Zinc is an essential nutrient for plant growth, involved in protein synthesis and necessary for growth regulation and enzyme systems. Plants absorb zinc as inorganic cations, which are held on exchange sites on clay and organic matter.

Zinc plays a vital role in a plant's ability to use nitrogen and transform it into yield and protein. As was the case in the North Carolina field, zinc deficiency prevented the grain sorghum from properly utilizing the available nitrogen, which can often influence growers to add more nitrogen to a yellowing crop.

Zinc deficiency is not unusual in other crops, particularly in corn. However, for most row crop growers in the Upper Southeast, grain sorghum is essentially a new crop.

The information available on grain sorghum production will take a few years to catch up with the huge increase in acreage. For example, in North Carolina, in 2011 there was only about 15,000 acres of grain sorghum harvested. This year 100,000 acres or more is possible.

Detecting Zinc deficiency is not always easy, even with soil testing. While levels of zinc in the soil may be adequate for corn or other fast growing crops, it is important to remember that grain sorghum, especially in the early going, is a notoriously slow growing crop.

For growers using poultry litter, and to a lesser degree cow or hog manure as a fertilizer source, zinc deficiency is likely to be less of a problem, regardless of the crop grown.

For example, North Carolina grower Travis Starnes hit 90 bushels of soybeans per acre last year using turkey litter as his source of fertilizer.

Zinc can be banded as a starter or broadcast and incorporated with equal response.

Banded zinc rates can be lower than broadcast rates because of greater efficiency. However, residual zinc levels

will be lower from banded than broadcast applications.

Several sources of zinc fertilizer are available. Zinc sulfate and liquid zinc products are the most common sources.