[permaculture] Phosphorus Matters II: Keeping Phosphorus on Farms | Energy Bulletin
Lawrence F. London, Jr.
venaurafarm at bellsouth.net
Tue Dec 8 17:30:19 EST 2009
Phosphorus Matters II: Keeping Phosphorus on Farms | Energy Bulletin
Published Jul 23 2009 by Permaculture Research Institute of Australia,
Archived Jul 24 2009
Phosphorus Matters II: Keeping Phosphorus on Farms
by Marcin Gerwin
Lupines. Photo: Carol Mitchell/Flickr
“Next to clean water, phosphorus will be one the inexorable limits to
human occupancy on this planet” wrote Bill Mollison in Permaculture: A
Designers’ Manual more than 20 years ago (1). It is that important that
we design phosphorus recycling into our food systems. Phosphorus is an
essential element for growing crops and no porridge, chocolate bar or
cherry jam can be made without it.
Mobilizing phosphorus present in the soil
In many soils phosphorus is naturally present in sufficient amounts,
however, it may be chemically locked up and not available for plants.
Most of agricultural soils in Western Europe and North America are
oversupplied with huge amounts of superphosphate fertilizers, which
results in binding phosphorus up with other elements so it ends up
unused in the soil. In consequence, the concentration of phosphorus may
be as high as 750 ppm, while only 45 ppm is necessary for growing grains
(2). To determine whether you have a sufficient level of phosphorus in
your soil, the surest way is to make a soil test. If the amount of
phosphorus seems to be okay, but your plants show signs of phosphorus
deficiency (purplish leaves, stunted stems), you may need help from a
specially skilled team of phosphorus extractors – fungi. Fungi are decay
experts in soils. The enzymes that they secrete allow them to break up
lignin, cellulose, chitin shells of insects and bones of animals, which
are too difficult to digest for bacteria. A single teaspoon of a healthy
soil may contain several meters of fungal hyphae, invisible to the naked
The tips of certain species of fungi have an extremely significant
function. The strong acids they produce allow them to literally dissolve
rocks and extract phosphorus from them. These fungi can form a mutually
beneficial relationship with plants roots and can transport phosphorus
to these plants. They are called mycorrhizal fungi.
Mycorrhizal fungi can extend the surface area of tree roots by 700 to
1000 times (4). They can harvest phosphates at great distances, many
meters down and away from the plant and they bring it back through the
fungal net, which is called plasmic streaming. Phosphorus is brought to
a tree in exchange for sugars created by plants, as fungi don’t have the
chlorophyll and the ability to photosynthesize.
Seedlings of trees, shrubs and perennials can be inoculated with
mycorrhizal fungi while you grow them in the nursery. Make sure you get
the right kind of fungal spores for your plants. You can inoculate roots
of existing trees and shrubs by digging holes in a root zone and
applying spores of mycorrhizal fungi near the roots. Seeds of annuals
and vegetables can be mixed with inoculum as well, however, plants from
the cabbage family (Brasicaceae), beets and spinach do not form
mycorrhizal associations at all. Instead of buying inoculum in a shop,
you can also experiment with making your own mycorrhizal inoculum.
The optimum range for phosphorus uptake by plants is pH 6.0 – 7.5, and
on either side of the pH scale phosphorus becomes immobile. A
conventional approach would be to adjust pH by adding sulfur in alkaline
soils or lime in acidic soils. It can be quite expensive on a larger
scale. But suppose you would like to grow an acid soil loving plant,
such as Northern highbush blueberry, then what? The optimum pH range for
this tasty fruit is as little as 3.5 – 4.8 pH, and it can fail
completely when pH is higher. Since phosphorus is immobile at this low
pH level, how can this plant grow at all? Well, it can receive
phosphorus through partnerships with certain species of mycorrhizal
fungi which do well in acid soils and don’t mind low pH when extracting
Mycorrhiza and herbicides
Using herbicides when mycorrhizal fungi are present in the soil may
bring unexpected consequences. Fungi can transport more than just
nutrients, but also various pesticides. A study in China revealed that
mycorrhizal fungi transported a toxic herbicide atrazine to the roots of
maize, which was hosting it (5). A similar thing could have happened on
this pasture in Australia. In the foreground: pasture with good
management (compost, compost tea and no herbicide), background: after
years of using pesticides, trees are left dead or dying (6).
You could also try to adjust the pH by increasing fungal or bacterial
domination in topsoil. You can apply brown organic mulches, such as
woodchips and shredded branches, to support fungi and to lower the pH.
Or, apply fresh green mulches and aerated compost teas to support
bacterial growth and raise the pH slightly above 7. The reason for this
is that bacterial slime is alkaline and acids secreted by fungi are,
well, acidic and they lower soil pH.
However, some nutrients are available for plants in low pH, while others
are available in high pH. The pH of soil should vary from micro-site to
micro-site and it is the role of a healthy soil biology to control it.
If we leave it to applications of lime or sulfur, the whole biological
system will be temporally determined by this input, and the quantity of
micro-sites of varying pH will be limited. So, instead of applying
minerals in order to mobilize phosphorus by a chemical reaction, you
could stimulate growth of a vigorous soil food web that will ensure
extraction of essential elements and support their continuous recycling.
Choosing phosphate fertilizer
Why it is necessary to change pH for some crops
Northern highbush blueberry grows happily only on acidic soils, because
it prefers to consume nitrogen in the form of ammonium, rather than in
the form of nitrates or nitrites (7). When pH is neutral or above, then
a certain group of bacteria, called nitrite bacteria, starts to convert
ammonium to nitrites. Since nitrates are not the favourite choice of
menu for the blueberry, they do not absorb nitrogen and wilt. When pH is
low, ammonium is plentiful, nitrite bacteria are out of work and
blueberries can flourish.
There are many soils around the world that are naturally deficient in
phosphorus, such as soils in the Amazon Basin, on Java or in Australia.
Others have been damaged by inappropriate farming practices – bare soils
were flushed by rains, which washed away phosphorus, they were depleted
by overharvesting of crops and their natural soil food webs were
destroyed, making it impossible for plants to feed on anything other
than artificial fertilizers. While soil food webs can be restored,
wherever there is not enough elemental phosphorus present, for any
reason, it must be brought back by the farmer. The other option is to
wait until mountain-generating processes raise the bottom of the sea,
where phosphate fertilizers end up. When the new mountain ranges are
formed, the rain will start to wash phosphorus out of the rocks, making
it available for plants again. But this will take some time – around
10-15 million years….
For organic gardeners one of the main sources of phosphorus are ground
phosphate rocks. Good quality phosphate rock fertilizer should be free
of all contaminants such as fluorides, heavy metals or radioactive
uranium. It can be applied directly on soil (100 kg or more per hectare)
tied to organic matter, mulch, compost and compost teas, to enhance soil
biology and enable feeding plants through the activities of bacteria,
fungi and other microorganisms. Another way is to incorporate rock
phosphate into compost with a fungal dominance, so that fungi will
transform rocks into a soluble form, or preparing a special
phospho-compost (8). Inoculating plants with mycorrhizal fungi improves
greatly effectiveness of phosphate rock fertilizers.
It has been discovered in Costa Rica, that phosphate fertilizers can be
applied on top of the mulch, rather than below it. This idea has been
conceived to prevent phosphorus from being bound up in the acid tropical
soil. And it worked. Yields of beans rose more than 3 times (9).
Clay washed out from between layers of phosphate rocks during mining can
also be used as a fertilizer. Particles of this clay are surrounded by
natural phosphates and it’s called a colloidal phosphate. Thanks to clay
the phosphorus is more easily available for plants than in phosphate
rocks. It can be used together with manure on compost piles or directly
on soil – manure acids will dissolve phosphates, which in turn will
stabilize the nitrogen in manure (10).
Superphosphate fertilizers are made from chemically treated phosphate
rocks. They are not recommended for use as they are highly concentrated
and reactive. When applied on the field they react with calcium, iron,
magnesium and aluminium, creating within seconds compounds that make
phosphorus unavailable for plants. They may react also with trace
elements, locking them up and causing deficiencies of micronutrients.
Superphosphates are water soluble and they can be easily washed away by
rains before plants have a chance to assimilate them, which later may
cause the eutrophication of lakes and rivers. Not to mention that high
concentrations of phosphorus in fertilizers (above 10) are lethal to
mycorrhizal fungi (11). Superphosphates, however, do have their
advantage: they were purified and do not contain toxic elements such as
uranium. There is a disadvantage, though. The waste product of the
purification process is stored in slag heaps, that are sometimes
unprotected and, since they contain uranium, they are radioactive.
Fluorides leaching from these heaps may also cause groundwater pollution.
Another material that is rich in phosphorus is guano – bird or bat
droppings. Bones of fish that are eaten by seabirds contain a lot of
phosphates, and as a result seabird guano also contains a high level of
phosphorus. Guano has accumulated over centuries on small islands on the
Pacific Ocean or on the coast of Chile and Peru, where it was mined in
such large quantities that its deposits are now severely depleted. In
contrary to phosphate rocks, it is a renewable resource, however, only
over a long period. Apart from phosphorus, guano also contains high
levels of nitrogen and calcium. It can be fresh, semi-fossilized or
fossilized, depending on the source.
Phosphates can also be found in mud from ponds, in freshwater mussels,
in fish waste, in algae or in recent volcanic ash. Many plants, such as
comfrey, lupine, sweetclovers, nettle or vetches accumulate phosphorus
and they can be used as green manure. Note, however, that they don’t
produce phosphorus in the way that nitrogen is fixed from the air by
legumes. Rather, they just extract phosphorus from one place and you can
put it somewhere else, leaving the source with less phosphorus.
Building your own phosphate factory
Bat house on a tree
If you would like to collect phosphorus from your local area, the
exciting way to do this is to establish a small bat colony. If there are
bats living in your neighbourhood, especially in buildings, you can
build a bat house for them. Bats will come to rest there and… they will
leave their droppings underneath. You can place a container under the
bat house and collect their guano. The additional benefit is that
insectivorous bats consume large amounts of moths, mosquitoes, flies,
grasshoppers and crickets among many others. They are high-class
specialists in insect control – in just one hour a single brown bat can
catch 1200 mosquitoes. In fact, they are so effective in eating
mosquitoes that in India an establishment of bat colonies around
Calcutta was considered as a way of dealing with excessive mosquitoes
If bats are not your kind of animal, you may consider another type of a
phosphate factory – a pigeon house. Pigeons mostly eat seeds, and these
are usually rich in phosphorus. Their manure is rich in nitrogen as
well, so it could be very useful on farms, and some people in the Middle
East still keep them. If you are wondering how the permaculture
principle of "every element should serve many functions" could be
applied with regards to pigeons, there is one interesting thing that
some breeds of pigeons can do: they can carry letters. Harry Potter fans
may feel a little disappointed and prefer owls for sending letters, but
the advantage of pigeons is that they can do it for real.
The adapted ones
Proteoid roots of Acorn
Banksia. Source: Annals of Botany
A small group of plants, which includes lupines and macadamia trees, has
developed a unique strategy to adapt to phosphorus-deficient soils.
Instead of forming mycorrhizal associations, they create densely
clustered roots that enhance phosphorus uptake. These roots received a
scientific name of proteoid roots, after the Proteaceae plant family.
Despite their unimpressive name, proteoid roots of white lupine have an
extraordinary ability: they excrete citrate and in this way increase
availability of phosphorus in the root zone (13). Well, why not call
them power roots instead? Or, phosphorus-I’m-coming-to-get-you roots?
They deserve a better name.
The intriguing thing about proteoid roots is that plants do not form
them when phosphate fertilizers are applied. To the surprise of a farmer,
Macadamia nuts on a tree
macadamia trees can show signs of phosphorus deficiency even though a
significant amount of phosphate fertilizer was added. When phosphorus is
present in soil, even in small quantities, these plants grow well by
themselves. And, when there really isn’t enough phosphorus, then compost
and mulch can be used, instead of phosphate fertilizers (14).
Protecting phosphorus from being washed away
Phosphorus loss occurs especially on bare, sandy soils, where you have
little trees and get heavy rains. While natural systems such as forests
can lose 0.1 kg of phosphorus per hectare per year, bare crop systems
can lose even 100 kg of phosphorus per hectare in one year (15). In
heavy soils or loams loss is generally very small. Most phosphorus in
the environment is in the insoluble form and unlike nitrogen, which can
be dissolved in water, it is washed away with soil particles or organic
Lupines in New Zealand. Photo: Anita 363/Flickr
Soil eroded after storms carried to the sea by Betsiboka river in
Photo: Earth Observatory
Since this is known, protecting phosphorus is easy. A good soil
structure can be created by adding organic matter and compost. Soil
biology can be further improved by brewing compost teas. Together with
compost they will add an army of nutrient recyclers to the soil: active
bacteria, fungi, flagellates, amoebas, ciliates and beneficial
nematodes. These microorganisms will retain phosphorus in their bodies
and the functioning of a whole healthy soil food web will allow
recycling it. It is also worth mentioning that certain species of
bacteria can also dissolve phosphate rocks and they help in converting
phosphorus into forms that are edible for plants (16). A no-dig system
can be introduced to prevent erosion and protect soil life, and trees
can be planted on at least 30% of land. And it takes mulch, mulch and
mulch to protect soil from rain.
Farmers can pull another ace out of their sleeves – charcoal! It is an
ancient soil amendment, tried and tested for thousands of years by
Indian tribes in the Amazon. They used it with pieces of pottery to
create Terra Preta, the black soil, which is still fertile today, an
exceptional thing in this region of the world. The porous structure of
charcoal provides a great habitat for microbes, it persists in the soil
for a very long time and it retains nutrients, including phosphorus
(17). Charcoal (or biochar) can be made not only from wood, but also
from agricultural residues, such as rice husks (18).
Roots of vetiver grass 6 months after planting.
Photo: The Vetiver Network International
To slow down run-off in the mountainous areas, crops can be grown
between rows of trees planted on contour, in an alley cropping system.
These hedgerows can be planted with nitrogen-fixing trees, or other fast
growing species. Prunings from the hedgerows can provide much needed
mulch for crops.
Instead of trees, vetiver grass can also be planted on contour. Its
roots grow 3-4 meters deep and it can reduce erosion by as much as 90%
and recharge ground water (19). Over the years, on steep slopes, natural
terraces will form behind the hedge, as soil will accumulate there. A
vetiver grass system is easy to establish and requires little
maintenance. It can also be used for stabilizing road embankments, river
banks, preventing landslides and for wastewater purification.
Some say that free market is the most efficient way of allocating scarce
resources. This may be true. If you are a farmer from Europe then
letting the invisible hand of the market allocate the remaining reserves
of phosphate rocks could be no problem for you. Let the most competitive
ones win! However, if you own half an acre of land somewhere in
Sub-Saharan Africa, your soil is poor in nutrients, yields are low and
you hardly make ends meet, then you can easily notice a simple thing –
with free market rules, scarce resources don’t go to those who need them
most. They go to those who can pay most.
In 2008 some 82 million people were added to our planet. The largest
part of this population growth took place in the South: in Asia, Africa
and in South America. All these young people, a population four times
larger than the population of New York, will need food, water, clothes
and a place to live. They will need land where crops will be grown for
them. And to grow these crops many nutrients are essential. One of them
is phosphorus. Since the reserves of phosphate rocks are scarce who will
Bill Mollison again:
Of all the elements of critical importance to plants, phosphorus is
the least commonly found, and sources are rarely available locally. Of
all the phosphate fertilizers used, Europe and North America consume 75%
(and get least return from this input because of overuse,
over-irrigation, and poor soil economy). If we really wanted to reduce
world famine, the redirection of these surplus phosphates to the poor
soils of Africa and India (or any other food-deficient area), would do
it. Forget about miracle plants; we need global ethics for all such
essential resources (20).
Field of rice in Bihar, India. Photo: yumievriwan/Flickr
It is possible to calculate a fair share of the remaining phosphate
rocks for each country, depending on the soil’s condition and number of
population. And that’s exactly what should be done. A global agreement
is necessary for sharing the last phosphate rock reserves in a common
Planting rice in Madagascar.
Photo: Gail Johnson/Flickr
Our current industrial agricultural system and the global economy that
supports it are inherently unsustainable. Extracting a limited resource,
such as phosphorus, and sending it to landfills or dumping it in the
ocean doesn’t make much sense. Sooner or later reserves of phosphate
rocks will become depleted, then what? There is some back up in the form
of deposits on the continental shelves and on seamounts in the Atlantic
and Pacific Oceans (21), but the cost of mining it can be very high and
even if industrial farmers were able to buy them, what about farmers
from Botswana? What about farmers from Madagascar or India? What will be
the cost of food, when the price of fertilizers goes up? Recycling
phosphorus is just common sense and it seems inevitable, if we wish to
continue living on Earth. It means that the exchange of our entire food
supply and waste management systems is inevitable as well. Honorable
presidents, distinguished prime ministers, sooner or later we will have
to do it.
Why wait till the industrial food supply system collapses from lack of
phosphate fertilizers or because they are too expensive to buy? Farming
the way nature does provides not only healthy soils and good yields, but
also nutritious food, flavoursome food. A juicy tomato with its
characteristic, charming smell, instead of a watery, tasteless, red
’something’. Our economy can be more local, so that it will be possible
to easily recycle nutrients, and as a result people will be more
connected. These changes can be for better, not for worse.
If we manage to close the phosphorus cycle in our countries soon enough,
we will have plenty of phosphate rocks left. We will be able to use them
for restoring degraded lands, for planting trees, and greening our
planet once again.
A big thank you goes to Geoff Lawton who provided many of the ideas and
practical solutions that are presented in this article. Geoff recorded
his thoughts and comments while teaching abroad and he sent them to me
as audio files. His insights are a backbone of this work.
1. B. Mollison, Permaculture: A Designers’ Manual, 2004, p. 192.
3. J. Lowenfells, W. Lewis, Teaming with Microbes, 2006, p. 53.
4. Ibid, p. 61.
5. Honglin Huanga, Shuzhen Zhanga, Xiao-quan Shana, Bao-Dong Chena,
Yong-Guan Zhua and J. Nigel B. Bellb, Effect of arbuscular mycorrhizal
fungus (Glomus caledonium) on the accumulation and metabolism of
atrazine in maize (Zea mays L.) and atrazine dissipation in soil.
6. See also: K. Lewis, B. McCarthy, Nontarget tree mortality after
tree-of-heaven (Ailanthus altissima) injection with imazapyr, Northern
Journal of Applied Forestry, 25(2):66-72, 2008. In this study a
herbicide imazapyr was injected to Tree-of-heaven (Ailanthus altissima),
which in some regions is an invasive tree. The results showed that
imazapyr injections not only killed all injected tree-of-heaven, but
also 17.5% of neighboring (within 3 m) noninjected tree-of-heaven and
eight other tree species 62 weeks after treatment. The possible ways of
transmission of the herbicide were root grafts, mutually shared
mycorrhizal fungi, root exudation and absorption, and/or leaf senescence.
7. Methodology: Integrated Production of Highbush Blueberry, edited
by Danuta Krzewinska, 2005, p. 7.
8. See: chapter 9 “Ways of improving the agronomic effectiveness of
phosphate rocks” in: F. Zapata and R.N. Roy, Use of Phosphate Rocks for
Sustainable Agriculture, FAO 2004. Available at:
9. R. Bunch, Five Fertility Principles, The Overstory #20,
http://www.agroforestry.net/overstory/overstory20.html, accessed on
10. P. Sullivan, Alternative Soil Amendments, ATTRA,
http://attra.ncat.org/attra-pub/altsoilamend.html, accessed on 13.01.2009.
11. J. Lowenfells, W. Lewis, op. cit., p. 151.
12. Bats, The Ecologist,
accessed on 15.01.2009. In some parts of the world bats may carry
viruses that are dangerous to humans. Before building a bat house in
your backyard, please make sure there are no health concerns.
13. J. F. Johnson, D. L. Allan and C. P. Vance, Phosphorus
Stress-Induced Proteoid Roots Show Altered Metabolism in Lupinus albus,
Plant Physiology, Vol. 104, Issue 2, p. 657-665.
14. A. L. Shigo, Troubles in the Rhizosphere, The Overstory #70,
http://www.agroforestry.net/overstory/overstory70.html, accessed on
13.01.2009. See also: G. Porter, R. Yost and M. Nagao, The Application
Of Macadamia Nut Husk And Shell Mulch To Mature Macadamia Integrifolia
To Improve Yields, Increase Nutrient Utilization, And Reduce Soil P Levels.
15. B. Mollison, op. cit.
16. R. Ivanova, D. Bojinova, K. Nedialkova, Rock Phosphate
Solubilization by Soil Bacteria, Journal of the University of Chemical
Technology and Metallurgy, 41, 3, 2006, 297-302.
17. Soil Fertility Management and Soil Biogeochemistry, Cornell
accessed on 16.01.2009.
18. S. M. Haefele, Black Soil – Green Rice, Rice Today, April-June
2007, p. 26-27.
19. Soil erosion, The Vetiver Network International,
http://www.vetiver.org/g/soil_erosion.htm, accessed on 16.01.2009.
20. B. Mollison, op. cit.
21. S. M. Jasinski, Phosphate Rock, Mineral Commodity Summaries,
January 2008, p. 124,
~~~~~~~~~~~~~~~ Editorial Notes ~~~~~~~~~~~~~~~~~~~
Thanks so much to Marcin for this well-researched article on this
important topic. We republished the first part of this series here. KS.
Original article available here:
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