Date: Fri, 4 May 2001 09:29:31 -0500 Reply-To: Sustainable Agriculture Network Discussion Group Sender: Sustainable Agriculture Network Discussion Group From: "Wilson, Dale" Subject: Humus formation Content-Type: text/plain; charset="ISO-8859-1" Hey Steve and Joel (and any other soil OM people out there), I have had occasion to delve into humic/fulvic substances at work, and keep thinking about it while working in my garden, I keep coming up with questions. Maybe you guys know about this. The answers are probably in the literature somewhere, but the literature is awful big! 1. To what extent is recalcitrant OM (ROM) simply chitin (or chitin-derived)? 2. To the extent that ligno-cellulosic material directly contributes, is transformation into ROM mainly an extracellular chemical process (eg free radical polymerization)? 3. Processing by extracellular enzymes seemingly must be done by fungi, are bacteria important at all in ROM formation? 4. Although stuff can rot in many ways, in diverse soils or in diverse types of piles, are there some well established "tricks" that can shift the balance toward ROM rather than CO2? (Temperature? pH? aeration?) 5. Are inorganic substrates really important in ROM creation? (You have written that you think this is true Joel, but is it just speculation?) 6. Are some quick-tests available for ROM content (NMR? NIRS?) to use on compost or soil? 7. It seems like anaerobic conditions are good for producing deposits of ROM in nature. Can these conditions be harnessed to produce ROM (sludge anyone?) in managed systems? Dale Date: Tue, 8 May 2001 19:41:18 -0600 Reply-To: steved@ncatark.uark.edu Sender: Sustainable Agriculture Network Discussion Group Comments: Authenticated sender is From: Steve Diver Subject: Re: Humus formation Comments: To: "Wilson, Dale" In-Reply-To: <8FEE1BDA0910D111BEB500805F1999C7048F5359@vela.phibred.com> Dale Wilson wrote: > I have had occasion to delve into humic/fulvic substances at work, and keep > thinking about it while working in my garden, I keep coming up with > questions. A lot of good questions, Dale. Keep on thinking like this and one day you may swear off GMO's in favor of healthy, organic produce right out of your humus-rich garden soil :-) Quick comments: Recalcitrant OM? My guess is there are common names for this type of organic matter, and that would be helpful to know what you're talking about. (Active OM, Passive OM, Friable Humus, Stable Humus?) Chitin same as ROM? That's wild. I usually think of chitin in association with insect exoskeletons and crab shells. Fungi and bacteria and how they influence OM. Good question. Bacteria produce enzymes, fungi produce antibiotics. Both use OM as food and both help build humus. Bacteria transforms N into useable forms; fungi shuttles calcium. A list of functions would probably go on forever. Tricks to shift to ROM instead of CO2. Yes, I think there are tricks. For example, chop or mow down green manures and incorporate them with a spading machine or other implement, spraying the cover crop residue with a microbial inoculant and thus pushing the equation in favor of humus formation instead of oxidation. The foremost humus product of farming and gardening is compost. It is magic, really. You take raw organic matter and through a biological, chemical, and physical transformation process known as composting, you wind up with humus, which I think qualifies as ROM. Biodynamic preps, EM, Petrik, Penac... microbial inoculants to shift the OM equation. Mulches and worms, super low maintenance approaches yet very important contributors to soil organic matter in its many different forms. Inorganic substances important in ROM. It seems so to me. A lot of these organic matter substances occur as organo-mineral complexes. Quick tests. I have not seen portable NMR or NIRS meters advertised, and would think they are expensive. A microscope can be used to view humus crumb, but they too are expensive. See the microscope image of clay-humus in my web article link below. I would like to see county extension offices start to offer soil and compost microscopic analysis for farmers and gardeners so people can see this sort of thing. It has already happened with plant disease diagnosis, and with a few lens and light modifications, the same thing can happen for humus. For example, Georgia Extension received a $1.2 million donation to install microscope and computer equipment in county extension offices at $6,000 each, for the purpuse of remote transmission of plant diseases and on-campus diagnostics. Hydrogen peroxide can be dropped onto soil samples to watch for differences in "fizz". A "quick test", but limited information. The chroma test, using circular chromatography, is still a very good qualitative test to see the humus condition, humus formation, biological activity, mineralization, fertile status and yield potential, poor aeration, etc. But it takes a half day or longer so it's not really a "quick test." The humus value test is similar to the chroma test, in terms of extract method, but much faster since you don't have to go any steps further to "develop" the chroma image. It tells you the degree to which organic matter has become humified. The potential pH test is "quick." All you need to do is prepare two samples, regular pH and a KCL-buffered pH. Differences in the two readings can tell you if you have good biological activity and humus formation, since well humified soils will have numerous exchange sites and a massive surface area. Poorly formed humus have weak exchange sites and the potassium will "knock off" the hydrogen ions. Thus, you hope to find very minimal difference in the pH readings, instead of wide swings between the pH readings. Simple and quick, but revealing. If you have humus value and chroma and potential pH, I think you can tell more about your soil from the humus perspective and soil biological activity -- the stuff that really matters to farmers and gardeners, than what you get back from a typical NPK soil test. For further explanations of these humus evaluation tests, see: Controlled Microbial Composting and Humus Management: Luebke Compost http://ncatark.uark.edu/~steved/cmc-compost.html Steve Diver Date: Wed, 9 May 2001 09:26:50 -0500 Reply-To: Sustainable Agriculture Network Discussion Group Sender: Sustainable Agriculture Network Discussion Group From: "Wilson, Dale" Subject: Re: Humus formation Content-Type: text/plain; charset="iso-8859-1" Steve, > Chitin same as ROM? That's wild. I usually think of chitin > in association with insect exoskeletons and crab shells. The cell walls of fungi are made of chitin. Fungi are more closely related to animals than people used to think. http://www.sdcs.k12.ca.us/uchs/AP.BIOLOGY/1996-97/Fungi/Fungi1.html "Chitin is the most abundant nitrogen-bearing organic compound found in nature." http://www.chipsbooks.com/chitin.htm "the second most abundant polysaccharide in nature (after cellulose)." http://www.uni-ulm.de/biologie1/Forschung/Chitin/chitine.html In most soils (I think), most of the digestible OM eventually becomes transient fungal biomass. The part of fungi most resistant to decay are the cell walls. So the fate of carbon in the soil must be determined to a large degree by the fate of chitin. Also, this stuff must be important in the ebb and flow of N in the soil, since it contains a lot of N, unlike cellulose. In fact, I'll bet the consumption of cellulose by fungi and the elaboration of cell-wall chitin is the principal mechanism of N tie-up from addition of cellulosic residue. (Another reason to use such residue as mulch rather than mixing it with the soil.) I found a few links on chitin degredation, but I have not fully explored these. It sounds like more is known about the fate of chitin in marine ecosystems than in soil. http://www.mdsg.umd.edu/MarineNotes/Mar-Apr97/side1.html http://www.nmw.ac.uk/soilbio/Download/newsletter5.PDF >> Although stuff can rot in many ways, in diverse soils or in >> diverse types of piles, are there some well established "tricks" >> that can shift the balance toward ROM rather than CO2? >> (Temperature? pH? aeration?) > Yes, I think there are tricks. For example, chop or mow down > green manures and incorporate them with a spading machine or > other implement, spraying the cover crop residue with a microbial > inoculant and thus pushing the equation in favor of humus formation > instead of oxidation. The foremost humus product of farming and > gardening is compost. Why do you think these practices encourage humus formation more than simply leaving residue on the surface? Is it a well established fact that these practices do shift the balance toward humus rather than complete oxidation? Naturally, if you IMPORT lots of compost into your garden you are going to get lots of humus. But on a large scale, it seems to me that leaving biomass in or on the soil where it is exposed to lower temperature and more surface area for adsorption, would reduce net oxidation rate and provide more time to form humic materials. > I have not seen portable NMR or NIRS meters > advertised, and would think they are expensive. The instruments are expensive but individual tests are potentially inexpensive because they are so fast. Many grain elevators have an NIRS (near-infrared reflectance spectrometer). If calibrations were available, these instruments could probably be used to quantify and characterize OM in soil and compost. http://www.nal.usda.gov/ttic/tektran/data/000010/41/0000104192.html http://www.precisionag.org/PDF/ch10.pdf Also this website looks interesting: http://www.oznet.ksu.edu/ed_agron605/AGRON855/text/sum4.html "While Preston reviewed in great detail some of the analytical methods of NMR, the applications and recent NMR studies that she reviewed are particularly interesting. 13C-NMR can be used to study decomposition processes, since there is a noticeable change in the ratio of O-alkyl to alkyl C, as well as an increase in aromatic C. This is due to the decomposition of easily-degraded carbohydrates and an accumulation of alkyl C. NMR can also be used to characterize plant biopolymers, since the majority of aliphatic C originates from cutin and suberin. The effects of cultivation are also studied with NMR, since high leaching reduces aromatic C...." Found a book that looks good, but haven't read it. http://www.oup-usa.org/toc/tc_0851991459.html > If you have humus value and chroma and potential pH, I think you > can tell more about your soil from the humus perspective and > soil biological activity -- the stuff that really matters to farmers > and gardeners, than what you get back from a typical NPK soil test. > Controlled Microbial Composting and Humus Management: > Luebke Compost http://ncatark.uark.edu/~steved/cmc-compost.html Thanks Steve, nice website! Dale Date: Thu, 10 May 2001 11:34:09 -0400 Reply-To: Sustainable Agriculture Network Discussion Group Sender: Sustainable Agriculture Network Discussion Group From: Alex McGregor Organization: Walden Farm Subject: Re: Humus formation Content-Type: text/plain; charset=us-ascii Dale, Thanks for the info on chitin in fungal cells. I had no idea that fungi used (or contained) so much N. Your post started me thinking about what you said about C & N in soils. You wrote: "In most soils (I think), most of the digestible OM eventually becomes transient fungal biomass. The part of fungi most resistant to decay are the cell walls. So the fate of carbon in the soil must be determined to a large degree by the fate of chitin. Also, this stuff must be important in the ebb and flow of N in the soil, since it contains a lot of N, unlike cellulose. In fact, I'll bet the consumption of cellulose by fungi and the elaboration of cell-wall chitin is the principal mechanism of N tie-up from addition of cellulosic residue. (Another reason to use such residue as mulch rather than mixing it with the soil.)" This may be true in undisturbed soils, but tillage and compaction kill off the fungi and cause a shift to a bacterially dominated system. And I assume that most of this initial bacterial "flush" is feeding on the hyphae, releasing those stores of N in the chitin starting the bacterial N cycle to produce nitrate. And some of the C is used in respiration, leaving the soil as CO2. So, it's the disturbance that adversely affects fungally dominated soils. But we've stuck to tillage because our field crops thrive in a bacterially dominated soil. Maybe it's the idea that if something works once we should keep doing it. Continual tillage has the effect of depleting the humus content of soil through respiration (CO2). In your musing about composting vs. no-till (or, more exactly, limited-till) you wrote: "But on a large scale, it seems to me that leaving biomass in or on the soil where it is exposed to lower temperature and more surface area for adsorption, would reduce net oxidation rate and provide more time to form humic materials." Definitely on a larger scale! Imagine the amount of compost necessary for a 500 acre wheat farm! What Steve D. was saying about compost, I think, is that composting will increase soil humus content and is the favored practice on most small farms- for good reason. The problem with leaving biomass at the surface is that you're talking about disturbed agricultural soils (I'm assuming). These are bacterially dominated, even after years of no-till. (Though some fungal species do rebound and fill some niches.) The "mulch at the soil surface loses most N through volatilization. And most of the C is returned to the atmosphere through respiration. So, there is little gain of N & C in these soils, unless a legume is plowed in for the N or grass is grown and killed for C from the roots. I have had the experience of my soil going from 4-5% OM to 8-9% content in 3 years using compost addition to the surface after an initial tillage, surface cultivation between crops and intensive growing- in a sandy soil in the Southeast. (To give you an idea of what Steve was talking about.) Back to large farms- Compost can be used to increase soil OM or humus content through the practice of composting and adding the limited amount derived to fields or sections. And maintaining the gain through proper soil management. This enables one to make a long term change across large areas. My conclusion: Composting has a place on every farm of every scale. How, where and when it's used is determined by the particular operation. And it's an important part of any system- from standard tillage to no-till. Alex McGregor Walden Farm Date: Thu, 10 May 2001 18:29:03 -0500 Reply-To: Sustainable Agriculture Network Discussion Group Sender: Sustainable Agriculture Network Discussion Group From: "Wilson, Dale" Subject: Re: Humus formation Content-Type: text/plain; charset="iso-8859-1" Alex, > This [dominance by fungi] may be true in undisturbed soils, but > tillage and compaction kill off the fungi and cause a shift to a > bacterially dominated system. And I assume that most of this > initial bacterial "flush" is feeding on the hyphae, releasing those > stores of N in the chitin starting the bacterial N cycle to produce > nitrate. And some of the C is used in respiration, leaving the soil > as CO2. I think that is the tendency, but it isn't so black/white because tillage intensity and frequency are highly variable. But I agree, frequent, homogenizing tillage is a bad thing. > But we've stuck to tillage because our field crops thrive in a > bacterially dominated soil. Perhaps. Maybe it is also the flush of mineralization that occurs with tillage (associated with decomposition of OM). But I suspect the main reason historically has been weed control. When I was out West, it sure seemed like a lot of farmers were into recreational tillage, perhaps driven by an exaggerated desire for tidiness (or maybe to get a good seedbed for their onions). > Composting has a place on every farm of every scale. How, where > and when it's used is determined by the particular operation. And > it's an important part of any system- from standard tillage to no-till. It seems kind of expensive, carrying around many tons of residue. I can barely manage to make compost and carry it around my yard. I did some searching in Bioabstracts and found this really interesting paper. The abstract is attached below. They obtained GREATER net N immobilization by leaving the straw on the surface (I never would've guessed that, so much for avoiding that by mulching). Apparently this resulted from the ability of soil fungi to transfer N into the litter layer from deeper in the soil. This is all WAY more interesting than the SAS program I should be writing (oh well). I also found a couple interesting websites: http://www.fpl.fs.fed.us/documnts/PDF1997%5Cmille97a.pdf http://life.csu.edu.au/argonomy/papers/134/134.html Dale TI: Litter placement effects on microbial and organic matter dynamics in an agroecosystem. AU: HOLLAND-E-A; COLEMAN-D-C SO: ECOLOGY 68(2): 425-433. PY: 1987 LA: English AB: Two different agricultural tillage practices were used to study how changes in the structure of the soil-litter system affected litter decomposition rates, microbial community composition, and soil organic matter dynamics. Surface straw placement results in spatial separation of carbon-rich litter (C:N ratio 80:1) and mineralized soil nitrogen. In contrast, when the litter is plowed into the soil, straw carbon and soil nitrogen are intimate contact. Our field studies in Colorado showed that fungal biomass in surface straw treatment was 144% of that in the incorporated-straw treatment, probably because fungi, with their extensive hyphal networks, are able to utilize both the surface straw carbon and the available soil nitrogen. Field studies using 14C-labeled wheat straw showed that a great proportion of added 14C was retained in the surface-straw treatment than in the incorporated-straw treatment. Maximum net N immobilization was higher and litter decomposition was slower in the surface straw than in the incorporated straw placements both with and without experimental nitrogen addition. Slower litter decomposition of the surface litter may contribute to reduced soil organic matter losses. Soil organic matter losses may also be reduced in no-till systems as a result of the increase in the ratio of fungal to bacterial activity because of the greater growth efficiency of fungi and the accumulation of carbon in the less decomposable fungal biomass. The surface placement of straw in no-till agriculture allowed management of microclimate and microbial populations so that losses of soil organic matter and nutrients were minimized. Date: Thu, 10 May 2001 22:55:23 -0400 Reply-To: Sustainable Agriculture Network Discussion Group Sender: Sustainable Agriculture Network Discussion Group From: Frank Teuton Subject: Re: Humus formation Content-Type: text/plain; charset="iso-8859-1" http://www.ar.wroc.pl/~weber/humic.htm#start http://forestgeomat.for.ulaval.ca/brf/regenerating_soils_98.html Date: Sat, 12 May 2001 10:08:14 -0400 Reply-To: Sustainable Agriculture Network Discussion Group Sender: Sustainable Agriculture Network Discussion Group From: Mary-Howell & Klaas Martens Subject: Humus, Organic matter, Chitin, etc In-Reply-To: <200105111042.tfo948.9sq.37tiu8v@emu> Content-type: text/plain; charset="US-ASCII" The recent discussion on soil organic matter has been very good. I would like to add a few more ideas that I feel are important to consider. The work done at Sanborn field in Missouri showed clearly that the use of nitrogen fertilizers was an important cause of organic matter loss. I don't know of any recent studies that look into the role of nitrogen use in soil organic matter depletion but it seems that this factor also needs to be considered. Dr. Albrecht further observed that nitrogen fertilizer also lowered the quality of organic matter in the soil substantially. I also think there needs to be much more discussion about the fact that all soil carbon is not the same - it is held in different ways, and some forms are far more benefical than others. As we consider carbon sequestration and building soil organic matter, perhaps aiming for the highest levels of carbon should not be the only focus. Instead, probably the questions we need to ask is "WHY are we trying to keep carbon in the soil? What should the carbon be doing in the soil? What forms of carbon best achieve these goals?" Healthy plants commonly give off up to half of the carbon they fix as root exudates that feed soil organisms in the rhizosphere. This large and important carbon source has, to my knowledge, not even been considered in recent studies of humus formation and carbon sequestration. It is undoubtedly rapidly incorporated into the bodies of living organisms, but only if there is a healthy diverse population of organisms present. We may not see all of the carbon 'sequestered' through photosynthesis into the living soil if we do not consider this form. We should be actively investigating ways to enhance the dynamic stability of this living form of soil carbon. The carbon holding potential of many soils may actually be depressed, especially under no-till regimes, because the microbial and larger soil animal populations are not optimized. The much maligned mixing of organic matter into the soil and stimulation of microbial feeding serves to mineralise nutrients and make them available to the crop. The common alternative, use of chemical fertilizers, also damages soil and depletes organic matter. I have read the often repeated statements that moldboard plowing reduces earthworm and microbial populations. I urge you all to look harder at recently plowed organic fields before accepting this theory. Earthworm populations explode imediately after plowing on our farm. Instead, plowing probably shifts the populations, as the change in soil structure and additional oxygen will favor some organisms and not ohers. That isn't necessarily detrimental, it all depends on the relative value of different types of organisms. If plowing favors a more beneficial mix of organisms, even if some type of organisms are adversely affected, it seems that in balance, occasional and judicious plowing has significant value, even for carbon sequestration. When direct observations contradict the prevailing assumptions, It seems wiser to reconsider the assumption than to ignore the observations. No-till systems that use cover crops, earthworms, and other soil organisms to loosen, mix, feed and aerate the soil, such as Steve Groff has developed, are achieving many of the benefits of plowing without some of the drawbacks and are important models to learn from. These systems are building active organic matter and sequestering carbon efficiently. But we should not draw conclusions about ALL no-till operations from what is demonstrated on Steve Groff's fields! I recently read of a different no-till system that was being touted for building soil and sequestering carbon using high lignin crop residues, no green manures, and relying on heavy use of chemical fertilizers to maintain yields. This system had impressive carbon levels in the top 2 inches after 40 years of this type of management, but when I took a calculator and figured the total amount of OM in his top 12 inches of soil it was far less total OM than what our conventionaly tilled soils have. I would be willing to bet that the diversity and quantity of living organisms in this man's soil are very low. My point here is that just building large amounts of "recalcitrant carbon" is not the best goal we can work toward. We could do that by dumping lignite coal on our fields. Organic matter is not just a way to store carbon in soil. It should support a large active and diverse community of organisms in the soil. Crops growing in soil with a healthy diverse mix of organisms in it are more disease resistant, more insect resistant, more tolerent of adverse weather, and more productive than those growing in a less active soil. Klaas Martens