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Foliar Nutrition

Many farmers have used foliar fertilizers with a great deal of success. Supplementary foliar feeding is a way of supplementing the plant's supply with nutrients quickly and specifically. In addition, research has shown that foliar nutrition also promotes the absorbtion of nutrients in the soil.


There are various ways in which foliar nutrition can be done, but the following three are the most important methods and each has a different aim.

General foliar nutrition is used for supplementary feeding and stimulation of plant metabolism. This type generally involves foliar fertilizers with a balanced content of macro and micro nutrients in a nutrient ratio which is suitable for virtually all plants.
images/stories/flower.gifCrop-specific foliar nutrition is usually used for satisfying specific nutrient requirements of various crops. For example, bitter-pit in apples is caused by a localized calcium deficiency in the fruit. Calcium applied to the soil will not cure this, as the calcium is not transported to the fruit in sufficient quantities. Calcium applied via the fruit and leaves is the only way of preventing this deficiency.
images/stories/flower.gifSoil-specific foliar nutrition is aimed at solving soil-specific nutritional problems.
The fixaton of certain nutrients in the soil is the reason for applying foliar fertilizers.


Reasons for nutrient deficiency


There are many different reasons for nutrient deficiency. For example:

  • Unfavourable weather conditions may inhibit the absorbtion, transport and processing of nutrients.
  • An unbalanced supply of certain nutrients reduces the absorbtion of other elements.
  • Certain growth stages in the life of a cultivated plant require particularly high and often quite specific levels of nutrients. Also, an adequate supply of nutrients obtained through the roots is not guaranteed because of nutritional problems of a physiological nature.
  • Even though fertilizer applied to the soil may be correctly calculated, in many cases, the plant may still suffer a nutrient deficiency, although the symptoms may often be invisible ( a so-called latent deficiency) .This can result in a considerable reduction in yield.

In the above cases, foliar nutrition is an excellent and cost effective method of ensuring the plant receives a balanced supply of nutrients, because the leaves quickly absorb the nutrients which are directly available to the plant.

Plant Nutrients

Basic elements
Ninety-two natural mineral elements are known to exist, but only sixty of these have been found in plants. Of these sixty, only sixteen are considered essential for plant growth.

To be considered essential for healthy plant growth, an element must fulfill four criteria.

  • It must be necessary for the plant to complete it's life cycle.
  • It's action must be specific, that is, not wholly replaceable by any other element.
  • It must be directly involved in the nutrition of the plant, that is, required for the action of an essential enzyme.
  • It must not antagonise the toxic effect of another element.

The sixteen elements that are generally considered essential for plant growth are divided into macro-elements (those that are required in relatively large quantities) and micro-elements or trace elements (those required in considerably smaller quantities.)
Macro-nutrients Micro-nutrients
carbon (C) boron (B)
hydrogen (H) chlorine (Cl)
oxygen (O) copper (Cu)
nitrogen (N) iron (Fe)
phosphorus (P) manganese (Mn)
potassium (K) molybdenum (Mo)
calcium (Ca) zinc (Zn)
magnesium (Mg)
sulphur (S)

Essential Elements; The lack of just one essential element can ruin the chances of a good crop, even if all the other essential nutrients are there.
Before deciding which plant nutrients should be provided for in a plant it is necessary to know the function of each element.
The macro-nutrients and micro-nutrients are almost always taken up by the plant in the form of ions, which are positively or negatively charged particles.

 

Macro-nutrients are those which the plants need in large quantities and consist of the following:

images/stories/flower.gif Calcium (Ca)
Responsible for the structural and physiological stability of the plant tissue ; for efficient cell division, cell wall formation and cell extension. It sometimes interferes with the ability of magnesium to activate enzymes.
images/stories/flower.gif Carbon (C)
A constituent found in all organic compounds.
images/stories/flower.gif Hydrogen (H)
A constituent of all organic compounds of which carbon is a constituent. It is important for the cation exchange in plant-medium relations.
images/stories/flower.gif Magnesium (Mg)
As the central atom of chlorophyll (leaf green), it is of particular importance in the process of photosynthesis. It also promotes the absorption and translocation of phosphorus, and appears to aid in the formation of oils and fats. It supports the assimilation of carbon dioxide(CO2) and the synthesis of protein.
images/stories/flower.gif Nitrogen (N)
Nitrogen is used in various forms to promote rapid vegetative growth, leaf, flower, fruit and seed development,and chlorophyll development, and to increase the protein content in all plants. Nitrogen is absorbed in the form of ammonium (NH4), nitrate (NO3) or urea (CO(NH2) 2).
images/stories/flower.gif Oxygen (O)
A constituent of many organic compounds. It is essential in the anion exchange between roots and the external medium.
images/stories/flower.gif Phosphorus (P)
It promotes and stimulates early growth and blooming and root growth. It hastens maturity and seed growth, and it contributes to the general hardiness of the plant.
images/stories/flower.gif Potassium (K)
It promotes disease resistance and good development of carbohydrates, starches and sugars, and it increases fruit production. It is also instrumental in regulating the plant's water retention.
images/stories/flower.gif Sulphur(S)
As a constituent of amino acids, sulphur promotes the synthesis of protein. Sulphur deficiency symptoms are therefore similar to nitrogen deficiency. It also promotes the synthesis of soils and good cell wall structure.


Micro-nutrients consist of the following:

images/stories/flower.gif Boron(B)
Promotes the formation of protein which is required in order to sustain meristem activity (meristem is embryonic tissue). Being part of the cell walls, it promotes the transfer of carbohydrates through the cell membranes and supports the assimilation to supply the roots and is important for blossom formation.
images/stories/flower.gif Chlorine(Cl)
Is essential for photosynthesis where it acts as an enzyme activator during the production of oxygen from water.
images/stories/flower.gif Copper(Cu)
Participates in the production of carbohydrates and proteins via photosynthesis; 70% of the copper in a plant is in the chlorophyll. It is also thought to be involved in nitrogen fixation.
images/stories/flower.gif Iron(Fe)
Acts as a catalyst in the photosynthesis and respiration process, and is essential for the formation of sugars and starches. Iron also activates certain other enzymes.
images/stories/flower.gif Manganese(Mn)
Activates one or more enzymes in fatty acid synthesis and the enzymes responsible for DNA and RDA formation. It also participates directly in the photosynthetic production of oxygen from water and may be involved in chlorophyll formation. Manganese is closely associated with copper and zinc.
images/stories/flower.gif Molybdenum(Mo)
Essential for the activation of nitrate reductase, which is the conversion of nitrate into nitrite. There is a higher Mo requirement when NO3 is supplied as a feed than with NH4. It's most important function is the fixation of nitrogen, particularly in legumes.
images/stories/flower.gif Zinc(Zn)
Similar to magnesium and manganese in its physiological activity, it influences the formation of starch and the synthesis of RNA, so promoting the production of protein.


Requirements and signs of deficiencies

The following table outlines the plant requirements for trace elements and the problems that arise when these are lacking. Each of these seven essential micro-nutrients are found in TRELMIX TRACE ELEMENT SOLUTION in the percentages shown.
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BORON(B) 0.111%

PLANT REQUIREMENTS DEFICIENCY SYMPTOMS
  • Boron is essential for reproduction and thus seed and fruit set.
  • Healthy root growth and the root reponse to gravity are dependent on Boron.
  • Sufficient Boron enables plants to become resistant to diseases of many types.
A lack of boron in a plant results in:
  • Poor flowering and seed set.
  • The deterioration of root and stem growing points.
  • Stunted roots.
  • Wrinkled leaves.
  • "Hard fruit disease" (especially citrus).
The crops most susceptible to a deficiency are: cabbages, broccoli, Brussel sprouts, cauliflower, carrots, radish and citrus.

COPPER(Cu) 0.319%

PLANT REQUIREMENTS DEFICIENCY SYMPTOMS
  • Copper is essential for plant respiration and photosynthesis.
  • Greening of leaves.
  • Development of flowers and thus seed and fruit production.
  • Copper is required to control nitrogen fixation by legumes, and iron uptake by all plants.
  • Copper will also help prevent wilting of leaves in dry periods.
A lack of copper in a plant results in:
  • Poor leaf colour and deformed leaves and flowers.
  • Fruit quality and production are adversely affected.
  • Wilted leaves and leaves will suffer from "treatment illness".
  • Citrus fruit developing thick oily skins with gum spots.
  • Trees develop abnormal shoots with skew leaves.
  • Up to 50% reduction in yield.

IRON(Fe) 2.260%

PLANT REQUIREMENTS DEFICIENCY SYMPTOMS
  • Iron is needed in large quantities to produce chlorophyll and thus green leaves. Iron is therefore essential for photosynthesis and thus all growth.
A lack of iron in a plant results in:
  • Chlorotic (yellow to white) leaves.
  • The veins may remain dark green.
  • Petioles of tomato plants become purple.
  • Stunted growth with a drop (up to 70%) in crop yield.

MANGANESE(Mn) 0.290%

PLANT REQUIREMENTS DEFICIENCY SYMPTOMS
  • Manganese is essential for photosynthesis and in particular, sugar production.
  • Manganese also controls the uptake of other ions and nutrients from the soil.
A lack of manganese in a plant results in:
  • Chlorosis (yellowing) of the leaves.
  • Leaves becoming spotted (marbled effect).
  • Reduced growth and flowering.
  • Cucumber, beans and many ornamentals are especially susceptible to Manganese deficiency.

MOLYBDENUM(Mo) 0.032%

PLANT REQUIREMENTS DEFICIENCY SYMPTOMS
  • Molybdenum is needed for sexual reproduction and the development of embryos.
  • Molybdenum is also necessary for the production of proteins (thus increasing the protein yield of a crop) and vitamins, in particular, vitamin C.
  • Molybdenum is required for chlorophyll production and thus the greening of leaves.
  • Molybdenum is essential for nitrogen fixation by legumes and for protection against aluminium toxicity in all plants.
  • A seed soak will ensure even germination in the field (e.g. maize)
A lack of molybdenum in a plant results in:
  • Yellow/orange spots on the leaves between the veins.
  • A reduced number of flowers which are small and sometimes do not open.
  • Deformed reproductive organs, thus fruit and crops suffer poor yields.
  • "Whiptail leaf symptom" in cabbages, etc.
  • "Yellow spot" disease in citrus.
  • Cabbages, cauliflower, broccoli and all legumes are most susceptible to deficiency.
  • Reduction in yield of crops (up to 80%).

ZINC(Zn) 0.244%

PLANT REQUIREMENTS DEFICIENCY SYMPTOMS
  • Zinc is essential for pollen grains and thus fertilization and fruiting.
  • Zinc increases sugar production and is essential for the production of hormones.
  • Zinc deficiencies are very common (especially in citrus) and are often caused by lime and phosphate applications.
  • Poor growth with short stems and internodes and small, curled leaves.
  • Flowers are small in size.

MAGNESIUM(Mg) 0.031%

PLANT REQUIREMENTS DEFICIENCY SYMPTOMS
  • Magnesium is the most important component of chlorophyll ( green pigment) and thus vital for photosynthesis.
  • Magnesium helps to control enzyme operations.
  • Magnesium is important for oil production (e.g. avocado)
A lack of magnesium in a plant results in:
  • Chlorosis (yellowing) between the leaf veins.
  • In some species, the lower leaves develop a purple colour preceding death.
  • Flower size and number is reduced.
  • Magnesium deficiency is common after heavy nitrogen, potassium or lime application.
  • Very common in tomatoes and cucumbers.

Key to the Classical symptoms of nutrient deficiencies

  Deficiency Symptoms Deficient Nutrient
( I ) The dominant symptom is chlorotic foliage
(1) Entire leaf blades are chlorotic
(1,1) Only the lower leaves are chlorotic followed by necrosis and leaf drop
Nitrogen
(1,2) Leaves on all parts of the plant are affected and sometimes have a beige case
Sulphur
(2) Yellowing of leaves takes form of interveinal chlorosis
(2,1) Only recently mature or older leaves exhibit interveinal chlorosis
Magnesium
(2,2) Only younger leaves exhibit interveinal chlorosis. This is the only symptom
Iron
(A) In addition to interveinal chlorosis on young leaves, grey or tan necrotic spots develop in chlorotic areas
Manganese
(B) While younger leaves have interveinal chlorosis, the tips and lobes of leaves remain green followed by veinal chlorosis and rapid, extensive necrosis of leaf blade
Copper
(C) Young leaves are very small and sometimes missing leaf blades altogether and internodes are short giving a rosette appearance
Zinc
( II ) Leaf chlorosis is not the dominant symptom.
(1) Symptoms appear at the base of the plant
(1,1) At first, all leaves are dark green and then growth is stunted. Purple pigment often develops in leaves, particularly older leaves
Phosphorus
(1,2) Margins of older leaves become chlorotic and then burn, or small chlorotic spots progressing to necrosis appear scattered on leaf blades
Potassium
(2) Symptoms appear at top of plant
(2,1) Terminal buds die giving rise to a witch's broom. Young leaves become very thick and leathery
and chlorotic. Rust-coloured cracks and corking occur on young stems, petioles and flower stalks. Young leaves crinkled
Boron
(2,2) Margins of young leaves fail to form, sometimes yielding strap-leaves. Growing point ceases to develop, leaving a blunt end. Light green colour or uneven chlorosis of young tissue. Root growth is poor in that roots are short and thickened
Calcium

 


Trace element deficiency table

PLANT ZINC IRON MANGANESE MOLYBDENUM COPPER BORON
Alfalfa Low Medium Medium Medium High High
Apples High - High Low Medium High
Asparagus Low Medium Low Low Low Low
Barley Medium High Medium Low High Low
Beans High High High Low Low Low
Broccoli - High Medium Medium Medium Medium
Cabbage - Medium Medium High Medium High
Carnation Low Low Low High High Medium
Carrots Low - Medium Low High Medium
Cauliflower - High Medium High Medium High
Celery - - Medium Low Medium High
Chrysanthemum Low Medium Medium Low High Medium
Clover Medium - Medium High Medium Medium
Cotton High - - Low Medium Medium
Cucumber Low - High Medium Medium High
Grapefruit High High High Medium High Medium
Grapes Low High High Low - Medium
Lettuce Low - High High High Medium
Maize High Medium Low Low Medium Low
Oats Low Medium High Medium High Low
Orange High High High Medium High Medium
Peaches High - High Low Medium Medium
Pears Medium - - Low Medium Medium
Peas Low - High Medium Low Low
Potato Medium - Medium Low Low Low
Radish - - High Medium Medium Medium
Raspberries - High High Low - Medium
Rice Medium High Medium Low Low Low
Roses - High High Low - High
Sorghum High High High Low Medium Low
Soybean Medium High High Medium Low Low
Spinach - High High High High Medium
Strawberries - High High - Medium Medium
Sweetcorn High Medium Medium Low Medium Low
Tomato Medium High Medium Medium Medium High
Turnip - - Medium Medium Medium High
Wheat Low Low High Low High Low



The influence of the least nutrient

No matter how much the other plant nutrients are poured into the soil (illustrated by the heights of the columns), only as much as the level of the least ( Boron in this case) will be available to the plant.
So in order for the plant to take up all the N, P and K and other elements, the level of B, Ca, Cu, etc. must be brought up to the same level, otherwise only the quantity up to the level of the least element will be available.
All the plant nutrients placed in any growing medium can only be the equivalent of the level of the lowest element available for the production of a crop.

 


 




The influence of pH

Put simply, pH is a measure of the acidity or alkalinity on a scale of 1 to 14. A reading of 7 is deemed to be neutral, alkaline if above and acidic if below. The following diagram gives an idea of pH values for a range of commonly found liquids.

 

pH values for commonly used liquids.
  pH  
battery acid <1
vinegar <3 acidic
orange juice >4
boric acid 5
milk <7
pure water 7 neutral
blood >7
sea water 8
borax >9
ammonia >11 alkaline
bleach >12
lye <14

The pH value of soil, as a general rule, ranges from about 4,0 to about 8,5. An azalea, for instance, enjoys a pH of between 4,5 and 5,5 . At pH 4,5 or less, there is damage to root membranes and less favourable conditions for growth of beneficial bacteria.

Optimum pH values for some other plants:

  • Camelias 5,5 to 6,5
  • Gardenias ±6,0
  • Magnolias 6,5 to 7,0
  • Hydrangeas 4,5 to 6,0 ( the lower value gives a blue colour, the higher value gives a pink colour.)

phgraph


The effect of pH on the availability of nutrient elements

The pH value of a particular soil plays an important role in the availability of micro-nutrients, as the following table illustrates:
Availability of Nutrient Elements
graph2
Nutrient deficiencies will become apparent if the pH is higher or lower than the recommended pH range for individual plants. For example, if the pH is consistently 7.5, one can expect interveinal chlorosis to occur, an indication of an iron deficiency.

The chart shows a pH range of 4.00 to 10.00. The width of the black section for each nutrient represents the maximum availability of that nutrient. The widest place denotes the most availability. The narrowest part denotes the least availability. The dotted line at pH 6.25 indicates the maximum number of elements at their highest availability.


Other phenomena that affect the absorbition of nutrients IONS

ANTAGONISM

Antagonism is the phenomenon whereby the effect of one nutrient ion reduces the effect of another.
This mostly happens at the uptake stage when the plant absorbs certain nutrients of a similar chemical property, or by the same mechanism, and one nutrient displaces another.
OK, Ca, and Mg are to be rated alike from the biochemical aspect regarding their volume and behaviour in the soil as in the plant, so these ions impede one another in the uptake and translocation of nutrients in the plant.
The same applies to Fe, Mn and Zn which also compete with each other for the nutrient uptake into the plant.

FIXATION

Fixation is the conversion of mobile nutrients into an immobile form, which is not available to the plant.
The pH of the soil can affect this and many farmers have seen how phosphorus (P) is fixed in acid soils through the formation of insoluble aluminium or ion phosphates.
An excess supply of the same nutrients can also cause other elements to be fixed.