WHAT IS FOLIAR FERTILIZER? 

Foliar fertilization is any fertilizing substance applied in a liquid form.

Modern foliar fertilizers are concentrated solutions using very high grade technical elements, in which the nitrogen, phosphorus and potassium are combined to the desired ratio in a controlled environment.

The fertilizing elements in this method are true solutions, soluble, and thus very plant available.

This is in contrast to soil applied (solid) fertilizer, which is applied as a powder or granules to the soil in dry form. This then, has to be dissolved, by moisture (rain) to be plant available via the roots. In other words, it has to dissolve into the soil solution to be available.

To these foliar solutions, trace elements in the form of chelates are added, along with other additives to give a balanced fertilizer, supplying not only NPK, but all the trace elements as well as growth hormones, vitamins etc.

Many different NPK formulation combinations can be made, depending on the application required. The same elements that make up foliar fertilizer are required for plant growth and development, and are formulated to meet quite specific plant requirements. (see Table 1.)

Plants are composed of the various elements in the proportions indicated below on which modern  foliar fertilizers are based.

16 elements are considered  essential  for plant growth,

 

Table 1. Internal Concentrations of Essential Elements in Higher Plants - Concentration in Dry Tissue 
 

These essential elements are divided into two groups: the macronutrients; those required in relatively large quantities including carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium and sulphur and the micronutrients, those required in small quantities; including iron, chlorine, manganese, boron, zinc, copper and molybdenum.

You will see that by far the biggest proportion is hydrogen, carbon and oxygen which makes up 96% of the plant and are freely available from the air and water.

All of the other elements make up the remaining 4%, of which the major elements nitrogen, phosphorus and potassium make up 2.7%, leaving 1.3% minor or trace elements.

Carbon, hydrogen and oxygen which form the actual plant structure are readily obtainable from air and water, specifically carbon dioxide or  water. Along with chlorine, which is found in most water sources, these elements are generally not considered in the formulation of foliar solutions.

 

The following illustrates the amount of each nutrient in Kgs/ Hectare, in pasture of 2000 kg DM/ Hectare:

Depending on the application required, foliar fertilizers can be formulated to meet very specific plant requirements.

For example a high nitrogen formulation is used when the demand in plants is for more nitrogen in relation to phosphorus and potassium, but the formulation is changed for growth periods that require higher phosphorus and / or potassium, in relation to the demand for nitrogen.

This often happens when a plant is under stress, which coincides with periods of great growth, such as when a plant is changing from a vegetative to a reproductive stage.

At the same time, the exact plant requirement for trace elements can be addressed, as a result of leaf analysis.

Certain soil conditions, such as  pH, excess moisture, or cool temperatures, may render a nutrient or nutrients unavailable to the plant root.

Nutrient demand curves indicate that there are stages in a plant's life-cycle when demand for some nutrients may be greater than its physiological capacity to supply itself, even when these soil nutrients are available in abundant supply. This often occurs during the development of fruit or grain.

Data from trials on crops, show that increases in yield and/or grade results from applications of foliar nutrients during these periods of peak demand.

Foliar fertilizers can be designed to meet a plant’s specific needs for one or more micro and macro nutrients--especially trace minerals and enables you to correct deficiencies, strengthen weak or damaged crops, speed growth and  grow  better plants, which is of course, the bottom line.

Foliar applications can be targeted to a particular stage of crop development to achieve specific objectives and is an excellent way to "fine tune" a high fertility program.

Plant hormones

Plant hormones, are specialized chemical substances produced by plants. Foliar fertilization is a particularly useful technique:  and are the main internal factors controlling growth and development.

Hormones are produced in one part of a plant and transported to others, where they are effective in very small amounts.

Depending on the target tissue, a given hormone may have different effects.

Auxin, one of the most important plant hormones, is produced by growing stem tips and transported to other areas where it may either promote growth or inhibit it.

It also retards the abscission (dropping off) of flowers, fruits, and leaves.

Commercially, synthetic auxins are used to initiate adventitous roots from plant cuttings  eg. in nurseries.

Weed control by another synthetic auxin, 2, 4-dichlorophenoxyacetic acid (2,4-D), is widespread as a selective herbicide against broadleaf weeds.

Tissue studies of plants have found more than 60 different mineral elements, although it has generally been accepted that 16 -17 elements are essential for plant growth.

Many farmers are well aware of the consequences of low levels of copper or cobalt in pasture, and in some areas selenium, as well as magnesium (grass staggers), even iodine and zinc and in many cases calcium (as in milk fever).

There are many cases where several of the nutrients are missing or are at such low levels that supplementation of the animal is necessary, otherwise the animal would die or be severely undernourished.

Subclinical trace mineral deficiencies occur more frequently than recognized by many livestock producers and can be a bigger problem than acute mineral deficiencies, because the specific symptoms that are characteristic of a trace mineral deficiency are not seen.

Instead, the animal grows or reproduces at a reduced rate, uses feed less efficiently and operates with a depressed immune system. The end result is inefficient production and lower profitability.

When micro-nutrients become a limiting factor, water, fertilizer and other high-energy production inputs are wasted.

In most cases the elements needed by the plant are also needed by the animal which feeds on the plant.

Some elements needed by the animal are not required by the plant, but plants  takes them up and makes them available to the animal, and therefore plays a significant role in animal health. Selenium, iodine and cobalt are examples.

Seven trace minerals, have been shown to be needed in supplementing animal diets. They are iron, copper, zinc, manganese, cobalt, iodine and selenium.

Soils:

Soils are derived from weathered parent material. 
If the original material was low in a particular element or non existant, so too is the resulting soil.

Soils can become depleted of minerals and trace elements which too are absorbed into the likes of meat, milk, bone, wool, vegetables and fruits, as well as the major elements, and many soils are naturally deficient in one or more of these elements.

Soils can be radically different, with localized deficiencies of trace elements  like copper, cobalt or selenium.

Because our supply of minerals comes through the food chain, from the plants and animals we eat, and because  these same minerals are essential ingredients of these same plants and animals, any that are missing can have serious implications for plant, animal and ultimately our own health.

One has to conclude then, that this is where fertilization should start.

Even though the major element solid type NPK fertilizer is required in the largest amounts, if used exclusively, sooner or later a deficiency of a minor element can occur in soils low in that particular element, and it too should be replaced.

Foliar nutrients can quickly correct a nutrient imbalance, and are by far the most effective way to apply micro nutrients or trace elements and supplement the major elements , because foliar nutrients are readily available and more easily utilized by the plant than soil nutrients.