Agronomy Journal Grow Your Career With ASA
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Published in Agron J 99:494-500 (2007)
DOI: 10.2134/agronj2006.0074
© 2007 American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Volesky, J. D.
Right arrow Articles by Anderson, B. E.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Volesky, J. D.
Right arrow Articles by Anderson, B. E.
Agricola
Right arrow Articles by Volesky, J. D.
Right arrow Articles by Anderson, B. E.
Related Collections
Right arrow Forage Management
Right arrow Root Growth

Forages

Defoliation Effects on Production and Nutritive Value of Four Irrigated Cool-Season Perennial Grasses

Jerry D. Voleskya,* and Bruce E. Andersonb

a Dep. of Agronomy and Horticulture, Univ. of Nebraska-Lincoln, West Central Research and Extension Center, 461 West University Dr., North Platte, NE 69101
b Dep. of Agronomy and Horticulture, Univ. of Nebraska, P.O. Box 830915, Lincoln, NE 68583

* Corresponding author (jvolesky1{at}unl.edu)

Received for publication March 12, 2006.

   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Irrigated cool-season perennial grasses are becoming an important complementary forage source in the Central Plains. A study was conducted to evaluate effects of clipping stubble height on dry matter (DM) production, growth rate, tiller density, and nutrient content of smooth bromegrass (Bromus inermis Leyss.) orchardgrass (Dactylis glomerata L.), creeping foxtail (Alopecurus arundinaceus Poir.), and meadow bromegrass (Bromus riparius Rhem.) under irrigated conditions on a Cozad silt loam soil (fine-silty, mixed, mesic Typic Haplustoll). Clipping treatments (35-cm canopy height cut to 7-, 14-, and 21-cm stubble heights) were applied to monoculture plots of these species for two growing seasons in a randomized complete block design. Stubble height effects on total DM production varied by species (P < 0.05). For orchardgrass and meadow bromegrass, DM production was similar at the 14- and 21-cm stubble heights (22.22 Mg ha–1), but significantly greater than production at the 7-cm stubble height (14.03 Mg ha–1). In contrast, DM production of smooth bromegrass and creeping foxtail was significantly greater at each successively higher stubble height. End-of-season tiller density of the 7-cm stubble height treatment was about 50% of the tiller density of the 14-cm and 21-cm stubble height treatments. Stubble height effects on nutritive value varied by species and clipping period. Stubble height did not affect crude protein (CP) content of creeping foxtail, but CP was lower at the 7-cm height for the other species. Defoliation strategies that maintain adequate residual herbage will optimize production of nutrient dense forage and maintain tiller density.

Abbreviations: CP, crude protein • DM, dry matter • IVDMD, in vitro dry matter digestibility


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
IRRIGATED cool-season perennial grasses can be used in complementary forage systems with warm-season rangeland and other forage resources (Nichols et al., 1993). Although there can be considerable annual variation in input costs and product value, economic returns from irrigated pasture enterprises can be competitive with irrigated corn (Zea mays L.), soybeans [Glycine max (L.) Merr.], or wheat (Triticum aestivum L.) (Volesky and Clark, 2003). Productivity and persistence of irrigated perennial grass pasture are critical factors in determining potential economic returns.

Response of cool-season grasses to defoliation has been evaluated in several studies (Belesky and Fedders, 1994; Bryan et al., 2000; Carlassare and Karsten, 2002; Gillen and Berg, 2005). Comparisons among studies can be difficult because of differences in species and intensity and frequency of defoliation. Furthermore, responses are likely to change across climates, soil types, and soil water and soil fertility conditions. For irrigated pasture, rotational grazing through multiple paddocks is a commonly used management method (Nichols and Clanton, 1985). Defoliation recommendations for many pasture species are characterized by stubble heights based on plant morphology and animal production (Blaser et al., 1986; Hall, 1998). Stubble height, an index of herbage remaining after grazing or cutting, has been widely used for native plant communities and seeded stands of grass (Clary and Leininger, 2000; Kalmbacher et al., 1986).

Mixtures of several different grasses are commonly used for irrigated pasture in the Central Great Plains with orchardgrass, meadow bromegrass, smooth bromegrass, and creeping foxtail used as the primary species. Although grown in mixtures, these individual species likely differ in their production potential and response to defoliation height. Research on orchardgrass has demonstrated that relatively small differences in defoliation height caused significant variations in plant productivity and persistence (Griffith and Teel, 1965; Clark et al., 1974; Mislevy et al., 1977). Frequent and severe defoliation of this species can cause stands to deteriorate (Griffith and Teel, 1965). Management recommendations for smooth bromegrass include avoidance of cutting or grazing to less than about 10 cm (Lamond et al., 1992). Brummer and Moore (2000) reported that it had less persistence than orchardgrass under severe, continuous grazing. Meadow bromegrass and creeping foxtail have been lesser-studied species with respect to specific recommendations for defoliation height and/or frequency. Meadow bromegrass has been reported to decline in density with heavy stocking rates under both continuous and rotational systems (Popp et al., 1997), while creeping foxtail tolerates close defoliation (Rumberg and Siemer, 1976). For many species, defoliation height also will affect tillering and rate of regrowth. When tiller apices of smooth bromegrass are removed by cutting, subsequent growth must develop from buds at or below ground level (Casler and Carlson, 1995).

For irrigated, cool-season grass pasture, a primary issue is identification of grazing management strategies that will optimize herbage production, persistence, and stand quality. This includes the critical question of when to make pasture rotations. Quantifying the combined effects of stubble height and frequency of defoliation would be valuable for the development of a decision-support tool for making pasture rotations. The objectives of this study were to determine the production potential of four irrigated cool-season grasses and their response to clipping stubble height.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
This study was conducted during 2003 and 2004 at the University of Nebraska West Central Research and Extension Center located near North Platte, NE (41°05' N, 100°46' W, elev. 890 m). Average annual precipitation is 502 mm with 84% falling from April through October. Average monthly temperatures are –5°C in January and 23.5°C in July. The study site was located on a Cozad silt loam soil (fine-silty, mixed, mesic Typic Haplustoll).

Monoculture stands of ‘Peak’ smooth bromegrass, ‘Latar’ orchardgrass, ‘Garrison’ creeping foxtail, and ‘Regar’ meadow brome established in fall 2001 were used for the study. Plots for each species measured 1.5 by 6 m and were arranged in a randomized complete block design with four replications. Plots were harvested four times in 2002 and stands of all species were rated as excellent. In 2003 and 2004, a seasonal total of 280 kg ha–1 of N was topdressed as ammonium nitrate in split applications of: 140 kg ha–1, 30 March; 56 kg ha–1, 1 July; and 84 kg ha–1, 15 August. Total N applied and application timing followed recommendations for irrigated cool-season grasses (Rehm et al., 1975; Moline et al., 1974). Irrigation water was applied via sprinklers to maintain root zone soil moisture at a minimum of 50% of available field capacity. Soil moisture profile was determined in each plot weekly from April through October using the time domain reflectometry method. Access tubes were located in the center of each plot and soil moisture measurements (% volume) were recorded at 20-cm increments to a depth of 100 cm. Irrigation and fertilizer management resulted in excellent cool-season grass growth throughout the April through October growing season. Irrigation water was applied 29 times in 2003 (598 mm total) and 24 times in 2004 (456 mm total). Rainfall during the growing season was 380 mm in 2003 and 516 mm in 2004.

Defoliation treatments began in April 2003, at the beginning of the second growing season. In each plot, two permanently located quadrats (19 by 100 cm) were established for each stubble height treatment. Quadrats were centered lengthwise on a drill row and the perimeter marked with landscape staples. In 2004, quadrats were established in new locations within the 1.5- by 6-m plot. During the year before application of treatments, quadrat locations were harvested (10-cm cutting height) in mid-May, June, August, and October. Treatments consisted of repeated hand-clipping to stubble heights of 7, 14, and 21 cm. These treatments were randomly assigned to quadrats. To reduce any effects of canopy shading or rhizomatous grass growth, a 30-cm wide border area surrounding each quadrat also received the assigned clipping treatment. The initial and all subsequent clipping events occurred when plant growth reached a target canopy height of 35 cm. The resulting percentage of canopy height removed was 80, 60, and 40% for the 7-, 14-, and 21-cm stubble height treatments, respectively. Depending on species, this height of initial growth was attained during the 3rd or 4th week of April each year. Height measurements were made at several locations across each quadrat area using a Plexiglas plate (0.05 m2) and a meter stick. When about 10% of leaf blades or inflorescences were touching the plate, the height was recorded. During the spring period of rapid growth, height estimates were made daily to identify individual quadrats that had reached the target height of 35 cm and were ready to be clipped to their respective treatment height. Height estimates were made every 2 to 3 d as growth slowed later in the growing season. With clipping dependent on plant growth reaching the target height, the interval between clippings varied over the growing season following typical seasonal growth patterns. The average number of times quadrats were clipped during a growing season was 6.7, 12.8, and 17.8 times for the 7-, 14-, and 21-cm stubble height treatments, respectively. Clipped herbage was collected, bagged, and dried at 60°C to a constant weight. Density of live tillers was determined on 31 October of each year from counts made in two randomly located, 19- by 20-cm sections of each quadrat. After determining tiller density, herbage was clipped to its respective stubble height, regardless of whether plant growth had reach the 35-cm target height or not. Herbage was then clipped to ground level and collected, dried, and weighed.

Total DM production was calculated as the sum of the weight of herbage collected during clipping throughout the growing season plus the residual herbage clipped to ground level on 31 October. Growth rate (kg ha–1 d–1) was calculated for each clipping interval across the growing season by dividing weight of herbage by the number of days in that interval.

For each species and treatment, clipped herbage samples were combined into four harvest periods: (i) 15 April to 31 May, (ii) 1 June to 15 July, (iii) 16 July to 31 August, and (iv) 1 September to 31 October. Residual herbage clipped to ground level on 31 October was not included. Samples were ground, first through a Wiley mill (Model 4, Arthur H. Thomas Co., Philadelphia, PA) equipped with a 2-mm screen and then through a Cyclone mill (Model MS, UD Corp., Boulder, CO) using a 1-mm screen. Samples were analyzed for nutritive value each year individually via calibrated near infrared reflectance spectroscopy by the Soil and Plant Analytical Laboratory at the University of Nebraska using a Foss NIRS system (Model 5000, Foss, Eden Prairie, MN). Calibration samples from each year (36 samples from 2003 and 44 samples from 2004) were selected based on spectra files of all samples from each year using WinISI II Version 1.50 software from Infrasoft International, LLC, Port Matilda, PA. Calibration samples were analyzed for in vitro dry matter digestibility (IVDMD) (Marten and Barnes, 1980). Nitrogen content of calibration samples was determined by the LECO combustion method (Model FP 2000, LECO Corp., St. Joseph, MI) and CP calculated as N x 6.25.

All statistical analyses were conducted with PROC MIXED for a randomized complete block design (Littell et al., 1996). Fixed effect factors were year, species, and stubble height for response variables of total production and tiller density. For nutritive quality data, clipping period was treated as a repeated measure. Blocks were considered random. Mean separation was performed using the protected least squares means (LSMEANS) procedure. Significance was declared at P ≤ 0.05. Regression analysis (PROC REG) was used to evaluate growth rate (dependent variable) and day of year (independent variable) relationships (SAS Institute, 1999). Contrasts were incorporated into the analysis of variance model to test for linear, quadratic, and cubic effects of stubble height treatments on each species.


   RESULTS AND DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Clipping Yield and Total Dry Matter Production
Stubble height effects on the yield removed at each clipping event were not consistent over species (Tables 1 and 2). For creeping foxtail, yield at the 14- and 21-cm stubble heights was less than that observed for the other three species at those stubble heights (P < 0.05). Rumberg and Siemer (1976) reported creeping foxtail to have quick recovery after harvest because only about 20% of all tillers are reproductive. This was consistent with our observations that a portion of creeping foxtail tillers were reaching the 35-cm target height, but the density of herbage in the upper canopy was less than that of the other three species. Meadow bromegrass yield at the 21-cm stubble height was greater than the other species. Clipping interval differed at each stubble height and averaged 22.5, 12.5, and 9.1 d for the 7-, 14-, and 21-cm stubble heights, respectively (P < 0.05, Table 1). The 7-, 14-, and 21-cm stubble heights were equivalent to removing 80, 60, and 40% of canopy height, respectively, and clipping interval days were not proportional to the percentage of canopy height removed. The 7-cm treatment had twice as much canopy height removed as the 21 cm treatment but it took 2.5 times as many days to reach the 35-cm target height. This was likely due to a greater proportion of tillers having tiller apices removed by clipping and minimal leaf area remaining.


View this table:
[in this window]
[in a new window]

  		Table 1. Significance of main effects and interactions within analysis of variance for harvest yield, clipping interval, total DM production, tiller density, and nutritive characteristics of four irrigated, cool-season grasses.

 

View this table:
[in this window]
[in a new window]

  		Table 2. Yield at each clipping event for four irrigated grasses when clipped to 7-, 14-, and 21-cm stubble heights after attaining a 35-cm target height, averaged across 2003 and 2004{dagger}.

 
Clipping stubble height effects and species responses for total annual DM production were consistent over years (Table 1, P > 0.05). Similar DM production between years was expected because the stands were well established and soil water and fertility were not limiting. Total water (irrigation applied + rainfall) during the growing season was 978 mm in 2003 and 972 mm in 2004. Overall, cool-season grass production (Table 3) was comparable with production observed in Utah under similar irrigation and N fertility levels (Waldron et al., 2002). There was a significant interaction between species and stubble height on total DM production. For the bunchgrasses (orchardgrass and meadow bromegrass), DM production was similar at the 14- and 21-cm stubble heights (22.22 Mg ha–1), but significantly greater than production at the 7-cm stubble height (14.03 Mg ha–1). In contrast, DM production of the rhizomatous grasses (smooth bromegrass and creeping foxtail) was significantly greater at each successively higher stubble height. For all species, low productivity at the 7-cm stubble height may be a function of low tiller appearance and leaf replacement rates due to inadequate photosynthate. The increasing yield response with higher stubble heights for the rhizomatous species is consistent with the relationship between leaf area index and net photosynthesis (Pearce et al., 1965). Average leaf length of both bunchgrass species is greater than that of smooth bromegrass and creeping foxtail (Barkley, 1986). For the bunchgrasses clipped to the 14-cm stubble height, there may have enough leaf area remaining to have no negative effect on growth.


View this table:
[in this window]
[in a new window]

  		Table 3. Total DM production of four irrigated, cool-season grasses as affected by repeated clipping to 7-, 14-, and 21-cm stubble heights after attaining a 35-cm target height, averaged across 2003 and 2004.

 
Although there have been numerous studies that evaluated stubble or grazing height effects on total production, most have been under rainfed conditions. Direct comparison of results between studies can be difficult to make because of differences in species, stubble height, and time interval between clipping or grazing. Some studies used a defined number of days as a clipping interval, whereas in others, clipping occurred when growth reached a specific target canopy height. In a mixed pasture dominated by orchardgrass, Carlassare and Karsten (2002) compared tall (27 cm grazed down to 7 cm) and short (20 cm grazed down to 5 cm) grazing regimes and reported greater total orchardgrass herbage harvested with the tall grazing regime. Belesky and Fedders (1994) reported improved orchardgrass yield when 75% of canopy height was repeatedly removed (20 cm clipped to 5 cm) compared with removing 50% of canopy height (20 cm clipped to 10 cm or 10 cm clipped to 5 cm). Similarly, Washko et al. (1967) reported that clipping orchardgrass that reached a 30- to 45-cm canopy height to a 3.5-cm stubble height rather than a 8.5-cm stubble height resulted in a greater yield. This is contradictory to our results, but clipping treatments were not identical and environmental conditions differed. In a study of tall fescue [Lolium arundinaceum (Schreb.) S.J. Darbyshire] by Burns et al. (2002), a range of target canopy heights and clipping heights were used to calculate daily growth rates and total production. Generally, tall fescue growth responded favorably to close clipping, but harvesting too frequently (shorter canopy target heights) was detrimental to DM production. For several Triticeae grasses, Gillen and Berg (2005) reported production was greater using a 10-cm stubble height compared with 15 cm, but noted that stands cut at the 10-cm height declined more rapidly than those cut at 15 cm. Malinowski et al. (2003) reported greater wheatgrass {[Agropyron cristatum (L.) Gaertn. x A. desertorum (Fisch. ex Link) J.A. Schultes] and Thinopyrum spp.} forage harvest at 7.5 vs. 15 cm for 1 or 2 yr depending on the species.

The clipping regime and stubble height treatments used in our study were designed to emulate an array of grazing management scenarios. Responses observed in clipping studies can sometimes vary from those observed in grazing studies (Binnie and Chestnutt, 1991). Stubble height and spatial distribution of grazing are likely to vary across paddocks because of selective herbivory. However, information on basic plant response to a variety of clipping regimes is valuable for development of defoliation strategies that can be evaluated under grazing conditions.

Growth Rates
A cubic regression model resulted in the best fit of daily growth rate across the growing season for all species and stubble height treatments (P < 0.05, Fig. 1 ). Typical of cool-season grasses in this environment, growth rates were greatest during spring, least during mid-June through mid-August, and increased slightly during late August and September. Average high temperature during July at this location is 31.3°C, which limits growth of cool-season species. Irrigation stimulated moderate growth (40–60 kg ha–1 d–1) during the hottest part of the summer. In contrast, when grown under rainfed conditions in semiarid areas, these species will have minimal summer growth or even become dormant because of dry conditions (Moser and Hoveland, 1996). Within the growing season, stubble height effects on growth rate varied by species. The initial 7-cm clipping events during spring reduced meadow and smooth bromegrass growth rate compared with the 14- and 21-cm stubble heights, and that trend continued throughout the growing season (Fig. 1). For orchardgrass, the most noticeable impact of the 7-cm stubble height began in July and continued through the remainder of the growing season. Stubble height effects on creeping foxtail growth rates were less discernible; however, measurable cumulative effects were reflected in total production (Table 3).


Figure 1
View larger version (34K):
[in this window]
[in a new window]

  		Fig. 1. Growth rate of four irrigated, cool-season grasses as affected by repeated clipping to 7-, 14-, and 21-cm stubble heights after attaining a 35-cm target height, 2003 and 2004. Curves were derived from cubic regression models. For clarity, actual values are not shown. All models were significant at P < 0.01.

 
Tiller Density
Species and stubble height had a significant effect on tiller density observed at the end of the growing season (Table 4). There was no interaction (P = 0.28) between species and stubble height indicating similar response for the four species. Among species, tiller density of creeping foxtail was greatest and tiller density of smooth bromegrass was the least. Increases in herbage production have been attributed to increases in tiller density or tiller weight, or a combination of both (Bircham and Hodgson, 1983). Tiller density under the 7-cm stubble height treatment was only 48 and 55% of that observed at the 21- and 14-cm heights, respectively (P < 0.05). This suggests that removing 80% of the canopy height dramatically reduced recruitment and/or survival of new tillers during the growing season. Published information on tiller density response to clipping or grazing height is limited for creeping foxtail and meadow bromegrass. However, several grazing and clipping studies reported orchardgrass stand deterioration over time due to closer or more frequent defoliation (Clark et al., 1974; Fales et al., 1995; Carlassare and Karsten, 2003). Stand losses of smooth bromegrass were more severe when cut at 4 cm compared with 10 cm (Paulsen and Smith, 1968). When low clipping height treatments were repeated over multiple years, Dobson et al. (1978) observed increases in invading species, particularly annuals. In irrigated pasture, maintenance of more dense swards with taller stubble height increases irrigation efficiency by reducing water runoff (Mundy et al., 2003). Irrigation water runoff can be a concern on heavier soils, particularly later in the grazing season as soil compaction increases.


View this table:
[in this window]
[in a new window]

  		Table 4. Tiller density of irrigated, cool-season grasses at the end of the growing season as affected by species and repeated clipping to 7-, 14-, and 21-cm stubble heights after attaining a 35-cm target height, averaged across 2003 and 2004.

 
Nutritive Value
There were no significant year or year interaction effects for CP concentration of herbage. However, significant species x stubble height, species x clipping period, and stubble height x clipping period interactions were present (Tables 1 and 5). For the species x stubble height interaction, stubble height had no effect on CP concentration of creeping foxtail; but CP was lower at the 7-cm height compared with the 14- and 21-cm heights for the other three species. This may be due to the relatively small proportion of creeping foxtail tillers that tend to become reproductive (Rumberg and Siemer, 1976). Smooth bromegrass herbage was significantly greater in CP than the other three species at all stubble heights.


View this table:
[in this window]
[in a new window]

  		Table 5. Crude protein (CP) of irrigated, cool-season grasses as affected by species, clipping period, and repeated clipping to 7-, 14-, and 21-cm stubble heights after attaining a 35-cm target height, averaged across 2003 and 2004.

 
For all species, the greatest CP concentration occurred during Period 1 (15 Apr.–31 May) and the least during Period 2 (1 June–15 July) (P < 0.05, Table 5). For creeping foxtail and orchardgrass, CP concentration was similar during Periods 3 (15 July–31 Aug.) and 4 (1 Sept.–31 Oct.). For smooth bromegrass, CP concentration was significantly greater during Period 3 compared with Period 4. However, for meadow bromegrass, Period 4 CP concentration was greater than Period 3. The level of CP concentration across periods was likely affected by N fertilizer application timing and amount. We used split-applications of ammonium nitrate with 140 kg ha–1 applied on 30 March, 56 kg ha–1 on 1 July, and 84 kg ha–1 on 15 August. Buxton et al. (1996) reported that CP concentration in grass forage is strongly influenced by soil N. Grass growth during June may have had less available N because of N uptake that occurred for the rapid growth during April and May. Plant phenology also affects quality characteristics (Buxton and Martin, 1989). We observed a portion of tillers entering reproductive stages under all stubble height treatments, particularly during June and that may have also contributed to lower CP concentration. Growth during September and October remained mostly vegetative.

Clipping stubble height did not affect herbage CP concentration during clipping Periods 1 and 2 (Table 5). However, during Period 3, CP was significantly lower at the 7-cm stubble height compared with the 14- or 21-cm stubble heights. During Period 4, each increasing stubble height resulted in significantly greater CP concentration. Herbage clipped at lower stubble heights would include a greater proportion of stem material that could lower CP concentration. For orchardgrass, Cherney and Cherney (2005) reported successive increases in CP and digestibility as clipping height increased from 10 to 25 cm by 5-cm increments.

Significant species x stubble height, species x clipping period, and stubble height x clipping period interactions were also present for IVDMD of clipped herbage (Tables 1 and 6). For smooth bromegrass, IVDMD was greater at each successively higher stubble height (P < 0.05). For orchardgrass, creeping foxtail, and meadow bromegrass, IVDMD was similar at 14- and 21-cm stubble heights and greater than that at the 7-cm stubble height. Similar to CP concentration, IVDMD of smooth bromegrass was greater than the other species at all stubble heights (P < 0.05). During clipping Period 1, IVDMD was greatest for smooth bromegrass and creeping foxtail, but during Periods 2 through 4, smooth bromegrass IVDMD was greater than the other species. Stubble height had no effect on IVDMD during Period 2; but during Periods 1 and 3, IVDMD was lower at the 7-cm height compared with the 14- or 21-cm stubble heights. During Period 4, each successive increase in stubble height resulted in significantly greater IVDMD. Although statistically significant species, stubble height, and clipping period interaction effects were found, CP levels were more than adequate to meet requirements of growing beef cattle regardless of species, stubble height or period (National Research Council, 1996).


View this table:
[in this window]
[in a new window]

  		Table 6. In vitro dry matter digestibility (IVDMD) of irrigated, cool-season grasses as affected by species, clipping period, and repeated clipping to 7-, 14-, and 21-cm stubble heights after attaining a 35-cm target height, averaged across 2003 and 2004.

 

   CONCLUSIONS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
The total DM production and nutritive value observed for these species supports their use in irrigated pasture in the Central Plains. Repeated clipping to a 7-cm stubble height resulted in the lowest DM production and end-of-season tiller density for all species. For orchardgrass and meadow bromegrass, DM production was similar at 14- and 21-cm stubble heights. However, smooth bromegrass and creeping foxtail had the highest DM production at a 21-cm stubble height. The magnitude of yield reductions caused by excessive defoliation (stubble height <14 cm) could result in unacceptably high forage costs. Leaving moderate amounts of residual herbage (stubble height ≥14 cm) between defoliations should favor herbage production and tiller density of our study species. Specific defoliation recommendations could vary depending if these species were grown in monocultures or mixtures.

Typical of cool-season grasses, we observed growth rates in May to be 250 to over 300% of those in mid-July indicating a need for flexible management. This might include lower stocking rates in summer compared to the spring, having alternative pasture available for the summer, or early season haying of a portion of the area. The results from this clipping study will provide the basis for development of defoliation regimes that will be tested in future grazing studies.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
A contribution of the Univ. of Nebraska Agric. Res. Div., supported in part by funds provided through the Hatch Act. Additional support was provided by Univ. of Nebraska Foundation Anna H. Elliott Fund.


   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 




This article has been cited by other articles:


Home page
 Agron. J.Home page
J. D. Volesky, B. E. Anderson, and M. C. Stockton
Species and Stockpile Initiation Date Effects on Yield and Nutritive Value of Irrigated Cool-season Grasses
Agron. J., June 16, 2008; 100(4): 931 - 937.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Volesky, J. D.
Right arrow Articles by Anderson, B. E.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Volesky, J. D.
Right arrow Articles by Anderson, B. E.
Agricola
Right arrow Articles by Volesky, J. D.
Right arrow Articles by Anderson, B. E.
Related Collections
Right arrow Forage Management
Right arrow Root Growth

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
The SCI Journals Crop Science Vadose Zone Journal
Journal of Natural Resources
and Life Sciences Education		 Soil Science Society of America Journal
Journal of Plant Registrations Journal of
Environmental Quality		 The Plant Genome