Processed crop residue helps lower greenhouse gas emissions in nitrogen-fertilized soils
Returning crop straw to farmland is a common practice that helps recycle nutrients, improve soil quality, and reduce waste. However, new research suggests that the way straw is processed before being returned to the field can greatly influence its environmental benefits.
Research conducted by scientists at Shandong Agricultural University, China, led by corresponding author Yuping Zhuge, examining the impact of different straw-return methods on nitrous oxide emissions in saline-alkali soils.
Scientists studied different straw management methods in nitrogen-fertilized saline-alkali soils and discovered that pelletized straw was the most effective at reducing nitrous oxide (N₂O) emissions. Nitrous oxide is a powerful greenhouse gas that contributes to climate change and is commonly produced in agricultural soils.
“Our results suggest that straw return should not be treated as a single management practice,” said Zhuge. “The physical form and processing pathway of straw can alter microbial nitrogen cycling, which in turn affects how much nitrous oxide is released from soil.”
The study examined how different forms of straw affected emissions when applied to soils receiving nitrogen fertilizer. Researchers compared four straw-based treatments: crushed straw, pelletized straw, composted cattle manure produced from straw-fed livestock, and biochar made from carbonized straw. A soil treatment without straw was also included for comparison.
The research was carried out using soil collected from a saline-alkali land improvement site in Shandong Province, China. These soils often have high salt levels, high pH values, and low organic carbon content, making crop production more challenging. Farmers commonly apply nitrogen fertilizer to maintain productivity, but this practice can increase greenhouse gas emissions.
Researchers tested two fertilizer rates equivalent to 120 kilograms and 240 kilograms of nitrogen per hectare during a 90-day incubation period. Results showed that increasing nitrogen fertilizer rates raised cumulative N₂O emissions by an average of 41.6%.
Despite the increase caused by fertilizer, all straw treatments helped reduce emissions compared with soils that received no straw. Pelletized straw delivered the strongest results. Under lower nitrogen levels, it reduced cumulative N₂O emissions by 45.7%. Under higher nitrogen input, emissions were reduced by 43.2%.
The study also found that straw applications changed the timing of nitrous oxide release. In untreated soils, emissions peaked around day 30. In soils receiving straw products, the emission peak occurred later, around day 60. This delay may influence how nitrogen moves through the soil and becomes available to crops and soil microorganisms.
Researchers investigated soil microbial communities to better understand these results. They focused on microorganisms involved in nitrogen cycling, which play an important role in generating nitrous oxide emissions.
One key finding involved ammonia-oxidizing bacteria (AOB), which are responsible for the early stages of nitrogen transformation in soil. The abundance of the AOB amoA gene showed a strong relationship with cumulative N₂O emissions. Straw treatments generally lowered the abundance of this gene, helping reduce greenhouse gas production.
The composition of the microbial community also shifted with straw additions. The abundance of Nitrosovibrio bacteria increased, while Nitrosospira populations declined. These changes indicate that straw management influences both the number and types of microorganisms involved in soil nitrogen cycling.
Among all treatments, pelletized straws created the most favorable conditions for reducing emissions linked to ammonia-oxidizing bacteria. Researchers suggest that processing straw into pellets may improve how carbon and nutrients are released into the soil, helping regulate microbial activity more effectively than other forms of straw.
The findings highlight an important lesson for farmers and agricultural decision-makers. Returning straw to fields should not be viewed as a single practice. Different processing methods can lead to very different environmental outcomes.
As agriculture continues to look for ways to reduce greenhouse gas emissions while maintaining productive soils, pelletized straws may offer a practical solution. It combines nutrient recycling with improved environmental performance and could become an important tool in sustainable farming systems.
Researchers noted that future field studies will be needed to confirm these results under real farming conditions. Nevertheless, the study provides strong evidence that pelletized straws can play a meaningful role in reducing agricultural greenhouse gas emissions while supporting long-term soil health.
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