Soil is one of the 4 fundamental requirements of life as we know it, along with water, air and the sun. We are not in danger of running out of the sun and it seems like soil too is infinite, as it’s the basic medium on which everything stands. Hence our focus as a race has always been focussed on the depleting breathable air and drinkable water. We just never understood enough about the soil or its role to realise that we are in fact fast running out of liveable soil. What is even more interesting and a relatively more recent find, is that healthy soil directly leads to cleaner air and cleaner water. Quite literally, great soil seems to be the silver bullet we ve been looking for.
The earth’s crust is upto 70km deep but it is really the top 5 to 10 inches that contain most of the life. This ultra thin layer, the top soil is super rich in organic matter and runs the highest risk of perishability currently. It is said that good healthy forest soil contains about 7-10% soil carbon by weight. This kind of soil would contain more than 10 billion bacteria in a tea spoon (5g) of soil. Why should we care? How does this go beyond just trivia? Because soil carbon is directly related to the availability of freshwater. The organisms in the soil alter its structure at a granular level, aerating it and increasing its capacity to hold water. In fact, some studies indicate that 1% increase in the soil carbon contributes to about 95000 lt of water availability per acre. Why does this happen? Because, soil’s ability to retain water is hugely influenced by its structure, the size of the pores, the size of the granules of soil, etc. for eg, clayey soils retain a lot more water than sandy soils do. Similarly, given all other things, the presence of soil life/soil carbon – essentially influences the soil structure thus enhancing its ability to retain water and make it available to the life that depends on it. While the science of it is interesting, the consequences of better soil retention are life changing!
If we look at the most contested water body in the country, the Cauvery, its basin occupies almost 82000 sqkm of area across 3 states. The 30 year average annual rainfall in the Cauvery basin is about 108cm. That is a lot of rainfall but the problem is that most of this rain falls in the monsoon that lasts 3 months in the year. How does the Cauvery flow throughout the year then? Mathematically it is expected to flow for 3 months in a year, flood the river basin and then slowly dry off. Nature fortunately has a different and a far more efficient design. This excess water that arrives during the monsoon is expected to be held in the soil that acts like a sponge that soaks up the excess, recharges millions of aquifers and springs, and oozes it through time, via millions of trickles that become streams and eventually the perennial Cauvery. Unfortunately over the last 2 decades, the soil carbon percentage here has dropped on an average to 0.3% (from around 3% – that is a 90% drop). Which means the sponge is incapable of holding on to this deluge. This is one of the reasons why we are experiencing alternate cycles of floods in the monsoons and water crises in the summers, year after year. This is also why the Cauvery today is barely a flowing river but more a series of standing reservoirs. What if we managed to increase the average carbon content to 3%, to the same level it was 20 years ago? This would mean throughout the basin – we are talking about approximately 280000 lt of water availability in the soil per acre i.e, approximately 5.8 trillion litres of increased water availability. On an average, this is roughly the amount of water 100million people need to survive in urban india annually!! The reality is a lot more complex than this and there is no one number that will capture data for the entire Cauvery basin but you get the gist of how great soil really amounts to the tap flowing at home in the summer all the way in Bangalore and Chennai.
That being said, how do we really increase the soil carbon? what steps can we take? We will come back with more on that in another post about forest systems. Availability of water in a consumable form is a fundamental aspect of our life that soil impacts. We will be looking at how it affects the air as well in the next part. Until then, put on your thinking caps and let the introspection begin.