There are two sources of flooding in Bangladesh

There are two sources of flooding in Bangladesh during monsoon. Water deposited in the upper watershed outside Bangladesh is brought by the rivers and we have upper-big or small-in the country. This destroys the standing crops, but it also brings silt and  nutrients to the soil. The second source of flooding is rainfall within Bangladesh. The water the rain water and the water coming from outside is not a problem by itself. The big problem is how fast this water can be drained off the land. To solve this problem, our people have, over the centuries, dug thousands of canals and built thousands of embankments. These canals must be re excavated and these embankments reconstructed every few years during the dry season.

Normally, cover of some kind are used for cold frames and hotbeds. The most satisfactory cover is the standard sash. It 3 ft feet wide and 6 feet long. Glass panes are imbedded in the frame and glazed to provide waterproof and airtight protection. In use the sash is placed lengthwise across the cold frame or hotbed. The standard sash is expensive; yet it is a satisfactory cover. A frame cover with glass permits the absorption of heat from the sun on clear days. And it enables the bed to retain it during the night and during cold period; it is possible in this way to provide temperature that are more uniformly favorable for plant growth than would be the case if the frames were  not so covered. Various other materials are used as covers for cold frames. Screen wire imbedded in a transparent material similar to cellophane makes a satisfactory cover. This material is usually tacked on frames of dimensions that perm it of convenient handling. Different grades and weight of cloth that range from heavy duck to light domestic are also used. The untreated cloth may be used, but treating the material with hot linseed oil or melted paraffin increases its durability, makes it more nearly waterproof and airtight, and renders it more effective in protecting the frame during unfavorable weather.
Methods of  Heating Hotbeds. Heating of hotbeds is accomplished in four principle ways
Hot water or steam.
Where hotbeds adjoin a greenhouse that is heated by steam or hot water, the heating pipes may be extended in to the beds also. Other provisions are sometimes made for steam or hot water. The pipes are usually placed about 5 or  6 ins below the seedbed surface. Where it is desired to protect plants against an occasional late frost or freeze, and where it is desirable to warm the air, but not necessary to warm the soil, the pipes may be suspended along the inside walls at about  the level of the seabed. Hotbeds heated with steam or hot water is very satisfactory because the temperature can be regulated accurately.
Organic Matter :
The heat liberated in the decomposition of organic matter can be used as a source of heat for hotbeds. Animal manures are used commonly and fresh manure from grain-fed horses is considered best. Hay, straw, and cornstalks are also used, thought the heat produced by these is much less. The hotbed is excavated to a depth of from 18 to 30 inches. The manure or other organic material is packed well into this basin, especially around the edges and in the corners. When the required amount has been added, a layer of good soil, 4 to 6 inches deep, is spread smoothly over the top. This constitutes the seedbed and its surface should be slightly higher than the level of the surrounding ground. When moisture is added, heat is produced by organic material and the seedbed above absorbs some of the heat. The greatest heating effect is at the beginning of the period, and the temperature gradually subsides. Hence, this type of hotbed is more satisfactory for use in the spring than in  the fall. If manure, or other organic material, is available locally, the chief expense of providing heat is the labor necessary to put the bed in operation
Flue Heat :
By another method, hotbeds are heated by flues. In the construction of such beds, a firebox  lengthwise of the bed to an outlet at the opposite end. Two lines of flues, properly spaced, give a more uniform distribution of heat than if only one line is used. Soil is placed over the flues to provide the planting bed. Hot gas and smoke from the firebox, passing under the bed, create the heating effect. Cheap fuel is essential for the practical operation of a flue-heated hotbed. Wood has been used more commonly than any other fuel, but high labor costs are making it more expensive. Careful and regular attention is required to provide uniform heat; hence the labor cost of operation is high. They are inconvenient to operate, particularly   when it is  necessary to provide heat day and night for a prolonged period.
Electricity  :
As electricity becomes more generally available, it is being used increasingly in the heating of hotbeds. Light bulbs, mounted on suitable panels, and suspended in the air within the hotbed, may be kept burring short to keep the air temperature above the danger point during short cold periods. Several low-watt-power globes distributed over the entire area to be heated are preferred to s smaller number  of high-watt-power globes. In addition to the hearting effect, light bulbs provide supplemental light which is advantageous in some cases; Special lead- and plastic-cover heating cables are now available for heating hotbed soil. The cable is laid back and forth across the bed 4 to 6 inches deep over it. A thermostat may be used to control the temperature at which the electric current will cut off and on. The soil temperature to be provided varies with the different kinds of plants to be grown in the hotbed. For tomato and sweet potato the thermostat is set so that current will be cut off if the soil temperature rises above 85° F. and will come on again if the temperature drops below 75°F. When the cable has been installed with a thermostat, a favorable soil temperature is provided automatically and the labor cost for operation is reduced to a minimum. The amount of electricity required, and hence the4 cost for heating hotbeds, depends principally upon (1) the temperature required, (2) the amount of cold weather which prevails, and ( 3) the type of  hotbed and covers used.
With sweetpotatoes in Texas, 13 kilowatt-hours of electricity were  required to produce 1000 plants when the bed was covered with standard sash, but 23 were required when a cloth covering was used. Beds banked with soil (as insulation) required 27 kilowatthours for each 1,000 plants, while 51 were required for the beds without insulation. The plants were 5 days earlier in the beds covered with standard sash and in the insulated beds than in check cooler, For several locations in Texas the electricity for heat to produce sweetpotapo slips ranged from 1.7 kilowatthours per 1,000 plants ranged from 7 to 13 kilowatthours at different locations, depending upon the amount of cold weather the prevailed during the period of operation. Oftentimes costs are  calculated upon the electricity required to provide heat for the area covered by one standard sash. Thus tests in Washington and Pennsylvania show that the cost during a certain period was almost 3 cent per sash are week; while under different conditions, in Maryland, the comparative cost was only about 1.5 cents per sash per week. very important in our country.

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