Article of Plant Nutrition and Chlorosis by Ludwig Taschner
The inexplicable chlorosis that often occurs with rose plants triggered off my thinking and a bit of research. Why would roses be perfectly happy and have dark green leaves up until their first flowering and then produce chlorotic new growth with the sprouting of new leaves for the second flush?
One often notices the yellowing of the leaves to various degrees with the veins usually remaining green. Sometimes all new growth is affected, sometimes only on half a plant or just a few stems. Once the weather changes, with enough rain, it corrects itself within days. It is commonly known as an iron deficiency and watering or spraying the bush with iron chelate is suppose to correct it, but it does not always happen.
The incredibly interesting soil health series compiled by Sonia Burger in the Farmer’s Weekly made me go a bit overboard when writing this article, and I will be quoting from her articles from time to time.
Although the basics of plant nutrition have not changed since my apprenticeship days, the understanding of the intricate working together of each of the macro and micro minerals has.
If you get bored and don’t feel like reading through it all, go to the end where it specifically deals with the needs of our roses.
Without plants there would be no food for any living creatures. There is a long list of creatures – including insects, mice and rabbits, kudu, horses, cows, sheep, pigs and vegetarians – who live on roots, tubers, leaves, wood, fruits, pollen and of course seed. Without the creatures that live on plants the meat eaters would have no meal either. Also, let’s not forget all the lekker stuff made out of plants like Coca, Opium, Dagga, aphrodisiacs, sugar, beer, wine, whisky and virtually all medicines. Of course, diamonds, coal and oil resulted from plants being compressed by millions of tons of rock millions of years ago. It is mind boggling if one thinks that plastics, fertiliser, pesticides and medicines are made out of coal or oil, which used to be plants.
The basic miracle of nature is that minerals dissolved in water are transported into leaves and are assimilated with carbohydrates. The carbohydrates themselves are the product of a process by which carbon dioxide taken out of the air is converted by chlorophyll under the influence of light, known as photosynthesis. Leaves fall off trees; plants dry out in winter or during droughts and even trees fall down. This organic matter is now subject to decomposition, or in other words a separating of elements into constituent parts. Decomposition requires microbes to convert organics back to in-organics or minerals.
It seems very simple – all the scientist needs to find out is how to hasten the process of taking the C out of the carbon dioxide (CO²) and harness the carbon monoxide and the world’s energy crisis is over. However, when nature is involved it gets pretty complex and is not easily copied as you will see below.
The speed at which plant material decomposes depends on temperature, moisture, air and the texture and it may take a month or years. Peat moss for instance is submerged fern which grew on or above a water surface. With no air getting to it at the bottom of a lake it never decomposed. Taken out of the lake and mixed with soil it does not take very long to decompose.
Plants developed and adjusted in accordance to the availability of water soluble minerals in the upper 1m crust of the earth. There are plants that adapted to growing in acid soils and others in a very alkaline situation, with most of them preferring a more or less neutral growing base. Scientist sorted this out long ago and we differentiate the various soil types on a scale of pondus Hydrogeni worldwide known as pH with pH 7 being neutral, lower values indicating acidity and higher values alkalinity.
Naturally, temperatures, soil depth, rain or fresh water availability, all played a role in plant development.
All this is just a refresher from old school stuff, but keep on reading. I get to specifics for the roses eventually.
It was Justus von Liebig, Professor in Chemistry, who was instrumental in the start of AgroScience around 1850. He established that plants need 10 basic elements to grow. (He also developed Aldehyde, chloroform, baking powder and meat extract.)
Of the 10 basic elements, the plants take Carbon (C), Hydrogen (H) and Oxygen (O) out of the air or water. Nitrogen (N), Phosphorus (P), Potash (K kalium), Lime (Ca calcium) Sulphur (S), Magnesium (Mg) and Iron (Fe) need to be available in the form of dissolvable salts in the soil.
The micro or trace elements include manganese, copper, zinc, boron, molybdenum and cobalt, sodium, chloride and silicon.
He further established that the nutrient requirements are in accordance to the nutrient that is the least available in the soil. For instance if there is insufficient Lime in the soil the plant cannot do with extra Nitrogen or Potash.
These minerals, including the various trace elements, have certain synergies with each other, but also very specific functions in plant development. If it is out of balance, plant growth becomes abnormal and any abnormality brings on pests and diseases.
Plants that grow well in one region because of the availability of the various elements shed enough material that is decomposed and the then separated minerals are absorbed again by the plants. Obviously, the decomposed material from plants that prefer to grow in acid, low ph soils is rich in acid minerals i.e. Sulphur. Alternatively, compost made from plants that grew in alkaline soil, and even manure from animals grazing such plants, is high in alkaline minerals i.e. Lime and Sodium combinations.
In nature fire, floods and erosion destroys most of the decomposed material and if this is not checked a completely different plant population establishes itself from seeds that are blown in and even seed or root rhizomes that were suppressed by the previous plant growth. Farmers know all about that.
In the old days when farming was carried out with hoes or animal drawn implements, farmers usually knew which soil was best suited for which crop and planted seed accordingly. These days with huge tractor drawn implements, huge fields are leveled, ploughed up and planted with one crop. Science is giving a helping hand. Equipment in satellites can read quality and depth of the soil and directs the implement or shows the farmer on his laptop computer what to do to create the right plant density and fertiliser combination and strength.
NOW we come to our gardens and ROSES. Almost every garden has several soil types and is subjected to various climates, often extremes. A garden is very personal and it will never do to have the same type of plants in every garden in a specific suburb or region, just because they grow so easily. Indeed we want to cram every possible plant in it, from huge shade trees and sun loving plants to acid soil loving Azaleas, Hydrangeas and Camellias and of course Roses who feel comfortable in a fair range from pH 6 to pH 7.5. All must grow happily in close proximity.
Every soil can be fixed to grow any plant in it, simply by bringing in the necessary additives. Extremes might entail blasting rock to be able to grow trees, draining out a swamp or filling up the soil level by a metre. It is simply a question of available finances.
The extremes in gardening became very clear to me when flying to South America recently. That Gauteng has become the largest man made oasis is very obvious at take-off. After flying for hours over the semi desert of the Karoo, Kalahari and Namibia and more hours over the Atlantic the other side of the Atlantic presents a different picture – dense forests as far as one can see. Then, out of that looms the huge concrete jungle that is Sao Paulo. Virtually not a tree in the city, gardens are small and most plants are grown in hanging pots.
In the semi desert of Gauteng and many similar cities and towns in South Africa people want a large garden in order to create there own little oasis. I suppose in the tropical forest of South America it is a constant fight to restrain the forest from overrunning the garden and with that huge green lung around them, the people are satisfied with growing their favourite plants in confined spaces.
Soil is explained in the encyclopedia as the upper layer of earth in which plants grow, consisting of disintegrated rock usually with a mixture of humus, which again is explained as the characteristic organic constituent of the soil formed by the decomposition of plant material.
The whole process must have started with mineral salts in the sea, eventually the formation of algae making use of this nutrition, then ferns and finally flowering plants. With the upheaval of our earth so long ago sea water was everywhere and plant nutritious mineral salts remained in the soil as the water drained away. It was then up to the plants to provide humus and from then on plant development became more and more sophisticated, adjusting to the different soils and climates.
Organic farming or gardening is the “IN” thing at the moment. As with all things, there are pros and cons. The pro is that plant roots are able to absorb a very balanced diet of nutrition which makes for healthy plants becoming healthy food. The con is that the release of various nutrients from organic matter will happen when the conditions favour microbial growth and this is not necessarily when the plant requires the nutrition the most, resulting in reduced harvest and higher production costs.
The more humus in the soil to a good depth of at least 50 cm the better the growth. Soil in South Africa is usually very poor in organics. Plants and plant debris is burned, never mind intentionally or not, or the wind blows away the upper drier loose particles. Compare this with Western European climate of no veldfires, frequent rain and moisture and with enough forests acting as wind breaks.
If the humus is made from several different components (plants) it is more fertile. Regrettably, most bagged compost on offer is of one plant source. Really good compost is “grown” in one’s own garden the old fashioned way by adding leaves and lawn clippings and vegetable left-overs, twigs and branches on a heap and turning it over every six weeks to two months until the heap has virtually turned into soil.
Compost that is still hot when in a heap is not fully decomposed. At this stage it causes a nitrogen drawdown. Organic gardeners should keep a drum in the back yard and make a tea by mixing chicken, rabbit or pig manure with water, stirring it occasionally for two three weeks and then pour this over the not yet fully decomposed compost. It will overcome the nitrogen drawdown and speeds up the composing process. Adding manure will have the same effect and non organic gardeners may sprinkle fertiliser over the compost for the same results.
Using this principle projects have been carried out most successfully in Soweto by digging trenches about 60 cm wide and 50cm cm deep filling them with plant debris turning it over in the trench and adding a little of the soil that was dug out. After only a few months vegetables are planted directly in the filled trenches with incredible results. When one crop is ready to be harvested the next trench is ready to be planted.
- Now let’s look at the seven main plant nutrients in detail:There is no shortage of Oxygen, which is taken out of air and water.
- Hydrogen and Oxygen are separated from the H2O which is water.
- The same applies to Carbon which is separated out of the CO2 in the air.
- Phosphorus is regarded as the fuel of life – the energy currency of all cells. It is an essential nutrient in all forms of life. It is the key element for photosynthesis harnessing the sun’s energy and stores it as chemical energy, which is converted into simple glucose and then complex sugars and then starch. Good phosphorus levels ensure better photosynthesis. Other forms screen destructive UV light and only let in that part of the spectrum required for photosynthesis. It allows sufficient uptake of nitrogen and magnesium which are vital for chlorophyll production. Good phosphorus levels contribute to the taste, nutrition, colour, size and shelf life of fresh produce and the lasting quality of the blooms.
Phosphorus is also one of the most abundant minerals in the human body, second only to calcium. It contributes to muscle growth and fertility, is required for kidney functions, it helps the heart beat regularity and plays a vital role in the body’s energy storage system. A body without phosphorus soon becomes tired and weak.
Phosphorus is a “lazy element” because it does not move from where it is applied in the soil and it does not leach. For this reason it is essential to mix it well with the soil when planting or when digging over a rose bed in winter. The pH of the soil has a significant effect on phosphorus availability. At a high level it ties up with calcium, at a low pH it joins with aluminium, iron and manganese. The formed phosphate compounds are insoluble.
In the form of Monocalciumphosphate, as it is in Superphosphate, it is water soluble for a few weeks. Once it has become a Bicalciumphosphate the roots need to excrete a citric acid which allows absorption of the phosphate.
- Phosphate is available as Superphosphate, in MAP, Bonemeal, guano manure and the centre figure of compound fertilisers give an indication as to how much phosphate it contains. For instance 2-3-2 fertiliser is very high in phosphates and should not be applied monthly to roses. The 5-1-5 or 8-1-5 are the better options. Soluble humic acid granulate (as in Vigorosa) again ensures absorption, microbe activity and the stabilisation of phosphates.
- Potassium is the cellular spark plug and the third of the macronutrients. It is an alkaline element essential for soil, plant, animal and human life. It is the major cation (an ion carrying a positive charge which moves to a negative charge) in intracellular fluids. Without potassium in the cells one would not be able to turn over a page as the instruction to do so would not be passed from brain to the cells that form the building blocks of the muscles in ones hand.
Potassium in the plant regulates the 50 enzymes responsible for catalytic reactions and is required to convert nitrogen into protein. It facilitates the movement of sugar and starches and influences stomata regulation.
Although about 90% of the potassium is found in soil it is insoluble. It is only released by microbial activity or weathering. Soluble potassium is found as a cation (K+) which is strongly attracted to and hence stored on the negative charged clay colloid. The humus colloid has less attraction but is also capable of storing potassium.
Plants access potassium via the soil solution. This is usually no problem in soils with high clay content, however in sandy soils there are few storage surfaces for potassium and most are carried away. Adding humus to sandy soil contributes significantly to the retention of potassium.
Whereas most nutrients found in living tissue are only released back to the soil through decomposition, potassium does not follow this rule. It is kept intercellular and for instance rain leaches potassium from manure and freshly cut grass.
Potassium is available as Potassium chloride (KCl), Potassium sulphate K2SO4, potassium nitrate (KNO3 and potassium bicarbonate (KHCO3) which also has a fungicidal action. Potassium chloride is used in most combi fertilisers.
In high pH soil calcium and magnesium with their double positive charge fill up most spaces in the soil and potassium is drained away and cannot be absorbed in sufficient quantities.
Sodium, if exceeding potassium, is taken up by the plant instead and this imbalance prevents uptake of manganese. On the other hand a lack of calcium levels increases potassium levels which lead to an imbalance in plant growth.
- Calcium is the soil doctor: Mostly we think of it as Lime (CaCO3). Calcium is the most important mineral in the soil and ensures good soil and plant health which ultimately translates into better human health. It is the transporter of all minerals.
Farmers know that balancing calcium levels and correcting soil deficiencies is the first priority in any fertility programme.
Up to 70% of the negatively charged soil particle is occupied by calcium. Although every farmer and gardener knew for over a century that the pH could be raised by adding CaCO3, however, the role of calcium as an essential nutrient was ignored and the synergistic interactions between calcium and other minerals were not well understood. The ideal pH is 6.4 at which all minerals are most available to the plant.
Calcium does not just adjust the pH, but also flocculates the soil improving spore space, resulting in good oxygen movement which again leads to more roots and microbes.
Balanced soils need the correct calcium to magnesium ratio as these work as tug-of-war teams in opening and closing the soil.
In the plant calcium plays a vital role in strengthening the cell walls and membranes. It strengthens the leaves and stems, making them more resistant to pests and diseases and it helps the plant to optimally make use of sunlight, carbon dioxide, water and nitrogen.
Adequate calcium levels make fruit and vegetable taste sweeter and to last longer, which includes the vase life for roses.
For normal to slightly acid soils add dolomite lime which contains 20% calcium and 10% magnesium. In brak soils rather make use of gypsum (calcium sulphate)
All the above translates into the same basics of gardening and successful rose growing which I have been preaching about over the past three decades.
If you dig up your flower beds to at least 50 cm depth ensuring drainage from that level further down and by mixeingliberal quantities of humus in the various available forms of compost, semi composted stuff, peanut shells, pine bark chips with superphosphate and or bone meal as an additive more than half the battle is won in providing nutrition and ensuring that the fertiliser applied later on is able to act to its fullest effect.
By working a layer of compost or even just the half decomposed mulch into the soil every winter enough basic material is made available for microbial activity and the monthly recommended dose of fertiliser ensures that extra growth we expect from a rose bush these days.
I am convinced that our constant “plugging” of regular fertilising of our roses over the past decades has brought about the desired result, with in roses flowering for a good 8 to 9 months of the year in South Africa. There is, of course, the danger of fertilising indiscriminately all season long so that the “goodness” of the soil is destroyed in the process, simply because the intricate function of the various minerals with microbes have become completely imbalanced. There are many farmers who have done this to their soil as well, with the crop just not responding to the fertilization anymore.
Worldwide research has resulted in the successful isolation and use of carbon acids. Carbon acids increase the uptake and consumption of nutrients and many farms have already been re-vitalised after introducing this into the soil. Headlines in the Farming press are witness of this:
Carbon Acids bring yields to life
Organic acids boost crop yield
Building soils with humic acid can fight disease
Export-quality citrus from carbon acids
Several years ago we were involved in trialing carbon acid products, researched by the CSIR, in our nursery.
Once this became commercially available I was quick in latching onto it, knowing that a combination of HUMIC ACID (one of the carbon acids) and fertiliser with the basic macro minerals N, P, K, Magnesium, Sulphur and lime would be a superior product and Ludwig’s Rose Farm commercialized it under the TradeMark Ludwig’s VIGOROSA®.
The only complaint we have heard over the past three years since it became available is that the rose bushes grow too high to reach the flowers.
Whereas farmers relied totally on the plants taking carbon out of the air, not working the stalks, stems etc back into the soil, allowing the microbes to reconvert this organic material to carbon, they are now applying a carbon product in a slightly acid form that stimulates microbial action and assists in improving storage of the other mineral nutrients and getting them dissolved and absorbed by the roots of the plants in an improved form.
All this still has not solved the problem of chlorosis. With the above in mind and from observation, it appears that the rose bushes go through a growing change once they have formed the blooms. They would rather just form hips and let them ripen, which does not suit us at all. Enforcing re-sprouting by removing the open blooms, watering and fertilising the slowed down process is reversed to one of rapid absorption. The new growth that is formed does not receive the nutrients in a perfect balance and this is amplified by increased evaporation of the water in the leaves in the accelerated heat. It needs to be appreciated that most minerals are dissolved in water in the soil; this solution is absorbed by the roots through the process of osmosis and travels up to the leaves. That is when the process of photosynthesis starts where all these various minerals are needed. With water disappearing too quickly the salty minerals remain stored and become concentrated and only cooler weather and lots of fresh water alleviates a temporary chlorosis.