by increasing its albedo. The particle films wash of easily during the rain. Therefore, regular reapplication is necessary. Another drawback is the difficult removal of white residues from the calyx areas. This causes the fruit to decrease in market value due to health concerns. The sunscreen that is used on apple consist out of organic -chemical and physical inorganic particles . The sunscreen absorbs high-intensity UV wavelengths and then dissipated trough the emission of long wavelengths. Sunscreen needs to be reapplied periodically due to the rapid surface growth of fruit.
It is clearly seen that sunburn is a great risk for the farmers in the apple industry. It prevents farmers to export their products as international markets highly values visually and aesthetically appealing products. It is therefore important for South African apple producers to satisfy the consumers demand through by preventing sunburn on apples. South Africa have different climatic conditions, geographic properties and limited resources than other apple producing regions. It is therefore necessary for the South African apple producers to develop systems and use products that are specific for their needs. Through reducing sunburn, the 50% of yield loss can be prevented. This will not only decrease food waist, but also increase the farmers income through exports.
By Amy Grundling
Portulacaria afra, or otherwise known as the Spekboom, is an indigenous South African succulent plant. It has bright green small, round leaves with a red stem, creating a refreshing appearance. The average Spekboom usually grows 1.5-2m in hight. The natural habitat of the Spekboon is warm, arid and semi-arid areas, especially renown in parts of South Africa such as Ado Elephant Park and the town of Prince Albert.
The Spekboom is increasingly drawing attention for its unique characteristics and various uses. One of the most important characteristics is that the succulent is effective in carbon sequestration. By absorbing free carbon for tissue growth, the succulent decreases the amount of pollution caused by the burning of fossil fuels, acting as a carbon sink.
Spekbome is an ideal shrub to plant in a water scarce country such as South Africa. The succulent is a drought-resistant plant, which can survive on 250-350mm of water per year. Spekboom is easily propagated, which makes it an ideal plant to plant in your garden without spending money.
The following steps will show you how to propagate your own Spekboom:
Step 1: What you will need.
You will need the following list of products
Step 2: Select and prepare Spekboom cuttings.
Select a few healthy cuttings from a vigorous Spekboom, preferable in late spring. The ideal cutting should be between 10 and 15 cm in length. Look for vigorous branches with thick and healthy leaves. Make a 45° angle cut and remove the leaves at the end of the cutting.
Step 3: Dip the cutting in root growth hormones.
Moisten and dip the end of the cutting in a root growth hormone that will stimulate root growth. This step is not necessary, although it will increase the speed of the cutting’s root growth.
Step 4: Prepare a rooting pot.
Prepare a rooting pot that have several drainage holes at the bottom. Fill the pot with succulent potting mix or your own mixture of course and standard potting soil. Insert the Spekboom cutting into the soil and press lightly around the stem.
Step 5: Water the cutting.
Lastly, water the cutting and allow the soil to drain thoroughly.
Step 6: Watch it grow!
Place the potted cutting in indirect sunlight for at least five hours a day and apply water once a week. Rooting will take place within 14 to 20 days.
For more information, please visit the South African National Biodiversity Institute website:
By Renée Grundling
World Wetlands Day was celebrated on the 2nd of February, an annual day to celebrate the Ramsar Convention signed at Ramsar, Iran in 1971. South Africa was one of the first countries globally to sign the treaty. This year's theme is 'Wetlands and Biodiversity'.
There are currently more than 2300 designated Ramsar Sites, sites of international importance, all across the world. The above photo is one of the newest Ramsar Sites (no.2385), officially declared in September, 2019, and can be found in the Kgaswane Mountain Reserve, Rustenburg, South Africa. This wetland system is situated on a plateau in the Magaliesberg mountain range and has a variety of special characteristics including peat.
For more information go to https://whc.unesco.org/en/ramsar/.
In the following video, Dr. Piet-Louis Grundling discusses the importance of Wetlands:
By Adelene van Zyl
What is Sustainability?
Sustainability can be defined as the ability to be maintained at a specific level. It is important that the current generation should provide and maintain sufficient resources for future generations to live at the same economic and environmental level as the current generation does. In addition, sustainability entails maintaining changes in a balanced environment. The Earth has a certain carrying capacity in order to function at a good and healthy rate. When we exceed the carrying capacity of the Earth, we are no longer sustainable and put current and future generations at risk of depleting resources.
Sustainability is divided into three main components according to the World Summit of Social Development in 2005. The three components are economic development, social development and environmental protection. Sustainable development will only be effective if these components are interlinked. Sustainability will only attract investments if it promotes economic growth. By increasing economic growth, living standards in communities will be improved. In order for higher living standards to be sustainable, environmental protection and resource management must be applied.
The United Nations also saw sustainability as a key component in moving forward in unity, when 178 countries adopted Agenda 21 for Sustainable Development at the Earth Summit in Rio De Janeiro in 1992. There are seventeen Sustainable Development Goals in the 2030 Agenda of which ten out of these seventeen goals involve agricultural practices. These goals are:
Sustainability in Agriculture
The main goal of sustainability in agriculture is to meet the current food and textile needs without compromising future generations’ ability to meet their food and textile needs. Sustainability in agriculture aims to improve soil health, decrease pollution and to improve the use of water in farming practices. It also aims to increase crop quantity and quality in an efficient and effective manner, without degrading the environment.
In conclusion, I would like to encourage you with a quote from Arthur Ashe to apply sustainability:
“Begin where you are, use what you have, and do what you can.”
Creators of the video: Adelene van Zyl, Amy Grundling, Calvin Cornell, Kaylin Dickson, Prince Lekame Moloto and Renée Grundling