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Vanishing topsoil is the greatest hidden cost of making bricks. There is the land on which a kiln has to be set up. This land kiln-owners buy. But there is also the land from which is dug out the clay that forms the raw material of the business. "The cost of land is one of the major investments in installing a brick-making unit, so purchasing land for topsoil is not a viable option. That's why we prefer taking such land on lease for three years," says Hari Om. And so kiln-owners make a beeline for the countryside. "The rent (for prime agricultural land) in rural areas is very low, between Rs 15,000 per bigha to Rs 25,000 per bigha for three years," informs Singh. The rate also depends upon the distance of the field-turned-raw-material patch from a town. "It reaches Rs 35,000 per bigha if the land is near the town," Singh adds. Moreover, "Among the lease conditions is the depth up to which the land will be dug, between four feet to five feet."
But soil, particularly topsoil at a depth of one to one-and-a-half metres, is not simply the physical material on Earth's surface: probably its most important component is the living organisms within it. Healthy soil contains extremely large numbers: a typical arable soil -- precisely the kind used to make bricks -- may contain 100 million bacteria/gramme. The rhizosphere, the thin layer immediately next to a plant root, typically has 1 million bacteria/gramme. Also, in one gramme of healthy soil there can be 15,000 to 20,000 different species of bacteria. Fungi are also very important -- especially mycorrhiza, which form close associations with plant roots. One kilometre of fungal hyphae have been detected in one gramme of soil.
Does not the land used to extract clay from lose, then, its microbial diversity, thus reducing its fertility and regenerative capacity? Kiln-owners agree that the land on which the kiln is located becomes completely unusable. Soil science bears this out. The burning process used to fire clay bricks changes soil chemistry and soil biology. The heat penetrates the soil up to a few centimetres. As a result, bacterial and fungal populations decrease immediately -- and substantially -- in the top 2.5 centimetre of the soil. Repeated burning permanently diminishes bacterial populations by more than 50 per cent and also decreases soil respiration. Similarly, long-term burning reduces total nitrogen and carbon and the potentially mineralised nitrogen content in the 0-15 cm soil layer.
But kiln-owners also argue that the land used to extract clay can be reclaimed. Disagrees J M Bhatnagar, deputy director and head, clay products division, Central Building Research Institute: "It takes years to reclaim that land. Bricks are made out of argillaceous mass (like clay), which are largely hydrous alumina silicate systems. These hydrous alumina silicates are the weathering product of rock mass, which takes hundreds to thousands of years in transforming to its present usable form. "It (the topsoil) is almost non-renewable," says Dilip Biswas, ex-chairperson, Central Pollution Control Board, Delhi. According to Biswas, it takes about 100 to 400 years to form the 10 millimetres of the topsoil; 30 millimetres of topsoil takes as much as 3,000 years to 12,000 years to form.
The Technology Information, Forecasting & Assessment Council -- tifac, an autonomous body under the department of science and technology, promotes use of flyash in bricks to save topsoil -- in a national seminar on building components made a presentation which shows that the current annual requirement of bricks in India is 150 billion. This means digging up nearly 300 million tonnes of topsoil: a mass stripping of around 20,234 hectares of agricultural land goes in brick manufacturing every year. But the actual damage could be more than what tifac has estimated (see box: Lump sum).