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Corn+Soybean Digest

Phosporus at Planting?

If your soils have ample phosphorus (P), you can skip the P in your pop-up corn fertilizer without sacrificing yield, according to new research by North Carolina State University.

“Overall, using only starter nitrogen (N) fertilizer would produce yields similar to those achieved with N and P starter fertilizer in soils that test very high for P,” says Deanna Osmond, North Carolina State University Extension soil scientist, who led the research.

Corn starter fertilizers have been used successfully to increase early plant growth, nutrient uptake and yields in research trials and on the farm. They also promote earlier maturity, improve southern corn billbug control and help suppress weeds through earlier shading. Use of starter fertilizers is increasing in North Carolina and the southeastern U.S.

Most research in the southeast supports the practice of including N and P in corn starter fertilizers. Osmond, Research Associate Sheri Cahill and David Hardy of the North Carolina Agriculture and Consumer Services department (NCDA&CS) showed that “producers can reduce the cost of P fertilizer application and slowly decrease the amount of P in the soil by applying only N in their starter fertilizer,” Osmond says.

“This will save money and help the environment at the same time,” adds Osmond, a watershed, soil fertility and nutrient management specialist.

In 2003, nearly half of soil samples submitted to the NCA&CS soil-testing laboratory tested very high in soil P, she says. (Although 2003 data is the most recent available, soil test data tend to remain relatively stable over time.)

The problem: “As soil-test P increases, off-site P loss increases through erosion, soluble P runoff or leaching,” Osmond says. Phosphorus can pollute drinking water supplies and surface waters and contributes to algae blooms.

The researchers studied North Carolina coastal plain, piedmont and mountain sites that contained very high soil-test P, according to 2007 state ag department soil testing records. The researchers sought to determine if, when used on very high P soils, starter P fertilizer would affect corn and cotton growth. The research was carried out at 38 locations for corn and 13 locations for cotton — 12 of those on the coastal plain.

Researchers treated one set of test plots with starter N and P fertilizers, using 32 lbs./acre N and 13.4 lbs./acre P (N+P). Comparison test plots received 32 lbs./acre of N fertilizer only. The nutrients were applied to the top of the soil in a band near the seed. The treatments were repeated four times at each location, and soil samples were taken from each site on planting day.

The researchers measured N and P concentration in early season plant tissue, and how many days it took for the corn to display silk and for the cotton to show earliest blooms. They also measured yields for both crops.

Corn yields were greater in the mountains than the coastal plain or piedmont, and cotton yields were greater in the coastal plain than in the piedmont. However, within each region there were no differences between the N-only and N+P corn and cotton treatments.

Moreover, the data indicated no yield differences resulted from the different treatments, Osmond and Cahill say.

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