An Indian Council of Agricultural Research (ICAR) institute has developed an anti-methanogenic feed supplement ‘Harit Dhara’.

Harit Dhara

• Harit Dhara is prepared using condensed and hydrolysable tannin-rich plant-based sources abundantly available in the country.
• It changes the composition of the volatile fatty acids that are the end-products of rumen fermentation (along with hydrogen and CO2).
• It roughly costs Rs 6/kg and it is to be fed only to animals aged above three months having fully functional rumen.
• When given to bovines and sheep, it not only cuts down their methane emissions by 17-20%.
• It also results in higher milk production and body weight gain.

Why it is significant?

• Belching cattle, buffaloes, sheep and goats in India emit an estimated 9.25 million tonnes (mt) to 14.2 mt of methane annually, out of a global total of 90 mt-plus from livestock.
• And given methane’s global warming potential – 25 times of carbon dioxide (CO2) over 100 years, making it a more potent greenhouse gas – that’s cause for concern.
• An average lactating cow or buffalo in India emits around 200 litres of methane per day, while it is 85-95 litres for young growing heifers and 20-25 litres for adult sheep.
• Feeding Harit Dhara can reduce these by a fifth.

How is methane produced by the cattles?

• Methane is produced by animals having rumen, the first of their four stomachs where the plant material they eat – cellulose, fibre, starch and sugars – gets fermented or broken down by microorganisms prior to further digestion and nutrient absorption.
• Carbohydrate fermentation leads to the production of CO2 and hydrogen.
• These are used as substrate by archaea – microbes in the rumen with structure similar to bacteria – to produce methane, which the animals then expel through burping.
• Harit Dhara acts by decreasing the population of protozoa microbes in the rumen, responsible for hydrogen production and making it available to the archaea for reduction of CO2 to methane.
• Tropical plants containing tannins – bitter and astringent chemical compounds – are known to suppress or remove protozoa from the rumen.

Need for India

• The 2019 Livestock Census showed India’s cattle population at 193.46 million, along with 109.85 million buffaloes, 148.88 million goats and 74.26 million sheep.
• Being largely fed on agricultural residues – wheat/paddy straw and maize, sorghum or bajra stover – ruminants in India tend to produce 50-100% higher methane than their industrialized country counterparts.

Answer this PYQ in the comment box:

Q.Consider the following:

1. Carbon monoxide
2. Methane
3. Ozone
4. Sulphur dioxide

Which of the above are released into atmosphere due to the burning of crop/biomass residue?

(a) 1 and 2 only

(b) 2, 3 and 4 only

(c) 1 and 4 only

(d) 1, 2, 3 and 4

Back2Basics: CO2 equivalents

• Each greenhouse gas (GHG) has a different global warming potential (GWP) and persists for a different length of time in the atmosphere.
• The three main greenhouse gases (along with water vapour) and their 100-year global warming potential (GWP) compared to carbon dioxide are:

1 x – carbon dioxide (CO₂)

25 x – methane (CH₄) – I.e. Releasing 1 kg of CH₄into the atmosphere is about equivalent to releasing 25 kg of CO₂

298 x – nitrous oxide (N₂O)

• Water vapour is not considered to be a cause of man-made global warming because it does not persist in the atmosphere for more than a few days.
• There are other greenhouse gases which have far greater global warming potential (GWP) but are much less prevalent. These are sulphur hexafluoride (SF6), hydrofluorocarbons (HFCs), and perfluorocarbons (PFCs).
• There are a wide variety of uses for SF6, HFCs, and PFCs but they have been most commonly used as refrigerants and for fire suppression.
• Many of these compounds also have a depleting effect on ozone in the upper atmosphere.

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