2. Present Status of Irrigation Bangladesh does not have a long history of irrigated agriculture. With favourable climate and fertile alluvial soils, the people were able to feed themselves until the late 1950's without resorting to irrigation. Now that population growth has over taken the productivity of traditional agriculture, food for the extra mouths can only be obtained with additional inputs like irrigation, although the organizational aspects for an effective irrigation system are yet to be developed. At present, the irrigation is confined to the dry winter months for growing Boro rice, wheat, vegetables, etc. The scarcity of water for irrigation during the growing season results in limited acreage for the crops. The river capacity is significantly less during the Boro growing season, limiting potential surface water use for irrigation. The crucial months of the season are February and March, during which the total river flows amounts to 6.35 million ha• m, in comparison to 79 ha• m in August (Rashid, 1978). Apart from the low flow during the winter, the development of surface water is con strained and complicated by requirements for navigation, domestic and industrial use, and saline water intrusion in the coastal estuary.
Groundwater should be used for irrigation only in areas where 1) suitable aquifers with good quality water are available, 2) annual replenishment of groundwater equals withdrawal, 3) withdrawal has minimal effect on other water use, and 4) water depth is such that the cost of pumping is reasonable.
Considering all of these factors, it is estimated that an area of more than 2 million ha can be brought under irrigation using groundwater (Khan, 1985). The estimated area to be brought under irrigation during the SFYP using both surface and groundwater amounts to 2.9 million ha. It is also estimated that a 75% increase in the irrigable area will result from increased installation of deep tube wells (DTW), shallow tube wells (STW) and low lift pumps (LLP). The government is supporting these small-scale irrigation projects because they are quick-yielding, are more cost-effective than large-scale irrigation projects and have a short gestation period.
However, the performance of the tube well irrigation system in the past has not been satisfactory. At present, the average command areas of DTWs, STWs and LLPs, with discharge capacities of 56, 14 and 56 Vs, are 24, 5 and 16 ha respectively (MPO, 1985). It has been amply demonstrated that, with good organization and management, a DTW can irrigate, on average, more than 40.5 ha of rice (Bhuiyan, 1984). Under-utilization of tube well capacity or poor performance of the tube well itself has been a chronic problem. The issue has been discussed by a number of investigators. Apart from non-optimal planning of the systems, other factors leading to unsatisfactory performance are social and organizational constraints, poor organization of users, poor water management practices and non-accountability in institutional systems.
3. Present Status of Aus and Aman Cultivation Although Aus and Aman rice combined cover 8.9 million ha (89% of the total cropped area) and yield 10.3 million t (84% of the total output), these two crops are still grown by "providence" methods•\that is, by impounding rainfall inside the cropped area or by flooding when the river water level is high. Because of the high uncertainty involved regarding the availability of moisture during the growing season, the farmers are reluctant to add additional inputs in these crops. This is reflected in the total HYV rice cultivated area in the Aus, Aman and Boro seasons. While 59% of the total Boro cultivated area is under HYV rice cultivation, that under Aus and Aman is only 6% and 14% respectively. Hence the crops that fill 84% of the country's food requirement and on which the overall food situation of the country is very much dependent are left to nature for their rearing. The possibility of attaining food self-sufficiency depends totally on ensuring a good harvest of Aus and Aman crops, and this can be achieved in two ways: 1) by increasing the present yield per hectare with ensured irrigation throughout the growing period; and 2) by planting the total Aus-Aman cultivable area in HYV in phases, so as to increase the overall yield. The cost involved in ensuring irrigation to Aus and Aman crops would be much less than the cost of irrigating Boro, first because Aus and Aman are predominantly rainfed crops and so require much less water from irrigation, and second, because water is readily available from both surfaces and groundwater sources during the Aus and Aman seasons.