Of Soil and Nutrition

Bharat Dogra

While malnutrition has been widely discussed, one aspect that has not received adequate attention is the close linkage between soil nutrition and human nutrition, and on this basis how soil depletion also contributes to malnutrition among human beings (and other forms of life).

It is by now widely recognised that excessive dependence on chemical fertilisers has been harmful for the natural fertility of land. Summarising the findings of several researchers, Frances Lappe and Joseph Collins write in their development classic 'Food First',

"Chemical fertilizers can increase yields but they cannot maintain or enhance the soil's organic matter. Organic matter, however, is the ultimate key to fertility; it maintains the porous soil structure, providing superior water-holding capacity (critical during droughts) and allowing oxygen to penetrate for use by soil organisms that break down manure, crop residues, and other organic matter. Relying primarily on chemical fertilizers can be self-defeating in the long term. The more one relies on chemical fertilizers instead of manure, compost, crop rotation and green manure, the more the organic matter declines, the less able plants are to absorb inorganic nitrogen in chemical fertilizers. This helps to explain why US agriculture, according to biologists Dr Barry Commoner, now uses about five times as much fertilizer as it did in 1947 to produce the same amount of crop."

Thus dependence on chemical fertilisers can be self-defeating in the longer run even from the limited viewpoint of increasing yields. In addition this is also harmful for human nutrition.

It is well-known that excessive use of chemical fertilisers causes a loss of flavour of food; what is less known is that it can also cause a loss of nutritive value and even create some serious health problems. According to prominent nutrition expert C Gopalan,

"the use of high analysis chemical fertilisers, which is part of the modern intensive agricultural technology, had not always gone hand-in-hand with appropriate measures for soil testing and soil replenishment, with the result that, as shown by the studies of FAO, there are disturbing evidences of micronutrient depletion of soils in some areas; these are likely to be eventually reflected in impaired nutritive value of food-grains grown in such soils."

Richard Douthwaite has written in his widely discussed book The Growth Illusion',

"Nitrogenous fertilisers can raise the amount of nitrate in the final crop to four or five times the level found in the compost-growing equivalent, while at the same time cutting vitamin C and dry matter levels. This change is potentially serious, since nitrates can be turned into powerful carcinogenic nitrosamines by bacteria found in the mouth, while vitamin C has been shown to protect against cancers."

Unfortunately very healthy alternatives which are available to reduce dependence on chemical fertilisers have been ignored. One of these alternatives is mixed cropping of legumes with cereals. As Lappe and Collins write :
"Turning worldwide attention via Nobel prizes and newspaper coverage to the miracles occurring under the ideal conditions of research test fields makes it easy to ignore proven traditional practices that could still be improved upon to use the soil better. For example, a proper cropping sequence can restore nutrients taken out by one crop with those put in by another—thus providing one alternative to imported chemical fertilizers.
Why is crop sequence so important? Some crops (like corn and wheat) are heavy consumers of nitrogen, while crops of the legume family (peas, beans and lentils), because they house nitrogen-fixing bacteria, actually take nitrogen from the air and put it back into the depleted soil."

The rich contribution of legume-cereals combination to soil nutrition is matched by their equally rich contribution to enhancing human nutrition. Frances Lappe writes about her extensive research,

"I was fascinated by the discovery that diets evolving independently in different parts of the world had a common, nutritionally sound base. Combining corn and beans in Mexico, or rice and lentils in India, or rice and soybean products in Japan, was no accident. These combinations created more biologically usable protein than if the diet centered on only one food. When eaten together, the two foods, because of contrasting amino acid patterns (the building blocks of protein), make up for each other's weaknesses. Thus, if Green Revolution grain displaces legumes in the traditional diet, not only does the overall protein intake fall, since legumes have two to four times the protein content of grain, but just as critical, the balanced combination of grains and legumes that improves the biological usability of protein is also undercut."

Despite these known scientific facts, the production of legume crops particularly pulses has been allowed to decline steeply in India and some other countries as so-called green revolution technology promoted cereal monocultures with a narrow genetic base, inflicting heavy damage on human nutrition as well as soil nutrition.

Vol. 46, No. 27, Jan 12 -18, 2014

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