Clayton Garner Jr. has grown tomatoes for more than 20 years. For much of that time, blossom-end rot — a physiological disorder resulting from insufficient calcium — was a fact of life.
But today he has a finely tuned system of watering and fertilization that seems to be keeping the problem at bay and boosting yield as well.
Garner and his father were among the first in North Carolina to try growing crops on plastic to improve quality and manage resources. His goal is to provide his customers with delicious, red, ready-to-eat tomatoes.
To achieve it, he is always trying new varieties, fertility regimes, cultural practices, marketing and outreach strategies. He carefully selects the ones that work and makes them part of his routine. Even so, blossom-end rot persistently remained a problem.
“I was probably losing 10 percent of my crop each year,” Garner said. “I was looking for a solution.”
Dianne Farrer, a regional agronomist  with the North Carolina Department of Agriculture and Consumer Services, responded to Garner’s call. She visited his farm, and they talked about the problem.
“Blossom-end rot is basically a calcium deficiency, but its dynamics are somewhat complex,” Farrer said. “Even if sufficient lime has been applied and calcium is present in the soil, blossom-end rot can still occur, particularly in times of drought. A good watering regime is essential for plants to be able to take up the calcium they need.”
“Soil pH was something I had questions about,” Garner said. “My soil report said I didn’t need lime even though the pH was about 5.5 and my plants seemed to need calcium. To me, that didn’t make sense.”
As they discussed the issue, Farrer continued to emphasize the importance of steady water availability and appropriate fertilization in preventing blossom-end rot.
“Watering needs to be regulated and precise,” Farrer said. “Nutrients like nitrogen and potash should be applied in the correct amount and in a suitable form. They have an effect on calcium uptake.”
Nitrogen reduces calcium uptake
Nitrogen, especially in the ammonium form, reduces calcium uptake. When excess potassium or magnesium is present, the crop may take up these ions instead of calcium. Reduced calcium uptake due to a buildup of salts in the soil is more likely to occur with crops grown on plastic because fertilizer is applied through drip irrigation directly to a localized area.
Farrer collected leaf samples to get a snapshot of the nutrient status of Garner’s tomato crop. A few days later, the NCDA&CS Plant Analysis Report confirmed that levels of nitrogen and magnesium were high.
Even though Garner’s soil report showed levels of calcium to be adequate, Farrer advised Garner to put out a pre-plant application of gypsum (calcium sulfate) prior to his next crop to give it a boost.
“On mineral-organic soils like Garner has in his fields, gypsum works better than lime at providing needed calcium,” Farrer said. “It is quickly available and adds sulfur as well.”
Garner continued to consult regularly with Farrer while refining his strategies for watering and fertilization.
He used to water heavily, wait 10 hours and then water again. Now, he waters in smaller amounts more frequently throughout the day so moisture inputs remain steady.
Today Garner has a strategy he can use from year to year.
A pre-plant application of gypsum is routine. He broadcasts fertilizer; plants field tomatoes in plastic-covered rows; waters regularly but sparingly, until fruit are the size of dimes; and then begins to add potassium nitrate through the drip irrigation system.
During flower and fruit, he uses plant tissue analysis on a bi-weekly basis to monitor the crop’s need for boron and potassium since low levels of these nutrients can limit fruit quality and taste even when there is sufficient water and nitrogen.
Farrer said the soils in Garner’s fields have high buffering capacity and hold nutrients fairly well. “But even so, we don’t want to take the risk of something not being there when the crop needs it,” she said. “Tissue test results tell a grower whether crop nutrient needs are being met.”
Plant tissue analysis involves collecting representative plant leaves from random locations throughout a reasonably uniform field. The sample is sent to the NCDA&CS Agronomic Services laboratory, where plant-nutrient content is chemically measured. The test is so sensitive that it can detect nutrient deficiencies before plants display any visible symptoms.
For this reason, tissue analysis plays a key role in optimizing the potential yield of high-value crops such as fruits, vegetables and crops grown on plastic.
“Since I changed my approach to water and fertilizer about three years ago, my yield has at least doubled,” Garner said.
“And this year was the best ever. There was virtually no blossom-end rot. I’m confident of the recommendations I get back on my agronomic reports. With that information, I know I can grow No. 1, grade-A, marketable fruit.”
Tissue testing through the NCDA&CS lab costs $5 (in state) or $25 (out of state) per sample. A few crops require additional tests that cost an extra $2. Testing is complete within two business days, and results are posted online at www.ncagr.gov/agronomi  under the “Find Your Report (PALS)” option.