Blog at Jains - HOW MUCH WATER DOES MY CROP NEED? Part 4. Rice
Rice Rice is the most irrigated crop in India and whole of South and South East Asia.
More than 75% of the rice production comes from 79 million ha of irrigated
lowland. Over 17 million ha of Asia’s irrigated rice may experience "physical
water scarcity" and 22 million ha may experience "economic water scarcity" by
2025 (Tuong and Bouman 2003). Really hardship scenario indeed.
RICE as grown in India is a water-guzzler, because farmers use on an average
15,000 litres to produce one kg of paddy, though water technologists at IARI
say no more than 600 litres is needed if proper water management techniques
are followed. Given that 45 per cent of the country's total irrigation water is
used solely for rice cultivation, the need to improve farming methods,
especially irrigation method, is imperative.
Besides being wasteful, excessive use of water results in lower yields and
adverse environmental effects such as soil salinity and waterlogging. Paddy
yields in irrigated regions of Tamil Nadu, Punjab and Haryana range from 5 to 6
ton/ha, where as in the high-rainfall areas of eastern UP, Bihar, West Bengal
and Orissa, the yields are about 1.8 ton/ha. The main reasons for the poor
yields are improper irrigation management and long duration waterlogging.
A large amount of water is lost in seepage and deep percolation. Loss from
deep percolation is estimated at 50 per cent in heavy textured clay soils and
about 85 per cent in light textured loamy sands and laterite soils. Studies in
eastern India show effective soil management can reduce percolation losses by
20 per cent and also reduce the risk of crop failure during droughts. Still the
water consumption in these cases are more than the water requirement of the
Farmers widely believe that water should be stored to stand above the surface
on paddy fields to prevent weed growth. But studies in West Bengal and Orissa
show that standing water of more than 10 cm height leads to heavy leaching of
soil nutrients and percolation losses resulting in very low grain yields.
Where does all the water go after one irrigates a crop field? Water moves out
of the field in 7 different ways after an irrigation that floods the field: 1.Direct
evaporation from the water surface, 2. Drift of water away from the field due
to wind, 3. Transpiration through the body of the crop plant (Mainly thru
leaves), 4. Evaporation from the wet ground exposed to the atmosphere, 5.
Run off of water from the field, 6. Infiltration to lower soil strata and 7. Deep
percolation to far deep soil profile and 8. Surface flow from rice fields to lower
Among these, the essential components of crop water use are only two:
transpiration and soil surface evaporation. Hence water use by crop is referred
to as ETP, Evapotranspiration. As the crop grows the surface evaporation gets
reduced and when the soil surface is fully covered by the canopy (leaf and
tillers of the crop) there is only one dominant component of crop water use:
In precision Irrigation the water given should only be equivalent to ETP. The
goal of perfect irrigation for rice is to reduce the components of wasteful
water losses, like surface flow and general soil evaporation and percolation. In
conventional irrigation major part of water loss are in fact the rest of the 8
When a farmer asks the question, HOW MUCH WATER DOES MY CROP NEED?
The answer is the ETP (evaporation plus transpiration). Accordingly, I have
estimated the water required for a good high productive rice crop. The
difference among the regions is due to difference in evaporation rate during
the growing season of the crop.
How Much water I need for Rice crop?
Table Water Requirement of Rice crop
Coastal Peninsular region North (West Godavari/AP)
Interior Peninsular region (Kurnool/ AP) October
Southern Coastal Peninsular (Tirunelveli) January
Central Semi -Arid region (Medak/Telengana) July
North temperate region (Kurukshetra/ Haryana)
North temperate region (Patiala/ Punjab) June
Precision wetting of the soil is maintained in irrigation for Rice through drip
method. In conventional method water is applied till the field is flooded to a
height of 8-10 cm. Therefore a major portion of the applied water moves away
from the field and the crop does not use it. This fraction of water is actually
wasted and not used by the crop resulting in very low water use efficiency and
water productivity. Over a period last 14 years I have proved that as for water
utilisation for growth and productivity rice crop is not different from any other
crop-like wheat, maize or pulses. This is contrary to the general perception of
For a 110 to 120 day growing period, rice requires only 3694 m3 to 6166 m3
water per hectare to produce 5-7 t/ha yield (harvested paddy grain) under drip
-fertigation assisted precision farming. Applying water as per the estimates
above is possible only through drip method of irrigation.
In conventional irrigation system the whole season consumes an average of
23750 m3 in all the above regions and the average productivity recorded
ranged from 2.0- 2.5 t/ha only in farmers field, though research station yields
under conventional irrigation reaches up to 4-5 t/ha.