Taking paddy cultivation atop
On a 400-sq.ft roof area, 80 kg of rice can be harvested in a year.
Growing Food: Abundant rainwater and sunlight make the terrace an ideal place for growing paddy.
Roofs and terraces in India receive vast amounts of sunlight and rainwater. These are also usually sterile spaces, biologically dead and put to no particular use except to store junk. Of course, clothes and ‘papads' are dried here and sometimes a few potted plants are kept.
In North India people used to drift up on summer nights to sleep and some still do. But what can you do then to make better use of a space that occupies roughly 40 to 50 per cent of a city's area? Why not use rainwater, grey water and grow rice? Here's how…
Flat roofs are common in low rainfall regions of the country. All flat roofs have a slight slope to drain the rainwater to down-spouts.
If made of reinforced cement concrete, they are usually very strong.
A thin HDPE sheet which is UV resistant needs to be placed with a small fold to hold about 3 inches of leaf litter and light soil.
The leaf litter in the case of growing rice should usually be of the pongaemia tree, locally called ‘honge'. The advice of a structural engineer would be preferable especially if the house is old but in general too. The area of the spread would depend on the roof area and the availability of grey water.
Grey water is water used for washing clothes and from the bath. Water from the kitchen is increasingly being seen as black water because of the huge organic load that comes from Indian cooking and vessels.
Grey water being generated can be easily calculated: 15 to 20 litres per person as bath water and anywhere between 60 to 150 litres as clothes wash water. In our case, we have 45 litres as bath water from three persons and 60 litres per day coming from the washing machine. A total of 105 litres every day is available as grey water for the plants.
Grey water flow
Since the grey water is to be used on the terrace it will need pumping. Also, it needs to be cleaned before it can be applied to the crop. What we did was to place our bathroom on the terrace. A small grey water tank was located just below the terrace level.
A small half H.P. pump has been installed to pump the grey water into a drum. Five plastic drums are placed in a descending fashion. The grey water goes to the highest placed drum and flows automatically when full to the next lower one and so on. Finally, from the fifth drum, the water is led into the paddy spread.
The drums are 90 litres in capacity and are filled with the typha plant which is taken from the local lakes or tanks. Nothing else is placed in the drum, no soil too. The plants grow vigorously and show good root growth. They thrive on the soap and detergent water. The water that comes from the final drum is colourless and good for the rice.
Paddy seeds are planted in water and the saplings transplanted after about 14 days into the prepared bed on the plastic sheet. Grey water is the only water supplied and rainwater supplements it.
Appropriate fertilizers can be added if necessary; however, Eco-san is good. Wait for 90 days and you have good old rice on your roof.
The re-use magic
No grey water has left your plot, rainwater has been used wisely and you are ready for the next planting. On a 400 sq. ft. roof area you can raise 80 kg of rice in a year. Not bad for used water, one can say.
Water wisdom is to take a waste and convert it to a resource. It is also about using a lot of common sense, experimenting and enjoying the process.
Harvesting rainwater, reusing grey water and cultivating plants is part of the million solutions that a city needs to manage its water wisely.
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