Fertilizers or Amendments? What to Use for Soil Food

Fertilizers or Amendments. Does the difference have you scratching your head?

Soil fertilizers or amendments. Confused? There’s a good reason. There’s not a sharp line between fertilizers and amendments. Fertilizers can be amendments and amendments can be fertilizers. They both can be soil food, but not always.

Fertilizers can be amendments and amendments can be fertilizers. They both can be soil food, but not always.

 

Organic fertilizers can feed plants and soil with more concentrated bursts of nutrients.

 Strictly speaking, an amendment is anything added to the soil that improves its physical condition.  Most of the time, this means organic matter. Both organic and conventional growers alike use organic matter to improve soil condition. In fact, organic matter improves soil condition, no matter what the extreme. It fluffs compacted soils, while stabilizing loose ones. It improves drainage, while holding onto water. It breaks up cloddy clay soil or aggregates sandy granular ones into crumbly aggregates, the building block of good soil tilth.

The reason organic amendments provide such a wide range of soil improvements is because they feed soil organisms with basic building blocks for energy and growth. When we feed soil organisms, they naturally build better homes to improve whole soil condition. At the same time, many organic amendments, especially nutrient-rich manures, kitchen waste, and leafy green material, will fertilize plants with the nutrients they need.

For the sake of thoroughness, a few amendments we use to improve soil condition are not organic soil food. Adding amendments like gypsum to break up clay soils or lime to raise pH can improve soil condition without feeding the soil or garden plants.

Fertilizers, on the other hand, are a legally-defined substance, containing, by law, known and legally-guaranteed percentages of the big three nutrients: nitrogen, phosphorous, and potassium. Using fertilizers, we can calculate the near-exact amounts of NPK added to meet our plants needs.

Organic amendments may also supply NPK in sufficient quantities to fertilize our plants. I'll discuss this more in Soil Food Part II: Amendment Quality. However, the nutrients of many organic amendments cannot be calculated exactly enough to sell as a legally-guaranteed fertilizer. Manures vary in nutrients based on which animal they came from; what the animal ate; and how the manures were stored. Compost nutrients are also notoriously inconsistent. Though they may be superior as soil food, and in some cases, as plant-nutrient sources, organic amendments without consistently known nutrient concentrations cannot legally be sold as fertilizers.

Chemical fertilizers, providing just a straight shot of chemical nutrients have little value as soil food. Though they feed the plants, they don't do much to improve soil condition or soil life - at least not on their own. Organic fertilizers, derived from natural sources, contain messy organic matter that does feed soils.The longer it takes for organic fertilizers to break down and release nutrients, the more soil food value they have. Therefore, organic fertilizers have the dual benefit of supplying known amounts of nutrients and providing soil food. Regardless, neither chemical or organic fertilizers alone will supply enough organic food for your soil. That's why the foundation of living soils comes from supplying and maintaining organic feasts for you soil. Adding organic amendments, which I'll keep talking about in the next blog posts, are one way to do this.