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Phosphorus Matters II: Keeping Phosphorus on Farms | Energy Bulletin
http://www.energybulletin.net/49686
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 
eye (3).

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 
phosphorus.

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

Photo: Birdfreak.com


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 
numbers (12).

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

Photo: Kahuroa


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 
matter.



Lupines in New Zealand. Photo: Anita 363/Flickr


Soil eroded after storms carried to the sea by Betsiboka river in 
Madagascar.
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.

Fair share

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 
get it?

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 
sense way.


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.

Acknowledgements:

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.

References:

   1. B. Mollison, Permaculture: A Designers’ Manual, 2004, p. 192.
   2. Ibid
   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: 
http://www.fao.org/docrep/007/y5053e/y5053e00.htm#Contents
   9. R. Bunch, Five Fertility Principles, The Overstory #20, 
http://www.agroforestry.net/overstory/overstory20.html, accessed on 
16.01.2009.
  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, 
http://www.theecologist.org/pages/archive_detail.asp?content_id=352, 
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 
University, 
http://www.css.cornell.edu/faculty/lehmann/research/biochar/biocharmain.html, 
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,

      (available at: 
minerals.usgs.gov/minerals/pubs/commodity/phosphate_rock/).

~~~~~~~~~~~~~~~ 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.
http://www.energybulletin.net/node/47740
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Original article available here:
http://permaculture.org.au/2009/7/23/phosphorus-matters-ii-keeping-phosphorus-on-farms/