All three major greenhouse gases are influenced by farming practices.
Farming’s contribution to greenhouse gas emissions has centred on methane produced by ruminant animals: cattle, sheep, goats. This is not where the focus should be, but it provides a helpful diversion from the main culprit for rising methane emissions: 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, 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 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 manure does not rapidly decompose, as it does in 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 because animals are forced to live in unnatural, crowded confinement and on unnatural feedstuffs and antibiotics. Moreover, the meat produced is nutritionally inferior for human consumption.
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 and carbon dioxide
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.
Nitrogen compounds are major greenhouse gases and also damage the ozone layer that helps protect the Earth from the Sun. Some of this nitrogen forms ammonia in the atmosphere, combining with moisture to produce acid rain.
Nitrate fertiliser use has skyrocketed since the 1950s, from about 5 million tonnes a 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 been done for the past 10,000 years or so, 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 a huge variety of soil microbes can deal with manure in a short time, providing conditions are right for their activity — which means no chemical inputs to interfere with their work.
Nitrate production is an energy intensive industrial process needing huge amounts of natural gas (methane) to heat nitrogen and hydrogen under pressure to 1000oC 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 fertilisers stimulate need a carbon source for energy — and 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, nitrous oxide and methane are also produced from burning the fuel to drive machinery. Efforts should be put into developing energy sources that are non-polluting and renewable for the machinery.
Farmers are part of the solution
Soils provide the greatest carbon sinks apart from the oceans. There is more carbon stored in soil than in the atmosphere and vegetation combined. Despite the huge losses that unsustainable agricultural practices have caused, this is still the case.
Sequestering carbon in soils can be achieved much more rapidly than tree planting. Many farmers are now doing that.
Grasses are the fastest carbon sequesters, not in their foliage or roots (though that also contributes), but because of the carbohydrates their roots exude into the soil. Grasses do this to support the microbes in their root zone, which in turn mobilise nutrients for the plant.
The greatest value are the mycorrhizal fungi that enter the plant roots. Their mycelium networks effectively enlarge the plants nutrient and water searching ability. The byproduct is glomalin, a very stable humus-forming compound.
Mycorrhizal fungi are very sensitive to nitrate and phosphate fertilisers, herbicides and fungicides. Plant root exudates are reduced when soluble fertilisers are applied.
Grasses need grazers — they have evolved symbiotically. Without grazers, the grasslands decline as they get old, photosynthesis ceases, glomalin is no longer produced and woodlands or deserts take over. Woodlands store carbon in their trunks, branches and roots, but release little into the soil, compared to grasses.
For grasslands to work properly, grazers have to be managed to prevent overuse. In natural herds, animals do this themselves, but when confined by fences they cannot migrate to allow pasture recovery. Farmers can do this and many now are.
Profit is the problem
The movement towards regenerative agriculture without chemicals has gained great momentum in Australia and other parts of the world. Many Landcare groups are now providing support. Large numbers of farmers are attending talks and workshops by regenerative farming advocates.
There is no inherent reason why food production should be a polluting industry. It is polluting because of the huge profits available to input suppliers who are supported by government policies.
Change is occurring despite governments and despite the hardships many farmers face. Farmers are among the primary victims of the climate crisis. Many are realising that increasing soil carbon is the best way of creating resilience, as it stores vast amounts of water.
The debate about agriculture’s contribution to greenhouse gases has been perverted. Methane is not the important issue — nitrate fertilisers and soil carbon loss are the important issues.
Alternative agriculture in its many forms and terms — organic, biological, biodynamic, ecological, agroecological, holistic — provides the solution.
Corporate influence on governments, farmer information services and agricultural education and research is the major barrier to changing agriculture from a greenhouse gas producer to a greenhouse gas sequester.