Retaining soil pasture answer to managing emissions
The loss rate was determined by the soil moisture content and the length of time the paddock was bare. ‘‘The wetter the soil, the higher the loss will be on a daily basis,’’ Wall said.
The amount lost varied from 0.7t-4t. On Troughton’s farm, that equated to 2 per cent of its total carbon lost during pasture renewal. The scientists investigated whether the loss could be gained back and compared the ability of ryegrass and clover pasture and mixed swards with stored carbon.
After three years, it showed that diverse swards could be better at taking up carbon than traditional ryegrass and clover mixes.
The next step was to compare plantain with ryegrass and clover to provide scientists with a second data point. Further work looked at the effect on carbon when supplementary feed was brought onto farms. The scientists hoped it would resulte in an increase in carbon levels and put that theory to the test over three years on an intensive Waharoa dairy farm.
The scientists measured the Traughton’s maize crop over the past two seasons and found 6-10t of carbon lost from the maize crop in the first year. That equated to about 5 per cent lost across the farm, Wall said.
Wall stressed that while the results were ‘‘grim’’, the final balance had yet to be determined. ‘‘If you want to increase your soil carbon you need more inputs than outputs.’’
‘‘When you cultivate, you will lose carbon.’’
Early work into nitrous oxide measurements showed a spike in emissions every time there was heavy rain on the farm.
Nitrous oxide is a greenhouse gas that is 300 times more potent than carbon dioxide and made up 11-15 per cent of New Zealand’s total greenhouse emissions. The main source of nitrous oxide is urine patches from dairy cows.