Jane Kuhn - Jul 17, 2017

Soil Test Basics for the Organic Farmer

Beth Burzynski takes a soil sample for testing in the research fields at the Center for Agroecology and Sustainable Food Systems.

Most farmers know that soil sampling is an imperative practice in organic farm management and soil stewardship. But sometimes it can seem like the reports are speaking a different language. Most of the labs generating reports are operating from the school of thought that caters to conventional, big scale, agriculture. But that doesn’t mean it’s useless. Here’s a few suggestions for approaching soil testing with organic practices in mind.

The typical recommendation is to conduct annual soil tests. Ideal time for taking samples is in the spring right before incorporating cover crop. This is assuming you plan to do your applications in the springtime. Comparatively, it you’re on a schedule to add amendments in the Fall, then the soil test should be conducted before you begin Fall tillage. Some folks like to amend in the Fall because the season offers more flexibility for applications in addition to the strategy of feeding your cover crops, so that your cover crops feed your plants! Darryl Wong, Research Lands Manager at the Center for Agroecology and Sustainable Food Systems recommends testing “as close to incorporation as you can get without pushing yourself up against a deadline... that’s going to be the most relevant to the cops.”

There are numerous independent and cooperative extension affiliated labs that will run soil tests. A&L is a popular choice that offers standard tests for around $15-20, however “other agricultural labs around the country will give similar recommendations” Darryl notes. Turn-around time is typically around 5-10 days depending on how busy the labs are, so results should come in soon after sending.

A lot of information is generated in the report, which can be daunting at first glance. But the soil test will come with explicit suggestions and there are some guides for breaking down what each element means for your soil. “In an organic system, the biggest thing to look at is the Organic Matter (OM), followed by ENR, which is based on the OM level” advises Darryl.

Organic Matter (OM) is the product of stable biological decomposition and an integral source of nutrients for plants. Ideal levels vary by soil type and farming practices, but typically aiming for at least 2-3% is sufficient.
Note: OM readings are only as reliable as the methodology used to collect the sample. Soil scientists recommend establishing a strict protocol for collecting soil samples, which includes defining how to clear the soil surface of leaf litter and field “trash,” as surface-level debris that ends up in a soil sample can throw-off the OM reading.

Estimate Nitrogen Release (ENR) is the estimated amount of Nitrogen that will be released throughout the season, measured in pounds per acre. First determine how many pounds a specific crop will take up (the USDA has a great tool for that here), identify what the ENR is in your soil, and also consider how much cover crop you had in the field (i.e. nitrogen contributions) to determine if supplemental nitrogen applications will be necessary and at what quantity.

The question then, is, how do the conventional interpretations and recommendations from big ag labs translate to the agroecological, organic farmer? The answer may lie in additional, complimentary assessments. “Soil testing does the big picture stuff, whereas something like nitrate strip testing provides an opportunity to look more closely” Darryl suggests. Nitrate strip testing “is a very simple tool that’s not that expensive, and takes just a little bit of time.” While previously not a common practice, nitrate strip testing is growing in popularity particularly out of necessity as awareness heightens around nitrogen pollution in nearby watersheds.

Traditional agriculture labs focus on the macronutrient profile; however, in organic farming the micronutrient profile needn’t be neglected. Darryl recommends Kinsey Ag Services if you want to have a report that evaluates micronutrients as well.

Organic farmers have to pay careful attention to soil health, which can be monitored via qualitative tests to assess traits like aggregation and compaction. In fact, Cornell has a soil health testing laboratory and has even published a manual that can be utilized as an at-home guide.

Standard annual soil tests are absolutely invaluable despite what can sometimes feel like a miscommunication between big and small ag. In order to understand your soil on a more ecological level, pay special attention to OM and ENR levels, in addition to administering additional tests. Also important, are the qualitative assessments you can make to observe soil-health indicators like detritus levels, soil smell, color, and aggregation size. Taking a multifaceted approach to soil sampling will produce a more well rounded summary that will serve you all season long.

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Jane works as a Field Production Specialist at the Center for Agroecology and Sustainable Food Systems, where her days are filled with tractor work, irrigation coordination, orchard care, and educating apprentices and interns. Her favorite way to end a long day's work in the sun, is running down the hill to Mitchell's Cove and jumping in the Pacific.


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