Soil matters

In 400 BC, Greek physician Hippocrates is said to have provided a list of things that should be considered during a proper medical evaluation. The list included the properties of local ground. Modern science recognises the distinct influence of soils on human health, but few studies have examined the connection outside Africa. In August 2023, researchers from the US and Australia published a study in the journal Scientific Reports, which for the first time conducts a large-scale evaluation of the relationship between the availability of micronutrients in the soil and nutritional status of people in India. Their findings hold clues for the country to not only improve soil health but also to address the long-standing challenge of malnutrition among children and women.

The researchers conducted a large-scale evaluation in which they analysed over 27 million soil tests, drawn from a nation-wide government programme on soil health called Soil Health Card, and the health data of 0.3 million children and 1 million women from the National Family Health Survey (NFHS). The study focuses on two key minerals—zinc, which plays a role in the growth of cells, building proteins and supporting a healthy immune system, and iron, which is used by the body to make haemoglobin that carries oxygen from the lungs to all parts of the body.

The researchers found that districts where soil zinc availability was low had significantly higher rates of stunting (when a child has low height for their age) and underweight conditions (low weight per age). The zinc-stunting relationship was the strongest even in wealthier households. The researchers also found clear association between soil iron availability and anaemia. At places where the availability of soil nutrients were satisfactory, they found a positive correlation with the height and haemoglobin levels of children and women. A one-standard deviation increase in soil zinc (equivalent to 24.3 per cent increase in the proportion of zinc tests) is associated with a reduction in stunting by 10.8 per 1,000 children and with a reduction in underweight conditions by 11.7 per 1,000 children, notes the study. Similarly, a one-standard deviation increase in soil zinc is associated with a 0.29 cm increase in women’s heights. And, a one-standard deviation increase in iron (equivalent to a 26.8 per cent increase in the proportion of iron tests) is associated with 0.038 gram per decilitre (g/dl) increase in haemoglobin for children and 0.037 g/dl increase in haemoglobin for women, the report states.

The findings hold significance for India for two reasons. One, India is home to one-third of the 2 billion global population suffering from micronutrient deficiency. Though NFHS data shows a decline in child stunting between 2015-16 and 2019-21, the rate is still significantly high at 35 per cent among children under five years of age. In 161 districts, more than 40 per cent children under five years of age suffer from stunting.

Two, micronutrient deficiency in Indian soils has increased at a rapid scale in recent decades. “Initially, the country’s soil was more deficient in nitrogen and phosphorous. It then developed potassium-deficiency, followed by sulphur-deficiency in the 1990s and 2000s. Now our soils are greatly deficient in zinc and other micronutrients,” says Arvind Shukla, who led the All India Co-ordinated Research Project on Micro- and Secondary Nutrients and Pollutant Elements in Soils and Plants (AICRP-MSPE) under the Indian Council of Agricultural Research from 2011 to 2022.

The project was launched in 1967 to analyse micronutrient deficiency in soil across the country. An analysis of 0.2 million soil samples from 28 states by scientists associated with AICRP-MSPE shows that 36.5 per cent of the country’s soil is deficient in zinc and 12.8 per cent is deficient in iron. Other micronutrients like boron is deficient in 23.4 per cent of soils, copper in 4.20 per cent and manganese in 7.10 per cent of soils. Since 2014, the project has shifted focus to analysing the link between soil health and human health.

“Factors like women’s nutrition and household wealth hold more importance when we look at child or adolescent stunting, and rightly so. But there is a need to simultaneously work on establishing a clear understanding of how soil health affects human health,” Leah Bevis, associate professor at the Department of Agricultural, Environmental and Developmental Economics, Ohio State University, US, tells Down To Earth. Bevis is also co-author of the Scientific Reports study.

To the aid

Studies are already underway to explore if the challenge of malnutrition can be addressed by improving the availability of micronutrients in soil and in plants.

In 2021, Bevis, along with two other researchers from the World Bank and The Alliance of Biodiversity International Center for Tropical Agriculture, US, conducted a study in Nepal’s Terai region, and found that a 1 ppm (parts per million) increase in soil zinc availability seems to increase child height by 7.5-25 per cent of a standard deviation, and decreases child stunting by 2-7.5 per cent.

In 2014, the AICRP-MSPE scientists also conducted a laboratory experiment in which they fed rats with zinc-biofortified wheat (cultivated using foliar application of zinc) produced on zinc-deficient soil. They found that rats fed low-zinc wheat had low zinc in their blood serum as compared to the rats fed high-zinc wheat. In 2016, AICRP-MSPE along with doctors from the All India Institute of Medical Sciences (AIIMS), Bhopal, carried out a study in Samnapur, a tribal village in Madhya Pradesh’s Mandla district. Some 15 families with teenagers were selected for biometric observations. For three years, the researchers surveyed the families for dietary recall, animal food intake, access to the food and fodder through external sources and use of inputs, especially zinc fertilisers, in their agricultural fields. Their blood samples were collected and analysed. “Analysis of zinc content in soil, grain, straw-feed, animal and human blood serum established a strong correlation and interdependence among the soil-plant- animal-human continuum,” says Shukla.

A research, published in the journal Applied Geochemistry in March 2000, also analysed the impact of selenium concentrations in soil on human health. It studied the distribution of selenium in samples of soil, grain and human hair collected from the Keshan disease belt of Hebei Province, China, and found that villages with highest incidence of Keshan disease had the lowest selenium concentration in soil.

Economic, effective

Though limited, study results indicate that it is possible to address malnutrition and micronutrient deficiency among people by improving soil health. This can also be an economic and effective way of addressing malnutrition in the country.

Consider this. In August 2022, the Union government approved fortification of the key staple rice in all government food schemes and entitlements under the National Food Security Act 2013. Since then, iron-fortified rice is being supplied as a pilot programme in 15 states. However, food and agriculture experts have time and again highlighted concerns regarding the indiscriminate distribution of fortified rice to even those suffering from thalassemia and sickle cell disease. Food Safety and Standards Authority of India’s statutory regulations have warned patients with thalassemia and sickle cell anaemia against consuming iron-fortified food or using it only under strict medical supervision. Such concerns can be avoided by improving soil micronutrient availability.

The Scientific Reports study from August 2023 states that foliar and soil application of minerals like zinc, iron, boron and sulphur to wheat and rice has also been shown to increase crop yields. In India, application of zinc to crops on zinc-deficient soils increases yields of rice, wheat, maize, and oats by over 75 per cent more than application of only nitrogen, phosphorus, and potassium fertiliser. Zinc-enriched fertilisers can enhance soil zinc for three to four years after application, which means that it could be an effective long-term intervention, requiring less short-term maintenance than other solutions. The study, however, calls for more studies to consider the costs of such an intervention and the human nutrition impacts of agronomic fortification. Shukla says doctors often prescribe zinc tablets or multi-vitamins or minerals for different health issues. One should compare spending on such multi-vitamins with the expenses involved in making the soil healthy.

Both Shukla and Bevis call for government initiated experimental research on a large scale in which zinc-enriched fertilisers or foliar application of zinc are promoted during sowing and then zinc levels in the blood are compared with a control group. “Research done by us and other scientists is the first step and an effective entry point for the governments to conduct their own experiments and develop policies,” says Bevis.

This was first published in the 1-15 December, 2023 print edition of Down To Earth