<h3>Methane</h3>
<p>Methane is a powerful but relatively short lived greenhouse gas.&nbsp; Averaged over 100 years, the global warming potential of one tonne of methane is 25 times that of one tonne of carbon dioxide. <strong><a href="faq-1,listing,330,what-is-global-warming-potential.html">What is Global Warming Potential?</a></strong></p>
<p>In New Zealand, most methane comes from belching by ruminant animals: sheep, beef cattle, dairy cows, and deer, and some from animal manure. Non-ruminants, such as poutry and pigs also produce methane from their manure but these constitute a very small source in New Zealand.</p>
<h3>Nitrous oxide</h3>
<p>Nitrous oxide is a much more powerful greenhouse gas than methane - 298 times more powerful than carbon dioxide over a 100 year timeframe on a per tonne basis.&nbsp; See <strong><a href="faq-1,listing,330,what-is-global-warming-potential.html">What is Global Warming Potential?</a></strong></p>
<p>Fortunately, the absolute amount of nitrous oxide emitted from agriculture is lower than methane. In New Zealand, most nitrous oxide is produced&nbsp;by the action of&nbsp;soil&nbsp;bacteria in urine patches in paddocks.&nbsp; Smaller amounts&nbsp;come from dung deposited during grazing, stored manures spread back onto pasture, and from nitrogen fertilizer.&nbsp;</p>
<h3>Soil carbon</h3>
<p>Soil is an important reservoir of carbon which means that relatively small changes in the amount of carbon stored in soil could have significant effects on net greenhouse gas emissions.</p>
<p>Management approaches that increase the amount of carbon stored in soils could offset some of the emissions of other greenhouse gases from agriculture, methane and nitrous oxide.</p>
<p>On the other hand, practices that deplete soil carbon and release it back into the atmosphere can add to the emissions of other greenhouse gases. From a climate change perspective, what matters is not the total quantity of carbon in soils, but whether this quantity changes over time.</p>
<p>Given the potentially significant contribution that changes in soil carbon could make to New Zealand&rsquo;s total agricultural emissions, it is essential to understand trends and identify management practices that can increase soil carbon &ndash; but equally, to avoid practices that would result in carbon losses.&nbsp;&nbsp;</p>
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