Herbaceous Field Borders have Minor Impact on Corn Yield

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W. Terrell Stamps, Research Scientist, 1-31 Agriculture Building, Division of Plant Sciences, University of Missouri, Columbia 65211; Thomas V. Dailey, Resource Scientist, Missouri Department of Conservation, 1110 South College Avenue, Columbia 65201; Ned M. Gruenhagen, Wildlife Biologist, US Department of the Interior, Bureau of Reclamation, 1243 N Street, Fresno, CA 93721; and Marc J. Linit, Associate Dean for Research and Extension, 2-44 Agriculture Building, University of Missouri, Columbia 65211

Abstract

Federal conservation reserve programs such as CP33, Habitat Buffers for Upland Birds, are designed to conserve grassland birds on working farmland by adding herbaceous crop field borders. However, farmers are naturally concerned about the impact of such borders on crop yields and profits. We conducted three years (2000-2002) of field studies in mid-Missouri to assess the impact of various compositions of herbaceous field borders on yield in adjacent corn fields. Border treatments of (i) a mixture of warm-season grasses and legumes, (ii) a mixture of cool-season grasses and legumes, (iii) tall fescue alone, and (iv) a corn border control were planted around plots of field corn. We compared corn yield in terms of both border treatment and distance into the corn field from the crop-border interface. While distance from the border had a significant impact on corn yield, border composition did not. Yield was consistently lower near the border for all border treatments, including corn-bordered corn. We conclude that the adoption of field border programs such as CP33 will have little or no impact on corn production and that the potential benefits of herbaceous borders outweigh the negatives.

Introduction

The prevalence of crop monocultures in the Midwestern United States has had a significant negative impact on grassland birds (19), particularly the northern bobwhite, Colinus virginianus (2). The northern bobwhite has declined significantly in many areas of the USA; losses have averaged 3% annually since 1966 (2,24). Other countries such as Great Britain have seen similar declines in game bird populations, and these declines have been attributed to modern agricultural practices and subsequent loss of habitat resources such as decreased invertebrate food for developing chicks, fewer feeding resources for adult birds, and lack of nesting sites (4,23).

There is a growing interest in the USA in the enhancement of habitat in agricultural landscapes for socially and economically important wildlife such as the bobwhite (8). The 1985, 1996, and 2002 Farm Bills supported a series of USDA programs, such as the Conservation Reserve Program (CRP), which provided monetary incentives or cost sharing for measures to improve soil retention, reduce pesticide runoff, and promote wildlife habitat over broad regions (18). The USDA National Conservation Buffer Initiative promoted these goals through a variety of techniques, including field border plantings or buffer strips. The conservation reserve program CP33, Habitat Buffers for Upland Birds, targets bobwhites specifically by providing 250,000 acres of CRP continuous signup across the 35 states of the bobwhite’s range. The program provides incentives for establishing herbaceous borders in and around cropland to provide food and shelter for bobwhites and other birds.

Birds benefit from herbaceous borders around crops because borders provide shelter and nesting sites, provide cover from predators, provide seed as a food resource in winter, and enhance insect food resources overall (3,14). Arthropods are a critical source of essential nutrients for reproducing females and chicks of most gallinaceous birds, including bobwhites (11,25). Diversifying farmland habitat increases biodiversity of arthropods (28) and can enhance game bird chick survival (23).

Vegetation buffers have been promoted widely and cost-sharing has been available, but producers have been slow to adopt this conservation approach. The potential benefits for wildlife are often outweighed by the apparent negatives of field borders. Although farmers’ perceive weedy buffers as a threat to crop yields from weed spread into cropland, there is evidence that such weeds do not increase weed occurrence in adjacent crops (27). Also, misplaced fertilizer spread and herbicide drift from the crop to the border may promote the growth of problematic weeds in the border at the expense of more desirable flora (13,15). On the other hand, sown grass strips have been shown to reduce a variety of weeds at the field margin (27,31). Crop yields are in general lower at the field margins compared to the centers because of competition for light, moisture or nutrients by the border plants (6,17). Field margins present the potential loss of income if subsidies fall below the value of the crop taken out of production or if maintaining borders increases labor or management costs. Conversely, field borders are often established on land that is marginal or not cropped at all and present little risk to crop productivity (1).

Other potential benefits of field margins include reduced soil nutrient and chemical runoff and reduced sediment transport. In a study in North Carolina, for example, vegetated filter strips reduced P and NH₄ runoff by up to 50% (7).

Field borders can have both positive and negative impacts on insect and other pest populations beyond their value as food for birds. While field margins may harbor invertebrate pests or hamper the movement of beneficial insects into adjacent crops (12,16), field margins also can be a resource for beneficial insects and pollinators (10). Frank (9) provided evidence that slugs move from wildflower margins into oilseed rape crops in Switzerland (9). On the other hand, a number of beetle and spider species are associated with field borders, and have led to the use of "beetle banks" in the European community to provide habitat for ground-dwelling beetles (29).

While vegetative buffers can have a positive impact on quail numbers (30), the often intangible and/or non-monetary benefits of increased farmland diversity have not outweighed farmer’s concerns about the impact of such practices on yields and returns. Demonstration of multiple benefits of field borders may motivate producers to adopt this practice in the future.

Our objective was to determine the effects of several herbaceous field borders on adjacent field corn production. Specifically, we wanted to compare corn yields among fields adjacent to (i) a cool-season grass-legume border; (ii) a fescue only border; a (iii) warm-season grass-legume border; and (iv) a corn, Zea mays L., (control) border.

Site Description and Experimental Design

The study was done at the Reform Conservation Area, Callaway Co., MO. The area is a 6100+ acre site with a mixture of forest, grasslands, and croplands and is owned by Ameren Union Electric. The Missouri Department of Conservation has been the management agency for the conservation area since its creation in 1977. Because of conservation considerations, crop fields were generally small and bordered by shrubs and trees.

We identified 12 crop fields in the Reform Conservation Area as blocks for planting either corn or soybeans, Glycine max (L.) Merr. (Fig. 1). The dominant soil in the area was a Mexico silt loam. Fields were disced and fertilized (corn, 120/60/60 NPK; soybean, 0/60/60 NPK) in March 2000. Corn was planted the second week of 2000 April. A corn-soybean rotation was used to provide three continuous years of each crop. The cooperating producer planted ‘Pioneer 33G26’ (Pioneer Hi-Bred International Inc., Johnston, IA) in rows on 30-inch centers and managed the fields using conventional agronomic practices for the area (e.g., tillage, fertilization, herbicide application, cultivation, and harvest).

Fig. 1. Aerial photograph of Reform Conservation Area, Callaway Co., MO, for 2001. Research plots planted to corn are in yellow, plots planted to soybeans are in light green, and the surrounding grey-green fields were not sampled.

Herbaceous conservation field borders 30-ft wide (the minimum width for CP33) were established surrounding the crop fields prior to crop planting. The border areas were originally part of the crop fields and were sprayed with glyphosate (Roundup, Monsanto Company, St. Louis, MO) and disced prior to planting. The four border treatments were: (i) a cool-season grass/legume mixture – including orchard grass (Dactylis glomerata), timothy (Phleum pratense), and red clover (Trifolium pratense); (ii) a single cool-season grass – tall fescue (Festuca arundinacea); (iii) a warm-season grass/legume mixture – little bluestem (Andropogon scoparius), side-oats grama (Bouteloua curtipendula), and lespedeza (Lespedeza stipulacea); and (iv) a control – the unsprayed (i.e., no insecticide or herbicide) crop, either corn or soybean to match the field crop (in this study, corn). Establishment of the non-crop borders followed National Resources Conservation guidelines. The composition of the non-crop borders were determined prior to the creation of CP33 and, while similar to CP33 composition requirements for the major components, are overall less diverse than required by CP33.

The six fields that were planted to corn each year were used in this study. Each field was divided in half and surrounded by two border treatments (Fig. 2). Every combination of two border treatments was planted around the six fields of corn, resulting in three replications per treatment arranged in an incomplete block design [incomplete block plan 11.1 (5)]. The experiment was repeated over three growing seasons (2000-2002).

Fig. 2. Schematic of plots and sampling scheme for corn fields bordered by 4 different field margins. Six fields were bordered by every combination of 2 border treatments to comprise one year’s set of plots. Five 6.5-ft sections of corn row were sampled 10 ft, 30 ft, and 60 ft from each border treatment. 1 = Cool season grass border, 2 = corn border, 3 = tall fescue border, 4 = warm season grass border.

Fescue and cool-season grass mixtures were initially planted with a Brillion planter on 7 April 2000. In 2000, growing conditions in the spring were poor because of drought, and initial weed competition was strong. The principal weeds in all of the borders were giant foxtail (Setaria faberi) and common ragweed (Ambrosia artemisiifolia). Other weeds present included cheatgrass (Bromus tectorum), shattercane (Sorghum bicolor), and yellow nutsedge (Cyperus esculentus L.). Plots were mowed and cool-season plots were over seeded with the original seed mixture in the fall to promote establishment. Warm-season grass plantings were sown 4-5 May 2000. Although initially high, weed pressure in cool-season vegetation and tall fescue borders declined to insignificant levels over the three years of the study, while warm-season vegetation borders retained a significant weedy component. Aside from the initial herbicide application prior to establishment, no other herbicides were used in the borders during this study.

Corn was planted 14-22 April 2000. In 2001, corn was planted 22-25 April in fields that were in soybeans in 2000. In 2002, corn was planted 18-26 April in same fields as 2000.

Corn ears were hand harvested from all plants in ten 6.5-ft long subplots in rows approximately 10 and 30 ft from the crop-border interface in 2000. In 2001 and 2002, an additional distance of 60 ft from the crop-border interface was sampled and the number of 6.5-ft samples was reduced to 5 per replicate. A further set of samples was taken only in the corn-bordered corn plots: five 6.5-ft sections were hand harvested within corn borders at 10 ft and 30 ft from the outside edge of the border to compare corn yield within the border to corn yields in the field. We counted the number of plants per 6.5-ft section to analyze data on a per-plant basis. Harvest was completed in September in all three years, and the harvested material was threshed by hand with the aid of portable threshers.

Moisture content was measured in the corn, adjusted to 15.5%, and converted to bushels per acre yield. Data were analyzed with SAS PROC MIXED (SAS Institute Inc., Cary, NC) as an incomplete block design with distance into field treated as a subplot. The random effects in the MIXED procedure were field within year and year by field within border treatment. We compared years, treatments, distances into fields, and the interactions, with least squares means tests (SAS LSMEANS).

Corn Yields in Relation to Composition of and Distance from the Border

Of the three main effects on corn yield, border treatment was not significant, but year and distance from border were significant. The year by distance interaction was the only significant interaction among years, treatments, and distances. Overall yield, disregarding border treatments and distances, was highest (156 ± 34 bu/acre) during the establishment year, 2000, and decreased significantly the following two years (103 ± 35 in 2001 and 54 ± 31 in 2002; DF = 9, P < 0.005). An extended drought during the 2002 growing season severely limited corn production. The border establishment year, 2000, was dropped from further analysis because no differences were found in yield among distance or border composition and because of the addition a third sampled distance into the plots in the following years.

The lack of border composition effects in any year, particularly the lack of differences in yield among the control corn-bordered plots and the other herbaceous-bordered plots, indicated border composition had little influence on corn yield.

Yield differed significantly with distance into the field for 2001 only. In general, yield was significantly lower at 10 ft from the border compared to further into the corn fields, for all border treatments except corn (Fig. 3). The overall poor yields and consequent reduced differences among distances in 2002 were attributed to an extended drought, although yields closest to the border were consistently lower than further into the fields for all border treatments (Fig. 4).

Fig. 3. Graph of corn yield by treatment and distance into the corn field from the border for 2001. Bars within a border treatment with different letters differ significantly at P < 0.05. CSG = cool season grass border, Fescue = tall fescue only border, WSG = warm season grass border.

Fig. 4. Graph of corn yield by treatment and distance into the corn field from the border for 2002. Bars within a border treatment with different letters differ significantly at P < 0.05. CSG = cool season grass border, Fescue = tall fescue only border, WSG = warm season grass border.

We also looked at yields in the border for the corn-bordered corn. Yield 10 ft from the outside edge of the border was significantly lower than all other distances into the corn field from the outside edge of the border (Fig. 5). Along with the results from the other border treatments, this result suggests differences in yield were due to generalized edge effects and not border composition effects. Edge effects in crops are a well-known phenomenon among a variety of crop/border combinations (1,6,17,21,22). Crop yields are often lower nearer to field edges, and the reduction is typically greatest in fields bordered by woody vegetation because of competition for nutrients and sunlight. Our finding of significantly lower yields 10 ft from the field edge agrees with this phenomenon.

Fig. 5. Corn yield for corn-bordered corn fields in 2001-2002, with yield from within the borders included (i.e., the outside edge of the border was treated as the corn-border interface). Numbers in parentheses at top are distances from the original field-border interface. Bars with different letters were significantly different from one another at P < 0.05.

In the context of USDA habitat buffers, one of the key questions for producers is whether or not herbaceous buffers reduce adjacent crop yield. We found no yield reduction due to type of buffer vegetation composition, similar to the findings of other researchers (26). Thus, in farm programs where woody vegetation is a component of farmland diversity, government–sponsored herbaceous buffers are economical for producers provided subsidies exceed the net value of a cropped edge. Field-specific estimates of crop-edge reduction via precision crop harvest make this possible.

Summary

Our results indicated border composition was not a significant influence on corn yield when conservation borders were established according to NRCS guidelines. Differences in corn yields were related primarily to distance into the field from the crop-border interface. The lack of more significant increases in yield as one moved further from the crop-border interface in 2002 likely was due to the poor growing season (a significant drought). Vegetative borders surrounding crops can provide a wide range of positive ecological services, from providing food and habitat for wildlife to reducing erosion and chemical runoff (7,10,23,30). Our results show that herbaceous borders do not adversely affect corn production any more than no border, and we suggest that potential benefits in terms of wildlife conservation far outweigh perceived (but unfounded) negative effects.

Acknowledgments

The authors would like to thank Mark Ellersieck, Experiment Station, Columbia, MO, for his statistical help; Henry Lindemann, Reform, MO, for farming; Aaron Brown, Drew Dittmer, Terry Woods, University of Missouri, Columbia, MO, and Chris Newbold, Reggie Bennett, Steve Bartley, MDC, Columbia, MO, for their assistance with field and lab work. The authors would also like to thank the Missouri Department of Conservation and the Missouri Department of Natural Resources for funding this project (Cooperative Agreement No. 204, Master Memorandum of Understanding No. MCC-82-01-00).

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