Dying fields

The Green Revolution and use of high-yielding varieties has led to depletion of vital micronutrients

Published: Sunday 31 October 1999

 Intensive cropping practices< (Credit: amit shanker / cse) agro-scientists in India are a troubled lot these days because there are indications that the soil in some of the most-productive regions of the country is losing its micronutrient content. "However, in India, little attention is paid to the possible health impact of depleting micronutrients in the soil," laments V K Nayyar, professor, department of soil, Punjab Agricultural University ( pau ), Ludhiana.

Booming population, over-extraction and intensive cropping are the main culprits behind the depletion of micronutients, say experts. "Intensive cropping removes crucial micronutrients from the soil. This, in the long-run, will lead to serious health problems," says C K Hira, senior nutritionist, department of food and micronutrients, pau .

Scientists cite other factors too. "This is happening due to the use of High Yielding Varieties ( hyv) , use of fertilisers rich in nitrogen, phosphorous and potassium (these are present in the ratio of 50:25:25) and changed cropping patterns," says J S Kanwar of International Crops Research Institute for the Semi-Arid Tropics ( icrisat ), Hyderabad.

There are 16 essential plant nutrients, out of which seven -- zinc, copper, iron, manganese, boron, molybdenum and chlorine -- are called micronutrients. Normally, there is an equilibrium of micro and macro nutrients in the soil. However, this equilibrium has been disturbed due to the above factors.

An analysis of around 225,000 soil samples from 16 states and two Union Territories indicate that zinc deficiency is a very serious constraint to sustainable productivity in 11 states. This is followed by deficiency of boron, iron, manganese and copper. Zinc deficiency is very high in the soils of arid and semi-arid regions of Haryana (61 per cent), Punjab (47 per cent), and Uttar Pradesh (45 per cent). Also its deficiency is widespread (36-54 per cent) in black and red alluvial soils of Madhya Pradesh, Tamil Nadu and Andhra Pradesh, leached soils of Meghalaya and West Bengal, and laterite soils of Orissa. Deficiency in iron, manganese and copper is far less when compared to that of zinc. However, iron deficiency is widespread in compact and sandy soils of Punjab and Haryana, black and red soils of Tamil Nadu and calcareous soils of Bihar. Manganese and copper deficiencies are not so widespread as that of zinc and iron, except, in Karnataka (19 per cent manganese and 31 per cent copper deficient soils). Boron deficiencies are most serious (49 per cent to 84 per cent) in the Terai and Teesta alluvial, red and lateric soils of West Bengal, Orissa and Meghalaya, as well as the soils of Bihar and Assam. According to I M Chibbar, department of soil, pau , Ludhiana, "Primarily the dominant and extensive wheat-rice cultivation pattern has contributed to deficiency of essential micronutrients in the soil of these states."

The problem started in the late Sixties with the Green Revolution. Scientists and policy-makers thought intensive cropping and introduction of high-yielding varieties would bring more food and nutritional security. In the process, crucial micronutrients were lost. Large-scale deforestation has also led to the reduction of organic matter and depletion of soil micronutrients.
Punjab: the deficient state A study conducted in 1959 found that 85 per cent of the state's soil was deficient in zinc. This resulted in low crop yield. Today, all the areas of the state are deficient in a majority of micronutrients except potassium while there is a hundred per cent nitrogen deficiency. Phosphorous is deficient in 80 per cent of the soil. On the other hand, there are traces of heavy metal in the soil.

This situation prevails in Ludhiana. Farmers here tend to replenish only nitrogen phosphorus and potassium. Now, to cope with the growing depletion of zinc, many farmers in Punjab are using zinc as fertiliser. However, a strange phenomenon has been reported from Kanganwal village of Ludhiana, where farmers use zinc as fertliser. Such areas are now showing iron and manganese deficiency. Thus, the problem of micronutrient depletion in Punjab seems to be getting worse day by day.
Effects on human health In the early 70s, a study conducted by the Post Graduate Institute of Medical Sciences ( pgi ), Chandigarh, revealed that consumption of zinc-deficient food grains can lead to retarded physical and sexual development, defective wound healing capacity and carbohydrate imbalance.

If micronutrients keep depleting, it will force plants to absorb some metals that are toxic to human health.For example, plants and invertebrates like molluscs have the ability to chose an alternative metal in place of what is absent or inadequate in the soil. Some plants absorb strontium instead of cal-cium and the former is toxic to humans.

There is evidence that animals suffer from a disease called Parakeratosis, due to this deficiency. Related to the problem of zinc deficiency is copper deficiency. Copper deficiency has been shown to be associated with problems in synthesis of proteins, like melanin and keratin, that are responsible for hardening of skin, hair and nails, anaemia, reduced growth, cardiovascular disorders, infertility and diarrhoea.

In India, the incidence of these diseases is found in sheep and children. Iron and copper is important for the formation of haemoglobin. Copper helps in bone and brain tissue formation while manganese helps in bone formation and reproduction. Selenium functions as an anti-oxidant with vitamin E and checks respiratory failure.

Chromium is a cofactor in insulin meta-bolism, improves glucose intake, lowers ldl cholesterol and increases hdl cholesterol. Iodine is the basic com- ponent of thyroxin, the hormone secreted from the thyroid that regulates the basal metabolic rate, contributes to normal growth and development of the body.

Redressal measures
To redress the situation, a system under Indian Council of Agricultural Research to monitor changes in micronutrients and trace elements relevant to plant, animal and human health should be strengthened. The monitoring institutions must be provided with the modern equipment and communication facilities for improving the quality of work on micronutrients/trace elements.

Proper soil surveys must be conduc-ted in regions brought under irrigation. "More interdisciplinary research is necessary by soil scientists, agronomists, plant, animal and human nutritionists and public health professionals. Intensive case studies by interdisciplinary teams will be necessary to build up the strategy for action plan," stresses Kanwar. Other easy solutions include going back to traditional farming systems and increased use of organic manures and multiple cropping with legumes.

According to researchers at pau , poultry manure, farmyard manure and piggery manure are effective for meeting zinc requirements of the soil. "To check iron deficiency, we should adopt green manuring. A solution of iron and magnesium should be sprayed every week in the field," says I M Chibbar. Other practices, like prolonged submergence of the field helps tackle iron and manganese deficiency. Unfortunately, little attention is given to such innovative methods.

With Richard Mahapatra .

Robbing resources
Estimates of micronutrient removal rates at high yeilds


  Fe Mn B Zn Cu Mo
Rice 6 915 4,500 90 240 110 12
Maize 5 6,000 1,600 - 650 650 -
Wheat 5 3,100 350 240 280 120 12
Sorghum 5 3,600 270 270 360 28 11
Perlmillet 4 680 80 - 160 33 -
Casava 4 4,800 1,800 600 1,800 187 -
Potato 30 4,800 360 1,500 270 360 -
Mung Bean 1 1,530 340 290 120 100 9
Chick pea 4 230 120 - 150 56 10
Pigeon pea 4 168 60 - 100 56 -
Groundnut 5 7,500 590 660 140 75 -
Soybean 4 3,600 2,200 - 780 1,800 18

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