Jacko Garrett believes so strongly in the benefits of zinc that he applies a zinc seed treatment to all of the seed he sells. But he never had the scientific proof to back his opinion until recent studies by University of Arkansas Rice Extension Specialist Nathan Slaton showed the merits of zinc seed treatments.

AIt proved to me that what we felt was right over the years was correct,@ says Garrett, owner of Garrett Farms, a registered and certified seed producer in Dansbury, Texas. AI=m more of a preventative farmer. I like to try to do what I can from the very beginning to prevent problems.@

Seed treatments shine

In trials conducted in Arkansas during the 2000 season, Slaton found 1/4 to 2 pound of actual zinc applied to the seed met the plant=s requirements in soils prone to zinc deficiencies. Depending on the seed treatment product used, that equates to 8 to 16 ounces of material applied per hundredweight.

Slaton also examined three different products--a zinc starter from AgTrol, zinc sulfate and a Helena Chemical product each at four rates. They were 1/4 pound, 2 pound, 3/4 pound and 1 pound actual zinc per acre.

ABasically by rate, they all responded very similarly,@ Slaton says.

He says zinc sulfate probably is impractical as a commercial treatment because it is difficult to dissolve enough in water to obtain the desired rates.

Got zinc?

The University of Arkansas recommends zinc only if the soil pH is equal to or above 6.0, the soil is a silt or sandy loam structure and the soil test zinc is less than or equal to 7 pounds per acre, Slaton says. About 60 percent of Arkansas= rice-producing land falls into this category.

As the soil pH increases, the amount of zinc that=s available in a form that the plant can use decreases.

Zinc deficiency doesn=t appear to be a problem with heavier soils unless the field was recently leveled.

If the field only meets one or two of the three criteria, Slaton says zinc is not warranted.

AIf you have a clay silt, a pH of 7 and a soil test zinc of 5, you still aren=t going to get a recommendation,@ Slaton says. AYou have to meet all three criteria.

AWhen the farmer meets those three criteria, it will be his choice at that point whether to use a granular product, whether to apply a zinc foliar treatment or whether to use a seed treatment.@

The zinc also has to be in a water-soluble form, so it=s readily available for the plant to take up.

By law, manufacturers only need to list the guaranteed analysis on the product label. They do not need to list the water solubility.

To find out whether the zinc material you=re considering is water soluble, contact your local county agent or consult the University of Arkansas= updated rice production guidelines.

AProducts that are less than 40 to 50 percent water soluble, we don=t recommend,@ Slaton says.

Small but critical

Zinc is one of a handful of micronutrients that rice needs in very small amounts in order to reach optimum yield potential. Without adequate levels, the symptoms can be dramatic and typically appear within 72 hours of flooding. They include a portion of the leaf nearest the stem becoming light green while the leaf tip remains darker green, leaves losing turgidity and floating on the water surface, and bronzing or brown spotting on the leaf surfaces.

Cool temperatures and/or cool water can increase the severity of the symptoms.

The symptoms shouldn=t be confused with salinity problems, which usually occur before flushing or flooding under dry soil conditions.

Replace what is used

A typical rice crop of 150 bushels per acre removes about 1/4 pound of zinc per acre. But rice plants are very inefficient at taking up zinc, using only about 1 percent to 5 percent of what=s applied.

Another characteristic of zinc is it doesn=t move well in the soil and essentially stays where you put it. Based on this phenomenon, Slaton looked at zinc seed treatments as a more efficient way deliver the micronutrient, since it places the nutrient much closer to the young rice plant than granular zinc applied broadcast. A zinc seed treatment typically costs $1.50 to $2 per acre.

Commercial labs typically run one of two soil tests--the Mehlich 3 and the DTPA--and the way the results are reported differs dramatically.

Knowing which test a soil laboratory ran is crucial to determine whether you need to apply zinc to your field.

AA lot of labs have gone to the Mehlich 3 because it=s a universal extraction test,@ says University of Arkansas Rice Extension Specialist Nathan Slaton. AYou run it once and get all of the numbers at once.@

The University of Arkansas zinc recommendations are based on the Mehlich 3 test. Those call for zinc if the soil pH is equal to or above 6.0, the soil is a silt or sandy-loam structure, and the soil test zinc is less than or equal to 7 pounds per acre.

The university has developed correlations between the Mehlich 3 results and those of DTPA. If you have questions or need help interpreting a soil lab report, contact your local county agent or Extension specialist or consult the university=s updated rice production guidelines. The guidelines are available in paper format at county Extension offices or on the university=s Web site, www.aragriculture.org