The challenge of increasing phosphorous (P) uptake by crops on a consistent basis has recently been reviewed by UK-based consultancy ADAS.
The issue is linked to the need for improved plant nutrition strategies and and the equally important priority of improving water quality
The work has identified three ways in which this objective may be achieved during the period ahead: reducing demand for P; targeting P fertiliser applications; and utilising P already in the soil.
Reducing demand for phosphorous
A crop transfers up to 80% of the phosphorous it captures to its seed in the form of a chemical called phytate.
However, this approach reduces the content of other nutrients, such as zinc.
If the crop used P for photosynthesis rather than storing it away, not only will the plant produce more biomass, but it will also result in a more nutritious final food product.
There has already been promising research in the area of low-phytate seed.
In 2004, scientists identified a single gene in barley that reduces the concentration of P in seed by 13-15%.
Finding ways to reduce this further (by 25%) could lower inorganic P fertiliser requirements of cereals by 10%.
Further research is required to understand the role of plant genes in improving the utilisation of P, as well as the knock-on effect this would have on seedling development.
Targeting phosphorous fertiliser applications
Farmers taking a bespoke, targeted approach to P application with a focus on feeding the crop, not the soil, can reduce the quantity of phosphorous applied.
By analysing grain post-harvest, farmers can accurately measure nutrient offtakes and determine what remains in the soil before deciding on further applications.
Seed fertiliser treatments and foliar fertiliser products are promising elements of a crop phosphorous nutrition strategy.
Again, more research is required to understand how they can improve crop phosphorous uptake efficiency.
Utilising phosphorous already in the soil
To access any available P, crops require an extensive root structure. The higher the density of roots and the greater their surface area, the more phosphorous they can potentially access.
The development of crop varieties with vigorous root systems with high numbers of root hairs should be an ongoing priority.
Soil conditioners, which do not contain any P, may improve the availability of the nutrient in the soil.
However, the capacity of these products to improve crop phosphorous uptake has not been independently trialled to a great extent just yet.
Some crops can act as useful phosphorous ‘scavengers’, with their residues increasing the amount of P available to the following crop.
According to the ADAS, buckwheat as a cover crop has been shown to increase grain P levels in the following spring barley crop, compared to bare fallow and other cover crop species.
Similar benefits have also been observed with white lupins and chickpeas.
