The World Soil Day is observed on December 5. The International Union of Soil Sciences (IUSS) made a resolution in 2002 proposing the date to be World Soil Day in order to celebrate the importance of soil as a critical component of the natural system and as a vital contributor to human wellbeing.
This was the birth day of King Bhumibol Adulyadej of Thailand, the longest reigning monarch, who played an important role in promotion of soil science and conservation. He was also a leader in land resource management. The Food and Agriculture Organisation of United Nations (FAO) supported the formal establishment of the World Soil Day as a global awareness raising platform.
The United Nations observed 2015 as the International Year of Soils (IYS) on the World Soil Day of 2015 and a discussion was held on many life-giving functions of soil. The topic for 2017 for the day was ‘Caring for the planet starts from the ground’. The topic for 2018 was ‘Be the solution for Soil Pollution’. According to FAO, 95% of our food comes from soil. Globally, 33% soils are already degraded. A massive soil conservation effort is essential to preserve the top soils from erosion. The yields of food crops depend primarily on the fertility of top soils and their agronomic management.
Recently, there has been a massive effort by the Government of India on testing the soils of arable lands of the country to determine their fertility status. Soil health cards have been issued to farmers with soil analysis report for proper management of their soils to get higher and profitable yields. There is overexploitation of soils for increasing crop yield in several parts of the country. Net sown area for food grains has remained unchanged at around 125 million hectares (mha), since 1970 to recent years. The food grain production of the country has, however, increased from 100 million tonnes to 265 million tonnes during the last 50 years.
Since the first Green Revolution, intensive research in agricultural universities and other crop and soil related organisations under Indian Council of Agricultural Research developed crop varieties suitable for different agro-climatic zones of the country and their package of practices such as, seed rate, fertiliser doses for different crops, plant protection measures and agronomic practices.
This resulted in increase in yields of food grains per hectare significantly resulting in 2.65 times increase in production. Similar yield increases have been achieved in several other crops resulting in overall increase in agricultural production of the country, while total net sown area for all crops has hovered around 140 million hectares. Multiple cropping on the same piece of land is now widely practised, wherever irrigation from some source is available or in its absence to raise a dry land crop.
There is a limit to sustaining high yields and raise multiple crops from a limited area without degrading the fertility level of soil.
Large quantities of chemical fertilisers have to be used to supply the required plant nutrients. Soil microflora, which are essential to maintain soil fertility get affected by high concentration of inorganic nutrients in the soil. Organic matter content of the soils, which is essential for microbial growth, is going down in most of the soils due to intensive cropping without ploughing in the crop residues or addition of FYM or compost. While we have a White Revolution, the cattle shed refuse scarcely reaches the farm land. Green manuring is theoretically attractive, but the crop has to be grown in the field for at least 45 days to fix a reasonable amount of atmospheric nitrogen.
Another 15 days is necessary for irrigating the field and ploughing in the crop to release the nitrogen fixed by it from the atmosphere. Most of the farmers do not have time to go through this process in a cropping season.Farmers should be given financial incentives, to incorporate crop residues in their fields soon after harvest (when the soil is still moist) to maintain organic matter status of the soil, instead of burning them, which cause atmospheric pollution. The current effort to offer agricultural machinery at subsidised rates to farmers and get this job done by them is not working.
Municipal solid waste (MSW) is another source of organic matter. According to report of the Central Pollution Control Board, about 84 million tonnes of MSW was supposed to have been produced in the country in 2015. Organic matter constitutes 40-60 per cent of this material. Technologies are available to process such material and use the organic fraction to produce compost, biogas and fertilisers.
Sweden uses all its MSW and imports trash from the neighbouring Norway to run its waste to energy programme. It uses 60 per cent of its household waste for composting and production of biogas. Land fill with organic waste is illegal. They give economic incentives as garbage collection fees, access to garbage collection centres and public awareness campaign. Application of fertilisers is, however, essential to sustain the existing levels of crop production and increase it further to feed a projected stabilised population of 1.5 billion people by middle of this century. There are misconceptions about use of fertilisers and organic manures. If we go to the basics, plants take up minerals from the soil in their ionic forms. Nitrogen is taken up by plant roots in the form of nitrate or ammonium (rice) ions, phosphorus as phosphate and all other nutrients in their ionic forms. When organic matter is added to the soil, it undergoes microbial decomposition to produce nitrate ion and ionic forms of all other nutrients. No organic matter as such can get into the plant body. Addition of organic matter to the soil improves its aeration, water holding capacity and other physical characteristics to facilitate root growth and nutrient uptake. It can temporarily hold fertilisers as complexes, reduce their toxic effects, when present in higher concentration and release them slowly.
Long term fertiliser experiments have shown that a mix of organic matter and fertilisers gives highest yields and can better withstand weather aberrations.
Effects of organic matter on quality of crops are marginal, since plant metabolism is genetically programmed. One cannot change them without tweaking some genes. This often may result in unpredictable consequences. Organic farming practised on a limited scale preserves the natural constituents of a crop as yield is low. Commercial farming involves addition of adequate fertilisers and adopt plant protection measures to maximise yields. This leads to dilution of natural constituents. Organic farm products are expensive and meant for elite consumers, whereas commercial farm products are to feed the masses.
Organic matter is bulky and contains 0.5-1 per cent nitrogen. If 60 kg nitrogen has to be applied to a crop, one has to apply 6-12 tonnes of organic matter as a substitute. This amount of organic matter is simply not available and cost of transport would be high.
Current climate change scenario has its effect on soil fertility. Higher temperature speeds up decomposition of organic matter and other soil processes, which affect soil fertility. Drier soil conditions impede root growth and decomposition of organic matter. Frequent cyclones followed by heavy rainfall and flooding may cause erosion of top soil affecting its fertility (Rosenzweig and Hillel, 2004).
Any loss of soil fertility needs to be recorded in soil health cards issued to the farmers with advice to take corrective measures. We need to produce about 100 million tonnes more than the present level of food grain production to feed a stabilised population of 1.5 billion (Population growth rate appears to have decelerated in recent time).
This can be achieved, if we take into account current rate of growth in agricultural production.
Apart from rice and wheat, there is enough scope to increase production of coarse cereals such as maize, Jowar, Bajra etc, and pulses to supplement the food grain production. People have now realised beneficial effects of millets on health.
Intense research is going on around the world to increase yields of all types of food crops and face the challenges of climate change uncertainties. There is a gradual shift for consumption of more protein rich diets with increase in income level of people. According to a report of International Food Policy Research Institute, the world meat production needs to be doubled by 2050 to meet the global demand (Acikgoz, 2018). This needs rearing of an increased number of farm animals and production of sufficient feed and fodder for their consumption. Recent technologies to produce synthetic meat by cell culture without slaughtering farm animals are making significant progress and are likely to be made available as early as next decade.
This will reduce pressure on land to produce feed and fodder to sustain a large number of farm animals.
(Dr Mitra is a former Dean, Professor and Head, Department of Soil Science and Agricultural Chemistry, OUAT)
