3 Red Flags In Your Soil Test

If these numbers are off in your soil test, it’s time to take action to improve your garden’s soil.

by Jesse Frost
PHOTO: iStock/Thinkstock

Getting a soil test is key to knowing how well your soil will function for you. If the pH is off or it there’s too much of a certain nutrient, it won’t perform like you need it to. Although soil tests generally come with recommendations on how to fix any deficiencies, it may be worth looking at alternative amendments to make sure your soil functions at the highest possible level for the longest amount of time. Like many things, if you invest in your soil, it will work well for you for many years to come. If you take shortcuts and use chemical inputs, you may have immediate results but no long-term sustainability.

Where to invest, however, is the big question. So let’s take a look at the most pressing readings from a basic soil test and identify the red flags—that is, the elements that are the most important for healthy soil.

A Note About Soil Tests

Soil tests should be gathered following the directions of the specific lab. Generally, many small samples should be taken from a plot and mixed together to get a good average of the soil in that area. This will provide the most accurate results. Also, there are many different places to get soil tests and several ways in which to test each sample in the lab. Because most beginning farmers will start with the basic tests from local extension agents, that is what this article will focus on, though with natural amendments not chemical (as is often recommend). For that reason, as you dig in, consider trying more comprehensive tests over time from private labs. These will come with more involved and comprehensive amendment recommendations.

1. pH

Few measurements indicate soil potential quite as well as pH. This is the measurement of how acid or alkaline a soil may be, and it can affect everything from disease and pests to nutrient uptake and yield. A pH measurement of 6.9 is the goal. Above that is alkaline and below is acidic. A measurement too far in either direction is a big red flag and should garner some attention.

To bring the pH up—that is, to add alkalinity—ground limestone (generally referred to as lime) is often applied. Calcitic limestone is preferred in areas already high in magnesium, which your test should indicate. Dolomitic lime is preferred in most other cases for its addition of both calcium and magnesium. In alkaline soils, sulphur or peat moss can be added to increase acidity. The amount per acre you add should be provided in your soil test results.

2. Organic Matter

Organic matter is the food of the soil, and it’s measured by percentage. Anything between 4 and 10 percent is considered good. Anything below could certainly use improvement.

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Improving your organic matter can be done in several different ways. Adding compost is one simple and effective way to add organic matter (and plant food to boot). How much you should add depends on your intentions with the soil—annual garden versus pasture versus perennial gardens—and depends on the quality of compost. For a garden, the compost should be fully broken down, so as to not tie up important nutrients. Raw manure, for instance, can harm growing plants more than help them. A pasture, on the other hand, will be more forgiving.

Another way to add organic matter is through cover cropping. A cover crop should be applied to gardens anytime there is bare soil. This will keep the soil organisms around while building organic matter above and below ground, smothering weeds in the process.

Finally, you can add straw, hay or leaves to increase organic matter, though any of these dry carbon sources should be added several months before planting, as they will tie up nitrogen during decomposition.

3. Cation Exchange (CEC)

The Cation Exchange Capacity (pronounced “cat-ion”) is the measurement of how capable your soil is to hold essential nutrients, including calcium, magnesium and potassium. Sandier soils, for instance, have a lower CEC, whereas soils with more clay tend to have a higher CEC. Although organic matter can improve your soil’s ability to retain nutrients, this particular measurement is hard to change significantly. For that reason, a soil’s CEC is better used as a management tool to determine how much of any one nutrient to add and how often. With no easy rule of thumb here, it is best to check with the testing agency for recommendations on how to navigate the CEC of your soil.

As you get to know your soil and work on improving it, you’ll sustain a healthier garden that will provide for your family and customers for years to come.

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