Don't believe everything you see and hear.
Biologist
Mohamed Hijri presents an interesting TED talk entitled:
A simple solution to the coming phosphorus crisis
http://www.ted.com/talks/mohamed_hijri_a_simple_solution_to_the_coming_phosphorus_crisis.html
He talks about two issues associated with the phosphorus nutrition of plants. The
first is the finite nature of phosphate reserves (the source of phosphorus
fertilizer), and the second is algal blooms arising from losses of phosphorus
from agricultural fields. We appreciate the recognition of the important role
of phosphorus in supporting agricultural production for a future global
population of over 9 billion. But he presents many statements as fact without any supporting references. Many of these
statements contradict a considerable volume of published peer-reviewed
scientific and technical literature. IPNI welcomes discussion of issues associated
with phosphorus fertilizer use, and the opportunity to clarify public
perception of those issues. Applying the right source of phosphorus fertilizers
at the right rate, right time and right place is consistent with maintenance of
an appropriate level of mycorrhizae in agricultural soils.
Biologist
Mohamed Hijri presents a very polished lecture in French on the important topic
of two issues associated with the phosphorus nutrition of plants. The first is
the finite nature of phosphate reserves; the source of phosphorus fertilizer,
and the second is algal blooms arising from losses of phosphorus from
agricultural fields.
While the
lecture is well presented, certain statements are presented as fact without any
reference to supporting literature. Here we point out that these statements
contradict a considerable volume of published peer-reviewed scientific and
technical literature
1. “There is a
global phosphorus crisis, and no one is talking about it.” In recent years,
there has been considerable international activity and discussion of phosphorus
issues. One example is the organization called Global TraPs – the Global
Transdisciplinary Processes for Sustainable Phosphorus Management, a
multi-stake holder forum based jointly in Germany and the U.S. In addition, the
International Fertilizer Development Center published a technical bulletin (Van
Kauwenbergh, 2010) called “World Phosphate Rock Reserves and Resources” which,
while highlighting the industry’s concern for finite resources, indicates that
the figures used by Professor Hijri are out of date, and shows that current
reserves are considerably larger, sufficient for over 300 years at current
rates of extraction. The reserve figures in this publication are in agreement
with the USGS (2013) publication of mineral commodity summaries. In addition,
the International Plant Nutrition Institute has published a 2013 article “World
Reserves of Phosphate Rock…a Dynamic and Unfolding Story” which points out that
over the past decade or so there has been concern that the world would soon
deplete its phosphate rock resources, and face a catastrophic phosphorus
shortage; however, recent and thorough estimates of world supply indicate that a
crisis is not imminent, and that we will not soon run out of phosphate rock.
2. “Peak
phosphorus will occur by 2030 and all reserves will be gone by 2100.” As
pointed out above, more recent published material (e.g. Scholz and Wellmer,
2013) and presentations show that this statement, usually attributed to Cordell
(2009), is based on outdated reserve estimates and methodology and has been
strongly criticized because it over estimates the urgency of the phosphorus
supply risk. The modeling approach in the graph used to demonstrate the peak of
phosphate production occurring in 2030 has also been shown to be inaccurate and
unrealistic (Hendrix, 2011). In addition, Sutton et al. (2013; figure 2.9 on
page 15) point out that many other important commodities, including crude oil
and natural gas, and the important micronutrient zinc, have much shorter
estimates for reserve life than does phosphate.
3. “Only 15%
of [phosphorus fertilizer applied] goes to the plant. 85% is lost. It goes into
the soil, ending its journey in the lakes.” While eminent soil fertility
scientists recognize that soil reactions with applied phosphate limit its
direct uptake by plants in the short term, the long term recovery can approach
90%, because phosphorus is retained in the soil in slowly available forms
(Syers et al., 2008). Estimates of the global phosphorus cycle depicted in
Figure 3.2 on page 23 of Sutton et al. (2013) indicate that the total transfer
of phosphorus from the terrestrial ecosystem to fresh waters is considerably
less than 85% of the total input of phosphorus to agricultural soils. It also
indicates that much of this transfer arises from erosion, a process that
carries indigenous soil phosphorus as well as that applied in the form of
fertilizers. So, the actual loss of phosphorus from fertilizer is both smaller
and less direct than indicated in the presentation by Professor Hijri. Industry
is engaging 4R Nutrient Stewardship to reduce these losses; examples include a
collection of articles under the topic of Lake Erie P Issues and a list of
activities at www.nutrientstewardship.com.
4. The
presentation suggests that a plant with mycorrhizae will take up 90% of applied
phosphorus in comparison to the 15% taken up by plants in conventional
agriculture. First, this comparison is misleading, since two factors are
changing at once, both rate of application and mycorrhizal presence, and it is
well known that recovery efficiencies decline as rates increase. An example of
a study actually measuring change in phosphorus uptake caused by mycorrhizae is
provided in Table 3 of Grant et al. (2005). Calculations from those data show
that the mycorrhizal benefit to phosphorus recovery declining from 69% at low
levels of P fertilization to no benefit at very high levels of P fertilization.
This is a considerably smaller benefit than is implied by comparing the
presented figures of 90% and 15% recovery, and does not take into account the
yield losses associated with reduced levels of P fertilization. Second, the
implication that plants grown in conventional crop production are without
mycorrhizae is incorrect. Mycorrhizae are present in most soils when crops
supporting them are grown. These crops include corn, soybeans, wheat and other
cereals. Third, studies comparing plants with and without mycorrhizae in the
field show much smaller increases in phosphorus uptake, often associated with
lower yields. For example, research conducted near Montreal (Liu et al., 2003)
showed that corn yield response to the presence of mycorrhizae was small (8%), occurring
only when corn was not fertilized with phosphorus, while fertilization with
phosphorus produced yield gains of up to 18%. In this experiment, fertilizing
at recommended rates reduced mycorrhizal hyphae density by only 11%. Similar
mutually beneficial effects of mycorrhizae and phosphorus fertilizer were shown
in research conducted in British Columbia (Bittman et al., 2003). In certain
low phosphorus soils of Australia, mycorrhizae have been shown to have
parasitic activity, reducing the yields of crops (Ryan et al., 2005). The
fertilizer industry’s 4R Nutrient Stewardship approach recognizes the value of
mycorrhizae in crop production (IPNI, 2012 page 2-7). Applying the right source
of phosphorus fertilizers at the right rate, right time and right place is
consistent with maintenance of an appropriate level of mycorrhizae in
agricultural soils.
We appreciate
the recognition of the important role of phosphorus in supporting agricultural
production for a future global population of over 9 billion. Industry welcomes
discussion of issues associated with phosphorus fertilizer use. Improvements in
the sustainability of such agricultural production depend on an accurate public
perception of these issues, and thus we encourage Professor Hijri to correct the
record on the four important points outlined above.
References
Bittman, S., C. G. Kowalenko, et al. 2006. Starter phosphorus and
broadcast nutrients on corn with contrasting colonization by mycorrhizae. Agron
J 98(2):394-401.
Cordell, Dana, Jan-Olof Drangert, and Stuart White. 2009. The
story of phosphorus: Global food security and food for thought. Global
Environmental Change 19:292–305.
Grant, C., Bittman, S., Montreal, M., Plenchette, C. and Morel, C.
2005. Soil and fertilizer phosphorus: Effects on plant P supply and mycorrhizal
development. Can. J. Plant Sci. 85: 3–14.
Hendrix, C.S. 2011. Applying Hubbert curves and linearization to
rock phosphate. Working Paper Series. WP 11-18. Peterson Institute for
International Economics. Washington, DC. p. 12
IPNI. 2012. 4R Plant Nutrition Manual: A Manual for Improving the
Management of Plant Nutrition, Metric Version, (T.W. Bruulsema, P.E. Fixen,
G.D. Sulewski, eds.), International Plant Nutrition Institute, Norcross, GA,
USA.
Liu, A., Hamel, C., Elmi, A. A., Zhang, T. and Smith, D. L. 2003.
Reduction of the available phosphorus pool in field soils growing maize
genotypes with extensive mycorrhizal development. Can. J. Plant Sci. 83:
737–744.
Ryan, M. H., A. F. van Herwaarden, et al. 2005. Reduced growth of
autumn-sown wheat in a low-P soil is associated with high colonisation by
arbuscular mycorrhizal fungi. Plant Soil 270(1-2): 275-286.
Scholz, R. and F.W. Wellmer. 2013. Approaching a dynamic view on
the availability of mineral resources: what we may learn from the case of
phosphorus? Global Environmental Change. 23:11-27
Sutton et al. 2013. Our Nutrient World: The challenge to produce
more food and energy with less pollution.
Global Overview of Nutrient Management. Centre for Ecology and
Hydrology, Edinburgh.
Syers, JK, AE Johnston, and D Curtin. 2008. Efficiency of soil and
fertilizer phosphorus use. FAO Fertilizer and Plant Nutrition Bulletin 18. Food
and Agriculture Organization of the United Nations, Rome, Italy.
USGS. 2013. Mineral commodity summaries. [Online]. Available at http://minerals.usgs.gov/minerals/pubs/
commodity/phosphate_rock/index.html#mcs (verified 19 April 2013).
Van Kauwenbergh, S.J. 2010. World Phosphate Rock Reserves and
Resources. IFDC. Muscle Shoals, AL, USA. www.ifdc.org
