Seabird Guano vs Bat Guano: What the NPK Label Leaves Out

Same Number, Different Bag

A gardener posted two boxes of guano on r/OrganicGardening and asked a question the thread never answered cleanly:

“Can someone please explain to me why these boxes are identical? Does one do something the other doesn’t? Even the analysis is the same percent of phosphorus…”

Twenty-eight replies followed. The one that got closest was also the shortest: one is a guano, the other is a fossilized guano, rock that gets mined.

That answer is correct. It also points at something no bag tells you. Two products can carry the same name, print the same phosphorus figure, and come out of deposits thousands of years apart in age. The number matches. The material does not.

The gap matters more than it looks. A grower buying five pounds for a flower bed can absorb it. A blender buying twenty tons to formulate against a guaranteed analysis cannot, because phosphorus that shows up in the first season and phosphorus that shows up across three seasons are not interchangeable inputs. Only one of them appears on the label.

There is a second cost, quieter than the first. When two materials share a name, price comparison stops working. A buyer looking at two quotations reads the same three numbers on both, picks the cheaper, and receives something that behaves differently in the ground. Nobody lied. The label simply was not built to carry the information that separates them.

This page is about which one you actually need, and how to tell them apart before a container loads. It covers what seabird guano is, where the fossilized kind parts company with the fresh kind, what a guano analysis leaves out, how far the numbers move between batches, and what to ask a supplier for.

The bat guano comparison sits in the middle. Most buyers reach for it first. It is not the comparison that decides the purchase, and the reason why is the most useful thing on this page.

Where Seabird Guano Comes From

Seabird guano is the accumulated droppings of fish-eating coastal birds. Cormorant, pelican and gull colonies nest on dry offshore islands, and where rainfall stays low their deposits build up faster than weather strips them away.

Diet explains the chemistry. Phosphorus and calcium dominate. Nitrogen does not. Marine birds excrete uric acid rather than urea, and uric acid holds nitrogen in a form that resists leaching for a while. That is why fresh deposits carry nitrogen at all, and why old ones stop carrying it.

Geography does the rest. The deposits worth mining sit where three conditions overlap: large colonies, almost no rain, and enough time. Break any one of those and the material either never accumulates or washes away before it matters. This is why the commercial map is so short. Peru, Chile, Namibia, a handful of Pacific islands, and very little else.

Peru is the reference point for the whole category. The Chincha Islands supplied most of the world’s guano through the middle of the nineteenth century, and roughly 20 million tons moved to Europe and North America between 1848 and 1875. The trade reshaped agriculture on two continents and financed a government on a third.

People still ask why we stopped. Two things happened close together. The best Peruvian deposits ran down inside a few decades of serious extraction, and the Haber-Bosch process arrived to pull nitrogen out of the air for almost nothing. Guano lost its nitrogen argument to industrial chemistry and never got it back.

What stayed in commercial supply afterwards was mostly the older, weathered material. So the seabird guano nutrients you can buy today are not the seabird guano nutrients that built the nineteenth-century trade. Same islands, same birds, different rock.

The birds themselves have not changed their behaviour. The deposits available for extraction have. Anything laid down in the last century sits on islands that are now protected, monitored, or both, and the material moving through commercial channels comes from older seams that were already there when the protections arrived. That shift is the entire subject of the next section.

Two Materials, One Name

Guano deposits get classified by age and genesis, not only by which bird produced them. The academic literature does this explicitly. One review chapter splits the category by age, by chemical composition and by geographical origin before it discusses agricultural use at all. The trade mostly does not. Buyers fall into the gap.

Fresh or lightly weathered guano still holds its nitrogen and potassium. Old deposits do not. Rain leaches soluble nitrogen out across centuries. Organic matter breaks down and leaves. What remains is a calcium-phosphate rock, dicalcium phosphate, sitting where a colony used to be. One Australian supplier describes its own material in exactly those terms: bird droppings laid down thousands of years ago, nitrogen depreciated away, phosphate left behind.

Two words. Two products.

The weathering runs on a gradient rather than a switch, which is why the market carries every intermediate stage at once. A deposit that sat under fifty years of light rain looks nothing like one that sat under five thousand. Both get bagged under the same two words.

What the market sells under one name

Analysis (N-P-K)	Sold as	タイプ
0-4-0	liquid seabird guano	weathered, diluted
0-10-0	200-mesh powder	weathered
0-11-0	Down To Earth · Old Farmer’s Almanac · ARBICO	weathered, US retail standard
0-12-0	Roots Organics	weathered
6-12-0	various	partly weathered
12-11-2	BlueGold, OMRI Listed	fresh
12-12-2.5	Blue Ocean	fresh

Read down the nitrogen column. Zero to twelve. Same product name on every row.

Search behaviour follows the confusion. People look up seabird guano 0-11-0 and peruvian seabird guano 12-11-2 as though they were separate products, which in practice they are. They look up seabird guano 12 12 2.5 because a bag in front of them says exactly that and nothing online explains why it differs from the bag beside it.

Colour carries almost as much information as the analysis. Weathered seabird deposits run grey to white, because calcium carbonate from fish bone dominates whatever is left. Fresh guano is darker. Bat guano is darker still, often close to black. If a supplier sends a photograph of pale grey powder alongside a certificate claiming twelve percent nitrogen, one of those two things is wrong, and it is worth finding out which before the order goes in.

A 2012 thread on Houzz shows how invisible this stays at the point of sale. The grower had bought bat guano at 3-10-1 alongside seabird guano at 1-10-0 to feed summer flowers. Both bags said ten percent phosphorus. One carried three times the nitrogen of the other. Nothing on the front of either package said so, and the grower only worked it out after photographing both labels and asking strangers online.

Weight and handling change with age too, which gives a buyer one more check. Weathered material mills to a fine, dense, almost chalky powder that flows cleanly. Fresher deposits hold more organic residue, clump in humid storage, and carry an odour that weathered rock does not. Anyone who has opened both knows which one arrived before reading the certificate.

High phosphorus seabird guano is the weathered end of that range, and it makes up most of what the world now supplies. The guano phosphate deposits still being worked commercially are, with few exceptions, old ones. Rutom mines and processes that type. Ours is not collected fresh, and the analysis reflects it: nitrogen 0.3%, potash 0.5%. Anyone selling high phosphorus guano at eleven or twelve percent phosphate is selling weathered material, whether or not the label uses the word.

None of which makes fresh guano a worse product. It makes it a different one, priced and used differently, and worth buying deliberately rather than by accident. The failure mode is not choosing wrong. It is not knowing a choice was being made, then blaming the material when the season underperforms.

What the Bag Doesn’t Tell You

Here is the part that costs money.

On a US fertilizer bag, the middle number in an N-P-K string is available phosphate, expressed as P₂O₅. Down To Earth prints 0-11-0; the 11 is available phosphate. Roots Organics prints 0-12-0; the 12 is available phosphate. Those two figures sit in the same units, and buyers compare them constantly. That is reasonable. It is what the units exist for.

Total phosphorus is a different quantity. It is the available fraction plus the phosphorus still locked in the mineral: the share that soil microbes and ion exchange release slowly, across seasons rather than weeks. Total phosphorus is what sits in the rock. Available phosphorus is what a crop can reach this year. The difference between them is not waste. It is inventory.

The label only shows available phosphate. Total phosphorus is absent from the front of the bag, and in most cases from the packaging entirely.

Two consequences follow.

A bag reading 11 and a bag reading 12 can sit on completely different total-phosphorus figures, invisibly. You cannot infer one from the other, because the ratio between them depends on the ore rather than on the brand. Two suppliers can both be telling the truth and still be describing materials that behave differently in year two.

And the slow-release behaviour that every guano supplier advertises comes out of that locked fraction. So the claim gets made without the number underneath it. One brand calls its material slow-release. Another gives a whole section to nutrients for now and later. Neither publishes the total phosphorus figure that would let a buyer check either statement.

We pulled the five guano articles ranking on page one of Google and searched them for the phrase “total phosphorus”. It appears in none of them. Neither does any explanation of what the middle number in the NPK string actually measures. The number gets used everywhere and defined nowhere.

Our two figures

Third-party analysis of Rutom’s micronized powder:

• Total P₂O₅ — 33.09% on the batch tested (SGS, method AOAC 958.01-2005)
• Guaranteed minimum: not less than 30%
• Available P₂O₅ — 12%

One caveat, stated plainly rather than buried. The 12% is our internal control figure. The SGS work covers total phosphorus, calcium, magnesium and heavy metals. It carries no available-phosphate line, so that number does not have the outside backing that the 33.09% has. We would rather write this sentence than let two figures sit side by side implying equal standing.

Ask any supplier, this one included, which published numbers came from an external laboratory and which are internal control values. The answer separates vendors faster than price does, and it costs nothing to ask.

Suppliers are not hiding the total figure. Most of them have never been asked for it, because the packaging convention trained everyone to stop reading at three numbers.

This is also why searches for seabird guano npk and guano npk return so little that helps a buyer. The NPK string was designed to compare finished fertilizers on what a crop gets this season. It was never designed to describe a mined mineral, and it hides the property that makes mined minerals worth buying in the first place. Anyone comparing seabird guano phosphorus across suppliers on the N-P-K line alone is comparing one third of the picture and calling it a decision.

Why the Numbers Move

Every serious guide to guano raises the same worry, usually late in the article and usually without resolving it: the analysis varies. One garden-science blog gives batch variability its own section and concludes, honestly enough, that a buyer cannot be certain what is in the bag. None of them say by how much.

We can, because it is our ore.

Calcium oxide across our deposits runs 28–40%, depending on which part of the seam a batch comes from. That is geology, not a manufacturing tolerance. Colonies did not deposit evenly. Weathering did not proceed evenly. Screening and milling change particle size, never the mineral underneath.

The batch SGS tested in June 2025 came in at 39.55% CaO, near the top of that range, with magnesium oxide at 3.20%.

So a guaranteed minimum and a batch figure are two different kinds of number, and quoting one where the other belongs misleads people. A minimum is a floor the supplier commits to across every shipment. A batch figure is what one specific lot measured on one specific day. Put the minimum in the contract. Ask for the batch data before the container loads.

Every mined input behaves this way. Rock phosphate, gypsum, langbeinite, all of them. The difference between suppliers is not whether the numbers move, because they all move. The difference is whether you get told the range and handed the lot data, or whether you get one tidy figure repeated on every document you are ever shown.

A supplier who quotes an identical analysis for every batch is quoting a marketing figure. That is not necessarily dishonest. It usually means the number came off a brochure rather than out of a laboratory, and it means you have no way to verify what actually arrived on the pallet.

Buyers who blend to a formula feel this first. If you are formulating to hit a target phosphate level, a five-point swing in the input changes the recipe, and discovering it after the batch is mixed costs more than one email would have. Growers applying straight material feel it later and more mildly, usually as a season that underperformed for no obvious reason.

There is a straightforward test for any supplier in this category. Ask what the range is. A vendor who has run enough batches to know will answer in one sentence. A vendor who has not will send you the brochure again.

One honest counter-argument deserves an answer here, because a well-informed buyer will raise it. An Australian supplier warns that a phosphorus figure quoted as a range, say 9 to 11 percent, can indicate material blended from several deposits of uneven quality. That warning is fair. A range can mean two very different things.

The distinction is whether the supplier can also produce the batch. Natural variation within one seam gives you a range や a lot-specific analysis, because each shipment was tested. Blending gives you a range instead of a lot analysis, because the blend changes and nobody tracked it. Ask for both. If the range comes with a batch certificate, the range is geology. If the range arrives alone, ask what is being averaged and where each component came from.

Variability also explains a complaint that surfaces every season on grower forums: the same product, bought twice, performing differently. Sometimes that is storage or soil. Often it is simply two lots from two parts of a seam, both inside spec, neither flagged to the buyer because nobody asked and nobody volunteered.

Seabird Guano vs Bat Guano

The nutrient contrast is covered well enough elsewhere that repeating it at length adds nothing. Here it is compactly, with two other phosphorus sources included because buyers shortlist all four together.

	Seabird guano (weathered)	Bat guano	骨粉	Fish bone meal
Typical analysis	0-11-0 to 0-12-0	7-3-1 · 10-3-1 · 3-10-1	3-15-0	3-16-0 · 4-12-0 · 4-17-0
Leads with	phosphorus, calcium	nitrogen	phosphorus	phosphorus
リリース	slow	faster	slow	moderate
Colour	grey to white	dark brown to black	off-white	grey-brown
ソース	island deposits	cave floors	animal by-product	fish processing

Insect-eating bats produce high-nitrogen guano. Fish-eating seabirds produce high-phosphorus guano. Fruit bats land somewhere between. That is the standard framing of seabird vs bat guano and it is broadly correct as far as it goes.

It is also not the comparison that should settle your order.

The spread inside seabird guano, zero to twelve percent nitrogen depending entirely on how long the deposit sat in the rain, runs wider than the gap between a weathered seabird product and a bat product. Buy on the analysis and the age of the deposit. The bird is a proxy, and a loose one.

Buyers weighing seabird guano vs bone meal usually land on a different axis. Bone meal is an animal by-product, which brings certification questions, market-access restrictions in some countries, and a customer segment that will not touch it. Guano is a mined mineral and carries none of those. Where the two overlap is phosphate level, and there bone meal at 3-15-0 looks stronger on the label than weathered guano at 0-11-0 until you ask the same question this page has been asking throughout: stronger on which fraction.

Seabird guano vs fish bone meal is a closer contest on both origin and phosphate. There the deciding factors are usually particle size, odour, and price per unit of phosphate rather than anything nutritional. Fish bone meal also brings a nitrogen contribution that weathered guano cannot match.

Notice what the fish bone meal column does. Three analyses sit in it, from 3-16-0 through 4-17-0, sold by different manufacturers under one product name. The pattern this page opened with is not unique to guano. It runs through every processed and mined organic input, and the only defence is asking for the specific analysis rather than the category average.

One safety note, and its boundary

Bat guano carries a hazard that seabird guano does not. Histoplasma capsulatum grows in soils enriched by bat droppings, and disturbing dry guano releases airborne spores that cause histoplasmosis when inhaled. State health departments publish attic and crawlspace guidance on precisely this problem. Two growers in New York died of lung infection linked to bat guano used as fertilizer, and the case was reported widely enough that customers now raise it unprompted.

Now the boundary, because this gets overstated in both directions.

The documented risk sits in mining, handling and dust exposure. It does not sit in dried, bagged product on a shelf. Workers extracting cave deposits without respiratory protection face a genuine occupational hazard. A gardener opening a sealed bag does not face the same one. Read the state health department guidance and the Bat Conservation International material before repeating anything stronger, and treat any supplier who uses this risk to sell against a competing product with the scepticism that deserves.

For the record, we do not sell bat guano. Describing it accurately costs us nothing, which is exactly why you should weight this section accordingly and check the sources yourself rather than taking our word for it.

What Fossilized Guano Is Not Good For

Three limits, stated before purchase rather than after.

Nitrogen. Weathered seabird guano is not the right choice if you need nitrogen. Ours tests at 0.3%. That is a rounding error, not a feed. A grower on a cannabis forum worked this out the slow way back in 2007 and told the thread you need a high N guano to go with the seabird guano in veg, then a high-phosphate one for flower. He was right. It should not have taken him a growing season to find out, and it would not have if the bag had carried one extra line. Pair weathered guano with an amino acid fertilizer, blood meal, or any fish-based nitrogen source, and plan the nitrogen separately rather than hoping the guano covers it. Growers running a full organic programme usually end up with two or three inputs where a synthetic user would have one, and this is the input that forces that decision earliest.

Organic matter. Most guano articles lead with high organic matter as a headline benefit, and for fresh deposits that is fair. Weathered material does not deliver it. With calcium oxide near 40%, phosphate above 30% and silica around 10%, very little room remains for anything else. Low organic matter is a property of mined phosphate rock rather than a fault in it. If soil biology is what you are buying, buy compost and buy the phosphate separately. Trying to get both from one weathered mineral input will disappoint you on both counts.

pH. The calcium that makes this material useful also pushes soil pH upward. On already-alkaline ground it will not help and may hurt. Check a soil test before ordering rather than after spreading. Growers on acid soils get a second benefit from the same calcium, which is one reason this material sells better into tropical and high-rainfall regions than into arid ones. Growers on calcareous soils should probably be looking at a different phosphate source entirely, and any supplier worth dealing with will say so rather than take the order.

None of these three limits is unusual for a mined mineral. What is unusual is finding them written down before the invoice rather than after it, and that is the only reason they appear here.

How to Read a Guano Label

Five things, in the order that matters for a purchase decision.

Heavy metals. Phosphate minerals concentrate trace elements. That is chemistry, not a supplier defect, and a serious vendor publishes the numbers rather than hoping nobody asks. Guano Australia states the principle on its own site: a reputable brand shows cadmium, lead and mercury on the label. Most US retail bags show none of them. Ours, from the June 2025 SGS work (AOAC 2006.03-2006):

Element	Result
鉛	<5 mg/kg
カドミウム	1 mg/kg
Mercury (Hg)	<1 mg/kg
Arsenic (As)	29 mg/kg
Chromium (Cr)	10 mg/kg
Nickel (Ni)	<5 mg/kg
Selenium (Se)	<5 mg/kg

Check these against the limits your own market applies. Organic input standards, mineral fertilizer regulations and individual certifier rules each set their own thresholds, and they do not agree with one another. A figure that clears one framework can fail another. The useful question is never whether a material is safe in the abstract, but whether it clears the standard you are registering under.

Units. Phosphorus and potassium report as oxides, P₂O₅ and K₂O, on documents from either side of the Pacific. Calcium and magnesium often do not. A Chinese analysis reports CaO. A US guaranteed analysis reports elemental calcium. Our 39.55% CaO converts to roughly 28% Ca. Compare like with like, or the same material looks four times richer on one document than on the other, and a buyer reading two quotations side by side reaches the wrong conclusion in about ten seconds.

Insolubles. Ask what fraction does not dissolve. Our powder runs about 10% SiO₂, silica that came out of the deposit rather than out of a mixing plant. Sand content is a live quality question in this category, common enough that buyers search for it directly, and a supplier who has never measured it has told you something useful about their process control.

Particle size. Micronized powder at 5,000 to 6,000 mesh passes drip lines. Coarser grades block them. Granular grades belong in soil incorporation and nowhere near an emitter. Match the grade to the application before price enters the conversation, because a cheap grade that plugs an irrigation system is not cheap by the end of the week.

Certification scope. OMRI listing, ECOCERT approval and USDA NOP compliance are three separate things covering three separate scopes, issued by three separate bodies. One does not stand in for another. Ask which body, which product, and when the certificate expires. A certificate covering a supplier’s granular line says nothing about their powder, and certificates lapse more often than websites get updated.

Put together, that is what a full seabird guano analysis should let you check. A document that answers fewer than four of those five is a sales sheet wearing the clothes of an analysis.

One practical note on requesting documents. Ask for them before negotiating price rather than after. A supplier who has the paperwork sends it within a day, and a supplier who does not will spend that day deciding what to tell you. The delay itself is informative, and it costs nothing to observe.

How to Use Seabird Guano Effectively

Seabird guano is a phosphorus input, so it belongs in the ground before roots need it rather than sprayed on once they do.

Work it into the top few inches at bed preparation, two to four weeks ahead of planting, and let soil moisture start mineralisation before the crop arrives. For transplants, a tablespoon or two in the hole, mixed through the backfill rather than sitting against the roots. Established plants take a side dressing during the growing season, worked lightly into the surface and watered in.

Avoid over-application. Calcium load and salt index both set a practical ceiling, and phosphorus a crop cannot use in one season stays in the soil rather than washing through. That sounds harmless until soil test phosphorus climbs high enough to trigger restrictions in nutrient-managed catchments, at which point the surplus becomes a compliance problem rather than an agronomic one. Follow a soil test wherever you have one. On alkaline soils, cut the rate or skip the input.

Micronized grades suspend well enough for foliar work and drip application at roughly 1:800 to 1:1000 in water. Agitate the tank, and run clean water through the lines afterwards. Granular grades are for incorporation only.

Timing matters more with weathered material than with fresh. The available fraction moves on the schedule any phosphate does. The locked fraction moves on the soil’s schedule, which means warm, biologically active ground releases it and cold or compacted ground does not. Autumn applications on temperate soils sit largely inert until spring.

That schedule has one useful consequence. Because the locked fraction cannot leach the way soluble phosphate can, an application that misses its window is delayed rather than lost. Growers on sandy or high-rainfall ground usually value that more than the headline analysis, and it is the strongest agronomic argument for a mined phosphate over a soluble one.

Store it dry. Fine powder at 1.2% moisture will pick up water from humid air and cake, which does not change the analysis but does ruin the handling.

Choosing a Supplier

The questions that separate suppliers in this category are narrower than most buyers expect, and none of them are about price.

Ask for the batch certificate of analysis. Not a typical analysis, not a brochure figure, the specific lot being quoted. Then ask which lines on it came from an external laboratory and which are internal control values, because a single document can carry both and look perfectly uniform. Ask for the range alongside the number. With a mined product the range is the honest answer, and a supplier who cannot give you one has not tested enough batches to know it.

Ask about sourcing. Extraction happens on islands that are also breeding sites, and harvesting outside the breeding season is the difference between a renewable input and a damaged colony. This is not a soft question. Certification bodies audit it, and that audit is what stands between this category and the collapse that ended the Peruvian trade the first time around. Ask which body, which scope, and when the certificate expires.

Then check units before comparing two quotations. Half the price gaps we get asked to explain turn out to be a CaO figure sitting next to a Ca figure on documents from two different countries.

One more, easy to skip and expensive to skip. Ask what happens when a batch falls outside the stated range. A supplier with real process control has an answer involving blending, rejection or renegotiation. A supplier without one will tell you it never happens, which is the least believable sentence in this trade.

Then ask how the material is packed and how long it has been sitting. Fine mineral powder is stable chemically and fragile physically. A lot that spent eight months in a humid warehouse arrives with the same certificate and different handling behaviour, and the certificate will not mention it.

A last word on price comparison, since it is where most of these conversations start. Per-tonne pricing across two suppliers only means something once the grade, the phosphate basis and the certification scope all match. Two quotations that differ by fifteen percent frequently turn out to be quoting different mesh sizes, or one quoting on total phosphate and the other on available. Line those three things up first and the price gap either disappears or becomes real. Either answer is worth having before an order goes out.

Rutom mines and processes weathered seabird guano in micronized powder and granular grades, certified by ECOCERT and CERES as an organic input. Particle sizes run from 2,500 to 6,000 mesh, with granular at 2 to 4 mm for base application. If you want the analysis for a specific lot rather than a sales sheet, ask for it. That is the document worth reading, and any supplier worth buying from will send it without being chased.

よくある質問

Is seabird guano the same as bat guano?

No. Seabird guano leads with phosphorus and calcium; bat guano leads with nitrogen. The larger difference is age. Most seabird guano sold today is weathered rock that lost its nitrogen centuries ago, which is why bags range from 0-11-0 to 12-12-2.5 under one product name.

Why does my seabird guano show 0-11-0 when another bag shows 12-11-2?

Because they are different materials. The 0-11-0 product is a weathered deposit with the nitrogen leached out. The 12-11-2 product is fresher. Both are seabird guano and both labels are accurate.

What is the difference between total and available phosphorus?

Available phosphate is what a crop can take up in the current season, and it is the number printed on the bag. Total phosphorus includes the fraction still locked in the mineral, released slowly by soil biology. Total phosphorus rarely appears on packaging.

Does seabird guano raise soil pH?

Yes, because of its calcium content. That helps on acid soils and hurts on alkaline ones. Check a soil test before applying.

Is seabird guano safe to handle?

Seabird guano does not carry the histoplasmosis risk associated with bat guano. Standard dust precautions apply to any fine mineral powder.

関連記事

• Blood Meal Fertilizer: 12-0-0 NPK, How It Is Made and Used — the nitrogen source this material does not provide
• Organic Fertilizer Supplier China: A Buyer’s Checklist — what to verify before placing a first order

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Sourcing seabird guano and want the lot data rather than a brochure?

Rutom Bio supplies ECOCERT and CERES certified seabird guano in micronized powder and granular grades, with batch analysis available on request.

→ Request a batch certificate of analysis

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参考文献・出典

1. Elisabeth C. Miller Library, University of Washington. Safety of bat guano
2. Louisiana Department of Health, Infectious Disease Epidemiology. Bat Guano In Attics And Crawlspaces (PDF)
3. Bat Conservation International. The Scoop on Bat Poop, April 2024
4. Bernhard, C. et al. Guano: The White Gold of the Seabirds, IntechOpen. Chapter 2, Classifications of Guanos
5. SGS-CSTC Standards Technical Services Co., Ltd., Guangzhou Branch. Testing Report MCHGZ2500817-01A, 13 June 2025. Methods AOAC 958.01-2005, AOAC 965.09-2005, AOAC 2006.03-2006. Available on request
6. Guano Australia. From Guano Land; The Good, the Bad & the Ugly
7. Association of American Plant Food Control Officials. AAPFCO 製品ラベルガイド — guaranteed analysis order and the elemental basis for calcium and magnesium