Soil fatigue has emerged as one of the key constraints in raising crop yields. Most of the arable land in India has been cropped for decades and some even for centuries. In the process, nutrient consumption has far exceeded the amount that could be replenished through organic or inorganic fertilisers. Apart from this, a substantial chunk of land is rapidly being degraded by wind and water erosion and other natural and induced factors. This is a major cause for worry.
Going by the estimates put out by the Indian Council of Agricultural Research (ICAR) in its latest document “Vision 2030”, about 120.72 million hectares of the country’s arable land of around 140 million hectares is degraded by erosion. Besides, some 8.4 million hectares suffers from soil salinity and water-logging.
Worse, the country is losing annually nearly 0.8 million tonnes of nitrogen (N), 1.8 million tonnes of phosphorus (P) and a whopping 26.3 million tonnes of potassium (K) as a result of all this. The problems are exacerbated by the imbalanced application of nutrients, especially N, P and K, and excessive mining of micronutrients, leading to deficiency of macro and micro nutrients in most soils. Besides, the use of compost, farmyard manure and other types of manures and organic fertilisers is woefully inadequate.
The net result is steady deterioration in soil health in all its dimensions — physical, chemical and microbial.
Farmers, fortunately, are well aware of this menace, though they are handicapped, economically and otherwise, to take corrective measures. This has been borne out by a recent “social audit” of soil health conducted by environment campaigner Greenpeace in five states — Assam, Karnataka, Madhya Pradesh, Orissa and Punjab.
“Indian farmers are worried about the state of soil and are keen to take up ecological fertilisation to tide over the degradation of soils. However, they are unable to do so due to lack of adequate government support system”, the Greenpeace survey has concluded.
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Significantly, as many as 98 per cent of the 1,000 farmers surveyed were ready to use organic fertilisers if these are subsidised and made easily accessible. An important indicator of soil health is the presence of living beings, such as micro-organisms, earthworms and the like. They help the soil breathe and maintain its physical structure, water-holding capacity and fertility. Unfortunately, the indiscriminate use of chemicals over the years has destroyed much of this vital soil fauna.
Farmers confirm that soils have been depleted of living organisms. All the respondents in the survey were categorical that they could not find living organisms in the soil anymore, though they did find them before 1980. However, over 80 per cent of these farmers say they had seen living beings in soils till as late as 2000, a clear indication that most soils have been deprived of their livestock in the past decade or so.
Producing enough organic manure to meet the entire need of farmers may not be possible in the shorter run. One of the possible options could be to promote biofertilisers and biofertiliser-enriched compost and manure.
Studies by ICAR have indicated that the use of biofertiliser mixtures leads to higher crop production apart from improving soil health. The biofertiliser-mix used in these experiments comprised rice straw compost enriched with the nitrogen-fixing bacteria Azospirillum and a mixture of rock phosphate and another bacterium that makes this phosphate water-soluble so that it can absorbed by plants. Its application enhanced rice yield 23 per cent in fields under the rice-toria (oilseed) cropping sequence and by some 10 per cent in soil under rice-wheat crop rotation.
In the past, many farmers used to grow green manuring crops, usually fast-growing legumes like cowpea, sun-hemp or Dhaincha, just to incorporate in the soil; once they rotted they became a nutrient-rich compost. But this practice has largely been given up in most states, barring Madhya Pradesh and Assam to some extent. This useful system needs to be revived wherever possible.
This apart, modern vermiculture (rearing selected species of earthworms) is another highly effective tool for re-introducing living beings into the soils. The addition of earthworm-rich vermicompost rejuvenates the soils and raises plant yields. Given the scale of the problem, these technologies need to be promoted vigorously.