The Value of Soil Sampling

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Tests provide useful information on whether nutrient applications are economically worthwhile

Soil fertility is one of the most important factors in soybean productivity, yet many farmers have only a general idea of their soil-nutrient needs. Not fully understanding what the soil holds can be costly due to lost production or unnecessary fertilizer applications.

Experts advise taking the guesswork out of soil fertility by doing regular and thorough soil sampling. There’s no time better than just after harvest.

“Soil sampling should be considered an integral part of every management plan since it impacts the way farmers will implement every other action on their crops,” says Bobby Golden, Ph.D., assistant professor of plant and soil sciences at Mississippi State University.

Samples are typically used to test for phosphorus, potassium and pH levels, plus minor nutrients, organic matter and cation-exchange capacity.

What Lies Beneath

Bernie Paulson, of McPherson Crop Management in Janesville, Minnesota, works with farmers to find out what’s in their soil. At a cost of just a few dollars an acre, Paulson says soil testing is a good investment to help make decisions about applying nutrients that can cost as much as $90 per acre.

“Precise fertilizer recommendations are formulated to provide a return for farmers while minimizing environmental exposure through unneeded nutrients,” Paulson says.

To maximize nutrient value and minimize environmental impact, Paulson follows the four R’s of fertilizer application; the right nutrient in the right place, the right rate and at the right time. He also makes use of university recommendations to ensure application rates are based on economics and environmental impact.

Tighter Crop Budgets

While sampling is always valuable, Paulson believes farmers should be especially aggressive in performing this task during times of low commodity prices so they can proceed confidently with their nutrient-management plans.

“We haven’t seen a drop in input prices, so first importance is understanding the economics of fertilizer applications,” Paulson adds. “Are there enough nutrients in the soil that farmers can forego putting some on, or do they know what they need to apply? With testing, at least they’ll know if they can reduce some of their input costs.”

“Soil sampling doesn’t always mean that farmers should expect to have to build up a lot of nutrients in the soil,” adds Golden. “Sometimes it can just mean a small addition or no addition at all, as long as you’re maintaining natural levels.”

Soil sampling can also reveal the presence of pests, like soybean cyst nematode (SCN). That information can help farmers make seed-variety selections based on SCN-resistance needs.

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While soil sampling is always important, crop consultant Bernie Paulson says it’s even more necessary when commodity prices are low so farmers know the value that their nutrient applications have.

No Time Like the Present

Soil samples taken more than a few years ago will have limited value for fertilizing next year’s crop, especially if yields have consistently increased or decreased by even a few bushels since the last time you sampled. Increased yields require and use more nutrients; decreased yields require less. Experts recommend sampling every three or four years. Be sure to compare this year’s soil samples to ones taken previously to track your nutrient levels over time.

“When times were good, a lot of farmers built up their soil nutrients,” Paulson says. “Now we’re looking at ways to control the budget and get our cost of production as low as possible. If we’re using old data, we lack the confidence in knowing what the soil really needs.”

Regular soil testing can help farmers better understand soil-nutrient availability, increase crop productivity and become even better stewards of the land.