Dr. Prasanna Mishra |
| Blog | Posted By: hindtodaynews on:8/1/2011 8:20:23 PM |
Dr. Prasanna Mishra
Top three meters of the earth’s surface is formed by natural disintegration of the parent rock. The process creates voids between the adjacent pieces. The aggregate voids amount to about 40-50% of pore space inside the overall volume which, in appropriate condition, can provide storage for rain water. This concept, if widely implemented, could render necessity of huge irrigation reservoirs redundant. In the context of the growing articulation of unavoidable trauma arising out of displacement of people due to various projects, we should seriously consider alternative solution to irrigation through conventional system. I do not expect that our irrigation engineers and their supporters would agree to this approach immediately; but time for an urgent discussion on this alternative to facilitate a consensus on the issue seems to have arrived.
Agricultural soil supports crop life. If 50% of the pore space within the topmost layer is filled with water, soil is said to be saturated. If water stands on such soil, it is said to be super saturated. We must appreciate that only less than half of the water available at saturation is utilisable by crop plants. While many crops, besides paddy, can tolerate presence of the excess water at saturation/super saturation state; many other commonly grown crops need unsaturated soils for survival. This shows that for growing different crops, availability of water has to be different. Soil-moisture regime (percentage of water-filled pores in soil) is the determinant factor for crop choice. High land and medium land are ideal for non paddy crops. If these lands are over-saturated, we lose this vast natural asset for growing non paddy crops. The reason why our irrigated commands are not having mixed pattern of cropping is due to non appreciation of this basic concept. If we continue to saturate all types of land; viz, upland; medium land and low land; paddy would continue to be the dominant crop and growth of other crops would continue to elude us
When irrigation is given, top soil gets saturated first. In order to lessen wetness of such soil, the incoming flow of water of the canals must stop long enough so that excess water drains out to make room for air. Canal water must stop flowing for some more time to allow at least half of the available moisture to be used up by the crop. Irrigation may resume only after that. For this to happen, our irrigation engineers have to reorient their perception. Fortunately about 50% of the total water available in saturated soil is loosely held (termed as gravitational water) and, if given sufficient time, can be easily drained out by gravity, leaving the other half which remains adsorbed by soil particles. Only half of it can be used through transpiration by plants. The rest cannot be easily extracted by plants. It remains in the soil and should be discounted from the next irrigation. Such management is possible if the command areas of our irrigation projects are put to detailed investigation for assessing the moisture regime at micro level. It would be improper exploitation of our land and water if we do not do this analysis on the plea that an irrigation project is too vast an enterprise to warrant detailed analysis of the ayacut and make release of water dependent upon the result of such analysis. Our irrigation systems, created with huge investment, nevertheless need fine tuning to make agriculture productive.
The subsurface water moves along the hydraulic gradient which keeps on changing from point to point according to the resistance offered by the sub surface soil. Technology is available to track the spread of subsurface water. We can locate areas within the ayacut which are water enriched through gravitational flow. Such area should receive discounted irrigation. Scientists working as system users had tried this principle and had successfully segregated non-paddy and paddy area in Hirakud command during 78-79 to 81-82.It is possible to repeat such experiment. Characteristics of the soil must be considered to get the desired effect. Lack of understanding of soil-water-plant relationship has led to a paddy dominant crop pattern in all irrigation command of Orissa. Pattern of moisture extraction by crop plants is a feature our irrigation engineers should make increasing use of. Irrigation laws drafted in India years ago look anachronistic today and need refinement in view of the evolution of large number of photo-insensitive varieties of different crops. Delivery patterns have to be re-fixed accordingly.
Scarcity of water at tail ends of the canals is widely known in the command area of Hirakud Irrigation project. In spite of spending crores of rupees repeatedly on repairs, tail end scarcity continues to be an issue and only confirms that such repairs are not a solution. It is possible to make tail ends as green as the head ends with right measures.We have to note that for every unit of water consumed by paddy, two units are required to help carry it around. Ultimately the unconsumed part finds its way to the drain. At least one unit out of this must be collected and put back to the canal. If it is said that ‘canal cutting has come to stay’ it is not without any basis. Farmers have done it as a measure of desperation. They noticed that under the continuous supply pattern, the highland and medium lands were getting too wet for any non-paddy crop. Initially they left such lands fallow. Soon they discovered that paddy can be grown on them provided some additional water could be organised later. Initially water had to be taken stealthily because it was resisted by farmers at the tail end. A game of hide and seek went on for some time till the farmers at tail end gave up fighting. Thereafter canals were cut openly and paddy area increased close to 100% in all the head end outlet areas. All the while people were observing that the water being drawn through the cuts was becoming surplus for the head end outlet commands and was flowing down the drain. They soon found a way to irrigate the lower part of the tail end outlets. The upper part remained un-commanded because outlets were dry. The only option to enliven the dry outlets was to pump water from drains and put it in the dry canals. Through a pragmatic approach, but in violation of the existing law, the irrigation system has been tinkered with but paddy area in rabi increased.
We have to rationalize the delivery pattern as per the people’s need. There is every reason to believe that conjunctive use of water will lead to a win-win situation. Antagonism among farmers in different reaches of the ayacut will end; harmony will be restored. Repeated use of used water is the only option. Twice the volume of water required for irrigation flows into the drain/ sub-surface layers as surplus. If this water is left unused it will create drainage congestion. If we cut open drains to let it out of the irrigation commands the efficiency of water use will remain low, while a sizable part of the command will be deprived of water. We have now two situations. On one hand we could have 50-70% Rabi command lying fallow and have 65% of water in the drains causing water logging. Need is to relieve drainage and provide irrigation to the rabi fallows. We have to adopt “Irrinage”. This term is being suggested in the world forums to give equal importance to drainage with irrigation.
Recycling by pumping has many advantages. Apart from removing drainage congestion and removing tail end scarcity, it has great scope for inducing a productive cropping pattern. Pumping from the drains also induces depletion in the moisture level of low lands. Paddy yields respond very well to the oxidized root zone environment. In addition such an environment lends itself excellently well for a third crop to thrive. This will mean a three crop pattern in low lands without additional irrigation. Let me hope government would take a holistic view and help our farmers.
( The writer is a former secretary to Govt. of India )