Abstract

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 tC ha^–1 when forests were converted to pasture. Under long-term pasture on flat land, soil C had declined in Allophanic, Gley and Organic Soils by 0.54, 0.32 and 2.9 tC ha^-1 y^-1, respectively. Pasture soils on stable midslopes of hill country gained 0.6 tC ha^-1 y^-1. Phosphorus fertiliser application did not change C stocks. Irrigation decreased carbon by 7 tC ha^–1. Carbon losses during pasture renewal ranged between 0.8-4.1 tC 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.

Keywords: carbon, soil, pasture, management, land use, New Zealand.