Soybean seeding rates being reduced

Over the last five years, North Carolina soybean growers have been putting fewer seeds in the ground yet harvesting roughly the same amount of soybeans. The result, as one might expect, is a healthier bottom line.

Indeed, Jim Dunphy, a soybean specialist at North Carolina State University, estimates that soybean growers statewide made about $26 million more in 2006 than they would have had they continued doing what they were doing in 2001.

It was Dunphy, a North Carolina Cooperative Extension specialist in the College of Agriculture and Life Sciences at North Carolina State, working with Extension agents across the state, who persuaded growers they could reduce seeding rates while maintaining yields.

Extension has a long history of conducting what are known as on-farm tests, experiments with different farming practices done on private farms under the same environmental conditions neighboring farmers face. Farmers can then see the results of these tests at field days, events where farmers are invited to tour a field and see the test, and other meetings.

Using funding from the North Carolina Soybean Growers Association, Dunphy said 96 on-farm tests of seeding rates were done across North Carolina between 2002 and 2005. Those tests compared seeding rates ranging from 25,000 seeds per acre to 200,000 seeds per acre.

North Carolina growers typically plant well more than one million acres of soybeans, while the crop's farm gate value is approximately $200 million annually, making soybeans the state's third most valuable field crop behind tobacco and cotton.

Until recently, Dunphy said North Carolina soybean growers typically planted around 200,000 seeds pre acre for what are known as full-season soybeans, which are usually planted in May. Growers used slightly higher rates for what are known as double-cropped soybeans, which are usually planted in June.

Double-cropping refers to the practice of growing a crop such as wheat over the winter, harvesting the wheat crop in the spring, then planting soybeans right behind the winter crop. Higher rates are necessary for double-cropped soybeans because the plants don't grow as large in the shortened growing season. The higher rates produce more plants, which helps make up for the yield lost to smaller plants.

The on-farm tests showed that growers could cut the number of seeds they put in the ground roughly in half without diminishing yield, Dunphy says.

This year, Dunphy asked county Extension agents who work with soybean growers to report on acreage in their counties and estimate seeding rates in 2001 and 2006 and any changes in yield. Dunphy says 50 agents representing 75.5 percent of North Carolina's soybean acreage provided information.

The agents indicated that growers have decreased seeding rates by just over 24 percent. On average, growers were planting about 68 pounds of seed per acre in 2001, while in 2006, the number dropped to just over 51 pounds per acre. During the five-year stretch, agents estimated that yield actually increased by around 5 percent.

The bottom line: Growers used less seed so their production costs declined. Yields were up a little, so they made a little more when they sold their crops. Dunphy estimates that statewide growers made about $26 million more in 2006 than if they had used the same seeding rates they were using in 2001.

Dunphy says most growers are now planting fewer seeds. “The more on-farm tests we had, it (lower seeding rates) became a pretty convincing argument,” Dunphy says. “It was proven so many times in so many fields in so many counties.”

Dunphy says he wasn't surprised by the results of the on-farm tests. Previous seeding rate experiments indicated lower rates might produce yields comparable to higher rates. And seedsmen, farmers who grow crops to produce seed to sell to other farmers, had commented on lower seeding rates.

Dunphy explains that when a new variety of a crop becomes available, the amount of seed available to seedsmen is often limited. Seedsmen often plant a limited number of seeds, so they tend to be aware of the yield from unusually low seeding rates.

Dunphy says adoption by North Carolina soybean growers of lower seeding rates has become so widespread in recent years that seed dealers have noticed a decline in sales.

Growers tend to use higher seeding rates as insurance they will end up being able to harvest a viable crop, Dunphy says, but his tests indicated, “Farmers were buying more insurance than they needed.”

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