Key Points:
- Archived soil samples and crop productivity data collected from the Millennium Tillage Trial (MTT) over the last ten years has been used to verify new Australian methodology for quantifying soil carbon (C) pools and modelling management induced changes in soil C.
- In a one year FAR / MAF Sustainable Farming Fund project involving Plant & Food Research scientists at Lincoln and CSIRO Land & Water scientists in Adelaide, mid-infrared (MIR) spectroscopy was successfully used to measure soil carbon pools in individual treatments of the MTT.
- The significance of this advance is that soil samples can be analysed more quickly and cheaply, identifying not only the total soil carbon content, but the individual soil carbon pools, such as the humus fraction, particulate soil carbon and the resistant or inert carbon fraction.
- The project also showed that an Australian version of the RothC model was able to predict changes in total organic carbon (TOC, R2 = 0.89) and particulate organic carbon (POC, R2 = 0.89) contents of soil at the MTT.
- The work identifi ed a signifi cant fraction (over 10%) of the soil C at the MTT site as being resistant carbon with charcoal or charcoal-like characteristics. This soil carbon is not biologically active. Whilst large amounts of charcoal C are typically found in Australia, there was little previous data on the levels in NZ soils.
- The project confi rmed the loss of total soil carbon, humus carbon and particulate soil carbon from a permanent fallow treatment, while those same soil carbon pools increased slightly under permanent pasture.
- Under a cropping rotation losses from soil carbon pools (total and humus fractions) over the ten years were smaller than in the fallow treatment, with evidence of a slightly greater loss under ploughing compared to no-till.