De Sangosse has launched a Phosphate Stewardship Guide. Developed in collaboration with ADAS, the guide brings together research, field data and practical agronomy to address what is widely regarded as a challenge across UK cropping systems.
“The limiting factor is not supply, it is availability,” says De Sangosse commercial technical manager Rob Suckling. “We know when phosphate is applied to most soils, it is very quickly fixed into a biologically unavailable form limiting uptake and efficiency.”
Of all the macronutrients, phosphate is considered the most immobile. “Increasingly, it is being recognised that it isn’t insufficient phosphate in soils; it’s the ability of plants to access it. Phosphate is very immobile in soils, so unless it is placed close to the root structure, it can’t be taken up.”
When soluble phosphate fertilisers are applied to soil, a process known as ‘fixation’ can occur. It dissolves as an anion, forming insoluble, solid compounds. In calcareous (alkaline) soils, phosphate is fixed by calcium cations (Ca²+). In acidic soils, phosphate is fixed by cations of iron (Fe³+) and aluminium (Al³+).
“As soon as phosphorus is applied, it begins interacting with soil components,” Rob said. “Availability can decline quickly, particularly where conditions aren’t ideal such as dry, cool soils. At the same time, early root systems are relatively small, which limits the crop’s ability to access the nutrient at a critical stage of development.”
Rob points to data from the ADAS Yield Enhancement Network (YEN), which highlights the scale of the issue. Analysis of more than 600 cereal crops shows significant variation in grain phosphorus content, even across the same soil indices – indicating that soil phosphorus level alone does not determine crop uptake.
“Phosphorus availability is a common constraint preventing crops reaching their yield potential,” says Dr Christina Baxter, Senior Research Scientist at ADAS. “In many cases, soils already contain sufficient reserves, but only a very small proportion is available to the plant at any one time. Improving access to that nutrient is fundamental to improving performance.”
The YEN data demonstrates just how variable phosphorus uptake can be, notes Christina. On average, only around 10–20% of applied phosphate is taken up by the crop in the year of application. The remainder becomes fixed to soil particles or stored in unavailable inorganic or organic pools, contributing to inconsistent crop response and the gradual accumulation of ‘legacy’ phosphorus.
Which is why the guide highlights the importance of soil condition and biological processes in contributing to phosphorus availability. Soil structure, root development and microbial activity all influence the crop’s ability to explore the soil and access nutrients. “If root systems are well developed and the soil biology is functioning properly, the crop has a much better chance of accessing the phosphorus that’s already present,” she says.
The guide also addresses the importance of environmental issues. When phosphorus enters a watercourse, it becomes biologically available, allowing algae to bloom, warns Rob. “Improving phosphate efficiency delivers both economic and environmental benefits,” he adds. “You’re making better use of what’s already in the system, reducing the need for additional inputs and lowering the risk of losses to water.”
To view the guide, please visit: https://www.desangosse.co.uk/solutions/phosphate-efficiency-pays/
