The Future of Soil Health Evaluation
Figuring out what makes for a healthy soil goes beyond its pH levels and how many nutrients it contains. As researchers dig deeper, they are now determining that a soil’s organic matter content, biological activity, structure and more all play a role in how well a particular soil can support plant life. Dr. J. Benton Jones, Jr. provides a closer look into the future of soil health evaluation.
Today, there are soil scientists who believe that maintaining a soil within the desired pH range and designated levels of essential plant nutrient elements, particularly phosphorus and potassium, is not enough to judge a soil’s fertility status.
What is being suggested is that what currently defines a fertile soil is not sufficient for defining what would be a healthy soil, as there are both physical and biological factors that relate to the latter but not the former.
New research suggests the additional soil factors that define a healthy soil are its organic matter content, biological activity, texture and structure, cation exchange capacity (CEC), electrical conductivity (EC) and heavy metal content.
Additional tests to determine these values are fairly easy to perform, aside from the biological activity test. However, how these various test results are interpreted for defining a soil’s health status has yet to be clarified in terms of soil type and the soil’s intended use, whether it be a home garden soil, including turf and landscape plantings, or a cropland soil devoted to the production of grain and vegetable crops. Ongoing research aims to answer several questions:
- Once the soil health status has been established, based on an evaluation of the above-mentioned test results, what recommendations would be made to the home gardener, grower or farmer if their soil is not considered healthy?
- What would bring the soil into the healthy category?
- What would be required to maintain the status considered essential for maximum plant growth as well as high product yield and quality?
In this proposed evaluation procedure for defining a healthy soil, considerable weight is given to organic matter content and biological activity. Determining a soil’s organic matter content is a fairly easy procedure, while the test for determining biological activity is not.
One of the proposed laboratory test procedures for determining biological activity is the SOLVITA Respiration Test System, a test method that has attracted the attention of those who are not satisfied with just a simple fertility evaluation of a soil.
Currently, there are soil-testing laboratories that offer this test procedure, including an evaluation of the obtained value. The level of biological activity in the field or container is determined by factors that are not easily controllable, such as temperature and the presence of a food source essential for the survival of soil micro-organisms.
Most soils are relatively sterile except for the area around plant roots as the roots provide a food source for micro-organisms that will vary widely in species and activity level. Adding a substance that contains micro-organisms to a soil will not ensure their presence, unless there is an accompanying food source, which may be either lacking or insufficient to sustain activity over an extended period of time.
For researchers proposing the concept of soil health as a means of defining the fertility status of a soil, the addition of organic materials to the soil, either in the form of organic composts, or by the use of cover crops between food crops, or some form of minimum tillage, are some of the suggested means for increasing and maintaining the organic matter content of a soil.
Unfortunately, Mother Nature has a major role to play here; with rising, seasonal air temperatures, the rate of soil organic matter decomposition increases. This is one of the major reasons why soils in southern United States, for example, are lower in organic matter content than those in the north.
Poorly drained soils will have a higher organic matter content than those that drain easily, while ease of draining is a desirable soil property. When a soil is tilled, the organic matter content of the soil will decline; therefore, minimally tilled soils will have higher organic matter contents than those not being tilled. The organic matter content of soils in containers placed in an environmentally controlled structure will decline faster than those in a more natural, uncontrolled environment.
Increasing the organic matter content of a soil may actually decrease plant growth, depending on the soil’s type, texture and level of essential plant nutrient elements. Soils high in organic matter are more difficult to manage and cooler in the spring as they hold water that keeps the soil wet and promotes biological activity that may compete with plant growth in terms of reducing the availability of some essential plant nutrient elements.
A History of Soil Testing
Testing to determine the fertility status of a soil and generate a lime and fertilizer recommendation began in the early 1920s, and during the 1950s, soil-testing labs were established by many land-grant colleges and universities to provide farmers with lime and fertilizer recommendations for managing the fertility of their cropland soil based on a soil test result.
Many different testing procedures were used, based on two factors: the scientists engaged in soil fertility research (many test procedures carry their name) and soil type. In 1976, the Council on Soil Testing and Plant Analysis, now known as the Soil and Plant Analysis Council, was formed to provide a forum for those engaged in soil-testing and plant-analysis research and its application for guiding growers in their use of lime, chemical fertilizers and other soil amendments.
In 1979, the Council published the Handbook on Reference Methods for Soil Analysis, with revised additions published in 1985 and 1992. The Council also initiated a soil analysis reference program so soil-testing labs could verify their analytical procedures, a program in wide use today. Today, there are both commercial soil-testing labs offering a wide range of analytical services as well as those supported by a land-grant college or university.
Soil Testing Now
Traditional soil testing is an accepted practice used by cropland farmers as a guide for the use of lime and fertilizer for maintaining the desired soil fertility status, as well as providing information on the nutritional needs of the crops.
For the home gardener, soil testing is not widely practiced, yet I would argue that more of it is needed to help growers avoid the possible occurrence of imbalances and excesses occurring from the excessive use of fertilizers, fertilizer supplements and soil amendments. Keep the following advice in mind when it comes time to test your rooting medium:
- Step 1: Check with the laboratory as to their services, cost and sampling and submission procedures.
- Step 2: Be sure the test procedures requested are routine services offered by the laboratory for the type of sample being submitted.
- Step 3: When testing for micronutrients, be sure the test requested matches the soil type and plant species requirement for that micronutrient.
Soil test results provide a means of monitoring the nutrient element status of the rooting medium, which helps growers determine what test values are changing as a result of the applied management and cropping practices. Changes occurring over time will also serve as a means for adjusting practices before an insufficiency occurs.
The alternative soil heath concept outlined here has yet to be widely put into practice. Today, there are research programs underway to determine the value of the soil health concept as a factor in assessing the fertility status of a soil, and then to develop recommendations that will establish what is required to establish and maintain a healthy soil. It’s an interesting subject both hobby growers and commercial farmers ought to keep their eyes on.