PK and Mg

The COMIFER PKMg Group has about fifty members (27% research and education, 40% development, 33% agricultural supplies), including twenty who are particularly active. It meets twice a year to take stock of scientific advances, share information and referrals, establish or update the rules and references of good fertilization practices.

Comifer champs colzaThe past work of the group led to the defining of the modes of reasoning bases currently used in France, primarily the PK COMIFER grid and tools derived from the same concepts (RegiFert, …).

The group also integrates the concerns of water protection against the risk of eutrophication, which requires good management, adjusted to the mineral and organic input needs of crops.

It also focuses on the evaluation of fertilizing qualities of new products or by-products appearing in agriculture (derived from the treatment of effluent or waste, industrial by-products, ...) from the perspective of nutrient recycling to save mining resources.

It allows you to share information or references related to the management of the resource, the regulation of fertilizers, and the economic environment.

Finally, it focuses on defining new approaches to nutrient bioavailability: new analytical methods and renovation of sustainable fertilizing.

COMIFER Membership and group participation provides first access and completeness of information on the work of the group.

For all contact: Christine LE SOUDER, group leader.


Nutrients PK and Mg

The COMIFER PKMg group is interested in phosphorus (P), potassium (K) and magnesium (Mg).

Comifer plantes2These three nutrients, needed by crops, have the common characteristic that their natural forms are in close interaction with the solid phase of the soil, meaning their availability to crops will largely depend on soil properties.

The annual flow of absorption by crops, and even more so, by export crops, are relatively small compared with the total stock of the ground. But only part of the total stock is bioavailable, a large part being included in some minerals at low to very low solubility in the short term. Their root absorption occurs in liquid phase,within this single bioavailable fraction.

The behavioral similarities of these elements in the functioning of soil-plant systems is what lead to P, K and Mg being treated in the same thematic COMIFER group, in order to abide by similar rules of good management of crop fertilization and soil fertility.

Phosphorus, potassium and magnesium are elements whose dynamics have been the subject of much reasoning over several years, taking into account the progressive development of mineral and organic soil stocks.

P, K or Mg deficiencies in crops, now relatively rare in France, following the significant fertilization performed in the 20th century, are likely to occur or recur but very gradually; also the reasoning on P, K and Mg nutrition of crops is often seen as secondary after that of N nutrition. It is nevertheless true that these elements can be limiting and poorly balanced crop nutrition leads to inefficient use of inputs.

Conversely, the risk of over-fertilization with P are important in context of strong livestock manure surplus. The transfer of P to surface water can lead to eutrophication, it is important to adapt the supply of P to crop needs, within the framework of agricultural practices avoiding losses to the environment.


Publications of the PKMg Group

fertilisation phos

Help with the diagnosis and the prescription of phosphate and potassium fertilization of field crops (1995)

This document compiles and organizes existing bases that aid in the diagnosis and the prescription of phosphate and potassium fertilization of field crops ...

28 pages



Additional elements for the PK fertilization reasoning method to assist in its implementation (1997)

This document provides additional information to the first brochure, offering concrete evidence to assist with practical implementation (effluent inputs, proposal to charts, grid adaptations), arguments to facilitate appropriation (evolution speeds of the contents) and the recommendations of two other European countries.

49 pages

fertilisation phos

PKMG Computing Grid and table of exports

Get the complete computing grid PKMg 2007 and 2009 Versions



The Co-published Brochures

analyse herbe

Grass analysis: a tool for control of phosphate and potassium fertilization of natural and temporary grassland

Institut de l'Elevage - ITCF - INRA - ACTA - Chambres d'Agriculture - COMIFER

A better reasoned phosphate and potassium fertilization on more than 10 million hectares of grassland, ...


Gilles THEVENET - Former President of COMIFER


The proceedings of the COMIFER-GEMAS conference

Denoroy, Pascal, Christine Le Souder, Jean-Claude Fardeau. 2005. "Understanding the functioning of agro-ecosystems to adjust the supply of phosphorus, potassium and magnesium to crop needs." Coll. COMIFER-GEMAS, Blois, in November 2005,




Selected Bibliography (not exhaustive)

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  • Baize, Denis. 2000. Guide des analyses en pédologie. 2eme édition revue et augmentée. Techniques et Pratiques. INRA Edition.
  • Bélanger, Gilles, Annie Claessens, and Noura Ziadi. 2011. “Relationship between P and N Concentrations in Maize and Wheat Leaves.” Field Crops Research 123 (1): 28–37. doi:10.1016/j.fcr.2011.04.007. 2012. “Grain N and P Relationships in Maize.” Field Crops Research 126 (0): 1–7. doi:10.1016/j.fcr.2011.09.016.
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  • Bouthier, Alain, Christine Le Souder, and Pierre Castillon. 2007. “Quels seuils diagnostiques pour gérer la fertilisation magnésienne des cultures annuelles ?” In Blois : COMIFER, Paris.
  • Bui, Elisabeth. 2013. “C:N:P Stoichiometry in Australian Soils with Respect to Vegetation and Environmental Factors - Springer.” Plant Soil. doi:10.1007/s11104-013-1823-9.
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  • Denoroy, Pascal. 2012. “Rénovation du raisonnement de la fertilisation P à la suite du CASDAR-RIP : quelles questions cela pose-t-il ?” presented at the COMIFER Groupe PKMg, March 29, Paris Agrinaples.
  • Denoroy, Pascal, Fabienne Butler, Pierre Castillon, Luc Champolivier, Remy Duval, Laetitia Fourrié, Daniel Hanocq, et al. 2011. “Vers un raisonnement innovant de la fertilisation phosphatée.” In , 11. Reims: Comifer, Paris.
  • Diacono, Mariangela, and Francesco Montemurro. 2010. “Long-Term Effects of Organic Amendments on Soil Fertility. A Review.” Agronomy for Sustainable Development 30 (2): 401–22. doi:10.1051/agro/2009040.
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  • Follain, Stéphane, Christian Schvartz, Pascal Denoroy, Christine Villette, Nicolas P. A. Saby, Dominique Arrouays, Blandine Lemercier, and Christian Walter. 2009. “A Method for Assessing Available Phosphorus Content in Arable Topsoils over Large Spatial Scales.” Agronomy for Sustainable Development 29 (2): 371–79. doi:10.1051/agro:2008046.
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  • Levasseur Pascal. 2005. Composition des effleunts porcins et de leurs co-produits de traitement. Quantités produites. ITP. Paris.
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  • Morel, Christian. 2007. “Mobilité et biodisponibilité du phosphore dans les sols cultivés : mécanismes, modélisation et diagnostic.” Océanis 33 (1/2): 51–74.
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  • Pellerin, Sylvain, Celine Guiard -Van Laethem, and Fabienne Butler. 2011. “Quels outils de diagnostic et d’aide à la décision pour accompagner la fertilisation dans 5-10 ans ?” In , 8. Reims: COMIFER.
  • Pellerin, Sylvain, Alain Mollier, Christian Morel, and Christian Plenchette. 2007. “Effect of Incorporation of Brassica Napus L. Residues in Soils on Mycorrhizal Fungus Colonisation of Roots and Phosphorus Uptake by Maize (Zea Mays L.).” European Journal of Agronomy 26 (2): 113–20. doi:10.1016/j.eja.2006.07.007.
  • Raynal, Christiane, Pascal Denoroy, and Christian Morel. 2013. “Fertilisation phosphatée des cultures de carotte: une méthode innovante de diagnostic et de raisonnement des apports.” Infos CTIFL, no. 293 (aout): 60–65.
  • Schvartz, Christian, and Jean-Luc Julien. 2009. “Peut-on établir une correspondance entre les teneurs P Olsen et Joret-Hébert ou Dyer à partir de la BDAT ?” presented at the Rencontre Comifer Gemas ; “Fertilisation et analyse de terre, quoi de neuf en 2009 ?”, November 25, Blois.
  • Vinatier, Jean-Marie, and Stéphanie Dietsch. 2003. “Evaluation des logiciels de plan de fumure utilisés en RHÔNE-ALPES.” Chambre Régionale d’Agriculture Rhône-Alpes.
  • Ziadi, Noura, Joann K. Whalen, Aimé J. Messiga, and Christian Morel. 2013. “Assessment and Modeling of Soil Available Phosphorus in Sustainable Cropping Systems.” In Advances in Agronomy, 122:85–126. Elsevier.