Knowledge for Development

Relevant publications

Phosphorus demand for the 1970–2100 period: A scenario analysis of resource depletion

D.P. Van Vuuren, A.F. Bouwman and A.H.W. Beusen Global Environmental Change 20: 428-439.2010The phosphorus (P) cycle has been significantly altered by human activities. For this paper, the sustainability of current P flows in terms of resource depletion and the ultimate fate of these flows, are explored. The analysis shows that rapid depletion of extractable phosphate rock is not very likely, in the near term. Under best estimates, depletion would be around 20–35%. In worst case scenarios, about 40–60% of the current resource base would be extracted by 2100. At the same time, production will concentrate in Asia, Africa and West Asia, and production costs will likely have increased. As there are no substitutes for phosphorus plant nutrients in agriculture, arguably even partial depletion of P resources may in the long run be relevant for the sustainability of agriculture. Consumption trends lead to large flows of phosphorus to surface water and a considerable build-up of phosphorus in agricultural soils in arable lands. This may allow a reduction in future P fertiliser application rates in crop production. Results also indicate a global depletion of P pools in soils under grassland, which may be a threat to ruminant production.


Phosphorus in agriculture

Soil Quality Institute Technical Pamphlet No. 2.A brief overview of the role of phosphorus in agriculture is given, including: Importance to Plant Growth, Livestock and Phosphorus, Environmental Impacts of Agricultural Phosphorus, Harmful Effects of Eutrophication: The Phosphorus Cycle, Managing Agricultural Phosphorus: The Role and Value of Soil Testing and What are the critical soil test levels for Phosphorus?


Methods of phosphorus analysis, for soils, sediments, residuals and waters

Southern Cooperative Series Bulletin No. #396. 2000The relative contribution of phosphorus (P) from agricultural nonpoint sources to surface water quality problems has increased in recent years as point sources of P have been reduced significantly. Phosphorus contributes to eutrophication, which restricts water use for fisheries, recreation, industry, and human consumption due to increased growth of undesirable algae and aquatic weeds, followed by oxygen shortages as the biomass decomposes. The increased attention on P has increased the demand for information on methods of analysis for soil, water, and residual materials for environmentally relevant forms of P. The purpose of this publication is to present these methods in a single document. Previously, the methods have appeared across a wide variety of documents or only in the scientific literature. It is not the intent of this publication to define a uniform set of recommended methods for agronomic soils tests, water, or residual materials. The methods presented here are intended solely to provide a set of uniform testing methods for environmental scientists working across an enormous range of soil and climatic conditions, with the hope that comparable methods may lead to improved communication and understanding of this complex issue.


Assessment of soil nutrient balance: approaches and methodologies

R.N. Roy, R.V. Misra, J.P. Lesschen and E.M. SmalingFAO Fertilizer and Plant Nutrition Bulletin 14. 2003Soil nutrient-balance exercises based on static modelling systems and linear upscaling are devoid of the dynamics and the interacting processes involved. Methodological estimations are fraught with problems such as limited data availability at spatial scales, scale-specific spatial variation of nutrient-balance input data, non-linearity in upscaling, and lack of reliable upscaling techniques. Extrapolating present balances into the future and ensuring their validity for the future presents practical problems.There is a need for a more simple and reliable model/approach that is readily adaptable to various situations. In spite of various limitations, nutrient-balance assessments do delineate the consequences of farming for soil fertility. Of further relevance is their emergence as a reliable tool for devising time-scale soil fertility interventions based on a sound policy framework. A recently concluded FAO-commissioned project, ‘Scaling soil nutrient balances’, and scientific interactions (FAO electronic conference, September 2002 - July 2003) have thrown further light on the critical issues concerning nutrient-balance assessment approaches. They may also help bridge methodological gaps. Further methodological refinements are feasible through making them more spatially explicit (accounting for spatial variation of soils and climate) and through improving the procedures for calculating nutrient flows and quantifying soil nutrient stocks. The introduction of mesolevel studies adds value to the existing national- and farm-level approaches. The mesolevel offers a suitable entry point for policy interventions. Although macrolevel uncertainties need to be minimized and validations improved, it may not be possible to validate all the nutrient flows; one can focus on validating the specific flows regarded as most important. A participatory approach for the development and validation of locally specific packages needs to be promoted. Larger pools and volumes of data may facilitate refinement of the models and make them more scalable. Intensive field checks can in part solve problems relating to data quality, map interpretation, resolution differences and groundtruthing at the macrolevel.New techniques such as reflectance spectroscopy can inject elements of precision, pace and ease into the assessment of soil properties and nutrient stocks. Classified satellite images and digital elevation models (DEMs) can bring significant improvements in mesolevel nutrient-balance studies. Stratification in sampling methods and the use of GIS for upscaling would help improve mesolevel assessments. Presentation of the assessment outcomes in terms of yield loss or monetary values enables policy-makers to understand the issues more readily. Programmes to assist national governments in enhancing their socio-economic and policy environment for soil improvement (with the aim of promoting productive and sustainable agriculture) would be a prudent and desirable proposition.


A rock and a hard place: Peak phosphorus and the threat to our food security

Soil Association. 2010In the UK, and internationally, there has been no serious discussion of, or action on, what peak phosphorus means for food security. A radical rethink of how we farm, what we eat and how we deal with human excreta, so that adequate phosphorus levels can be maintained for crop production without reliance on mined phosphate, is crucial for ensuring our future food supplies. In this report the actions needed to close the loop on the phosphorus cycle to address future shortages and prevent further environmental damage from phosphate pollution are set out.


The story of phosphorus: global food security and food for thought

D. Cordell, J.-O. Drangert and S. White Global Environmental Change 19: 292–305.2009Food production requires application of fertilizers containing phosphorus, nitrogen and potassium on agricultural fields in order to sustain crop yields. However modern agriculture is dependent on phosphorus derived from phosphate rock, which is a non-renewable resource and current global reserves may be depleted in 50–100 years. While phosphorus demand is projected to increase, the expected global peak in phosphorus production is predicted to occur around 2030. The exact timing of peak phosphorus production might be disputed; however, it is widely acknowledged within the fertilizer industry that the quality of remaining phosphate rock is decreasing and production costs are increasing. Yet future access to phosphorus receives little or no international attention. This paper puts forward the case for including long-term phosphorus scarcity on the priority agenda for global food security. Opportunities for recovering phosphorus and reducing demand are also addressed together with institutional challenges.


Symbiotic nitrogen fixation and phosphorus acquisition. Plant nutrition in a world of declining renewable resources

C.P. Vance Plant Physiology 127: 390-397.2001The world is on the brink of a new agriculture, one that involves the marriage of plant biology and agroecology under the umbrella of biotechnology and germplasm improvement. Although N and P fertilizers will continue to play a major role in intensive agriculture, depletion of natural resources, loss of biodiversity, and long-term unsustainability necessitate alternative strategies be investigated and implemented to buffer against food insecurity and environmental degradation. Furthermore, because improved N and P use by plants has immediate and direct benefit in extensive agriculture in developing countries where access to fertilizers is limited, funding for research at international centres should be a high priority. The following recommendations deserve attention:(a) re-emphasize the use of legumes and symbiotic N2 fixation to improve soil N and P fertility while reducing fossil fuel consumption and providing a source of dietary N; (b) develop intercropping schemes that foster efficient N and P use; (c) continue to isolate, characterize, and develop fundamental understanding of individual genes holding promise of application to improving N and P use; (d) enhance the expression of genes and increase the synthesis of gene products, such as those involved in transport of nutrients and exudation of organic acids, through both traditional plant breeding and transgenic technology and incorporate these traits into adapted germplasm; and (e) assess the factors limiting rhizobial and mycorrhizal interactions with plants with the goal of site-(region) specific inoculation.


Peak phosphorus: opportunity in the making

A. Ulrich, D. Malley and V. Voora IISD2009The long-term security of our global food and water supplies may be impacted by the mismanagement of our phosphorus nutrient resources. Essential to plant growth and all life, phosphorus is mined from rock phosphate deposits and synthesized into mineral fertilizers destined for agricultural fields. Easily-mined rock phosphate reserves are dwindling and the constraints this could place on fertilizer production pose risks to our long-term ability to feed the planet. Fortunately, opportunities to accomplish this are abundant. Adopting agricultural practices that improve plant nutrient uptake and limit phosphorus runoff can lower application requirements. Phosphorus recovery from manure and human and food waste can also lower dependence on mineral fertilizers. For instance, phosphorus recovery systems could become standardized within wastewater treatment plants. Composting manure as well as human and food waste also represents an important source of phosphorus. Closing the loop on our food systems and moving toward phosphorus independence are crucial to ensuring the long-term security of food and water supplies. Treating phosphorus as a finite resource shifts the management paradigm from mitigating a noxious substance to recovering and recycling a precious element.


Phosphate recovery: phosphorus availability in the 21st century. Management of a non-renewable resource

I. Steen Phosphorus & Potassium 217:1998High-grade phosphate ores, particularly those containing few contaminants, are being progressively depleted and production costs are increasing. The outlook for global phosphate rock supply and management of this non-renewable resource is examined. Today, the annual global production of phosphate is around some 40 million tonnes of P2O5, derived from roughly 140 million tons of rock concentrate. Overall, mineral fertilisers account for approximately 80% of phosphates used worldwide with the balance divided between detergents (12%), animal feeds (5%) and speciality applications (3%), for example, food grade, metal treatment etc. Considering the dominant role of fertilisers in global phosphate consumption, it is evident that the development of future world phosphate production will be driven by the development of agriculture, which in turn is driven by global population growth and its food requirement. It therefore follows that agriculture’s share in the use of phosphate will increase in the future. Estimates of world phosphate reserves and availability of exploitable deposits vary greatly and assessments of how long it will take until these reserves are exhausted also vary considerably. Furthermore, it is commonly recognised that the high quality reserves are being depleted expeditiously and that the prevailing management of phosphate, a finite non-renewable source, is not fully in accord with the principles of sustainability.


Distribution of phosphorus resources between rich and poor countries: The effect of recycling

H.-P. Weikard and D. Seyhan Ecological Economics 68: 1749–1755.2009Phosphorus (P) is an essential input into agriculture with no substitute. Thus international and intertemporal P allocations greatly impact food security which requires increased food production for a growing world population. As high-quality phosphorus mines are being depleted, recycling gains importance and developed countries explore new technologies for P recycling. The effects of P recycling in developed countries on global extraction of rock phosphates and the imports of developing countries are analysed. A resource extraction model is developed for a competitive fertilizer market that reflects the fact that most developed countries have P-saturated soils while soils in many developing countries are P-deficient. The model presented here extends a simple “cake eating problem”. Two types of countries that differ in demand and recycling options are considered. Results show that P recycling in developed countries does not only prolong the resource life-time, but it also increases the developing countries' share of the resource.


Addressing phosphorus related problems in farm practice

E. Bomans, K. Fransen, A. Gobin, J. Mertens, P. Michiels, H. Vandendriessche and N. Vogels Soil Service of Belgium: Final report to the European Commission2005The focus of this document is on the role and use of phosphorus in the agricultural sector of the European Member States, on phosphorus legislation and on legal and practical measures that can be taken to reduce the losses of P from agricultural activities to the aquatic environment. The contribution of agriculture to the phosphorus loads in surface waters is estimated by the EEA between 20 and more than 50% and includes both point sources (waste water from farms and seepage from manure stores) and diffuse contamination (such as sheet runoff from fields, or seepage from soil into groundwater or from a multiplicity of minor point sources, as found on agricultural land). Due to reductions in the discharge from household and industry sources, the relative contribution from agriculture has risen in recent years, and has reached more than 50% in particular in areas with intensive agriculture.


Use of phosphate rocks for sustainable agriculture

Food and Agriculture Organization2004In order to ensure food security in developing countries, there is a need for the sustainable intensification of agricultural production systems towards supporting productivity gains and income generation. In this context, novel, soil-specific technologies will have to be developed, pilot tested and transferred to farmers in a relatively short time. Phosphorus (P) is an essential nutrient element for plants and animals. The appropriate and sound utilization of phosphate rocks (PRs) as P sources can contribute to sustainable agricultural intensification, particularly in developing countries endowed with PR resources.


Phosphate availability and the ultimate control of new nitrogen input by nitrogen fixation in the tropical Pacific Ocean

T. Moutin, D.M. Karl, S. Duhamel, P. Rimmelin, P. Raimbault, B.A.S. Van Mooy and H. Claustre Biogeosciences Discuss. 4: 2407–2440. 2007Due to the low atmospheric input of phosphate into the open ocean, it is one of the key nutrients that could ultimately control primary production and carbon export into the deep ocean. The observed trend over the last 20 years, has shown a decrease in the dissolved inorganic phosphate (DIP) pool in the North Pacific gyre, which has been correlated to the increase in di-nitrogen (N2) fixation rates. Following a NW-SE transect, in the Southeast Pacific during the early austral summer (BIOSOPE cruise), data on DIP, dissolved organic phosphate (DOP), and particulate phosphate (PP) pools and DIP turnover times (TDIP) along with N2 fixation rates are presented. A decrease in DIP concentration is observed from the edges to the centre of the gyre. Nevertheless, the DIP concentrations remained above 100 nmol L−1 and TDIP were more than a month in the centre of the gyre: DIP availability remained largely above the level required for phosphate limitation. This contrasts with recent observations in the western Pacific Ocean at the same latitude (DIAPALIS cruises) where lower DIP concentrations (<20 nmol L−1) and TDIP<50 h were measured during the summer season. During the BIOSOPE cruise, N2 fixation rates were higher within the cold nutrient-rich waters from the ocean depths rising to the surface (upwelling) near the Chilean coast. This observation contrasts with recently obtained model output for N2 fixation distribution in the South Pacific area and emphasises the importance of studying the main factors controlling this process. The South Pacific gyre can be considered a High P Low Chlorophyll (HPLC) oligotrophic area, which could potentially support high N2 fixation rates, and possibly carbon dioxide sequestration, if the primary ecophysiological controls, temperature and/or iron availability, were alleviated.


Scientists warn of lack of vital phosphorus as biofuels raise demand

L. Lewis The Times, June 23.2008Battered by soaring fertiliser prices and rioting rice farmers, the global food industry may also have to deal with a potentially catastrophic future shortage of phosphorus, scientists say. Researchers in Australia, Europe and the United States have given warning that the element, which is essential to all living things, is at the heart of modern farming and has no synthetic alternative, is being mined, used and wasted as never before. Massive inefficiencies in the “farm-to-fork” processing of food and the soaring appetite for meat and dairy produce across Asia is stoking demand for phosphorus faster and further than anyone had predicted. “Peak phosphorus”, say scientists, could hit the world in just 30 years. Crop-based biofuels, whose production methods and usage suck phosphorus out of the agricultural system in unprecedented volumes, have, researchers in Brazil say, made the problem many times worse. Already, India is running low on matches as factories run short of phosphorus; the Brazilian Government has spoken of a need to nationalise privately held mines that supply the fertiliser industry and Swedish scientists are busily redesigning toilets to separate and collect urine in an attempt to conserve the precious element.


Phosphorus uptake and balance in a soyabean-maize rotation in the moist savanna of West Africa

I.J. Ogoke, A.O.Togun, R.J. Carsky and K.E. Dashiell Journal of Agriculture and Rural Development in the Tropics and Subtropics 105: 15–27.2004This study investigated the effect of maturity class on phosphorus (P) balance in a soyabean-maize rotation in the West African moist savanna. Four soyabean varieties of different maturity classes were grown with or without P fertilizer followed by a maize crop. Soyabean stover P content averaged 1.77 kg ha−1 compared with 5.13 kg ha−1 in the grain. The late soyabean variety TGx1670-1F accumulated a significantly higher P in the grain (6.56 kg ha−1), and stover (2.57 kg ha−1) than the others. While P harvest index averaged 79%, P application increased grain P by 63-81% and stover P by 100% or more. When either soyabean grain or grain+stover was exported, P balance was negative and was not statistically different for varieties when no P was applied. At 30 or 60 kg P ha−1, P balance was negative but significantly lower in TGx1670- 1F compared with other varieties. Increasing P rate applied to soyabean significantly (p < 0.01) increased maize grain P by 35-66% in the second year. When P was exported only in soyabean grain, cumulative P balances after maize grain harvest (with no P or 30 kg ha−1 applied previous year) were not significantly different for previous soyabean crops. At 60 kg ha−1, however, P balance in previous TGx1670-1F plot was significantly lower than for other varieties. A further export of soyabean stover reduced P balance. Significant residual P effect was observed emphasizing the need to focus P fertilizer application in the cropping system rather than on the single crop. Also with more P in soyabean grain, a reduction in the extent of P depletion will be achieved by returning soyabean stover to the field after threshing.


Impact of desert dust on the biogeochemistry of phosphorus in terrestrial ecosystems

G.S. Okin, N. Mahowald, O.A. Chadwick and P. Artaxo Global Biogeochemical Cycles 18: doi:10.1029/2003GB0021452004Leaching, biomass removal, and partitioning of phosphorus (P) into reservoirs not available to plants can limit the long-term productivity of terrestrial ecosystems. The importance of atmospheric P inputs to the world’s soils is evaluated by estimating the total soil P turnover time with respect to dustborne P additions. Estimated turnover times range from 104 to 107 years. The estimates presented provide a unique perspective on the importance and patterns of aeolian deposition to terrestrial landscapes. Dust source regions are areas of intense soil P cycling on large scales, but are too water-limited for this rapid cycling to have a major influence on ecosystem dynamics. By contrast, semiarid desert margins receive significant aeolian P from neighbouring deserts and are likely influenced by dustborne P additions for the long-term maintenance of productivity. This is particularly true for the semiarid steppes of Africa and Eurasia. The prevalence of large dust sources in Africa and Eurasia indicates that these areas may generally be more influenced by dustborne P additions than soils in the Americas. Significant western hemisphere exceptions to this pattern occur on very old landscapes, such as the forests of the southeastern United States and the Amazon Basin. The Amazon Basin is highly dependent on aeolian deposition for the maintenance of long-term productivity. Dust deposition to terrestrial environments has not been constant with time. Variability in past P deposition related to geologically recent climate change may provide the strongest controls on present and future soil P in the Amazon and elsewhere.


Influence of nitrogen, phosphorus and potassium application on the yield of maize in the savanna zone of Nigeria

J.O.S. Kogbe and J.A. Adediran African Journal of Biotechnology 2: 345-349.2003Field trials testing the effects of five rates each of N, P and K application on three hybrid and two open-pollinated maize varieties were conducted in three separate experiments on an Arenic haplustalf (USDA) at Ilora in the derived savanna and Typic paleustalf (USDA) at Mokwa in the southern guinea savanna of Nigeria. The hybrid maize varieties planted were 8516-12, 8321-18 and 8329-15 and were compared with the open-pollinated maize, TZSR-Y and TZSR-W. Nitrogen was applied at rates 0-200 kg ha-1 in the first trial, while P and K were supplied as basal nutrients. In the second trial, P was applied at rates 0- 80 kg P2O5 ha-1 using basal N and K fertilizers. In another trial, K was applied at rates 0-120 kg ha-1 with blanket application of N and P. The hybrid maize gave higher yields and used N and P more efficiently than the open pollinated at both trial locations. The yield of maize was higher in the southern guinea savanna than in the derived savanna. The performance of the hybrid varieties followed in the ascending order of 8516-12, 8321-18 and 8329-15. The optimum rates of N and P for maize grown in the derived savanna were 100 and 40 kg ha-1 respectively. In the southern guinea savanna the open pollinated and hybrid varieties responded up to 150 and 200 kg N ha-1 respectively. The 8516-12 showed higher N and P use efficiency than other varieties. Consequently, planting such variety could be advantageous, using minimal dose of fertilizer most especially, where farmers have less access to fertilizer.


Phosphorus dynamics in the North Pacific subtropical gyre

K. Björkman, A.L. Thomson-Bulldis and D.M. Karl Aquatic Microbial Ecology 22: 185–198. 2000Phosphorus (P) dynamics were studied during several research cruises to Stn ALOHA and in the ‘Climax region’ of the North Pacific subtropical gyre (NPSG) in 1996–1997. The aim of this study was to: (1) investigate the coupled uptake and regeneration of inorganic phosphate (Pi) and the production of dissolved organic phosphorus (DOP), (2) quantify the size of the biologically available P (BAP) pool, and (3) estimate the relative bioavailability of select organic P compounds to the natural microbial assemblages. At all stations, the microbial community was dominated by prokaryotes (>99.5% of total cell numbers); Prochlorococcus spp. was the dominant pigmented group (>97% by numbers), comprising 20 to 30% of the total prokaryotic population. Phosphate uptake rates were 3.0 to 8.2 nM d–1 (median = 3.5 nM d–1) and P pool turnover times ranged from 2 to 40 d (median = 9 d). The BAP pool generally exceeded the Pi pool, suggesting rapid turnover of at least a portion of the much larger DOP pool. The net production of DOP was approximately 10 to 40% of the net P uptake. Both the dissolved and the particulate organic matter pools were enriched in carbon (C) and nitrogen (N) relative to P, compared to the Redfield molar stoichiometry of 106C:16N:1P. The half-saturation constant, Km, values for Pi uptake were higher than the ambient Pi pool concentrations, and uptake rates were positively correlated with exogenous Pi additions over the range tested (Pi = 25 to 250 nM). The bioavailabilities of exogenous adenine and guanine nucleotides were generally higher than other organic P compounds that were tested. The net Pi regeneration rate from nucleotides was up to 50 times higher than the net Pi uptake rates, indicating a large potential for the regeneration of Pi from specific organic compounds. These P pool dynamics observed in the NPSG are consistent with a microbial community currently under P control.


Efficient phosphorus application strategies for increased crop production in sub-Saharan West Africa

A. Buerkert, A. Bationo and H.-P. Piepho Field Crops Research 72: 1-15. 2001Comparable data are lacking from the range of environments found in sub-Saharan West Africa to draw more general conclusions about the relative merits of locally available rockphosphate (RockP) in alleviating phosphorus (P) constraints to crop growth. To fill this gap, a multi-factorial field experiment was conducted over 4 years at eight locations in Niger, Burkina Faso and Togo. These ranged in annual rainfall from 510 to 1300 mm. Crops grown were pearl millet (Pennisetum glaucum L.), sorghum (Sorghum bicolor (L.) Moench) and maize (Zea mays L.) either continuously or in rotation with cowpea (Vigna unguiculata Walp.) and groundnut (Arachis hypogaea L.). Crops were subjected to six P fertiliser treatments comprising RockP and soluble P at different rates and combined with 0 and 60 kg N ha−1. For legumes, time trend analyses showed P-induced total dry matter (TDM) increases between 28 and 72% only with groundnut. Similarly, rotation-induced raises in cereal TDM compared to cereal monoculture were only observed with groundnut. For cereals, at the same rate of application, RockP was comparable to single superphosphate (SSP) only at two millet sites with topsoil pH-KCl<4.2 and annual average rainfall>600 mm. Across the eight sites NPK placement at 0.4 g P per hill raised average cereal yields between 26 and 220%. This was confirmed in 119 on-farm trials revealing P placement as a promising strategy to overcome P deficiency as the regionally most growth-limiting nutrient constraint to cereals.


Closing the loop on phosphorus

EcoSanRes Factsheet 42008Between 1950 and 2000, about 1 billion metric tonnes of P has been mined. During this period, about 800 million metric tonnes of fertilizer P were applied to the Earth’s croplands. This has increased the standing stock of P in the upper 10 centimetres of soil in the world’s croplands to roughly 1,300 million metric tonnes, an increase of 30%. Close to a quarter of the mined P (250 Mt) since 1950 has found its way into the aquatic environment (oceans and fresh water lakes) or buried in sanitary landfills or sinks. For 1990, the amount of phosphate discharged into oceans was double the amount of phosphate applied as fertilizer. Of the next billion tonnes of P mined between 2000 and 2050, a significant percentage of phosphorus can be recovered by using sustainable agriculture and sanitation. This should be a priority for the global policy agenda.


Phosphate deposits of the world: Volume 2, Phosphate rock resources, volume 2

Edited by A.J.G. Notholt, R.P. Sheldon and D.F. Davidson Cambridge University Press1989This multi-author book details phosphate rock resources throughout the world, noting locations, geology, tectonics, stratigraphy, production and references.


Local phosphate resources for sustainable development in sub-Saharan Africa

J.D. Appleton Economic Minerals and Geochemical Baseline Programme Report CR/02/1212002A summary of quantity, quality and location of resources and their potential application in sub-Saharan agriculture is given. This includes investment required to mine resources, and other constraints, including environmental constraints, and which soils would benefit most in an agricultural context.


Life cycle assessment of phosphorus alternatives for Swedish agriculture

A life cycle assessment (LCA) study by SLU, the Swedish University of Agricultural Sciences, has assessed the environmental impact of four ways to supply Swedish agriculture with phosphorus fertiliser of acceptable quality as regards cadmium content: Mineral fertiliser, certified sewage sludge, struvite precipitated from wastewater, and phosphorus recovered from sludge incineration. These were examined with respect to impacts on global warming, eutrophication, energy demand and cadmium flows to farmland. Using sewage sludge directly on farmland was the most efficient option in terms of energy and emissions of greenhouse gases, but also added most cadmium to the soil. Phosphorus recovery from incinerated sludge was the most energy demanding option and gave most emissions of greenhouse gases. Despite great concerns about cadmium in Swedish fertilisers and sludge, it was found that almost no regular analyses for cadmium are made on imported food by the authorities, although food imports are constantly increasing.(SLU, 18/7/2012)


The impact of first-generation biofuels on the depletion of the global phosphorus reserve

The large majority of biofuels to date is ‘first-generation’ biofuel made from agricultural commodities. All first-generation biofuel production systems require phosphorus (P) fertilisation. P is an essential plant nutrient, yet global reserves are finite. Researchers Lars Hein and Rik Leemans (from the Environmental Systems Analysis Group, Wageningen UR) here argue that committing scarce P to biofuel production involves a trade-off between climate change mitigation and future food production. They examine biofuel production from seven types of feedstock, and find that biofuels at present consume around 2 % of the global inorganic P fertiliser production.For all examined biofuels, with the possible exception of sugarcane, the contribution to P depletion exceeds the contribution to mitigating climate change. The relative benefits of biofuels can be increased through enhanced recycling of P, but high increases in P efficiency are required to balance climate change mitigation and P depletion impacts. The authors conclude that, with the current production systems, the production of first-generation biofuels compromises food production in the future.[Lars Hein (WUR) and Rik Leemans. AMBIO. 2012. Vol 41. No. 4. 341-349]


Evaluation of phosphorus indices after twenty years of science and development

The P Index was proposed as a nutrient management tool in 1992 and has been implemented as such in the USA for the past decade. The goal of P Index use today is to help producers manage P, particularly manure-based P, while minimizing P losses and the associated environmental impacts. Included within this goal is the identification of critical source areas and strategic placement of best management practices. However, lack of water quality improvement in agricultural watersheds and discrepancies in P loss ratings between P indices have raised questions about continued use of the P Index.The papers reviewed in this Special Section of the Journal of Environmental Quality conclude that P indices can provide accurate assessments of P loss but must be evaluated appropriately. Evaluation will require compiling large regional P loss datasets at field and small watershed scales. Simulation models may be used to generate P loss estimates; however, models must be calibrated and validated to ensure their accuracy. Further development of P indices will require coordinated regional efforts to identify common P Index frameworks and standardized interpretations. Stringent P Index evaluations will expand the utility of P indices for critical source area identification and strategic best management practice implementation by regulatory, education, and scientific communities alike.(Journal of Environmental Quality 41, 09/2012 via the Soil Science Society of America, 23/10/2012)