catlover_gardener

NPK of compost

catlover_gardener
June 15, 2009

What is the NPK of finished compost? How does one know how much to the soil? Can you add too much?

Comments (74)

  • leira

    Not really trying to stoke any fires here, but it seems to me that even if compost is only .5-.5-.5 in some analysis, it's likely to be used in such a quantity as to "out fertilize" a sprinkling of 10-10-10 for example. Just a thought.

    I think anubis_pa is making a very good point, here, and I'm not seeing others talk about it.

    I worked about 20 gallons of compost into my 72 sq. foot garden this Spring (which isn't nearly as much as I would have used if I'd only had more available). Even at 0.5-0.5-0.5, I'd need a full gallon of a granulated 10-10-10 fertilizer to get as much N-P-K for that area as the compost...and while I haven't used chemical fertilizers since childhood, I don't recall using the stuff at that sort of volume.

    (This assumes that NPK numbers are by volume, rather than by weight, and I can't recall at the moment...but even if it's by weight, we can assume that the numbers would be at least vaguely similar.)

  • Dan _Staley (5b Sunset 2B AHS 7)

    Leira, this is good thinking and there are several issues regarding availability and ability of the soil to make compost available as nutrients that are problematic in this thought process.

    However, we know that when soil analyses are done, they are done on a weight/volume, and may recommend, say, 3 lb P per 1000 sf (vol being covered at depth). If the OP needs 2 lb P for her 1000 sf and she has compost at .5 .5 .5, then that is a LOT of compost to apply.

    That is: 100 lb of compost at .5 .5 .5 is 100*.005 = .05 so 100 lb compost at .5.5.5 has .5lb P. So to apply enough compost to make up the deficiency, the OP has to hire a dump truck to bring in enough compost for her 1000 sf garden to make up the difference. A 500 sf garden would need a 1/2 ton truck to haul in, which IME is ~6-8 [.6] wheelbarrows. Hauling in 7 wheelbarrows for 500 sf and turning in should take ~2 hrs with cleanup if you're frisky and young, not counting going to the rental place and back twice. More if you want deeper than a tiller can go. Others can share their experiences turning in this much by hand.

    To compare to a three-bin compost system at 4x4x3 per bin, IME this gives you maybe 40-80 lb finished compost in the last bin (willing to hear otherwise).

    HTH.

    Dan

  • dchall_san_antonio

    This topic hasn't come up in years. I think the reason why is because most people seem to understand it. This thread is an excellent summary of compost fertility.

    Yes the NPK is low per 100 pounds. It is not unusual at all for people to apply hundreds of pounds to their garden. Thus the fertilizer value is pretty fair.

    Yes you can use too much. I'm a lawn kind of guy and using more than 1 cubic yard per 1,000 square feet is to risk smothering the grass. One cubic yard weighs upwards of 700 pounds. If you are not putting it on a lawn, then you cannot use too much.

    joe.jr said,
    If compost isn't fertile, my plants sure seem fooled. Nutrients don't magically appear in soil, so they're coming from something despite the fact that I practice fairly intensive planting. I live on a hilltop, so runoff isn't carrying any nutrients to my raised beds. If anything, it's leaching them. The only source of nutrients is the compost.

    ValerieRU posted a link a few months ago which goes into this. A Russian soil scientist published a paper in 1900 that put three commonly known facts together that woke me up.
    Fact 1: Carbon-rich organic material (including humus and compost) has the ability to absorb ammonia gas from decaying protein.
    Fact 2: It also has the ability to absorb moisture from the soil and from the air.
    Fact 3: Ammonia gas is highly soluble in water.
    With these facts the theory is that the compost absorbs ammonia gas and moisture from "thin air." Then when the air temperature drops below the dew point, that ammonia laden moisture drains out of the bottom of the surface compost providing a fast acting fertilizer directly to the roots.

  • Dan _Staley (5b Sunset 2B AHS 7)

    Well, I'm with you and I get it, and we must consider that nitrification is an issue, and it is true that colloids have long chains that are capable of attracting NH3 or NH4+.

    Simply having humus in the soil doesn't necessary supply available N to plants for assimilation - the reasoning above neglects volatilization and leaching. If simply having various forms of N in humus meant plants could use these forms, we wouldn't have N limitations in many forest or woodland stands, and we wouldn't have had to invent the Haber process to obtain N to deliver to plants.

    This is what I meant by the whole of it is greater than the sum of its parts; all of the soil working together is what makes good soil. And why I used the pounds thing with reference to a typical home composting bin - the finished bin does not contain enough weight to deliver sufficient nutrients in my example.

    Dan

  • swanz

    dchall, what you posted was interesting and confirms something I've suspected. For example peat moss is very poor in nutrients. I don't fertilize or care for my lawn except for cutting it. The soil is sandy and fairly poor. There's a small patch of it where I raked in some peat moss a couple of years ago. That section has stayed very green, thick and lush without the addition of any amendments or nitrogen. It has in my opinion nitrogen sequestering qualities which are under rated.

  • Kimmsr

    Many people here seem to be locked into Justus Von Leibig's false theory that all that plants need to grow is NPK, when plants really need much more in terms of nutrients to grow up strong and healthy. Using only NPK as a basis of feeding your soil leads to unhealthy plants that are more attractive to insect pests and plant diseases and require a gardener to need to do things to control them, things that would be unnecessary if the soil was in good health with a well balanced availability of all the nutrients plants need to grow.

  • Dan _Staley (5b Sunset 2B AHS 7)

    It has in my opinion nitrogen sequestering qualities which are under rated.

    Equally likely the soil there has better water holding capacity and cation exchange capacity.

    Many people here seem to be locked into [a] theory that all that plants need to grow is NPK

    I think this is largely a function of product labeling.

    Dan

  • swanz

    Equally likely the soil there has better water holding capacity and cation exchange capacity.

    Nope, small patch was as dry and dreary as the rest of the lawn for years.

  • catlover_gardener

    OK then, someone, please tell me...can I just add fert and compost to my veggies? In layman's terms, bz the above was too intricate, interesting but intricate.

    Thanks!

  • swanz

    Yes.

  • idaho_gardener

    can I just add fert and compost to my veggies?

    I just found out today that adding fertilizer to compost makes both work better.

  • toxcrusadr

    Curious how you found that out - did you conduct an experiment? Do tell.

  • glib

    This has got to be the overgeneralization group. If he conducted the experiment with beans, surely adding fertilizer made things worse. Even compost can be too rich for beans. It can be marginal for carrots too. Some veggies like it more, other veggies like it less and prefer ordinary soil and fertilizer, or ordinary soil and nothing else.

    Fertilizer, as is well known, most of the time provides mainly N. P and K reserves deplete far more slowly than N reserves, in virtually any soil. Generally, unless one composted a very brown pile, and the compost is still composting, it will have significant amounts of N. In most cases, 2 inches of the stuff will provide decent fertilization for the year. Cabbages growing on beach gardens excluded.

  • swanz

    You're over analyzing. I make the soil as fertile and compost rich as possible. 98% of crops thrive. Some need nothing more than just sticking the seed or plant in the rich soil and not amending otherwise throughout it's growing cycle( such as some beans).

  • joe.jr317

    dchall, do you happen to know of where to find that article or what thread it was? I'm interested in reading it.

  • dchall_san_antonio

    Start here and follow the links to read the article by Ovinsky.

  • avid_hiker

    Great job Gardengal. I did not go any further than your post. Anything else would be either redundant or misleading.

  • dchall_san_antonio

    avid_hiker you missed a lot. Gardengal neglected to answer the OP's question and she spent most of her time trying to ward off an argument that seems to follow her around. Plus if you had read further, you would have come across my captivating prose on the topic! ;-)

  • Dan _Staley (5b Sunset 2B AHS 7)

    Ovinsky's work has been updated. The work in toto found in any basic soil science text.

    If you don't know about all the subsequent knowledge gained in the past century about N in the soil, you may want to visit a used bookstore and see if you can pick up a basic soil science book, cheap. Community Colleges often have basic horticulture classes that should cover these knowledge gains as well. Some of this updated knowledge is also found in agronomy classes, forestry classes, agriculture classes, ecology classes, specifically wrt fire and its effects on soil N...if you get the chance, check 'em out!

    Dan

  • valerie_ru

    I have read tons of books on soil science. New and old.
    There are some (very few) of them where there is a mention about dew in soil. And even they give only references about this subject to previous works.
    The last (back in time) book where there were estimations is written by Kostychev. He made experiments by himself. How much dew is deposited in the soil? And what are the best conditions for it? But this book is a rarity. It was written approximately in 1880-th.
    Making experiments, he defined that the best conditions for dew in soil is thin 2-inch layer of compost or tilling the soil no more than 2 inches.
    Now in no-till systems it is called the retention of moisture. This name talk itself about complete misunderstanding. Its not only retention but is also an attraction of moisture from the air. The other benefit is a nitrogen solving in dew. Ovsinsky gives numbers of nitrogen in dew. Not too small...

  • Dan _Staley (5b Sunset 2B AHS 7)

    Ovsinsky gives numbers of nitrogen in dew. Not too small...

    Usable N is what one cares about.

    And dew not evaporating but being adsorbed is part of the available soil moisture in the solum.

    If I were to guess the total amount deposited in the solum, that number doesn't help an argument for...for...um...I'm not really sure for what exactly because there is no acknowledgment of usable N , assimilation, volatilization and leaching, nor why if this idea is so great why N is limiting in so many ecosystems (except where man deposists too much and has upset the N cycle).

    Again, plopping some compost in the garden isn't immediately going to give the OP the shot of NPK implied in the original question and not clarified.

    Dan

  • valerie_ru

    Nitrogen in dew is present in the forms of HNO3 (nitric acid) and NH3 (ammonia).
    They bound with soil minerals and form "available" for plants forms of N, P, K, Ca, Mg and so on.... That is why they are used in production of chemical fertilizers. Nitric acid is one of the most strong among all acids at all.

    why if this idea is so great why N is limiting in so many ecosystems

    Tell me please, where did you find ecosystems with lack of nitrogen?

  • Dan _Staley (5b Sunset 2B AHS 7)

    Tell me please, where did you find ecosystems with lack of nitrogen?

    Most forest ecosystems, many riparian systems (e.g. compare, say, the Tongass riparian with and without salmon), etc.

    Nitrogen in dew is present in the forms of HNO3 (nitric acid) and NH3 (ammonia). They bound with soil minerals and form "available" for plants forms of N, P, K, Ca, Mg and so on

    Um, no.

    Dan

  • valerie_ru

    Forests?
    I was thinking that forests are unlimited source of nitrogen.
    Google "ramial chipped wood".

  • Dan _Staley (5b Sunset 2B AHS 7)

    I was thinking that forests are unlimited source of nitrogen.

    That would be incorrect thinking. I return to my entreaties for purchasing basic texts1, reading them, and understanding the knowledge therein.

    Viz.: Although forest floor and mineral soil represent the largest pools of N in forest ecosystems, the majority (90 percent) of N contained within them resides in organically-bound forms that are unavailable to plants...[pg 557]

    B.V. Barnes, D.R. Zak, S.R. Denton and S.H. Spurr, Forest Ecology (4th ed.), John Wiley and Sons, New York, NY (1998) 774 pp.

    This is related, directly, to the assumptions in the replies that imply that the implied OP question can be solved by sprinkling compost from the pile in the veggie garden. This is false, unless 'sprinkling' means 'piling on many inches thick, turning well and waiting'. Soil cannot be improved in a day to provide all the nutrients plants need. It takes time, critters, and organic matter in addition to mineral soil (moisture helps too).

    Dan

    1 Texts more recent than texts written in the 19th century.

  • Dan _Staley (5b Sunset 2B AHS 7)

    Let me add that as an undergrad, I did a small amount of fieldwork with a Russian ecologist who was absolutely wonderful. The approach of doing relevés, IMHO, is much better than the Western randomized approach for certain and several purposes, and I enjoyed my time around these visiting scholars. The knowledge and wisdom is there. And I'll never outdrink them, ever. ;o)

    Dan

  • idaho_gardener

    valerie_ru wrote Forests? I was thinking that forests are unlimited source of nitrogen. Google "ramial chipped wood".

    Uuuhhh Raaahh! My Mackissic Merry Mac 12pt chipper is on its way now. I have an acre with a lot of trees/shrubs that get pruned. I'll have literally tons of ramial chipped wood.

    I did forget to order the 1/2" and 1/4" screens for the chipper, so I'll have to jump on that.

  • valerie_ru

    the majority (90 percent) of N contained within them resides in organically-bound forms that are unavailable to plants

    Its true ... and not true...
    They are unavailable to plants but they are available to microbes and after them are available to plants.
    Add this book to your library: "Krasilnkov. Soil microorganisms and higher plants" .
    You may trust him. His portrait is hanging on the wall of fame at Luis Pasteur institute in Paris.

    idaho_gardener,
    you are a lucky man!

  • Dan _Staley (5b Sunset 2B AHS 7)

    The very next passage after the one I typed states that soil microorganisms control N availability, and discusses the processes that I mentioned several times upthread.

    That is: again, many terrestrial ecosystems are N-limited, due to the processes that I mentioned several times upthread.

    BTW, one of the outcomes of the FACE studies is that increasing atmospheric CO2 will not "feed" forests that are N limited (many of them are, esp 2nd growth), so forests likely cannot be counted on as a carbon sink for management schemes to mitigate man-made climate change.

    Dan

  • valerie_ru

    "Essentially there's no topsoil on that site," Schlesinger said

    Essentially. If there were topsoil the results could be better.
    Those ecosystem is too young and thus it may have nitrogen deficiency. If we are talking about good established ecosystem, in aged pine forests there are many ferns which provide nitrogen to soil. Its enough for trees with 1 meter in diameter.

  • valerie_ru

    Interestingly how amerindians at Amazon basin made fertile soil in jungles. They added charcoal (with NPK=0) to soils and after thousands years those soils in Terra Preta (Peru) are still fertile. Those old things are often better than new one.

  • Dan _Staley (5b Sunset 2B AHS 7)

    N limitations in many ecosystems is basic knowledge. It's simply how it is.

    Dan

  • valerie_ru

    Dan,
    I have no time to read all that books. Maybe some grains of the truth are really there.
    I just know that there are N-limitations on naked rocks.
    But if you add compost on top of them and plant trees then there will be no any N-limitations forever (ad infinitum). I know many examples in Crimea.

  • Dan _Staley (5b Sunset 2B AHS 7)

    I'm glad to see, Valerie, that you are curious, willing to do the work, seek to educate yourself and gain some knowledge on this issue!

    Thanks for your reply! Bye now!

    Dan

  • valerie_ru

    Thank you very much!
    I am also wise enough not to follow links that lead to the links that lead to the links ... and so on.
    Good luck to you!

  • idaho_gardener

    Dan, interesting links. Thanks for the info.

    Val, yes, I am a very lucky guy. Now, if only that chipper would arrive. Instant gratification takes too long.

  • Dan _Staley (5b Sunset 2B AHS 7)

    ig, if I may suggest thinking about what mushrooms will appear after the chipping, how you can foster their growth, and maybe purchasing some spores after your chips are spread. One of my best landscape jobs I did when I had my practice was an old GF's house, where I got some chips that popped morels the next spring...mmm...

    Dan

  • dchall_san_antonio

    So is there some agreement in the debate that forests have the N bound up in humates that microbes need to process before the plants can use them?? If so then it seems like the Ovinski thesis about 2 inches of humus on top of the soil is still a good thing.

    I used to investigate aircraft accidents and had an unfortunate opportunity to work in a field of wild plants adjacent to a farmers corn field in South Carolina. The corn field was sand and the field I was working in was 15 feet deep of peat and then the bed of sand started. These two fields were 30 feet away from each other. Back then I had no interest in the soil but I sometimes wonder about what I was seeing. The airplane punched a very clean hole into the peat and stopped abruptly when it hit the sand. The resulting jet fuel fire burned away most of the top growth making our work very easy but it would have been similarly easy for a soil scientist to really look into that situation. It would not have exactly made lemonade out of the very sad situation but maybe some good would have come of it.

    Also, huge thanks to Dan and to Valerie for keeping the apparent disagreement/agreement civil. Realizing that this thread is modestly adrift from the original intent, y'all have made the best of the drift.

  • Dan _Staley (5b Sunset 2B AHS 7)

    So is there some agreement in the debate that forests have the N bound up in humates that microbes need to process before the plants can use them?? If so then it seems like the Ovinski thesis about 2 inches of humus on top of the soil is still a good thing.

    It's back to availability, immobilization and what I wrote above: Simply having humus in the soil doesn't necessary supply available N to plants for assimilation - the reasoning above neglects volatilization and leaching. If simply having various forms of N in humus meant plants could use these forms, we wouldn't have N limitations in many forest or woodland stands, and we wouldn't have had to invent the Haber process to obtain N to deliver to plants.

    The first link in my multi-link reply yesterday goes right to a page that details this issue and additional reasons why N may be unavailable.

    Dan

  • valerie_ru

    Dchall,

    Thank you very much for your story about 15 feet of peat over the sand. Its very instrucrive story! Your remark about keeping agreement/disagreement civil led me to the thought that civilization is exactly the line between agreement and disagreement. Very nice!

    Dan,

    That book in your link is interesting. Ill read it when I have time.
    At this moment I have opened it on the page you have linked, and what I see?

    Other elements that limit nitrogen fixation include molibdenum, iron, and sulfur which are essential cofactors of nitrogenase. Pasture legumes are limited by molibdenum in parts of Australia, foe example due to low level of molibdenum availability in the highly weathered soils, particularly at low pH. ... Phosphorus, iron, sulfur or molibdenum, may, in these cases, be the ultimate "master element" that limits production, even though nitrogen is the factor to which primary production responds most strongly in shirt-term experiments.

    If so, why we have to speak about N limitations if real limitation is Mn (molibdenum)?
    I know about molibdenum. I very well know about molibdenum.
    Do we have to start costly Haber-Bosch process and cart tons of nitrogen fertilizers here and there, year by year, across continents and oceans, or we may just spread out few grams of molibdenum over hectares for 100-1000 years? Or we can shift pH to make molibdenum available and begin the process of nitrogen fixation. We have to solve real cause of problems instead of offering evasive and temporary solutions.

    For me soil is an edge between lithosphere and atmosphere. Since atmosphere has 70% of nitrogen, for me soil will never have N limitations by definition. (If just only nitrogen will be removed from air by Haber-Bosch process.) :-)

  • Dan _Staley (5b Sunset 2B AHS 7)

    Where's the &%@╣┐¼╕!!! [killfile] for this site?!

    Dan

  • bpgreen

    "Where's the &%@╣┐¼╕!!! [killfile] for this site?! "

    If you're tired of reading the posts on a topic, you can simply stop clicking that topic.

  • Dan _Staley (5b Sunset 2B AHS 7)

    [killfile] is for individuals.

    Dan

  • valerie_ru

    When I first time read about molibdenum Mb (it was many years ago) as an element of nitogenase complex of nitrogen-fixing bacterias, I immediately search WWW on content of molibdenum and other micromutrients in different plants. Was I surprised when I found that most high concentration of molibdenum is in Valeriana (Valeriana officinalis, often used as cardioactive drug). I quickly remembered that Valeriana extract is an important addition to compost in Rudolf Steiners biodynamic. Since that time I highly respect Valeriana and recommend it everybody not only for making compost but also for internal consumption.

  • catlover_gardener

    I am so sorry I asked this question!!!!!!!!!
    Somewhere somehow,I think someone answered my question, and I am going to find it. LOL!!!!

  • jolj

    I know I am late to the party, catlover gardener,
    Gardengal 48 is right about the fertilizer.
    pt03...well he never wrong & has the FARM(to big to be called a garden)to prove it.
    But nancybeetoo said it simple with"soil test". Test your compost if you like, but test you garden for 3 years or every other year as you build the soil web. This is the best way to get what is missing to your plants.20 mineral elements.
    http://www.calciumproducts.com/supercal_98g.cfm
    http://www.azomite.com/index.php
    You need to build up your balance in the garden, as well as add humus. No one thing will do that. To much air will dry roots out & to much water will rot roots.
    Balance all things.

  • PRO
    tapla

    Nicely said.

    Al

  • ngrrsn

    I agree with gardengal 48 and Jolj. And so do most university agriculture experts, extension offices, and documented and verifiable scientific studies. I am taking a course on this now. Oh, and to the comments about you can't have too much compost...well, that is inaccurate. One contributor said it is balance. I agree, but to know what the balance is or what is needed to maintain that balance requires testing. Most of us can't afford a complete soil test (it isn't just about NPK), so we guess as best we can. Sure, there are some NPK and other nutritional elements to compost, but compost is still considered an amendment, not a fertilizer. Part of it is WHEN or HOW do those nutrients become available to the plants. Anyway, this is several years after the original post, so I hope the poster is still gardening and is successful. :)

  • Oil_Robb

    If you are worried about a N deficiency, you can do what I do and you might not have to usie any granular fertilizer. Depending where you live (zone) after you harvest in the fall (mid sept) and the weather is warm dump on lots of fresh maure and till it in the same day to capture the N and let it sit untill spring (usually 5 months 150 days) and you will cover the N dilema and improve the organic content in your garden.

    I understand that its hard to do with city gardeners whom dont want to offend thier neighbors.

    I have seen and heard people make the claim that other than the ground upon which they were built they have raised bed that are 8x20' by 3' high that is 100% compost and added to annually, the pictures show great vegetable crops, If this is true how can somone have TOO MUCH compost?

  • TheMasterGardener1

    It depends on the nutritional value of the compost. You can not grow in 100% composted horse manure, you can grow in composted leaves mixed with composted manure. The leaves have way less nutrition than the composted manure.

    You could grow in 100% kitchen waste compost I am sure....

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