Planting soybeans with a grain drill gained acceptance over a decade ago. This acceptance was based mostly on the higher field efficiency due to greater seed box capacity and width as compared to planters owned by the same individual. However, grain drills are typically less accurate in both metering and placing soybean seed when compared to row crop planters. These two deficiencies resulted in the need for higher seeding rates to establish similar stands compared to planters. Research also indicated that as row spacings were reduced, higher plant densities were required to maximize yield in the higher yielding environments compared to planters. The introduction of genetically modified seed has increased soybean costs by nearly 60%. The increased seed cost and the introduction of split row planters have renewed interest in the impact of soybean row spacings, seeding rates and planting equipment.

A study was conducted in 2000 to assess the impact of soybean row spacing, seeding rate and planting equipment in a conventionally tilled field in Douglas Co. Kansas. Treatments consisted of three target seeding rates: 160,000, 190,000 and 210,000 seed/acre; and four primary row spacing-equipment combinations. These four equipment treatments consisted of 7.5 and 15 in rows planted with a grain drill and 15 and 30 in rows planted with a planter. An additional treatment consisted of 30 in rows planted with the grain drill. Due to grain drill metering limitations, this treatment was only conducted at the low plant density. A John Deere 455 Drill and a John Deere 1780 split-row planter were used. All planting equipment was adjusted by the producer to fit planting conditions.

Asgrow 'AG3701RR' soybean variety was planted on May 23, 2000 into a conventional till system. There was little crop residue remaining from the previous corn crop and the surface 2 inches of soil were fairly dry. The farmer adjusted both pieces of planting equipment to plant into similar conditions. The study was conducted in southern Douglas County, KS. A randomized complete block design with three replications was used. Each plot was 30 ft wide by approximately 900 ft long. Plant stands were taken on three transects across each plot on August 24, 2000 by counting the number of plants in 20 ft of row for each treatment. Plots were harvested on September 19, 2000 by harvesting the center 20 ft from each treatment using a John Deere 9600 combine equipped with a GreenstarTM yield monitor. All plots were harvested in the same direction and at approximately the same speed. Grain yields were determined by weighing the grain from each treatment using a weigh wagon as well as utilizing the mass flow information from the yield monitor. For simplicity, only the weigh wagon results are reported here. Analysis of variance was used to determine treatment effects with orthogonal contrasts utilized to determine differences between treatment pairs of interest.

Emergence rate (expressed as percent of seed drop) and established stand were most affected by planting equipment used (Table 1). Overall, the emergence was over 17 percentage points higher with a planter than with the drill. The planter also established plant stands that had over 35,000 more plants per acre than the drill at similar seed rates.

Growing conditions in July and August were not conducive to high soybean yields as indicated by the plot average yield of 13 bu/acre. No significant differences between the individual treatments occurred based on the analysis of variance procedures for either method of measuring grain yield (Table 1).

Orthogonal contrast analysis indicated some individual differences between pairs of treatments. When planted in 15 in rows, the planter produced grain yields that were 6.4 bu/acre greater than when planted with a grain drill. Across all row spacings (30 in - drilled were excluded), the planter produced yields that were 3.7 bu/acre greater than the drill. Previous research has indicated that in lower yielding environments when significant water stress was encountered, wide rows had a slight advantage over narrow rows. This could be a possible reason for the planter yields being higher than the drill, since the planter treatments were at wider row spacings, although the yields from 7.5 in row with a drill are higher than 15 in rows with a drill when measured with a weigh wagon. As expected, plant density had little effect on soybean grain yields. This may not have been the case if grain yield had exceeded 50 bu/acre, as previous research has indicated that at that yield level, higher plant densities are required to maximize yields when utilizing narrow rows.

The results of the first year of this study indicate that soybean plant establishment is greater with a row crop planter than with a grain drill. Grain yields from the planter were approximately 5 bu/acre higher than yield from the grain drill when planted in 15 in row. These results further support previous work that indicated that in low yielding environments, plant density and row spacings have little impact on soybean yields.