handful of soil sample University of Minnesota Extension
SOIL STORY: Farmers can learn a lot by sampling their soil. Fields may need lime, phosphorus or potassium. Soil sampling in the fall provides farmers time to make those decisions before spring planting.

Why fall is the best time for soil sampling

Fall soil sampling may be the key to spring crop management decisions.

Spring or fall? It may not be the most hotly contested debate, but there seems to be farmers on both sides of the soil sampling subject.

Trying to find the right time to sample soil that will provide true data to make effective decisions for the next growing season is not an easy task. However, University of Missouri agronomy specialist Travis Harper says farmers can do more with the information found by fall soil sampling.

"Not only are weather conditions typically more favorable as compared to the spring season," he says, "but you will then have the winter months to think about upcoming management decisions based on the soil analysis."

Harper shared his thoughts on soil sampling in the Ag in Focus newsletter. Here are his five reasons why fall is better than spring, or any other season, for soil sampling.

1. Ideal conditions for accurate samples. Most soil sample reports are inaccurate. They are not representative of the area being sampled, primarily because not enough cores were taken. The University of Missouri Extension recommends a minimum of 15 to 20 cores from the area being sampled. An adequate number of cores is usually not collected in the summer, because the ground is hard and it’s hot outside. An adequate number of cores may not be collected in the spring, because the ground may be overly wet and collecting a quality core may be difficult. Fall provides pleasant working conditions as well as soil that is not too dry or wet.

2. Lime can be applied in a timely manner. On most ground in Missouri, occasional liming is necessary to maintain an adequate pH for crops. After lime is applied, it can take up to six months for the lime to raise the pH of the soil to the required level. Applying lime in the fall will ensure that the pH is correct in time for a spring-planted crop.

3. Fertilizer can be purchased prior to the end of the year. Fertilizer is often cheaper in the fall or the winter than it is in the spring, when demand is greatest. If you sample in the fall, you will know exactly what you need, and you can buy it when prices are lowest. Buying fertilizer needed for next year prior to the end of this year could potentially provide some tax advantages. Check with your tax professional.

4. Soil testing laboratories aren’t as busy. The majority of farmers, gardeners and homeowners test their soil in the spring. Soil testing labs are swamped this time of year, and it can take several weeks to get results. This is often too late to apply fertilizer in a timely fashion. Turnaround time in the fall is much faster.

5. Ideal time for phosphorus and potassium or manure applications. Phosphorus and potassium applied in the form of commercial fertilizer, and nearly all nutrients applied in manure form, are not immediately available to the plant. It takes time for these nutrients to become available for a plant to use. So if you apply these products in the spring, they may not necessarily be available for that year’s crop. If you apply in the fall, they will be of benefit to the next year’s crop. And to know how much to apply, you need a soil test.


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