April 25, 2007 Agronomy

High soybean yields begin with early planting if conditions are right

Palle Pedersen, an agronomist with Iowa State University, believes old planting date recommendations for soybeans may be too late.

According to Pedersen, in order to increase yield potential, producers must take the risk and plant earlier. He also believes that there are factors more important than soil temperature (old recommendations say to wait until the soil temperature reaches 55-60 degrees) such as good seed quality, the calendar and seedbed conditions.

The seedbed is the most important factor, Pedersen said, because little is gained from early planting unless seedbed conditions are ideal. He cautions not to plant early if the soil is too wet and if there is a history of seed diseases in your fields, consider a fungicide treatment as protection. In great soil conditions, soybeans will respond favorably to early planting.

Kansas

Gary Kilgore, an agronomist with Kansas State University, advises producers not to plant early unless they have deeper topsoil. But most Kansas producers plant in clay pan soils, where there is only four to five inches of topsoil. Because only about two inches of moisture can be stored in this soil, Kilgore recommends that Kansas producers plant in the first half of June.

Iowa

In the southern two-thirds of Iowa, Pedersen recommends planting around April 25, but growers must have perfect seedbed conditions. For the northern third of the state, he recommends May 1, but again, with ideal conditions.

Illinois

Studies show that in Illinois, producers should be able to start planting the last week of April, but if planting can’t begin until mid-May, there should not be much yield loss. Emerson Nafziger, an agronomist at the University of Illinois, emphasizes that it is more important to plant when conditions are favorable, rather than a certain date.

Indiana

Purdue University research shows that optimal soybean planting depth is .75 to 1.5 inches. But not even half of Indiana producers plant in that range. Most are still drilling and therefore are planting earlier to increase yields and sinking beans deep in cool soil. Researchers suggest that while producers are seeing yield increases by planting earlier, they need to do a better job of managing that early season environment.

Seed Population

Seeding Recommendations

Planting more seeds as insurance usually does not pay off especially with the rising seed costs. According to Pedersen, Iowa planting recommendations were changed in 2006 for growers using planters. For a planter with 15, 20, 22, 30 or 36 inches, farmers can get by with 125,000 to 140,000 seed per acre.

But if a grower is using a drill with a row spacing of 7.5 to 10 inches, it will take a much higher seed population, 160,000 to 200,000 seed per acre, according to Pedersen.

The numbers are similar for Kansas. Kilgore recommends 120,000 to 140,000 seed per acre no matter what the soil type if using a planter. On irrigated soil, he suggests 160,000 to 175,000 seed per acre. And for producers using a grain drill, he recommends increasing seed population by 10 percent.

Row Spacing

Data collected over the last 20 years shows that narrower row spacing can actually increase yield. Fifteen-inch rows instead of 30-inch rows are recommended because with narrower rows, the canopy can close earlier. When the canopy closes earlier, the crop growth rate and the crop yield can be positively affected. Plus, the beans can out-compete the weeds.

In Kansas, researchers have found a 10 percent yield gain when switching from 30-inch rows to 15-inch rows. Iowa results are also positive when switching from 30- to 15-inch rows; studies showed four to four point five bushels more per acre. In Illinois, the increase is one to two bushels.