INTRODUCTION

Weed control is a significant cost associated with corn production on the Coastal Plain, especially with conservation-tillage production systems. Atrazine is one of the most commonly used herbicides for corn production in the Region, although there is concern about atrazine's potential to leach in Coastal Plain soils. Due to environmental concerns, alternative weed control measures are needed that will reduce farmer reliance on traditional herbicides. Planting corn with narrow row spacings (>30 inches) is one management tool to make corn plants more competitive with weeds. Earlier canopy closure with narrow row widths shades emerging weeds and reduces their growth. Since cultivation for weed control is usually not an option with narrow row widths or conservation tillage, weed control strategies should be similar when these two practices are used. Planting hybrids tolerant to herbicides such as Roundup may be an important component of narrow row/conservation tillage production systems because of the broad-spectrum weed control that can be obtained when herbicides such as Roundup are applied. Herbicides such as Roundup breakdown rapidly in the soil and are probably more environmentally friendly than many of the traditional herbicides used by farmers. Based upon our soybean research results, we hypothesized that higher corn grain yields can be obtained with narrow row widths than with traditional 30- to 38-inch row widths, especially when conservation tillage and deep tillage are used.

OBJECTIVE

Develop economically and environmentally sustainable narrow-row production systems for corn grown on the Coastal Plain.

APPROACH

Corn was grown with different combinations of surface tillage (double disking versus no disking), row width (15 and 30 inches), and deep tillage (no deep tillage verus deep tillage) in 1997, 1998, 1999. Deep tillage was done with a ParaTill when the 15-inch row width was used, and with in-row subsoilers when the 30-inch row width was used. Final plant populations were 24,000 and 29,000 plants per acre with the 30-inch and 15-inch systems, respectively. In 1999, three split-field comparisons were conducted to compare a traditional corn production system (disked, in-row subsoiled, 30-inch row width) to a more innovative production system (no surface tillage, deep tilled with a ParaTill, 15-inch row width). This comparison was also made in our split landscape study in 2001. In all cases, the hybrid DeKalb 687 was used in these studies.

RESULTS

Grain-yield increases due to deep tillage and conservation tillage (no surface tillage) were greater with the 15-inch row width than with the 30-inch row width (Fig. 1). These responses were very similar to those found for soybean (see Research Results - Soybean). Averaged over 3 years, corn grain yields of the best narrow-row system (15-inch width, no surface tillage, and ParaTilled) was 28% higher than the yield of the traditional production system (30-inch width, disked, in-row subsoiled). In three similar split-field comparisons, the narrow row system had an 8, 22, and 70% higher yield than the traditional system (data not shown).

In our split-landscape study, corn grain yields were higher in 1999 and 2001 with the Innovative cropping system than with the Traditional cropping system on the Norfolk loamy sand, Ocilla sand (2001 only), and Bonneau sand soils (Fig. 2). Grain yields were similar or higher with the Traditional cropping system on the wetter Rains soil. Similar soil-type differences in response to cropping system were found for cotton in 2000 (see Research Results - Cotton) and for deep-tilled wheat and soybean grown in a separate study between 1997 and 2001 (see Research Results - Wheat). Although these results are only preliminary, they indicate that farmers may be able to manage these diverse soil types differently with respect to surface tillage to optimize grain yields.

Maximum canopy closure occurred more thoroughly and an average of 12 to 14 days earlier with the narrow row width system (data not shown). This earlier closure was associated with superior weed control with narrow row widths in all of the split field comparisons (Fig. 3, see Research Results - Weed Ecology). In our split-landscape study in 2001, no post-emergence application of herbicide was needed with the narrow row system because of the excellent weed control that the narrow rows provided. In addition, water runoff was found to be substantially less with the 15-inch row width system, compared to 30-inch system (see Research Results - Water Quality).

CONCLUSIONS

Data indicate planting with narrow row widths will result in higher corn grain yields on the Coastal Plain and require fewer herbicide inputs. The benefits from conservation tillage and deep tillage were greater when narrow row widths were used, similar to the responses found in soybean. High-yielding, herbicide-tolerant hybrids are becoming available in South Carolina. These hybrids probably will be well-suited for narrow row/conservation tillage systems because of the broad-spectrum weed control that be achieved when herbicides such as Roundup are used with these hybrids. Additional research is needed to refine the individual production practices that will be used with these narrow-row systems, such as the optimum seeding rate and method of nutrient application.

Row width, deep tillage, surface tillage, and interaction effects all significant at 0.05 probability level. Source: Frederick, Bauer, and Busscher, 1999, unpublished data.

 

This webpage was last updated on January 11, 2007