INTRODUCTION

If left unchecked, weed plants would out-compete crop plants for water, nutrients, and light because of the high weed seed numbers found in most crop fields and due to their rapid plant growth rates. Although necessary, chemical weed control is relatively expensive and, in some cases, represents a potential environmental risk. Production practices such as narrow row widths, conservation tillage, cover crops, and planting herbicide-tolerant varieties each have the potential to reduce weed numbers and/or shift the types of weed species present. However, little is known about how weed populations are impacted by these practices when used collectively as part of an integrated cropping system.

OBJECTIVE

Determine how new cropping systems affect weed populations and population shifts.

APPROACH

The number and weight of weed species present were determined after corn harvest at four locations per soil type on both sides of the Agroecology split-landscape study in 2001 and prior to cotton planting in 2002. In this long-term study, an innovative and a traditional cropping system (Table 1) are being compared for differences in profitability, environmental conservation, and ecological impact. Each weed sampling location was one-square-meter in area, with weed ecology determined for a Rains sandy loam, Norfolk loamy sand, Ocilla sand, and Bonneau sand soil found on both sides of the field. After determining weed density, each species was harvested and dried at 70oC. Sampling sites were marked using GPS. Herbicides used in the split-landscape study in 2001 were as follows:

Innovative Cropping System: 1.0 qt/acre Atrazine and 1.0 qt/acre Roundup Ultra prior to planting, no post-emergence application

Traditional Cropping System: 1.0 qt/acre Atrazine and 1.2 qt/acre Dual prior to planting, 1.5 qt/acre Atrazine and 0.67 oz/acre Accent 1 month after planting.

RESULTS

Weed numbers measured in the fall of 2001 were the same or usually less with the Innovative cropping system, compared to the Traditional cropping system (Table 2). Sicklepod, large crabgrass, and yellow nutsedge were the most prevalent weeds at that time (Table 2). Averaged over the four soil types, there were 3.2 times more sicklepod plants on the Traditional side of the field than on the Innovative side. Sicklepod was primarily found on the Rains soil type. Large crabgrass was only found on the Traditional side of the field. However, in contrast to the sicklepod results, large crabgrass was primarily found on the drier Bonneau and Ocilla sand soils. Yellow nutsedge was also more prevalent on the Traditional side than on the Innovative side, but only on the Bonneau soil. For winter weeds, differences between cropping systems depended upon the weed species and soil type (Table 3). Averaged across soil types, the number of wild garlic plants was 6 times greater with the Traditional cropping system than with the Innovative cropping system. Differences between cropping systems were less consistent for the other weed species present.

CONCLUSIONS

Control of most summer weed species was far superior with the Innovative cropping system, even though much less herbicide was used (especially atrazine). Superior weed control with the Innovative system was found for both grass and broadleaf summer weeds. Cost saving to the grower as a function of whole-farm operation is currently being determined (see Economic Analysis). It is also interesting that summer weed numbers in several cases were found to be very dependent upon soil type, especially when the Traditional cropping system was used. Under these conditions, significant opportunities exist for the precision application of herbicides using GPS technologies. Fewer differences were found between cropping systems with respect to winter weeds. Consistent differences were only found for wild garlic, which was more prevalent with the Traditional cropping system.