September, 1996
Field Crops 28.423-8

Planting Corn In Rows Narrower Than 30-Inches

Joe Lauer, Corn Agronomist
University of Wisconsin

Summary

Growers in the northern Cornbelt will have the greatest probability of success with narrower row corn production. The yield increases with narrower rows have been relatively small and quite variable in the central Cornbelt of the US. Narrower rows may increase stalk breakage, especially at higher plant populations. Growers must balance the expected yield increase and year-to-year variability against the costs involved in converting to narrower row equipment.

Row spacing has been dictated by the size of the power unit used to plant, cultivate, and harvest corn. Prior to 1940, the distance was limited by the width of a horse and the standard row spacing was 40 to 44 inches. After the introduction of hybrid corn it became apparent that higher plant densities were needed, but farmers were limited to hill planting so that fields could be cross cultivated in order to control weeds. It was not until the 1950's and 1960's when fertilizers became inexpensive, irrigation expanded and herbicides became available for weed control that farmers seriously considered narrower rows for producing corn.

A survey of corn producers in several Corn Belt states shows that row width has decreased since 1970 with a significant increase in the use of 30-inch rows. Many experiments comparing 30-inch row spacings with wider row spacings have been conducted across the corn belt. In Wisconsin, increased yield from 30-inch rows versus 36- to 40-inches is not always consistent, but is usually positive averaging 5 percent with a range of -1 to +15 percent under intensively managed conditions (Table 1).

Growers are interested in narrowing rows further to 20- or 15-inch rows. Many experiments evaluating row spacings narrower than 30-inches have been conducted in recent years. In two experiments in Wisconsin, yield increases for rows spaced narrower than 30 inches averaged about 2 percent.

The larger and more consistent yield responses seem to occur in the northern Cornbelt. In Michigan trials (1989-91), 22-inch rows yielded 8.8 % percent more than 30-inch rows. In Minnesota trials (1992-93), 20-inch rows outyielded 30-inch rows by 9.9 %. Pioneer Hi-Bred International, Inc. reported a four percent advantage for 22.5-inch rows versus 30-inch rows in trials conducted from 1991-94 (Paszkiewicz, et al., 1994). In some respects, the greater advantage for narrower rows observed in the northern Cornbelt is similar to row spacing effects with soybean.

In the Central Cornbelt, yield responses seem smaller and more variable. In Illinois, 20-inch rows out-yielded 15-inch by only 3.0 %. In Iowa, similar small yield responses to 15-inch row spacings compared to 30-inch row spacings were observed when grown at comparable populations. In Indiana, the average yield increase for 15-inch rows was 2.7%. The yield responses is quite variable from year to year and location to location. The comparative yield of the 15-inch rows ranged from a -3.1 % to a +8.2 %. No common thread could be identified to predict when the better responses would occur. Stalk breakage was also more prevalent in the narrower rows.

Corn silage production in a New York study compared 15- and 30-inch rows. Dry matter yield increased 5% regardless of hybrid. No row spacing effects were observed on silage quality.

Narrow rows make more efficient use of available light and also shade the surface soil more completely during the early part of the season while the soil is moist. This results in less water being lost from the soil surface by evaporation. The more uniformly you can seed plants the better as long as soils have adequate moisture. Uniform seeding maximizes photosynthesis and the proportion of water that is used in growth processes rather than evaporated from the soil.

But, under conditions of drought, evaporative loss is small because there is little moisture on the surface to be evaporated. Transpiration loss from the leaf surface is greater, since more leaf area is exposed to radiation from the sun. Even distribution and high population become a disadvantage because transpiration is now the main pathway by which water is taken from the soil. The more leaf area exposed to radiant energy, the greater the water loss.

Narrower rows should allow quicker canopy closure and thus quicker shading of the ground thereby improving weed control. Unfortunately there is little hard evidence to support this in corn. The disadvantage to narrower rows is that mechanical cultivation for weed control is more difficult, if not impossible. Even post-emergence herbicide treatments are made more difficult by narrower rows. After the growing point moves above ground, corn will not tolerate being driven over as well as soybeans do.

Numerous farmers have reported 'success' in switching to row spacings less than 30-inches. However, it is often not clear from the manner in which these testimonies are reported in the farm press whether actual comparisons were made between the narrower rows and the original, wider rows. In addition, some farmers not only switch to narrower rows but also increase seeding rates in anticipation of the benefits of 'spreading out' the plants more uniformly with the narrower rows. Consequently, some of the reported 'success' stories of narrower rows may be confounded with yield increases due to higher plant populations. Some of these farmers may have been able to achieve the yield response simply by increasing their plant population in the first place, without switching to narrower rows.

Before going to a 30-inch row spacing consider hybrid selection, machinery suitability for this row width (also silage harvesting equipment), the extra time needed to plant, cultivate and harvest, and the extra fertilizer and pesticide for band application over the row. Machinery needs to consider when changing row spacing:

  • Replacing rims and tires for tractors and combines is the most expensive consideration when adopting narrow row corn production. Replacement cost may range from $4800 to $8000, although the cost is less if purchased with the new equipment.
  • The combine head will obviously need to be modified or replaced. For example, a 6-row 30-inch row head would now become an 8-row 22-inch head. The procedure is relatively simple and costs about $200 per row. Row widths narrower than 20-inch are more difficult to accommodate.
  • The planter itself will need to be modified or replaced. Additional row units will be required. Frame extensions and/or reinforcement of the inner frame may be required.
  • IInsecticide rates (per acre), if applied through the planter, will increase with narrower rows. This is because insecticide is usually applied on a linear foot basis (so many ounces per so many feet of row). The application costs for 15-inch rows, for example, would be double that of 30-inch rows. Similar rate increases may occur for starter fertilizer and herbicide if growers desire to maintain the same application per row.

Key References

Nielsen, R.L. 1988. Influence of hybrids and plant density on grain yield and stalk breakage in corn grown in 15-inch row spacings. J. Prod. Agric. 1:190-195.

Paszkiewicz, S.R., P.R. Carter, S.T. Butzen, and K.D. Reese. 1994. Narrow row influence on corn yield. Agronomy Abstracts p. 164.

Table 1. Percent corn yield advantage for various row spacings in Wisconsin studies. Only data from plant populations between 20,000 and 30,000 plants/acre are included.
Location (Authors) Year Conducted Row spacing compared Average percent increase with narrower rows
Arlington (Berge et al., unpublished) 1965, 1966, 1968 30 v. 40 0
Arlington (Andrew and Peek, 1971) 1966, 1967, 1968 30 v. 40 +9
Hancock (Andrew and Peek, 1971) 1966, 1967, 1968 30 v. 36 +1
Hancock (Weis et al., unpublished) 1976, 1977, 1978 30 v. 36 -1 to 0
Marshfield (Peters et al., unpublished) 1982, 1983, 1984 30 v. 36 +7 to +10
Ashland (Mlynarek et al., unpublished) 1984, 1985, 1987, 1990 30 v. 36 0 to +3
Lancaster (Carter et al., unpublished) 1992, 1993 30 v. 38 +12 to +15
Lancaster (Lauer et al., unpublished) 1994, 1995 30 v. 38 +3 to +13

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