The Gist of Science Reporter: September 2015


The Gist of Science Reporter: September 2015


Our Soil Our Future

“Soils don’t have a voice, and there are only a few people to speak out for them. They are our silent ally in food production ... /r This was Jose Graziano da Silva, Director-General of the Food and Agriculture Organization (FAa) speaking on the occasion of the launching ceremony of the International Year of Soils 2015.

The soils are in danger because of expanding cities, deforestation, unsustainable land use and management practices, pollution, overgrazing and climate change. The current rate of soil degradation threatens the capacity to meet the needs of the future generations. The main goal of the International Year of Soils is, therefore, to raise awareness about the importance of healthy soils and to advocate for sustainable soil management in order to protect this precious natural resource.

But, it is so sad and alarming that one-third of the soils all over the world have already been degraded. If the current trend continues, the global amount of arable and productive land per person in 2050 will be a quarter of what it was in 1960. The world will have over 9 billion people in 2050, 2 billion more than today. Accordingly, the food production will have to grow by 60% to feed this increased population, demanding intensive agriculture.

The pressure on soils is bound to increase and soils are not easy to fix once they degrade: it can take up to one thousand years to form one centimetre of topsoil. That same topsoil can be quickly washed away by erosion. Soils are typically made up of about one-third water, one-third minerals and one-third organic materials. But, if we take these three elements separately and mix them together, we won’t get soil. Soil is much like a living organism. It is a complex and dynamic system that forms habitat for an immense diversity of species, including human beings.

It is composed of living and non-living components. The living component includes from large creatures like earthworms, ants, etc. to microscopic forms like bacteria, fungi, protozoa, and micro-arthropods. The physical and chemical properties of the soil are attributed to the non-living components of the soil. This largely includes the geological part, the solid material, which we often call the ‘soil’.

The na ture of the soil varies across different geological landscapes, their formation in turn affected by different climatic, physical and chemical factors. Fertile soil remains as the base for the economic prosperity of a nation through food, fuel and fabrics. Soil could even sustain civilizations. It supplies nutrients for growth of plants which include agricultural crops also.

Soils act as reservoirs of carbon and harbour dead bodies of organisms like animals, plants and microorganisms. Soils can influence the cycling of nutrients and energy in the ecosystems. Soil also plays a major part in the Nitrogen and Sulphur cycles. In a forest land, the soil is always covered by leaf litter composed of dead leaves, twigs and roots of plants. There is a detritus food-chain going on within the soil, where the dead organic matter is decayed by certain micro-organisms in the soil. During decomposition, the organic matter is transformed into inorganic material such as compounds of nitrate, ammonium, and phosphate which supply nutrients for plant growth.

For soils, quality is of prime importance. It means its ability to maintain biological diversity and productivity. In the broader sense, it is the ability to sustain quality of water and air and providing conditions for plants, animals and human populations to live. Organic matter present in the soil als determines its quality. A higher content of soil organic matter denotes its higher cation exchange capacity, higher water-holding capacity and higher infiltration capacity. When a soil naturally possesses better aeration and increased soil particle aggregation, it can lessen soil erosion due to reduced runoff of nutrients and improved moisture infiltration and retention.
Erosion is an inevitable action which implies the removal of the surface of the earth by abrasive actions of wind, water, waves, or glaciers. Based on the reason and factors, erosion can be of two types: Geological and Accelerated.

Geologic erosion is a slow process, typically occurring at a rate that is much slower than the rate of soil formation. This rate would depend on protection offered by vegetation. The roots of plants can intertwine with each other and hold the soil particles together. The vegetation over-ground such as grasses and certain other plants, which have even gained the name ‘sand-binders’, can protect the soil from washing away while the trees can reduce the wind speed so that the loose soil is not flown away.

The opposite happens in the case of accelerated soil erosion. Here the rate of soil loss is fas ter than the ra te of soil formation. When there is a violent influx of wind or water, the individual particles of the soil become detached from the aggregates and are washed away or blown away for great distances. They are deposited somewhere else as dust or form new soils that are washed into streams, rivers, and oceans. The extent of accelerated soil erosion depends on natural conditions like climate, slope, vegetation cover, soil and the nature of land exploitation patterns.

Intensive agricultural practices also lead to soil erosion, salinization, and even desertification leading to permanent loss of the land, suitable for agricultural production. As per a recent estimate, about 25 billion metric tons of soil erodes each year from agricultural land which includes 17 tons per cultivated hectare and 4.5 tons per person.

The climatic condition of a region has a major part to play. In the arid and semiarid regions of the world (e.g., Northwest China, parts of Asia, Australia, southern South America, and North America and North Africa), wind erosion is a far more serious problem for agricultural lands.

Irrigation can also contribute to soil erosion by inducing salinization, the increased concentration of salts in the topsoil. It happens in almost all irrigated lands of the world due to increased evaporation, invasion of seawater and suseptibility of soils to salty groundwater. This gradually leads to soil degradation and eventually decreases the availability of productive land suitable for food, fiber, and fuel production.

A continuous struggle is going on between those who are polluting the soil and those who are trying to remediate its aftermaths. Industrial revolution and intensive agricultural practices have made pollution of the soil an incurable epidemic. People may have been aware of the effects of water-pollution, but nobody spoke about the effects of pollution on the soil. May be because it was not obvious as in the case of water and air pollution, but the consequences were far more fearsome. There was not even a single law relating to the regulation of soil-pollution over the past hundred years and this is true even in the highly civilized and economically developed countries. All the heavily industrialised cities of the world have a very pathetic condition pertaining to the health of their soil environment.

Only recently, ‘soil-heatlh’ has been slowly grabbing public attention, largely due to the efforts of voluntary orgainsations and environmental protection agencies. However, once polluted, it takes decades and billions of money to get the soil cleaned and brought back to life.

Pesticide residues in the soil belong to ‘Non-Pointsource-Pollutants’ which means, they do not have any identifiable source. Pesticides may come to the soil from the air, when sprayed onto the soil surface or mixed into the soil.

Air polluting pesticide particles may settle down on the soil surface due to gravity or by way of precipitation. Fertilizers, household chemicals, detergents, construction materials, dust, etc. can also reach the soil. Pollutants that are soluble in water have the highest mobility. They are readily carried by rainwater or flood water, cleaning the soil for a while, but eventually affecting the groundwater. On the other hand, most ‘heavy metals’ and other chemically stable substances do not directly dissolve in water. Some may chemically react with water to form compounds that form sediments in the soil.

Conservation of soil is the need of the hour. Although chemical fertilizers replenish the nutrient pool necessary for plant growth, they do not regenerate the organic matter present in the soil quantitatively or qualitatively. They also fail to maintain the heterogeneity of the organic materials found in the soil. Only the slower decomposition of organic materials could replenish the fertility of the soil.

Many people cannot differentiate between a forest land and agricultural land, because, as per them, both provide greenery and all the benefits of vegetation. But, after harvest, the soil in the crop field is left bare and exposed to the effects of soil-erosion. So, whatever that is present as natural in the soil must be conserved for maximum sustainable usage.

Reduced Tillage: Tillage is an important factor that decreases soil quality. Reduced tillage practices could increase Soil Organic Matter and moisture content of the soil, and also improve the soil food web. However, there is a great disadvantage in reduced tillage that it requires a greater use of herbicides due to the increased spread of weeds and soil pathogens. If this is not taken into account, it may affect the crop yields due to the incereased prevalence of pathogens, pests, diseases and weeds.

Diversified Cropping: Also termed as multiple cropping, growing of cover crops could ensure conservation of soil. Cover crops can reduce the leaching of soil nitrogen through immobilizing them as nitrates within the plant biomass. They can compete with weeds in establishing over a particular area and could effectively reduce the effects of soil erosion.

Organic Amendments: Green manures, chicken and cow manure, pig slurry, grass cutting, garden composts, kitchen wastes, etc. are examples of organic amendments or mulches. They can maintain the soils with higher organic content, making them fit for long-term agricultural production. Organic amendments can also improve soil aggregation, soil aeration, water-holding capacity, and cation exchange capacity of the soil.

Bioremediation of Pollutants: Chemicals present in the soil may be those that are purposefully applied to the soil such as pesticides and fertilizers or those that make an accidental entrance to the soil. Microorganisms present in the soil may use the pollutant as a source of energy for their metabolism or would make it less harmful by changing its composition.

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