In agricultural systems, low phosphorus-use efficiency and high soil phosphorus fixation significantly limit crop yields and ecological sustainability, posing a serious threat to food security. Modified biochar technology is regarded as a promising strategy for soil remediation. However, the relationship between soil phosphorus fractions and greenhouse gas emissions under modified biochar application are less studied.

In a study published in Global Change Biology–Bioenergy, researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences and their collaborators investigated the effects of applying pristine biochar (BC) and magnesium-modified biochar (Mg-BC) at two rates (1% and 2.5% by weight) to degraded red and black soils. They found that both biochar types improved overall soil physicochemical properties and enhanced enzyme activities, with Mg-BC showing more pronounced benefits.

Researchers found that biochar application, particularly Mg-BC, significantly altered soil phosphorus composition. It increased the pool of labile phosphorus, while reducing the more stable, moderately labile, and residual phosphorus fractions. The magnesium in Mg-BC interacted with soil elements such as calcium, iron, and aluminum, thereby promoting greater phosphorus availability in the soil solution.

Moreover, researchers revealed that biochar application had a complex influence on greenhouse gas emissions. It increased carbon dioxide emissions by 8% to 138% but reduced nitrous oxide emissions by 11% to 44%. Further analysis revealed that Mg-BC, by regulating soil pH and improving nutrient availability and enzyme activity, simultaneously enhanced phosphorus availability and lowered nitrous oxide emissions in degraded acidic soils.

Structural equation modeling showed that biochar type and dosage had only a minor direct effect on carbon dioxide, but they strongly suppressed nitrous oxide emissions, accounting for 82% to 89% of the observed reduction.

“Our results showed that biochar application, especially magnesium-modified biochar, can mitigate potent nitrous oxide emissions by improving soil pH, nutrient status, and microbial activity in degraded soils. This modified biochar not only boosts the availability of essential nutrients such as phosphorus, but also helps reduce greenhouse gas emissions,” said LIU Wenjie from XTBG, one corresponding author of the study.