Study shows soil-building benefits of manure and crop rotation, so why didn’t they say so?

The secret to building soils is… wait for it… manure and diverse crop rotation. Underwhelmed? Researchers in Iowa (Delate et al, 2013) came to this result after conducting ten years of field research. Only this wasn’t their conclusion. Instead, the headline of the Leopold Center press release reads: “Iowa State study shows soil-building benefits of organic practices.” This is misleading for two reasons.

First, the researchers ignore the fact that manure application and diverse crop rotation, practices that improve soils, are not exclusive to organic production. There are plenty of conventional farmers here where I work, in the Columbia Basin of Washington, that use manure and have diverse crop rotations (just like the 3- and 4- year rotations in this study). Even in the Midwest, there are many conventional farmers who stray away from a corn-soybean rotation, and many of them use manure too. So, while manure and crop rotation might be more common in organic production, it is not organic production per se that improves soils.

Young maize plants growing in wheat residues. Image by CIMMYT via Flickr.

Young maize plants growing in wheat residues (in a “conventional” no till system that includes use of herbicides). Image by CIMMYT via Flickr.

Second, this study seems to have been designed to show that organic production comes out on top in any soil building comparison. If, before this study was designed (it started in 1998), I had stated that manure application and diverse crop rotation would build soils better than not using manure and having a short rotation, no one would have disagreed. Yet this experimental design compares a “conventional” system of a corn-soybean rotation, full tillage with no manure vs 3- and 4-year rotations (including soil-building alfalfa) with one or two applications (per rotation cycle) of composted manure. (I have other issues with use of manure in organic farming, too.)

Let’s stop here and ask: does this research, which took ten years, tell us which system will be better for the soil? Even if some herbicides and fertilizer were used, the improvement in soil would be evident. So why compare organic vs worst-case conventional when better comparisons were available?

What if, instead of using the worst-case conventional system, they had compared the organic systems with the best conventional system? Consider a no-till system, with three or four crops in rotation (there are no-till farmers that grow more), with cover crops* and manure. That, it seems to me, would be a better comparison, and would not waste resources confirming what we already know.

We can still gain a few lessons from the soil aspects of this study (pests and profits were also compared). First, it takes time to build soils. Some soil properties that did not show differences after the first four years did show differences after ten years. Second, to move towards greater sustainability we need to discern which practices are valuable. When practices are wrapped in labels like “conventional” or “organic”, the best way forward can be obscured. Researchers should throw out the labels and look at whatever mix of practices makes the most sense. After all, bulk organic amendments like manure, and diverse crop rotations, are good for the soil in any farming system.

*For many examples of farmers using cover crops to build soil and prevent erosion, see Plant Cover Crops.

Delate K., Duffy M., Chase C., Holste A., Friedrich H. & Wantate N. (2003). An economic comparison of organic and conventional grain crops in a long-term agroecological research (LTAR) site in lowa, American Journal of Alternative Agriculture, 18 (02) 59. DOI:

Andrew McGuire is an Irrigated Cropping Systems Agronomist for Washington State University Extension. He works with farmers in the Columbia Basin of Central Washington in improving soils through cover crops and high residue farming systems.


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37 comments to Study shows soil-building benefits of manure and crop rotation, so why didn’t they say so?

  • One has to wonder what the objective was. Now, the Leopold Center does some great work, and I know at least one of the authors personally from my time studying sustainable ag at ISU. I really would like to think that they had good intentions.

    Yet, why ask such as restricted question? It seems silly to compare worst-case to best-case when a much more nuanced question could have been asked. To be fair, they started the experiment a long time ago, but as you say, even then it was well known that cover crops and rotations were a good thing.

    I’ve often wondered why organic proponents aren’t simply sustainable agriculture proponents. Organic agriculture is difficult to do, and some would say impossible for certain crops and in certain locations. Many farmers prefer the flexibility of choosing synthetic pesticides or fertilizers if needed. Many farmers just don’t want the additional paperwork of certified organic. For whatever reasons, a great majority of farmers are just never going to convert to organic. But maybe, when provided with evidence, they would be more likely to try cover crops or more diverse rotations.

    In 2007 there were 2,577,000 organic and 355,000,000 conventional acres of crops planted in 2007 (so organic is about 4.68% of all US cropland – actually more than I thought!). Let’s say that this research convinces enough farmers to increase that to 5.68% of US cropland. Ok, that’s nice, another 575,770 acres of sustainably farmed cropland. But what if, instead of making this organic vs conventional, they made it “look how great rotation and cover crops are”? Maybe they could convince 10% of farms to move to cover crops and rotations. That would be 5,500,000 acres.

    The narrow framing of the research actually reduces the benefit that they could have on American agriculture. Why would they do that?

    • Keith Hayes

      I think it’s part of an advertising and public image campaign. Organic farming underperforms compared to conventional farming and it’s more expensive and labor intensive and the organic practitioners know it. Reframing the Iowa study makes people feel better paying a premium on produce that has no difference from the “conventional” produce. But you know these people better than I do.

      • Certainly part of the problem is that organic is both a production system and a marketing system, with the marketing usually taking priority. So, for effective marketing, they need a black and white comparison, organic vs. conventional, even if this does not fit reality very well.

    • “Why would they do that?”

      Maybe they chose as their their conventional system based on what the majority of farmers are doing in their region?

      • Jason

        I think that is the point. In Iowa at least, the crop diversity has dropped severely. It might be good to look at the research coming out of this group in general. They tend to frame it as Low External Input agriculture, not organic per se.

        • I still think it would have been more valuable to frame the research such that results would be applicable to more than 6% of acres. Is it more important to boost sales of organic or to actually improve ag sustainability across America?

    • Raoul

      Hi Anastasia, The reason you thought the 4.68% organic land was high is because it is. 2,577,000 is only 0.7% of 355,000,000. One percent of 355,000,000 would be 3,550,000 acres. To add to that, according to the small print in those statistics, the organic one includes pasture land, and overall acreage is just crop land. I wonder though if the overall number (355 million), includes the organic acreage as well.

      Best regards,
      Raoul

  • mikeb

    Thanks for this article. It has always been one of my pet peeves to see “organic” appropriating farming methods as their own. This the fruit of a movement that decides upon a separatist stance against “conventional” farming, which actually doesn’t exist. There’s just organic and everyone else.

    Manuring and crop rotation are no more “organic” than bread and wine are “catholic.” When I worked at an organic farm, the primary way of dealing with soil deficiencies was adding greensand, rock phosphate, blood and seed meals, and the like

    Anastasia said, “Organic agriculture is difficult to do, and some would say impossible for certain crops and in certain locations.” This is indeed the case for apples here in Maine. In order to make sure I had covered all perspectives, I had my farm pay for me to attend and organic apple growing workshop. All I have to say is that some of what they recommended was asinine, like letting trees become infected with borer then digging the larvae out with a wire.

    As for the final question in the essay, “Why would they do that?”

    Because they are propagandists, that’s why.

  • I have to wonder in Organic farming systems, where synthetic fertilizers are avoided, how does one replenish, over time, elements such as iron, phosphorous, calcium, zinc, magnesium, etc? Nitrogen replenishment can come from fixing but what about those other elements? You may say through manure but that just throws the problem onto the fields from which those animals ate.

      • LOL! But, it seems, about 10,000 tons of meteorite material does fall on earth per year. So let’s consider it. If it were all iron, that would be about 1.6 oz of iron per square mile or about 71 milligrams per acre. That doesn’t seem to be near enough.

    • Jason

      Mineral amendments are allowed. Limestone flour, elemental sulfur, boron, etc. I currently have 783 acres certified organic and several hundred more in transition.

      Much of what we do is be patient. Use perennial crops and biota that associate with roots them mine deep soil layers, replenishing the topsoil.

      Let’s ask the question another way: Synthetic fertilizers come from where? Phosphate deposits from Moroco? Natural gas from Trinidad? How are these replenished? Meteors?

      • Mikeb

        Organic is in the same boat and you know it.

        Their rock phosphate is just as depletable as the triple phosphate used by other farmers. Natural gas from Trinidad (in nitrogen fertilizers) is just as allowed in organic as it is in “conventional.” They just launder it through cows.

        I’ve helped offload the hundreds of bags of inputs trucked to an organic farm every spring–the phosphate rock, the blood and seed meals, the greensand, the limestone, the bottles of liquid fish and kelp, the cases of plastic pots, the “certified organic starter mixes”.

        I’ve assisted with the tons of leaves that get dropped off at the same farm, brought their by the truckload, and these trucks were not powered by meteor dust.

        And how about all that plastic used in organic? I’ve run a plastic-laying machine at an organic farm. They go through miles of it every season. It gets thrown out at the end of the year. It’s not made from meteors.

        And how about all the diesel fuel used to power the tractors and the bucket loader that turns all the vegetable compost dropped off by commercial restaurants and cafeterias, whose refuse is certainly not “certified organic”?

        And the gasoline for the chainsaws, mowers, portable water pumps, generators, and delivery vans?

        And the alloys in their irrigation systems? And the electricity for powering their greenhouses? Pyrethrum from Kenya–how does it get there?

        Then you start counting the actual calories of food coming off organic acreage versus the calories of input per acre and suddenly things get…complicated.

        Organic “perennial crops and biota” suddenly look like the pittance that they are. Stop being so uppity.

        • Mikeb

          Also: now that the US is exporting natural gas, the comment about Trinidad begins to look a little facetious.

        • Jason

          Yes. You are making the same point I am and then accusing me of being uppity? Hmmm…

          All farming is input intensive. The comment I was responding too suggested organic farms didn’t use inputs and I said that is not true. There was then a snide remark about meteors. And now you are being snide regarding Trinidad? All I ask is to focus on the substance of the conversation.

          What I am suggesting is a way to reduce external inputs, not remove them. If one looks at the research done by the Iowa State folks it shows that the reduction of external nutrients is very significant using the supposedly well known methods that are not widely adopted. Here’s a quote:

          Reintegration of crop and livestock production, as represented by the forage legumes and manure applications present in the more diverse systems, is not simply another aspect of cropping system diversification. Instead, it embodies an important principle in sustainable agriculture: system boundaries should be drawn to minimize externalities. Animal manure is produced regardless of whether feed grains are shipped to centralized concentrated animal feeding operations, or produced within integrated crop-livestock farming operations. In the former case, the manure may become a waste product and water pollutant if quantities exceed available land area for field application [33], whereas in the latter case, it contributes directly to crop nutrient requirements, improves soil quality, and reduces fossil fuel subsidies associated with grain transport and external N fertilizer inputs [14].

          End quote.

          What organic farms tend to do now is recycle and capture nutrients from conventional farms in the form of manures. A few years ago these were free to pick up from most confinement feedlot operations. With the increase in fertilizer costs there is now a market developing for manure and both organic and conventional agriculture tend to pay for the manure. External input costs are now approaching levels where it may be cheaper to pull nitrogen from the air rather than from a fertilizer plant, but that is a situation in flux. I grow clover seed and know that the cost/lb of N and the time required to deal with adding complexity to a cash crop production system is significant. Hence the easy solution of an account with Wilbur Ellis and a fertilizer spreader.

          Now let me ask this. If a study were done on the percentage adoption of agronomic methods such as crop rotation, cover crop use, sod crop rotation, hedgerow borders, no-till zones near water ways, etc. which farms are more likely to do these, certified organic or not?

          I truly am not judgmental about whether a farm is organic or not. I agree that looking at actual practices on a case-by-case basis and adopting best practices on the widest scale possible is most important. But what I see is organic people bashing conventional farming and conventional farming poo-pooing ignorant organic folks and that is what bothers me. There’s plenty to learn about what works no matter where it comes from or who is doing it. It is dumb human nature to put oneself into a camp or tribe and then it is us vs them.

          • Keith Hayes

            If you don’t mind me jumping in an offering some points…

            “What organic farms tend to do now is recycle and capture nutrients from conventional farms in the form of manures.”

            A fundamental law of nature, I’m sure you know, is Conservation of Matter. Matter can’t be created, only converted. So what does it matter as long as the end result is that the matter is converted to a form that plants can use (using a cow or chemical factory to make the same organic matter). We should try and reduce inputs and environmental impacts, of course. But many observers note that organic seems inefficient at this and they seem to limit themselves with a bunch of ad hoc rules. For example, if you treated a sick dairy cow with antibiotics, the milk it produces is no longer organic certified…but the manure is? How can that be? It makes no sense.

            “…it may be cheaper to pull nitrogen from the air rather than from a fertilizer plant”

            I don’t think you’ll find a single farmer that disagrees with this statement. But it’s easier said than done.

            “Now let me ask this. If a study were done on the percentage adoption of agronomic methods such as crop rotation, cover crop use, sod crop rotation, hedgerow borders, no-till zones near water ways, etc. which farms are more likely to do these, certified organic or not?”

            I don’t think you’re asking the right question. If an organic farm developed a way to produce better quality crops, at higher yields with fewer inputs, then whatever competitive advantage that confers would last only one growing season because it would be immediately adopted by conventional farmers so there would be no difference in the following years. If it were conventional farmers making these breakthroughs, we’ll often find organic farmers who refuse to utilize the new methods if they aren’t considered part of their “organic doctrine”. The organic farmers are the ones that are limiting themselves.

            Then there’s the fact that a lot of land for farming is leased; At least in my state (Illinois). How do you convince a farmer to rotate his crops with pasture and cover crops when there is no guarantee he’ll be able to recoup the investment he made to land that isn’t even his?

            • Jason

              Good questions! This is a very complex discussion topic. I want to preface this by saying that when I come here I find it very interesting to learn about the perspectives of those involved in GE research. I value it very much and have learned a lot. I like going to the source for information and have a distrust of hyperbole from those removed from the process of creating GE crops. With that preface I would also ask that those of you who aren’t organic farmers step back a bit and try not to recite prejudices or put forth assumptions you may have.

              Now I’ll connect this to what you’ve written: “Matter can’t be created, only converted. So what does it matter as long as the end result is that the matter is converted to a form that plants can use (using a cow or chemical factory to make the same organic matter).”

              My response: While matter can’t be created or destroyed it does change form! And the form is what is important here, especially the embedded energy of the form and its source. I recall reading a paper some years ago (and don’t be too harsh on me if the details are wrong here) that calculated how many years it took to produce the fossil fuels consumed in a single day in say the year 2004 (perhaps date of paper). It was something ridiculous, like our economy consumes the quantity of fossil fuels in a day that took 100,000 years to create. So organic farms (in the spirit of the “movement” not necessarily any particular farm) are supposed to not use synthesized fertilizers partially because these are derived from non-renewable resources and biological processes can substitute, such as nitrogen fixation from legume-rhizobial symbiosis.

              You wrote: ““…it may be cheaper to pull nitrogen from the air rather than from a fertilizer plant”

              I don’t think you’ll find a single farmer that disagrees with this statement. But it’s easier said than done.”"

              My response: Actually, to clarify, up until quite recently perhaps, and for the past 50 years or so it has been cheaper to pile on fertilizer produced via natural gas. Why? Because natural gas has been superbly cheap for quite a long time now. Cheaper than the cost to plant and disc in a legume cover crop. Because organic farmers are “constrained” so to speak, they have maintained and improved upon traditional means to maintain soil fertility through rotations. So we have evolved an entire fertilizer industry dependent upon cheap sources that may disappear quickly as economically reliable in a relative blink of an eye in the long view of human history, and especially geology.

              You wrote: “If an organic farm developed a way to produce better quality crops, at higher yields with fewer inputs, then whatever competitive advantage that confers would last only one growing season because it would be immediately adopted by conventional farmers so there would be no difference in the following years.”

              My response: My sense is that the competitive advantages of non-organic farms are going to be less so as input costs rise. They will then look for examples of farms that have adopted low external input systems, including organic farms. And adoption of something new is not all that quick in farming. Change one thing and you change many things at the same time. But a recent issue of John Deere’s magazine really pushed cover crops and rotations. Hearing about these techniques from a source many farmers trust is really important for more rapid adoption. Cultural hurdles can be huge.

              Good point re. leased land. I think in your state more than half the land is leased each year and many of those are year-to-year hand shake deals. I think if you google “sustainable farmland lease” and look into templates from groups like Progressive Farmers you will see examples of how to address this. My leases tend to be long term, 5 years or so, and tend to be crop share based rather than straight cash rent. Puts me in a long-term frame of mind and aligns my interest with the land owner. We both should want better soils and higher net income for both of us by reducing costs and increasing revenues.

              • Keith Hayes

                “”"So organic farms (in the spirit of the “movement” not necessarily any particular farm) are supposed to not use synthesized fertilizers partially because these are derived from non-renewable resources and biological processes can substitute, such as nitrogen fixation from legume-rhizobial symbiosis.”"”

                Understood. But what if we can generate fossil fuels from biomass (more conversion of matter). It’s an active field of energy research right now because fossil fuels don’t just provide energy, it’s also a raw material that can be used to make anything from fertilizers, drugs and plastics.

                So if we can derive petroleum from biomass and use it to make a fertilizer, would organic agriculture still reject it? In it’s current doctrine, it seems like it would reject this process.

                Or perhaps we can genetically engineer a plant to pull the nitrogen it needs directly from the atmosphere. I’m almost certain that organic agriculture would reject this technology also.

                There may need to be some reform to organic principles if the purists would allow it.

                If nothing were to change on the tech front. Organic will still run into resource problems. They already have to supplement manure with other nitrogen sources from the ocean for example. With organic ag being a niche market currently, this isn’t much of a problem. If we converted all of ag to organic principles (not saying you advocate for this, but many organic practioners have) then it would be an ecological disaster as marine biosystems become effected with overfishing.

                “”My leases tend to be long term, 5 years or so, and tend to be crop share based rather than straight cash rent. Puts me in a long-term frame of mind and aligns my interest with the land owner. We both should want better soils and higher net income for both of us by reducing costs and increasing revenues.”"

                It sounds like you have something good worked out between you and your landowner. I wasn’t sure if you owned all your land. I only hope that other farmers that lease can negotiate these terms from their landlords.

                • Jason

                  Fuels derived from contemporaneous organic matter are usually termed biofuels or synfuels, and there is a whole industry, as you say, also working on bioplastics, etc. In some cases these would be immediately ok under current organic law (as far as I am aware). In fact, biodiesel and similar renewable liquid fuels are often encouraged in organic farming, as are tools such as electric tractors.

                  The economic challenge is that fossil fuels are mined from concentrated, 3-D deposits as opposed to harvested from 2-D landscape surfaces, and come with unique chemical characteristics based on the pressures and temperatures they have experienced that are difficult/energy intensive/expensive to recreate using biomass feedstocks. Both spatial and chemical advantages to fossil fuels make me believe that biomass products will always be higher cost until fossil fuels deplete significantly enough so their cost rise substantially.

                  I think you are correct that if a GE organism were used to create an organic molecule that it would be rejected under current law.

                  Sticking with the materials flow theme…farming as currently practiced in nearly all forms I am aware of, is a linear flow process. Materials are mined in one place, transported and dispersed on farms, plants and animals collect matter from air and soil and grow, then the harvest is removed, consumed by people, and deposited as waste in sewage and garbage systems. The only way to make agriculture sustainable is to create closed loop systems out of material flows, especially for the non-atmospheric elements. This would mean human wastes must be collected and put back on the land. The last culture that I know of that practiced this humanure cycling between urban and rural areas was the Chinese. Then came cheap synthetic fertilizers….

                  • Keith Hayes

                    “”"The economic challenge is that fossil fuels are mined from concentrated, 3-D deposits as opposed to harvested from 2-D landscape surfaces, and come with unique chemical characteristics based on the pressures and temperatures they have experienced that are difficult/energy intensive/expensive to recreate using biomass feedstocks.”"”

                    And yet we can make diamonds just fine. They even look like and have the same properties as the “natural” ones. If an industry demands it, the technology and research will find a way to convert petroleum from biomass. It isn’t perfect yet. My line of questioning has more to do with whether or not such a solution could be accepted and adopted by organic agriculture once it become perfected. It appears to me that when organic standards were established in the law, it was already an obsolete system and didn’t seem too accomodating of the possibility of emerging technologies, even if they were consistent with the “spirit” of organic agriculture.

          • Mikeb

            “It is dumb human nature to put oneself into a camp or tribe and then it is us vs them.”

            And yet that is exactly what you’ve done.

            “Conventional” farmers don’t put themselves into a camp because there is no “camp” called “conventional farming.” There is only “organic” and everyone else, the Great Unwashed. There are no conventional standards, no conventional fairs, no conventional USDA labels.

            It was the “organic” identified who started all the line drawing and finger-pointing. It’s been downhill all the way. Now we have Ronnie Cummins claiming that “conventional” farmers poison children and ruin the environment. We have Michael Pollan saying the we live in a “world of pesticide residues” because of conventional farming. We have a whole movement that won’t tolerate a single dose of an antibiotic to cure a cow of mastitis but that finds homeopathy A-OK. Its absurdities need to be questioned and combated daily.

            • Jason

              I get the sense that you don’t like phonies. It is a trait you and I share. I am personally not opposed to the use of antibiotics for acute ailments. I am personally against feeding non-therapeutic doses of antibiotics to increase rate of weight gain. I personally don’t tend to agree with Ronnie. I often agree with Michael Pollan. I don’t believe homeopathy works beyond the placebo effect. I do think water pollution, air pollution, and soil loss are problems largely created by contemporary farming practices. I tend not to place a lot of personal blame on individuals for these problems because I see them as systemic problems. Most farmers are making rational choices given the sets of incentives and constraints out there.

              The world is full of absurdities. One of my favorite authors is Kurt Vonnegut. You have chosen to go after a particular set of absurdities and perceived phoniness and that is fine. What I don’t tend to like is being attacked or having assumed guilt by association.

      • theoldtechnite

        Thanks for answering the question. I have to agree that Organic is in the same boat as conventional for getting those elements as no biological or chemical process will create them. But, why is Organic against synthetic fertilizers? It seems the line drawn is you can do anything so long as you, yourself, don’t initiate and carry through the chemical reaction to render the elements in question into usable forms. But if the exact same reaction occurs on its own, then your good. Why ?

        Note, you do not need natural gas for synthesizing ammonia and nitrates. We currently use NG because its a good source of hydrogen and a source of energy. But any source of hydrogen and energy will do to create the NH3 needed.

      • I just noticed that you allude that phosphates for conventional come from Mexico. Where do phosphates for organic come from?

        • Jason

          Moroco, not Mexico, holds the largest reserves of rock phosphate. Organic farms can buy crushed rock phosphate. Organic farms are not allowed to purchase certain guano products (also high in phosphate) for reasons I can’t recall.

          • Sorry, i read it wrong. But, you seem to be saying both conventional and organic go to the same source(s) for phosphorous.

            But, why aren’t synthetic fertilizers allowed, particularly nitrogen? The reason given so far is because they use up non-renewable resources. But, nitrogen fertilizer can be made without geologic hydrocarbons, disassociating water for the hydrogen and using wind/solar/nuclear for the energy for heating and compression. So why isn’t the rule, no fertilizers from petroleum processes, rather than, no synthetic fertilizers?

            • Jason

              Good question. Might be best to look at a source for this, such as Rodale, but I’ll give it a shot…

              Synthetic fertilizers are usually in salt forms that are highly water soluble. This makes them break down quickly into parts and become plant available nutrients. From an agronomic perspective this has the advantage of rapid uptake by plants. From a soils and environmental perspective this can cause problems, such as leaching (nitrate pollution) and soil imbalances (burning of soil organic matter, loss of fungal diversity, salt build-up).

              Approved forms of amendments in organic farming, such as manures and compost, are slow release forms. This can be a challenge for matching plant needs with nutrient availability but it avoids many of the environmental and soil quality risks.

              About non-fossil fuel sources…these are interesting options. I do think they would be non-allowed due to the form, not just the source. My sense is that these options will become available as fossil fuel derived sources get more expensive. Wind to ammonia may be likely given wind is common in rural areas.

        • Jason

          Morocco, not Mexico, holds the largest reserves of rock phosphate. Organic farms can buy crushed rock phosphate. Organic farms are not allowed to purchase certain guano products (also high in phosphate) for reasons I can’t recall.

  • I hate the term “synthetic fertilizer”! Ammonia, nitrate and urea are the main natural forms of nitrogen in the environment for plants, fungi and bacteria that cannot fix it from the air themselves. If nitrogen fertilizers are produced using renewable energy then what’s the problem? (http://www.agmrc.org/renewable_energy/ethanol/using-the-wind-to-fertilize-corn) And as far as I understand it (having zero farming experience) manure is actually a waste product and using it as fertilizer is a way of reducing its environmental impact but not an ideal one. As Steve has pointed out on several occasions (here’s one example http://www.youtube.com/watch?v=o0UAClKwYVY), the greenest option (better energy efficiency, fewer GHG emissions) is to turn manure into biogas to burn as fuel.

    • Jason

      See my reply to First Officer above about synthetic N. Of course one can debate the semantics of “synthetic” or “natural” etc. Are humans part of nature?

      Regarding manure and biogas this is an option with very large dairies in particular. As far as I am aware, smaller scale biogas doesn’t pencil out yet in the US, but home scale units are used in developing countries, such as India. The residue from biogas can also be used as a fertilizer so its not an either or.

      • That brings up another issue, i think. Manure can’t really be considered a source of nitrogen, only a concentrator. Afterall, the animals from whence it came do not fix nitrogen. So, if no synthetic nitrogen fixing is allowed, we must then be constrained by the natural rate of nitrogen fixing, lightning, bacteria, etc. Then an equation forms whereby fixed nitrogen removal per acre per year through harvesting must be equal to or less (due to losses through nitrogen reverting back to unfixed forms) than the rate of nitrogen fixing per acre per year. Bringing manure into the farm still requires acreage elsewhere for that nitrogen fixing.

        Does Organic farming, then, bump up against this limit in trying to meet or exceed the yields per acre that conventional farming has?

        • Jason

          I think about this stuff all the time :)

          Factories currently fix more nitrogen than is fixed by “natural” methods. When most folks look at that statistic there is often a leap to: “Then if we don’t fix that N agricultural yields will plummet and starvation will set it!”

          My sense is that the story is much more complex and interesting. Look at the discussion on the post “Forgo a hamburger, feed a person” for a lot of good back and forth about what is grown and why and how much is actually needed to feed people.

          Think of it this way. When I drive around and look at farm country I see vast areas with grass species that don’t fix N. And in the winter I don’t even see cover crops that could be fixing N. Instead fields are often bare, or perhaps growing a winter grain. So the productivity of farmland is actually under utilized from an ecosystem science perspective.

          If fields were mostly kept in diverse swards of forage type plants, such as clovers mixed with perennial grasses, the N content of the soil would actually build quite rapidly as soil organic matter builds. C:N rations stabilize around 12:1, meaning for 12 parts carbon there is 1 part nitrogen potentially available via mineralization. Most N that plants uptake each year on good soils can come from organic matter stores and synthetic fertilizers should generally only be supplemented as needed following a winter soil test for mineralizable nitrogen (this would be best practice but I don’t think is widely adopted).

          So to summarize I would claim:

          1. Most farm production is unnecessary waste in developed countries that we find things to do with (e.g., feedlots and ethanol).
          2. Therefore most synthetic fertilizer is unnecessary and wasted too, especially considering annual grains only use 30-40% of applied fertilizer (the rest goes into water and air).
          3. Swards of perennial legumes and grasses that would mimic prairies, cover the land and collect sunlight 365 days a year are the most productive form of agriculture (from a net return on investment and capture of potential primary productivity perspective) and would rebuild topsoil, especially soil organic matter levels, and these would be sufficient to supply available N in a rotation with annual crops.

          I would also add that getting animals out on pasture and having fewer problems with concentrated manure is the way to go, but due to seasonality, specialties, etc. barns and sheds will be used and manure will accumulate and need spreading.

          • A couple of questions:

            If you are growing a cover crop instead of a winter grain, doesn’t that decrease the annual yield for that land?

            How do cover crops capture and convert light energy to fixed nitrogen 365 a year during the winter months? Yes the sun shines but wouldn’t the ambient temperature be too low for much photosynthesis to take place in temperate areas?

            Would a plant’s nitrogen uptake be dependent on how, “hungry”, the plant is at the time?

            • Jason

              Your questions get to the definitions of yield and what you are deciding to account for.

              A winter cover crop isn’t a cash crop that will be harvested as grain or hay and then sold. It will usually be tilled under or sprayed out and the “yield” of interest is the value that the cover crop gives to the soil and how this lowers input costs for the cash crop. For example, a typical red clover stand will make available to a follow on crop 150 lbs of N per acre. It will also add to soil organic matter in general, which will improve soil properties that increase yield or decrease the risk of loss in other ways.

              My farms are in locations where we will have winter activity so the 365 days of potential productivity applies. During heavy cold snaps or rain events this won’t be true. But anytime the sun comes out and the daytime temps get into the 50s you can see the grass grow. By contrast, if we are winter fallowing ground there’s not much growing to hold the soil and be productive, as in have leaves to photosynthesize.

              The nitrogen required for a plant is dependent upon the stage it is in growth cycle. What farmers would like to do is give a plant what it needs when it needs it, but this is practically difficult to do with precision in most cases.

              Interestingly, what perennial plants do well is associate with fungal hyphae and feed them sugars in return for minerals. This can give plants access to source rock and deep soil layers beyond the root zone. If you measure available nutrients in many mature ecosystems they will be exceedingly low and yet productivity is high. Why? Because free soil nutrients are immediately scavenged by roots and fungi. It is when the soil is highly disturbed and soil biology is poorly developed that you can measure high amounts of plant available nutrients.

              What annual crop systems do is mimic the conditions of immature ecosystems with poor resource use efficiency. Gross grain yields may look high, but net yields may not be that impressive when energy and materials flow accounting is done if you have to dump on a lot of external inputs.

              • Speaking of questions about yield, at the end of the day, how many bushels would a typical Indiana or Iowan Organic acre get on average of each of your rotated harvested crops, using no external manure or external compost, as compared to an adjacent acre that also rotated the same harvested crops, using the same methods, but used synthetic nitrogen fertilizer? Both acres would receive external phosphorous, etc, as needed. Years of laying fallow must also be averaged in for each acre.

      • As long as humans are dependent on terrestrial ecosystems services and get infected by terrestrial pathogens, they are very much part of nature.

        If nitrogen fertilizers are produced in a more sustainable fashion (not using fossil fuels) then excluding them simply because they are somehow “unnatural” (which they are not) makes no sense to me. In fact, a better solution would be nitrogen fertilizers that ARE synthetic and therefore are not either immediately chewed up by soil microbes to produces nitrous oxide (200-300 more potent GHG than CO2) or leach away to cause eutrophication when it hits the ocean. An “unnatural” (non-toxic) nitrogenous compound that binds tightly to soil particles and that would be slowly metabolized to release nitrogen would be a much better alternative. I’m a big fan of the idea of perennial crops as long as the yield equation of output over input as well as carbon footprint and yield per land area outperforms annual crops. Biofortified had a discussion on it previously (http://www.biofortified.org/2011/05/commercial-perennial-crops/) and I’d love to see more discussions of it in the future. I can also recommend a look at the publications from the Land Institute (http://www.landinstitute.org/vnews/display.v/SEC/Publications%3E%3EScience), whose focus is on developing perennial variants of annual crops. Wes Jacksons OSU talk on this can be found at http://www.youtube.com/watch?v=4hWjj_mQCS0 .

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