Biochar curbs phosphorus runoff from fertilized agricultural lands

The Persistent Problem of Phosphorus Loss

Organic fertilizers like manure and biogas slurry are widely used to enrich agricultural soils, but their long-term application can lead to an excess of nutrients like phosphorus. When this phosphorus washes away from fields, it can pollute rivers and lakes, causing harmful algal blooms. A new study from researchers at Zhejiang University and collaborating institutions examines how different organic soil amendments affect the movement of phosphorus, identifying a promising tool for more sustainable agriculture. The investigation shows that tiny, mobile particles known as colloids are major carriers of phosphorus from these soils.

Tracking Tiny Phosphorus Carriers

The research team focused on water-dispersible colloidal phosphorus, or Pcoll, which consists of minuscule particles between 1 and 450 nanometers in size. Due to their small size and surface charge, these colloids remain suspended in soil water and are easily transported into adjacent water bodies during rain or irrigation events. The study found that these phosphorus-carrying particles accounted for an average of 74 percent of the total dissolved phosphorus in the soil solutions tested, confirming their importance in nutrient loss from farmland.

A Real-World Soil Investigation

To understand the effects of different farming practices, a team led by Kamel Mohamed Eltohamy and Xinqiang Liang collected soil from 12 field sites across China's Zhejiang Province. These sites had long-term histories of amendment with one of three common organic materials: manure, biogas slurry, or biochar. By analyzing these real-world samples, the scientists could assess how each amendment influenced the amount and type of colloidal phosphorus released from the soil.

Biochar Shows a Clear Advantage

The results showed a distinct difference among the amendments. Soils treated with manure or biogas slurry alone contained high concentrations of mobile colloidal phosphorus, indicating a greater risk of nutrient runoff. In contrast, soils where biochar was applied, either alone or with other fertilizers, had significantly lower levels of mobile phosphorus. This suggests that biochar is effective at keeping the nutrient within the soil, where it is available for crops rather than becoming a pollutant.

How Biochar Traps Phosphorus

The study points to two primary mechanisms for biochar's effectiveness. First, its porous structure and large surface area allow it to directly absorb phosphorus-carrying colloids from the soil solution. Second, biochar improves soil aggregation, creating a more stable soil structure that physically traps the colloids and prevents them from being washed away. This dual action makes biochar a potent agent for reducing phosphorus mobility in agricultural systems.

The Chemistry of Colloidal Phosphorus

A deeper compositional analysis revealed that the makeup of phosphorus-carrying colloids changes with their size. The smallest nano-sized colloids were mainly composed of organic carbon-calcium complexes. Medium-sized colloids, however, were more associated with organic matter complexed with manganese, iron, and aluminum. The fine-sized fraction showed a mix of both types. According to Paul J. Milham of the Hawkesbury Institute for the Environment, understanding these chemical associations is necessary for developing targeted strategies to manage phosphorus in different soil environments.

Toward Smarter Agricultural Practices

This work provides clear evidence that the choice of organic amendment has a substantial impact on phosphorus retention in soil. The findings support the use of biochar as an effective amendment to reduce the environmental risk associated with phosphorus loss from agricultural lands. By incorporating biochar into fertilization strategies, farmers can help maintain soil fertility and crop productivity while safeguarding the health of local water ecosystems. The research offers valuable information for developing future agronomic and environmental policies.

Corresponding Author:

Ye Ye or Xinqiang Liang

Original Source:

https://doi.org/10.1007/s44246-023-00048-2

Contributions:

Kamel Mohamed Eltohamy: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Data Curation, Writing- Original draft, Visualization, Writing—Review & Editing. Paul J. Milham: Investigation, Writing—Review & Editing. Mostafa Gouda: Writing—Review & Editing. Daniel Menezes-Blackburn: Writing—Review & Editing. Sangar Khan: Writing—Review & Editing. Liu Boyi: Writing—Review & Editing. Jin Junwei: Writing—Review & Editing. Xinqiang Liang: Supervision, Project administration, Funding acquisition. The authors read and approved the final manuscript.