Re­tain­ing soil pas­ture an­swer to man­ag­ing emis­sions

Hauraki Herald - - FARMING -

he said.

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.

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