Abstract
Studies were coducted in Thakurgaon area during Rabi season 2001-02 to Boro season 2004-05 in order to suggest some important criteria related to improved water management practices for rice based cropping system using shallow tubewell. About hundred percent farmers of the study area reported that they received enough water from the respective STWs for different crops. Most of the farmers of the study area used earthen canal as a distribution system. The actual discharges of nine selected STWs in three locations were varied from 16 to 28 lps for 4 to12 HP engines. The farmers in Thakurgaon area using oversized engine. Appropriate engine size should be used to reduce irrigation cost. There were significant variations in the water loss in open channel system. These varied from 6.66 l/s/100m to 7.87 l/s/100m, whereas the water losses from hose pipe varied from 0.14 l/s/100m to 0.35 l/s/100m. The economic performance of supplemental irrigation by using hose pipe for Rabi and T.Aman crop cultivation with irrigated condition is highly profitable. For improved compacted earthen water distribution system, saving of irrigation water and distribution time and increase of irrigated area respectively were 29-38%, 25-29% and 40-44% in comparison to that of uncompacted earthen channel. Similarly for hose pipe distribution system, the above parameters were respectively 94-96%, 56-61% and 80-86% in comparison to that of uncompacted earthen channel system. To obtain greater conveyance efficiency hose pipe and improved compacted earthen channel should be used to distribute water in the irrigated fields. The study shows that continuous standing water is not necessary for optimum yield of rice. Moreover, without sacrificing much yield, about 41 percent and 37 percent of valuable irrigation water can be saved over treatment T1 (continuous standing water) by practicing the treatment T2 (Irrigation depth of 7 cm after 3 days of dissapeariance of standing water) respectively. For optimum utilization of irrigation water, water saving technique like irrigating after 3 days of standing water as suggested in this study, should be followed properly. The highest yields of 3.47 t/ha and 3.20 t/ha for wheat were obtained from the plot of 40 cm wide bed during 2003-2004 and 2004-05 rabi seasons. About 25 percent water was saved by this practice over that of the border irrigation method (flat bed).The highest net return of Tk 24517 and Tk 20,844 and benefit – cost ratio (BCR) of 2.11 and 2.35 were obtained from 40 cm bed (B1) in 2003 – 04 and 2004 – 04 rabi seasons. So field plots of 40 cm bed width having 30 cm wide furrow is seemed suitable for obtaining good wheat yield. The yield obtained for boro rice were 6.6 0 t/ha, 6.73 t/ha for flat bed (farmers practice) and 6.20 t/ha, 6.36 t/ha for 40 cm wide raised bed during 2004 and 2005, boro seasons, respectively which is not significantly different with that of farmer's practice. In the study locations the aquifers have the potentiality to transmit sufficient water. The groundwater table is not gradually declining day by day during dry season, with the increasing demand for pumping. Moreover, the aquifer was found to be recharged fully after the monsoon. At present 46 % of the land area is under irrigation and an additional 8 percent of rice land and 22 percent of non rice land could further be irrigated with the available groundwater.