Nov. 23, 2015

Scientists urge new soil-carbon model for climate change era

In the fight to protect the environment, achieve food security and promote sustainable development, agricultural scientists who recognize soil’s key role in the global carbon cycle are advocating for new and improved research models that accurately forecast climate change.

“Soil is more than dirt under your feet,” said Johannes Lehmann, Cornell professor of soil sciences.
Nutrient, energy and carbon exchanges between soil organic matter, the soil environment, aquatic systems and the atmosphere are an engine that drives agricultural productivity, water quality and climate, he said.

“Soil organic matter makes up and absorbs more carbon than the world’s vegetation and the atmosphere combined,” said Lehmann. “So small changes in the soil carbon content have huge impacts on the climate.”

 

Lehmann and Markus Kleber, of Oregon State University, have published “The Contentious Nature of Soil Organic Matter” in Nature, Nov. 23, as part of a scientific package on soil importance. For the Food and Agriculture Organization of the United Nations, 2015 has been the year of the soils. World Soils Day is Dec. 5.

Another Cornell paper, “The Reinforcing Feedback Between Low Soil Fertility and Chronic Poverty,” written by Christopher Barrett, professor and director of Cornell’s Charles H. Dyson School of Applied Economics and Management, and Leah E.M. Bevis
, doctoral candidate, appears concurrently in the journal Nature GeoScience.

In the recent past, scientific dogma stated that large humic substances are produced from decaying leaves, grass and plant matter, but emerging understanding of soil organic matter goes a step further and accounts for underlying microbial processes. Lehmann and Kleber suggest these new concepts – such as the “soil continuum model” – could assist today’s scientists by accurately accounting for soil carbon, thus helping to forecast climate change and warming temperatures.

Organic matter retains nutrients as well as pollutants in the soil, which improves plant growth and protects water quality, said Lehmann and Kleber. Soils are an important source of aquatic carbon, with implications for biogeochemical processes in rivers, lakes and estuaries, they said.

Over the years science has built an erroneous model on how plant material is broken down and recombined into large humic substances, Lehmann said. “This understanding could not be confirmed by modern analytical tools. In the last 10 years, soil scientists have clearly shown that humic substances and large complex molecules are not formed in soil.”

“We need to be able to predict the behavior of soil carbon in a warming world,” Lehmann said. “That’s only possible if we have the right kind of model and we can mathematically predict what could happen in 50 or 100 years from now.”