Agriculture’s Greenhouse Gases by Alan Broughton

All three major greenhouse gases are influenced by farming practices: methane, nitrogen compounds and carbon dioxide.

Methane: the contribution of farming to greenhouse gases has centred on methane produced by ruminant animals. This is not where the focus should be. It provides a helpful diversion from the main methane increasing culprit, which is gas mining and use. Ruminants do belch out methane and have been doing so for many millions of years. Nature does not allow waste. In natural systems the methane is consumed by methanotrophic bacteria that live in the soil. In healthy farm ecosystems they continue to play this role, but being very sensitive to synthetic fertilisers and many pesticides they fare poorly in farming systems that rely on chemical inputs.

Ruminants in confined feedlots often produce less methane than grazers, because of their more concentrated lower fibre diet. However, methanotrophs are not active on bare concrete, and the manure is not rapidly decomposed as in a well-managed grassland, so methane and ammonia enter the atmosphere. Feedlots should be phased out, not only because of their net greenhouse gas production but also because the animals are forced to live in non-natural crowded confinement and on non-natural feedstuffs and antibiotics, and the meat produced is nutritionally inferior. Animals need to be removed from feedlots and reintroduced into cropping systems to recycle nutrients and replace herbicides. Rice fields also produce methane. Much of the world’s rice production occurs on what were once natural swamps. In those natural ecosystems, which also produced methane from the anaerobic decomposition of organic matter under water, different kinds of methanotrophs took care of that methane. Synthetic fertilisers and pesticides inhibit their work in rice fields.

Nitrous oxide: the greatest producer of nitrous oxide and nitrogen dioxide is nitrate fertilisers – urea, ammonium sulphate, potassium nitrate, mono- and di-ammonium phosphate and anhydrous ammonia (ammonia gas drilled into the soil). Only a small proportion of applied nitrate fertiliser is used by plants, usually no more than 20%. The rest pollutes the atmosphere as nitrous oxide and nitrogen dioxide, or waterways and aquifers as nitrates and nitrites. The nitrogen compounds are major greenhouse gases, damaging the ozone that helps protect the earth from the sun’s heat. Some of this nitrogen forms ammonia in the atmosphere, combining with moisture to produce acid rain. Nitrate fertiliser use has skyrocketed since the 1950s around the world, from about 5 million tonnes per year to close to 200 million.

In natural ecosystems the nitrogen needed by plants is made available by soil microbes. Farming systems can make use of these microbes as has done for the past 10,000 or so years, unless poisoned by farm chemicals. The greater the damage done to soil microbes, the greater the amount of nitrate needed to get the same yield. Undecomposed manure also emits ammonia and nitrous oxide into the atmosphere. Dung beetles, earthworms and the huge variety of soil microbes deal with manure in a short time, providing conditions are right for their activity, which means no chemical inputs to interfere with their work.

Carbon dioxide: nitrate production is an energy intensive industrial process needing huge amounts of natural gas (methane) to heat nitrogen and hydrogen under pressure to 1,000 degrees to make ammonia which is further processed into nitrate fertilisers. An estimated 3% of global carbon dioxide is the result of burning natural gas for this purpose. Nitrate fertilisers gradually destroy soil organic matter, turning it into carbon dioxide. The bacteria that the fertilisers stimulate need a carbon source for energy – they take it out of the soil. Excessive soil tillage does the same thing. Bare soil also loses organic matter as it becomes oxidised to carbon dioxide. Carbon dioxide (and nitrous oxide and methane) is also produced from burning the fuel to drive the machinery. Efforts should be put into developing energy sources that are renewable.

*Alan is a Gippsland teacher and author of Sustainable Agriculture Versus Corporate Greed. Previously published by Green Left Weekly.