Both soil-applied and foliar-applied nutrients have a place in modern agricultural production systems. Historically, the vast majority of nutrients were applied to the soil, either as manure or some other type of organic material, or as synthetic fertilizer materials. This method has a number of distinct advantages.
Perhaps the most significant advantage of soil-applied nutrients is that this method supplies nutrients where the plants are designed to take in nutrients: at the roots. The roots of higher plants are adapted to take in nutrients and water from the soil and distribute them throughout the plant through the plant’s conductive tissues. Conversely, plant leaves are more adapted to keeping materials out of the plant due to their structure and composition since few nutrients are taken into plants via the leaves in a natural system. Because of this, plant roots can assimilate more nutrients into the plant than can the leaves of a plant.
However, foliar-applied nutrients also have a number of distinct advantages over soil-applied nutrients. One of the most significant of these is the rapid intake of nutrients. Because these materials are applied directly to the plant rather than the soil, their intake is not dependent on the nutrient moving through the soil and into the root. Therefore, they can have an immediate impact on the plant, which is critical when a given nutrient is lacking. Most modern foliar fertilizers have been formulated to ensure quick penetration into the plant, which can speed this process even further.
Another major benefit of foliar-applied nutrients is the fact that these nutrients bypass the soil altogether. Soil fertility is more complicated than the simple presence or absence of an element in the soil. For that element to be assimilated by the plant, it must be in a form that the plant can take up. Often a potential plant nutrient may be present in the soil, but certain soil conditions, such as pH, may cause that nutrient to be held in a form that cannot be taken up by the plant. If more nutrient is applied to the soil, it still may not benefit the plant because the underlying reason for the deficiency still exists. In these situations, foliar applications of nutrients may be the most effective way of supplying the needed nutrient to the plant.
Modern agronomic production is very sophisticated and requires a number of different techniques to meet the nutrient needs of the crop. Therefore, the best approach is to fully assess the situation to determine the best application method. Both application methods have distinct benefits and should be a part of the plant nutrient toolbox.