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2006. Plant Management Network. This article is in the public domain.
Accepted for publication 8 August 2006. Published 17 November 2006.

Stockpiled Prairiegrass-Brassica Hybrid Mixtures Tolerate Repeated Defoliation in Autumn

D. P. Belesky, Research Agronomist, and J. M. Ruckle, Biologist, USDA-Agricultural Research Service, Appalachian Farming Systems Research Center, 1224 Airport Rd, Beaver, WV 25813-9423

Corresponding author: D. P. Belesky. david.belesky@ars.usda.gov

Belesky D. P., and Ruckle, J. M. 2006. Stockpiled prairiegrass-brassica hybrid mixtures tolerate repeated defoliation in autumn. Online. Forage and Grazinglands doi:10.1094/FG-2006-1117-01-RS.

Abstract

Stockpiling herbage helps redistribute nutrient availability and supplements quantity to sustain or finish livestock, depending on production objectives. In the Appalachian region of the USA, autumn stockpiled herbage is harvested, with little expectation for useable regrowth. Brassica spp. and prairiegrass (Bromus catharticus Vahl.) grow vigorously in autumn and tolerate defoliation providing a means to extend productivity in autumn. Mixed stands of prairiegrass and a brassica hybrid were established in late June of 2003 and 2004, with clipping begun in mid-September to determine production and nutritive value of regrowth herbage. Stockpiled prairiegrass-brassica hybrid stands tolerated repeated clipping, but stockpiled yield and the number of regrowth harvests decreased with increased duration of the stockpile interval, and no regrowth harvests were obtained when the stands were stockpiled until mid-November (130 days after planting). Regrowth accounted for as much as 35% of total yield in autumn when stockpiled harvests were made prior to late October (about 115 days after planting). Nutritive value expressed in terms of nonstructural carbohydrates, crude protein, and total digestible nutrients varied depending on year, but decreased with successive clippings or increased stockpiling duration. Herbage and nutrient yield of a prairiegrass-brassica hybrid mixed stand declined substantially after mid-October, in part, reflecting a shift in growth from leaf to tuber in the brassica component of the stand. Stockpiling stands of prairiegrass-brassica hybrid beyond mid-October essentially eliminates any meaningful regrowth production. Regrowth from stands clipped prior to mid-October extends the duration of growth of the mixture and makes a modest contribution to total herbage production in autumn.

Stockpiling Prairiegrass-Brassica Hybrid Mixtures

Stockpiled herbage can supplement quantity and redistribute availability to satisfy livestock nutrient requirements, reducing the need for purchased feed. Typically, autumn stockpiled herbage is used, with little expectation for regrowth production. The potential for regrowth depends somewhat on the sward components, when the stand is planted, when it is first defoliated, duration of stockpiling interval, and weather conditions.

In central Appalachia, ‘Matua’ prairiegrass grew vigorously in autumn (2), but was damaged by winter injury and succumbed to disease the following year. Mowing or grazing Matua prairiegrass in autumn improved winter survival (10), providing a source of herbage to extend the grazing season while benefiting survival. Prairiegrass cultivars with disease resistance, upright growth habit (‘Dixon’) (13), or ability to tolerate cold weather (‘Lakota’) (14) would be suited to growing conditions in many parts of the US, but response to autumn clipping is unknown.

Forage Brassica spp. also are well-suited to autumn stockpiling and have relatively high nutritive value (5,6,18). The high crude protein and relatively low fiber contents of brassicas are comparable to a concentrate feed source for livestock (18) and should be supplemented with fiber for efficient rumen microbe function and nutrient use by the grazer (4). Spring-planted brassicas tolerated repeated defoliation (8), with greater nutritive value when defoliated at 30-day compared to longer regrowth intervals (9).

Establishing a companion grass along with a brassica species could offset the potential shortage of herbage energy or fiber. A mixed stand of prairiegrass and brassica hybrid was established successfully in mid-summer, and was productive during autumn in southern West Virginia (3). Nutritive value of the stockpiled mixture was acceptable when expressed as TDN:CP and was attributable, in part, to the energy provided by prairiegrass (3). The accumulation pattern and nutritive value of herbage stockpiled during autumn argue in favor of prairiegrass or mixtures including prairiegrass where production stability rather than greater herbage quantity is a goal. Our objective was to determine the pattern of herbage production and nutritive value of a prairiegrass-brassica hybrid mixture sown in mid-season for stockpiling, and clipped repeatedly after the stockpile harvest was made, to extend herbage availability in autumn.

Establishing Prairiegrass-Brassica Hybrid Mixed Stands

Plots were established on an upland site of the Allegheny Plateau in southern West Virginia (37°46′N; 81°00′W; 2850-ft elevation above sea level). Soil was a Clymer series, channery loam (coarse-loamy, siliceous, active, mesic Typic Hapludult) on a hill-top site with < 5% slope. Two Roundup, glyphosate [N - (phosphono-methyl) glycine] applications (2.2 lb a.i./acre each) and tillage eliminated existing cool- and warm-season grasses. Soil supplied moderate amounts of P (about 13 lb/acre) and ample K (about 220 lb/acre), at an initial pH of 7.03 in the surface 6 inches of soil.

Plots were sown 28 June 2003, and on an adjacent site on 30 June 2004 to Dixon prairiegrass, ‘Tyfon’ brassica hybrid [turnip (Brassica campestris var. rapa L.)-Chinese cabbage (B. pekinensis (Lour.) Hanelt.)], or a mixture with both species (Fig. 1). Main plots (10 by 30 ft) were solid-seeded or mixed species and planting method (broadcast or sod-seeded) in replicated (three) blocks with main plots divided to accommodate seven 3- by 10-ft harvest strips. Stands were broadcast or no-till seeded (Tye Pasture Pleaser) to prairiegrass (40 lb seed/acre), brassica hybrid (8 lb Tyfon seed/acre), and the mix at 40 lb prairiegrass and 4.5 lb Tyfon seed/acre. The area was culti-packed after seeding. About 140 lb of N per acre as 19-19-19 fertilizer was applied to each plot in a split application with 70 lb of N at planting and 70 lb of N after the first clipping of a particular strip.

Fig. 1. Stands of brassica-hybrid, prairiegrass, and a prairiegrass-brassica hybrid mixture grow vigorously in autumn and are well-suited to stockpiling.

Measurements and Data Analysis

Clipping began 74 days after planting in 2003, and 63 days after planting in 2004. A new sampling area (yield strip) was cut from standing herbage at 14-day intervals throughout autumn in each year. A regrowth sample was cut from a previously clipped plot at 4-week intervals beginning four weeks after the initial clip (Table 1) and continued as long as mean canopy height was ≥ 10 inches. Each yield strip was harvested with a collection-bag equipped, rotary mower adjusted to allow a 4-inch residue height. Yield strips were assigned at random within a plot at the initial harvest. Herbage was dried at 140°F in a forced-air oven, weighed, and ground for nutritive value analysis. The botanical composition of each strip scheduled for harvest was determined prior to clipping. Botanical composition was determined visually using a point-intercept method (18) and principal stand components recorded. The "other species" category was presented as a summation of the species recorded and included white clover (Trifolium repens L.), plantain (Plantago spp.), Poa spp., tall fescue [Lolium arunidinaceum (Schreb.) Darbysh.], and orchardgrass (Dactylis glomerata, L.), with each representing less than 5% of the stand.

Table 1. Initial and regrowth harvest events (days after planting) presented as stockpile duration (days after planting) for prairiegrass-brassica hybrid stands in 2003 and 2004.

 ^x Regrowth harvests not made. Mean canopy height criteria not met.

 ^y Regrowth harvests made, but samples were damaged during processing.

Nitrogen was determined by combustion of dry plant tissue (Carlo Erba EA 1108 CHNSO analyzer, Fisons Instruments, Beverly, MA) and expressed as crude protein (CP;% N × 6.25). Total non-structural carbohydrates (TNC) were determined by an autoanalyzer (Alpkem RFA 300, Astoria-Pacific, Intl. Clackamas, OR) procedure (15). Computations for estimates of nutritive value, presented as total digestible nutrients (TDN), included TNC and CP, where TDN:CP = 2.19 (TNC:CP) + 3.99. Data for dry matter yield, nutrient yield, components of botanical composition, CP, TNC, and TDN were analyzed as a randomized complete block design containing three replications of each main plot, using PROC-MIXED procedures of SAS (SAS Institute Inc., Cary, NC). No data for the third clip (day 92 after planting) of 2004 are included in the analysis because samples were damaged during processing. Results for nutritive value parameters (CP, TNC, and TDN) were expressed as actual concentrations (%) and harvestable nutrient yield (concentration of a given parameter multiplied by herbage mass; lb/acre). Regression parameters were computed using PROC-REG procedures of SAS (SAS Institute Inc., Cary, NC). Botanical composition data were transformed prior to statistical analysis and back-transformed for presentation. Harvest dates were considered fixed effects and replication random in the model. Years were analyzed separately within the mixed model because χ² test indicated heterogeneity of variance.

Rainfall and Temperature

Precipitation patterns differed between years with relatively dry conditions occurring for most of both growing seasons when bi-weekly means were compared to the 30-year mean (Fig. 2). Overall, total precipitation in 2003 (20.5 inches) and 2004 (19.8 inches) was similar, but much less than the 30-year mean (32 inches) for the interval. Relatively low amounts of precipitation shortly after planting in late June affected stand establishment in 2003 but precipitation was abundant in July of 2004 (3). Minimum air temperatures were slightly above the long-term mean in 2004, while maximum air temperatures were similar to the long-term mean early, and tended to be greater than the long-term mean late in the season in each year. The autumn growth intervals of both years were essentially frost-free.

Fig. 2. Biweekly and 30-year mean maximum and minimum air temperatures, and precipitation for the period from 1 July through 15 December 2003 and 2004, at Beckley, WV.

Stand Composition of Prairiegrass-Brassica Hybrid Mixtures

Stand composition differences associated with planting method were not significant; therefore, botanical composition of the stand is presented as a mean of planting methods (Fig. 3). Occurrence of weeds was less in regrowth than in initial harvest herbage and the proportion of prairiegrass increased in the stand. The proportion of prairiegrass doubled in the regrowth of mixed stands when the first cut was made 74 (2003) or 63 (2004) days after planting. The proportion of prairiegrass increased slightly in regrowth harvests when first cuts were made 104 or 117 days after planting. The proportion of brassica hybrid in the stand was constant or decreased slightly when comparing initial and final regrowth harvests in 2003 and 2004. Increases in prairiegrass as a fraction of the stand were compensated by a decrease in the proportion of weeds. Weeds represented as much as 45% of the stand early in the 2003 growth interval, especially at the initial harvest. Sown components represented at least 90% of the stand in 2004 and reflect favorable growing conditions occurring immediately after sowing that year (3).

Fig. 3. Sward composition of the initial (I) and final regrowth (F) of a prairiegrass-brassica hybrid mixed stand during 2003 and 2004. Values representing the number of contacts (as a percentage) are the mean of three replicates.

Cumulative Yield During the Stockpiling Interval

The influence of harvest date on cumulative yield, CP, TNC, and TDN concentrations of the prairiegrass-brassica hybrid mixed stand was significant (P < 0.01) in 2003 and 2004, reflecting fluctuations and changes in ambient conditions in autumn and the growth patterns of the stand components. Stockpiled prairiegrass-brassica hybrid stands could be clipped for regrowth production in autumn, provided the initial clip occurred before the end of October (about 120 day after planting) (Fig. 4). Cumulative yields ranged from about 2400 lb/acre when clipping began 74 days after planting in 2003 to 135 lb/acre when the initial clip was made 157 days (late November) after planting. Yields ranged from about 3750 lb/acre for stands clipped 63 days after planting in 2004 to 946 lb/acre when clipped 152 days after planting. Declines in herbage mass during autumn could be associated with leaf loss caused by weathering, susceptibility to disease and insect damage (9), and allocation of photosynthate to tubers in brassica hybrid. Yields were less when compared to well-managed tall fescue grown and stockpiled for autumn use in the Piedmont of Virginia (15). Details of stockpiled herbage productivity and nutritive value data are presented elsewhere (3).

Fig. 4. Dry matter yield of a prairiegrass-brassica hybrid mixed stand in 2003 and 2004 as a function of planting method. Values are means of three replicates. Bars surmounted by different letters differ (P < 0.05).

Regrowth contributed from 35 to about 10% of cumulative yield (Table 2). No regrowth harvests were made when stands were stockpiled for more than 117 days after planting. The number of regrowth harvests differed between years and was probably a function of stand establishment and growth associated with weather patterns each year. Mixed stands clipped 74, 88, or 102 days after planting in 2003 produced two regrowth harvests each. Making the first stockpile harvest 63 days after planting led to three regrowth harvests, and clipping 75 or 92 days after planting in 2004 led to two regrowth harvests. Increasing the duration of the stockpile interval decreased total herbage mass yield and decreased the number of regrowth harvests in 2003 (Fig. 4). Delaying the initial harvest until 104 days after planting did not significantly influence DM production in 2004, reflecting the distribution of rainfall that year. Irrespective of actual herbage mass, 95% of total yield was achieved prior to the end of October. The proportion of regrowth production relative to total stand production during autumn was similar to that obtained for swards first clipped in spring (10). Depending on when and how often stands are grazed or clipped in autumn, herbage production in the subsequent growing season could be affected, although beneficial effects appear to be species-specific (12).

Table 2. Fraction of cumulative yield (expressed as a percentage) attributable to regrowth harvests (denoted by days after planting, DAP) of stockpiled prairiegrass-brassica hybrid mixtures in 2003 and 2004.

 ^x No regrowth harvests made. Mean canopy height criteria not met.

 ^y ND = no data. Samples damaged during processing.

Much of the existing information concerning prairiegrass productivity and nutritive value is based on the cultivar Matua that was susceptible to winter injury and required careful autumn management to sustain the stand. Dixon prairiegrass regrew and was productive in growing seasons subsequent to the stockpiling interval. The nutritive value and productivity of Dixon appears to be comparable to Matua, and has the added advantage of persistence under winter conditions in a humid-temperate climate.

Nutritive Value

Stockpiling influenced concentrations and nutrient yield of CP, TNC, and TDN for prairiegrass-brassica hybrid mixtures. Some data from monospecific stands of prairiegrass and brassica hybrid are presented for comparative purposes (Fig. 5). Crude protein concentrations of prairiegrass-brassica hybrid stands increased with delayed initial (stockpile interval) and successive (regrowth) harvests during autumn (Table 3). Crude protein concentrations ranged from a low of 7.42% in early-season stockpile to about 20% CP in a number of regrowth harvests of the mixture; but in some cases delayed autumn harvest decreased CP concentration of Matua prairiegrass (7). The sustained CP concentrations we observed were probably attributable to application of 70 lb of N per acre after the initial, or stockpile, harvest. While we did not determine nitrate concentrations in herbage, applying N in autumn when plant growth is slow could lead to nitrate accumulation in herbage leading to animal health concerns. Crude protein expressed in terms of harvestable yield showed that Dixon prairiegrass CP yield increased slightly in autumn of 2003, but in 2004 CP yield was stable until about 130 days after planting, declining thereafter. Monoculture brassica hybrid CP yield was low in 2003 and was similar to that of monoculture prairiegrass in 2004 (Fig. 5). Harvestable CP yield in the mixed prairiegrass-brassica hybrid stand declined both years and reflects the influence of brassica hybrid on total herbage production.

Fig. 5. Regression lines for cumulative harvestable yield of crude protein (CP), total non-structural carbohydrate (TNC), and total digestible nutrient (TDN) for initial and regrowth herbage of the prairiegrass or brassica hybrid monocultures, and the prairiegrass-brassica hybrid mixed stand in 2003 and 2004. Values are the mean of six replicates.

Table 3. Means ± standard error of the mean for crude protein (%) in initial and regrowth harvests for prairiegrass- brassica hybrid stands in 2003 and 2004.

 ^x No regrowth harvests made. Mean canopy height criteria not met

 ^y ND = no data. Samples damaged during processing.

Increasing CP concentrations coincided with declining TNC concentrations in stockpiled and regrowth herbage of monospecific and mixed species stands. The TNC concentrations of prairiegrass-brassica hybrid stands declined with delayed initial and with subsequent regrowth harvest (Table 4). Concentrations ranged from 17.0 to 3.6% in 2003 and from 20.7 to 6.0% in 2004. The harvestable yield of TNC was relatively stable in the prairiegrass monoculture in 2003 but varied in 2004 (Fig. 5). Harvestable TNC yields in the brassica hybrid monoculture and the prairiegrass-brassica hybrid mixed stand declined during autumn in both years. The relatively large amount of CP compared to TNC could lead to inefficient N use by the grazer because of insufficient energy in herbage. Prairiegrass sustained availability of TNC (TNC yield) throughout autumn.

Table 4. Total non-structural carbohydrates (means ± standard error of the mean) concentrations (%) in initial and regrowth harvests for prairiegrass-brassica hybrid.

 ^x No regrowth harvests made. Mean canopy height criteria not met

 ^y ND = no data. Samples damaged during processing.

The TDN of prairiegrass-brassica hybrid herbage was greater in regrowth material relative to TDN of the initial stockpile herbage (Table 5). TDN ranged from a low of 45% for herbage stockpiled the longest in 2003 to 82% for regrowth herbage from early stockpile treatments, and tended to increase with increasing duration of the stockpile interval. The TDN of herbage ranged from 61% for herbage stockpiled and clipped 117 days after planting to 86% in regrowth herbage from the same treatment in 2004. The TDN tended to decrease with increasing duration of the stockpiling interval in 2004. The TDN yield of the prairiegrass monoculture was stable and somewhat greater than that of the brassica hybrid monoculture or the prairiegrass-brassica hybrid mixed stands throughout autumn in both years. Differences in nutrient yield, including CP, TNC, and TDN, were greater in 2004 than 2003 because of differences in production between years. Application of N after the first harvest sustained CP concentration but not yield. Stockpiled and then repeatedly defoliated prairiegrass monocultures sustained harvestable TDN yield in autumn.

Table 5. Means ± standard error of the mean for total digestible nutrients (%) in initial and regrowth harvests for prairiegrass-brassica hybrid stands in 2003 and 2004.

 ^x No regrowth harvests made. Mean canopy height criteria not met.

 ^y ND = no data. Samples damaged during processing.

In general, nutritive value of mixed stands in autumn met accepted recommendations for livestock, regardless of when defoliation occurred. Assuming that stocker cattle would be grazing the mixed stand, herbage mass would be likely to satisfy intake early in 2004 but fall short for most of 2003. Herbage mass probably would meet small ruminant production needs. Greater herbage mass satisfies the acquisition of herbage and bite mechanics of grazers. Herbage mass interacts with nutritive value to influence grazer performance. The nutritive composition would not compensate for declining productivity after mid-October, ultimately leading to insufficient dry matter (intake) and compromised grazing animal performance.

Summary

To our knowledge, this is the first report presenting the nutritive value of regrowth herbage from stockpiled prairiegrass-brassica hybrid mixtures. Establishing prairiegrass-brassica hybrid stands for stockpiling provided an extended duration of herbage production in autumn, some regrowth from stands stockpiled for no more than 117 days after planting, and the potential for continuing production from the prairiegrass component of the stand. The pattern and composition of nutritive value occurring in regrowth differed from that of stockpiled herbage (3) or brassica (8,18) and prairiegrass stands (2,10), reflecting differences in local growing conditions interacting with plant development.

Acknowledgments

The authors thank M. Huffman, E. Mathias, and C. Ellison for technical assistance with plot maintenance and sampling, and Dr. E. Felton and Mr. E. Nestor, West Virginia University, for nutritive value estimates. Also thanks to D. M. Burner, J. MacAdam, M. A. Sanderson, and anonymous reviewers for excellent suggestions to improve the text.

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