Modern agriculture faces a dual challenge. First, the widespread use of plastic films, like low-density polyethylene (LDPE), has led to significant soil contamination with microplastics (MPs). Second, vast regions of farmland consist of alkaline soils, where phosphorus—a nutrient essential for plant growth—is often “locked up” and unavailable to crops. These two problems compound one another, as MPs can further disrupt the soil’s nutrient dynamics and threaten crop productivity. This is especially bad news for vital, phosphorus-demanding crops like soybeans. A new study by Min Sun and colleagues, published in Ecotoxicology and Environmental Safety, investigates a powerful synergistic solution: combining biochar with phosphate fertilizer to heal the soil and boost yields.

Biochar is known for its ability to improve soil health, retain nutrients, and support microbial life. The researchers hypothesized that integrating biochar with phosphate fertilizer could overcome the combined stresses of MP pollution and low phosphorus bioavailability. To test this, they conducted a pot experiment using alkaline soil, deliberately contaminated it with 1% LDPE microplastics, and then applied 2% biochar along with various levels of phosphate (P) fertilizer. They then planted soybeans and tracked their growth, nutrient uptake, and the soil’s microbial community .

The results revealed a distinct “sweet spot” for this combination. Applying phosphate fertilizer alone, even at high doses, provided no significant increase in soybean biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More or yield in the contaminated soil. However, the synergy between biochar and moderate levels of fertilizer (specifically 60 kg P ha−1 and 90 kg P ha−1) produced dramatic results. Compared to the equivalent fertilizer-only treatments, the biochar-plus-moderate-P groups saw soybean yields skyrocket by 74.38% (B-P60) and 84.16% (B-P90). This was supported by massive gains in total plant biomass, which increased by 40.73% and 42.58%, respectively. The plants were not just bigger; they were also better fed. Total phosphorus uptake by the soybeans increased by 58.19% in the B-P60 group, showing the treatment was successfully unlocking the vital nutrient from the soil.

The study found this remarkable success was not just a simple chemical fix; it was a biological overhaul. The biochar application fundamentally “reshaped” the soil’s fungal community structure. Most importantly, it significantly increased the abundance of key fungal genera, including Aspergillus and Fusarium. These fungi are not pests; in this context, they are powerful allies. They are known to be “phosphorus-solubilizers”—they release organic acids that dissolve mineral-bound phosphorus, effectively “unlocking” it and making it available for the soybean roots to absorb. As an added benefit, some of these same fungal species, Aspergillus and Fusarium, are also known to be capable of degrading polyethylene, helping to mitigate the microplastic pollution itself.

This transformation was most profound in the rhizosphere—the critical, narrow band of soil immediately surrounding the plant roots. The biochar addition made the fungal network in the rhizosphere more complex and competitive. This “rhizosphere effect” was the key mechanism driving the higher yields. The study’s modeling confirmed that changes in the rhizosphere (like a 130-135% increase in available phosphorus) directly promoted the plant’s nutrient uptake, which in turn boosted the final soybean yield. By fostering a healthier, more active microbial community, the biochar-fertilizer combo created a highly efficient nutrient-cycling system right where the plant needed it most.

In conclusion, this research provides a clear, actionable strategy for farmers facing the dual crises of microplastic contamination and nutrient-poor alkaline soils. It demonstrates that simply dumping more fertilizer is not the answer. Instead, a sustainable solution lies in using biochar as a synergistic tool to stimulate beneficial soil fungi. This approach activates the soil’s own biology to unlock nutrients, mitigate pollution, and ultimately produce a significantly larger harvest.

Source : Sun, M., Li, X.-Y., Yuan, H.-Y., Zhuang, Q.-L., Deng, H.-G., Tao, B.-X., & Zhang, B.-H. (2025). Synergistic effects of biochar and phosphate fertilizer on fungal communities and soybean productivity in microplastic-contaminated alkaline soils. Ecotoxicology and Environmental Safety, 306, 119287.