Selecting legumes as cover crops could help growers boost productivity, improve soil health and sequester more carbon in their soils compared to other cover crop varieties.
Research carried out in China revealed legume cover crops increased soil organic carbon (SOC) by 38% compared to just 16% for non-legumes, while non-legume crops like ryegrass actually slowed carbon accumulation.
And with legume crops such as hair vetch also shown to boost soil microbial activity, the findings could have significant implications for producers aiming to improve soil health and carbon retention, say researchers.
In a study conducted across three orchards in China, researchers used advanced methods, including SOC fractionation and high-throughput sequencing, to identify how cover crops influence SOC composition and microbial activity.
They found that legumes enhanced both soil nutrients and microbial diversity, which in turn enrich SOC.
“Legume cover crops increased both particulate organic carbon and mineral-associated organic carbon, key components of stable soil organic carbon,” they wrote in a study published in the journal Geoderma.
Particulate organic carbon consists of decomposable plant materials, while mineral-associated organic carbon binds with soil minerals for longer-lasting carbon storage. This added stability in soil carbon storage not only enhances soil structure but also slows carbon release into the atmosphere, providing a climate benefit, they said.
Specifically, the study reported increases in dissolved organic carbon (DOC) by 84%, ammonium nitrogen by 42%, and microbial biomass carbon by 105%, which collectively created conditions conducive to SOC formation.
In contrast, non-legume cover crops, like ryegrass, presented challenges.
Their high nitrogen demand led to ‘microbial nitrogen starvation’, which decreased microbial efficiency in processing SOC, thereby slowing carbon accumulation.
The report’s authors said this nitrogen limitation created a ‘negative priming effect’, which can accelerate the decomposition of existing SOC, effectively counteracting new carbon sequestration.
The findings also emphasised the importance of site-specific factors like soil texture and nitrogen availability in SOC outcomes.
For instance, the study said that clay-rich soils had higher SOC accumulation due to their ability to hold onto dissolved organic matter. This suggests that tailoring cover crop strategies to local soil conditions can further enhance SOC retention in orchards.
