Sorption materials for phosphorus reduction in drained agricultural fields: Gaps between the results from laboratory evaluation and field application

Phosphorus (P) losses from drained agricultural fields are a major cause of eutrophication. In this study, we evaluated the performance of three types of phosphorus sorbing materials (PSMs), including P polymer sorbent pellets, designer biochar pellets, and iron shavings materials, in removing dissolved P at both laboratory and field scales. The laboratory experiments revealed the following order of P removal efficiency with initial P concentrations of 1 mg L⁻¹ and 50 mg L⁻¹: designer biochar > P polymer sorbent > iron shavings. Based on the laboratory results, the designer biochar and P polymer sorbent were considered promising PSMs, especially the designer biochar achieved excellent P removal efficiency (>90%). On the contrary, subsequent field-scale applications demonstrated another story. Field results indicated that the designer biochar pellets could reduce up to 37% dissolved P from the drainage systems during a three-month period. Unfortunately, we encountered difficulties gathering data regarding the efficacy of P polymer sorbent pellets for P removal since the pellets disintegrating into small particles and being partially washed out through the drainage pipes. This failure case shows the importance of long-term field-scale validation monitoring and improving the toughness of materials under complex changes. Overall, our study has shown the discrepancy between laboratory and field evaluation, highlighting the critical needs to refine the laboratory evaluation methods and narrow the gaps between laboratory -scale research and field-scale application.