We’ve created an enormous bubble of population and economy. If we try to get the good data and do the arithmetic, it’s just unsustainable. It’s either got to be deflated gently, or it’s going to burst. ~ James H. Brown, an American ecologist.
In every continent, the population and economy are placing new demands for more food, fresh water, energy, variety of commodities, and manufactured products. We resist the notion that there might be limits to the rate of growth we are used to. The cumulative impact of surging per capita consumption, rapid population growth, and human dominance over every ecological system has created the very real possibility that we may soon reach a dangerous “planetary scale ‘tipping point’”.
In the parable of the boy who cried wolf, warning of danger that turned out to be false, bred complacency to the point where a subsequent warning of a danger that was all too real was ignored. Past warnings, such as Malthus’s warnings at the end of the eighteenth century that the growth of population will always outturn its ability to feed itself, were often ignored and perceived as false. Reference can be made to the Limits to Growth, published in 1972 by Donella Meadows. The warnings were often ignored and perceived as false.
But worryingly, over the past two decades, multiple indicators have been showing that real physical limits are being reached. We can hardly afford to ignore those indicators to ensure our safety. Some of the nonrenewable natural resources we depend upon the most are being depleted quantitatively and qualitatively. Soil, including topsoil, is one such natural resource. Soil health is showing signs of fatigue due to intensive and unscientific cultivation. In spite of the impressive increase in food production in the last half century, humanity is finding it very difficult to provide more food for more people.
Experts are unanimous in mentioning the multiple threats confronting the ability of the world to expand food supplies. Soil is an essential nonrenewable natural resource at dynamic equilibrium with its environment. Since different climatic zones have different characteristics, soils also differ according to these variations. It plays a central role in terms of economic and social development. It is the bedrock of food security and nutrition. It ensures food, fodder, fiber and renewable energy supplies to sustain human, animal and plant life. It acts as a pantry for plants, storing and recycling nutrients and minerals that plants need to grow.
Healthy soils protect the planet from climate change. Plants absorb carbon dioxide (CO2) from atmosphere and stabilize the same in the soil. A study published by the Joint Research Centre ( JRC) in Nature Climate Change shows that soil acts as a huge sink of greenhouse gasses through increased storage of organic carbon. According to Columbia University’s Earth Institute, ‘soil removes about 25 per cent of the world’s fossil fuel emissions each year.’ Globally, the soil is reputed to contain the largest terrestrial carbon pool estimated at approximately 2344 Gt (1 Gigaton = 1 billion tones) of organic carbon in the 3 meters, 1500 Gt in the first 1 m and 615 Gt stored in the top 20 cm of the soil profile.
This is much higher than the 560 Gt of carbon (C ) found in the biotic pool and twice more than atmospheric CO2. Soils are habitats for beneficial soil microbes. Microbes form synergistic relationship with plants to protect them from stress and provide them with nutrients, among other tasks. One teaspoon of healthy soil contains 100 million to one billion individual bacteria alone. Soil is so important in our life that Mahatma Gandhi had very poignantly said in 1946, ‘To forget how to dig the earth and tend the soil is to forget ourselves.’ It has appropriately been stated that, ‘We are only 15 cms away from our annihilation, this 15 cms. being our topsoil.’
Topsoil is the uppermost layer of soil, usually the top 5 inches (13 cm) to 10 inches (25 cm). Topsoil regenerates naturally. According to FAO, soil can take hundreds to thousands of years to form a centimeter of topsoil. It has the highest concentration of organic matter and micro-organisms and this is where most of the Earth’s biological soil activity occurs. In the last four decades, the overexploitation of topsoil has led to the loss of a significant amount of productivity on almost one-third of the arable land on earth. Each reduction of organic matter in soil by 50 per cent reduces many crop yields by 25 per cent.
Every inch of erosion of topsoil diminishes grain yields by 6 per cent. Much of the topsoil can be severely degraded or lost before the end of the end of the century. In China, topsoil is being lost 57 times faster than its natural replacement process, in Europe seventeen times faster, in the US ten times faster. Ethiopia is now losing almost two billion tons of topsoil every year. India faces an acute problem of soil erosion. A national database on land degradation prepared by the Indian Space Research Organisation in 2016 shows that 120.7 million hectare (mha), or 36.7 per cent of India’s total arable and non-arable land suffers from various forms of degradation with water erosion being its chief contributor in 83 mha (68.4 percent).
Water erosion results in loss of organic carbon, nutrient imbalance, soil compactness, decline in soil biodiversity and contamination with heavy metals and pesticides. According to New Delhi based National Academy of Agricultural Sciences (NAAS), the annual soil loss rate in our country is about 15.35 tonnes per ha, resulting in loss of 5.37 to 8.4 million tonnes of nutrients. Moreover, the eroded soil causes siltation of water reservoirs and reduces reservoir capacity, which is estimated 1 to 2 percent, annually which further impact irrigation in its command areas. Due to water erosion major rainfed crops in India suffer an annual production loss of 13.4 million tonnes.
The economic value is estimated by NAAS as Rs 205.32 billion. Waterlogging damages soil by causing salinization. Around 1.07 mha arable land in India suffers from physical degradation due to waterlogging and this results annual loss of 1.2 to 6.0 million tonnes of grain in India. Soil erosion may be a slow process that continues relatively unnoticed. Major reasons for soil erosion are: overgrazing, deforestation, urbanization, natural causes, certain agricultural practices such as intensive farming, low use of fertilizers, excessive tillage, poor irrigation etc. Climate change is also a major factor. It drives desertification by altering atmospheric circulation patterns and drying out the land and vegetation. The same extra heat that evaporates more water vapour from the oceans also speeds up the evaporation of soil moisture ~ leading to longer, deeper, and more widespread droughts.
As refilling of the atmospheric ‘basins’ of moisture takes a lot of time, many areas of the world experience longer period without rain in between the intense downpours. These exposures to hotter temperatures for longer periods lead to more widespread and even deeper droughts. Once it is devoid of vegetation, the surface begins to absorb more heat. When the soil moisture is gone, the ground is baked and the topsoil becomes more vulnerable to wind erosion. Overgrasing leads to erosion of topsoil in several ways.
The obvious course is by removing the ground cover (the grasses) exposing the soil to wind and water erosion. The removal of the ground cover can also hasten desiccation destroying the organic matter, and ruining the soil structure, thus making it easier for the soil to erode. Overgrazing can also destroy the soil structures by compaction of the soil by the animals, reducing infiltration and increasing the run off. Apart from physical degradation, chemical degradation of soil health is the outcome of salinisation, alkalinisation, acidification, soil toxification through chemicals.
(The writer is a retired IAS officer)