Agriculture: Tamil Nadu

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Reduction in soil fertility

The Times of India, Jun 17, 2015

Karthikeyan Hemalatha

Soil fertility in Tamil Nadu reduced by half in 30 yrs, says govt paper

Indiscriminate fertilizer and pesticide usage, coupled with mono-cropping and non-application of base manure like cow dung and green manure (dead plants), has taken a severe toll on the organic content in soil and thereby soil fertility across the state, says the draft organic farming policy of the state government, which is yet to be rolled out. The issue has come into focus now in the wake of Kerala raising concerns of high pesticide level on vegetables grown in Tamil Nadu.

Experts in the field say organic matter in the soil dropped from 1.2% in 1971 to 0.68% in 2002. Organic matter has further reduced to 0.5 % in several districts, according to a study conducted a year ago by the Department of Soil Science and Agriculture Chemistry of TNAU. This is against a desirable level of 0.8% to 1.3% of organic carbon, say experts.

Madurai is the worst with just 0.23% of organic content in soil, followed by Krishnagiri (0.36). Erode and Vellore are well above the ideal limit with 4.04% and 4.2% respectively. Scientists at Tamil Nadu Agricultural University say that carbon content of soil depends on the amount of carbon matter that is replenished. "Is some districts in the Cauvery delta region, farmers leave behind the rest of the crop after harvest. This recharges the carbon content. However, this practice is dwindling across the state," said vice chancellor of TNAU K Ramasamy.

Organic matter in soil includes humus - which is made of decaying plant and animal matter - as well as insects, earthworms and micro-organisms. Healthy soil ideally has 25% air and between 5% and 10% of living organisms and organic matter like dead leaves and animals. But as fertiliser and pesticide usage increases, the level of organic matter comes down. "Any fertilizer is a salt. These salts prevent growth of micro-organisms," said director of Ecoscience Research Foundation, Sultan Ahmed Ismail.

Scientists agree soil quality gets affected even if chemicals are not directly used on them. "In our studies on population of earthworms - which are good indicators of soil health - even places like Guindy National Park had a low count. This is due to poor water management and soil erosion," said Ismail.

Indiscriminate use of chemical pesticides and fertilizers has resulted in soil quality deteriorating in several districts. This becomes a vicious cycle with farmers further increasing chemical fertilizer usage to reap better yield. "When a neighbouring farmer left water stagnant on his field for three to four days, the water turned ash in colour due to chemicals on the field," said an organic farmer from Thiruvannamalai, C Parasuram. "Though I practice organic farming, water in my well too has become salty and undrinkable as chemicals from nearby farms percolate into ground affecting ground water in the whole area," he said.

But hope is not lost. Officials from Tamil Nadu Agriculture University say those practicing organic farming have started seeing positive changes. "In our surveys, we have found that organic carbon content in soil, where organic farming is being practiced, has gone up and stabilized," said professor and head of Department of Sustainable Organic Agriculture, Tamil Nadu Agricultural University, E Somasundaram.

Farmers also need to be told to rotate crops to keep soil healthy. Paddy crops always need to be followed by legumes like peanuts for increasing nitrogen content in soil. "In traditional farms, animals had a role. Now cows have gone missing - as farmers use tractors for ploughing - and key nutrients from their dung and urine are missing, adding to the deteriorating health of the soil," said an ecologist, V Arun.

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