Fuel for the Soil Factory

My Albrecht studies continue with an article titled Loss of Soil Organic Matter and Its Restoration. Like The Drought Myth, it was packed with insights and information. The metaphors were especially striking. He referred to the soil as a breathing, working entity, like a factory where organic matter is fuel, bacteria is fire, and nitrogen is the building material of choice. It uses the equivalent of 1 horsepower per acre to burn organic matter, “exhaling” more than 25 times as much carbon dioxide per day as an adult man at work.

The organic matter (its supply of fuel) has been building up gradually for 25,000 years in North America, since a glacier receded and left minerals in its wake. Then came the pioneers who tilled the soil, and a steep decline in soil organic matter (SOM) began. With the loss of SOM came a proportionate decline in agricultural productivity, and the trend continues to this day (compensated for by chemical inputs, of course). In this article, Albrecht outlines ways in which this trend can be halted or even reversed.

As I was reading over my notes and trying to figure out how I could best summarize what I’d learned, I started to put the information into a format I’m very familiar with: a how-to. Maybe my mind was trying to tell me that this was the best way for the information to “stick,” so I just went with it and here is the result:

Introduction

The agricultural productivity of land has historically been correlated with the percentage of organic matter in the soil. Modern agricultural practices have resulted in the loss of soil organic matter (SOM) through erosion, tillage, and crop removal. Its restoration will not only improve the productivity of the land, but it can also reduce the need for chemical inputs and improve productivity during drought.

Steps

1. Understand how SOM improves the productivity of the land. The process of decomposition breaks down organic matter into nutrients that plants can use to grow. Without an adequate supply of SOM, nutrients must be supplied through other means, typically by purchasing chemicals.

2. Take soil tests. Find out what percentage of your soil is organic matter.

3. Set an SOM goal for your soil. To determine how much SOM should be in your soil, you should consult with a soils expert. Generally, the cooler and wetter the climate, the more SOM should be present in the soil. Some target figures for the United States are:

  • northern Missouri, 3.54 percent or 70,800 pounds per acre
  • southern Missouri, 2.20 percent or 44,000 pounds per acre
  • southern Minnesota, 4.44 percent or 88,800 pounds per acre
  • Arkansas, 1.96 percent or 39,200 pounds per acre

4. Fertilize and lime the soil in preparation for a sod or grass crop.

5. Plant a sod or grass crop, preferably a legume like red clover. Leave the sod in for as long as possible, or work it into a rotation. There are numerous benefits to planting sod:

  • limits erosion
  • increased moisture storage in subsoil, which is a good defense against drought
  • heavy root growth and partial root death adds SOM

6. Add a mixture of crop residues and manures that resembles SOM in terms of the carbon to nitrogen ratio. Not all organic material is created equal. If you want to add 15,000 pounds per acre of SOM to the soil, simply dumping a 15,000 pound mixture of organic matter like manure, legumes, and straw on a single acre is not enough. Soil bacteria needs adequate nitrogen to process all of the carbon in the organic matter and turn it into nitrates, which the plants can readily absorb. Otherwise, the carbon in the organic matter is released as carbon dioxide instead of being turned into SOM. To prevent this from happening, compost the mixture with a nitrogen source (e.g. liquid manure, urine) until a better carbon to nitrogen ratio is reached.

Tips

  • Poultry manure is especially high in nitrogen.
  • It will be more difficult to build SOM in warmer areas because of the high rate of decomposition; however, a longer growing season can also permit two crop plantings, one of which can be a green manure, which will make more SOM available to plants.

Questions for further study

  • How can you find out what a good SOM percentage would be for a particular area?
  • What is a good C:N ratio for compost? And how is it measured/tested?
  • How do you know how many minerals (especially Ca) the soil needs?
  • How exactly does the chemistry of decomposition and plant take-up of nutrients work?
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1 Comment »

  1. Hans-Peter said

    Hey, I read in an ATTRA article that an acre of living topsoil typically has 900 pounds of earthworms, 2,400 pounds of fungi, 1,500 pounds of bacteria, 133 pounds of protozoa, 890 pounds of arthropods and algae, and even small mammals.

    Here’s the link in case you’re interested: http://www.attra.ncat.org/attra-pub/PDF/soilmgmt.pdf

    Also, I read in the Biological Farmer by Gary Zimmer that evaluating the soil’s pH level is a good way to determine how much calcium to add to the soil. Acidity or alkalinity don’t directly influence the growth of the plant, but they do affect the ways in which plants grow through nutrient release. It would be cool to see if other articles available online discuss this topic.

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