Soil’s carbon power relies on topsoil retention (and maybe a little bacterial boost)

Topsoil critical for carbon trappings

An almost 2-decade experiment in New South Wales has revealed the vital role of agricultural topsoil in carbon storage.

Published today in the journal Crop & Pasture Science, the research investigated four agricultural topsoil forms to determine how land management could influence its ability to store carbon.

1.2m soil layers were sampled annually for 18 years, measured for carbon and nitrogen and then analysed throughout the experiment. By analysing concentrations of these two elements across a substantial soil extent, the research group from the NSW Department of Primary Industries was able to compare where within the layers carbon tended to accumulate.

Both carbon and nitrogen were found within the first 30cm – or topsoil layer – which highlights the importance of managing land to retain topsoil and prevent erosion over time.

“In an environment where plant production is limited by rainfall, pastures are a viable means of increasing soil organic carbon,” the authors write.

“Attempts on carbon sequestration on … soils in this environment must include practices that minimise loss of topsoil.”

Bacteria can eat up potent greenhouse gas

Norwegian researchers have trialled using bacteria-enriched fertilisers to consume agricultural nitrous oxide (N₂O) emissions

In experiments published in the journal Nature Bacteria of the genus Cloacibacterium were found to reduce nitrous oxide emissions by between 50-90% across several soil types. 

As a key greenhouse gas, N₂O is emitted during agricultural and land modification practices and is a key byproduct of synthetic fertiliser manufacture.

A mixture of a Cloacibacterium strain called CB-01 was chosen for its ability to quickly grow and survive in soil and multiplied on a bed of organic waste from biogas production. Over 100 days of investigation, the quantity of CB-01 specimens remained high while consuming N₂O emissions. The researchers then applied their findings to all European emissions from these environments, finding a 2.7% average decrease in emissions was possible in CB-01 strains that contain enzymes that reduce N₂O to nitrogen gas. Applying this process to all mineral and natural fertilisers, it could be possible to reduce European N₂O emissions by 25%, they suggest.

In a separate comment, University of Tennessee microbial ecologist Frank Löffler and biosystems engineer Guang He, who were not involved in the study, writes “at the root of increasing N₂O emissions lies one of the greatest inventions of the 20^th century: the Haber–Bosch chemical process, which enables the large-scale production of synthetic nitrogen-containing fertilisers”.

“Given the factors that might influence performance of the bioaugmentation approach [as delivered by the CB-01 experiment], a suite of N₂O-reducing microorganisms adapted to various environmental conditions and fertilisers will be needed to achieve effective and cost-efficient soil inoculation on a large scale.”