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Floods washed away 287 million tonnes of topsoil, says study

Divya Gandhi
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North Karnataka lost soil nutrients worth Rs. 1,625 crore in 2009

Cause for concern: Soil loss was highest in Gulbarga, Belgaum and Bijapur districts, which have fine-grained black soil. — File photo
Cause for concern: Soil loss was highest in Gulbarga, Belgaum and Bijapur districts, which have fine-grained black soil. — File photo

A year after one of Karnataka's most severe floods claimed scores of lives and inundated farmland, it emerges that its impact on the rural economy could be more long lasting than previously believed.

An assessment of the 13 flood-hit districts in north Karnataka has revealed that 287 million tonnes of topsoil was washed away, translating into Rs. 1,625 crore worth soil nutrients.

A research paper on soil and plant nutrient loss during the 2009 floods, published in the latest issue of ‘Current Science', talks about the serious implications on crop productivity and rural livelihood security unless corrective steps are taken.

Soil loss was the highest in Gulbarga district, followed by Belgaum and Bijapur, which have fine-grained black soil, says the research paper written by A. Natarajan of the National Bureau of Soil Survey and Land Use Planning (Bangalore) and scientists from three other soil research institutes in the country.

In a span of just five days in October last, north Karnataka lost the quantity of nutrients normally applied over a period of one-and-a-half decades. The loss of the fertile black soil was three times higher than red soil owing to its clayey consistency and poor infiltration rate. The total soil nutrients lost included Rs. 888 crore worth of phosphorus, Rs. 464 crore of micronutrients, Rs. 161 crore of nitrogen and Rs. 110 crore of potassium. On the other hand, sand and silt were deposited in nearly two lakh hectares of cultivated fields along river courses.

It would take “a considerable period of time to restore the status of nutrients,” considering that hundreds of years of soil formation produced just a few inches of agriculturally productive soil, the writers pointed out. An area of about 10.75 m ha, almost equal to half the total geographical area of Karnataka, was affected by the floods.

The downpour was intense and occurred in a short period of time, adding to the destruction, especially in the catchment and command areas of the Krishna and Tungabhadra. For instance, north Karnataka received 70 per cent of its entire quota of annual rainfall in under a week.

The paper recommended that the deep and wide gullies seen in several fields be plugged and the soil conserved before the next sowing season. Planting erosion-resistant species, like bamboo, along river banks and constructing field bunds could help ameliorate the situation, it adds.

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