Cover cropping can increase farming yields

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Red clover as a cover crop is lush between rows of grapevines with new sprouts in spring in an Oregon vineyard. Cover crops can increase soil organic carbon as well as crop yields, according to new LLNL research. Image by Adobe stock.

Cropland management practices that restore soil organic carbon (SOC) are often looked at as climate solutions that also enhance yields. But how often these benefits align at the farm level — the scale of farmers’ decision-making — remains unclear.

In a new study in Nature Sustainability, a Lawrence Livermore National Laboratory (LLNL) scientist and collaborators examined concurrent SOC and yield responses to cover cropping, including their direct connection. They found that cover cropping simultaneously increased yields and SOC in 59.7% of 434 observations. Cover cropping, grown on fallow soils otherwise left bare, increases organic matter inputs to the soil in the form of crop detritus and root fluids such as sap, gum and resin that has various benefits to plants.

“By increasing yields and soil organic carbon all at once, targeting cover crops on low-carbon soils is an opportunity to benefit both food security and climate,” the study authors said.

Despite the various benefits that SOC is thought to provide, agricultural expansion and intensification have dramatically depleted SOC across the world. Practices that sequester SOC when soil carbon inputs are greater than outputs have gained increased attention for their potential to restore soil functionality while simultaneously drawing down atmospheric carbon dioxide.

Whether farmers will voluntarily adopt carbon sequestering practices depends upon more than just their potential to mitigate climate change or restore soil health. How a practice influences crop productivity and farm profitability is central to farmers’ management decisions.

Recent meta-analyses and remote sensing studies show that cover cropping variably affects crop yields, with estimates ranging from increases of 6% to 33% depending on cash crop type, cover crop type, fertilizer additions and other factors like aridity, to small yield decreases.

The team, which includes LLNL scientist Allegra Mayer, based its study on how often cover cropping simultaneously increases SOC and yields (co-benefits) at the same location, increases or decreases one but not the other (trade-offs), or even decreases both SOC and yields (co-costs). Cover cropping is considered one of the most promising approaches to increase SOC in agricultural soils, in part because it increases net primary productivity relative to a bare fallow, and carbon inputs to soil.

“Understanding the potential for co-benefits will help inform decision-making at the farm level and will help identify areas of overlap between benefits for farms and society,” the authors said.

The analysis unveiled that increases in SOC helped increase crop yields in soils with initial SOC concentrations below 11.6 grams per kilogram (g/kg); for example, a change from 5 g/kg to 6 g/kg increased yields by 2.4%. These yield benefits of SOC did not decline as nitrogen inputs increased or when legume cover crops were used, suggesting fertility inputs cannot substitute for SOC effects. Integrating legume cover crops into systems with simplified farming rotations or with nitrogen inputs led to the largest yield increases (up to 24.3%), with legumes also increasing SOC more than non-legumes.

The new meta-analysis of 92 experiments spanning five continents, unveiled that cover crops increased crop yields concurrently with SOC in 59.7% of 434 paired observations — providing co-benefits for farmers and society a majority of the time.

“By building comprehensive models to identify and quantify important predictors of yield and SOC changes from cover cropping, our study not only helps identify farming systems most likely to see co-benefits from cover cropping, but also informs policymakers seeking to quantify the impact of cropland carbon sequestration on global food production capacity,” the authors said.

Other institutions in the study include the University of California, Berkeley and University of Oregon.