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How does cotton agriculture cause soil exhaustion?

  1. Jul 8, 2017 #1
    I remember reading recently that in the Antebellum American South, part of the reason that white southerners wanted to expand slavery westward is that cotton agriculture would cause soil exhaustion. After growing cotton on a given piece of land for a few years, the soil would be degraded in such a way that one could not profitably grow cotton on the given piece of land until the soil was treated somehow. Once the soil was exhausted on a cotton planter's plantation, the planter would buy more land out west and move with his slaves to the planter's new lands out west rather than restore the soil on his plantation back east.

    How does cotton agriculture cause soil exhaustion chemically? I mean, does growing cotton make the soil too acidic or too alkaline? Or, if cotton growing does not cause soil exhaustion due to pH, how does cotton growing cause soil exhaustion?

    Once the soil exhaustion has occurred on a piece of land due to cotton agriculture, how do farmers restore the soil? If the answer is crop rotation, what crop restores the soil if the soil exhaustion was due to cotton agriculture? Or do cotton farmers restore exhausted soils by using fertilizers such as manure or what?
  2. jcsd
  3. Jul 9, 2017 #2


    Staff: Mentor

    I'm not an expert in agronomy or very knowledgeable about cotton cultivation, but what happens, I'm reasonably sure, is that the soil is depleted of nutrients such as decaying vegetation that was in the soil prior to the cotton being planted.
    Neither, as far as I know.
    They fertilize the soil or plant a different crop that adds nutrients back to the soil. Clover is one plant that naturally "fixes" nitrogen in the soil by taking it from the air. Some commercial fertilizers, such as ammonium nitrate and urea, also add nitrogen to the soil. Manure also does this.

    Commercial fertilizers for home use on lawns list the percent composition of three components: N - nitrogen, P - phosphorus, K - potassium.
  4. Jul 9, 2017 #3

    jim mcnamara

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    This has been a historical problem, worldwide. I had graduate soils courses from John Tedrow at Rutgers. He advocated, for example, that a lot of empire building was the result of crummy agricultural practices - like ancient Rome - they expanded the way you describe, using new land for agriculture. Tobacco farming and terrible agricultural practices in Montgomery County, Maryland (USA - was Frederick County then) caused a huge exodus of farmers during the 1840's, mostly moving into Appalachia. Guano saved the day, restoring soils via imported marine guano from the Chincha Islands off Peru. Agriculture - mostly other crops - returned to the area in the 1860's

    Guano (sea bird and mammal excrement, no poop jokes please) there was literally in mountainous deposits. https://en.wikipedia.org/wiki/Guano
    The picture there is amazing.

    To answer your question, crops like tomatoes, corn, cotton, and tobacco have very high NPK requirements (Nitrogen, Phosphorous, Potassium) and will not grow when the levels of these nutrients are too low. The main reason for the tobacco problem is that most of the plant matter grown (leaves) were removed from the area. Same for cotton. I'm using tobacco as an example.

    All of the nutrients in the leaf crop left the soil system and never returned substantially in any form like green manure (plants grown in other fields and then plowed into the tobacco field) or the addition of cow and sheep manure. One temporary workaround was to plow deeper, moving unused nutrients up into the active root growth zone. You can only do this a small number of times before it becomes an empty exercise.

    Corn requires a LOT of nitrogen. Ammonia(NH4) is literally drilled into modern corn field soils because it is almost pure nitrogen in a form plants can use. It affects soil pH, so other things are added later on the fallow late Fall field to counteract the rise in pH.

    Edit: Arsenic levels in those old cotton fields which are now upland rice fields has been an issue.
    Arsenic was applied to the cotton field to control boll weevils. Rice grown there (some batches) tested positive for arsenic at very low levels. I'm not dredging up all of the news links only to have a debate on food safety - not what this thead is about. So I am heading it off right now. I hope.
    Last edited: Jul 9, 2017
  5. Jul 9, 2017 #4
    Thank you, very informative.

    This brings to mind a related question - when I hear about harvesting things like corn stalks to convert to ethanol (difficult because you need to break down the cellulose), the usual comment is that this is 'just a waste product anyhow'. But I figure that returning it to the soil must be helping with the nutrients in the soil, and removing the corn stalks will have some detrimental effect. Or are those stalks just not very nutrient rich, and most nutrients are in the corn kernels that were removed anyhow? Or maybe just the fiber content is important for the soil to retain moisture, reduce erosion, or some other function? Or is just adding a little more commercial fertilizer all that is required to offset the removal of the stalk material?
  6. Jul 9, 2017 #5
    Microorganisms in soil will gradually break down any kind of organic waste into useful plant nutrients.
    It's more efficient though to compost the waste then apply the compost to soil.
    Gets the same result (or better) in a fraction of the time.
  7. Jul 12, 2017 #6
    I have never heard of this importation of marine guano into Frederick County from the Chincha Islands off Peru. Do you have a source for this?

    Does all types of guano contain Nitrogen, Phosphorus, and Potassium?

    Does horse manure contain all three of the nutrients N,P, and K?
  8. Jul 12, 2017 #7

    jim mcnamara

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    Sure. It was not limited to just Montgomery/Frederick Counties. Tidewater Virginia and Delaware also imported it.

    This discusses the guano trade in Maryland in the 1840-1860+ timeframe in Maryland.
    My original source was an old textbook from the 1950's - 'History of Montgomery County'


    Guano is just marine deposits in this context. There is also bat guano. Many caves have dozens of feet of deposition.

    Horse manure (because of urine) contains N, the usual rating for some samples I saw:
    horse manure 1:1:0
    blood meal 1.0.0
    fish meal 1.1.0, 1:1:0 (%N %P %K)

    Commercial manure often has stuff added. So I cannot predict what you will see in your local garden supply place.

    Commercial dried guano is often rated slightly higher. You can buy diluted liquid guano for use around your garden - a mix of bat and marine sources. It is .01-.011-.01 so it does not burn plants. It is really a manure tea.

    It also costs a lot, IMO.

    Guano is also a new issue for Peru - apparently commercial harvesters are trying to "pilfer" the stuff off the Chincha Islands.
    Last edited: Jul 12, 2017
  9. Jul 12, 2017 #8
    Okay....The ratio you gave for horse manure is: 1:1:0. I take that to mean that horse manure has one part nitrogen for one part phosphorus, and I also take your ratio to mean that there is no potassium in horse manure.

    I'm not talking about commercial horse manure that has nutrients added to it. If you just took horse manure that just came out of a horse's rear end, how would that horse manure do at restoring the soils for commercial cotton agriculture? The problem would be that the horse manure would not restore potassium to the soil. How important is having potassium in the soil for commercial cotton agriculture?
  10. Jul 12, 2017 #9

    jim mcnamara

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    NPK are the results of standard tests for easily available NPK. Of course excrement contains some potassium.

    Suggestion: read up a little on manure. Do you know what hot manure is, for example. It burns plants badly. Fresh (hot) manure has to age or be worked into soil a couple of months before the growing season. The variability of NPK in manure from your pet horse varies with what you fed him. So the most nearly correct answer is that NPK can exist but in undetermined amounts. Also NPK labelling usually uses a zero ( 0 ) for anything less than .5. So, .4 K would get a zero. Even though there is some in there. Nobody will get mad if you use .4 --- they may think you are, um, unusual. Or selling bat guano tea.

    That is why I used 'commercial', putative standard label values. Seriously, please consider reading on the use and application of manure. It will be useful someday unless you plan to live in Manhattan all your life. You appear to be in a non-urban area. Ask a farmer or livestock producer.
    See: https://en.wikipedia.org/wiki/Plant_nutrition

    In other words, your assumptions about some of the content here are not helpful for us to give good answers.

    To answer what I think is the implied question:
    1. in 1840 agricultural practices in most of the US were beyond horrible. They wrecked the soil and moved on every 15-20 years or so.
    2. people who know what they are doing, like one of your neighbors who went to ag college, in addition to livestock manure, also use green manure Ask them what that is, and come back with more questions. It corrects micronutrient problems and some other macronutrient issues.

    Potassium is important (a required macro nutrient for cotton and tobacco, any plant. Period. And yes, some manures are low in potassium. And no, in 1840 they could not even spell potassium.

    Sir Humphry Davy isolated it in 1807. It was not connected to plant growth requirements until much later. In 1840: Farmers also believed that mice came from bread or wheat kernels left in a dark place - spontaneous generation. It was a frighteningly different world back then. Life expectancy was awful. I'm old. My great grandfather came back from the Civil War, and then had 8 kids. 7 of them died from scarlet fever in two days. Your family has similar stories.
  11. Jul 12, 2017 #10
    I don't understand why horse manure would have Nitrogen in it due to urine. Are you saying that the horses would pee on their excrement? Why would horse manure have nitrogen in it due to urine?
  12. Jul 12, 2017 #11

    jim mcnamara

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    Stabled horses defecate where? Stabled horses urinate where? Same is true in a corral. Horses back then were like cars now. Not really pets or food, rather tools. Urea is a molecule in urine that that breaks down by bacteria giving ammonia among some other things. Urea by itself can be used a nitrogen fertilizer in very dilute solution.

    So cleaning the stable or horse corral was the easiet way to get manure quickly. Still is. Horses in a corral tend to make messes in one general area. Plus, you get hoof and fetlock problems/infections in horses kept in unclean conditions.

    Corral cleaning is "fun". In the sadistic sense for an observer. You should try chipping frozen manure/urine on a bright January day at 15°F. I did it for years.

    We are getting off-topic here. Manure can also have nitrogen from partially digested plant proteins (proteins are built from amino acids - amine means a nitrogen atom attached to carbon and some hydrogen atoms). Bacterial breakdown of manure improves the plant bioavailability of some of these nutrients. Another reason to avoid fresh manure.
    Last edited: Jul 12, 2017
  13. Jul 12, 2017 #12
    The role of Nitrogen for healthy plant growth is well understood, Phosphorus also.
    Potassium is less well understood, but plants get sick without enough of it, and also sick with too much.
  14. Jul 12, 2017 #13


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    Potassium is forms an ion which is involved in generating the cell's membrane potential (in animals anyway, K+), along with other ions (Na+ and Cl-.
    If potassium has a limited availability, this may explain its requirement (assuming plant cells work the same way).
  15. Jul 13, 2017 #14

    jim mcnamara

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