In this paired site comparison, parent material, slope, aspect, rainfall and farming enterprise are the same. Levels of soil carbon in both paddocks were originally the same.
On the Left Hand Side (LHS) is a 0-50 cm soil profile from a paddock in which groundcover has been actively managed (cropped and grazed) to enhance photosynthetic capacity.
On the Right Hand Side (RHS) is a 0-50 cm soil profile from a conventionally managed neighboring paddock (10 meters through the fence) that has been continuously grazed and has a long history of phosphate application.
The carbon levels in the 0-10 cm increment are very similar. This surface carbon results from the decomposition of organic matter (leaves, roots, manure etc), forming short-chain unstable ‘labile’ carbon.
The carbon below 30 cm in the LHS profile has been sequestered via the liquid carbon pathway and rapidly incorporated into the humic (non-labile) soil fraction. Non-labile carbon is highly stable.
On the LHS, 50 centimeters of well-structured, fertile, carbon-rich topsoil have formed as a result of the activation of the ‘sequestration pathway’ through cropping and grazing management practices designed to maximize photosynthetic capacity. Superphosphate has not been applied to the LHS paddock for over thirty years. In the last 10 years the LHS soil has sequestered 168.5 t/ha of CO2. The sequestration rate in the last two years (2008-2010) has been 33 tonnes of CO2 per hectare per year.
Due to increased levels of soil carbon and the accompanying increases in soil fertility, the LHS paddock now carries twice the number of livestock as the RHS paddock.
Levels of both total and available plant nutrients, minerals and trace elements have dramatically improved in the LHS soil, due to solubilization of the mineral fraction by microbes energized by increased levels of liquid carbon. In this positive feedback loop, sequestration enhances mineralization, which in turn enhances humification.
As a result, the rate of polymerization has also increased, resulting in 78% of the newly sequestered carbon being non-labile. The stable, long-chain, high-molecular weight humic substances formed via the plant-microbe sequestration pathway cannot ‘disappear in a drought’. Indeed, the humus now present in the LHS profile was formed against the backdrop of 13 years of below-average rainfall in eastern Australia.
A major cause of soil dysfunction, as illustrated in the RHS soil profile, is the removal of perennial groundcover for cropping and/or a reduction in the photosynthetic capacity of groundcover due to continuous grazing. In the post-war era, a range of chemical fertilizers have been applied to soils in an attempt to mask reduced soil function, but this approach has merely accelerated the process of soil carbon loss, particularly at depth. The net effect of inappropriate management practices has been compromised landscape function, losses of biodiversity, markedly reduced mineral levels in plants and animals and an increase in the incidence of metabolic diseases. This will no longer do.
Australia is not the only country in which subsoils – and hence landscape function – have deteriorated as a result of inappropriate land management and fertilizer practices. In New Zealand, a country blessed with vast tracts of inherently fertile topsoil, carbon losses are occurring at depth under heavily fertilized pastures, due to the inhibition of the sequestration pathway. To date, alternative management practices have been either dismissed or ignored by establishment science in that country.
It is important to note that the rapid improvements to soil fertility and soil function recorded in the LHS soil profile are dependant on the enhanced photosynthetic capacity that accompanies regenerative forms of cropping and grazing management.
