By Amy Grundling 

Fruit trees set more fruit than what they can structurally support or properly develop. This occur more often in trees that was not pruned during the previous season.  The excessive fruit remain small due to increased competition for carbohydrates and other nutrients. This increased demand for carbohydrates weakens the tree, which makes it more susceptible to pests, diseases and water stress. Excessive fruit in one season can also cause the tree to have alternate bearing or limb breakage. Thinning the fruit is therefore necessary to prevent these problems.

Fruit thinning is the removal of certain flowers and fruitletts after fruit and natural dropping have occurred. The benefits of thinning immature fruits include:

1. The remaining fruit receive more carbohydrates and therefore develop into bigger fruits.
2. The fruits receive more sunlight which improves the fruit colour and flavour.
3. The chance for limb breakage decreases due to the lighter load of fruits.
4. The spread of disease decreases. For example, fruits that are close to each other can spread brown rot from one to another.

 
Thinning Methods
There are two main thinning methods that are used, which include hand- and pole-thinning. Hand thinning is slower than pole thinning, but more accurate. Hand-thinning is when some fruits are removed to ensure the remaining fruits do not touch each other at maturity. Therefore, on short spurs only 2 to 3 fruits can be left. On long branches fruits that are double, small, disfigured and damaged fruits should be removed. Pole-thinning involves using a pole due to the size of the tree which is too large for hand-thinning. A cloth is attached to the tuber hose at the end of the pole, to decrease bruising of fruits and branches.

​The amount of fruits that should be thinned depends on the species and the individual tree’s fruit load. Stone fruits such as apricots and plums are small, therefore they should be thinned 5 cm to 10 cm apart from the branch. Nectarines and peaches are larger fruit, therefore they should be thinned 7.5 cm to 12.5 cm. Unlike stone fruits, which produce one fruit per bud, pome fruits produce cluster fruits on one bud. Therefore, pome fruits need to be thinned so that one fruit per bud are available to develop. The overall rule is that for every 15 cm of branch there should be one fruit.

Thinning should be done at the correct time of season depending on the type of specie. The method and amount of fruit thinning is also determined by the species of the tree. Thinning is an important management practice in the fruit industry to develop a constant fruit yield every year of high quality.

 
 

By Amy Grundling & Renée Grundling

Having your own vegetable garden may be a dream come true hobby or simply a way to reduce grocery costs and improve a quality way of life. Growing your own vegetables puts you in charge of what is entering your body. You decide what you want to grow, how you want to grow it and how you want to treat it with nutrients and pesticides. You can therefore decrease unwanted elements frequently used in commercial farming and increase the organic nature of your diet.
 
Given our current Covid-19 situation, a vegetable garden can become a sustainable and safer solution to obtaining fresh produce. Not only will you avoid contact with contaminated grocery stores, but this will also keep you busy in self isolation or quarantine. Gardening has many health benefits including improving your state of mind, wellbeing and developing a sense of place and responsibility in your home. You may even enjoy the sun, fresh air and birds chirping while you tend your garden.
 
South Africa is entering its Autumn and Winter months, an ideal time to plant various types of vegetables depending on your location in South Africa. One can use the information below (Seeds for Africa, 2020) as a guide:

​Reference:
Seeds for Africa, 2020. VEGETABLE PLANTING GUIDES. [Online]
Available at: https://www.seedsforafrica.co.za/pages/western-cape-vegetable-planting-chart-1
 
 

By Adelene van Zyl

Compost is decomposed organic matter, which aids in plant growth. Compost ensures that plants can easily absorb nutrients from the decomposed organic matter. It keeps your soil healthy and ensures that the soil contains all the necessary nutrients. It is therefore important to consider what you add to your compost heap to prevent over supply of one nutrient and under supply of another.

Composting is a cost-effective way to ensure healthy plant growth from a small garden to a commercial farm. However, it is important to understand that generating compost from a sustainable compost heap will take time. Give yourself a time-span of one year for the compost heap to fully become sustainable and generating good quality compost.

How to structure a compost heap:
You can use any large container, depending on how much compost you want over a long period. The type of container is also not set. However, do consider limitations of materials and modify your container accordingly. If you use a plastic container, ensure holes on the side for aeration. If you use a wood container, ensure holes underneath to allow water penetration and preventing rot. The principle of making a sustainable compost heap is to use what you have.

Layers of a compost heap:
There are different methods one can use to determine how many layers should be in the compost heap and what plant materials you should use in each layer. The following is a basic example and should be altered according to what you have available.

The first layer is your ‘browns’ which consist of branches and leaves which already appear brown. This can be divided as separate layers as well. Examples are mulch from a chopped tree, old branches and leaves.

The second layer is your ‘greens’ which consist of freshly cut grass, fruits and vegetables. This is the layer where you can use any plant-based material. Examples are fruit and vegetable peels, rotten fruits and vegetables, used coffee or tea bags and eggshells. Make sure that no yeast-based products are added in the compost heap, as this will cause mold growth and ruin the whole compost heap.

The third layer is soil or manure. This layer need not be as thick as the other layers, but it is necessary to optimize the breakdown of the other two layers. You can add these layers on top of each other as indicated on the figure.
 
How to take care of your compost heap:
It is important to water the compost heap at least once every second week. This will aid in the breakdown of organic matter. You should also mix your compost heap at least once a month to ensure proper breakdown of the plant material. If you want to speed up the process, you can add compost activator as indicated on its package. Compost activator is usually added once one set of the three layers are present or when there is a large amount of browns relative to the greens. 

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.

1. Continuous Fertigation Application refers to a continuous flow of fertilizer along with irrigation water.
2. Three Stage Application fertilizer is only injected into irrigation after the crop have been irrigated and the soil is wet and after the fertilizer has been applied, it is flushed from the soil.
3. Proportional Fertigation Application refers to the direct proportion between the amount of fertilizer in the water and the amount of water used for irrigation.
4. Quantitative Fertigation Application refers to the specific amount of nutrient application to each different block.

​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 

Training is the practice in which you direct the formation of a young tree to form a strong and balanced framework. It is better to direct tree growth with training than to correct it through pruning. However, pruning is a useful practice to encourage productivity by maximizing yield and fruit quality, through removing unwanted plant material.

The main objective of pruning and training include:
1. Maintaining a balance between shoots and roots at planting.
2. Encouraging strong wide crotch angels and preventing the tree to grow too tall. If the tree is too tall, it will increase labour and make it difficult for machinery to reach the top during harvesting.
3. Stimulating shoot growth.
4. Permit the correct amount of light to reach the tree interior.
5. Achieving orchard uniformity and well distributed fruiting wood.

Time is Key
Fruit trees needs to be pruned during the winter, which is the dormant season. Pruning too early in winter should be prevented to reduce winter damage (frost). Therefore, pruning before bloom (late winter) and early spring is ideal. By removing plant material during this time, more carbohydrates are stored in the tree, which will be used to form better quality and quantity fruits in the next season.  By removing leaves during the late spring, it decreases unwanted vigorous regrowth in summer. Vigorous regrowth is unwanted, because the shoots are not used for fruit production and it blocks sunlight to reach the tree interior.

Different Training Systems for Stone and Pome Fruit
Pome Fruit:
Pome fruit tree branches grow vertically, therefore it needs to be trained and pruned into a pyramid shape. The top of the tree should be smaller on top and increase in width the lower the branches are. This ensures that efficient sun light reaches the lower branches. It is therefore important to consider the location the upper and lower branches should be considered when pruning.

Stone Fruit:
Stone fruit tree branches grow laterally, therefore it needs to be trained into a strong and balanced framework of scaffold branches. Pruning and training must be used to form a vase-shaped tree. The open centre allows air circulation and light penetration into the tree’s interior. Pruning and harvesting is also easier, because the fruit bearing surfaces closer to the ground.

The Difference Between a Heading and Thinning
Heading Cut: remove the growing tip of the branch. By removing the apical meristems, growth at the side buds are encouraged. Heading cuts result into a denser growth and prevent the fruit tree to grow too tall.

Thinning Cut: remove a side branch back to the larger parent branch or trunk. These cuts are used do reduce the canopy density to promote light penetration. Thinning also increases vigour of primary branches.

The Difference Between Spur and Lateral Bearing Habits
Spur Bearing:
Spurs are short shoots that bear fruit. Spur bearing fruit trees yield fruits normally at the age of three years. During the second year, the tip of the shoot forms vegetative growth and buds at the base develops fruits. Spur bearing trees develop smaller fruits at higher quantity. Therefore, the trees should be pruned regularly to ensure higher quality of fruits. 

Lateral Bearing:
​Lateral bearing trees yield fruits during their second year. The shoots extend to develop the next seasons vegetative growth and the fruit buds develop at the previous season’s growth. This results into fruit development at the tip of the lateral shoots. The previous year’s young shoots should therefore be left when pruned. 

By Adelene van Zyl

International Trade is sometimes regarded separate from sustainability, but in this interview Dr. Sifiso Ntombela from the NAMC, shares that international trade is absolutely necessary to reach 100% sustainability in a country. 

For more information on the NAMC (National Agricultural Marketing Council) go to https://www.namc.co.za/

By Amy Grundling

Sunburn is a physiological disorder that occurs on fruit species, such as apples, due to excess exposure of sunlight [1]. This disorder causes large crop losses of up to 50% of the total crop yield in the South African apple industry [2]. 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 [3]. 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 [4]. 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 [1]. 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 [1]. 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 [1]. 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 [1]. 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 [1]. 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.

References

1. Racsko, J. & Schrader, L. ,2012. Sunburn of Apple Fruit: Historical Background, Recent Advances and Future Perspectives. Critical Reviews in Plant Sciences. 31. 455-504. 10.1080/07352689.2012.696453.
2. Mupambi, G., 2017. Water Relations and Sunburn in Apple Fruit, Stellenbosch: Stellenbosch University.
3. Schrader, L. E., Zhang, J., and Duplaga, W. K. 2001. Two types of sunburn in apple caused by high fruit surface (peel) temperature. Plant Health Progress, http://www.plantmanagementnetwork.org/pub/php/research/sunburn (last accessed Sep. 6, 2019)
4. Felicetti, D. A. and Schrader, L. E. 2008a. Changes in pigment concentrations associated with the degree of sunburn browning of ‘Fuji’ apple. J. Amer. Soc. Hort. Sci. 133: 27–34.

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

1. Spekboom cutting,
2. Potting soil,
3. A pot, and
4. Root growth hormone.

 
Step 2:  Select and prepare Spekboom cuttings.

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 and Ren​ée Grundling

Oil has been the most important source of energy in the world since the 1950’s. According to UK Oil and Gas PLC, oil primarily supplies energy to factories, heat homes and produce fuels of all kinds. Modern agriculture is largely automized or semi-automized and is dependent on electricity and fuel to maintain large production machinery and implements.

The conflict between countries regarding oil supply and demand is not a new problem. A result of this conflict led to the creation of the Organization of Petroleum Export Countries (OPEC) in 1960 with its first five members being Iran, Iraq, Kuwait, Saudi Arabia, and Venezuela. [1]

A shift came in 1973 when oil was used as a political weapon in the Yom Kippur War. An embargo was set between Israel and the Arab States of Egypt, Syria and Jordan, motivated by the United States of America (USA), to inflate oil prices, effective immediately. This influenced South Africa in 1974 as the first Oil Crisis when oil production slowed down due to oil shortages worldwide, leading South Africa to re-invest in coal derived fuel by companies such as Sasol.

In 1979 an Anti-Western policy was set up by Islamic rule in Iran which caused the second Oil Crisis. This led to an eight-year war between Iran and Iraq which caused non-OPEC countries to produce more oil than OPEC countries. In the 1980’s, non-OPEC countries had a 70% market share, upon which the USA increased oil production tremendously. Conflict arose primarily over a waterway between the Persian Gulf and Oman, called Strait of Hormuz, leading to the Arabic Sea. This waterway was and still is the only way of transporting oil to and from the Middle East.

In 1991 the USA intervened in the Middle East and established military defence bases and signing defence agreements with the Gulf monarchies. This intervention of peace lasted until 2001 when the USA decided to decrease oil consumption from the Middle East.

Conflict between the United States of America and Iran grew further and caused oil prices to spike in 2003. This conflict decreased production and gave China the opportunity to increase oil supply in 2006 and 2007. Steady oil production continued to 2014, until Saudi Arabia manipulated the market in order to prevent the USA from supplying more oil, causing prices to drop. Recent conflicts between the USA and Iran stems from political skirmishes involving nuclear device productions, deals and sanctions, all of which leads to rumours regarding warfare between these two countries and fluctuating oil prices. [2]

How might this influence South Africa?

Due to the instability of geo-politics and variables regarding oil supply and demand, it is difficult to determine exactly what will happen and how it might influence South Africa. Currently, South Africa is mainly dependent on coal produced energy and amounts to 59% of the country’s energy consumption. Crude oil and gas only amount to 16% and 3% respectively. The main concern for South African electricity is not oil fluctuations, but rather excessive coal consumption due to this
resource being depleted at an increasing rate.[3] South Africa’s fuel prices, however, is very much dependant on the Rand/US Dollar exchange rate and international crude oil prices.

South Africa should therefore turn its focus to biogas and biofuels. These are renewable energy sources that is produced by anaerobic digestion of organic materials and used in the agricultural sector, minimizing costs of the farmer by substituting natural gas. Biogas has added benefits such as reducing exhaust emission pollution and one’s carbon footprint [4] . Biofuel is a product of biogas when CO 2 is removed to increase the energy content and allow storage under high pressure [6] . Biofuel can be biodiesel or bioethanol, both of which is made from different biomass and has different products and implements in which it can be used.

Bioethanol is a biofuel that can be used in engines that run on petrol and is made from fermented sugar. [5] This type of biofuel is commonly produced using agricultural wastes such as corn straw and sugarcane bagasse.[6] Biodiesel, as the name implies, is a diesel substitute and is produced using a process called “transesterification”. This type of fuel is produced from various fats and oils from feedstocks such as canola and soybean. [6] Farmers can therefore literally grow the fuel for their farm machinery and implements [6] .

Biogas and biofuels will most likely become a reality much sooner than what we may think. Transitions from electricity and fossil fuels to natural gas and biogas will enable the user to slowly become independent from energy and crude oil providers such as Eskom and imports from the Middle East. The agricultural sector, as an added benefit, will not only be able to use their home-grown fuel, but can also create a lucrative income for themselves.

References
[ 1 ] Meredith, S., 2020. Energy infrastructure attacks are ‘probable’: Oil traders fear supply disruptions
in the Middle East. [Online]
Available at: https://www.cnbc.com/2020/01/07/us-iran-tensions-oil-traders-fear-supply-
disruptions-in-middle-east.html
[Accessed 3 Febuary 2020].
[ 2 ] Parvaneh, D., 2019. Why The US And Iran Are Fighting Over This Tiny Waterway. [Online]
Available at: https://www.vox.com/videos/2019/8/22/20828858/us-iran-hormuz-oil-tanker
[Accessed 1 Febuary 2020].
[ 3 ]Ratshomo, K., 2018. South African Energy Report, Pretoria: Department of Energy.
[ 4 ] Farm Energy, 2019. Introduction to Biodiesel. [Online]
Available at: https://farm-energy.extension.org/introduction-to-biodiesel/
[Accessed 1 Febuary 2020].
[ 5 ] Farm Energy, 2019. Warm Climate Feedstocks for Biodiesel. [Online]
Available at: https://farm-energy.extension.org/warm-climate-feedstocks-for-biodiesel/
[Accessed 1 Febuary 2020].
[ 6 ] Sarkar, N., Ghosh, S.K., Bannerjee, S. and Aikat, K., 2012. Bioethanol production from agricultural
wastes: an overview. Renewable energy, 37(1), pp.19-27.