A summary of the SMaRT soybean planting population trials

Current planting population research and MSU recommendations can help Michigan soybean producers be more profitable.

Increasing seed costs have motivated soybean producers to identify the most profitable planting populations for their farms. In response to this issue, the SMaRT (Soybean Management and Research Technology) project worked with cooperating farmers to conduct six planting population trials in 2011. This article summarizes the results of these trials.

Procedure

Four planting populations (120,000; 140,000; 160,000; and 180,000 seeds per acre) were compared in a randomized complete block experimental design at six locations. Each population was planted in four replications at all except one location. Four of the six sites were planted in 15-inch rows in an effort to help producers fine-tune planting populations in this increasingly popular row spacing.

Results

Planting population did not affect soybean yields when the results of five of the six trials were combined. One location could not be included in the combined analysis because there were only three replications at this site. Because the yields were essentially equal for all of the planting populations when the locations were combined, the lowest planting rate was the most profitable at these sites in 2011 (Table 1).

Table 1. Planting population effects on soybean yields and income in 2011

Planting population (seeds/ac)

120,000

140,000

160,000

180,000

Average yield (bu/ac)

47.8 a

47.6 a

47.3 a

47.4 a

Gross income ($/ac)

$540

$538

$534

$535

Seed cost ($/ac)

$43

$50

$57

$64

Gross income – seed cost ($/ac)

$497

$488

$477

$471

Assumptions: Soybean market price = $11.30 per bushel. Seed cost = $50 per 140,000 seeds

When interpreting the 2011 results, it is important to understand that four of the six sites were planted in 15-inch rows. Three of these were planted with split-row planters and one was planted with an air drill. This equipment provides better seed metering, depth control and seed-to-soil contact than most drills.

Information collected from multiple sites improves the reliability of research data. However, due to year-to-year variability, data collected from multiple years is even better. Because of this, all the planting population trials planted in 15-inch rows in 2010 and 2011 were combined and analyzed. The results are presented in Table 2. The 120,000 and 160,000 planting populations were the only populations conducted in both years. When all nine locations were combined, the higher population increased soybean yields by 1.4 bushels per acre, but increased income by only $2 per acre.

Table 2. Planting population effects on soybean yields and income when
planted in 15-inch rows (average of nine trials conducted in 2010 and 2011)

Planting population (seeds/ac)

120,000

160,000

Average yield (bu/ac)

50.8 b

52.2 a

Gross income ($/ac)

$574

$590

Seed cost ($/ac)

$43

$57

Gross income – seed cost ($/ac)

$531

$533

Assumptions: Soybean market price = $11.30 per bushel. Seed cost = $50 per 140,000 seeds

Michigan State University recommends dropping 175,000 seeds per acre in 7.5-inch rows, 150,000 seeds per acre in 1-inch rows (split-row planter units) and 130,000 seeds per acre in 30-inch rows. These planting recommendations assume a warm germination test of at least 90 percent. If your planting populations are higher than the MSU recommendations, consider reducing your soybean planting population in 2012 as a way to increase income.

This article was produced by the SMaRT project (Soybean Management and Research Technology). The SMaRT project was developed to help Michigan producers increase soybean yields and farm profitability. The SMaRT project is a partnership between MSU Extension and the Michigan Soybean Checkoff program.

Related Events

Related Articles

Related Resources