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a 12148 Rist Canyon Rd., Bellvue, CO 80512
b Fort Lauderdale Res. Educ. Ctr., Univ. Florida, 3205 College Ave., Davie, FL 33314
c Everglades Res. Educ. Ctr. and Soil and Water Sci. Dep., Univ. Florida, 3200 E. Palm Beach Rd., Belle Glade, FL 33430
* Corresponding author (pbusey{at}turfgrass.com).
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Abbreviations: SPR, soil penetration resistance
Received for publication August 20, 2007.
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Goosegrass invasion of sports turf may result from traffic-caused compaction because of its ability to germinate and grow under compaction (Carrow and Petrovic, 1992). This is consistent with the fact that goosegrass tolerates low soil oxygen (Waddington and Baker, 1965) which is associated with compaction (Waddington, 1992). If traffic-caused compaction is the mechanism to explain goosegrass infestation in traffic areas, then it might operate by differentially decreasing bermudagrass growth and increasing the competitive advantage of goosegrass. This would justify the alleviation of soil compaction, such as through cultivation, as a method of cultural management to control goosegrass. Bulk density and SPR measurements can be used to assess soil compaction. In contrast to soil core sampling for determining bulk density in the laboratory, penetrometers are easier and quicker to operate and do not disturb the ground. Vazquez et al. (1991) showed that SPR measurements were 10 times more sensitive than bulk density measurements for indicating soil compaction of sand soil in Florida.
An alternative explanation for goosegrass competition in trafficked areas is that goosegrass seeds germinate strongly in response to fluctuating temperature, typical of conditions of bare ground and scalped and thin turf that result from traffic (Nishimoto and McCarty, 1997). If canopy cover is important in goosegrass competition this would justify enhancing recovery from wear, or other methods to increase canopy cover, as a means of cultural management to reduce goosegrass invasion in trafficked areas.
There are no data to document the association of goosegrass growth and infestation with traffic. No study has been conducted on the separate effects of wear and compaction on bermudagrass (Dunn et al., 1994; Carrow et al., 2001) or to verify that either compaction or canopy cover determines whether goosegrass competition occurs in trafficked areas. The objective of this study was to evaluate soil compaction and canopy cover as determinants of goosegrass competition in bermudagrass turf in sand soil.
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MATERIALS AND METHODS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Experimental Design and Data Collection
On golf courses, the experimental design was a randomized complete block with 15 blocks each consisting of a golf tee. For each tee there were two plots consisting of the two tee slopes parallel to the longest axis. The tee slope next to the cart path, from which golfers walked up onto the tee, was the traffic plot and the tee slope opposite the cart path was the no-traffic plot. Within each traffic and no-traffic plot, goosegrass cover (%) was estimated visually and the number of goosegrass plants was counted in 15 randomly distributed quadrats (0.25 m2). Twenty SPR readings were taken at random locations within each plot. The penetrometer used was a Field Scout SC-900 (Spectrum Technologies, Plainfield, IL), which digitally displays readings in kPa in 2.5-cm soil depth increments. The instrument error was ± 103 kPa for SPR and ± 1.25 cm for depth. The SPR measurements were recorded at 2.5, 5.0, 7.5, 10.0, and 12.5 cm depths. Four undisturbed soil cores were collected from traffic and no-traffic plots from the golf courses tees using a hammer driven core sampler 5.1 cm diam. to a depth of 9.0 cm. The soil was analyzed for bulk density, microporosity, macroporosity, and saturated hydraulic conductivity using standard methods (Hummel, 1993).
On sports fields, the experimental design was a randomized complete block with six replications (two foul areas x three fields). Within each foul area, a rectangle parallel to the base line, 30 m long and 9 m wide, was marked and gridded in 3 by 3 m cells. A line was drawn from the dugout gate to the home plate and 10 cells within 3 m on either side of the line were designated the traffic plot, and the remaining 20 cells were the no-traffic plot.
Within each cell one quadrat (1 m2) was randomly selected and goosegrass cover was estimated visually and the number of goosegrass plants counted. One SPR reading was randomly taken in each cell. Due to presence of rock, on the sport fields SPR measurements were collected only to 7.5 cm depth. For each SPR reading a soil core sample was also taken to determine gravimetric soil water content (Gardner, 1986).
Goosegrass plants and cover, and SPR (2.5, 5.0, and 7.5 cm depth) data were tested for homogeneity of variance using the chi-square distribution. Since variances were not homogeneous, with the exception of goosegrass cover, the Wilcoxon's signed rank test was used to detect differences between traffic and no-traffic treatments. Samples within a plot were always considered repeated measures. Soil property data were analyzed by ANOVA using SAS software (SAS Institute, Cary NC).
Compaction Experiments in Containers
Two greenhouse experiments were conducted at the University of Florida, Fort Lauderdale Research and Education Center, Davie using PVC containers 22.8 cm long, with 0.8 cm wall thickness, and 19.5 cm i.d. Containers were filled with Margate fine sand (siliceous, hyperthermic Mollic Psammaquent), a native soil (Pendleton et al., 1984) with 91% sand, 9% silt, and pH 5.9. Soil was dried and mixed with water to 0.25 g g–1 water content. A PVC ring 7.5 cm high was clasped with a clamp to the top of each container before compaction. Because soil subsided 3 to 6 cm during compaction, the ring permitted adding more soil to the container before compaction, thereby bringing the soil to the same level for all containers. Soil was compacted by dropping a 13.5-kg weight from a height of 42.0 cm onto a piece of wood cut to fit the inside of the container, before planting grasses.
Goosegrass and Bermudagrass Grown Separately in Compacted Soil
A randomized complete block design was used to evaluate effects of three soil compaction levels on the growth of goosegrass and bermudagrass grown separately. The experiment was done in two runs with four replicates and five replicates for the first and second runs, respectively. Treatments were low compaction (three drops), medium compaction (10 drops), and high compaction (42 drops). The resulting bulk densities were 1.19, 1.29, and 1.37 g cm–3, respectively, for low, medium, and high compaction in the first run, and 1.08, 1.18, and 1.28 g cm–3 in the second run, and an average across runs of 1.14, 1.24, 1.33 g cm–3.
Six seedlings of goosegrass with two to three leaves per seedling were transplanted to compacted soil in each goosegrass container. Four stolons of ‘Tifway’ bermudagrass [Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt-Davy] were planted in each bermudagrass container. In the first run, two replicates were planted 26 May 2005, and the other two replicates 1 June 2005. After 8 d, all containers were fertilized with soluble fertilizer at 144 kg N ha–1 (36–3–5, elemental N-P-K), and a second fertilization of 48 kg N ha–1 was done 30 d after planting. In the second run, all containers were planted 8 Aug. 2005 and 8 and 30 d after planting were fertilized at the same rate as in the first run. Before harvest, each container with goosegrass was thinned to three plants per container in the first run and four plants per container in the second run. All containers were watered regularly by hand, not allowing plants to wilt.
Plants were harvested 43 d after the day of planting for both runs, and shoots, including leaves and stolons, were separated from roots, dried at 60°C for 24 h, and weighed to determine root and shoot growth. Runs were tested for homogeneity of variance using the chi-square distribution. Since the variances were not homogeneous (P < 0.05) except for goosegrass root weight, they could not be readily pooled. Therefore data for the two runs were analyzed separately by ANOVA to determine treatment differences at P = 0.05. When compaction treatment was significant, linear and quadratic effects were tested to evaluate the nature of the response as a function of compaction level in arithmetic increments, low, medium, and high, using SAS (SAS Institute, Cary NC).
Goosegrass and Bermudagrass Grown Together in Competition in Compacted Soil
The growth of goosegrass and bermudagrass competing together in containers was evaluated in a 2 x 2 x 2 factorial experiment in a randomized complete block design with four replications. Factors were two levels of soil compaction (1.07 and 1.26 g cm–3 bulk density), two levels of N application rate (48 and 96 kg N ha–1 mo–1) for 3 mo after initial establishment fertilization, and two levels of weekly mowing height (1.3 and 2.5 cm). The two levels of soil compaction were produced as described previously with either 3 or 42 drops, respectively, before planting the bermudagrass.
Tifway bermudagrass stolons were planted in containers in compacted soil on 14 and 15 Feb. 2006. Containers were placed in the greenhouse and goosegrass was not planted until later. All containers were fertilized during the initial establishment phase with soluble fertilizer at an N rate of 48 kg N ha–1 (36–3–5, elemental N-P-K) on 6 Mar. 2006; 144 kg N ha–1 on 13 Mar., 20 Mar., and 27 April, and 48 kg N ha–1 on 4 May and 9 June. Before mowing height treatments, turf was initially mowed with a hand-held, battery-powered grass shear at 3.8 cm height on 3 and 24 May, and 2.5 cm height on 13 June 2006. Clippings were harvested, dried at 60°C for 24 h, and weighed. Containers were assigned to different blocks depending on their total bermudagrass clippings, which did not differ between low and high compaction. On 19 June 2006, when bermudagrass had covered the surface of the containers, mowing height and fertilization treatments began and goosegrass was seeded in all containers with 0.25 g per container (about 600 seeds). Mowing was done weekly and fertilization was done monthly. All containers were watered regularly by hand, not allowing plants to wilt. Goosegrass emergence was determined by counting the number of seedlings in each container until 43 d after planting, when all the containers were thinned to five seedlings. In addition, numbers of tillers per goosegrass plant were counted before harvesting.
Plants were harvested between 203 and 206 d after planting bermudagrass stolons, and between 70 and 76 d after planting goosegrass seed. Goosegrass and bermudagrass plants were separated, and shoots, including leaves and stolons, were separated from roots, dried at 60°C for 24 h, and weighed to determine root and shoot growth for each species in each container. Data were analyzed by ANOVA using SAS software to determine treatment differences at P = 0.05 (SAS Institute, Cary, NC).
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RESULTS AND DISCUSSION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Goosegrass canopy cover and plant density were greater, P < 0.05 and P < 0.01, respectively, in traffic plots compared with no-traffic plots (Table 1 ), pooled across locations. Soil penetration resistance was increased by traffic at 5.0 cm depth (P < 0.05) but not at other depths. The SPR for all depths did not reach 2 to 3 MPa, the point that SPR becomes critical for root growth (Lipiec and Hatano, 2003).
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There was no effect of traffic on any other soil property (Table 1). Bulk density was low for sand soil. Saturated hydraulic conductivity was lower than the acceptable minimum of 15 cm h–1 (United States Golf Association, 2004). Total organic carbon content showed no difference between traffic and no-traffic plots on tees. Goosegrass canopy cover and plant density were not correlated with SPR or any other soil property.
Compaction Experiments in Containers
Goosegrass and Bermudagrass Grown Separately in Compacted Soil
In both the first and second runs, goosegrass root dry weight was affected by compaction treatments (P < 0.05) showing a negative linear regression (P < 0.01) with compaction level (Fig. 1a
) but the quadratic effect was not significant. Root distribution was not measured; however, it was observed that roots were abundant in the shallow depth (5–7 cm) and few roots were seen below 7 cm for both high and medium compaction treatments. These results are similar to results obtained by Agnew and Carrow (1985) and O'Neil and Carrow (1983) where Kentucky bluegrass and perennial ryegrass roots were distributed in the first 5-cm depth of the soil in the heavy compaction treatments.
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For bermudagrass, no differences were observed in root and shoot growth due to compaction treatments (Fig. 1c and 1d). Bermudagrass establishment was slow and highly variable. Probably bermudagrass stolons did not have enough time to develop and be affected by soil compaction.
Goosegrass and Bermudagrass Grown Together in Competition in Compacted Soil
Goosegrass seedling emergence was reduced 41% by compaction. While probably due to poor seed-soil contact under high compaction, this was inconsistent with goosegrass being adapted to compaction. Increasing soil bulk density has been shown to delay and reduce seedling emergence by decreasing the volume of voids in the soil (Nasr and Selles, 1995).
There was no treatment effect of compaction or other factors on goosegrass shoot and root dry weight, measured from plants that had been thinned to five seedlings per container. In contrast to the prior experiment with goosegrass and bermudagrass grown separately, which had large goosegrass plants, in the competition experiment, where they were grown together, plants were smaller due to mowing and competition. The roots of these small goosegrass plants did not reach 5 to 7 cm length, thus were not limited by the compacted layer.
There was interaction (P < 0.01, Table 2 ) between compaction and mowing height on bermudagrass root dry weight (Fig. 2a ). Either low mowing height or high compaction was deleterious to bermudagrass root dry weight, but in combination their effect was no different than either factor alone. There was interaction (P < 0.01) between fertilization rate and mowing height on bermudagrass root dry weight. Low mowing height reduced bermudagrass root dry weight under low fertilization, but not under high fertilization. The three-way interaction of compaction, fertilization, and mowing was not significant. There was interaction (P < 0.05, Table 2) between compaction and fertilization on bermudagrass shoot dry weight. Compaction reduced bermudagrass shoot weight only at the low level of fertilization (Fig. 2b). This was not consistent with Sills and Carrow (1983) who showed that in perennial ryegrass (Lolium perenne L.) the most detrimental effects of compaction are on root weight and occur at the high rate of N. The present study used a complete fertilizer precluding an evaluation of the N effect as distinguished from a fertilization effect. The negative effect of compaction on bermudagrass root growth occurred as a part of interaction with mowing height, and the effect of compaction on bermudagrass shoot growth occurred only as an interaction with fertilization rate. Despite the compaction effects on bermudagrass, in no case did compaction directly or indirectly affect goosegrass dry weight.
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Cultural practices such as N fertilization rate and mowing height have been shown to affect almost every agronomic measure of growth in bermudagrass, with high fertilization increasing ground cover, and lower mowing height reducing biomass (Guertal and Evans, 2006). Although an indirect method has been presented for estimating turfgrass leaf area index, direct methods are tedious and imprecise (Kopec et al., 1987). Numerous studies have shown an effect of low mowing height increasing populations of other weed species in turfgrass (Busey, 2003). Increased shading would be expected from a larger bermudagrass canopy under high mowing height, and this would be expected to reduce goosegrass seed germination, which is dependent on fluctuating temperature typical of bare ground and scalped and thin turf that results from traffic (Nishimoto and McCarty, 1997). In the present study, the strong effect of short mowing height in reducing bermudagrass canopy cover, based on bermudagrass shoot weight, appears to explain the effect of increased goosegrass seedling emergence and increased tillering.
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CONCLUSIONS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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ACKNOWLEDGMENTS |
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NOTES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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