M.Nurul Huda Al Mamun
Soil Resource Development Institute, Bangladesh.
Abstract:
Farmer in the southern parts specially in the coastal areas of Bangladesh usually practice mono cropping where soil salinity limits upland crop production. This area is known to be one of the most agriculturally and socio-economically backward regions of the country. Drainage conditions of the land vary from poor to very poor, results in water stagnation in kharif season, and causes delay of sowing rabi crops. Intensification of agriculture largely depends on the extent of irrigation facilities during post monsoon season. A large area can be brought under multiple cropping system if such facility is ensured. Shortage of quality irrigation water is one of the major constraints for growing a second crop in the dry season. About 470mm excess rainfall is received during monsoon season, can be stored in the Farm pond/ tank and utilized for irrigation of upland crops during the rabi season. Storage structures need to be excavated to an average depth of 2.25m in one-fifth of the mini/micro watershed area, ensure better drainage facilities and multiple cropping in the area on a sustained basis, will encourage crop diversification in the cropping system. It is estimated that about 3.0m depth of water will remain in the storage structure at the end of Kharif season. Out of this, about 0.5m will be lost due to evaporation and deep percolation /seepage over a period of several months and about 1.5m will be utilized to irrigate the crop in rabi/summer season, remaining 1.0m water may be used for growing fish.
Key words: Farm pond technology, Harvest of rainwater, Crop diversification, Coastal saline area.
Introduction:
The farmers in the southern parts of Bangladesh usually practice mono cropping, especially in the coastal areas where soil salinity limits upland crop production. Wetland rice culture is the dominant practice followed by the farmers in the area. Cultivation of upland crop in the dry season is difficult due to rise of salinity. But salinity does not occur in harmful levels in the wet season, although ion uptake may be considerably reduced by a slight rise of soil salinity. The development of the agricultural sector is not satisfactory in the southern part of the country, particularly in the coastal saline area. This area is known to be one of the most agriculturally and socio- economically backward regions of the country. The yield of almost all the traditional crops in this area is poor (M. Ahsan,2001). 0.34 million hectares are affected by very slight to slight salinity. Most of the areas are almost flat, low lying and the soils are heavy textured. The drainage conditions of the lnad vary from poor to very poor which results in water stagnation in kharif season (SRDI staff, 1973). These limitations restrict the cultivation of high yielding rice varieties in kharif season and delay of sowing rabi crops.
A large area can be brought under multiple cropping system if extend of irrigation facilities during post monsoon is ensured. Shortage of quality irrigation water is one of the major constraints for growing a second crop in the dry season. Ground water aquifer without salinity suitable for irrigation are found at depths from 300 to 400 meters and the exploitation of this is extremely expensive and technically difficult (Sen, 1996). In contrast, ground water at shallow depth ranging from 1.0 to 5.5 meters is saline and unsuitable for irrigation. A possible alternative described by Khandalwal et.al.(1990) is to store rainwater during monsoon in farm ponds/tanks or canals/creeks. The very slightly to slightly saline area is the most suitable for rainwater harvesting in farm ponds for irrigation in dry season (M. Ahsan, 2001).
About 90% of the rainfall occur during May to October , excess rainwater in the monsoon season causes severe water logging all over the area due to lack of adequate drainage facilities. On the other hand, there is an acute shortage of good quality water for irrigation in winter and summer. If, excess rainwater stored in places like farm ponds, main drainage channels and closed small tidal canals/creeks, can meet the irrigation requirements of a considerable area( Sen et.al. 1998).
The monthly water balance of Shoronkhola, Bagerhat have been roughly estimated using 75% of average rainfall and potential evapotranspiration (PET). A simple water balance analysis involving rainfall and PET for a location in coastal saline area indicates excess rainwater.It shows that excess rainwater occurs mainly during the month of May to September. In May, a rather high rainfall occurs but the crop water demand is quite high. The October the amount of rainfall is nearly equal to that of May, but the water demand is much less. Although the amount of excess rainfall is almost nil but it is considered as wet month. The amount of rainfall is significant from November to April. It was roughly estimated that there was an excess of about 470mm rainfall during monsoon season without considering deep percolation and seepage loss (SRDI staff, 1988) and this water may be utilized for irrigation of a second crop during the rabi crops. The present result is comparable to Mainul Ahsan(2001), who expressed excess of about 532 mm rainfall during the monsoon season at Batiaghata thana in Khulna district.
Materials and methods:
The technology essentially involves land development including land shaping, land grading and bunding for smooth removal of excess water towards the storage structures (M.Ahsan,2001). Leveling of the land to improve draining out of excess water and uniform leaching of salts for providing better water and nutrient control (Sen,et.al.1996). Construction of the field bunds around the plots to regulate outflow of water from the field. Storing of excess rainwater in the storage structures during monsoon season for subsequent utilization in rabi and summer crop cultivation. Cultivation of rabi and summer crops on the surrounding of the ponds and introduction of high yielding varieties during kharif season. Pisciculture in the excavated pond throughout the year.
Construction methodology:
Storage structure will be excavated to an average depth of 2.25m in one-fifth of the area of the mini/micro watershed. Bunds of about 1m height and 1.5m width on the periphery of the storage structure may be constructed with the excavated earth so as to attain effective depth of water storage up to 3.0m (M.Ahsan,2001).The excavated soil may be spread on the remaining four-fifth of the area to raise it up to 0.50m. It will reduce the drainage problem during kharif and will help timely sowing of rabi crops, which is normally delayed due to the excess soil moisture after kharif rice harvest. Field bunds may be made in order to regulate the smooth and efficient removal of excess water towards the structure, as to maintain the optimum depth of water submergence in the field (ICAR). The surface soil of the excavated area may be used as top dressing on the remaining plots. It is advisable to avoid spreading of any poor quality subsoils (acid sulphate) on the surface of the land. Further, depending on soil characteristics liming material may be used at places to ameliorate soil/water in crop field/fish ponds (M.Ahsan, 2001). In some of the SAARC countries about 80% excavation cost of farm ponds is provided by commercial private banks and NGOs with minimum interest rate and farmers are providing only 15% of these costs (BCC, 1995-96). In Bangladesh, bank and NGO
may provide credit to the small farmers. Assistance from soil experts of Salinity Management and Research Centre, SRDI about soil condition of the specific area may be necessary during excavation of the farm pond (M.Ahsan,2001).
Results and discussion:
Utilization of the technology:
The bunds around the pond and around each plot may be utilized for plantation of horticultural crops, such as coconut, banana, papaya etc. The reserve of rainwater in the excavated storage structure may be utilized for growing crops in rabi or summer crops, fresh water aquaculture and supplemental irrigation in kharif during dry spell (CSSRI,1987).It is estimated that about 3.0m depth of water will remain in the storage structure at the end of kharif season. Out of this, about 0.5m will be lost due to evaporation and deep percolation/seepage over a period of seven months and about 1.5m will be utilized to irrigate the crop in rabi/summer season, remaining 1.0m water may be used for growing fish (Sen,1996). It is estimated that about one-third of the land may be utilized for growing a third crop.
Conclusion:
The drainage needs are considerably reduced by diversion of some of the excess rainwater from the adjoining cultivated area to the pond, a good quality water source is created to meet the irrigation need of rabi crops, raising the level of the adjoining cultivated area by using the soil of the pond diminishes the water logging problem which facilitates cultivation of the high yielding varieties of rice with improved management practices, multiple cropping in the area on a sustained basis will become possible and crop diversification will be enhanced and additional income can be generated by the farmers with the introduction of pisciculture in the dugout farm pond .
References:
Ahsan, M. Prospect of rainwater harvest in farm ponds for irrigation in the coastal saline areas of Bangladesh. Proceedings of the annual workshop on soil resources 14-15 February, 2001.oil Resources in Bangladesh: Assessment and utilization. pp. 33-37.
Bandyopadhyay, A.K.1988. Coastal saline soils of India and their management. CSSRI, Regional Research Station, Canning Town, ICAR Bull, 13: 122-123.Bharat Chamber of Commerce (BCC). 1995-96. Pashchimbanger
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