Archived Issues

Fertilization—tightening the belts

Saving money and maximizing profit means being diligent about what to use and where to use it

By David Williams

The demand for nitrogen as a fertilizer is being recognized in agricultural markets across the globe. In African nations and in other tobacco markets, the need for fertilizer has ballooned fertilization prices, not only for nitrogen but also for potash, which should benefit Canadian mineral markets, where potash is plentiful.
Costs are up for fertilizer in the United States, as its production is linked to petroleum. Prices spiked sharply in 2006, and while those kinds of increases may not happen again, it is a good indicator that prices could sustain an upward push for the foreseeable future. But in pricing fertilizers, many basic economic principles are at work as well.
“The price is largely influenced by the basic law of supply and demand,” said Dr. Bill Easterwood of YARA North America, a supplier of both dry and liquid forms of nitrogen for agriculture. “The way it’s going right now, you have freight cost increases, the rising cost of oil, the increasing demand for nitrogen from China and India and the devaluation of the dollar. Many developing countries are demanding better diets so feed grain for animals is at a premium. Also, grain reserves are at an all-time low, and that’s a major concern.”
So it is more important than ever for flue-cured growers to check and re-check how efficiently fertilizer is being used and how much it affects the bottom line—the price of the leaf at market.
“You have got to look at trends that currently exist,” Easterwood said. “We have got to get the product to our customers, even though costs are going up. Growers have to look at their return on their investment for crops they are currently growing.”
The following suggested practices were recommended by Gerald F. Peedin, tobacco crop science specialist and contributor to the Web site for Carolina Tobacco Services.

Start with a test
Good agricultural practices indicate testing soils before transplant to determine what enrichments are required, if any. Most soil fertilization programs aim for a soil target pH of 6.0 for mineral soils.
Checking the base fertilizer to ensure the soil gets adequate—but not excessive—amounts of the required chemicals is paramount at this stage. Many newer “traditional” N-P-K fertilizers may be missing all three basic elements—nitrogen, phosphorus and potassium. In addition, base fertilizers should provide a maximum of 30 pounds per acre of chlorine, but not more than that as it will reduce quality and not increase yield at higher levels.
Check your soil testing results to determine if magnesium (lime) or sulfur needs to be added. Different soil conditions in different parts of the country will bring widely varied results, so be sure to add what is needed for your unique situation.

Half and half—and adjust for leaching
Soil nitrogen is usually applied twice—within 10 days after transplant and again at side-dress. Apply not more than half the required nitrogen after transplant to avoid the chance of nitrogen leaching before the crop acquires the nutrient. Add the remaining amount of nitrogen at side-dress. This holds true whether using dry nitrogen or liquid.
Adding sulfur at a rate of 20 pounds per acre, or chloride, on deep, sandy soils is usually a good practice. Soil tests will not identify deficiencies, and some fertilizers do not contain these elements in adequate amounts.
In addition, overusing nitrogen can increase sucker growth and lead to problems with MH residue, hornworms and aphids. It can also lead to extended curing time and result in more unripened leaf.
Leaching adjustments need to be carefully calculated to avoid wasting money on unneeded nitrogen due to a heavy-handed adjustment. Determine leaching through topsoil depth to clay, the age of the crop when leaching occurred and the estimated inches of water that moved through the fertilized root zone. It is also important to remember that the additional nitrogen applied through leaching adjustments is in addition to the recommended total amount of nitrogen added. If more nitrogen than recommended was used on the first application, include that in your adjustments for leaching.
In most cases, the amount of nitrogen used relates to the texture of the soil and the depth of topsoil before hitting clay. Ranges vary from 50 pounds per acre in soil with a depth of five inches to 80 pounds in soil with a depth of 20 inches or more. Use an amount in the lower portion of the 50-80 pound range for finely textured, more fertile soils and an amount in the upper portion of the range when dealing in soils of more coarse texture.
Also adjust the nitrogen rate down 5 to 10 pounds if the crop follows a legume crop or the previous crop was known to have been over-fertilized.
The perfectly timed nitrogen application should be as topping time occurs, when there will be very little nitrogen left in the soil and nitrogen starvation begins. If nitrogen is still left in the soil at that time, ripening will be delayed as the plant continues to take up nitrogen.
Studies on drowned and partially drowned tobacco indicate that applying fertilizer to these type of situations usually do not improve the crops significantly as far as grade index or average market price. However, applying a fertilizer at side-dress that contains both nitrogen and potassium can be beneficial.

It may be in there already
While phosphorus is not an extremely leachable mineral and potassium is very leachable in soils, these chemicals have been overapplied through the years. In North Carolina’s Coastal Plain area, for example, it is common for phosphorus to be present in high levels in 85 percent of the fields used for tobacco, while potassium is present in high levels in 60 percent of the fields.
Again, it is a best practice to use the soil tests to determine what is best in any grower’s specific situation. There is an environmental concern as well, as overapplication can contribute to water contamination through rainwater runoff.

At side-dress
Keep the potassium recommendation from the soil test in mind when selecting a side-dress material. With a recommendation of less than 120 pounds per acre of potassium per acre [Note: sodium nitrate is not available-GWE], calcium nitrate or ammonium nitrate can be used. Add potassium to the side-dresser if the test suggestion is over 120 pounds of potassium per acre, or if severe leaching occurs. While ammonium nitrate is the least expensive, care should be taken to apply not more than half as much as used for calcium nitrate, so as not to increase nitrogen application.

Cost-saving suggestions
- Take care when upgrading fertilizers. Many “premium fertilizers” that contain micronutrients and some water-insoluble nitrogen can cost up to $20 more a ton over regular-grade fertilizers, but field tests have not proven a yield or quality increase over conventional fertilizers.
- Consider the blend. Blended fertilizers generally cost less per ton than conventional fertilizers and can perform as well as manufactured fertilizers of the same grade if they are properly blended.
- Buy in bulk. It saves money over bagged fertilizers and reduces labor.
Easterwood also recommends taking a good look at the nitrate source before selection. Historically, it has been the fertilizer of choice for tobacco and the most profitable to the grower.