Seaweeds: A Promising Source for Sustainable Development - Environmental Sustainability: Role of Green Technologies - page 74

and they control nutrient defi ciency in plants.
Carbohydrates and other organic matter present in
seaweeds alter the nature of the soil and improve
its moisture retaining capacity. Hence, large quan-
tities of seaweeds including sea grasses such as
Cymodocea , Diplanthera , Enhalus , and Halophila
are used as manure in all parts of the country
either directly or in the form of compost.

them. To counter this loss, surfactants can be
used to increase the effi ciency of penetration of
the leaf surface and the duration of the sprays
on the leaf be increased depending upon the
situation. At certain cases, application of high
nutrient concentrations in foliar spray causes
severe leaf damage due to phytotoxicity. To avoid
this situation, repeated applications of dilute
formulations, therefore, is necessary to supply
the plant's nutrient requirements without damag-
ing the foliage. Since there are different types
of seaweed extracts available in the market, it is
important for the farmer/grower to know the type
of species used in preparation of SLF and how
to properly use it for specifi c crops. The timing,
dosage, and frequency of application are very
important when dealing with seaweed extract.
Application rate and frequency may vary based
on location, time of season, soil type, and crop.
Proper application is important because higher
concentration of seaweed extract may damage the
plant resulting to loss in yields (Spinelli et al. 2010 ).

7.1.2 Seaweed Liquid Fertilizer (SLF)
Seaweed extracts exhibit growth-stimulating
property on crop plants. Hence, its formulation
can be used as a bio-stimulant in agriculture. The
bio-stimulant present in seaweed extract increases
the vegetative growth (10 %), the leaf chlorophyll
content (11 %), the stomata density (6.5 %), the
photosynthetic rate, and the fruit production
(27 %) of the plant (Spinelli et al. 2010 ). In spite
of the proven capability of SLF on growth and
yield promotion of various crops, the extraction
procedure from seaweeds, its concentration, and
mode of application have not been standardized.
The liquid seaweed extracts from seaweeds are
usually prepared by hydrolyzing the material
under pressure; however, the preparation may
vary from species to species depending upon the
amount of dried material available. The method
of extraction signifi cantly differs from person to
person and also the mode of application to crops.
Seaweed extracts are used in several ways, such
as drench in soil during transplantation, during
fi eld preparation (Lingakumar et al. 2002 ), seed
treatment (Immanuel and Subramanian 1999 ), or
as foliar application.
Foliar applications of liquid fertilizer supply
the plant with nutrients more rapidly than methods
involving uptake by root due to seed/root treat-
ment. Growers, therefore, can apply SLF as foliar
treatment to quickly correct nutrient defi ciencies.
Foliar treatment has some drawbacks, mainly due
to the structure of the leaf and the temporary
nature of the nutrient supply. Leaves, particularly
those with thick cuticle, have low absorption
rates. Therefore, multiple applications of liquid
fertilizers are necessary to supply a suffi cient
quantity of the nutrients to the plants. Further,
once applied, foliar nutrients may be washed off
by rain or irrigation water before the plant absorbs

7.2 Present Status of Seaweed

Fertilizer Usage

Though seaweed and its derived product are
increasingly used in the production of agricultural
crops, the mechanism of action of seaweed extract
on enhancement of productivity is still unknown.
The recent challenge in sustainable food produc-
tion is due to the increasing occurrence of biotic
and abiotic stress due to climate change, which
may lead to the reduction of agricultural produc-
tivity globally. Under this situation, SLF may
work as a good inducer for sustainability in
agricultural production coupled with maintenance
of soil health. In India, seaweeds are not used
extensively except for production of phycocol-
loids. However, being a rich source of vitamins,
minerals, and growth promoters, they can be of
immense help to the coastal farmers for their use
as a source of organic fertilizer. Hence, there is a
need for popularizing the use of seaweed as health
food and liquid organic fertilizer through mass
scale fi eld trials and organization of public aware-
ness programs (Mohanty et al. 2013 ).