The nutrients that run through the leaf and petiole of cotton offer a glimpse into how the plant is doing. Therefore, analysis of the leaf and petiole is the best approach to optimize cotton yields, says an agronomist with the North Carolina Department of Agriculture.
Speaking at the recent Southeast Cotton Conference in Rocky Mount, N.C., Bobby Walls, the chief of the NCDA Plant/Waste/Solution Section, said leaf and petiole analysis is a snapshot of the nutrients in the plant tissue at a particular time during the growing season.
Walls says there are three approaches farmers can take with nutrient management: Trial and error; a little more, just in case it rains; or leaf and petiole analysis. The thought with trial and error is, “if one pound is good, two pounds is better. The thought with a little more is, “I'll add a little more just in case it rains.”
The first two are hit and miss. The last one is the “best approach you can use.
“A lot of emphasis today is placed on nutrient management,” Walls says. “I think it's because of inputs costs, but also the impact that regulations have on nutrient management. It involves nutrient management.”
By taking leaf and petiole samples during the season, farmers can measure the exact amount of nutrients that the plant is taking up. “Your soil may contain the right amount of nutrients, but is the plant taking it up?” Walls asked participants at the Southeast Farm Press-sponsored conference.
“An in-season leaf and petiole analysis will let you know what the plant is able to take up and it will verify if the plant has received an adequate supply of those essential nutrients,” Walls says. “We know that healthy plants contain a predictable concentration of essential nutrients, which serve as a guide.”
North Carolina producers can benefit from the service offered through the NCDA. The service costs $4.
Farmers can send in leaf and petiole samples for analysis to the state lab in Raleigh, Walls says.
Petiole samples are best sampled at intervals beginning the first week before bloom until seven or eight weeks after bloom. Two or three weeks of sampling is necessary in order to give you a baseline that's meaningful.
Petioles give the best indicator of nitrogen in the plant. Nitrate nitrogen in the petiole is correlated with yield, especially early in the season. Petiole analysis reveals if nitrogen is low or excessive. For example, a nitrate level more than 10,000 parts per million (ppm) or below 5,000 ppm can both have a negative impact on yield if not corrected.
Leaf samples are the most accurate way to evaluate major elements, secondary elements and micronutrients. Leaf samples should be taken from the uppermost, mature cotton blade on the stem, which is usually the third to fifth leaf from the terminal. The leaf sample should be taken one week before to one week after bloom.
Walls points out that producers can take two approaches to leaf and petiole analysis, either predictive or diagnostic.
Predictive will help you catch nutrient shortages before they happen. Diagnostic will help you clear up problems as they occur in the field.
“With the predictive approach, you're taking a proactive approach to tissue sampling,” Walls says. “You're sampling before you see the off-coloring in the plant. This approach allows you to refine any imbalances that might occur. It also allows you to get a good assessment on yield potential.”
For diagnostic analysis, you've already seen the “off-color” plants in the field and “you really want to know what's causing it.”
Analysis can verify the nutrient deficiency or identify toxicity or excessive accumulation of nutrients that might be affecting yields. “A leaf and petiole analysis will help you pinpoint any of your production problems related to plant nutrition,” Walls says.
When problem solving, take samples from both good and bad areas, as well as areas where there are different soil types. When monitoring the status of healthy plants, take samples from a uniform area in regard to soils. Take at least 15 to 20 leaves per sample.
The NCDA lab analyzes samples within two days of their arrival. The analysis is mailed to the grower, as well as posted on the Internet at http://agronomy.agri.state.nc.us/
A cover sheet explaining the technical terms and index values accompanies the report and is also available at http://www.ncagr.com/agronomi/pwshome.htm/
The Plant/Waste/Solution Section of the NCDA Agronomy Division is located at 4300 Reedy Creek Road, Raleigh, N.C. 276007. Phone: 919-733-2655.