Periodic soil sampling is essential to your farm’s bottom line. Conventional wisdom is to take samples every four years. Twelve samples per every 25 to 40-acre area is the sweet spot in nutrient management.

You want to sample for phosphorous, potassium, pH, nitrogen and zinc. Of course, you can test for others as well, depending on location, but those are generally the big five.

Every ten years you’ll want to do a more specific grid soil sampling. Then you’ll need samples about every 2 to 2.5 acres. Pop results into a Geographic Information System (GIS) to map nutrient availability across your fields. Voila! Informed decision-making.

Testing the soil nutrient levels in your fields guides your fertility decisions. Balanced fertility management maximizes production. With soil samples, you’ll be spending money on nutrients only where needed and in correct amounts. This is more efficient and cost effective than applying standard fertilizer everywhere.

Since you only do it once every four years, you want to get it right. But when is the best time to get the most helpful results?

The Case for Fall Soil Sampling

There are some common reasons many farmers have switched from spring soil sampling to fall. First, post-harvest offers downtime that isn’t available during the busy spring season. Also, the sooner you have your testing results, the sooner you can design your fertility program.

That leads to another consideration – pricing. Retailers often offer pre-buy deals in the fall because it’s their down season too. Whereas, in the spring you’ll pay premium prices.

Testing labs are also not as busy during the fall. Faster results mean the choice to purchase fertilizer in the fall not only for the discounts, but for tax purposes.

And finally, fall soil sampling is less likely to be hindered by unpredictable spring weather. The window from harvest to frozen ground is wider than the window from frozen ground to planting. So, it’s often easier to get samples in the fall, unless you have very hard, dry soil.

But these are all based on business management practices. Does the science support it?

Pros and Cons of Spring Soil Sampling

A University of Kentucky study found that soil nutrients fluctuate seasonally with the lowest measures during fall. Equally important, the four nutrients that are most affected by seasonal fluctuations are among the big five soil sample targets: nitrogen, phosphorus, potassium, and pH. In a nutshell, spring soil samples are more accurate than fall.

Spring soil sampling is particularly reflective of nitrogen availability for the immediate growing season. The soils have had adequate time to equilibrate since the last growing season. Also, the soil moisture in spring makes sampling more consistent.

Soils have had the chance to recover from last season’s other challenges like too much or not enough rain, harvest compaction, washouts, and field tiling events. Spring offers a better environment to collect high quality, representative soil samples.

Additionally, spring soil sampling allows for nutrients from residues to have had time to enter the soil rooting zone. This is where you take your soil samples. Therefore, tests will more accurately reflect the current nutrients available for upcoming crops.

Cons for spring sampling include the short window from ground thaw to planting. You may not get sample results in time to plan for and order fertilizers. The tendency in that case is to just skip it altogether. Or you may be tempted to collect samples from frozen ground. Also, a mistake. They’re far less accurate.

So, from a farm management perspective, fall soil sampling is better. But from an accuracy standpoint, spring is better. What to do?

The Secret to the Most Accurate and Efficient Soil Sampling

Soil sampling should be highly informative to farmers. Accurate information is useful in monitoring changes in soil fertility over time. It’s also useful for developing balanced fertility plans and on-farm nutrient efficiency. You want the most usable, informative test results from consistent, well-conducted soil samplings possible.

So what’s the secret to having it all?

The secret to taking the pressure off spring or fall soil sampling is to split the difference. Take samples in spring when they are most accurate. Rather than hustle to get samples tested, formulate a fertility plan, and hope to implement it, simply switch to fall application. This would take the pressure off trying to do it all in the spring.

You would have adequate time to get your sample results, review your data, and make your fertility plan with accuracy. You’d also have time to get exactly what you need – be it lime or specific fertilizers – exactly when you need it for a fall application.

Whatever you decide to do, make sure you’re consistent. Do it the same time of year each time to eliminate as many variables as possible.

TSGC: Your Success Partner

Tri-States Grain Conditioning (TSGC) strives to provide you with the most up-to-date information on farming and grain storage. From field prep to harvest, we’re your partner in success.

When it’s time to safely store and monitor your farm’s considerable grain assets, let us help you keep your grain healthy and free from mold and insects until you’re ready to sell. To talk to one of our grain storage advisors, call 1-800-GET-TEMP.

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