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
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