Changing our SOCs – a progress report

Soil organic carbon (SOC) is critical to soil health. It’s the basis of the soil food web and it plays an important role in maintaining soil structure, retaining water and nutrient cycling. Soils are also large reservoirs of carbon, and globally contain more carbon than the atmosphere and vegetation combined.

It’s important we know what’s happening to soil carbon levels in New Zealand, because a small increase or decrease could have significant impacts on carbon footprints at farm, industry and national scales. The National Soil Carbon Monitoring Project, a collaboration between Manaaki Whenua and the University of Waikato, and funded by the New Zealand Agricultural Greenhouse Gas Research Centre (NZAGRC), is currently assessing whether soil carbon stocks under New Zealand’s agricultural land are increasing or decreasing, and whether land use influences any change that may be occurring. Data will also improve our ability to predict how SOCs are likely to change when land use changes via improvements to the national soil carbon inventory model.

Benchmark sampling at 500 sites across New Zealand, which began in 2018, has now been completed and final data analysis and a journal manuscript on the benchmark sampling are close to completion – watch this space for results. Resampling of sites has also commenced and initial results of whether changes are occurring will be in hand within a year.

Carbon flows in a simplified dairy farm system. The green arrow shows carbon inputs via

photosynthesis, grey arrows internal cycling, and red arrows the various pathways by which

carbon can be lost. Arrow thickness is proportional to the carbon flow. Increasing soil carbon

requires increasing inputs, decreasing losses, or both.