Issue 19, September 2010

Special issue: Soil Carbon

In this issue

Ian Lynn collecting samples during the high country carbon survey.

Editorial

This issue of Soil Horizons reports on our soil carbon (C) research addressing the need to enhance the terrestrial C pool and reduce carbon dioxide (CO₂) emissions to the atmosphere.

Peter Stephens 1946–2010

We would like to pay tribute to Peter, who died earlier this year. He was a much respected colleague and friend, and a number of Peter’s close colleagues have contributed to these words.

Shallow landslides affecting soil C stocks in hill country near Raglan.

Effects of mass-movement erosion

The Soil Carbon Monitoring System (CMS) estimates soil C stocks for each land use in New Zealand to determine the effect of changes in land use on soil C.

Soil C monitoring in the South Island High Country.

A High Country C monitoring project

A MAF Sustainable Farming Fund (SFF) grant and other organisations have supported us to investigate the effects of grazing on ecosystem C stocks in South Island High Country grasslands.

Figure 1. C accumulation in a Japanese soil (black top layer is about 1 m, C = 16.8%) helped by volcanic ash deposition in the past 7000 years.

C storage in Allophanic soils: possibilities and challenges

Reducing the emissions of greenhouse gases such as carbon dioxide into the atmosphere remains a huge challenge for the 21st century. Maintaining or increasing C storage in soil is of fundamental importance in dealing with this challenge.

Figure 2. Soil electrical conductivity map showing soil C content [numbers on map] varying between 2.6% and 11.8% in a paddock where pine forest has recently been converted to pasture.

Proximal soil spectroscopy for soil C estimation and mapping

Soil samples in the New Zealand National Soil Archive are being scanned to collect visible-near infrared (Vis-NIR) soil spectra. The Archive contains approximately 25 000 soil samples, dating from 1939, and is housed near our Palmerston North site.

Figure 1. Examples of macropore networks in the top 50 mm of soil under trees in two apple orchards in Hawke’s Bay determined using X-ray computed tomography. The grey coloured areas are macropores. Left: Macropore network of the integrated orchard system. Macroporosity is 2.9% (volume) and mean macropore radius 0.38 mm. Right: Macropore network of the organic orchard system. Macroporosity is 8.3% (volume) and mean macropore radius 0.41 mm.

Soil form, carbon storage and stabilisation

Soil C can change under different land uses. For example, soil C has been shown to decline with intensification of dairy farming on flat land, and with irrigation in Canterbury.

Figure 1. Soil C for 0–30 cm depth at sheep/beef farms, dairy farms on Non-Allophanic Soils (NonA) and dairy farms on Allophanic soils in Taranaki and Waikato (A), and Tussock. Error bars are standard error of the mean.

Changes in soil organic matter under pasture over the last 27 years

Roger Parfitt and colleagues from Landcare Research, GNS and University of Waikato have measured soil C under the same dairy and sheep/beef pasture sites on three occasions over the last 27 years.

Figure 1. Average soil total C and total N concentrations to 10 cm depth for major land uses (number of sites sampled in parentheses). Error bars represent one standard error of the mean. Note the difference in scale for C and N (updated from Sparling and Schipper (2004)).

Land use and soil type affect soil C – lessons from 15 years of soil quality monitoring

The ETS (Emissions Trading Scheme) is now a reality, and C accounting is more important than ever. Accounting for all the soil C and how it changes over time is not an easy task.

Soil erosion in New Zealand is sinking carbon (C) at 3 million tonnes per year

Over two hundred million tonnes of sediment are lost from New Zealand to the ocean every year, primarily during storms. Intense rainfall erodes soil from steep slopes and this ends up in waterways as sediment.

Figure 1. Equipment used to collect the soil surface CO2 efflux in order to measure its isotopic composition.

Quantifying the loss of soil C from soil organic matter, as a consequence of climate or land-use change

Soils are the largest pool of C in terrestrial ecosystems, and some of the C in soil organic matter is resistant to decomposition, taking from decades to millennia to decompose (hence its description as ‘historical’ C).

Soaking up the veterinary antibiotics through black C

‘Black carbon’ (i.e. char, charcoal, and soot) is a high C-rich material and has a significant influence on the mobility and retention of chemicals in soils.

The comparatively low seasonal temperature range of maritime climates is one factor that causes relatively low annual soil organic matter decomposition rates, compared to regions experiencing higher seasonal temperature range.

Effects of monthly versus annual mean temperature data for modelling soil organic matter decomposition

Global models generally agree that warming will lead to a loss of soil organic C, while increasing CO₂ is expected to stimulate plant net primary productivity and increase C stocks. However, predictions of the combined effect of increased CO₂ and climate change vary greatly between models.

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