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Thursday, February 7, 2013

Soil Building: The Key To Sustainable Farming




Will we will be able to meet the growing global demand for food over the next few decades?  Will we be able to do that in a way that does not degrade the environment?  Surprisingly, the answers depend on how well we manage the soils we farm.

Soils are not just dirt.  They are dynamic living systems with highly complex physical and chemical properties.  Whether they are healthy and have desirable features depends on how they are tended, and historically many farming practices degraded soil quality rather than improved it.  Fortunately, over the past several decades we have learned a great deal about how farmers can significantly build the quality of this critical resource.  It is extremely important that this knowledge is extensively applied (I will be specifically addressing the situation for the millions of acres of rain fed, row crop land in the American Midwest).

What A Healthy Soil Can Do For Farmers and the Environment


Healthy soils are rich in "large aggregates" - collections of the base minerals of the area (sand, clay, fragments of parent rocks, etc) which are held together with the living organisms and life generated complex polymers like humus from broken down plant matter and glomalin from beneficial fungal growth.  These aggregates are loosely arranged with many "macropores" created by past plant roots and by the work of earthworms and other tunneling organisms.  Water is able to quickly infiltrate into the soil, even after heavy rains or rapid snow melt,  and be stored for later use.  Because of the rapid infiltration and the aggregated structure of the soil, there is little, if any, runoff that moves at a velocity which would carry silt, fertilizers or chemical residues into neighboring streams.  A healthy soil is thus more "drought proof" and far less likely to contribute to water pollution issues.

Because of the macropores, a healthy soil is better aerated. Oxygen is available for the needs of plant roots and there are fewer instances where oxygen becomes limiting.  That leads to better crop growth and far fewer events where anaerobic soil microbes make the "trace greenhouse gases" nitrous oxide and methane which are a major part of agriculture's contribution to climate change. Healthy farmed soils can, under certain scenarios, "sequester" carbon dioxide from the atmosphere - something which could, over hundreds of millions of acres - be a significant mitigation strategy for climate change.

Healthy soils are also lively places with many fungal and bacterial symbionts that help plants better absorb nutrients and biologically "fix" their own nitrogen supplies.  Some also help to suppress pathogens and nematodes that might otherwise damage their roots.  Between the cycling population of microbes and the stable soil aggregates, a healthy soil is a good buffer for the nutrients that plants need - preventing them from being wasted by moving to surface or ground water, and evening out the supply over time.

How Does Nature Build Healthy Soils?


It turns out, not surprisingly, that the best way to build soil in a place like the American Great Plains is to imitate the way that nature builds soil.  Before that region was put under the plow in the 1800s, the prairie grasslands of the US Midwest had wonderfully healthy soils - particularly in the Northern tier where the parent mineral base is deep and well drained because of the influence of glaciation in the last Ice Age.  Nature builds soils from the top down.  The above ground parts of plants from each season fall onto the ground and slowly decompose.  In the meantime they protect the soil from the splashing assault of rain drops and they block the evaporation of moisture from the soil surface.  Natural soil building does not involve physical disturbance - things like plowing.  The other main feature of the prairie ecosystem was that there was a mixture of perennial and annual plants growing and feeding the soil biosystem via their roots for as many frost-free days as each season allowed.

Normal row crop farming involves a great deal of soil disturbance.  The crop residues were normally tilled under at the end of the season leaving the soil exposed.  Some weeds might grow between crops, but the soil is not being fed nearly as much as in a prairie ecosystem.  Finally, the soil is compressed by the passage of heavy farming equipment.  Under these conditions soils tend to decline in quality over time.

How Can Farmers Imitate Natural Soil Building?

Starting in the 1960s, farmers have been developing ways to farm that don't involve much if any tillage or other disturbance of the soil.  Crop residues are left on the surface where they protect against erosion and block evaporation.  The full season soil feeding of a grassland can be imitated by the planting of cover crops which grow between one harvest and the next planting.  These cover crops can include legumes that help to produce nitrogen for the next crop or alternatively they can scavenge nitrogen or other nutrients that remained in the soil both to save them for release in the next crop cycle and to prevent them from becoming pollutants.  Without periodic tillage, soils can become compacted.  Fortunately, GPS and even more sophisticated guidance technologies, now allow farmers to practice "controlled wheel traffic" meaning that no tire ever drives over most of the area of a field so that soils remain well aerated.  Precision fertilization can then ensure that no nitrogen fertilizer is placed in the compacted tracks so that it is much less likely to be released as nitrous oxide.  A combination of these practices: continuous no-till, cover cropping, controlled wheel traffic and precision fertilization does a very good job of increasing soil quality over time.  These soils are more "drought proof" because they capture and store water better.  They are more fertile because of nutrient buffering in the improved organic matter.  Over time, the "weed seed bank" is diminished because tillage does not keep exposing more seed.  These soils are very good at preventing pollution of both surface and ground waters with nutrients.  They can, under the right circumstances, lead to a net sequestration of carbon in soils.



How Does This Compare With Soil Building in Organic Farming Systems?


The founders of the organic movement early in the 20th century were far ahead of their time in their appreciation of the importance of building soil quality.  Although it is not a required element for organic, cover crop is a more common practice in organic.  However, one of the main ways that organic farmers improved soils was by bringing in large quantities of manure, compost or other organic amendments and tilling these into the soil.  This practice does in fact improve soil quality over time, but not in any way that imitates nature and it has its own environmental issues.  Because organic farmers have little if any option for herbicides, tillage has been the main way that weeds are controlled.  Recently there have been efforts to develop a "roller-crimper" system to do no-till in organic.  The most practical use of a roller crimper by be in combination with herbicides (as has been a practice in no-till systems in South America).

So How Much Of This Kind Of Soil Building Farming Is Happening?


Some, but not enough.  I don't want to imply that it is easy for a farmer to manage land in the way described above or that it is a one size fit all solution for every situation.  It takes the integration of many technologies and presents its own set of practical challenges.  Although such a system is ultimately more productive and more stable, there can be difficulties during the transitional period. Residue covered soils can be slower to warm in the spring and can harbor different pests.  It is logistically difficult to get a cover crop planted during the busy harvest season.  Specialized equipment is required.  All of this is further complicated by the fact that most modern farmers lease a substantial proportion of the land they tend - typically on an annual cash rent basis.  The building of soil quality is a wise long-term investment, but only if a farmers knows that he/she will be the one tending that land in the future.  Although there are very significant areas being farmed with one or more of these ideal practices, the full suite of soil building approaches are probably only being applied on a small percentage of the total area.  There is a real need for developing more enlightened and long-term land lease structures and agricultural credit policies to enable more farmers to be in the business of building soils for the future.

Cover crop image from USDA-Natural Resources Conservation Services.  No-till corn image also from NRCS

You are welcome to comment here and/or at savage.sd@gmail.com.  To learn of future posts follow @grapedoc on Twitter.

7 comments:

  1. Steve, I continually run into the claim from "organics" advocates that the use of pesticides and "chemical fertilizers" "decimate" soil organisms and leave the soil "dead." The argument put forth is that the use of these "chemicals" needs to be stopped before soil can be "healthy" again. How true is this?

    If there is some truth to it, doesn't the addition of organic matter renew these organisms?

    It seems to me that one would have to dump a whole lot of the wrong chemical all at once to wreak the havoc on soil that these "experts" claim is happening regularly in any farming that is not "organic."

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  2. Michael,
    Yes, I've heard that. It can only be said by someone completely unaware of soil microbiology. Soil microbes use fertilizers to grow. Most crop protection chemicals have no effect on most of the things that live in soil. We can only culture 1% of the organisms that live in soil and still numbers are in the range of a billion/gram. Even in cases where methyl bromide is used, re-colonization is rapid. The old saying, "nature abhors a vacuum" is absolutely true of soil.

    There are shifts in the relative balance of species based on farming practice. The soil building I describe tends to shift towards more of a fungal dominated microbial community rather than a bacterial one, but both are always there. Plowing organic matter into soil creates a burst of microbial activity, but often so much so that oxygen demand is too high and so the microbes that make methane and nitrous oxide come into play. Such bursts don't happen in natural soils.

    The more natural way to feed the soil biosystem is through a combination of surface layer decay and the exudates and remnants from roots at deeper levels. The most disruptive thing for soil microbial communities is tillage. That is why organic matter addition is required if you are going to till. If you don't till, you don't need to import tons of OM.

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    Replies
    1. Thanks, Steve. I'm inclined to think that this stuff doesn't matter for those of us who are very small farmers (we have a one-acre CSA and no room to rotate or cover crop). I'm going to just keep gathering our cow manure, composting it, and spreading it on the soil, tilling it in, using "chemical fertilizer" as a supplement and spraying to keep insect damage at bay. Is there anything inherently wrong with that system, in your opinion? Organic advocates continually try to guilt-trip us.

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  3. Steve
    Thanks for leaving a comment on my site, today. You are doing great work here. Looks like you and I see things quite similarly as I am in agreement with you on Huber(ish) and GM labeling, etc. I shall start following you. If you're ever back at CSU, drop me an email.

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  4. Your points might actually be valid, but- You've made a pleasant argument for the honorable Monsanto Corp.-Tongue planted firmly in cheek. They're BS from the pit of hell, and an enemy that should be met at the edge of family farm at the end of a muzzle. The present administration has put their top officials in charge of the FDA. Monsanto hires groups of thugs to trespass, pick crops to test, then sue mom and pop farms out of existence for patent infringement that have NEVER planted Monsanto's genetically modified products, nor saved any of the Monsanto seeds for the following year. They've only saved some of the seeds from their previous crops, yet due to the unwanted GMO crops pollen blown onto other farms that don't want it. Monsanto then sues family farms out of business, and out of their homes and land. Funny how you didn't mention any of their crimes against the American farmer. Look it up, do some research.
    Your argument won't be heard due to you appear to be in the pocket of an evil pile of dog squeeze.

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    1. Anonymous,
      Do you actually know anything about this that you didn't just read on the internet? I'm not in anyone's pocket, but I'd be happy to introduce you to real customers of Monsanto who appreciate their products very much and to real people who work for that company who are working very hard to make farming more sustainable. What you have believed are myths propagated and re-propagated in the echo chamber of anti-technology by people who don't actually know anything about it except what they have read from each other.

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    2. I'm not a scientist in this field, and nope, I didn't get any of this from internet reading, but if I did we all know it must be true because it's in print.
      I live in farm country, spoken to a bunch of my neighbors and folk that farm crops, I've seen multiple interviews with burned farmers, that now have no land.
      I also work with BASF and have been through the GMO labs and spoken with the scientists multiple times. I'm close to a top BD scientist that refuses to feed this stuff to his own children due to what has happened in lab tests. I can assure you they are real 98.6 deg people.
      I don't have any problem with technology, but once it's prematurely introduced, the affects and adjacent crops seeds are now modified. What's the long term effects? Monsanto doesn't know, or care.

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