If a couple extra bushels of wheat per acre makes a difference to you, placing 10 to 15 pounds of starter phosphorous with the seed may be a practice to consider, say western Canada soil fertility specialists.
Those two bushels aren’t a huge difference, points out Geza Racz, a professor and researcher with the University of Manitoba’s Department of Soil Science. But even at $3 wheat, that works out to about $6 per acre. Over 1,000 acres, that represents $6,000.
“It may look small but depending on the market and how many acres you are cropping, it can add up,” says Racz. Research, he says, indicates one of the most effective crop fertility programs has the bulk of nitrogen and phosphorous banded one to two inches away from the seed row, with 10 to 15 pounds of starter phosphorous placed with the seed.
That practice also makes sense to Tom Jensen, Northern Great Plains director with the International Plant Nutrition Institute in Saskatoon.
Jensen says the starter phosphorous is particularly important in a cool dry spring. If phosphorous is immediately available to seedling roots, it can improve the popup effect and emergence of the new crop. “If we have a cool dry spring, followed by an early frost in the fall, it can make quite a difference if the crop has an extra few days of maturity before that frost,” says Jensen.
Pros and cons of P and N together
The two crop fertility specialists described the pros and cons of dual banding phosphorous and nitrogen when asked the long-standing question, “Is there any problem with placing the two nutrients in the same band a couple inches from the seed row?”
Overall it is likely a good practice, they say, although not perfect either.
Here is what happens: P205 phosphorous commonly used in the form of 11-52-0 granular or 10-34 (ammonium polyphosphate) liquid generally doesn’t move far in the soil. Jensen says 11-52-0 (ammonium phosphate), for example, may only move one-quarter to half an inch before it begins to react with other compounds in the soil and basically stops.
“In the short term, that first season, only a small amount of phosphorous remains soluble and available to the plant,” says Jensen. “With P205 it can be a little as one-third of a pound per acre that remains dissolved and available to the plant.”
However research shows that when phosphorous and nitrogen are banded together in the same row, slightly more phosphorous remains soluble and available to the plants. As the nitrogen converts from ammonium to nitrate the natural acidification process helps to keep a bit more of the phosphorous soluble and available to plant roots.
The downside is that the high concentration of nitrogen is toxic to these tender new seedling roots. Initially the roots will grow toward the nitrogen/phosphorous row and then stop because of this toxicity. “Once that nitrogen concentration decreases or as some people describe it, once that band mellows, then the roots can grow into it,” says Jensen. That mellowing period can delay nutrient uptake by the crop and slow growth.
On one hand the nitrogen/phosphorous blend is a benefit by keeping more phosphorous soluble, but on the other hand the high concentration of nitrogen can temporarily discourage nutrient uptake by plant roots.
Toxicity caused by the high concentration of nitrogen can slow nutrient uptake for 40 to 50 days, says Racz. After that, the roots can make better use of the nutrients. “A lot of producers like to dual band their nitrogen and phosphorous, which makes it worthwhile to add starter phosphorous in the seed row,” he says.
Racz says in wheat, for example, if the air seeder places seed in the soil with a narrow one-inch spread, about 10 pounds of starter P205 per acre is sufficient. With wider seeding tips spreading seed over two to three inches, about 15 pounds of P205 per acre is recommended.
“If a producer is planning to apply 30 pounds of phosphorous to a cereal crop, a good practice is to band 20 pounds with the nitrogen and then put the other 10 pounds in the seed row,” he says. “That is the best of both worlds.”
Racz referenced research results by Western Co-op Fertilizer (Westco) that showed wheat yields under various fertility practices. Wheat grown without phosphorous yielded 2,760 kg per hectare; wheat with nitrogen and phosphorous dual banded yielded 2,960 kg per hectare; wheat grown with nitrogen and phosphorous in a dual band, along with starter phosphorous yielded 3,080; and wheat with the full rate of phosphorous placed with the seed yielded 3,030.
“At one time it was thought placing all phosphorous with the seed was the most productive, but this research shows there might be slightly better yields by putting starter phosphorous in the seed row and the rest in a band with nitrogen,” says Racz.
Jensen adds that although most of the phosphorous applied this growing season gets tied up quickly, it isn’t lost. Over the longer term, it does become available to the future crops.
With nitrogen, for example, 50 to 60 per cent of the nutrient is available to the crop in the year of application, whereas with phosphorous only 15 or 20 per cent is available to the crop in the year of application.
“Some of the best long term research we have which comes from Britain shows that over 10 years as much as 90 per cent of the applied phosphorous will become available to the crop,” he says. “It changes from being less soluble to becoming more soluble in small amounts each year. It is very efficient.”
Lee Hart is field editor of Grainews, based in Calgary. Contact him at 403-592-1964 or by email at [email protected]