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Journal of Wastes and Biomass Management (JWBM) 3(2) (2021) 62-68
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10.26480/jwbm.02.2021.62.68
Cite the Articl e: Parbati Th apa, Kabita Po udel (2 021). Azolla: Potential Biofertilizer for Inc reasing Ri ce Produc tivity, A nd Gover nment Pol icy for Implemen tation.
Journ al of Wa stes and Biom ass Mana gement , 3(2): 62-68
.
ISSN: 2710-6012 (Online)
CODEN: JWBMAO
RESEARCH ARTICLE
Journal of Wastes and Biomass Management
(JWBM)
DOI: http://doi.org/10.26480/jwbm.02.2021.62.68
AZOLLA: POTENTIAL BIOFERTILIZER FOR INCREASING RICE PRODUCTIVITY,
AND GOVERNMENT POLICY FOR IMPLEMENTATION
Parbati Thapa*, Kabita Poudel
Institute of Agriculture and Animal Science, Lamjung Campus, Sundarbazar 07, Sundarbazar Municipality, 33600, Nepal.
*Corresponding author email: parbatimgr03@gmail.com
This is an open access article distributed under the Creative Commons Attribution License CC BY 4.0, which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly cited.
ARTICLE DETAILS
ABSTRACT
Article History:
Received 10 June 2021
Accepted 15 July 2021
Available online 05 August 2021
Rice is the staple food for the significant population of Asia. Due to projected population growth in this region,
the demand for this food is also predicted to be increased exponentially soon. Nitrogen (N) plays a dominant
role in increasing rice yield as it is the most critical yield-limiting nutrient of rice. Chemical N fertilizers which
are a major source in supplying N nutrients to rice, have adverse effects on overall soil and environmental
health in the long term. The application of free-floating aquatic fern Azolla as a biofertilizer can be an
alternative to improve rice yield without degrading the environment. It provides a natural source of many
nutrients, especially N, improves the availability of other nutrients, plays a critical role in weed suppression,
enhances soil organic matter, and improves efficiency of the inorganic fertilizers while maintaining the
suitable soil pH condition for rice growth, which overall contribute to rice yield increment. Therefore, Azolla
application has tremendous potential to improve soil health and boost yield sustainability.
KEYWORDS
Azolla, Biofertilizers, Rice, Sustainability, Yield.
1. INTRODUCTION
Asia, the most populated region globally, has been facing pressure to
increase the yield of its primary staple food, rice. Moreover, the United
Nations has projected population growth to be highest in most regions of
Southeast Asia by the end of 2050 (United Nations, 2019). A group
researchers mentioned that yield per land increment or expansion of
cultivated land of rice could increase rice production (Molotoks et al.,
2018). However, due to the lack of favorable land excluding forest area, it
is almost impossible to expand cultivated land (Saito et al., 2019). Thus, a
significant focus now lies in increasing yield per land, contributing highly
to nutrient availability. Macronutrients Nitrogen (N) is critical yield-
limiting nutrients of rice (Saito et al., 2019). Chemical N fertilizer plays a
dominant role in supplying the nutrient requirement of rice is in Asia
(Safriyani et al., 2020).
About 80% of supply is met by urea as a source of N fertilizer. However, in
flooded conditions, any forms of chemical N fertilizer are prone to nutrient
loss (Ghosh and Bhat, 1998). In addition, Continuous use of chemical
fertilizer results in adverse environmental and health consequences in the
long run (Yang et al., 2021a). Similarly, presented the decline in rice yield
with time as a long-term effect of urea resulted from low Nitrogen use
efficiency (NUE) (Ladha et al., 2000). Inefficient use of N fertilizers on
irrigated rice and negative balances of potassium (K) were reported as the
crucial reasons for rice yield growth decline in intensive irrigated rice
farming (Dobermann et al., 1998; Dobermann, 2000).
Organic amendments have a positive role in vigorous crop growth and
yield enhancement (Amanullah et al., 2016). Therefore, global interest in
these substances as alternatives and supplements to chemical N fertilizers
has been raised. Soil organic matter affects the soil's biological, chemical,
and physical properties and overall health. It facilitates soil fertility by
providing other mineral nutrients through mineralization, improving
overall soil productivity (Zhao et al., 2016). Low organic matter in soil is
one of the major constraints for decreased rice yield in Asian soils (Islam
et al., 2010). The use of organic fertilizers can be an excellent alternative
to inorganic fertilization in crop production for sustainable agriculture
(Amanullah et al., 2015).
The application of Azolla as a biofertilizer provides natural source
nutrients and has tremendous potential to improve soil health and boost
yield sustainability (Akhtar et al., 2020). Azolla, a free-floating widely
distributed aquatic fern, offers significant potential as an N source in rice
production. The importance of Azolla as organic manure in rice was first
demonstrated in North Vietnam in the year 1957 and subsequently
introduced in the USA, Indonesia, Japan, Philippines, China, and India
(Wagner, 1997). As it can grow compatibly with rice in waterlogged
conditions, its potential for a nutrient supplement for rice has been
stressed (Subedi and Shrestha, 2015). Azolla can fix atmospheric nitrogen
due to its symbiotic relationship with blue-green algae Cyanobacteria.
Bilobed leaves of Azolla lie overlapped, where dorsal leaves cavity houses
Cyanobacteria, which fixes atmospheric nitrogen, and relatively thin
ventral leaves provide buoyancy that remains partially submerged in
water. The symbiont liberates a substantial amount of biologically fixed
nitrogen as the host absorbs ammonia through branched hairs present in
the cavity. Unbranched hairs transport fixed carbon from the host to the
Cyanobiont (Peters et al., 1989). An average of 35-50 % ammonia fixed by
the cyanobacterium is released to the field, and for this reason, Azolla is
used as a biofertilizer in the rice fields (Pereira, 2017). Nitrogen fixation
and a high growth rate can enable Azolla to accumulate more than 10 kg N
ha−1 day −1.
Journal of Wastes and Biomass Management (JWBM) 3(2) (2021) 62-68
Cite the Articl e: Parbati Th apa, Kabita Po udel (2 021). Azolla: Potential Biofertilizer for Inc reasing Ri ce Produc tivity, A nd Gover nment Pol icy for Implemen tation.
Journ al of Wa stes and Biom ass Mana gement , 3(2): 62-68
.
Thus, it is extensively used as a suitable biofertilizer in rice fields,
improving N within few weeks and contributing up to 40–60 kg N ha−1 per
rice crop (Kannaiyan, 1993). Application of inoculated Azolla 300 kg ha−1
into the rice after transplanting showed increased rice yield equivalent to
urea application of 100 kg N ha−1. Besides N replenishment in the rice field,
it improves soil organic content, enhances the availability of other
macronutrients, curbs NH3 volatilization, and suppresses weeds that play
a significant role in rice productivity (Bhuvaneshwari and Singh, 2015). In
contrast to chemical fertilizer, it is eco-friendly and acts as soil
remediation (Palengara, 2021).
This aquatic fern is used as a basis of green manure and decomposed
organic material, widely known as compost (Razavipou et al., 2018). Since
Azolla has various contributions in increasing rice yield without degrading
the environment while meeting the desired result, it is imperative to shed
light on the contribution of Azolla biofertilizer. Thus, an intensive review
on Azolla that improves rice yield was carried out with the following
objectives: i) To know the effects of Azolla in various factors which
contribute to yield improvement of rice ii) To know the role of Azolla in
yield of rice improvement.
Figure 1: Rice production in world (Source: Using data of FAOSTAT
2019)
Figure 2: Projected population in 2050 (Source: Using World Population
Prospects data − UN 2019)
Figure 3: Milled Rice Domestic Consumption by Asian Country in 1000
MT (Source: Using data of United States Department of Agriculture –
2021)
2. METHODOLOGY
We collected information from more than 70 papers on the roles of Azolla
in increasing rice yield. The collected information was arranged
systematically under Headings, namely: Factors contributing to rice yield
improvement, Contribution of Azolla in rice yield, limitations of use of
Azolla in rice field, government policies to implement biofertilizers. Under
the headings ‘Factors contributing to rice yield improvement’
subheadings: Soil organic matter content, availability of other mineral
nutrients, Contribution of Azolla in weed suppression, nitrogen
contribution, soil pH, increasing the efficiency of the inorganic fertilizers
were listed. The research papers were collected from journal articles,
proceedings, reports, and online internet sources.
Table 1: Distribution of Azolla spp. in Asia
S.N
Azolla
species
Distribution
1.
Azolla
caroliniana
Canton, Hong Kong
2.
Azolla
filiculoides
China, Japan
3.
Azolla
pinnata
Bangladesh, Burma, China, India, Indonesia,
Japan, Korea, Malaysia, Nepal, New Caledonia,
New Guinea, Pakistan, Philippines, Sri Lanka,
Taiwan, Thailand, Vietnam
Source: (Thomas A Lumpkin & Plucknett, 1980)
3. DISCUSSION
3.1 Factors contributing to the rice yield improvement
3.1.1 Soil organic matter content
Azolla compost impact plant growth and yield positively and improve the
organic matter in the soil (Gupta and Potalia, 1990). It maintains its
reserve for a long time by releasing its content materials slowly, which
provides advantages over raw, unrotted organic matter and chemical
fertilizers (Kandel et al., 2020). The high organic C content of Azolla
contributes to the increase in organic C. According to 90% of Azolla was
degraded in 4 weeks (Watanabe et al., 1989). The Azolla that had been
absorbed into the soil would shortly be mineralized. It would generate
humic substances as a result of the mineralization process which would
also yield soil organic C (Bhardwaj and Gaur, 1970). Some researchers
found that incorporation of Azolla increased the organic matter and the
rate of Azolla (Bhuvaneshwari and Kumar, 2013). It was reported that
inoculation of Azolla built up a considerable soil organic carbon content
(Setiawati et al., 2018; Setiawati et al., 2020). A group researcher finding
suggested that Azolla and cow manure equal combination increased the
soil organic C content ranging from 1.3− 1.7 % (Setiawati et al., 2018).
Similarly, it was reported that Azolla treated soil oxidizable organic C
increased 25.51% (Halder and Kheroar, 2013). Other researchers
recorded a significant increase in the population of heterotrophic bacteria
in addition to increasing cellulolytic and urea hydrolyzing activities
(Kannaiyan and Subramani, 1992). Similarly, a study reported higher soil
microbial populations of bacteria, fungi, actinomycetes, and higher
enzyme activities in Azolla incorporated soil, increasing nutrient recycling
in the soil (Krishnakumar et al., 2005).
Table 2: Composition of the Nutrients in different species of Azolla
Species
Crude
protein
(%)
Crude fat
(%)
Crude
fiber (%)
Crude
ash (%)
Azolla
pinnata
20.4
3.33
15.5
17.2
Azolla
Microphyll
20.2
3.5
15.8
16.3
Azolla
filiculoides
19.7
4.2
10.3
18.5
Azolla rubra
19.0
4.1
14.2
15.5.
Azolla
caroliniana
18.8
3.9
14.0
16.7
Azolla
maxicana
18.6
3.8
15.1
17.2
Source: (Datta, 2011)
5% 1%
3%
90%
1% Africa
Northern
America
South America
Asia
Europe
Oceania
0
1
2
3
4
5
6
Asia Africa Europe South
America North
America Oceania
population in billions
156000
108000
36100
35600
21200
14500
12900
10650
8200
4850
0 50000 100000 150000 200000
China
India
Bangladesh
Indonesia
Viet Nam
Philippines
Thailand
Myanmar
Japan
Nepal
1000 Metric Tons
Journal of Wastes and Biomass Management (JWBM) 3(2) (2021) 62-68
Cite the Articl e: Parbati Th apa, Kabita Po udel (2 021). Azolla: Potential Biofertilizer for Inc reasing Ri ce Produc tivity, A nd Gover nment Pol icy for Implemen tation.
Journ al of Wa stes and Biom ass Mana gement , 3(2): 62-68
.
3.1.2 Availability of other mineral nutrients
Macronutrients Potassium (K), Phosphorous (P) are other yield-limiting
nutrients of rice yield (Saito et al., 2019). Azolla has a remarkable ability
to accumulate K in its tissues in a low K environment; it decomposes
rapidly and releases nutrients N, P and K into the field after field water is
drained (Bhuvaneshwari and Singh, 2015). It solubilizes Zinc (Zn), Iron
(Fe), and Magnesium (Mg), making them available to the rice crop, and
releases plant growth regulators and vitamins that promote the rice crop
to grow faster (Bhusal and Thakur, 2021). Its continuous application
increased the soil nutrient availability (Subedi and Shrestha, 2015). In
general, the use of Azolla improves soil nutrient availability through
biological activity, which also helps to build up the micro flora for
mineralization. Mineralization is the process of decomposing organic
compounds and releasing nutrients into the soil.
As a result, research suggests that Azolla need more P to develop properly
(Rivai et al., 2013). However, when Azolla decayed, it released soil-
available P into the soil (Watanabe et al., 1989). A study show result
showed no significant difference at the beginning of available soil P in
Azolla added paddy soils (Rivai et al., 2013). However, there was an 89%
increase in Azolla added available soil P at rice panicle initiation. Similarly,
found that P and Ca contents were also higher in Azolla, averaging 124.83
ppm and 345.3 mg/100g (Halder and Kheroar, 2013). A group researchers
two subsequent year research similarly showed that Azolla treated soil
showed a 29.12 % increase of K, and Azolla and cow dung treated soil
showed a 42.94 % increase of P over the initial value (Dey et al., 2018).
These findings show the positive results of integrated soil nutrient
management practices, which are lacking in many Asian countries.
Table 3: Nutrient composition of Azolla
S.N
Constituents
Dry matter (%)
1
Ash
10
2
Calcium
0.4-1.0
3
Chlorophyll
0.34-0.55
4
Crude fat
3.3-3.6
5
Crude protein
14.0-30.0
6
Iron
0.06-0.26
7
Magnesium
0.5-0.65
8
Nitrogen
4.0-5.0
9
Phosphorus
0.5-0.9
10
Potassium
2.0-4.5
11
Soluble sugars
3.4-3.5
12
Starch
6.5
Source:(Salma & T, 2020)
3.1.3 Azolla in Weed suppression
Weed alone can reduce the Rice yield ranging from 15 − 20% and up to
50% in severe cases (Sureshkumar et al ., 2016). A thick Azolla mat in a
rice field has the side benefit of suppressing weeds. Azolla covering water
surface reduces light penetration of soil surface, resulting in the
depreciation in the germination of weeds (70% of the weed). Thus, the
growth of Azolla reduces aquatic weeds in flooded rice fields like
Echinochloa crus-Galli, Cyperus sp., Paspalum sp. and so on and, therefore,
lead to improved crop growth and productivity (Biswas et al., 2005;
Monajjem and Hajipour, 2010). The degree of suppression increases with
an increase in the percent of Azolla cover and water depth
(Kalyanasundaram et al., 1999). Application of preassumed at 10 t ha-1 +
Azolla at 1 t ha-1 recorded the least weed count and highest weed control
index in rice crop, as the thallus growth formed a very thick mat on the
surface of the water, curtailing the interception of light by weed seeds and
seedlings (Gnanavel, 2015; Gnanavel and Kathiresan, 2002). A study
reported that weeds were suppressed by 69 – 100% at rice flowering and
86 – 95 % at harvest depending upon weed species due to the use of the
Azolla (Janiya and Moody, 1984).
3.1.4 Nitrogen contribution by Azolla
Nitrogen fertilization is one of the determining factors yields of grain in
rice plants (Chaturvedi, 2005). Azolla would be easily decomposed in
paddy fields and supply more N for rice growth (Raja et al., 2012). NUE
and recovery of N by rice are very low as 10% and never exceeds 50%
(Vlek and Byrnes, 1986). Loss from urea ranges from 11 −54% when it is
broadcasted in a rice field after transplantation (Schnier, 1995). Thus,
Azolla biofortification could be a potential approach to increase NUE in
rice fields (Yao et al., 2018a). Lumpkin and Plucknett have stated that the
association of Azolla and Anabaena Azolla can fix atmospheric N at a rate
exceeding that of the legume Rhizobium symbiotic relationship (Lumpkin
and Plucknett, 1985). The N-fixing capacity of Azolla has been estimated
to be 1.1 kg N ha-1 day-1, and this fixed N is sufficient to meet the entire N
requirement of the rice crop within a few weeks (Lumpkin and Plucknett,
1980). Azolla compost is considered beneficial for urea fertilizer (Inubushi
et al., 2014).
Azolla biofertilizer corporation increased the nitrogen recovery of the
crop by 49 –64% and decreased N loss by 26 – 48% (Yao et al., 2018a).
Azolla as green manure in waterlogged soil resulted in rapid
mineralization with a release of 60 - 80 % of the N within two weeks (Ito
and Watanabe, 1985). Azolla filiculoides incorporated in paddy soil in pots
have the N fixation ability of 128 kg N ha-1 in 50 days (Tuzimura et al.,
1957). Azolla pinnata incorporated in rice fields have an average N-fixing
ability of 0.3-0.6 kg ha-1 day-1 (Becking, 1976). Similarly, Singh has
reported the N-fixing ability of 2.3 ha day-1 in fallow paddy fields (Singh,
1980).
Farmers can manage around 30-60 kg N by incorporating Azolla at the rate
of 16000 kg ha-1 in rice crops instead of supplying through N fertilizers,
given the sustainability of soil health (Samal et al., 2020; Sanjay and Singh,
2020). A group researchers reported that symbiosis between Azolla and
cyanobacteria supplied 30-60 kg ha-1 N fixation (Kollah et al., 2016).
Inoculation of Azolla on flooded water decreases the NH3 volatilization by
12–42% (Yao et al., 2018a). Basal application of Azolla at the rate of 10-12
t ha-1 enriches soil N content by 50-60 kg ha-1 and reduces 30-35 kg of N
fertilizer requirement of rice crop.
Inoculation of green Azolla at the 500 kg ha-1 rate increases the soil N
content by 50 kg ha-1 and reduces the nitrogen fertilizer by 20-30 kg ha-1
(Roy et al., 2016). A group researchers explained that Azolla grown in
standing rice crop buffered soil N availability, absorbing available excess
N in the early rice growth stage, and releasing N at a later stage, increasing
NUE (Sisworo et al., 1990). Full Azolla cover on floodwater surface in rice
field prevent the rapid increase of pH associated with urea hydrolysis,
which indeed controls N volatilization; significant causes of low NUE (Kern
and Vlek, 2007; Reddy et al., 1990). Azolla improves the N fertilizer
efficiency (Macale and Vlek, 2004).
3.1.5 Soil pH
Soil pH influences myriads of soil biological, chemical, and physical
properties and processes that affect plant growth and biomass yield
(Neina, 2019). Slightly acidic to neutral pH of the soil in the field is a
favorable environment for plant development since nearly all nutrients
are available at this pH. Soil pH 6 is considered as a suitable conditions for
rice growth (Abdul Halim et al., 2018). It was reported that in flooding
condition, soil pH also increased simultaneously (Ding et al., 2019). Asghar
found that incorporation of Azolla reduced the soil pH condition (Asghar,
2018). Similarly, findings suggested that application of Azolla maintained
floodwater pH near to initial value compared to where Azolla was not
incorporated (Zinov’ev and Sole, 2004; Kern and Vlek, 2007).
3.1.6 Increasing the efficiency of inorganic fertilizers
The influence of incorporated and associated Azolla allows better use of N
and better conditions for assimilating other nutrients, thus improving
crop nutrition (Samarajeewa et al., 2005). The physiological efficiency of
Azolla N was significantly higher than that of urea N because the plants
absorbed more N from the area than from the Azolla (Watanabe et al.,
1989). The integrated use of organic and inorganic fertilizers is desirable
to sustain crop yields and maintenance of soil health (Meelu and Singh,
1991; Prasanna et al., 2008). Adding chemical fertilizer to organic manure
promotes the process of mineralization and thus increases nutrients in the
soil (Hashimi et al., 2019).
Incorporation of the Azolla fern enables better use of the nitrogen added
by the mineral fertilizer (Bhuvaneshwari and Singh, 2015; Manna & Singh,
1990). Azolla improves the N fertilizer efficiency (Macale and Vlek, 2004;
Prasanna et al., 2004). The use of 86 kg N ha-1 and 1000 Azolla kg ha-1
application increased 15.54% rice growth, 25.49% yield and improved the
N fertilizer agronomic efficiency (AE), agro-physiological efficiency (APE),
utilization efficiency (UE), and N efficiency ratio (NER) in Indonesia
(Safriyani et al., 2020). Ammonia volatilization (AV) from paddy fields is a
principal pathway of N loss (Zhang et al., 2014).
Journal of Wastes and Biomass Management (JWBM) 3(2) (2021) 62-68
Cite the Articl e: Parbati Th apa, Kabita Po udel (2 021). Azolla: Potential Biofertilizer for Inc reasing Ri ce Produc tivity, A nd Gover nment Pol icy for Implemen tation.
Journ al of Wa stes and Biom ass Mana gement , 3(2): 62-68
.
Integrated use of N fertilizer reduction and Azolla cover markedly reduced
AV and improved NUE compared with conventional N application rate
(Kern and Vlek, 2007; Yao et al., 2018b). Azolla application in rice field
significantly reduce NH3 emission and enhance apparent nitrogen
recovery efficiency (ANRE) without decreasing rice yield (Yang et al.,
2021). Azolla has the ability to release the absorbed minerals through the
process of mineralization during the decomposition. N and P, and other
nutrients applied through inorganic sources are rapidly released back into
the medium and made available for uptake by rice during grain
development which might have been lost through the volatilization in
absence of Azolla in the rice field, which increased the efficiency of the
inorganic fertilizers (Subedi and Shrestha, 2015).
3.2 Contribution of Azolla in Rice Yields
Azolla application desirably affects plant growth and biological yield and
increases OM, enhancing nutrient quality (Gupta and Potalia, 1990). Azolla
incorporation in paddy fields increased grain yield, straw yield, caryopsis,
and dry matter (Anjuli et al., 2004). Its incorporation increases the paddy
yield by 8-14% (Yao et al., 2018a). The rice yield increases up to 13% when
Azolla was used as a biofertilizer in rice crops (Watanabe, 1977). A study
reported that Azolla application increased the yield components of rice
(Kannaiyan and Rejeswari, 1983; Islam et al., 1984).
An increase in grain yields of rice from 14 - 40% has been reported, with
Azolla being used as a dual crop and by 15-20 % being monocropping
during the fallow season (Samal et al., 2020). A group researcher had
reported the highest rice grain yield when the application of Azolla
compost at 5.0% of soil weight, which was on average 13.8% higher than
that of the non-amended control (Razavipour et al., 2018). Singh found
that either the application of 30 - 40 kg N ha-1 through ammonium sulfate
or incorporation of 8-10 t of Azolla ha-1 fresh produced the exact rice yield,
47% increase in grain yield over control (Singh, 1977).
A combination of Azolla with a lower dose of N in planted paddy fields gave
a higher paddy yield. The judicious combination of Azolla and N provides
a better yield (Singh, 1979). The rice yield can be increased by 36.6 -38%
by using Azolla as a dual crop (Barthakur and Talukdar, 1983). Azolla dual
cropping increases rice yield by 14-40% and 6-29% higher grain yield by
growing A. pinata as a dual crop with rice (Moore, 1969; Le Van, 1963).
The application of Azolla along with neem cake coated urea recorded the
maximum grain yield of rice (Sukumar et al., 1988). These all findings
show that the application of Azolla as a biofertilizer has positive and
significant improvement in the rice yield.
3.3 Government Policies to implement biofertilizers
Many governments of Asian countries have implemented policies which
have directly and indirectly supported in the biofertilizers
implementation. The Indian government is advocating the use of
biofertilizers by extending and providing subsidies. Through the National
Project on Development and Use of Biofertilizers (NPDB), the Government
of India has been encouraging the use of biofertilizers in agriculture
(Ghosh, 2004). State level governments are also emphasizing the
biofertilizers usages. The government of Odisha, for example, has trained
farmers to utilize Azolla as a biofertilizers (Mishra and Dash, 2014). The
government of Bangladesh has put forward the policies to support the
production and implementation of bio-fertilizers. It has also supported the
ongoing research on Azolla for wet land Boro rice: Mature technology
(Goswami et al., 2014).
Similarly, Nepal’s Agricultural Biodiversity Policy 2006 has emphasized on
use of bio fertilizers (Amendment in 2014; Atreya, 2015). Countries;
China, Myanmar, Lao PDR, Thailand, Cambodia and Vietnam government
have shifted their focus in promoting sustainable agriculture, thus
emphasizing the policies in biofertilizers promotion (Atieno et al., 2020).
Thailand Institute of Scientific and Technological Research (TISTR) have
selected and commercialized blue-green algae for use as biofertilizers.
Over the last two decades, Thailand's biofertilizers research has been
actively supported by BIOTEC and the Thailand Research Fund (TRF)
(Damrongchai, 2000). China's policy "Action Plan for Zero Growth in the
Application of Chemical Pesticides and Fertilizers," implemented in 2015,
seek to cut chemical fertilizer use by at least 20% by 2020.
Biofertilizers promotion was recently added as a strategy in the 2013
National Development Plan for Bioindustry in China (Ruan et al., 2020).
The government of China has assigned extension programs to promote
biofertilizers to biofertilizers producer agencies (Atieno et al., 2020).
Strategic Program on Development and Utilization of Biotechnology in
Agricultural and Rural Development Until 2020 launched by Vietnam
government in 2000 advocate the application of organic inputs like
biofertilizers. This strategy is supported by policy frameworks with
regulations on production, distribution and implementation of such bio-
inputs (FAO, 2017). Philippines government has developed program to
promote the use of Azolla incorporation instead of heavy incorporation of
chemical fertilizer during rice production (Rosegrant et al.,1985).
3.4 Limitation of Use of Azolla in the rice field
Rice could not absorb all nutrients applied and increase the possibility of
nutrient loss (Fageria and Moreira, 2011). Fageria reported 50-70% N loss
through leaching, runoff, and denitrification (Fageria, 2014). Furthermore,
some researchers reported that N physiological efficiency decreased as N
fertilizer application increased (Eagle et al., 2001). Thus, the judicious
application of the Azolla should be considered while applying it in the
paddy field. The economics of using Azolla is fundamental because
technology is very labor-intensive, and it is suitable for adoption in
locations where farm labor is affordable. Sometimes, therefore, farmers
may have little to no economic benefit in choosing Azolla over chemical
fertilizer because the possible additional labor costs, irrigation of land
resources, application of phosphate fertilizer, and pesticides may make
Azolla's usage uneconomical (Kandel et al., 2020).
4. CONCLUSION
Nowadays, there is a major concern to meet the increasing demands of rice
without degrading the environment and soil health in the long term. So, in
recent times, most Asian countries governments have formulated policies
advocating on use of biofertilizers. Considering these aspects, use of Azolla
as a biofertilizers can be viable option for the rice producer as it increases
rice productivity and also improves soil health sustainably. Azolla has the
potential to suppress weed, increasing the availability of N, P, K, and other
mineral nutrients, which all contribute to increasing the rice yield. Azolla
biofertilizer has a tremendous ability to maintain suitable soil pH and fix
organic C and N, improving mineralization, improving microbial activity,
and status soil that can increase soil increase and ultimately enhance yield.
Considering the agronomic benefits and reducing the urea (N-fertilizer)
demand in the rice cropping system, Azolla could develop low-input
cropping systems for rice production. However, before using Azolla, the
economics of using Azolla should be considered because technology is
very labor-intensive, and it is suitable for adoption in locations where farm
labor is affordable. Sometimes farmers may have little to no economic
benefit in choosing Azolla over chemical fertilizer because the possible
additional labor costs, irrigation of land resources, phosphate fertilizer
application, and pesticides may make Azolla's usage uneconomical. Thus,
the economics of Azolla application in different farm conditions should be
studied for better recommendation on using the Azolla as a potential
biofertilizers for enhancing rice yield.
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