New tests unlocks soil fertility information

An innovative soil test developed by AgResearch is offering the pastoral and arable sector the information it needs for better land and fertiliser use.

The hot water extractable carbon (HWC) test offers straightforward, robust and accurate results on soil fertility status, especially the mineralisable nutrients bound to soil organic matter.

The HWC test was developed to fill a gap in the methodology for a quick and reliable measure of soil carbon status. The test strongly correlates with more expensive and time consuming tests such as mineralisable-N, soil microbial biomass carbon as well as soil aggregate stability. It is a simpler, cheaper and more accurate measurement than previous tests for assessing impacts of farming management practices on soil organic matter and related properties.

The test is simple, after a 30 minute pre-wash, soils are extracted for 16 hours at 80°C with water then analysed for organic carbon. The test has been gaining interest from the international science community, having been widely cited in a number of international papers.

It is now being used by other research institutes, consultants and regulatory authorities as a biochemical indicator in laboratory and field trials and to assess soil carbon status changes over time. It is also now widely used by international soil scientists to examine impacts of land use change on soil organic matter and soil quality. It could also be used as an environmental monitoring tool to better shape environmental policy.

AgResearch scientist Dr Anwar Ghani says that one of the unique attributes of this technique is that it can be used on air dried soils, enabling researchers to look back in time and test levels of HWC in archived soils.

“It means you can measure the HWC in archive samples with very little change in terms of its value from fresh samples. It offers an opportunity to be able to look and compare where things were in the past to where we are now,” he says.

“The overall aim is that farmers are able to see the impact of soil management on their soil organic matter and soil fertility, and how they can influence it.”