Stubble Guideline 4: Stubble and soil carbon

LEARN ABOUT SOIL CARBON AND NUTRIENT CYCLING IN STUBBLE RETAINED SYSTEMS

Guideline #4

Retained stubble systems are commonly regarded as beneficial for the accumulation of organic matter and soil carbon in soils, however increasing the amount of total soil carbon in cropping systems is notoriously difficult to achieve.

Stubbles are generally rich in carbon but low in other nutrients, and this stubble management guideline describes the interactions between stubble and soil organic carbon, as well as ways to enhance nutrient cycling in no-till stubble retained systems.

What we discovered

This guideline addresses key learnings from our work on the Stubble project, as well as the Soil Carbon project.

Key messages include that:

• Stubble is mainly comprised of carbon, with smaller amounts of other nutrients such as nitrogen, phosphorus and sulphur. 
• Soil carbon is the main component of soil organic matter. 
• Conversion of carbon in stubble to soil carbon by microbes requires water and nutrients.
• Climate, soil moisture and soil type affect the rate of stubble breakdown and the build-up of soil organic matter.
•  There were no differences in soil carbon across burnt, standing, mulched or disced stubble treatments during a three-year trial conducted in the Riverine Plains region, even when post-harvest applications of fertiliser were made to support microbial activity.
• Greenhouse gas emissions may be increased by the application of nutrients to feed microbes.
• Soil carbon builds slowly in cropping systems and can be difficult to measure.

Learn more about how stubble interacts with microbial soil populations and organic carbon.