Author: Sashi Bhusan Kumar Yadav Bsc Ag. Scholar IAAS Pakhlihawa
Rice is grown on an area of 2.6 million hectares of land among which 1.8 million is irrigated of which 1.4 million ha lies in the terai or plains. The remaining 0.40 million ha is in river valleys upland valleys & terraces on hills & mountain. It is unique type of crop among the major food crop as it has capacity to grow in wide range of hydrological situation, soil, types & climate. It is mainly grown in wetland condition. In Nepal rice grown in almost parts of terai and major parts of hill and few parts of mountain region.
The continuous flooding of rice field does not increase yields so, water can be drained from rice field for 7-14 days at tillering stage. Saturating the field during the crop cycle uses 3000 litres of water to produce 1 kg of rice grain. Water is the single most component for sustainable rice production especially in traditional rice growing areas of Nepal and depletion of water resources is an increasingly worrying aspect of rice production in Nepal.
Challenges for irrigation in Nepal
Old infrastructure & poor performance of the existing irrigation system, weak participation of water uses association weak linkage between agriculture & irrigation, continuation of subsistence agriculture practices etc are key challenges for Nepalese irrigation sector development.
Effective use of water can be achieved by following process:
- Construct field channel to control the flow of water to and from our field.
- Prepare the land to minimize water loss & create a hard pan.
- Level the field for uniform distribution of water throughout the field.
- Construct the bund and repair any cracks or holes.
- Changing planting method from puddled to non-puddled or transplanting or dry direct seeding.
- Applying water saving technologies such as Alternate wetting and drying.
Water requirement of rice at different growth stages
Average water requirement in this period is 50-60 mm which is about 5% of total water required by rice throughout growing periods. Summer ploughing reduces water required for land preparation. There is less water requirement of dry seed bed preparation and direct seeded method.
The field are usually flooded & few days after flooding field is ploughed. After ploughing 200-250 mm of water is required during puddling. Large quantity of FYM should be applied in the field since its application increases water holding capacity of light textured soil & thus saves water.
Seedling transplantation should be done when there is shallow depth of water in the field. After transplantation water level should be around 3 cm with increases 5-10 cm with increasing plant height & remain there until field is drained 7-10 days before harvest. Direct seeded rice field should be flooded only once as the plants are large enough to withstand shallow flooding (3-4 leaf stage).
Continuous flooding helps to ensure sufficient water control weeds. Proper water management is necessary for the formation of chemical treated soil layer to ensure sufficient time for weeds to absorb. Shallow depth of water should be maintained at the time of application & this water should be kept for a certain length of time (5-7 days). Normally, it is recommended to keep water standing for at least one week after chemical application. Draining of water or overflowing after application should be avoided.
Critical stages of water requirement
Critical stage refers to a stage when scarcity or deficit of water causes comparatively greater reduction in yield which cannot be made by favourable water supply at earlier or later stages. Hence, water deficit during these stages should be avoided.
Following are the important critical crop stages for water stress in rice plant.
Allow the water to aerate the soil and stimulate root penetration, tillering production, firm root anchorage, correction of micronutrients imbalance and removal of toxic substances from the soil.
-Panicle initiation: Maintain 2-5 cm flood water to avoid drought stress
About 70% loss in grain yield is due to stress at reproductive stage after flowering there is great decrease in water requirement. The moisture stress reduce the number of grain panicle and thus the yield is decreased. To facilitate uniform maturity and harvesting of the crop, irrigation should be stopped after grain hardening stage.
A study showed that termination of irrigation 14 to 17 days before the harvest resulted to a uniform maturity of the crop and economized 16 cm of irrigation of water, while suspension of irrigation 3 weeks before the harvest saved 22 cm of water. In later case there was marginal decrease of only 200 kg grain per hectare.
Role of irrigated water in insect and disease management
Irrigated water has positive role in disease and insect management in rice crop. Continuous flooding and poor drainage encourages the hopper population. Regulation of irrigation water is to be modified in line with pest control. Intermittent flooding and draining the field frequently during mid-season, lowers the brown plant hopper build upto a significant extent.
Similarly different diseases of rice could be controlled with wise use of water. In order to control the bacterial leaf blight of rice, good drainage should be provided to field. To control stem rot disease of rice, field should be drained and soil should be allowed to crack before re-irrigating the field. The rodents activity in the field should be checked by flooding the rice field.
Drainage needs of rice
Excessive irrigation leads to water logging. Water logging also occurs due to excessive rainfall floods, rise of ground water level etc. Continuous stagnation of water leads to accumulation of toxic biochemicals substance and silts deposition. In different places the problem of excess water is associated with the salinity and alkalinity problem.
Certain stages of growth like early flowering have been reported to be more susceptible to water logged condition than other stages of crop growth. thus drainage is imperative and should be synchronize with the period just following tillering and flowering. Even 4 days complete submergence during the late vegetative phase. The drainage period could last from 3-7 days depending upon the type of soil.
It has been estimated that a 10% decrease in the water use for irrigated rice could lead to water saving of approximately 1,50,000 million m3 almost one-fourth of all the fresh water used worldwide for non-agricultural activities. Several studies have indicated that irrigated rice can be easily cultivated using 8,000-10,000 m3/ha which is approximately 50% of current use without affecting yield.
The main difficulty with water saving is that the water is not priced properly, especially in schemes where they charge the user by irrigated area and not by volume of water used. With such schemes, there is no economic incentives to save water. There are several ways to reduce irrigated rice water consumption including: limiting rice cultivation to only the rainy season, using and developing more water efficient varieties, promoting upland rice, developing drought tolerant varieties of rice, modifying the planting date and making more efficient use of rainfall water, changing rice planting practices etc.
wet seeding of rice uses about 20-25% less water than the traditionally transplanted rice. Other technique include replacing transplanting by direct seeding, intermittent flooding, maintaining the soil in sub-saturated condition, alternative wetting and drying , supplementary irrigation either for crop establishment or critical growth stages, water recycling and conjunctive use to enable farmers to reuse seepage, percolation losses from canal and field using alternative to flooding technique as overhead sprinkler, furrows etc. with newly developed aerobic varieties , adopting simple conservation that is, maintaining only supersaturated soil condition during cultivation of the crop, significantly reducing land preparation (puddling) water and keeping water within the field by reducing outflow discharges.
Precaution for irrigation
Water is consumed during the production process of rice crop. Yet large range of climate generate a variety of hydrological regimes and an uneven distribution of water resources and water use conditions. The rule of thumb to adopt water scarcity is to consume less water, followed by modify water demand, maximize efficiency in water use and improve the economic, technical and environmental performance of water consumption, together with diversification of production and cropping pattern, changes in management systems and structures and financial sustainability.
During irrigating the rice crop, withholding of water should be done for few days still seedlings establishment. Field to field irrigation system should be avoided. The water should be drained from the field for about days prior to the application of fertilizers. In order to avoid leakages of water through main bunds, small bund may be formed parallel to the main bund of the field at a distance of 30-45 cm within the field. The depth of water should be maintained 5 cm or less in the field to minimize percolation loss.
In waterlogged condition open drain of about 60 cm depth and 45 cm width across the field should be constructed. In case of the areas where irrigation facilities are not available, all the rainwater in paddy field should be stored by making 25-30 cm raised bunds. Water should be drained off completely for 5 to 7 days following tillering and flowering stages. This helps to remove the toxic substances like sulphides and regulates oxygen supply to roots.
Hence, water for food production is increasingly becoming scarce with increased demand from other sectors such as domestic, industrial and environmental uses. Thus farmers should use water in wise way. Water saving technique has to be introduced to meet the competitive demand.
हाम्रो मोबाइल एप डाउनलोड गर्नुभयो ? अब सबै खाले कृषि मापक, अर्गानिक कृषि, नवीनतम कृषि, व्यावसायिक पशुपालन, खेती प्रविधि, बाली रोग तथा किरा व्यवस्थापन सहित सम्पूर्ण कृषि प्रविधिसम्बन्धि जानकारीको लागि हाम्रो एप डाउनलोड गर्न तलको फोटोमा Click गर्नुहोला |