One of the key concepts of Lecture 1 was that soil fertility is a feature of soil health as applied to agroecosystems. It is the capacity of a soil to provide nutrients that plants require for growth. 2. Key indicators of soil health include
- a) The ability of the soil ecosystem to mineralize nutrients and make them available to plants
- b) A moderate pH, which promotes nutrient retention and makes nutrients available to plants
- c) Good structure, or tilth, that resists degradation and provides adequate air and water to roots
- d) Good biotic habitat, particularly for beneficial organisms 3. One of the main ways to support these goals is by increasing the carbon content of the soil in the form of soil organic matter (SOM) a) SOM has three main constituents.
As summarized by Cornell University Cooperative Extension, these are: i. Plant debris and living microbial biomass ii. Detritus (active soil organic matter, made of partially decomposed plant, animal, and microbial tissues) iii. Humus (stable soil organic matter
The microbes help decompose the plant debris and the detritus, while humus (a black, sticky substance) is the final product of decomposition c) SOM has many benefits for the soil, supporting the key indicators of soil health listed above.
Some of these functions include those below (and see the Cornell University Cooperative Extension Fact Sheet 41 [franklin.cce.cornell.edu/resources/soil-organicmatter-fact-sheet] for more functions and details): i. It provides the source of substances for mineralization ii. SOM, especially the humus fraction, helps maintain soil pH biochemically iii.
It helps soils resist crusting and decreases erosiveness iv. Plant debris and detritus fractions of SOM provide food for the microbial biomass 4. All these benefits of SOM make it “money in the bank” for the agroecosystem. Maintaining and increasing SOM are the basis of the soil health practices described in this lecture.