Can We Replace Man-Made Fertilizers With Manure?

From November of 2018, here's a look at why we use inorganic man-made fertilizers even though we know that manure does a better job of improving soil structure and health. Andrew McGuire's answer, after doing the math, is that there's just not enough manure in the world to produce the amount of food people on the planet require. Here's a summary of his findings. You can read the two articles this is drawn from (along with all his citations) here and here. How Much Manure Can We Produce? The process of making manure starts with plants that are eaten by livestock who then give us the "end" product. McGuire started by looking at the losses of organic matter in this process: • 57-81% between feed and fresh excreted manure (ASABE, 2005) which goes to the animal's growth and maintenance • 4-8% lost in collection and transport (10-40% of excreted manure, NRCS 1995)   Using these loss figures, and average yields

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3 thoughts on “Can We Replace Man-Made Fertilizers With Manure?

  1. The nutrients in inorganic manufactured fertilizers also come from someplace else, as John Marble points out. Florida, Idaho, North Carolina and Utah extract and process 10% of the world’s rock phosphate used in the manufacture of fertilizer. Canada has the world’s largest deposit of potassium- containing salts mined for fertilizer production. All of the forms of inorganic commercial nitrogen fertilizer are derived from anhydrous ammonia which is manufactured by reacting nitrogen gas derived from the air and converting it by pressure to a liquid state which requires a lot of energy.

    The earth’s supply of extractable P and K are not infinite and inorganic manufactured fertilizer may become as scarce as manure. At least manure is renewable( to the extent grass will grow to feed animals) does not acidify and salinify the soil, and supports rather than destroys soil organisms. If you must transport nutrients from areas of plenty to areas of need in order to grow food, it may as well be manure.

    The big question that people have been trying to solve for eons is how to produce food in a way that does not catastrophically deplete soil nutrients. Can we feed ourselves within the limits of the nutrients the earth can sustainably provide?

  2. Not enough manure? Grow your own. Before a crop comes off, plant a cover under it. This was custom until chemicals came along. How do agronomists think there are fields in production for centuries? Light tillage and post-harvest grazing. All I’ve ever seen chemical fertilizer do is make plants tastier to insect pests. If Gabe Brown in ND can take his soil from 1.5% organic matter to 11% in some fields, then anyone can. He receives average 16 inches of moisture a year and gets record crops without irrigation or chemicals.

  3. Thanks for this.
    I also exhibit little evidence of being a mathematical genius, but the math here seems almost extraneous. It seems to me that the physics here are pretty basic: we can only increase nutrients in our soils by bringing them from somewhere else. I suppose a philosophical exception might be the collection of N from the atmosphere by legumes.

    I remember my cognitive dissonance when I visited an organic farm where the operators were using a 3/4-ton pickup to drive 70 miles to load up chicken manure that had been processed through a grinder mill and stored under cover until dry. They would then haul it home and carefully spread it on their fields. The explanation for this process was that the farm would not function without all of that transfer of nutrients. I’m happy they have found a way to grow food, but the system seems impossible to sustain.

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