An interesting study published on 18 March in Phytobiomes, a new open-access journal published by APS, provides further evidence of the risks associated with the use of phosphorous fertilisers. According to the authors, excessive inorganic phosphorous fertilization negatively affects plant growth by altering soil microbes.
Phosphorus is a key component involved in many physiological and biochemical processes, including photosynthesis and is therefore essential to all living cells―and that includes plant cells. Microorganisms in the soil are responsible for driving important processes such as nitrogen fixation ― making nitrogen available to plants ― and the phosphorous cycle.
Therefore, so-called microbiome dynamics can significantly influence the availability of nutrients for plant growth. Without adequate phosphorous in soils, crops end up stunted, discoloured, and produce low yields.
In their study, the researchers from Cornell University and The Pennsylvania State University looked at the microbial functions critical to crop health. In particular, they examined changes in these functions as a result of the soil’s nutrient history.
More specifically, the scientists conditioned soils using four different nutrient treatments, including high phosphorous and used the modified soils to grow alfalfa (Medicago sativa), an important foraging crop owing to its high nutritional quality, high yields, and high adaptability. Then, they looked at the influence of nutrient-mediated changes to the soil microbiome composition and activity ― measured using high-throughput DNA sequencing ― on the yield of alfalfa through four generations of growth.
They also examined whether the function of soil microorganisms remained altered even after the treatment, e.g., high phosphorous, was no longer used. Intriguingly, a higher phosphorous content was linked to poorer crop performance, compared to alfalfa plants that were grown in soil treated with lower levels or no phosphate at all.
Changes in soil nutrients rapidly altered the structure and activity of the soil microbiome. The so-called phosphate-conditioned microbiomes were functionally resistant to additional phosphorous, resulting in negative effects on plant growth.
The results highlight how components added to soil to enhance crop yield and productivity, can have long-term impacts on soil properties. As the authors write, “Different microbiomes can then have measurably different effects on plant traits.” In other words, the type of microbiomes present in soil as well as their functions can dramatically influence plant traits such as flowering time, drought tolerance, and disease resistance.
Farmers often apply phosphate fertilizers to improve crop growth. Moreover, manures or composts are often used to increase the nitrogen content in soil, which also leads to an increase in phosphorous concentrations. Both approaches result in phosphorous levels much higher than what is needed for plant growth. Furthermore, nitrogen and phosphorus from agriculture runoff contribute to environmental pollution.
Although more research is still needed, the findings could lead to new strategies in precision agriculture. Reducing the use of fertilisers could be beneficial to both plant growth while lessening some of the environmental impacts of agricultural crops.
(1) Kaminsky, L.M. et al. Medicago sativa has Reduced Biomass and Nodulation When Grown with Soil Microbiomes Conditioned to High Phosphorus Inputs. Phytobiomes (2018). DOI: 10.1094/PBIOMES-06-18-0025-R