Dairy farmers Mark and Jennifer McDonald began beautifying their 138ha Methven dairy farm a decade ago.
Carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) 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. Methane is a relatively short lived gas, breaking down within a few decades.
Globally, agriculture is the largest source of anthropogenic N2O emissions, accounting for an estimated 56-81% of the total. In New Zealand, agriculture accounts for an estimated 94% of the anthropogenic N2O emissions.
N2O – also known as laughing gas – is one of the most potent greenhouse gases, warming the planet. When I say most potent, each molecule of N2O is about 300 times more powerful than one molecule of carbon dioxide in terms of greenhouse potentiality. N2O is both potent like methane and persistent like carbon dioxide.
Similarly, one tonne of biological methane traps about 33 times more heat than a tonne of carbon dioxide over 100 years.
About 80% of our country’s total N2O emissions come from urine patches on paddocks. A recent report from the Government indicated that the N2O 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 N2O emissions includes nitrification of ammonium (NH+4) – an aerobic biochemical process. Nitrification yields nitrite (NO-2), but when limited by oxygen supply, nitrite can be an electron acceptor and reduced to nitrous oxide. In other words, the wetter they become in soils, the greater will be the rates of nitrification and N2O production. When soils become anoxic, nitrate can be sequentially reduced to N2O 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, practicing appropriate use of pesticides and other agrochemicals, managing pasture to maintain complete soil cover and careful applying farm dairy effluent to avoid saturation and to optimise organic matter.
The options for reducing N2O 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 give a wide range of ecosystem benefits 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.
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.