Organic phosphorus (Po) compounds in soil often comprise a large component of soil total P (up to 84% for pasture), and represent a potentially significant source of P for agricultural production. Information on the quantities and forms of soil Po remains relatively limited, but we do know that inositol phosphates and their numerous metal-ion derivatives often constitute the dominant form of soil total Po. In addition, other phosphate esters, such as sugar phosphates, phospholipids and nucleic acids have often been identified in smaller quantities within soils. Various soil microorganisms, such as mycorrhizal fungi and phosphate-solubilising microorganisms (PSMs), can access inositol phosphates and other Po compounds. These microorganisms play an important role in the mineralisation of soil Po and the release of inorganic phosphorus compounds to soil solution or for direct plant uptake. Our research aims to explore the extent to which the coupled microbial and enzyme system with agricultural soils might be manipulated in order to increase the value derived from soil Po compounds as part of agricultural production. Specifically, we describe research focussed on inoculation experiments in which selected fungal and bacterial strains, alongside extracellular phosphatase enzymes, are trialled for their efficacy with respect to the mineralisation and solubilisation of Po compounds within soils. For example, arbuscular mycorrhizas (AMs) belonging to the phylum Glomeromycota could be introduced to soil ecosystems in order to benefit from the symbiotic endobacteria living inside the fungus whose genes are involved in mineral P acquisition. Such AMs could be mixed with strains of some of the most beneficial PSMs for Po mineralisation, e.g. Azospirillum spp., Bacillus spp., Penicillium spp. and Rhizobium spp. In addition, bacterial strains such as Bacillus amyloliquefaciens FZB24, FZB42 and FZB45, could be inoculated in soils due to their ability to secrete extracellular phosphatase enzymes. Our research focuses on the extent to which inoculations could increase the availability of phosphorus within soils for agricultural production, focussing largely on livestock farms and associated grass quality and yields. In particular, we will examine whether inoculation of livestock slurries and manures provides a vector for indirect manipulation of soil microbial and enzyme systems within livestock farms. The ultimate aim of this approach is to reduce the reliance of agricultural production on finite inorganic phosphorus fertiliser reserves.
Availability of organic and inorganic phosphorus compounds as phosphorus sources for Carex
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