Crop Observation and Recommendation Network
provided by the Agronomic Crops Team

by Dr. Jim Beuerlein
Dept. of Hort. and Crop Science
The Ohio State University

In 2001, we established a series of research plots at five Ohio locations to determine the effect of seeding rate on soybean yield. Two Roundup Ready varieties, Asgrow AG 2602 and Dekalb DKB 36-51, were used. The Asgrow variety had a relative maturity of 2.6, the Rps 1k Phytophthora gene and a partial resistant of 5.5. The Dekalb variety had a relative maturity of 3.7, the Rrps 1c Phytophthora gene and a partial resistance of 4.7. The seeds of both varieties were treated with fungicides (Rival, Apron) to aid in disease control. The six seeding rates averaged over varieties, locations and replications (40 plots) produced harvest populations of 70,000; 106,000; 116,000; 125,000; 159,000; and 167,000 plants per acre. These populations equate to about 70 percent of the intended seeding rate. Following are the recorded final populations and yields from each seeding rate and variety averaged over five test sites.

Effect of Seeding Rate on Soybean Yield for two varieties and six test sites in Ohio in 2001:

For seed costing $15.00 per 50 pound unit with 2500 seed per pound and grain worth $5.00 per bushel, the most profitable seeding rate based on this data was from 155,000 to 178,000 seeds per acre. Within that range, the increased seed cost was equal to the value of the increase in yield. For seeding rates greater than 178,000, profit decreased because seed cost increased while yield decreased slightly. For seeding rates less than 155,000 seeds per acre, profit increased with increasing seeding rate, up to 155,000 seeds per acre. This data agrees well with similar data collected in numerous other studies conducted during the past 20 years.

A key point to keep in mind is that the seed used in this study was treated with fungicides to aid in stand establishment and improve the general health of the root system. The results above may not be applicable to untreated seed in planting seasons that are good for disease development. Further, a fungicide seed treatment study conducted at the same test sites resulted in yield increases of 1.6 to 3.7 bu/ac depending on the combination of fungicides used. In all but the very driest springs, the use of fungicide seed treatments is highly profitable in that $2 to $3 worth of fungicide will increase yield by 2 to 5 bu/ac, producing a profit of $7 to $22 per acre for the use of seed treatment fungicides. All soybean seed should be treated every year for every field regardless of the variety, soil type, planting date, tillage or crop rotation.

The following tables contain the cultural practices used at each site and the rainfall received from May through September.

* Roundup=Roundup Ultra Max throughout; **Canopy = Canopy XL throughout.