Increasing the quantity of carbon stored in agricultural soils has the potential to offset emissions of greenhouse gases to the atmosphere, while soil carbon losses would further add to those emissions.
However, realising this mitigation potential is technically challenging when soil carbon stocks are already high (as they are in New Zealand), potential changes in soil carbon are small and spatial variability is high.
The current NZAGRC programme has three distinct components:
(1) testing specific management practices that may increase the long term soil carbon store in field situations;
(2) developing and using models to predict how a range of management practices may influence long and short tem soil carbon storage; and
(3) identifying those factors that influence the stability of current or newly added soil carbon.
We have also supported international work to map on farm soil carbon and will participate in the international research programme CIRCASA.
Dr David Whitehead, Manaaki Whenua - Landcare Research (2010-present)
Professor Frank Kelliher, AgResearch (2010-2017)
A review of soil carbon change in New Zealand
Schipper, L. A., P. L. Mudge, et al. (2017). "A review of soil carbon change in New Zealand’s grazed grasslands." New Zealand Journal of Agricultural Research 60(2): 93-118.
Soil organic matter is a potential sink of atmospheric carbon (C) and critical for maintaining soil quality. We reviewed New Zealand studies of soil C changes after conversion from woody vegetation to pasture, and under long-term pasture. Soil C increased by about 13.7 t C ha−1 to a new steady state when forests were initially converted to pasture. In the last 3–4 decades, resampling of soil profiles demonstrated that under long-term pasture on flat land, soil C had subsequently declined for allophanic, gley and organic soils by 0.54, 0.32 and 2.9 t C ha−1 y−1, respectively, and soil C had not changed in the remainder of sampled soil orders. For the same time period, pasture soils on stable midslopes of hill country gained 0.6 t C ha−1 y−1. Whether these changes are ongoing is not known, except for the organic soils where losses will continue so long as they are drained. Phosphorus fertiliser application did not change C stocks. Irrigation decreased carbon by 7 t C ha−1. Carbon losses during pasture renewal ranged between 0.8 and 4.1 t C ha−1. Some evidence suggests tussock grasslands can gain C when fertilised and not overgrazed. When combined to the national scale, different data sets suggest either no change or a gain of C, but with large uncertainties. We highlight key land-use practices and soil orders that require further information of soil C stock changes and advocate for a better understanding of underpinning reasons for changes in soil C.
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