Carbon Sequestration: Finding the Best Organic Management Practice

Organic standards require practices that boost soil health and performance – in physical structure, as well as chemical and biological make-up. Carbon sequestration has been an important tool in the fight against climate change, and by improving soil health, farmers contribute to the reduction of carbon dioxide in the atmosphere. 

Now, recent research led by the University of Maryland in conjunction with The Organic Center delves further into the unique ways that organic farmers can improve their climate-fighting capabilities, quantifying how specific soil management techniques can optimize carbon sequestration.

The recent study, Soil organic carbon is affected by organic amendments, conservation tillage, and cover cropping in organic farming systems: A meta-analysis, looks at which organic best management practices have the largest impact on carbon sequestration in organic systems. Robert Crystal-Ornelas, Resham Thapam, and Katherine L.Tully conducted the study and looked at four widely promoted best management practices (BMPs), including crop rotation, cover crops, reduced tillage, organic soil amendments, and their impact on soil organic carbon in farming systems. The study focused on 2 soil health indicators: organic matter and microbial biomass. 

The research screened through 6,392 articles looking at how each best management practise affects soil organic carbon or microbial biomass. The results were filtered to include articles on organic farming, the use of soil health metrics, treatment involving a best management practice, and eliminated duplicated articles. However, the study did not look at the combined results of multiple BMPs being used concurrently. There were 33 articles found on soil organic carbon and 7 on microbial biomass used for the meta-analysis. 

The research showed that BMPs on average lead to an increase in Soil Organic Carbon (SOC) of 18% and Microbial Biomass (MBC) of 30%. It also showed BMPs (like cover crops) demonstrated benefits that were seen only in the long term after 4-5 years, and in shallower depths. On the other hand other BMPs, like adding organic amendments and conservation tillage, showed significant benefits in both the short and long term at all depths. 

Each Best Management Practice vs. Amount of Soil Organic Carbon

(Figure 1) The graph shows how much soil organic carbon increased (ln (Response ratio)) in relation to how each best management practices based on sample size (how many studies covered the BMP). The vertical line represents the line of no effect, meaning that any lines that cross it indicate that the best management practice did not have a significant effect on soil organic carbon. The results show that soil organic carbon increased with organic amendments and conservation tillage, but cover crops did not have a significant impact because it crossed the line of no effect. 

Although all three of these practices mentioned increase carbon sequestration, the study discovered that using organic soil amendments had the greatest effect in the shortest amount of time (based on the 24% increase in SOC and its consistent increase over 30+ years on organic farms shown) suggesting its use is the most effective at improving soil quality and building resilience in the face of climate change.

To read further details on the study:

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