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Production Papers

Response of Perennial Cool-Season Grasses to Clipping in the Southern Plains

USDA-ARS, Southern Plains Range Res. Stn., 2000 18th St., Woodward, OK 73801

^* Corresponding author (bgillen{at}spa.ars.usda.gov)

Received for publication December 23, 2003.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Many forage-livestock systems in the Southern Plains depend on the use of winter wheat (Triticum aestivum L.) and rye (Secale cereale L.) to support rapid gains of growing beef cattle (Bos taurus L.) from November through May. Complementing these annuals with cool-season perennial grasses could reduce inputs and soil erosion, but these perennial grasses have not been extensively tested under dryland conditions in this region. We determined the production potential and response to clipping of four Triticeae grasses under dryland conditions on a Grandfield fine sandy loam (fine-loamy, mixed, superactive, thermic Typic Haplustalf). ‘Barton’ western wheatgrass [Pascopyrum smithii (Rydb.) A. Löve], ‘Luna’ intermediate wheatgrass [Elytrigia intermedia (Host) Nevski subsp. intermedia ], ‘Jose’ tall wheatgrass [Elytrigia elongata (Host) Nevski], and ‘Bozoisky-Select’ Russian wildrye [Psathyrostachys juncea (Fisch.) Nevski] were harvested at either 10 or 15 cm at 30-, 45-, or 60-d intervals. Forage production was different among species in only 1 of 3 yr. Despite above-average winter and spring precipitation, production declined for all grasses over years, averaging 2270, 1860, and 880 kg ha^–1 in 1998, 1999, and 2000, respectively. There were no consistent differences in crude protein or in vitro digestible dry matter concentrations among the wheatgrasses. Crude protein concentration was higher for Russian wildrye in April and June but higher for the wheatgrasses in May. In vitro digestible dry matter was lower for Russian wildrye in May compared with the wheatgrasses. Warm-season grasses invaded all plots over years. Western wheatgrass was most resistant to invasion. Intermediate and tall wheatgrasses were not adapted to the conditions of this study, and any further research should focus on western wheatgrass or Russian wildrye.

Abbreviations: CP, crude protein • IVDDM, in vitro digestible dry matter • PLS, pure live seed

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
INTRODUCED PERENNIAL forage grasses of the Southern Plains are primarily warm-season grasses including Old World bluestems (Bothriochloa spp. Kuntze), weeping lovegrass [Eragrostis curvula (Shrad.) Nees], bermudagrass [Cynodon dactylon (L.) Pers.], and Kleingrass (Panicum coloratum L.). Native grasslands in this region are also heavily dominated by perennial warm-season grasses. This is, in large part, due to the concentration of seasonal precipitation from midspring through summer.

To improve the seasonal balance of forage availability, many forage–livestock systems in the Southern Plains utilize winter wheat and rye from November through May. Perennial cool-season grasses have long drawn interest as either a complement or substitute for winter wheat and rye. There are at least two possible advantages of perennial cool-season grasses compared with the annual cool-season grasses. First, input costs may be reduced because pasture would not have to be re-established annually. Second, soil erosion should be reduced because of the perennial cover. However, climatic patterns are not favorable for cool-season perennial grass growth. This fact is partially supported by the lack of a prominent cool-season perennial grass component in the native grasslands. In the case of the annual grasses, the mismatch between precipitation and seasonal plant growth is successfully addressed by storing moisture in fallow soils during summer and re-establishing annual pastures in September.

Cool-season perennial grasses of the Triticeae tribe are commonly used for dryland hay and forage production in the Northern Plains and Great Basin regions of North America (Asay and Jensen, 1996). While the Northern Plains also has peak precipitation in late spring and summer, temperatures are lower, and the overall length of the growing season is shorter than in the Southern Plains. The use of Triticeae grasses in the Southern Plains has been limited primarily to irrigated or lowland sites (Launchbaugh, 1958; Schuster and de Leon Garcia, 1973; Lauriault et al., 2002). Introduced wheatgrasses have shown limited adaptability under dryland conditions in this region (Malinowski et al., 2003). Western wheatgrass, a native grass, and Russian wildrye have had greater stand longevity in southeastern Colorado (McGinnies et al., 1963), but their productivity is not well documented in the Southern Plains. In addition, knowledge of the impacts of intensity and frequency of defoliation on plant productivity and vigor is basic to the evaluation of forage grasses. Harvest regime may affect the comparative productivity rankings of grass species (Heinrichs and Clark, 1961). The objectives of this research were to assess the production potential and adaptation of four Triticeae grasses for dryland forage production in the Southern Plains and to determine the effects of clipping height and frequency on that production and adaptation.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
This study was conducted from 1997 through 2000 at the USDA-ARS Southern Plains Experimental Range in northwest Oklahoma (36°35' N, 99°35' W; elevation 630 m). Average annual precipitation is 564 mm with 72% falling from April to September (Table 1). Average monthly temperatures are 2.3°C in January and 28°C in July. Minimum and maximum recorded temperatures are –27 and 45°C. The study site was located on a Grandfield fine sandy loam (fine-loamy, mixed, superactive, thermic Typic Haplustalf).

Clipping treatments began in September 1997, at the beginning of the third growing season, and continued for 3 yr. Clipping was imposed by splitting the main plots into subplots measuring 4.1 by 6.1 m. Clipping treatments consisted of a factorial arrangement of two clipping heights—10 and 15 cm—and three harvest intervals—30, 45, or 60 d. These treatments were randomly allocated to the subplots. Clipping was done with a rotary mower, and forage above the designated clipping height was collected in a bag. Clipping began in autumn when sufficient forage mass was available for practical sampling, paused during winter when growth was negligible, and began again on the same plots in spring when forage mass began to accumulate. Autumn growth was inconsistent, so autumn harvest periods varied over years: 11 September to 10 November 1997, a single harvest on all plots on 16 December 1998, and 15 October to 15 November 1999. The starting and ending dates for the spring period varied less than 1 wk among years and averaged 5 March and 4 June. The grasses were in the early vegetative stage of development at the start of the spring clipping period (extended leaf heights of 20 to 30 cm) and in the flowering stage at the end of the spring clipping period. Once clipping treatments were initiated, the plots were fertilized annually with urea at a total rate of 90 kg N ha^–1 split evenly between applications in early September and late March.

A production year included parts of two calendar years because growth began in autumn of one year and continued through spring of the following year. In this paper, a given year designates a forage production year. For example, forage production for 1998 includes forage harvested from the autumn of 1997 through the spring of 1998.

The actual sampling area within each plot varied based on the amount of standing crop. On dates with relatively low amounts of standing crop, two strips, each 0.51 by 6.1 m, were harvested from the middle of each plot. On dates with relatively greater standing crop, a single strip, 0.51 by 6.1 m, was harvested from the middle of each plot. After sampling, the remainder of the plot was clipped to the assigned treatment height, and the forage was left on the plot. All forage from the sample area within each plot was bagged and dried at 60°C for 7 d before weighing.

Subsamples of 200 to 300 g were uniformly ground and analyzed for N (Kjeldahl procedure; Bremner and Breitenbeck, 1983) and in vitro digestible dry matter (IVDDM; Tilley and Terry, 1963, as modified by White et al., 1981). Nitrogen concentration was multiplied by 6.25 to estimate crude protein (CP) concentration.

The canopy cover of invading warm-season grasses was determined each year in late July. Four quadrats measuring 29 by 61 cm were randomly located within each treatment plot. Within each quadrat, the canopy cover of sand dropseed [Sporobolus cryptandrus (Torr.) Gray], windmillgrass (Chloris verticillata Nutt.), yellow bluestem [Bothriochloa ischaemum (L.) Keng var. ischaemum], and other warm-season grasses was estimated using the cover classes of 0 to 5, 6 to 25, 26 to 50, 51 to 75, 76 to 95, and 96 to 100% (Daubenmire, 1959). Quadrat values were averaged within treatment plot for statistical analysis.

All statistical analyses were conducted with PROC GLM (SAS Inst., 1999). The statistical design was a split-plot analysis of variance with repeated measures over time. The whole plot factor was grass species. The split factors were the clipping treatments of harvest interval and clipping height. The repeated measures were year or month, depending on the variable being analyzed. When significant (P < 0.05) treatment differences occurred, mean separations were accomplished using Fisher's least significant difference at = 0.05 (SAS Inst., 1999).

Because of limited forage production in autumn, all nutritive value analyses were limited to the spring harvest dates, March to June. Harvest interval could not be used as a treatment factor for nutritive value because different treatments were harvested on different dates and were, therefore, not strictly comparable. To assess the change in nutritive value over clipping dates, statistical analyses were limited to the 30-d harvest interval. The 30-d treatment was chosen because it had three dates of harvest each spring and was considered the best treatment to determine the effect of species and date on nutritive value.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Forage Production
Autumn Forage
Autumn forage production was only substantial in the first year clipping was imposed. This resulted in two-way interactions of year with each of the three treatment factors for autumn forage production (P < 0.05, Table 2). Averaged over all treatments, autumn forage production was 32%, less than 1%, and 9% of total forage production for the three study years. These differences in autumn forage production were likely caused by precipitation patterns. In autumn of the first year, precipitation was well above average in both September and October (Table 1), resulting in relatively high forage production. In the second year, only 4 mm of precipitation was received in September (Table 1). Of the 178 mm of precipitation in October, only 19 mm was received before 27 October. Soil moisture was low during most of September and October when temperatures were favorable for plant growth and little autumn forage was produced. In the third year, precipitation was above average for September, but only 14 mm was received in October and November, again resulting in low autumn forage production.

Total Forage
There was an interaction between grass species and year for total forage production (P < 0.01, Table 2). The only difference in forage production among grass species occurred in 1999 when intermediate wheatgrass had the highest production and Russian wildrye was lowest. Production was similar among species in 1998 and 2000. Production of intermediate wheatgrass is often greater than production from Russian wildrye in the first 3 to 6 yr after establishment in the Northern Great Plains (Kilcher, 1958; Heinrichs and Clark, 1961; Whitman et al., 1962; White, 1985). As stands age, intermediate wheatgrass tends to thin, and production drops below that of Russian wildrye (Whitman et al., 1962; White and Wight, 1981; Currie and Smith, 1970). Production of tall wheatgrass has been reported as equal to production from intermediate wheatgrass in the Southern Great Plains (Schuster and de Leon Garcia, 1973) and the Intermountain Region (Holechek et al., 1989; Jensen et al., 2002) and greater than production from intermediate wheatgrass in Oregon (Borman et al., 1992).

Western wheatgrass, native to North America, is generally considered less productive than introduced species of the Triticeae tribe (Schuster and de Leon Garcia, 1973; Frank and Karn, 1988; Asay et al., 2001). However, there are examples in which production from western wheatgrass was equal to or greater than production from intermediate wheatgrass (Launchbaugh, 1958; McGinnies et al., 1963), tall wheatgrass (Holechek et al., 1989), or Russian wildrye (Newell and Keim, 1947). This was also the case in the current study.

Total forage production was influenced by an interaction between clipping height and year (P < 0.01, Table 2). Clipping at a 10-cm height resulted in greater harvested forage in all 3 yr and still produced 28% more herbage in the last year of the study than the 15-cm height. However, clipping at 10 cm caused greater stress on the grasses because the decline in forage production from 1998 to 2000 was greater in the 10-cm treatment (65%) compared with the 15-cm treatment (54%). A lower clipping height would be expected to produce more harvested forage unless the lower height dramatically reduced plant vigor.

There was no interaction between grass species and clipping height (P = 0.24), indicating similar tolerance to clipping height among the four species. Under drought conditions, Malinowski et al. (2003) reported greater forage harvest at 7.5- vs. 15-cm clip heights for 2 yr for intermediate wheatgrass but for only 1 yr for tall wheatgrass. Currie and Smith (1970) found that while intermediate wheatgrass declined whether grazing height was 5, 10, or 15 cm, Russian wildrye performed best at a grazing height of 7.5 cm. Schuster and de Leon Garcia (1973) found production was not affected by clipping height for tall, intermediate, or western wheatgrass under irrigated conditions. Response of harvested production to clipping height depends on site conditions and the adaptation of a given species to those conditions.

Clipping interval affected production only in 1999 (Table 2). In that year, the 60-d interval resulted in higher production than either the 30- or 45-d intervals, which were not different from each other (P < 0.05). Forage production was not affected by clipping interval in 1998 or 2000 (Table 2). There was no difference among grass species in their response to clipping interval (P = 0.52). Russian wildrye was more tolerant of shorter clipping intervals than intermediate wheatgrass when clipped at 4 cm (Heinrichs and Clark, 1961). Russian wildrye was also more tolerant of shorter clipping intervals than western wheatgrass when clipped at 7.5 cm (Newell and Keim, 1947). The shortest clipping height of 10 cm was apparently lenient enough to eliminate differential species responses to clipping intervals in the current study.

Nutritive Value
Crude protein concentration was affected by the interaction of grass species, month, and year (P < 0.01, Table 3). Overall, the three wheatgrasses exhibited similar patterns in CP concentration over time while Russian wildrye was somewhat different. The wheatgrasses were similar in CP concentration in all months over 3 yr with only two exceptions. Western wheatgrass was lower in CP concentration than intermediate and tall wheatgrasses in April of 1999. In June of 2000, intermediate wheatgrass was lower in CP concentration than western wheatgrass but similar to tall wheatgrass.

The results from the April and June samples are supported by previous studies that reported higher CP concentrations for Russian wildrye compared with various wheatgrasses (Newell and Keim, 1947; Heinrichs and Carson, 1956; Heinrichs and Clark, 1961; Lawrence, 1978; Gesshe and Walton, 1981) although Whitman et al. (1962) found no differences. Gesshe and Walton (1981) support our finding that the CP concentration of Russian wildrye relative to the wheatgrasses depends on sample date. The wheatgrasses have been reported to have similar CP concentrations (Heinrichs and Carson, 1956; Dotzenko, 1961; Schuster and de Leon Garcia, 1973; Holechek et al., 1989) with the exception of Lawrence (1978), who found western wheatgrass had a lower CP concentration than intermediate and tall wheatgrasses.

In vitro digestible dry matter was also affected by the interaction of grass species, month, and year (P < 0.01, Table 4). Concentration of IVDDM in April varied among the grasses and years with no clear pattern. In 1998, IVDDM concentrations were similar between western wheatgrass and Russian wildrye and higher for these grasses than for intermediate or tall wheatgrass. However, tall wheatgrass had the highest IVDDM concentration in 1999, and there was no difference among grasses for IVDDM concentration in 2000. In May, IVDDM concentration was lower for Russian wildrye than the wheatgrasses in all years. This reflected the relatively advanced phenological stage of Russian wildrye at the May sample date as discussed above under CP concentration. In June, IVDDM concentration was similar among grass species for all years except 2000 when intermediate wheatgrass was lower than the other three grasses. White and Wight (1981) found Russian wildrye had higher IVDDM than intermediate wheatgrass in 3 of 8 yr while Frank and Karn (1988) reported higher in vitro digestible organic matter concentration in intermediate wheatgrass relative to western wheatgrass.

Resistance to invasion was affected by an interaction between harvest interval and year (P < 0.05, Table 5). Invasion of warm-season grasses was similar among harvest intervals in the first 2 yr. By the third year, invasion was greatest at the 30-d rest interval, followed by the 60-d and then the 45-d rest intervals. The 60-d interval may have allowed more invasion than the 45-d interval because it placed the defoliation in the boot to early-heading phenological stage, a sensitive period for defoliation for many grasses. Resistance to invasion by warm-season grasses was also affected by clipping height (P < 0.01). As the clipping height was reduced from 15 to 10 cm, the canopy cover of warm-season grasses increased from 19 to 24%.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
The primary forage production period for these cool-season grasses in the Southern Plains is early March to early June. While growth begins in early autumn, production from September to early December averaged only 14% of total annual production. The cool-season perennial grasses were no more effective in producing autumn forage than winter wheat.

Forage production only differed among species in 1 yr out of 3. Russian wildrye had higher nutritive value than the wheatgrasses early and late in the spring growing season, but western wheatgrass was most resistant to invasion by warm-season grasses.

It is questionable whether these grasses are adapted for dryland forage production on upland sites on the Southern Plains. This concern is highlighted by the decline in production over years during a period of favorable precipitation as well as the increase in warm-season invading grasses. Lower clipping height or increased frequency of clipping did not hasten this decline except that warm-season grass invasion was increased with 30-d rest periods.

The concern over adaptation was further emphasized for intermediate and tall wheatgrasses two growing seasons after the conclusion of this study. Precipitation from September 2001 through May 2002 measured 62% of normal. This drought caused an estimated 95% stand reduction in the intermediate wheatgrass plots and 50% stand reduction in the tall wheatgrass plots. Western wheatgrass and Russian wildrye maintained uniform stands. Of the grasses included in this study, further research should focus on western wheatgrass or Russian wildrye for use on upland sites in the Southern Plains.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

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This Article Abstract Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (5) Citing Articles via Google Scholar Google Scholar Articles by Gillen, R. L. Articles by Berg, W. A. Search for Related Content PubMed Articles by Gillen, R. L. Articles by Berg, W. A. Agricola Articles by Gillen, R. L. Articles by Berg, W. A. Related Collections Forage Management Other Forage Crops