In many cases, the best investment for a grower is his soil. Soil that’s properly maintained for nutrients and fertility depending upon the crops to be grown can make the difference between a decent crop and an exceptional one, or even a disastrous one.
No matter how good the grower, no one can tell whether their soil meets the standards or what amendments it may need by simply looking at it. Observing what grows well where can certainly offer some insight into the health of the soil underfoot, but only through a soil test can a grower truly know how to build his soil as needed. Without the information provided by a test, a grower runs the risk of spending time and money applying fertilizers that may not be needed and could even harm future crops and the environment.
This invaluable tool is relatively inexpensive. Most land-grant universities and extension programs offer lab testing services, and there are many commercial labs as well. State departments of agriculture often make lists of certified labs available to growers. Most labs have good online descriptions of the services they offer, and detailed instructions for how to collect and send in samples.
Instructions will vary based upon management practices and what the soil is being tested for. Usually the grower will take eight to 10 samples from a specific depth from different areas of the land being tested and mix them together to submit. As soil types can vary widely within small areas, and nutrient levels can also fluctuate depending upon previous crops and management practices, individual tests should be conducted for each plot.
Ideally, samples should be taken in the fall to provide enough time before planting to develop and implement a nutrient management plan based on the results. Avoid fertilizing or adding other amendments before taking the samples. Try to take samples when the soil is relatively dry, and use clean implements to avoid contamination.
The traditional soil tests look for acidity and nitrogen, phosphorous and potassium (NPK) levels. Acidity plays a role in determining how well a plant will be able to access the nutrients in the soil. Nitrogen is responsible for growth, but too much can result in plants with lots of leaves but no flowers or fruit. Phosphorous grows and strengthens roots, buds and flowers. Potassium levels determine a plant’s overall vigor.
But soil tests can reveal much more about what’s present or lacking in a growing plot. Depending on the laboratory, levels of a range of extractable nutrients, including critical ones like calcium and magnesium, as well as potentially toxic elements such as lead, can be tested for. Many labs will even return nutrient management recommendations – quantities of fertilizer, lime to raise acidity or sulfur to lower it, and other amendments that should be added to the soil – based upon information provided about the types of crops intended for the plot.
Testing for the level of organic matter in the soil is also important, as this determines water holding capacity, water and air infiltration rate, and how well the crops will be able to use different types of applications of amendments. Many labs can also test for microbial activity, fungi and bacteria that can also affect nutrient levels and the ability of plants to access them.
Soil testing should be done regularly, at least every two years, to establish a baseline and see how each year’s fertility treatments and crop growth change the nutrient levels available to plants. The next challenge is what to do with the soil test results. We’ll cover that in next month’s column.
We want this column to be useful to our readers, and encourage you to submit questions about specific crops, management issues, or other growing-related topics. We’ll include your question in a future issue. Send questions to firstname.lastname@example.org.
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