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Before you cut inputs, sample soil

A wet fall and spring, high fuel costs and recent good yields (prior to harvest) could have an impact on soil fertility this coming season, according to the experts.

They suggest that growers who don't have a representative soil sample, get one as soon as possible to make sure that fertility is not a limiting factor for yields this season.

“We've had a wet harvest season, and it continues to be wet,” said Cliff Snyder, southeast director, Potash and Phosphate Institute, Conway, Ark. “People are going to be spraying and getting ready to plant and may not have had a soil sample. I'm concerned that some may be operating from a three-year-old or older soil test.”

Snyder recommends that growers take advantage of the first opportunity they have to get a soil sample. “They need to act quickly because the labs are going to be swamped when the weather breaks.”

Snyder noted that wet soils can have a number of detrimental effects on fertility — including reducing the formation of beneficial fungi on roots. The fungus-root association enhances phosphorus and micronutrient absorption from the soil. Flooding or wet soils also slow the release of phosphorus from organic matter.

Another important key is to sample areas of fields that appear to be in need of specific management attention, according to Snyder. “We have a lot of people doing site-specific management or intensive grid sampling. But I'm a believer in soil management zone concepts — identify certain areas of a field that are different, try to manage them accordingly.”

In addition, “take stock of what past crop yields were and what nutrients they removed,” Snyder said. “Many Extension people, fertilizer dealers and crop consultants have some guidance on how to determine nutrient removal per bushel. Look at that to make sure that you're at least putting back what you harvest.”

Lanny Ashlock, an agronomist with Cullum Seeds and former University of Arkansas Extension soybean specialist, is concerned that higher fuel costs will push growers to cut back on fertility, especially nitrogen.

Ashlock urges growers to “find a way to soil sample. If you can't, I'd look at my most recent soil test if it's within the last two or three years. They need to sample before they start cutting inputs.

“We did a lot of plant tissue analysis last year,” Ashlock said. “The soil test said fertility was low, the plant was calling back saying we were cutting it short.”

Soil sampling is even more critical in light of increasing no-till acreage, according to Snyder. “We can get an acid layer forming right in the upper couple of inches of soil. If growers put phosphorus out this fall and the fall is very acidic, it will be tied up and less available to the plant.

“I advocate, when possible, putting some phosphorus beneath the soil surface or putting a higher rate on top to help overcome that tie up that can occur.”

As the season progresses, if growers see problems in developing plants, “one of the first things they need to do is get a plant tissue sample,” Snyder said. “There may be some time to benefit from a sidedress or a knife application of any deficient nutrients. The key is to identify that early in the vegetative growth period.”

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