The Enid News and Eagle, Enid, OK

July 27, 2013

What’s right amount of chloride in soil?

By Roger Don Gribble, Extended Forecast
Enid News and Eagle

ENID, Okla. — There has been some interest in looking closer at chloride fertilizers as a result of some leaf spotting on the wheat variety Duster.

There is some talk about the spotting being associated with lack of chloride in our wheat soil fertility programs. Oklahoma State University has been looking closely at this discussion and would offer a few thoughts about what might be happening.

As OSU soil fertility specialists work through some of the observations, they offer some findings. The first would come from a soil test. When a soil test for chloride is low, a plant response is likely, but the response is not consistent. The second finding would be if you think there is a chloride deficiency in a field, it is imperative you test the subsoil to make an accurate assessment of availability. A third finding is there will be no particular chloride fertilizer source any better than others when compared on a pound by pound basis.

And, a final discussion is there appears to be varieties more susceptible to a chloride deficiency than other when a soil test identifies a low chloride reading.

First of all, what would be a low soil test for chloride in Oklahoma? For Oklahoma, we ask producers to sample to a depth of 18 inches. The optimum soil test level would a chloride level of 35 pounds per acre or above. At that level, a producer should have enough chloride to reach the yield goal he has selected and fertilized for. If a producer is unable to get to the depth of 18 inches, we say if you use a 6-inch soil sample, we take that number and multiply by three and compare that to the 35 pounds to determine whether additional chloride is needed.

We are truly blessed in Oklahoma to have soils that have adequate chloride levels. In 2000, Hailin Zhang, OCES soil fertility specialist, conducted a small survey and analyzed 200 samples, 0-24 inches for nitrate, sulfate and chloride. Of the 200 samples, 68 percent had more than 60 pounds of chloride and 32 percent fell between 30 to 60 pounds of chloride available for plant uptake. There were no samples below 30 pounds per acre.

Brian Arnall, OCES precision nutrient management specialist, in a 24-sample series he worked with, found the average level for chloride to be 96 pounds per acre in the 0 to 18-inch samples. However, Arnall did find one site that measured 21 pounds per acre in a 0 to 18-inch sample. This indicates the importance of knowing where you stand on chloride by soil sampling.

If needed, the most common chloride fertilizer would be potassium chloride, 0-0-60. Often times, chloride deficiency and potassium deficiency are found together. In this case, an application of potassium chloride solves both problems.

Literature mentions there is a varietal difference in chloride response. Jagger, a Kansas State University release often was mentioned as a susceptible variety in that research. There is growing work suggesting the OSU variety Duster may have similar susceptible symptoms.

In summary, chloride fertility should be monitored and addressed if recommended by a soil test. There could be a likelihood wheat may respond to an application of 10 to 20 pounds of chloride per acre in a deep, well-drained sandy soil that has not been fertilized with potash over time. Your OCES ag educator can help you with a soil test and provide you with equipment to reach the 18-inch depth needed to know what your chloride levels are in your soil.

Gribble is Oklahoma Cooperative Extension Service northwest area agronomist.