Journal
NEW ZEALAND JOURNAL OF AGRICULTURAL RESEARCH
Volume 60, Issue 2, Pages 93-118Publisher
TAYLOR & FRANCIS LTD
DOI: 10.1080/00288233.2017.1284134
Keywords
Carbon; soil; pasture; management; land use; New Zealand; grazed
Categories
Funding
- Ministry of Business, Innovation and Employment's Science and Innovation Group
- New Zealand Agricultural Greenhouse Gas Research Centre
- New Zealand Ministry of Primary Industries
- University of Waikato
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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 Cha(-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 Cha(-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 0.6tCha(-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 7tCha(-1). Carbon losses during pasture renewal ranged between 0.8 and 4.1 t Cha(-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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