Soil Fertility on Organic Farms

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Throughout this manual we have discussed how organic farmers strive to build healthy soil in order to create the best possible environment for plant growth. A healthy soil is primarily defined by its fertility, which in turn depends largely on the interactions of its physical, chemical, and biological properties.
Of those three essential soil properties, organic farmers perhaps give greatest emphasis to the biological properties that work to create long-term pools of nutrients for plants. Much of their attention, however, is also devoted to the soil’s physical and chemical properties that are vital to plant growth.
In this publication, we’ll discuss the factors influencing the physical, chemical, and biological properties of soil. Much of the discussion on such topics as nutrient management and fertilization will, by necessity, be complex and contain some technical language, formulas, and mathematics.
We will organize our discussion around these topics:

  • The organic approach to soil fertility. Organic farmers use management practices that enhance basic soil properties.
  • Soil testing and the sufficiency level approach. Most testing labs rate soil nutrient levels based on the premise that farmers “fertilize the crop, not the soil.” We’ll explain how to convert those soil test values to nutrient application rates.
  • Nutrient management on organic farms. Its goals are to feed the soil, not just a single crop, and to avoid overapplying nutrients.
  • Using manures, composts, and legumes. We’ll describe how these materials can be analyzed and how to calculate proper application rates for these nutrient sources.
  • Using commercial nutrient sources, including lime, mineral dusts, humates, and plant and animal byproducts.
  • Environmental and regulatory considerations that relate to soil fertility on organic farms.
  • Recommended reading for further study on the complex subject of soil fertility.
Keith R. Baldwin
North Carolina Cooperative Extension Service