Abstract SYMPHOS 2011

SUSTAINABLE AGRICULTURAL PRACTICES IMPACT ON
PHOSPHATE ROCK PRODUCTION
Agriculture & fertilization KN13
James L. Hendrix
University of Nebraska-Lincoln
Lincoln, NE 68588-0643, USA
In many areas of the world sustainable agricultural practices are being touted as a necessity for a sustainable
world. In the United Kingdom, China, and other nations the use of phosphorus fertilizers has been highlighted as
an area in which more sustainable practices can be employed. The possible advantages of using organic sources
for the phosphorus required by intensive agriculture are investigated. The potential for replacing inorganic
sources of phosphorous is estimated.
Limitations to the use of organic sources of phosphorus are considered and their impacts on the possible
general use of organic sources are discussed.
BENEFICIAL MICROORGANISMS FOR THE SUSTAINABLE USE OF
PHOSPHATES IN AGRICULTURE
Agriculture & fertilization KN14
Hani Antoun
Département des Sols et de Génie agroalimentaire et
Centre de recherche en Horticulture, Pavillon Paul-Comtois, Université Laval
2425 rue de l’Agriculture
Québec (Qc) CANADA G1V0A6
Phosphorus (P) is an essential nutrient for plant growth and reproduction; however the concentration of P in soil
solution is very low, varying from 0.001mg L-1 in very poor soils to 1 mg L-1 in heavily fertilized soils. The inorganic P
- -2 (Pi) is absorbed by plant roots mainly as phosphate anions (H PO and HPO4 ) which are chemically very active and
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in the presence of cations like Ca +2 in alkaline soils or Al +3 and Fe +3 in acid soils, they form sparingly soluble P, not
available for plants. Therefore, to secure high crop yields farmers are using amounts of Pi- fertilizers exceeding plant
requirements, which result in an important yearly accumulation of Pi in soils. Soil organic P (Po) is another important
reserve which can form from 20 up to 80% of total soil P. To be available for plant Po must first be mineralized
by soil microorganisms to orthophosphate anions. Since the fifties when large scale field inoculation trials were
performed in the former Soviet Union with phosphobacterin, a plant inoculant based on the Pi solubilizing bacterium
Bacillus megaterium var phosphaticum, empiric observations indicated that it is possible to improve plant P
nutrition by using phosphate solubilizing microorganisms (PSM). However although there is a huge literature on
PSM, there is until now important variability in the results obtained. This variability clearly reflects the complexity
of the different interactions taking place between the different constituents of the soil-plant ecosystem: soil, plant,
microorganisms and fauna. Weather and crop history are also factors affecting the results obtained in field trials. In
this presentation the complexity of the soil-plant ecosystem will be discussed by showing some important points
overlooked in previous studies and that should be considered when developing the PSM beneficial inoculants of the
future. Different strategies for using PSM will be presented, that will allow the use of soil reserves in Pi and Po, while
also using chemical P fertilizers in a rational manner for a sustainable agriculture, or for the direct use of phosphate
rock for organic agriculture.
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