Foliar fertilisation is any fertilising substance applied in a liquid form.
Foliars in their most basic form, often used by home gardeners use animal manures, or seaweed collected from the beach, suspended in water, until all the 'goodness' has been extracted.
This is time consuming where a lot of effort is required for a small amount of nutrient.
By contrast, modern foliar fertilisers 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 fertilising elements in this method are true solutions, soluble, and thus very plant available.
This is in contrast to soil applied (solid) fertiliser, 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 seaweed and /or humic acid, or other additives depending on preference, to give a balanced fertiliser, 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 fertiliser 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 fertilisers 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:
|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 fertilisers 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