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2006 Annual Report: Soybean Row Planting Width

Objective

One of the unexpected results from the development of Roundup ReadyŽ technology was the question of the best row spacing for soybeans. With Roundup®, it was thought that it did not matter how quickly your soybeans canopied since it was such an inexpensive chemical that killed all weeds by the roots and left the soybeans unharmed.

However, the dry conditions in Northwest Missouri the past few years have people talking about the subject again. Many of the 30, 36 and 38 inch row soybeans have not canopied. This has required a second, post-emergence application of chemicals to control weeds. Also, research conducted in other areas has shown a yield boost with 15-inch rows over other row widths.

This study was designed to compare the yields as well as the economics of different row widths for Roundup Ready soybeans.

Methods and Materials

Three different row widths were used as these represented how the majority of the soybeans are planted in this region. Planting populations were kept as close as possible using standard spacing adjustment equipment available from the manufacturers. No special equipment was used for this trial. The three treatments and their planting populations were:

  • 30-inch planted - 172,000 seeds/acre
  • 15-inch planted - 182,500 seeds/acre
  • 8-inch drilled - 195,000 seeds/acre

The plots were 10 feet wide and 250 feet long. Each treatment was replicated three times. Roundup Ready soybeans were no-till planted into corn stubble on May 22, 2006. The plots were harvested on November 7, 2006.

Results

Soybean row spacing yield data for 2006
Table 1 - Soybean row spacing yield data for 2006

All treatments emerged at approximately the same time with very little variation noted in the germination. All three plots were sprayed on June 14 with 2.0 pt/acre of Glystar Plus. The 30-inch row spacing beans required a second post emergence spraying of 2.0 pt/acre on July 6 due to fairly heavy weed pressure.

Yield results for this demonstration are shown in Table 1. The average for all the treatments was 45.8 bu/acre with a standard deviation of only 1.5 bu/acre.

Four-year yield averages for soybean row spacings
Figure 1 - Four-year yield averages for soybean row spacings

A four-year comparison of the yields for the three row spacings is shown in Figure 1. These averages show no significant yield differences between the treatments in Northwest Missouri. The biggest advantage has been that in 3 out of 4 years, the 30-inch rows required two post-emergence herbicide applications.