14-06-2014, 02:32 PM
Aerobic rice –An efficient water
management strategy for
rice production
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Introduction
Asia’s food security depends largely on the irrigated rice fields, which produces three
quarters of all rice harvested. But rice is a profligate user of water, consuming half
of all developed fresh water resources. The increasing scarcity of water threatens the
sustainability of the irrigated rice production system and hence the food security and
livelihood of rice producers and consumers. In Asia, 17 million ha of irrigated rice
areas may experience “physical water scarcity’’ and 22 million ha may have “economic
water scarcity’’ by 2025 (Tuong and Bouman, 2001). Therefore, a more efficient use
of water is needed in rice production. Several strategies are being pursued to reduce
rice water requirements, such as saturated soil culture (Borrel et al., 1997), alternate
wetting and drying (Li 2001, Tabbal et al., 2002), ground cover systems (Lin Shan et al.,
2002), system of rice intensification (SRI, Stoop et al., 2002), aerobic rice (Bouman
et al., 2002), and raised beds (Singh et al., 2002). It is reported that SRI and AWD
systems have high water productivity with some amount of saving (approx. 20 per
cent) without any compromise on productivity. However, water requirement of these
production systems is also very high as land preparation consists of soaking, followed
by wet ploughing or puddling of saturated soil. Further, when standing water is kept in
the field (5–10 cm) during crop growth, large amount of water (about 10–15 per cent)
is lost through seepage and percolation. Every drop of water received at the farmer’s
field by way of rainfall, surface irrigation or pumped from aquifers, is valuable and
needs to be used effectively. Aerobic rice provides for effective use of rain that falls on
the farmer’s field, as there is no standing water and the farmer can skip irrigation if soil
moisture status is sufficient for crop. This is not possible if water is already standing
in the filed.
Irrigated rice has a very low water-use efficiency as it consumes 3000–5000 liters
of water to produce 1 kg of rice. The traditional rice production system not only
leads to wastage but also causes environmental degradation and reduces fertilizer use
efficiency. Along with high water requirement, the traditional system of transplanted
rice production in puddled soil on long run leads to destruction of soil aggregates and
∗ The following are the members of the Aerobic Rice team : G.S. Hemamalini, R. Latha, R. Venuprasad,
Hima Bindu, Manjunath Janmatti, Erpin Sudheer, Adnan Kanbar, Vinod M. S, Naveen Sharma,
M. Toorchi, H.R. Prabuddha, R. Dhananjay, R. Vasundhara, R.P. Veeresh Gowda, Kalmeshwer Gouda
Patil, K. Manjunatha, T.M. Girish, K.K. Manohara, Patil Malagouda, B.T. Sridhar.
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132 Food and water security in developing countries
reduction in macro pore volumes, and to a large increase in micro pore space which
subsequently reduce the yields of post rice crops, ex. wheat.
Added to this, irrigated rice fields will cut off the oxygen supply from the atmosphere
resulting in the anaerobic fermentation of soil organic matter. Methane, a major end
product of anaerobic fermentation is released from the submerged soil to the atmosphere
through roots and stems of rice plants. Its concentration in the atmosphere has
more than doubled during the last 200 years. Its current atmospheric concentration
of 1.7 ppm by volume, up from 0.7 ppm in the pre industrial times, is much lower
than the 360 ppm of carbon dioxide, up from 275 ppm. The global annual emission
of methane is estimated to be 500 Tg (1 Tg=1 million tonnes; Wahlen et al., 1989)
with an apparent net flux of 40 Tg/yr (Cicerone and Oremland, 1988). The current
burden of methane in the atmosphere is approximately 4700 Tg. But one molecule
of methane traps approximately 30 times as much heat as does a molecule of carbon
dioxide. The heating effect of the atmospheric methane increase is approximately half
that of the carbon dioxide increase (Dickinson and Cicerone, 1986, Ramanathan et al.,
1985). Continued increase in atmospheric methane concentrations at the current rate of
approximately 1 per cent per year is likely to contribute more to future climatic change
than any other gas except carbon dioxide (Cicerone and Oremland, 1988). Aerobic
rice cultivation will curb methane production and saves water without affecting the
productivity. It is the time to save water from the irrigated system of rice cultivation by
adopting the aerobic rice cultivation. Varieties or hybrids with enhanced productivity
for aerobic cultivation must be bred to address the water scarcity and pollution.
Water requirement for paddy
Water requirement of low land rice varies from 1,650 to 3000mm(Table 12.1). Aerobic
rice production system eliminates continuous seepage and percolation losses, greatly
reduces evaporation as no standing water is present at any time during the cropping
season, and effectively uses the rainfall and thus helps in enhancing water productivity,
concomitant loss of soil sediments, silt and fertility from the soil. A comparison of
water requirement of lowland flooded rice and aerobic rice system clearly shows that
aerobic rice system can save about 45 per cent of water
Sugarcane and paddy are among the first options to be explored if we have to
effect substantial savings in water used in agriculture, as these are considered as the
most water intensive among all crops. Breeding for drought tolerance has and is being
attempted by several scientists and groups across the globe by spending considerable
amount of money, time, and effort on this activity. Several traits have been found
to contribute to enhanced drought tolerance in crop plants and each scientist seems
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134 Food and water security in developing countries
to have confidence in a particular trait or a set of traits. Effects on enhanced drought
tolerance have also been demonstrated. It is at the point of establishing the link between
these individual or group of traits and grain yield that many scientists have failed.
There are just a few instances where the utility of a trait has been shown to have a
demonstrated impact on enhanced yield.
Water deficit for a crop could occur at a particular stage or at different stages during
crop growth. While breeding for drought tolerance, it is very tricky to estimate the exact
intensity, timing or severity of stress that a crop could encounter. Thus the ability to
withstand stress at any stage of crop growth would be an invaluable asset to a plant
that has to contend with the unpredictability of drought.
The concept of deficit irrigation (DI) was proposed by English et al. (1990). DI
advocates applying less than optimum levels of water to the crop so that there is no
wastage due to several other factors. The concept of DI has been researched in several
crops across the world. DI is known to enhance the quality of the produce in fruit
crops. It is expected to save considerable amount of water drawn from reservoirs and
effect savings in electricity, investment of public funds in water storage devices, etc.
By applying the concept of DI to rice we perceived that the whole cropping season
can be subjected to certain levels of sub-optimum water regimes which would effect
in savings in water. It is proposed that farmer could not irrigate the crop, even though
there could be water in his reservoir or in the canals.
Aerobic rice is both a concept of growing rice and appropriate genotypes suited
for such a growth. While it is similar to upland rice which is topographically high
altitude rice, given a toposequence, aerobic rice is one which grows any rice field that
is never flooded right through the cropping season. These could be slightly sloping
lands, may be sandy and have higher degrees of percolation unlike lowlands. The
difference between aerobic and conventional irrigated rice is given in the Table 12.2.
The overall stages of Aerobic rice development is presented below in different heads.
Screening for drought tolerance
Seventeen farmers’ selections and seventeen breeders’ selections based F3 PPB and
plant type respectively were evaluated under two moisture regimes of 0.8 IW/CPE
(Well-watered) and 0.6 IW/CPE (Low moisture stress) in the same farmers filed. These
ratios are decided by calculating the water holding capacity of the soil. The measured
quantity of water (40 mm) was given through Parshall Flume and the cumulative pan
evaporation was considered based on the USWB CLASS-A-open pan evaporimeter.
Depending upon the daily evaporation in USWB CLASS-A open Panevaporimeter,
irrigations scheduled at 0.8 IW/CPE ratio received irrigations once in five to six days
whereas irrigations scheduled at 0.6 IW/CPE ratio received delayed irrigations at 10 to
12 days in the vegetative phase. With in the advancement of the reproductive development
the stress level was brought to 1 IW/CPE ratio respectively. Irrigation was similar
to any aerable crop like maize, wheat or sorghum. Plots could be bunded or unbunded,
to reduce the conveyance losses.
12.3.4 Advanced yield trial
Six stabilized aerobic rice lines are in All India trials across six locations, since 2005.
Kharif. Lines for the trials are nominated by breeders of the drought network and
scientists from IRRI, Philippines. In each location the nominated lines are evaluated
in three replications each in three hydrological situations, namely aerobic, drained
puddles and irrigated conditions. All the six lines performed significantly superior
over national and international checks at all locations (from two year data).
Crop establishment was excellent, with no symptoms of deficiencies or toxicities of
Iron, Zinc or any other micronutrient considering the fact that the plants were not
being grown under irrigated condition with standing water as is usually done. Because
planting densities are lower, crops are relatively healthier. Irrigation is by furrow, as
with maize or sorghum, and can be limited to once in every 5 or 6 days. Yield averages
4 to 5 tonnes per hectare with good grain quality parameters