Society relies heavily on inorganic phosphorus (P) compounds throughout its food chain. This dependency is not only very inefficient and increasingly costly but is depleting finite global reserves of rock phosphate. It has also left a legacy of P accumulation in soils, sediments and wastes that is leaking into our surface waters and contributing to widespread eutrophication. We argue for a new, more precise but more challenging paradigm in P fertilizer management that seeks to develop more sustainable food chains that maintain P availability to crops and livestock but with reduced amounts of imported mineral P and improved soil function. This new strategy requires greater public awareness of the environmental consequences of dietary choice, better understanding of soil-plant-animal P dynamics, increased recovery of both used P and unutilized legacy soil P, and new innovative technologies to improve fertilizer P recovery. In combination, they are expected to deliver significant economic, environmental, and resource-protection gains, and contribute to future global P stewardship.
Plant roots and soil microorganisms contain significant quantities of low molecular weight (MW) phosphorylated nucleosides and sugars. Consequently, upon death these can represent a significant input of organic-P to the soil. Some of these organic-P substrates must first be dephosphorylated by phosphatases before being assimilated by the soil microbial community while others can be taken up directly from soil solution. To determine whether sorption or phosphatase activity was limiting the bioavailability of low MW organic-P in soil we compared the microbial uptake and C mineralization of a range of 14C-labeled organic-P substrates [glucose-6-phosphate, adenosine monophosphate (AMP), adenosine diphosphate (ADP) and adenosine triphosphate (ATP)] to that of the parent compounds (adenosine and glucose). In a fertile grassland soil we showed that at low organic-P substrate concentrations (<0.5mM) phosphatase activity did not limit microbial uptake or mineralization in comparison to their non-phosphorylated counterparts. However, at high substrate concentrations (1–10mM) the mineralization of the organic-P compounds was significantly lower than that of the non-phosphorylated compounds suggesting that phosphatase activity or microbial transporter capacity limited bioavailability. Sorption to the solid phase followed the series glucose<adenosine<G-6-P<AMP<ADP=ATP. However, sorption of the organic-P compounds to the solid phase did not appear to greatly affect bioavailability. The high adenosine mineralization capacity of the microbial biomass suggests that nucleosides may represent a significant source of C and N to the soil microbial biomass. We conclude that at low organic-P substrate concentrations typical of those in soil, neither phosphatase activity nor sorption greatly limits their bioavailability.
Biochar additions to soil have been reported to enhance soil fertility whilst simultaneously storing carbon (C). We tested whether either fresh or field-conditioned (aged) biochar amendment to two contrasting agricultural soils would alter the mineralisation of organic N compounds. The mineralisation of 14C-labelled amino acids and peptides were determined over 20 days within each soil. An exponential kinetic decay model was subsequently fitted to the mineralisation data. Overall, statistical analysis revealed significant but small differences between the two biochar treatments and the unamended control treatment. We conclude that biochar has very limited impact on the mineralisation rate of low molecular weight dissolved organic N compounds in these agro-ecosystems.
Mechanical biological treatment (MBT) of mixed waste streams is becoming increasingly popular as a method for treating municipal solid waste (MSW). Whilst this process can separate many recyclates from mixed waste, the resultant organic residue can contain high levels of heavy metals and physical and biological contaminants. This review assesses the potential end uses and sustainable markets for this organic residue. Critical evaluation reveals that the best option for using this organic resource is in land remediation and restoration schemes. For example, application of MSW-derived composts at acidic heavy metal contaminated sites has ameliorated soil pollution with minimal risk. We conclude that although MSW-derived composts are of low value, they still represent a valuable resource particularly for use in post-industrial environments. A holistic view should be taken when regulating the use of such composts, taking into account the specific situation of application and the environmental pitfalls of alternative disposal routes.
Organic acids such as malate, citrate and oxalate have been hypothesized to be involved in the long-term podzolization process and also to offer short-term protection to plants and microorganisms against aluminium under acid soil conditions. However, the reactions of organic acids in soil remain poorly understood. The aim of this study was to characterize the reactions of citrate and oxalate in Picea abies forest soils of contrasting Al status. 14C-labelled citrate and oxalate were added to soil at low levels close to steady state organic acid soil solution concentrations and their fate followed over a subsequent 24h period. Organic acid decomposition was greatest in surface horizons (t 1/2=0.5h) compared to subsurface horizons (t 1/2=8h) and the long-term field addition of Al to soil did not influence the mineralization rate or biomass-C yield by the microbial community. In experiments where the levels of Al were manipulated in the laboratory, only at high Al concentrations (≥5mM) was organic acid mineralization significantly affected. Similar experiments with non-Al complexing glucose indicated that this effect could be attributable to a direct Al complexation effect on the organic acids and partly due to an indirect toxic effect of Al on the microorganisms themselves. In conclusion, while the release of organic acids from plants may offer protection against rhizotoxic Al, the efficiency of this mechanism will be reduced by the rhizosphere microbial community.
No abstract is provided for this article.
SUMMARY Livestock production is a significant source of methane (CH 4 ) and nitrous oxide (N 2 O) emissions globally. In any sheep-producing nation, an effective agricultural greenhouse gas (GHG) mitigation strategy must include sheep-targeted interventions. The most prominent interventions suited to sheep systems are reviewed in the current paper, with a focus on farm-level enteric CH 4 and soil N 2 O emissions. A small number of currently available interventions emerge which have broad consensus on their mitigation potential. These include breeding to increase lambing percentages and diet formulation to minimize nitrogen excretion. The majority of interventions still require significant research and development before deployment. Research into the efficacy of interventions such as incorporation of biochar is in its infancy, while for others such as dietary supplements, successes in isolated studies now need to be replicated in long-term field trials under a range of conditions. Enhancing understanding of underlying biological processes will allow capitalization of interventions such as vaccination against rumen methanogenesis and pasture drainage. Many interventions cannot be recommended at a regional or national scale because, either, their mitigation potential is inextricably linked to soil and weather conditions in the locality of use, or their use is restricted to more intensive, closely managed systems. Distilling the long list of interventions to produce an effective farm-level mitigation strategy must involve: accounting for all GHG fluxes and interactions, identifying complimentary sets of additive interventions, and accounting for baseline emissions and current practice. Tools such as whole farm GHG models and marginal abatement cost curves are crucial in the development of tailored, practical sheep farm GHG mitigation strategies.
The aim of the study was to investigate the ability of Zea mays L. roots to regulate the amount of free amino acids present in the rhizosphere. The active
The incorporation of common organic wastes (e.g. compost, biosolids, recycled paper waste) into soil promotes contaminant removal and stabilization, and diverts waste from landfill or incineration. However, implementation is constrained by public perception, timescale, cost and the pollutant burden of the organic waste itself. In addition, the high nutrient content of most organic wastes can lead to low biodiversity value at restoration sites. These potential negative aspects are now being countered by the mixing of waste streams, thus providing a multifunctional solution to land remediation where pollutant removal is not the only long-term goal.
Two species of Nematoceras (Orchidaceae) from subantarctic Macquarie Island are characterised, illustrated and details of distribution and ecology are provided.Nematoceras sulcatum M.A.Clem.et D.L.Jones, recently identified by field studies and confirmed by comparative morphological and DNA analyses
