Simpler Soil Test Could Improve Tracking of a Vital, Limited Nutrient

Scientists have developed a simpler, cheaper way to measure a biologically important form of phosphorus in soil, offering a clearer view of how nutrients move through farmland and helping to guide more sustainable farming practices. Phosphorus is essential for plant growth and food production, but the natural sources used to make phosphorus fertilizers are limited, making it important to understand how the nutrient is stored in soil and how it becomes available to crops.

In a study published in the Journal of Agricultural and Marine Sciences, an international team including scientists from Sultan Qaboos University, the James Hutton Institute and the Environment Authority of Oman improved a laboratory method for measuring DNA-bound phosphorus (DNA-P), a small part of soil's organic phosphorus that is linked to living microorganisms. The team tested the refined method on 32 soil types from across the United Kingdom.

The researchers found that enzyme treatments used in the earlier method were not needed, cutting both cost and complexity, while an ultrafiltration step remained necessary to accurately separate DNA-bound phosphorus from other phosphorus-containing compounds. DNA-bound phosphorus made up only a small share of total organic phosphorus in the soils tested, but its levels were strongly linked to soil pH, microbial biomass phosphorus, organic matter and phosphorus dissolved in soil water.

Those links suggest DNA-bound phosphorus is tied closely to living soil microorganisms rather than to phosphorus held in more stable, long-term reserves. The researchers say the improved method gives scientists a better tool to study biologically active phosphorus in soil and to examine how soil microbes help make nutrients available to plants, which could support future work on soil fertility and nutrient management.