Sorting through some of the differences between soil health tests can be challenging. Penn State offers a Soil Quality Assessment Worksheet that may be beneficial.
It is very encouraging that soil health is receiving a lot of attention lately from many different quarters, such as innovating farmers, crop consultants, USDA-NRCS, the agricultural industry, conservation community, water quality experts, and Cooperative Extension. It was a concept that was ignored for too long and we realize that soil biology needs to be integrated into our agronomic tool kit. However, we are still struggling to find the best information to use. Evaluation tools of soil health are still in their infancy and we are still trying to sort out which ones are the most suited and cost effective.
Laboratories are developing tests and are already offering them. Some tests we have evaluated are the Soil Nutrient and Health Tool (Woods End Lab), Phospholipid Fatty Acid Analysis (Ward Lab), Food Web Analysis (Soil Foodweb Inc), and the Cornell Soil Health Test (Cornell University). All these labs ask for is just a sample taken similar to what you would take for a soil fertility test. The only exception is the Cornell test which also asks you to take penetration resistance measurements with a penetrometer (soil compaction tester) in the field. This makes the tests convenient for the farmer.
The Soil Nutrient and Health Tool gives you Solvita CO2 burst, water extractable nitrogen and carbon, nitrate-N, Soil Labile Amino Nitrogen, mineralized carbon, aggregate stability, P-saturation and Calcium saturation. The Phospholipid Fatty Acid Analysis is a chemical footprint of the microbial cell membranes which gives a measure of microbial biomass and community composition. Food web analysis is an analysis of bacteria, fungi, protozoa, nematodes and mycorrhizae (obtained by looking at samples under a microscope). The Cornell Soil Health Test gives aggregate stability, available water capacity, surface and subsurface hardness, organic matter, active carbon, potentially mineralizable carbon, root health rating, pH, extractable P, K and minor elements. It will be clear that the tests evaluate different things and therefore give different results.
The costs of the tests were $49.50 for the Soil Nutrient and Health Tool, $39.50 for the PFLA test, $144 for the Soil Food Web Analysis, and $45 for the basic Cornell test (in 2013, prices may have changed since then). We found that the Soil Nutrient and Health Tool and the Cornell Test were able to pick up major soil health differences (like a visually very degraded, continuously moldboard plowed field with very limited organic matter inputs compared with a field next to it that had been in continuous no-tillage with a diverse crop rotation and regular cover crop use). The PFLA and Soil Food Web didn’t show clear differences between these. However, even the Soil Nutrient and Health Tool and Cornell Test did not show clear differences between fields that had more subtle management differences that should have resulted in soil health differences (such as corn-soybean rotation with chemical fertilizer and no cover crops versus alfalfa/canola/rye/soybean rotation with manure inputs or a 30+ year continuous no-tillage versus chisel/disked field).
We recently took more samples from contrasting fields from grazing farms that we had analyzed with the Soil Nutrient and Health Tool but had difficulty finding clear differences based on the test results. Therefore, we went back this spring to taking an infiltration ring and a shovel to do a qualitative evaluation of some fields. In one field, one inch infiltrated in 10-22 seconds, while in another field an inch had not infiltrated after 55 minutes! We dug up some soil and observed large differences in soil structure and color. The field with extremely high infiltration capacity had been in perennial warm season grass for over one year. Its structure was extremely mellow and one could see the dark color. Another field where an inch of water infiltrated in about 2 minutes had been severely compacted last spring but its structure had been restored significantly by the use of a multi-species cover crop of hairy vetch, alsike, red and yellow clover, and annual ryegrass. The field with the lowest infiltration showed greyness and orange mottles near the surface while the subsurface was bright orange. It had a weak cover of crimson, alsike and yellow clover. We saw that an area in the same field where perennial ryegrass had been planted a year ago showed significant improvement with higher infiltration and better soil structure. These results provided us with food for thought about practices that could help improve soil health on this farm. The moral of the story is to keep the pulse on new information on soil health tests, but in the meantime, use a qualitative assessment which is free of charge. A resource that is available from Penn State Extension to help you with this is the Soil Quality Assessment Worksheet. Another good piece of information to have is the organic matter content which you can get with your regular soil fertility analysis (Penn State Ag Analytical Lab offers it for $5, just check the box on the sheet that goes with the sample).
By performing a qualitative soil health evaluation every year and organic matter content every three years or so you have valuable information to assess whether your practices are helping to improve your soil.