Method Of Water Harvesting
There are three method of harvesting and recycling of runoff water.
i) Inter plot water harvesting: – In this method harvested water is directed to the crop. This method is suitable for area where rainfall is scanty (< 500 mm) and even there is difficulty of maturing a single crop. In this technique a portion of the area is cultivated & remaining area is used for harvesting water. Usually the uncultivated area is compacted or treated in such a way that runoff would be induced. Surface modification may be required to get runoff. Such method is suitable for arid regions. Runoff may be induced by using cover films (plastic or rubber) preparing hydrophobic layer (wax) compacting surface or spreading sodic soil on surface.
ii) Inter row water harvesting: – There may not be enough rain to support a crop in some areas & therefore by conserving more water in furrows and planting the crop in furrows may give some yields.
iii) Water harvesting in farm Ponds: – A portion of the excess runoff water after allowing maximum in situ moisture conservation is collected in farm ponds. As far as possible the pond should be located in the lower patches of the field to facilitate better storage and less seepage losses. The size of the farm pond should be worked out considering annual rainfall probable runoff and the catchments area. Generally, 10 to 20 per cent of the seasonal rainfall is considered as runoff in medium and deep black soils. A farm pond of 150 m3 capacity with side slopes of 1.5: 1 is sufficient for each hectare of catchments area in black soils. The farm ponds may be circular squared or rectangular. However eared or rectangular ponds are more convenient for harvesting of runoff water.
Under low rainfall situations to increase the runoff from catchments area the soil surface is treated with sodium salt betonies clay hydrophobic compounds like sodium ciliolate sodium rosinate etc. asphalt bitumen and water proofing membranes like paraffin. Some mechanical measures to increase runoff can be adopted such as land surface smoothening reducing surface depressions compacting the soil surface by rollers of spreading the clay blanket before rolling in sandy soils.
There are three important stages involved in water harvesting.
1. Collection of water in form pond.
2. Storage of water & problems
3. Applications of stored water to the crops.
1. Collection of water in form pond: – From the parameters like annual rainfall probable runoff and area of catchments the size of the farm pond can be work out. The location of the farm pond should be such that there v. should be proper storage and facilities to whiles storage and facilities to utilize stored water for crop production e.g. if farm is located in rocky and porous part, it would difficult to use stored water for crop production. Under such circumstances water may be increased and surface area may be required to convey for long distance. As for as possible pond should be located in lower patches of the field to facility better storage and seepage losses. The size of the farm pond should be decided by the quantum of water to be stored and nature of the soil strata. If the stratum is hard, rocky then it would be desirable to have shallow pond. If the structure is clay wool in that case depth may be increased and surface area may be reduced to have minimum evaporation. If the pond is located in upper patches water can be. How gravitationally and may create problems or water logging in low lying areas if proper care is not taken.
2. Storage of water problems: – Seepage and evaporation losses of stored water are the major problems of farm ponds. Nearly 40 to 50% quantity of stored water is lost through seepage and evaporation. When the pond is with murrum strata or under neath the total losses can be to the extent of 72% out at which 80% losses are due to seepage alone. In general the seepage losses in deep black soils are low. For preventing the seepage losses in farm ponds located in coarse textured soils the sealing materials such as natural clay, saling sodic soils, bentonite bituman, soil + cement mixture stones or brick in cement mortar asphalt compounds polyethylene / rubber sheets or plastering with soil + cowdung wheat straw etc. can be used for lining the pond surfaces depending upon the easy availability and cost of the material. However compacting and lining with natural clay soil is most economical.
The evaporation losses from free water surface can be reduced by spreading the materials on water surface such as plant residues oil emulsions long chain fatty alcohols i.e. Cetyl alcohol gum mixtures polyethylene oxides. Floating blocks of wax rubber and plastic floats are more effective in controlling the evaporation to the extent of 80 percent.
3. Application of stored water to the crops: – Since available water in the farm pond is a scare commodity its optimum use is the important consideration in entire runoff farming. In the case of application of water for crop production two considerations need to be borne in mind. First is the method of application and second the stage of crop growth.
For efficient application furrow irrigation or alternate furrow irrigation methods should be used than surface irrigation which will increase water use efficiency of stored water. When the stored water is to be used for post rainy season (Rabi) crops the water should be applied at the most critical growth stages.
For example: Rabi sorghum – When 2 irrigations are to be applied
First – stem elongation stage – 30 – 35 DAS.
Second – Flowering 65 – 70 Days. When stored water is limited and only one irrigation is possible in that case water may be applied before flowering to avoid storage losses. Here water should be stored in soil profile rather than in farm pond.
Safflower – 60 – 65 Days – Rosette stage.
Gram – 65 – 70 Days – pod development stage.
The research findings from Solapur have indicated that grain yields of Rabi sorghum safflower and gram can be increased by 100, 40 & 60% respectively by applying single irrigation at boot stage rosette stage & pod development stage respectively to above crops.
All these things discussed above should be combined into a method of management called "watershed based farming system". In this new approach the attempt is made to utilize water in all its stages and then excess water is drained out in to a farm pond connected to the field by protected grass water ways.