How Healthy Is Your Soil? Cornell Soil Health Testing Program Can Tell You
Posted: October 24, 2011
Farmers understand that healthy soils are important for producing high quality, high yielding crops. But what exactly IS a healthy soil, and how can a farmer judge how healthy his or her soils are?
According to the Cornell Soil Health Assessment Training Manual, a healthy soil has the following characteristics:
1) Good soil tilth, or overall physical character, 2) Sufficient depth for adequate root growth, with minimal compaction, 3) Sufficient but not excess supply of nutrients, 4) Small population of plant pathogens and insect pests, 5) Good soil drainage, 6) Large population of beneficial organisms, 7) Low weed pressure, 8) Free of chemicals and toxins that may harm crops, 9) Resistant to degradation, with a high degree of aggregate stability, and 9) Resilience when unfavorable conditions occur.
The Cornell soil health testing program uses a variety of field- and lab-based techniques to measure each of these characteristics, to arrive at a summary soil health rating. The comprehensive package, recommended for vegetable production, agronomic rotation crops and for first time soil health assessment, is $75.
So how does this work? The test requires that you collect a soil sample, take soil penetrometer readings, and provide some general information on the sample form. Collecting the soil sample for a soil health test is very similar to collecting one for a Penn State soil nutrient test, except that you keep at least 1.5 quarts of soil rather than the pint or so of soil needed for a typical soil test. Also, the soil sample is not dried, but rather kept cool and shipped to the Cornell lab within two days. It is recommended to include a blue ice pack with the sample.
Field penetration resistance is a measurement of the soil’s strength, measured with a field penetrometer. As the penetrometer is pushed through the soil layers, it measures the soil resistance, which is what a plant root would have to push its way through as it grew. Armed with my new penetrometer (Dickey-John, courtesy of my colleague Tianna Dupont; about $200), I took 10-15 penetrometer readings for each of the four fields I tested. Readings are taken at two inch increments for 0-6 inch depth and for 6-18 inch depth.
Once the soil sample and the penetrometer data are collected, the final step is to fill in information about the specific field, including soil name, tillage depth, manure and organic matter additions, crop history and future crops.
Results and Interpretation: We received two reports for each soil sample we sent to the Cornell lab. The first was a soil nutrient analysis report, with information on pH, P, K, Ca, Mg and organic matter. The second report provides an assessment for soil physical characteristics (aggregate stability, available water capacity, surface and subsurface hardness), biological characteristics (organic matter, active carbon, potentially mineralizable nitrogen, root health rating), and chemical characteristics (pH, extractable P, extractable K, and minor elements). Each of these characteristics is given a rating, from which is derived an overall soil health score. The overall score can fall into one of five ranges: very low, low, medium, high, and very high.
Of the four fields we tested this summer, three received a rating of medium, and one received a high rating. More importantly, the results allowed us to look at specific characteristics that were rated lower so that we could identify ways to improve the soil health. For example, soils from one grower’s farm showed above optimum P levels and significant surface and subsurface compaction. For these fields, lowering the annual application of animal manures, as well as appropriate use of tillage to address the compaction, should improve the soil health. Results from the other grower’s field indicated low soil biological activity, despite regular cover cropping with rye. Adding a legume cover crop or compost could increase the biological activity in these fields.
If you are a producer, you should be interested in maintaining or improving your soil health. The tools offered by the Cornell program will help in many ways. I encourage you to download the manual, read through the sections on soil health and soil management, and consider using their soil health testing service. If you need a penetrometer, contact your local Extension educator to see if one is available to borrow. The more you know about your own field soils, the better you can manage them.