Carbon dioxide, methane and nitrous oxide are the three main greenhouse gases.
Carbon dioxide and nitrous oxide are considered long-lived gases because significant amounts remain in the atmosphere for a long time, even centuries. Whereas methane is a relatively short-lived gas and most breaks down within a few decades.
Globally, agriculture is the largest source of anthropogenic nitrous oxide emissions, accounting for an estimated 56-81 percent of the total. In New Zealand, agriculture accounts for an estimated 94 percent of the anthropogenic nitrous oxide emissions.
Nitrous oxide, also known as laughing gas, is one of the most potent greenhouse gases. When I say most potent, each molecule of nitrous oxide is about 300 times more powerful than one molecule of carbon dioxide in terms of greenhouse potentiality. Nitrous oxide is both potent like methane and persistent like carbon dioxide.
Similarly, one tonne of biological methane traps approximately 33 times more heat than a tonne of carbon dioxide over a 100-year period.
About 80 percent of our country’s total nitrous oxide emissions come from urine patches on paddocks. A recent government report indicated that the nitrous oxide emissions have increased by almost half since 1990.
Agricultural emissions are linked to intensive farming.
The transformation of N-containing compounds in soils to produce nitrous oxide emissions includes nitrification of ammonium – an aerobic biochemical process. Nitrification yields nitrite, but when limited by oxygen supply nitrite can be an electron acceptor and reduced to nitrous oxide. In other words, in soils, the wetter they become, the greater will be the rates of nitrification and nitrous oxide production. When soils become anoxic, nitrate can be sequentially reduced to nitrous oxide and inert nitrogen. This is called de-nitrification.
Methane emissions are higher on farms with higher stocking rates and higher dry-matter consumption. Some of the options to reduce methane are lowering replacement rates, reducing the dry matter feed per cow, and lowering stocking rates.
Minimising human-induced erosion and maintaining good soil quality are essential for maintaining soil ecosystem services such as nutrient and water buffering, productive capacity, assimilating waste and minimising impacts of sediment and other contaminants on water bodies.
Other good practices include optimum cultivation, avoiding over grazing and heavy grazing under wet weather leading to compaction, avoiding under or over-fertilisation, practising appropriate use of pesticides and other agrochemicals, managing pasture to maintain complete soil cover and careful application of farm dairy effluent to avoid saturation and optimise organic matter.
The options for reducing nitrous oxide could be reducing nitrogen inputs through judicious use of fertilisers, using low nitrogen feeds and improving pasture quality.
There is every benefit in protecting the sensitive areas on farms. Wetlands deliver a wide range of ecosystem services such as improving water quality, flood regulation, coastal protection, and providing recreational opportunities and fish habitat.
Basically, these changes involve farm management practices rather than expensive infrastructural changes.
Waikato Regional Council continues to work with the farming community, farming industry and other stakeholders to increase the understanding of the above issues and provide advice on sustainable agriculture practices to decrease the impact of the greenhouse gases.
Climate change affects all of us, including the primary sector. Reducing greenhouse gas emissions is a priority.
Bala Tikkisetty is a sustainable agriculture advisor at Waikato Regional Council. Contact him on 0800 800 401 or bala.tikkisetty@waikatoregion.govt.nz.
