The State of New Zealand’s Soil Car­bon

North & South - - Enterprise -

The govern­ment’s plan to plant a bil­lion trees is a cru­cial plank in its cli­mate change strat­egy. It’s also no se­cret that our huge dairy in­dus­try is one of our big­gest green­house gas emit­ters. But France’s “4 per 1000” cli­mate ini­tia­tive has high­lighted a dif­fer­ent is­sue at the heart of New Zealand agri­cul­ture: the state of our soil-car­bon stocks.

Pro­fes­sor Louis Schip­per at the Univer­sity of Waikato has stud­ied New Zealand’s soil-car­bon lev­els ex­ten­sively. He reck­ons our soils are ac­tu­ally in pretty good shape. The chal­lenge, he says, is to main­tain the soil car­bon we’ve got – and to build a bet­ter un­der­stand­ing of the con­se­quences of re­cent man­age­ment prac­tices and lan­duse con­ver­sions, such as the move from dry stock to dairy.

The sci­ence, Schip­per points out, is only par­tially com­plete. It’s clear both pas­ture and forestry are ef­fi­cient ways to se­quester car­bon (with pines, there’s less in the soil but that’s off­set by the amount stored in the plant it­self ). Where things get trick­ier is around how pas­tures are man­aged, and the ex­ter­nal in­puts used to sup­port growth.

Sev­eral stud­ies have shown that the use of phos­pho­rus fer­tiliser, while in­creas­ing pas­ture growth, has no mea­sur­able ef­fect on soil-car­bon lev­els. But there haven’t yet been any long-term tri­als of the ef­fects of ni­tro­gen-based fer­tilis­ers (cru­cial to in­ten­sive dairy­ing and at the heart of the fresh­wa­ter pol­lu­tion de­bate) on soil-car­bon lev­els, which Schip­per says is a big, im­por­tant gap in our knowl­edge. New Zealand re­search does, how­ever, al­ready show that ir­ri­ga­tion can de­crease soil-car­bon stocks.

What every­one in the field agrees on is that main­tain­ing or in­creas­ing soil-car­bon lev­els could play a vi­tal role in off­set­ting CO² emis­sions, while im­prov­ing soil qual­ity. And the best way to do this – whether with pas­ture, pine for­est, na­tives or veg­eta­bles – is to keep soil cov­ered with grow­ing plants as much as pos­si­ble.

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