Agronomists say base test on soil type

Over the past two years, corn growers in eastern North Carolina have noticed fertility problems on sandy soils. Agronomists are at a loss to pin-point one specific reason. A common factor is that growth concerns tend to show up on lighter, sandier soils rather than on heavier soils.

Growers can limit the effects of fertility problems on sandy soils by testing and applying nutrients according to soil type, says Bob Edwards, regional agronomist with the North Carolina Department of Agriculture and Consumer Services.

Growth problems often occur on sandy soils for several reasons. Fertility certainly changes more readily in sandy soils, especially when there is excessive rain. Besides fertility, pre-emergence herbicide stress may also be involved. Nematodes such as stubby root and others may also be a factor and hardpans that limit root development can also form on some of these soils under no-till conditions.

In 2003, cool weather early in the growing season stunted growth of crops on lighter-textured soils. This year, excessive rain had the same effect.

“If we have stress early in the season about the time corn’s germinating and beginning to grow — whether it be a lot of rain or cold weather — then corn on this lighter-textured soil doesn’t recover,” Edwards says. Tests generally show a low pH with marginal calcium and low magnesium. “This is happening to growers who are on top of their management.”

Luby Measley, who manages Parrott Farms in Kinston, N.C., has seen the problem in sandy fields.

“The last two years we’ve had problems with either cold weather or rain,” Measley says. “This year, we had two heavy rains as the corn was trying to come up. I had to replant some of the corn acres.”

Measley came back and applied sulfate of potash magnesia to help correct the problem. That particular field had average yields of 92 bushels per acre, although judging from the stalk size the fertility concerns for the next season are justified. As is his annual practice, Measley will do a soil test.

“I suggest to growers to take their soils samples by soil type,” Edwards says.

David Hardy, chief of the soil testing section at the North Carolina Department of Agriculture and Consumer Services, agrees.

“Growers know their soils better than anybody else,” Hardy says. “Because fertility on sandy soils can change significantly from year to year, growers need to be concentrating on management units whether it is by intensive grid sampling or by splitting up the fields based on soil types.”

The Parrott Farm used GPS to soil test and apply nutrients about four years ago, Measley says. They won’t use GPS every year, but will soil test each fall.

Corn and soybean production on the farm is no-till. Edwards points out that soil samples on no-till land need to be taken at four inches, instead of eight inches. “When you till, you mix the lime deeper and so you take the sample at eight inches,” Edwards says. “If you take the sample down to eight inches with no-till, you will be over-applying lime and could tie up micronutrients.” Edwards also recommends early sampling so that lime can be applied well in advance of the crop being planted. He also says this is more important in no-till than conventional-tillage systems.

“Since lime does not readily move into the soil with water, with chronic soil pH problems, it is more beneficial to incorporate lime to better manage fertility,” Hardy says.

Hardy says lime is still one of the best investments growers can make. Since magnesium is subject to leaching on sandy soils, dolomitic lime that contains calcium and magnesium is usually encouraged.

“The number one fertility problem we see year in and year out is low soil pH,” Hardy says. “This growing season, about 40 percent of the samples where in-season growth concerns with corn were found had soil pHs below 5.5.”

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