Beside classical fertilisers (N, P, K), plants need other micro elements such as Mn, Mg, Na, Ca, Mg, Co etc. to promote development and to develop resistance against stress factors such as drought, disease and pest. Many agricultural scientists claim that plant roots do not benefit substantially from classical method of fertilizer application since it is applied on the surface of the soil. This is the reason in the last decade there has been a rapid growth in the use of foliar fertilisers containing macro-elements and micro-elements. But are they really effective?
Before we get carried away with all of the benefits of the foliar fertiliser, we need to get the basics right. Foliar fertiliser is not the substitute to soil fertiliser application. Plants are designed to absorb nutrients through their roots. Leaves have waxy cuticle preventing water, nutrients and other substance to enter into the plant. When liquid fertiliser is sprayed on foliage, some of the nutrients get absorbed through the leaves. Heavy spraying will lead to considerable runoff from the foliage and the liquid fertiliser will soak into the soil. In this case some nutrients get absorbed through leaves but the majority of the nutrients are picked up by the plants through its roots. In some cases foliar application in high concentration can lead to leaf burn as the water evaporates leaving behind fertiliser salt.
Foliar fertiliser is effective when used in conjunction with soil fertiliser application. Foliar fertiliser is used to meet specific plant nutrient needs such as micro elements. Since micro elements are required in relatively small quantities by the plant, foliar fertiliser turns out to be the best proposition. Researchers are often seen citing the argument that the foliar feeding is up to 20 times more effective which is true. There is no doubt that leaf is highly efficient method of application, but they can absorb only relatively small portion, hence their ‘20 times effectiveness’ gets greatly over sold.
Many scientists often say classical fertilisers deliver additional production per hectare but the cost is also relatively high. What they don’t tend to realize is that minerals applied to the leaf do not travel throughout the plant and so foliar fertiliser application will never be able to replace soil fertiliser application. In classical fertiliser application the nutrients are taken to every corner of the plant through root uptake. Nutrients applied through foliar application travel max to max adjoining tissues, but no further. So even though foliar fertiliser application turns out to be cheaper, it is not beneficial for the entire plant.
In foliar fertiliser application, fruits as adjoining tissues get benefit from foliar application as it helps combat fruit disorder. Yet this is localised application and does not benefit trunk and root. So this cannot be construed as an effective method to handle soil imbalance. Foliar fertiliser application is just a temporary solution to meet the fruit and leaf deficiencies, but it can never be used as a replacement of soil fertiliser application. Though foliar application provides almost immediate way to feed the pant, macro and micro-elements are better absorbed through roots.