Plant Nutrition
Understanding Plant Nutrition
While soil health is very important, farming is a business, so the aim is to harvest a good crop, make a nice profit, but do so in a sustainable way.
To achieve this the link between soil health and plant health must be understood.
There are many factors affecting a plant’s health, some of these are beyond our control, for example the weather, but we can influence the nutrition available to the plant. All living systems require nutrients to drive their biochemistry and create energy. For a plant to function and reach its yield potential, the correct quantity and a variety of nutrients should be available.
In fertile soils, nutrients exist in large quantities and few additions are necessary to grow excellent crops. However, this is rare, especially on land that has been farmed intensively for many years, the soils can become depleted. This depletion is principally caused by the removal of plant material from the land, which effectively moves the nutrients off-site to where they are processed & consumed. This is known as an open loop system. The waste products seldomly return to the land and thus the nutrient cycle is interrupted.
Another reason for nutrient loss is through leaching. Although this is a natural process, poor quality soils will lose nutrients much faster than healthy soils.
In comparison, an example of a closed loop system is a natural forest. These are some of Nature’s most productive and diverse eco-systems. Here every plant and animal that perishes is returned into the soil, thus the nutrients are never lost, only “cycled”.
Composting surplus plant matter and crop residue by returning it to the soil can reduce this nutrient loss, but this is seldom enough for intensive farming.
The Basics of Plant Nutrition
Which nutrients are required?
Healthy Plant growth and development use nutrients from the soil and air and these can be supplemented with fertilizer as required for intensive farming. Each nutrient has many functions in the plant, different levels of requirement, and characteristics. Nutrient demand increases with the growth of plants, and deficiencies or excesses of nutrients can result in damage to plants by slowing or inhibiting growth and reducing yields.
Plants require >18 nutrients (elements) for optimal growth and development. Some of these elements are utilized within the physical plant structure, namely carbon (C), hydrogen (H), and oxygen (O). These elements, obtained from the air (CO2) and water (H2O), are the basis for carbohydrates such as sugars and starch, which strengthen of cell walls, stems, and leaves, and are also sources of energy for the plant, animals and people that eat the food.
1.
Macro Nutrients
Nitrogen (N), Phosphate (P), and Potassium (K) are required in large quantities by the plant, and are important for plant nutrient content, the function of plant enzymes and biochemical processes, and building strong plant cells. Deficiency of these nutrients cause poor plant growth, health, and yield, so these are most important nutrients supplemented by addition of fertilizers.
2.
Minor Nutrients
Calcium (Ca), Magnesium (Mg), and Sulphur (S) are very important for soil chemistry (pH) and structure and vital to healthy plant growth, and resilience to disease and pest.
3.
Micronutrients
Although are used in small quantities by the plant, but nevertheless are necessary for plant survival. These micronutrients include iron (Fe), boron (B), copper (Cu), chlorine (Cl), Manganese (Mn), molybdenum (Mo), zinc (Zn), and nickel (Ni).
Plants also contain Sodium (Na), Silicon (Si), Iodine (I), Selenium (Se) cobalt (Co) and other elements in small quantities their contribution to plant health and resilience of crops is recognized in plant nutrition.
The Basics of Plant Nutrition
- From naturally occurring Biological cycles – living things die off and recycle nutrients to use.
- Originate in the soil & rocks (inorganic minerals)
- Applied as fertilisers
Nutrient Cycles:
Carbon, Nitrogen, Phosphorus and Sulphur are primary examples of Nutrients that have well understood macro cycles. For example, the atmosphere is comprised of almost 80% Nitrogen (N), yet this Nitrogen is not available to the plants because it is bound in a strong N2 molecule. To be taken up by the plant’s roots, it needs to be converted into Ammonia (NH4 ) and Nitrates (NO3 ). This process known as Mineralization occurs naturally thanks to the specialised bacteria that are capable of “Fixing” this Nitrogen. Once the plant has used the Nitrogen, it is released back into the atmosphere in a process known as denitrification. These and other Nutrient cycles are fascinating refer to the Videos and Articles section of the learning centre.
Nutrient cycling within the soil food web
Inorganic minerals:
Most minerals were once a part of the parent rock that has been broken down into smaller particles. Some minerals may have been deposited in the soil over time through the actions of wind and water, and others are deposited there after plant and animal materials decompose. When talking about these minerals they are often grouped together as positively charged ions known as Cations.
Although many of these minerals are abundant in the soil, they are often unavailable to the plant and require assistance from the soil life to make them available.
Fertilizers:
Nutrients can be provided to plants in the form of added fertilizers. Fertilizers are commonly grouped as either
a) Synthetic (chemical) because they are manmade, or
b) Organic because they originate from living things
c) Another source of fertilizers is mined materials, which depending on their chemical composition can be applied to the soil as-is or must undergo further processing like acid-treatment to facilitate uptake of nutrients.
Why do we need to add Fertilizer?
Fertilisation has been key to increasing production per hectare in the last century and in so doing, meeting the food demands of the world. However, if it is done incorrectly, it can cause tremendous harm to our soils, ecosystems, and the planet.
Talborne Organic Fertilizers are carefully designed to avoid damaging the soil and environment. Instead, they actively replenish nutrients in damaged and depleted soils while promoting natural nutrient cycles, therefore you apply less and less fertiliser over time.
How do soil microbes help plants access nutrients?
Regardless of where the nutrients come from, it is crucial that they are available to the plant. Most synthetic fertilizers are salt based, meaning nutrients are pushed into the plant using osmotic pressure. This can lead to imbalances in the plant, reduced soil life as well as lead to limited root growth. Organic nutrition is much more complex and relies on soil life to make nutrients available to the plants as and when they require them. Although the processes are far too numerous and complex to be discussed in any depth here, some examples of this process in action are:
- Essential minerals contained in the soil are mostly in the form of unavailable compounds. For example, plants need a lot of Calcium, but when it is bonded to Carbonate, you get CaCO3 – Lime, and none of this calcium can be taken up by the plant. Plants need the help of specialist microbes to release the nutrients from their bonds first. Certain Bacteria produce Organic Acids which solubilise these minerals and make them available to the plants.
- A plant’s roots only make contact with a very small amount of soil, but plants can access water and minerals far outside the rootzone. They do this with the help of Fungi. These form fine filaments which reach far and wide, and in return for the plant feeding them sugars, they provide the plant with the nutrients and water it needs to grow.
- Another recent discovery called Rhizophagy proved that root tips absorb entire microbial cells and extract needed nutrients from those cells, then release some of the microbes back into the soil to repeat the process all over again.
- Fertilizers can also be absorbed by leaves in a process called endocytosis. This is commonly referred to as foliar feeding and although it can be very useful, it typically should not replace the primary means of absorbing nutrition, which is through the plant’s roots.
- See these and other fascinating synergies between plants and soil life in our Videos and Articles section of the learning centre.
Nutrient deficiencies
There are many ways to determine nutrient deficiencies, but whenever the problem is serious you will quickly be able to see signs of trouble by looking at the plant’s leaves. The below chart is a good starting point for spotting symptoms of deficiency, however it can sometimes be misleading, so calling on an experienced agronomist might be necessary.
Other tools for confirming deficiency diseases include leaf and sap analysis. These should be used in conjunction with soil analyses, because sometimes a deficiency in the plant might not be due to a deficiency in the soil, but rather a problem whereby the plant cannot access the nutrient.
Resilience to stress:
Like in humans, plants that are under-nourished will suffer stunted growth, and are far more susceptible to pests, disease, and environmental factors like heat, cold, drought or flooding.
When nutrients are lacking, important molecules like chlorophyll, DNA, RNA, proteins (amino acids), and lipids (fats) cannot be manufactured and enzymes which carry out important functions shut down.
Stunted growth:
- Depending on which nutrient(s) are deficient, stunted growth is essentially when a plant fails to reach its genetic potential. This can be mean fewer and smaller roots, leaves and fruits.
- Plants that are grown with synthetic methods are almost entirely dependent on receiving nutrients in the form of salt-based fertilizers. Except in carefully controlled systems such as hydroponic growing, farmers are not able to fertilize exactly according to a crop’s needs, so the plant will go through stages of deficiency and excess (feast and famine) leading to stunted growth.
- In a healthy soil, naturally farmed plants will develop synergies with their ecosystem which consistency provides nutrients to allow for optimal growth. These plants rely less on fertilizer and are more resilient as a result.
Pests & disease:
- Deficient plants have far less potential to photosynthesize. This is the process where plants convert energy from the sun into other forms of chemical energy such as sugars and fats. Sucking and biting insects are not able to feed on plants that contain high levels of sugars (Brix)
- Plants that do not produce sufficient sugars or imbalanced sugars (Nitrogen without Magnesium) will also not be able to support a large group of synergistic soil microbes which are proven to provide plants with various defense mechanisms when called upon.
- Studies are pointing more and more to the fact that a plant’s immune system is largely based in the soil. Plants can signal distress and call their microbial community for help. They respond by providing hormones, enzymes, and other products that plants can use to fight disease.
Environmental stress:
- With the impacts of Climate change, it is important that our food supply is resilient to the dangers of extreme conditions, such as heat and drought, excessive rain, and extreme cold.
- In times of drought, plants that are sufficiently nourished will have strong and well-developed roots which are fully colonised by friendly microbes. These microbes can extract water where it is scarce and also excrete substances like glomalin which binds soil particles improve water retention.
- During flooding, strong and deep roots will help anchor the soil and plants in place. Roots with healthy soil biomes will shield the roots from pathogenic bacteria which result from anaerobic conditions during water logging.
- Plants with high levels of nutrients have also shown to cope better when exposed to extreme heat and cold.
Fertilising Do’s and Don’ts
Do's
+ Do use Talborne Organics’ completely formulated Organic fertilizer because it will provide a sustained release of macro and microelements in one application.
+ Do only use inputs that will build and not harm the soil biology.
+ Do make use of soil and sap analysis, and qualified consultants to guide your nutrition application. The benefits of doing this vastly outweigh the small cost of sampling and analysis. Also, consider tracking the health of your soil as it is very rewarding to see actions put in place to build soil health pay off in the long run. Think long-term!
+ Do keep in mind that Talborne Organic Fertilizers nutrition is not instantly available to the plant. Plan your application around when the crop needs it most. Nutrients will release more slowly than Synthetic fertilizers but will sustain the plant for longer.
+ Do soil remediation before planting or fertilizing. This essential step is often left out due to cost, but the cost of not doing it is much higher. Remediation is only done occasionally and will not be a recurring cost
+ Do understand your soil health and nutrient management. Your soil is your biggest asset therefore, it justifies spending time to learn how to maintain it just as you would for any other asset.
+ Do combine Organic fertilization with other soil-health, regenerative farming practices such as minimal disturbance of the soil, cover cropping, application of compost or green manure, crop rotation or intercropping, and other methods of soil enhancement.
Don'ts
– Don’t view soil correction and crop nutrition as a cost that must be minimized. This line of thinking avoids the reality that your crop’s success depends on your soil. Investing in your soil is probably the best investment that any grower can make.
– Don’t use chemical pesticides, fungicides, and nematicides – if it is deemed necessary, opt for natural products and solutions, there are surprisingly many available.
– Don’t use herbicides such as Glyphosate and other chelating agents as they can bind with trace elements making them unavailable to plants. They also disrupt soil ecosystems by killing off the food chain like algae.
– Don’t overapply fertilizer, rather opt for smaller more frequent applications. A consultant will be able to advise you accordingly.
– Don’t use excessive amounts of animal manures. Although they have their merits and are relatively inexpensive, they are do not supply balanced, high nutrient levels. You might have to apply 3 times more than Talborne Organics VITA fertilizer, and because manures nutrient content is variable, soil imbalances such as Phosphate toxicity can result. Manures should not be sourced from Factory farming or feedlots due to potential for contamination of heavy metals, antibiotics and growth stimulants which kill off soil microbes. High levels of salts (sodium) in feed rations of factory-farmed animals, add to sodium (Na) build up in soils.
– Don’t use compost or manures that are not correctly and thoroughly composted. Often growers will use compost which is not fully broken down and the incorrect C:N ratio can mean the microbes consume more Nitrogen than they release, essentially robbing the plant of Nitrogen for a period. Also ensure composting is done aerobically (aerated system), and to the correct temperature to prevent pathogens like E. coli contamination in the soil.
– Don’t blindly accept advice from salespeople that claim to have your best interests in mind, rather do your research and ask questions. Unfortunately, there are too many product pushers in the agricultural industry, offering a “magic” solution.
– Support the people and input products that have legal compliance, product safety standards, proven products and an established reputation over many years.
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