DHR AG Service

Ever since Dr. H.B. Tukey et.al back in the 1950's, showed the true importance of foliar feeding of plant nutrients, it has been widely used in agriculture as a dramatic and fast way of getting nutrients into plants. Foliar feeding is not only useful for regular fertilizing to gain higher quality crops, but it is especially important for the correction of nutrient deficiencies and the addition of micronutrients.

Dr Tukey’s research used radio-active phosphorous and radio-potassium to spray crops. They then measured with a Geiger counter, the absorption, movement and utilization of these and many other nutrients within plants.

They compared the nutrient uptake at the roots from a soil application versus foliar spraying and found that a 95 percent efficiency of uptake compared to about a 10 percent efficiency from soil applications

They also found the speed of absorption and use by foliar applications was immediate, whereas from soil applications absorption and plant usage was very very slow.

Furthermore in soils that have a high pH or low pH, certain nutrients become unavailable for uptake into the plant in the soil. However with foliar spraying you can get the minerals into the plant until you make corrections to the soil.

Foliar spraying also stimulates nutrient uptake from the soil. The leaves after spraying will generate more carbohydrates that it will transport down to the root and release as exudates. This will stimulate the microbial life in the soil and the microbes will thrive around the root mass making more nutrients available to the plant.

Therefore it is a very good idea to use liquid fertilizers to supplement your nutrient programs to give your crops the optimum amount of nutrients it needs to get fast and efficient goodness into the plant so it can work harder to produce top quality food.

Under Which Conditions Should You Use Foliar Feeding?

Under most conditions, foliar feeding has an advantage over soil applications.

Limiting conditions - A foliar feeding is recommended when environmental conditions limit the uptake of nutrients by roots. Such conditions may include high or low soil pH, temperature stress, too low or too high soil moisture, root disease, presence of pests that affect nutrient uptake, nutrient imbalances in soil etc.

For example, micronutrient availability is greatly reduced in high soil pH. Under such conditions, foliar application of micronutrients might be the more efficient way to supply micronutrients to the plant.

Nutrient deficiency symptoms - One of the advantages of foliar feeding is the quick response of the plant to the nutrient application.

The efficiency of nutrient uptake is considered to be 8-9 folds higher when nutrients are applied to the leaves, when compared with nutrients applied to soil.

Therefore, when a deficiency symptom shows up, a quick, but temporary fix, would be applying the deficient nutrient through foliar application.

In specific growth stages – Plants require different amounts of nutrients in different growth stages. It is sometimes difficult to control the nutrient balance in soil. Foliar applications of essential nutrients during key stages can improve yield and quality.

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

ELEMENT

PPM

%

Hydrogen

60,000

6

Carbon

450,000

45

Oxygen

450,000

45

Nitrogen

15,000

1.5

Potassium

10,000

1.0

Calcium

5,000

0.5

Magnesium

2,000

0.2

Phosphorus

2,000

0.2

Sulphur

1,000

0.1

Chlorine

100

0.01

Boron

20

0.002

Iron

100

0.01

Manganese

50

0.005

Zinc

20

0.002

Copper

6

0.0006

Molybdenum

0.1

0.00001

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:

Table 2

Nitrogen 90

Phosphorus 7

Potassium 44

Sulphur 6

Calcium 5

Magnesium 4

Sodium 3

Zinc .03

Copper .01

Boron .05

Cobalt .0002

Selenium .000008

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.

EFFICIENCY OF UTILIZATION OF FERTILIZER SPRAYS:

Here are some striking examples of comparisons of foliar fertilizers versus soil applications.

Such ratios favoring foliar applications exist only under extreme conditions of soil fixation. Nevertheless, they single out the effectiveness of leaves as organs for absorption.

Related to the marked efficiency in absorption of nutritional sprays may be indirect effects of this method of applying fertilizer on other plant processes.

Comparative efficiency of foliar and soil applications of fertilizer.

Approximate ratios of amounts required for comparable Authority responses

Nutrient and salt

Type of Crop

Foliar

Soil

Authority

Zinc (ZnSO4)

Annual crops

1

12

Lingle & Holmberg (1956)

Phosphorus (H3PO4)

beans,tomatoes

1

20

Wittwer, et al. (1957)

Iron (FeSO4)

grain sorghum

1

25

Withee & Carlson (1959)

Magnesium (MgSO4)

grain sorghum

1

100

Krantz (1962)

celery

1

50-100

Johnson, et al.(1957, 1961)

Where isotopes showed that it was 8 -10 times more effective to foliar feed a plant as far as the amount of nutrients required and the speed with which those nutrients were utilized, the above authorities found the figure to be between 12 and 100 times more effective.

The readily- available nutrients are more easily utilized, as they are directly available to a plant and because they do not have to be dissolved by moisture before going into the soil solution and where they may be subjected to insolubalization by incident anions such as carbonate, bicarbonate, hydroxide, etc, known as fixation.

Also important in foliar fertilizers, is whether or not the products being used are chelated. Chelation, allows a nutrient to "maintain its own identity" within the spray tank, and not get tied up by other nutrients or pesticides being used with it.

These days we have materials available which are ideally suited to spray applications.

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.

Producers have been using foliar fertilizer since the early 1950's. Even though the subject of foliar fertilization was little understood, 'experts' told farmers that they shouldn't use them, because in comparison to solid type fertilizers, foliars contained less nutrient.

Nutrient demand curves indicate stages in a plant's life-cycle when the need for some nutrients may be greater than its physiological capacity to supply itself, even when these soil nutrients are abundantly available. Highly soluble potassium and nitrogen-based fertilizers can be easily washed out from the soil, and phosphate fertilizers can attach themselves to ions of potassium, magnesium, aluminum and iron into chemically insoluble form for plants.

Foliar nutrients on the other hand are mobilized directly into plant leaves, which is the goal of fertilization to begin with, increasing the rate of photosynthesis in the leaves, and by doing so stimulate nutrient absorption by plant roots.

Foliar fertilization is by far the most effective way to apply micro nutrients or trace elements, and supplement the major elements. The readily available nutrients are more easily utilized, because they do not have to be dissolved by moisture and go into the soil solution.

Foliar fertilizers used in conjunction with solid fertilizers, can be used to quickly correct a nutrient imbalance and stimulate increase in root uptake. In addition, foliar fertilization can correct deficiencies, strengthen weak or damaged crops, speed growth and grow better plants, which is of course, the bottom line.

Fertilization:

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.

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