This document printed from the University
of Illinois Extension From the Fields at http://www.extension.uiuc.edu/rockfordcenter/
Soybean Plants Per Acre
December 24, 2007
Jim Morrison
Extension Educator, Crop Systems
Rockford Center 417 Ware Ave, Suite #102
Rockford, IL 61107-6412
Phone: 815-397-7714
FAX: 815-397-8620 morrison@uiuc.edu
How many soybean plants per acre are needed? Since seed selection decisions are now being made for 2008, this is an appropriate question to ask. To answer that question, data from population studies from three University of Illinois agronomy research centers in northern Illinois have been analyzed and reported by Eric Adee, agronomist at the Northwestern Illinois Agricultural Research and Demonstration Center near Monmouth.
The analysis consisted of studies conducted from 1998 through 2007 at DeKalb, Monmouth, and Urbana. Various row widths, varieties, and tillage systems were represented and harvest population was also collected. Plant populations ranged from 31,000 to 235,000, and yields ranged from 35 to 78 bushels per acre, according to Adee.
Statistical analysis revealed that average yield response across all plant populations was fairly flat, ranging from 51 to 54 bushels per acre. The highest yield was 54.3 bushels per acre with 125,000 plants. The optimum number of plants varied from 100,000 to 109,000 plants per acre.
In conducting the analysis, Adee notes that two assumptions were made. First, 90 percent of the seeds would develop into harvestable plants and secondly, seed cost would be $31.50 per unit of 150,000 seeds. The result is a seed cost of $0.23 per 1000 seeds.
One of the main questions in applying this data to field situations is how many seeds need to be planted to make sure there are enough plants. Farmers know how their equipment performs in different soil types and conditions, and can adjust seeding rate depending upon those situations.
According to Adee, data from this analysis shows that 125,000 plants per acre will be adequate to maximize yield. Soybeans have outstanding ability to "flex" or adjust with the conditions they encounter.
