As fertilizer costs continue to increase, cotton producers are looking at ways to be more efficient without sacrificing yield and quality. Fortunately, says University of Georgia soil scientist Glen Harris, there are several things that can be done towards this end.
Fertilizer prices have increased for a number of reasons, said Harris, speaking at the recent Cotton Production Workshop in Tifton, Ga. “The main reason is because more people are living on less land, and the food to feed those people is being produced on less land — that trend is expected to continue in the coming decades,” he says.
In addition, says Harris, the world is experiencing its strongest economic growth in 30 years. “A lot of developed countries have more money that they can spend on fertilizer to grow the crops needed to feed their people. The fertilizer needs of China, India and Brazil alone are very high.
“We talk about China in terms of markets, but they have as much total land area as the United States and about as much in cropland. China has 1.3 billion people and 55 percent of its population are farmers. China also has much more irrigation than the United States,” says Harris.
An obvious reason for the increase in the price of nitrogen is the increase in natural gas prices, he says. Natural gas is used to fuel the process of manufacturing nitrogen, and it's a main ingredient for nitrogen fertilizers.
“We're getting our nitrogen from wherever there is cheap gas. This has been occurring now for a few years. The United States will continue to get a lot of its nitrogen fertilizer from Latin America and the former Soviet Union,” says Harris.
Phosphorus and potassium prices basically are an issue of supply and demand, he says. Whenever the demand for potassium is greater than its supply, prices will increase.
“Phosphorus works in the same way. The good news is that the manufacturing capacity for phosphorus was recently increased. While the demand for potash has remained at a steady level in the United States, Asia and Latin America have increased their use. Some new potash plants have gone on line, but it remains to be seen if that'll keep up with the demand,” he says.
Phosphorus and potassium applications should be guided by soil sampling, says Harris, and soil testing probably is one of the most underrated tools in making more efficient applications. “We scout for insects, and we don't spray until we know for sure what is in our fields. We also look for weeds before we spray. We should be taking a soil sample before we apply fertilizer.”
Most growers are doing a good job of soil testing and applying lime and fertilizer, he says. “We'd like to see soil pH in the 6 to 6.5 range. If you drop below 5.5, then you begin having problems, and this can have a direct impact on getting the most value from your fertilizer dollar. If you drop below 5.5, toxicity becomes a factor. And if you get above 7, you start to lose efficiency.”
With many farmers booking fertilizer further in advance than usual, some have been asking questions about making applications in the fall, says Harris.
“If you're applying only phosphorus, there would be no problem with that. Phosphorus is fairly immobile in the soil, and it will be there when you plant cotton in May. Potash is a little more mobile in the soil, so you might lose potash if you apply it early. Nitrogen is highly mobile in the soil. If you put it out early, regardless of the form of fertilizer being used, and if you don't have a cover crop, good luck finding nitrogen in May.”
There are things growers can do to improve the efficiency of their nitrogen applications, says Harris, including making split applications. “The most efficient way to make a split application is to put out some preplant, some at sidedress, and some through foliar applications. Try and do at least two out of the three, probably at preplant and at sidedress.”
This recommendation, he says, is based on data from the 1980s. “The reason for putting out nitrogen at preplant is to get the crop growing and to get it to first square. The sidedress application is when nitrogen demand increases. Foliar applications are good if you come up short, and you need to feed cotton during the bloom period.”
The split application recommendation, he continues, is based on a rate and timing study that used 0, 30, 60 and 90 pounds of nitrogen per acre. The 60 and 90 pounds were split applications, and the rates were made with and without foliar applications. In this case, the 60-pound plus a foliar was the best treatment. At 90 pounds, yields dropped.
The study was repeated this past year at Tifton with similar results, he adds. “We got the same response with 30 pounds plus a foliar, but the 90-pound rate was better than 60 pounds.”
Another popular issue during a time of increased fertilizer prices is the use of poultry litter used as fertilizer on cotton, says Harris. Georgia is the No. 1 poultry-producing state in the country, and the industry continues to grow.
“Based on old prices and the availability of nutrients — since all nutrients in poultry litter aren't as available as in a bag of fertilizer — I put the price of poultry litter at $25 per ton. Based on prices today, I'd put that closer to $35 per ton. Some people try and put a dollar value on the other nutrients in poultry litter, and on the organic matter. But our value is based only on N, P and K. I don't think you can count on the other factors enough to put a dollar value on them.”
Without a doubt, cotton will respond to poultry litter, he says, but the fertilizer value of poultry litter varies depending on a number of factors, including moisture, temperature, feed rations, number of batches before cleanout, storage and handling. Due to variability, it is recommended that litter be analyzed for nutrients by a reputable laboratory before application rates are determined.
“A good, basic strategy is 2 tons per acre of poultry litter preplant incorporated followed by 30 to 60 pounds per acre of sidedress nitrogen, depending on soil type. This approach should avoid unnecessary P buildup and should not cause rank growth, boll rot, or defoliation problems typically associated with excess N. In addition, the availability of N from poultry litter, because it is an organic material, is less predictable than from commercial fertilizer. Therefore, sidedressing with commercial fertilizer N assures adequate N availability when the crop needs it the most.
There also is interest in other by-products and biosolids being used on row crops such as cotton, says Harris. These materials may have some value as fertilizers, soil amendments, or liming materials, and they may be free or available at very low cost, he says. However, great caution is needed when considering the use of any by-product to insure it can be used, safely, effectively, and economically, he adds.
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