A new study finds that a nitrification inhibitor outperforms biochar in increasing crop yields and reducing nitrous oxide emissions in alkaline soils
A new study has found that a nitrification inhibitor outperforms biochar in improving fertiliser efficiency, increasing crop yields, and reducing nitrous oxide emissions in alkaline soils. Nitrous oxide is a powerful greenhouse gas. The findings highlight a practical approach to cutting agricultural emissions while maintaining high productivity.
Comparing biochar and nitrification inhibitors in alkaline soils
Farmers typically rely on nitrogen fertilisers to sustain crop production, but in many alkaline soils, a large proportion of that nitrogen is lost before plants can use it.
In this new study, the researchers compared the performance of biochar and the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) in calcareous soils. These soils have high pH levels that accelerate nitrogen transformations and losses.
“Our results show that DMPP was consistently more effective than biochar at stabilising nitrogen in calcareous soils,” said Tongbin Zhu, corresponding author of the study. “This translated directly into higher nitrogen use efficiency, greater crop yields, and much lower nitrous oxide emissions.”
Evaluating sustainable solutions for nitrogen management in agriculture
The researchers conducted two consecutive growing seasons of controlled-pot experiments with pak choi, a widely cultivated leafy vegetable. Eight fertiliser treatments were tested, including standard nitrogen, phosphorus, and potassium fertilisers; fertilisers combined with biochar at low and high application rates; DMPP alone; and combinations of biochar and DMPP.
Across both growing systems, DMPP increased crop nitrogen uptake by up to 49% and boosted yields by up to 49% compared with conventional fertilisation methods. Nitrogen use efficiency improved by up to 18%, and cumulative nitrous oxide emissions were reduced by 77-85%.
“Reducing nitrous oxide emissions while maintaining or increasing yields is one of the biggest challenges in sustainable agriculture,” Zhu said. “DMPP offers a practical solution for farmers working with alkaline soils.”
Why biochar fell short in calcareous soils
Biochar did not deliver the expected benefits in this experiment. While it increased microbial nitrogen immobilisation, it also accelerated nitrification. This led to reduced nitrogen use efficiency and stimulated nitrous oxide emissions, especially at higher application rates. Even when combined with DMPP, biochar did not enhance the inhibitor’s effectiveness.
To understand this variation, the researchers measured key nitrogen transformation processes in the soil. DMPP strongly suppressed the activity of ammonia-oxidising bacteria, reducing nitrification rates by more than 50% and prolonging nitrogen availability in forms that crops could access. This prolonged nitrogen residence time allowed plants to absorb more fertiliser nitrogen before it was lost to the environment.
“Biochar is often promoted as a universal soil amendment,” Zhu said. “Our findings show that its effects depend strongly on soil type and application rate. In calcareous soils, biochar alone may not be the best strategy for nitrogen efficiency.”
The authors emphasise that their results do not diminish the value of biochar in other soil systems. Instead, they underline the importance of precision nitrogen management strategies tailored to specific soils.
“Choosing the right nitrogen management approach is critical for food security and climate mitigation,” Zhu said. “For calcareous soils, nitrification inhibitors like DMPP provide a more reliable path to sustainable crop production.”
