I have been receiving many questions about the advantages and disadvantages of planting corn in 30-inch rows compared with 36- to 40-inch rows. It might be appropriate to review some principles of row spacing and the data we have for corn grown in Wisconsin.

In general, plants can utilize resources most efficiently when they are arranged in a "box-like" fashion in the field. Optimum distribution of resources such as light, moisture and nutrients is achieved when neighboring plants are spaced equidistantly. Plants within the row at a population of 30,000 plants/acre are 7 inches from their neighbors, while plants in 40-inch rows are spaced 5.2 inches. For 30,000 plants/acre to be spaced equidistantly, row spacing would need to be 14.5 inches.

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.

In Wisconsin, increased yield from narrow rows (30-inches 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). Yield increases for rows spaced narrower than 30 inches average about 2 percent (data not shown).

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. The relatively low and variable yield response to narrow rows in corn make the decision about whether or not to switch complicated. The observed yield increase may not make the move to narrower rows economically sound unless the grower is replacing old equipment. Before going to a 30-inch row spacing the grower should 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 herbicide for band application over the row.

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