© 2006 Plant Management Network.
Using Prescribed Fire, Tillage, and Fertilizer to Manage Broomsedge-Infested Pastures
Twain J. Butler, The Noble Foundation, 2510 Sam Noble Parkway Ardmore, OK 73401; Larry A. Redmon, Texas A&M University, College Station, TX 77843; Jim F. Stritzke and Carla L. Goad, Oklahoma State University, Stillwater, OK 74078
Corresponding author: Twain Butler. firstname.lastname@example.org
Butler, T. J., Redmon, L. A., Stritzke, J. F., and Goad, C. L. 2006. Using prescribed fire, tillage, and fertilizer to manage broomsedge-infested pastures. Online. Forage and Grazinglands doi:10.1094/FG-2006-0424-01-RS.
Broomsedge (Andropogon virginicus L.), a short-lived perennial bunchgrass, is generally considered to be low in nutritive value for cattle and has invaded millions of acres of pastureland across the southeastern USA. Studies were initiated on broomsedge-infested bermudagrass [Cynodon dactylon (L.) Pers.] pastures in southeastern Oklahoma during the spring of 1995 and 1996 to determine the effects of prescribed fire, tillage plus improved soil fertility, and improved soil fertility alone, on broomsedge growth. A one-time spring tillage was followed by application of 100 lb N per acre plus P and K according to soil test recommendations. Additional fertility treatments included no fertilizer, and 100 and 200 lb N per acre with recommended P and K. The one-time spring tillage reduced broomsedge plant density by 71% the first year and stem density by 89% the second year when compared to the no-fertilizer check. Nitrogen rates did not affect broomsedge density the first year, but broomsedge stem density was reduced the second year by 48% with 100 lb N per acre and by 69% with 200 lb N per acre compared to the no-fertilizer check, due to an increase in bermudagrass DM production. These data indicate that broomsedge can be effectively managed with proper fertility and tillage.
Broomsedge is an Invasive Weed of Pastures
Beef cattle producers operate on a relatively narrow profit margin. In fact, Standardized Performance Analysis (9) data indicate that the average return on assets (based on market value) is only 1.6% for Oklahoma, Texas, and New Mexico cow herds. It is critical, therefore, that beef cattle production systems maximize gain per unit area of land relative to their input costs.
One problem faced by many livestock producers across the southeastern USA involves broomsedge, also known as broomsedge bluestem. Broomsedge is a native, warm-season, short-lived perennial bunchgrass growing on millions of acres of pastureland in the southeastern USA. Broomsedge often occurs in nearly pure stands and has been reported to occur mostly in old crop fields of low soil fertility (10). Broomsedge is generally recognized as an unpalatable weed that is low in nutritive value (7). The fact that broomsedge crude protein (CP) declines from 11.2% in June to 7.8% in July and to 5.9% in September was noted as early as 1930 (4). Broomsedge digestibility decreases have also been documented by Thurman (14). In that study, in vivo dry matter digestibility was 58.1% when broomsedge was cut to a 6-inch height compared to only 43.2% when cut to a 24-inch height (14). Broomsedge has also been more prevalent in lightly grazed pastures compared with heavily grazed pastures, where little or no broomsedge was present (10).
Although prescribed burning is an accepted management tool for controlling weed species and unwanted insects in both native and introduced forage species (11), and for improving growing cattle performance (1), there is little information regarding the effect of prescribed fire on broomsedge production. Tillage can be utilized on bermudagrass, since bermudagrass can regrow from stolons and rhizomes following minor tillage operations (5,6); however, the effect of tillage on broomsedge has not been reported. The objectives of this study were to study the response of broomsedge production to prescribed fire, tillage plus improved fertility, and improved fertility alone on broomsedge-infested bermudagrass pastures, and to compare the CP value of broomsedge to bermudagrass.
Procedures for Assessing Fire, Tillage, and Fertility for Control of Broomsedge
Six broomsedge-infested sites in six counties of southeastern Oklahoma were identified during the spring of 1995 for establishment of these studies. Sites were selected by county extension agents on the pastures of producers who were interested in suppressing broomsedge. Broomsedge densities were determined for all sites prior to treatment by counting plants in four 18- × 36-inch, permanently-located quadrats in each plot, which were 12 × 30 ft. Soil samples were obtained from each site and sent to the Soil, Water, and Forage Analytical Laboratory (SWFAL) at Oklahoma State University in order to quantify conditions where broomsedge is prevalent.
At three sites (Atoka, Bryan, and Pittsburg counties), two replications of a split-plot experiment were initiated in April 1995. The main plots in 1995 were spring-prescribed fire prior to green-up in March or no fire. Subplot treatments were: (i) no-fertilizer (control); (ii) 100 lb N per acre; (iii) 200 lb N per acre; and (iv) 100 lb N per acre plus a one-time tillage in April of 1995. Phosphorus (18-46-0) and potassium (0-0-60) were applied based on soil test recommendations from the SWFAL, and nitrogen (34-0-0) was applied as a single application in May. Phosphorus and potassium rates varied depending on site, but ranged from 46 to 65 lb P2O5 per acre and 0 to 60 lb K2O per acre. Tillage was implemented utilizing an off-set tandem disk, which cut the vegetation to a three-inch depth. At three additional sites (Pontotoc, Pushmataha, and Choctaw counties), the burning treatments were not applied due to adverse weather conditions. Fertility treatments as described above, however, were used with four replications. Broomsedge plant densities were determined on all six sites in August 1995 by counting plants in four permanently-located quadrats to determine treatment effects the first year.
In 1996, all six sites were burned in early spring prior to green-up to remove old standing forage material. The areas were then fenced to exclude grazing so that DM yield estimates could be obtained. Nitrogen, P, and K were applied during May 1996 at the same rates as in 1995. At all sites except Choctaw County, forage DM yield was estimated in all plots in June 1996. Total DM yield estimates were obtained by visually estimating percent composition and hand clipping all above ground biomass in two 18- × 36-inch quadrats in each plot. Forage yield was not determined at the Choctaw County site because cattle had invaded the area and grazed much of the forage. Harvested forage was oven-dried at 130°F to constant moisture and weighed. A portion of the harvested forage sample from each plot was then analyzed for total N using a LECO FR-228 dry combustion analyzer (LECO Corporation, St. Joseph, MI) (13). In addition, broomsedge and bermudagrass components were hand-separated from the no-fertilizer and 100-lb-N-per-acre treatments. Total N for each of these separated components was also used to determine CP (15). In August 1996 broomsedge stem density was estimated by counting broomsedge stems in the four 18- × 36-inch permanently located quadrats. Broomsedge stem density was measured instead of plant density since stem number can more accurately describe plant vigor. The data were analyzed using the GLM procedure of SAS (Version 6.11, 1996; SAS Institute Inc., Cary, NC) and treatment means separated using a Fisher’s protected LSD at the 0.05 level (12). Sites, broomsedge density, and DM yields were considered independent variables in the model and when interactions were not significant, data were pooled across sites.
Soil Fertility Effects on Broomsedge
The soil characteristics were previously reported in a companion study (2). Soil pH values ranged from 5.3 to 6.3 and K was slightly deficient at three of the six sites with values ranging from 155 to 421 lb/acre. All sites were deficient in P (7 to 19 lb/acre). This is a common occurrence in southeast Oklahoma and supports the findings of Peters and Lowance (10) that broomsedge can thrive on soils with low P, which could explain the presence of broomsedge in these pastures.
Spring Burning Alone Does Not Reduce Broomsedge
Broomsedge plant density (averaging 1.7 plants/ft2) did not differ between plots prior to initiation of treatments (data not shown). In the companion study, Butler et al. (2) reported that the density of broomsedge jointed stems was not affected by spring burning; however, broomsedge jointed stem density and yield were reduced by 96% with prescribed burning in late summer when soil moisture conditions were limiting. Broomsedge and bermudagrass DM yield was also not affected by spring burning (Table 1). Thurman (14) similarly reported that spring burning had little effect on DM yield of broomsedge when compared to a mowing treatment.
Table 1. Dry matter (DM) production for broomsedge, bermudagrass, other forage, and total DM production in June 1996 at sites in five counties in southeastern OK.
x Means within columns and sites followed by same letter do not differ (P < 0.05).
y Nitrogen applied with P and K according to soil test in both 1995 and 1996; Tillage applied only in 1995.
z Pontotoc and Pushmataha counties were not burned in 1995.
At the Choctaw County site, the plot area and an adjacent area had been fenced to exclude cattle. The cooperating producer’s cattle broke into the fenced area and grazed the burned plot area extensively, essentially avoiding the unburned broomsedge. Although this event precluded gathering standing crop data in late June, an estimate of standing crop was made at the end of the season in September. At this site, there was 1900 lb DM per acre of standing broomsedge in the burned area compared with 5300 lb DM per acre in the adjacent unburned area, indicating cattle preference for the burned treatment. Klingman and Easly (8) also reported cattle preference for broomsedge that had been burned due to removal of old standing material, and a reduction in broomsedge vigor due to close grazing.
Effectiveness of Tillage Plus Fertility
Broomsedge plant or stem density was pooled across sites, since there was no site-by-treatment interaction. The one-time tillage treatment in late spring in destroyed most of the established broomsedge plants. Broomsedge seedlings emerged after tillage, but were not competitive with bermudagrass under the improved soil fertility treatments. Therefore, density of jointed stems of broomsedge was determined to be a better estimate of long-term treatment effects than plant density. By August 1996, the one-time tillage plus 100 lb N per acre reduced broomsedge stem density by 78% compared to 100 lb N per acre alone and by 89% compared to the no-fertilizer control (Table 2). When harvested in June 1996, mean broomsedge DM production for tilled plots was reduced between 13 and 76% depending on site when compared to the no-fertilizer treatment, and by 25 to 73% when compared to the 100-lb-N-per-acre treatment. Tillage plus 100 lb N per acre increased bermudagrass yields compared to the no-fertilizer treatment at all five sites and increased bermudagrass and total yields at two sites (Atoka and Pittsburg counties) when compared to the 100-lb-N-per-acre treatment. Total DM production ranged from 2410 to 4980 lb/acre with the tillage plus 100 lb N per acre treatment compared to only 1000 to 2070 lb/acre in the no-fertilizer treatment (Table 1). It appears that tillage can effectively reduce the density and production of broomsedge without decreasing bermudagrass production.
Table 2. Density of broomsedge plants (August 1995) and stems (August 1996) as affected by treatment in Atoka, Bryan, Pittsburg, Choctaw, Pontotoc, and Pushmataha counties, OK.
x Nitrogen applied with P and K according to soil test in both 1995 and 1996; Tillage applied only in 1995.
y Means within columns followed by same letter do not differ (P < 0.05).
Effect of Adequate Fertility
Spring-applied N had little effect on broomsedge plant density in August 1995 when pooled across sites (Table 2). Broomsedge stem density, however, was reduced by August 1996 after two annual applications of 100 or 200 lb N per acre plus P and K according to soil test recommendations (Table 2). Decreased broomsedge stem density was attributed to increased bermudagrass density after appropriate soil fertility had been applied for two years. The 200-lb-N-per-acre rate reduced broomsedge stem density by 69% compared to 48% with 100 lb N per acre when compared to the no-fertilizer check in the second year. Klingman and Easley (8) reported similar rates of N fertilizer suppressed broomsedge by 99%. The 200-lb-N-per-acre rate increased total DM production compared with the 100-lb-N-per-acre treatment only at the Atoka and Pittsburg sites (Table 1). Most of the increase was attributed to bermudagrass. Broomsedge DM production only increased in the fertilized plots at the Pushmataha site (Table 1). Broomsedge was apparently not able to compete with bermudagrass in the higher fertility environment and may not respond to increased levels of fertility as readily as bermudagrass.
There was no site-by-CP interaction, so CP of total harvested forage was pooled across the five harvested sites. The CP increased with both levels of N and 200 lb N per acre increased CP over the 100-lb-N-per-acre rate. Crude protein levels were 7.7%, 13.2%, and 15.9% for the no-fertilizer, 100-, and 200-lb-N-per-acre treatments, respectively. There was no difference in CP between broomsedge and bermudagrass at the 0- or 100-lb-N-per-acre levels. Crude protein in June averaged 7.0% for broomsedge and 6.4% for bermudagrass in the no-fertilizer treatment and 10.2 and 11.7%, respectively with 100 lb N per acre. Although generally considered low in forage nutritive value (CP), broomsedge responded similarly to other warm-season grasses by increasing with N fertilizer (3).
Summary and Conclusions
Solid stands of broomsedge in pastures are indicators of low levels of management, such as insufficient fertility. If bermudagrass is present in a broomsedge-infested pasture, tillage and proper fertility are management tools that can enhance pasture utilization and productivity. Spring burning is a less-effective management tool. During the first year of reclamation, broomsedge should be heavily utilized at the same time as an appropriate soil fertility program is initiated. An adjunct treatment would be to remove old growth broomsedge with an early spring prescribed fire prior to green-up. Application of N, P, and K based on soil test recommendations should follow to stimulate bermudagrass growth and increase CP of the forage. Based on these data, after two or three growing seasons there should be a dramatic improvement in pasture productivity, due primarily to an increase in bermudagrass and a decrease in broomsedge for the following reasons:
Burning removes old broomsedge growth and allows livestock to consume young broomsedge plants that are more nutritious. Mowing could be utilized in burn-sensitive areas to remove this material if desired. However, burning does not increase DM production.
Tillage is detrimental to bunchgrasses such as broomsedge and appears to favor rhizomatous species such as bermudagrass.
Applying N fertilization can increase forage CP, increase total DM production, and when applied in conjunction with P and K, appears to alter the competitive balance in favor of bermudagrass.
1. Bernardo, D. J., Engle, D. M., and McCollum, F. T. 1988. An economic assessment of risk and returns from prescribed burning on tallgrass prairie. J. Range Manage. 41:178-183.
2. Butler, T. J., Stritzke, J. F., Redmon, L. A., and Goad, C. L. 2002. Broomsedge (Andropogon virginicus) response to herbicides and burning. Weed Technol. 16:18-22.
3. Coleman, S. W., Moore, J. E., and Wilson, J. R. 2004. Quality and utilization. Pages 267-308 in: Warm-Season (C4) Grasses. L. E. Moser, B. L. Burson, and L. E. Sollenberger, eds. Amer. Soc. Agron. Monogr. 45, Madison, WI.
4. Dustman, R. B., and Van Landingham, A. H. 1930. The chemical composition of consecutive cuttings of Andropogon virginicus and Danthonia spicata. Agron. J. 22:719-724.
5. Evers, G. W. 1995. Methods of rose clover establishment into bermudagrass sod. J. Prod. Agric. 8:366-368.
7. Griffin, J. L., Watson, V. H., and Strachan, W. F. 1988. Selective broomsedge control in permanent pastures. Crop Prot. 7:80-83.
8. Klingman, D. L., and Easley, T. 1971. Control of broomsedge. Weeds Today 2:9-10.
9. McGrann, J., and Parker, J. 1998. IRM-SPA Handbook. Cow-calf enterprise standardized performance analysis (SPA) measures and summary description. Tex. Agr. Ext. Ser. SPA-11.
10. Peters, E. J., and Lowance, S. A. 1974. Fertility and management treatments to control broomsedge in pastures. Weed Sci. 22:201-204.
11. Pinkerton, B. W., and Rice, J. S. 1992. Differential response of bermudagrass cultivars to headfires and backfires. J. Prod. Agric. 5:562-565.
12. Steel, R. D., and Torrie, J. H. 1980. Principles and Procedures of Statistics: A Biometrical Approach, 2nd Ed. New York, NY.
13. Sweeney, R. A., and Rexroad, P. R. 1987. Comparison of LECO FR-228 "Nitrogen determinator" with AOAC copper catalyst Kjeldahl method for crude protein. J. Assoc. Off. Anal. Chem. 70:1028-1030.
14. Thurman, C. W. 1969. Broomsedge as influenced by differential preparations, defoliations, and fertilization practices. Ph.D. dissertation. MSU, State College, Mississippi. (Diss. Abstr. 69-19809).
15. Van Soest, P. J. 1994. Nutritional Ecology of the Ruminant, 2nd Ed. Cornell Univ. Press, Ithaca, NY.