North Dakota farmers who used nitrogen fertilizer this year can expect to find higher than normal levels of soil nitrate in their fields after harvest, according to Jay Goos, soil scientist at North Dakota State University.

Drought stress reduces plant growth, and thus its demand for nitrogen, so much of the anhydrous ammonia or urea fertilizer used by farmers last fall or spring is still in the soil as nitrate, he explains.

In research he conducted this year, Goos looked at fields of wheat and barley that were fertilized with 67 or 135 pounds of nitrogen per acre or received no nitrogen fertilizer.

"At four sites, we had very poor yields, with wheat yields ranging from 0 to 15 bushels per acre, and barley yields around 20 bushels per acre. The nitrate-nitrogen remaining in the soil at these four sites after harvest averaged 40 pounds per acre when no nitrogen was applied, and 140 pounds per acre when 135 pounds of fertilizer was applied," says Goos.

In other words, he says, about three-fourths of the nitrogen fertilizer applied is still in the soil and will be available for the next crop.

It is still important for growers to soil-test this fall to find out how much nitrogen is actually in their soil, Goos says, but many farmers will find out that they need to apply very little fertilizer for their next crop.

Sampling the soil of drought-affected fields will require some special precautions, according to Goos. "Our data show that virtually all of the nitrate left over from fertilization is in the top six inches of soil. Soil samplers must be careful not to contaminate deeper soil samples with topsoil. Also, samplers may want to take more samples per field than normal, because plant growth was often quite variable across a field, and because there was little rainfall to allow diffusion of nitrogen away from fertilizer application bands," he explains.