Soil phosphorus and reducing its loss from crop production systems using the activities of native soil microorganisms

Authors: Lehman, R - Michael; Taheri, Wendy

Submitted to: Sustainable Agriculture Reviews
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/2015
Publication Date: 1/20/2017
Citation: Lehman, R.M., Taheri, W.I. 2017. Soil phosphorus and reducing its loss from crop production systems using the activities of native soil microorganisms. Sustainable Agriculture Reviews. 22:15-36.

Interpretive Summary: Dwindling supplies of phosphate ores and rising costs for P fertilizer are affecting the economics of food production and consumption. The prospects for scarce P resources are compounded by widespread degradation of water resources by excessive P (and N) inputs that are linked to agricultural production practices. We analyze the scientific evidence regarding P dynamics in soils and the interactions between soil microorganisms and P. A synthesis of this evidence produces a vision for future agricultural management practices that emphasize increasing the amount, diversity, and activity of soil microorganisms to achieve more efficient use of P resources. Improving the efficiency of P use in crop production will require decreased reliance on measurements of a static pool of inorganic soil P that is most subject to fixation in the soil or export to surface waters. Instead, approaches to measure biologically-catalyzed fluxes of plant-available P are needed to maintain a more conservative P cycle. An overall goal of management would be to reduce P inputs and maintain agricultural soils at lower P levels, in forms that are less likely to be exported from the system. Revolutionary changes in soil and nutrient management founded on sound science are essential to meeting the needs of the growing global population.

Technical Abstract: Dwindling supplies of phosphate ores and rising costs for P fertilizer are affecting the economics of food production and consumption. The prospects for scarce P resources are compounded by widespread degradation of water resources by excessive P (and N) inputs that are linked to agricultural production practices. Synthetic fertilizers contain inorganic P, which has a higher likelihood than organic P of becoming fixed in the soil, unavailable to plants, or being associated with highly-erodible soil fractions. An underutilized approach to reduce P export is to exploit the activities of soil microorganisms to retain more P on-site, in forms that can be repeatedly made plant available. Studies have shown that a stable biomass of soil microorganisms at steady-state can produce a flux of plant available P that is sufficient for plant growth. A higher stabilized soil microbial biomass contains P that is rapidly cycled as biomass turns over. This flux of microbial P is supplemented by fluxes of soil P that are made plant available by a variety of biologically-catalyzed reactions. Maintaining conditions in agroecosystems that support a diversity of soil microorganisms is also important so that specialized microorganisms are represented. Obligate plant symbiotic arbuscular mycorrhizal fungi (AMF) have been shown to provide many benefits to plants, particularly uptake of immobile nutrients such as P. AMF numbers and diversity are commonly depleted in conventional agricultural production systems. Agricultural practices that minimize tillage and increase plant diversity with rotation, cover cropping, and inclusion of perennials have been shown to increase AMF numbers and diversity which should increase P use efficiency. Inefficient use of P resources will be perpetuated by basing P management on measurements of a static pool of inorganic P that is most subject to fixation or export. While recognizing that P exported in farm products needs to be periodically replaced, there are significant benefits in moving towards a biologically-diverse and active soil system which maintains more P in an organic form that participates in an active, but conservative cycle. An overall goal of management would be to reduce P inputs and maintain agricultural soils at lower P levels, in forms that are less likely to be exported from the system. A considerable challenge exists in measuring the capacity of the soil to maintain fluxes of plant available P using an approach that can routinely compare different agricultural practices and support P fertilizer recommendations to producers.