When farmers need nutrient management advice, they often turn to the Agronomic Services Division at the North Carolina Department of Agriculture and Consumer Services. Sometimes, these interactions work in reverse.

Two years ago, Bill Hering of Hering Farms in Faison called regional agronomist Tim Hall with a question about tissue test results. That call and subsequent dialogue triggered a series of field tests and, ultimately, a refined protocol for tissue sampling of leaf lettuce.

Hering, who grows a wide variety of produce, has used agronomic testing services regularly for years. In 2009, he submitted several tissue samples so he could monitor the nutrient status of leaf lettuce. The plant analysis report indicated that calcium levels were low to deficient. This news puzzled him because the crop looked healthy and he had applied sufficient calcium, in the form of gypsum, before planting. He called NCDA&CS regional Agronomist Tim Hall to get a second opinion.

After visiting Hering’s fields, Hall reviewed the agronomic reports and noted that soil pH was acceptable, no lime was required, and therefore, the crop should not need calcium. Not long afterwards, another grower contacted Hall and related a similar story. Lab results were indicating a need for calcium, but in the field, the leafy greens did not seem to have a nutrient problem.

“Both of these growers are hard-working and conscientious,” Hall said. “They have years of experience with agronomic testing services. Their concerns spurred me to look more critically at what was going on in their fields.”

Hall took the issue back to the division’s home office. Brenda Cleveland, section chief in charge of plant analysis, speculated about the unexpected results.

“Usually, the most recent mature leaf is the appropriate leaf to collect when gathering a tissue sample,” Cleveland said. “With lettuce, however, leaves are in a rosette, and it is not always easy to decide which leaf is the most recently mature one. My first thought was that the sampling procedure was incorrect or inconsistent, but I knew there were other possibilities to consider. The sufficiency values themselves had to be scrutinized.”

Cleveland and Hall contacted Hering and asked if they could systematically collect tissue samples from his crop and run some follow-up tests. He agreed. They decided to sample leaves from two different locations on the plant and compare the nutrient concentrations. Each week during the spring and fall seasons of 2010, they collected samples of recent mature leaves and more mature, outer-perimeter leaves. The two sets of tissue samples showed clear differences in their nutrient concentrations.