Rainwater harvesting in greenhousesFebruary 29, 2008
|I visited China and was struck by the intelligent use of rainwater in Poly houses. Persuading a student to repeat the experiment here was the hard part and harder still was getting a lousy Rs 25,000/- to help Anil Kumar set up this experiment. TIDE came forward and helped the student. It is to the credit of Svati Bhogle and Chandankeri of TIDE that they have persisted with the idea and set up at least 3 more poly houses with the same idea. The are very excited about it and have written up a proposal and got funds for setting up 10 more 200 square metre poly houses. Now imagine there is a potential to integrate the small and marginal farmer with value added agriculture and improve his income dramatically and THIS IS A RAINFED POLYHOUSE. No bore well, no energy,no carbon emissions and IMAGINE again if we make it completely organic and use ECOSAN as fertiliser. What a gain? But who will help take this idea forward?Suppose we set it up on a fluoride affected area. Villagers can grow fluoride free crops and also take back 20 litres of Fluoride free water to drink every day. The same in Arsenic affected area.Will we rise to the occasion? Poly-houses for rainwater harvesting, an Indian and Chinese experience|
|S VISHWANATH discovers how sustainable poly houses possess the potential to solve the ongoing water problem in Karnataka.|
Rainwater harvesting is the process of collecting and storing rainwater for future productive use.
Its role and significance are seeing a revival today owing to the enormous pressures on our limited water resources, depleting ground water levels. Apart from providing water security, the role of rooftop rainwater harvesting can also be in providing food security and growing value added crops.
China, for example, has pioneered the low cost poly-house model with rain water harvesting and drip irrigation to grow crops in a hostile terrain. In the Chinese model, poly-houses are built using a mud wall, mostly bamboo structural roofs coupled with steel and a plastic sheet for the roof. Since sources of water such as surface and ground water are simply not available, rainwater falling on the roof is collected and brought inside the poly-house where it is stored in an underground cellar.
The water is then pumped by using a manual or electrical pump and a gravity-based drip irrigation system has been adopted to water the plants inside the poly-house. Excellent results have been reported with many crops, vegetables and flowers.
The State of Karnataka is the second largest drought prone state next only to Rajasthan. India as a whole suffers from drought at regular intervals. In such a situation it is imperative that answers be found for food security for our rural agricultural sector where more than 70 per cent of our population resides. Steps ahead lie in the introduction of these poly-houses for the growth of value added plants in a safe, controlled environment devoid of pests, where crops/vegetables/flowers can be grown in carefully monitored conditions. The floriculture industry has already adopted the poly-house technology.
Economical poly houses
Poly-houses however should be made of more economical, easy for assembling and efficient, so that it can reach more and more farmers.
With the introduction of drip irrigation, it is possible to reduce the amount of water used for the same. Water availability however is still an issue because groundwater levels are falling and there is high content of salts in the groundwater in many places. One solution in Karnataka also could be the systematic collection of rainwater falling on the rooftop of the poly-houses, storing them and using the drip irrigation system for the plants inside.
Preliminary work has suggested that the total water requirement for vegetables such as capsicum or flowers such as anthurium can be met through poly-house rooftop rainwater harvesting. For example, the rough annual demand for a 175 square metre poly-house is of the order of 52,000 litres.
The semi-annual demand for a crop of duration six months is 26,000 litres of water. In a place with an annual rainfall of 400 mm, the rainwater falling on the roof of the poly-house is of the order of 70,000 litres.
Assuming a collection efficiency of 80 per cent, 56,000 litres of rainwater can be harvested, which is more than the annual demand.
In theory at least, the poly-house becomes self sufficient for its annual water and power requirement. With the annual rainfall as low as 200 mm, a semi-annual crop can be cultivated.
This methodology has the potential of creating a substantial armoury of drought proofing our agriculture. Further research is needed in developing efficient systems of collecting rainwater without losses and low cost storage systems.
A student of GKVK, Shri Anil Kumar T D, studying in II year M Tech (soil and water conservation engineering ), is currently carrying out a research titled – Studies on Techno-economic feasibility of roof water harvesting system with greenhouse. It is being carried out under the guidance of Dr S B Batagurki, Associate Professor in the U A S Hebbal Extension Unit with assistance from Shri Krishna Manohar and Shri T N Tulasidas.
Such and future research will establish the applicability of the technology of rooftop rainwater harvesting for poly-houses in the Karnataka context which show an exciting potential.