managing soil organic matter - Grains Research & Development ...

200 years, recent assessments suggest there is ahigh to moderate potential to increase the carboncontent of soils across extensive areas of Australia(see Figure 1.1).Recent measures of soil organic matter (0-30 cm)in Australian soils suggest they can contain betweenthree tonnes of carbon per hectare (0.3 per centcarbon for desert loams) and 231 tonnes of carbonper hectare (14 per cent carbon for intensive dairysoils; see http://www.daff.gov.au/climatechange/australias-farming-future/climate-change-andproductivity-research/soil_carbonfor the report).For Australian dryland agricultural soils the organiccarbon content is more typically between 20-150tonnes carbon per hectare (or about 0.7-4.0 percent depending on soil bulk density).Quantifying existing soil organic carbon stocks inkey soil types under important farm managementregimes within some of Australia’s agriculturalregions was a key output of the Soil CarbonResearch Program (SCaRP), and has providedvaluable information to baseline soil organicmatter stocks across different environments(see Figure 1.2).Management and site factors interact to influencethe actual amount of soil organic matter in relationAustralian soils are low in soilorganic matter content by globalstandards, with the exception ofsoils that support high net primaryproductivity such as well-managedpastures and irrigated systemsunconstrained by water availability.to the attainable amount of soil organic matter (asdefined by climate and soil type). While there is astrong relationship between rainfall and the amountof soil organic carbon, regional data indicates thateven within a rainfall zone soil organic carbon canvary widely and the highest variability occurs in areasof high rainfall, which support increasing biomassproduction (Griffin et al. 2013). Such variabilityis likely due to a range of factors influencing netprimary productivity, including agronomic and soilmanagement as well as variations in soil type andmoisture – the influences of which are discussed inthis publication.7MANAGING SOIL ORGANIC MATTER: A PRACTICAL GUIDEFigure 1.1 Potential for soil organic matter gainresulting from a combination of effective rain(considering amount and availability) and residuepressure, which reflects plant and livestock removalsof organic matter (Baldock et al. 2009). Figure 1.2 Soil organic carbon (tonnes per hectare)stocks in surface layers (0-10 cm) for south westWestern Australia. Areas of low confidence (e.g.subsystems that only have one site) are maskedout in white. Lines constitute agricultural soil zones:grey is remnant vegetation (Griffin et al. 2013).