The Conventional Problem: Inefficiency and Lock-Up

When we apply phosphorus in its water-soluble form (such as superphosphate), only about 10–15% of the phosphorus is taken up by plants. The remaining 85–90% becomes “locked up” in the soil:

• Chemical Lock-Up: In acidic soils, phosphorus reacts with aluminum, iron, and manganese; in basic soils (pH >7), it reacts with calcium. These reactions make phosphorus unavailable to plants.
• Erosion Losses: Australian soils, for example, lose an estimated 5½ tonnes of top soil per hectare each year to erosion. For a soil with 10mg/kg of available P, this makes an estimated to lose of about 2.7kg/ha of total P. This is the equivalent of 30.6kg/ha of super or a $20/ha lose each year.  This not only depletes soil fertility but also contributes to waterway pollution.

Because phosphorus barely moves in soil, much of it remains inaccessible. This leads many farmers to believe they must continually apply more phosphorus—further fueling a cycle of inefficiency and environmental harm.

The Biological Side: Harnessing Nature’s Own Phosphorus Cycle

Dr. Christine Jones’s work introduces a new way of thinking about phosphorus: instead of relying solely on chemical inputs, we can use biological methods to unlock the phosphorus already present in our soils. Two key biological pathways are involved:

1. Symbiotic Relationships with Mycorrhizal Fungi

• Extended Root Reach: When mycorrhizal fungi colonize plant roots, they effectively extend the root zone by up to 45 centimeters. This expanded network can access phosphorus from a greater volume of soil.
• Enzyme Production: These fungi release enzymes called phosphatases, which help solubilize phosphorus that is otherwise locked up. They also secrete organic acids to improve phosphorus solubility.
• Enhanced Nutrient Uptake: With the fungi’s help, plants receive phosphorus in a more readily available form, often as amino acids. This bypasses the energy-intensive process of converting inorganic forms like nitrate or ammonium into useful organic compounds.

2. Phosphorus-Solubilizing Bacteria

• Feeding on Root Exudates: Plants continuously exude sugars (or “liquid carbon”) from their roots. This provides energy to phosphorus-solubilizing bacteria that live near or on the roots.
• Microbial Partnerships: Not only do these bacteria fix phosphorus, but they also stimulate biological nitrogen fixation. This link between the phosphorus and nitrogen cycles is crucial for overall soil building.
• Maintaining a Healthy Microbial Community: When water-soluble phosphorus fertilizers are applied in excess, the resulting phosphoric acid can “burn” soil microbes. This discourages the formation of beneficial microbial structures—like the protective “dreadlock” rhizosheaths around roots—thus reducing natural phosphorus solubilization.