Soil Cover Crops for Winter

This is an example of a soil test I did recently for a new development. They, like most new developments have no top soil to work with and instead are working with subsoils. Subsoils are the interface between soils and the rock substrate from which soils originate (in combination with top-down organic matter accumulation). Roots can reach to subsoils so their health is important for trees and any other deep rooting plant. Especially if those subsoils are especially high in clays or sand. When your yard/landscape/garden is starting with subsoil a robust plan to increase organic matter and microbial activity, diversity, and abundance is the first step in a 2 - 3 year action plan. That action plan ought to be aimed at a stable state in which the plants with their microbes do the majority of the work for maintaining soil and thus plant health.

Example of soil test results and responses...

1. Your soils are in a good pH zone to accommodate most plants (5.5 – 7.0).

2. Low phosphorous needs to be addressed by adding microbes to help release the “locked” phosphorous. P-fertilizers are both in rapid decline globally, leach readily through the soils and into waterways wreaking havoc. Having microbes do the work for you is the best solution. Your pH is good for the majority of beneficial soil microbes. The soil density is a problem; more below.

3. Available nitrogen forms are typically low in all soils though usually not this low in clay soils. Based on the density of your soils they are likely sub-soils which explains why they are nutrient deficient. Changing the soil texture (reducing density and increasing porosity) will help nitrate retention. More recommendations with regard to soil architecture and nutrients below.

4. Potassium being low is also troublesome because it is usually high in all soil types. This also suggests these soils are sub-soils. Potassium application is recommended after applications of organic matter, microbial inoculations, and cover crops.


7. Low Magnesium will be a significant issue for proper uptake of nutrients by plant roots and their microbial partners. Correcting this you can use a variety of products, including Epsom salts. Please be cognizant that some forms of Mg in ‘fertilizer’ can change the soils’ pH. Just be careful what you use to increase magnesium concentrations. Avoid those with a sulfur (S/SO) attached or a calcium carbonate (CO) attached.

8. Ferric iron (Fe) is low, the test recommends addition of 5lbs/acre (or 0.5lbs/1000 sq ft); however applications in incremental doses is recommended. The high aluminum and soil density can be exacerbated if too much iron interacts with the high aluminum. Then a film is formed around the clay particles reducing plant root’s ability to access available nutrients in the soil. You will know if your plants are experiencing iron deficiencies ...

9. Calcium – the addition of calcium is recommended. Do not apply any calcium with a carbonate attached (CO3). Thus, you can’t use lime to increase the calcium levels; search for a calcium attached to another fertilizer or find elemental calcium ... I recommend adding prohexadione calcium at a rate of 12 oz/ 100 gal water. One application before retesting NPK.

10. Soil Organic Matter should be the first item in your soil health regime. Additions of high doses of leaf litter and other forms of organic material would be my first step in remediation. If you can locate leaf litter and spread it >3” deep this autumn, terrific. Growing an autumn/winter cover crop mix is critical and foundational to fixing your soils. Including legumes in the plants added in the spring is also critical to insuring good nitrogen access throughout the growing season without adding N-based fertilizers. N and P based fertilizers can disrupt the beneficial microbes in soils.

11. Micronutrient deficiencies – this will be addressed when the organic matter and other nutrients are “fixed”...

12. Architecture/density ....

Remediation summary

  • First, plant a winter cover crop mix - cut all of these before blooming and keep cut material on soils

  • Add as much leaf litter as you can (3” deep or more) this Autumn...

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