PubMed · 14823871
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R W SPALDING. 1951. Phosphorus.. https://pubmed.ncbi.nlm.nih.gov/14823871/
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Excessive soluble P in runoff is a common cause of eutrophication in fresh waters. Evidence indicates that drinking water treatment residuals (WTRs) can reduce soluble P concentrations in P-impacted soils in the short term (days to weeks). The long-term (years) stability of WTR-immobilized P has been inferred, but validating field data are scarce. This research was undertaken at two Michigan field sites with a history of heavy manure applications to study the longevity of alum-based WTR (Al-WTR) effects on P solubility over time (7.5 yr). At both sites, amendment with Al-WTR reduced water-soluble P (WSP) concentration by >or=60% as compared to the control plots, and the Al-WTR-immobilized P (WTR-P) remained stable 7.5 yr after Al-WTR application. Rainfall simulation techniques were utilized to investigate P losses in runoff and leachate from surface soils of the field sites at 7.5 yr after Al-WTR application. At both sites, amendment with Al-WTR reduced dissolved P and bioavailable P (BAP) by >50% as compared to the control plots, showing that WTR-immobilized P remained nonlabile even 7.5 yr after Al-WTR amendment. Thus, WTR-immobilized P would not be expected to dissolve into runoff and leachate to contaminate surface waters or groundwater. Even if WTR-P is lost via erosion to surface waters, the bioavailability of the immobilized P should be minimal and should have negligible effects on water quality. However, if the WTR particles are destroyed by extreme conditions, P loss to water could pose a eutrophication risk.
In this overland flow simulation experiment, the relationships between flow path length, flow rate and the concentration of different P fractions were investigated. Overland flow was simulated using a 3 mx0.12 m laboratory flume. To remove the impact of rainfall on P lost in overland flow, simulated rainfall was not used during these experiments. Instead overland flow was generated by pumping water into the flume at the surface of the grass sod. The experimental setup allowed for the variation in flow path length and flow rate between and during experimental runs. The results demonstrated that an increase in flow path length caused an increase in Total Dissolved P (TDP), Dissolved Reactive P (DRP) and Total Reactive P (TRP) concentration in overland flow (p<0.01) while an increase in flow rate resulted in a decrease in the concentration of these P fractions in overland flow due to dilution (p<0.01). Total P (TP), Particulate P (PP) and Dissolved Organic P were not affected by the variables tested during this study. When flow path length was increased in conjunction with flow rate, there was an increase in TDP, DRP, and TRP concentrations despite the impact of greater dilution. The results indicate that variations in flow path length during a rainfall event may play a role in determining the concentration of dissolved P fractions in overland flow at field scale.
BACKGROUND: Global phosphorus (P) reserves are being depleted, with half-depletion predicted to occur between 2040 and 2060. Most of the P applied in fertilizers may be sorbed by soil, and not be available for plants lacking specific adaptations. On the severely P-impoverished soils of south-western Australia and the Cape region in South Africa, non-mycorrhizal species exhibit highly effective adaptations to acquire P. A wide range of these non-mycorrhizal species, belonging to two monocotyledonous and eight dicotyledonous families, produce root clusters. Non-mycorrhizal species with root clusters appear to be particularly effective at accessing P when its availability is extremely low. SCOPE: There is a need to develop crops that are highly effective at acquiring inorganic P (Pi) from P-sorbing soils. Traits such as those found in non-mycorrhizal root-cluster-bearing species in Australia, South Africa and other P-impoverished environments are highly desirable for future crops. Root clusters combine a specialized structure with a specialized metabolism. Native species with such traits could be domesticated or crossed with existing crop species. An alternative approach would be to develop future crops with root clusters based on knowledge of the genes involved in development and functioning of root clusters. CONCLUSIONS: Root clusters offer enormous potential for future research of both a fundamental and a strategic nature. New discoveries of the development and functioning of root clusters in both monocotyledonous and dicotyledonous families are essential to produce new crops with superior P-acquisition traits.