With that in mind, now is the time to assess whether cotton fertility is sufficient. The department recommends that tissue samples be collected the first week of bloom and at least once again during the third or fourth week.

Research has shown that petiole nitrate nitrogen is the best indicator of the nitrogen requirement of a maturing cotton crop. This analysis is also a reliable way to check a cotton crop’s need for potassium.

NCDA&CS regional agronomist Wayne Nixon is a strong advocate of the use of tissue testing to monitor the nutrient needs of cotton.

“Appropriate fertilization is essential if you want to make good cotton,” Nixon said.

“Providing optimal amounts of potassium during the first four weeks of bloom helps ensure proper fiber length. During the last four weeks of bloom, it promotes fiber thickness, or micronaire. After heavy rains, when potassium may have been washed out of the root zone, tissue analysis helps growers monitor nutrient levels and ensure that they stay sufficient.”

Boron and sulfur are two other nutrients important to cotton production. Low boron can limit boll set, and optimal sulfur is essential for good fiber quality and yield.

Nixon said soils in his region — northeastern North Carolina — frequently have low sulfur.

“I encourage the application of at least one pound of sulfur for every 10 pounds of nitrogen when the soil test sulfur index is below 40, and even this rate may be insufficient on very sandy soils,” he said.

“Tissue test results, however, will take out the guesswork and give an accurate indication of what is needed.”

The window of opportunity to collect and submit tissue samples, get results and adjust fertilization is narrow, so growers are advised to act now.

Details of the recommended cotton tissue sampling protocol for 2011 are available online at www.ncagr.gov/agronomi/uyrplant.htm (select the “Using Tissue Analysis to Monitor Cotton Nutrition” link).

Once samples arrive at the lab, testing is completed within two business days. Reports are then posted on the Agronomic Services Division website.