Eight years ago when Jane Iseley began growing organic tobacco, there were no established guidelines for fertilization. Her first attempt was, to a large extent, guesswork.

“I started out following the rule of thumb that only 45 percent of the nitrogen present in an organic fertilizer would be available,” said Iseley. “I applied 80 units of nitrogen and that proved to be too much.

North Carolina Department of Agriculture Regional Agronomist Robin Watson made a visit to Iseley’s farm and walked through the fields with her. He explained the various factors that could affect the availability of the fertilizer — formulation, soil type and weather conditions.

He showed her how to collect leaf tissue samples, submit them for analysis, access her reports online, download the results and use them to adjust fertilizer application more precisely.

“I pointed out that the 45 percent rule is not hard and fast,” said Watson. “Actual nutrient availability is affected by many factors, such as weather and soil type. Red clay has finer particles and holds water better than some soils. By holding water, it also holds nitrogen better. The only way to get a really good handle on crop nutrient use is through tissue analysis.”

“For the most part, tissue testing is an underused tool,” Watson went on. “It is potentially useful for any crop, but for high-value crops, it really is indispensable. And in the case of organic tobacco, it has two important uses. It enables a grower not only to fertilize more precisely, but also to time harvest more precisely.”

“Watson’s advice made all the difference in the world,” said Iseley.

“Organic fertilizers cost about three times as much as conventional fertilizers. By using tissue analysis to adjust fertilization rates, I was able to save money by using less fertilizer. By using it to decide when to harvest, I was able to produce quality leaf as well. Without it, I would have primed a week earlier. Tissue analysis is a wonderful tool.”

Tissue samples to predict optimum harvest should be collected and submitted every two weeks throughout the harvest period. Laboratory analysis requires about two working days. At a cost of $5 per sample ($25 per out-of-state sample), tissue analysis is an economical investment.

Although best known for its soil testing services, the Agronomic Division of the North Carolina Department of Agriculture also checks plant tissue, composted materials, animal wastes, industrial and municipal wastes, fertilizer solutions and source water for nutrient content and other chemical properties relevant to agricultural production.

To support these testing services, it has a staff of 13 regional agronomists.