Role of foliar nutrition in plants
The predominant route for nutrients to enter plant tissue is via uptake through the roots. However, there are many situations where nutrition through leaves, fruit or shoots can be a very effective complementary delivery system. Leaves are not ideal for water and nutrient uptake, because their architecture is to protect crops against water loss as well as fungi and pest attack. The cuticle, (the outer cell layer on leaves sealed with wax) works as a barrier to the entrance of nutrients into the plant. However, nutrients in the ionic form can penetrate either through the cuticle via small cracks or through the stomata, the pores in leaves for gas exchange.

Foliar applications can be done  either with aqueous solutions or suspension of nutrients. Application rates are low, 0.5 to 10 kilograms of foliar fertilizer per hectare, dissolved in 50 – 2500 liters of water. The water rate depends on canopy size and density. Foliar fertilizers are often used to supplement micronutrients (Mn, Fe, Zn, Cu, B, Mo) and occasionally the secondary (Ca, Mg, S) and Primary nutrients (N, P, K)

Foliar application to treat absolute deficiency
All nutrients play an essential role for growth and development of crops. The shortage of a single nutrient becomes a bottleneck of production since vital metabolic pathways are impaired. As a consequence, shape and color of crops deviates from those fully nourished. Visual symptoms can tell an experienced grower which nutrient is lacking. Foliar application of the nutrient concerned will provide an immediate relief of the problem and a normal crop yield can be achieved.

Sometimes there are no visible symptoms, but foliar sprays are applied to treat latent deficiencies (hidden hunger). The need for such treatments is determined by a chemical analysis of the crop. For almost all crops critical nutrient values are available which indicate the adequate nutrient content in the tissue. If the analysis for a particular nutrient is below its critical value, foliar nutrition can be made to prevent the problem. Yield responses to foliar nutrition can be substantial.

Foliar nutrition to prevent deficiencies in fruits
Nutrient availability is not the only bottleneck for adequate nutrient supply to crops. Limited nutrient transport to different plant parts can also cause localized deficiencies. In particular the transport of boron and calcium in the plant relies on the transpiration flow, which means that tissue with low transpiration rates, eg. Fruit, can easily become deficient in calcium and boron.

Efficient foliar fertilizers
Efficiency of foliar applications depends on crop type, leaf coverage, weather conditions and product quality. It is estimated that foliar treated crops will absorb about 15 – 40% of nutrients applied. Efficiency of the foliar fertilizer is improved when the formulation contains additives like wetting agents to enhance the coverage of leaves or stickers that prevent nutrients being washed off by rainfall. Together with our alliance partners Haifa chemicals Ltd., Nouryon Functional Chemicals B.V(formerly known as Akzo-Nobel), Yara International , Minera Santa Rita, Kheme Chemicals and Tessenderlo Chemie; PR Agro offers growers an extensive portfolio of foliar fertilizers combined with the knowledge about optimum application rate and timing