Bangladesh is entering a stage of massive expansion of itsirrigation program in order to meet the present food deficit. Emphasis is given togrowing Boro rice during the dry winter period with total irrigation. But Aus and Aman rice, which cover 89% of the total cropped area and produce 84% of the totalrice output, are still grown as rainfed crops. The high uncertainty of adequaterainfall during the Aus and Aman seasons has seriously affected their yields. With the use of supplementary irrigation, yields of these crops can be increasedby up to 70% depending upon the rainfall pattern. The average maximumsupplementary irrigation requirement is about 25% of the total crop waterrequirement and the cost of input labour is cheaper during these seasons, resulting in a better benefit-cost ratio in comparison to irrigating the Boro crop. Because of differences in strategy in irrigation during Aus and Aman seasons, astrong and effective farmers' organization is needed. The control, delivery andmanagement of supplementary irrigation by such a farmers' organization, ifestablished, will help in achieving better efficiency and utilization of the presentirrigation system and in reaching the government's desired target of food self sufficiency.

View full abstract

This paper reports new dephosphorization techniques forsewage. The authors have invented reliable dephosphorization techniques bycombining the rotating biological contactor system with the “ferrous ion elutingmethod”, a new dephosphorization techniques. Ferrous ions are eluted throughthe corrosion of iron from rotating contactors like iron discs submerged in thecontacting tank. The ferrous irons thus eluted chemically combine withphosphorus in sewage to form an insoluble amorphous substance, which then sediments and is removed.

View full abstract

It is important for water economics, especially for efficient watersaving, to plan for suitable management of irrigation systems on farms.
In this study on water saving, the following subjects were investigated, evaluated and discussed.
(1) Irrigation scheduling for effective control of moisture flux:
The phenomenon of the upward/downward moisture flux between the rootzone and the moisture storage zone was investigated as an effective phenomenon for water saving irrigation.
Three methods of irrigation scheduling were comparatively evaluated.From the practical viewpoint, “fixed amount irrigation at variable intervals”was found to be the best of the three, on the basis of the results of theevaluation made of each type of scheduling.
(2) Drip irrigation for water saving:
Recently this system has been popular and has brought economical andeffective irrigation, because it is a system of partial irrigation. According tothe results of experiments carried out in sugar cane fields, the yield was keptat the same level as that in ordinary irrigation, while the amount of irrigatedwater was half of the amount in the usual system.
(3) Planting ratio:
The results of investigation on the planting ratio in the irrigation projecthave clearly shown that about 90% of crop planting is done in the springsummer season and aboilt 30% in the autumn-winter season. This factor cannot be neglected in irrigation planning for farms.

View full abstract

This research aims at calibrating sprinkler nozzles to simulate tropical rainfall with respect to rainfall characteristics such as intensity anddropsize distribution. Also the distribution uniformity of the simulated rainfallshould be high enough to produce better results when simulating in the field.“Rainjet 836c” square pattern sprinkler nozzle was selected for this purpose.One-, two-, three- and four-nozzle arrangements were used, and rainfall of different intensities was obtained by varying the nozzle pressure.
The simulated rainfall was within the intensity range of 18.84-95.05mm/hand the distribution uniformity was sufficiently high, ranging between 75 and 93%. The drop size distribution was analysed by “flour pellet method, ” and itwas found that the drop size distribution of the simulated rain follows Gumbeldistribution. The relationship between the intensity and the median volume dropdiameter was also found: the median volume drop diameter of the simulatedrainfall lies between 1.69 and 2.15mm. An increasing trend in drop size distribution and median volume drop diameter with respect to intensity was found in simulated rainfall, and this trend is similar to that of actual rainfall.

View full abstract