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Agricultural Review

Farmers, consider options when soil sampling

North Carolina farmers send more than 200,000 samples to the state's soil testing lab from mid-October through February.

Eager to plan for the next season, they often find themselves at a standstill waiting for test results. The situation is unfortunate because soil tests don't have to be done every year or, for that matter, in the fall.

"Soil testing is one of the best tools available to farmers, and we want to help them use it to their best advantage," said Agriculture Commissioner Steve Troxler. "That's why the N.C. Department of Agriculture and Consumer Services has a statewide network of agronomists to give advice on optimal use of the service. Better-informed growers often discover that they have more flexibility in sampling and nutrient application."

Agronomist Dianne Farrer recently shared a few general soil sampling rules.

"First of all, soil sampling is not necessary every year, even where GPS is used," Farrer said. "Only fields subject to nutrient- or waste-management regulation must be sampled annually, which are usually fields where animal waste is applied.

"In typical cropping situations, sandy soils should be tested at least once every two years and clay soils every three to four years," she said. "If growers change crops or are concerned about leaching, they often sample more frequently, but it is not always necessary. There is an alternate approach."

Farrer illustrates her point this way: Suppose a grower has clay soils and a soil report that is a year or two old. He doesn't really need to sample again for another year, but would like to get recommendations for a different crop. Instead of sampling again, he can find his most recent soil report on the Agronomic Services Division's website and use the new "change crops" feature to generate a revised set of recommendations.

Warren Hardy of Seven Springs grows corn, soybeans and wheat. For several years now, he has sampled in spring instead of fall. He stumbled on the idea by accident one year when crop harvests for his area were unusually late. Because the man who normally samples for him was busy with other fields, Hardy didn't receive a soil report until May. Several months later, he put out his fall lime application using the recommendations from the spring report.

"I had GPS and soil sample data," Hardy said. "I used the previous year's yield map and the soil sample information from the spring. It worked for me. Since then, I've continued to find it more convenient to sample in spring."

Spring sampling can be effective for conscientious farmers, Farrer said, because it gives them extra time to look at data and compare prices for lime and fertilizer. "They can be ready to buy when the market is most favorable," she said. "On top of that, if they can move away from annual sampling, then they save additional time and money."

Hardy confers with Farrer if he has concerns about using fertilizer recommendations from an existing report. Soil phosphorus levels don't change very rapidly, and nitrogen recommendations are based on the crop to be grown, not on soil test measurements. Potassium levels, on the other hand, can be significantly depleted by crop uptake or leaching.

In cases of extreme or unusual weather, such as severe drought or periods of excessive rain that promote leaching, growers are advised to consult with a regional agronomist or other agricultural adviser about revising existing lime and fertilizer recommendations. If the crop is the same and weather is typical, then recommendations on NCDA&CS soil reports are generally reliable for two years.

As harvest approaches, growers across the state will automatically begin the process of soil sampling for next season. Those who use GPS technology annually are encouraged to sample judiciously, using the service primarily for preliminary identification of problem areas and establishment of baseline information on field variability. Growers who do not use GPS are advised to concentrate on fields most vulnerable to changes in fertility, for instance those with sandy soils.

In either case, it is beneficial to submit samples as early as possible. Sturdy shipping containers that can hold up to 36 soil sample boxes are available free of charge from the Agronomic Services Division. Its website also provides a bar-code tracking feature. When bar-coded packages arrive at the lab, senders receive email notification of successful delivery.

For some growers with recent soil reports, fall sampling may not be necessary. Soil information already on hand can be used to make management decisions as long as relevant site-specific factors are considered. Consultants can offer guidance on the development of nutrient-management strategies to optimize profitability and protect natural resources.

To find contacts for NCDA&CS regional agronomists, go to or call J. Kent Messick, Field Services Section chief, at 919-733-2655.


NCDA&CS Public Affairs Division, Andrea Ashby, Director
Mailing Address:1001 Mail Service Center, Raleigh NC 27699-1001
Physical Address: 2 West Edenton Street, Raleigh NC 27601
Phone: (919) 707-3001; FAX: (919) 733-5047

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