Steven S. Waller

Defoliation Effects on Yield and Bud and Tiller Numbers of Two Sandhills Grasses

Intensive grazing strategies for the Nebraska Sandhills must be based on time and frequency of defoliation of key warm-season grasses. A 3-year field study was conducted in the Nebraska Sandhills to determine the effects of defoliation on yield and bud and tiller number of sand bluestem [Andropogon gerardli var. paucipilus (ash) Fern.] and prairie sandreed [Calamovilfa longifolia (Hook.) Scribn.]. Defoliation (7 cm) treatments imposed on a 1.5 X 1-m plot were: a single defoliation on 10 June, 10 July, or 10 August; 2 successive defoliations on 10 June and 10 August; or 3 successive defoliations on 10 June, 10 July, and 10 August. All plots were harvested in October to obtain aftermath yield. Control plots were harvested only at the end of the growing season (October). Defoliation treatments were initiated in 1986, 1987, and 1988 on different plots and the effect of year of initiation as well as the effect of 3 successive years of repeated treatment (1986 plots) was evaluated. Annual dry matter (DM) yield, and bud and tiller numbers were measured. Following the initial year of treatment multiple defoliations increased yield of both grasses while bud and tiller numbers were similar to those of the control plants. After 3 years of repeated treatment, annual DM yield of sand bluestem for all defoliation treatments was lower than the control. A single defoliation of sand bluestem in August or a June-July-August defoliation reduced bud number compared to other treatments and the control. A June-August defoliation of prairie sandreed over a 3-year period increased annual DM yield compared to all treatments and the control although defoliation treatments reduced bud number. The optimum time and frequency of defoliation for annual DM yield and bud and tiller number was a single June or July defoliation for sand bluestem and a June-August defoliation for prairie sandreed.

Seedbank characteristics of a Nebraska sandhills prairie.

Evaluating seedbank ecology is critical for understanding plant community development and successional patterns and for identifying factors regulating population dynamics. The relationships among seedbank composition, seedbank depth, seed dormancy, and vegetative expression were evaluated for a range site on a Valentine fine sand soil (mixed, mesic Typic Ustipsamments) in the Sandhii Prairie. Twenty soil samples were collected at each of 2 depths (0 to 515 to 20 cm) in early June 1990 and 1991 from 12 macroplots (32 X 32 m) representing 3 range condition classes. A seed extraction and germination trial was conducted to determine the diversity, size, and germinability of the persistent seedbank. Seedling emergence was counted in a greenhouse, with and without a 1Cday prechilling(3 to 5°C) stratification treatment, to characterize seedbank dormancy. Fourteen grass species, 17 forb species, and Schweinitz flatsedge (Cyperus schweinitzii Torr.) were identified in the seed hank. Two additional genera (Carex and Euphorbia) also occurred in the seedbank. Only 10 species occurred in 8 or more macroplots in both years. Aboveground botanical composition was not correlated with (P > 0.10) seedbank species composition. More germinable seeds occurred in the 0 to 5 cm depth (P < 0.01) than the 15 to 20 cm depth. Also, the species diversity and seed number were greater in the shallower depth. Germination percentage was low for all types of vegetation. Lambsquarters (Chenopodiutn album L.) and annual eriogonum (Eriogonum annuum Nutt.) had the largest seedbanks, but germination was less than 6 % . Sand dropseed [Sporobolus cryptandrus (Torr.) Gray] and sand lovegrass [Eragrostis trichodes (Nutt.) Wood] were the most abundant perennial grasses and accounted for about 60% of the germinated seeds. Prechilling increased seedling emergence of grasses (P < O.Ol), forbs (P < O.Ol), and grass-like species (P < 0.01). Perennial grasses emerged first, forbs later, and grasslike species exhibited a bimodal emergence pattern. Based on germination percentage and emergence data, sand dropseed has the potential to colonize openings in the Sandbills prairie, possibly to the exclusion of many annuals occurring in the seedbank.

Defoliation Effects on Production and Morphological Development of Little Bluestem

Response of key warm-season grasses to time, frequency, and duration of defoliation is needed to develop grazing systems for the Nebraska Sandhills. A 3- year (1986 to 1988) study was conducted on a Valentine fine sand (mixed, mesic Typic Ustipsamments) at the Gudmundsen Sandhills Laboratory near Whitman, Nebraska, to determine the effect of defoliation on little bluestem [Schu 2 defoliations on 10 June and 10 Aug.; and 3 defoliations on 10 June, 10 July, and 10 Aug. Control plants were huvested only at the end of the growing season (October). All plots receiving summer defoliation were harvested in October to obtain aftermath yield. Treatments were initiated in 1986,1987, and 1988 and the effects of l,2, and 3 years of defoliation on dry matter (DM) yield, bud and tiller numbers, and tiller weight were measured. Experimental design was a split block with 4 plants as replications. In the first yeu of treatment annual DM yield from control plants was 2 times greater than that from all defoliated plants, but bud and tiller numbers were similar. In the second year of treatment, all treatments reduced annual DM yield and morphological development below that of the control if precipitation was subnonnal, but not if precipitation was above normal. In the third year of defoliation, with above-nonnd precipitation, single June or July defoliations produced DM yields and morphological development similar to that of the control, but single August or multiple defoliations generally reduced yield md development. Little bluestem may not persist if exposed to multiple, close defolitions during the growing season.

Dependence of 3 Nebraska Sandhills Warm-Season Grasses on Vesicular-Arbuscular Mycorrhizae

Vesicular-arbuscular mycorrhizae (VAM) are rare or absent in actively eroding soils of the Sandhills. The objective of this study was to determine if 3 major Sandhills warm-season grasses used in reseeding eroded Sandhills sites are highly mycorrhizal dependent, and evaluate the response of VAM at different phosphorus (P) levels. In 2 greenhouse experiments, sand bluestem [Andropogon gerardii var. paucipilus (Nash) Fern.], switchgrass (Panicum virgatum L.), and prairie sandreed [Calamovilfa longifolia (Hook) Scribn.] were grown in steam-sterilized sand in pots and inoculated with either indigenous Sandhills VAM, Glomus deserticola, or noninoculated. In the second experiment, VAM inoculated and control plants were treated with 5 P levels ranging from 5.4 to 27.0 mg P pot-1. Increasing levels of P fertilizer caused an initial increase, then dramatic decrease, in percentage colonization by Glomus deserticola but bad no effect on percentage colonization by indigenous Sandhills VAM. Mycorrhizal inoculated plants had a greater number of tillers, greater shoot weight, root weight, tissue P concentration and percentage P recovered, and a lower root/shoot ratio and P efficiency than noninoculated plants. Noninoculated sand bluestem had significantly lower shoot P concentration but greater P efficiency over all P levels thin any other grass-VAM treatment combination. Phosphorus fertilizer and VAM effects were often complementary at P levels up to 16.2 to 21.6 mg P pot-1, with no change or a decrease in plant responses at higher P levels. These 3 major Sandhills warm-season grasses were highly mycorrhizal dependent. Successful reestablishment of these on eroded sites in the Sandhills may be greatly improved if soil reinoculation with VAM occurred prior to revegetation.

Intake, digestion, and nitrogen balance of sheep fed shrub foliage and medic pods as a supplement to wheat straw

Abstract Low animal performance in arid and semi-arid areas of Morocco is mainly due to protein and energy deficiencies of available forages. A metabolism trial was conducted to evaluate the influence of supplementation with shrub foliage and medic ( Medicago sp.) pods on nitrogen (N) utilization by sheep fed low-quality roughage. Diets were wheat ( Triticum aestivum L.) straw (WS), WS plus alfalfa ( Medicago sativa L.) hay (AH), WS plus oldman saltbush ( Atriplex nummularia Lindl.) foliage (AN), WS plus blue wattle ( Acacia cyanophylla Lindl.) foliage (AC), and WS plus medic pods (MP). Alfalfa feeding level was set to provide a crude protein (CP) concentration of 90 g kg −1 dry matter (DM) in the diet. Shrub foliage and medic pods were offered ad libitum. Average intake levels for AN, AC, and MP were 37.2, 32.4, and 47.2% DM, respectively. Chemical composition and in vitro dry matter disappearance (IVDMD) were measured. Digestible dry matter intake (DDMI) was greatest ( P −0.75 ), followed by the alfalfa diet (30.0 g kg −0.75 ). Unsupplemented wheat straw and blue wattle diets had the lowest DDMI (21.3 g kg −0.75 ). The daily N balance for the supplemented diets was greatest ( P −1 ). A degradability trial was then conducted to investigate the rate and extent of DM and CP digestion of the same forages in the rumen. Forage samples were incubated for 0, 2, 4, 8, 12, 24, 48, and 72 h. Rate and extent of DM digestion were highest ( P P −1 ). Extent of CP degradation was greatest ( P

Browse foliage and annual legume pods as supplements to wheat straw for sheep

Abstract Cereal stubble and straw are widely used as animal feeds for sheep in arid areas of Morocco. The inherently low protein concentration of these feeds limits their intake and therefore potential of production. A 14-week feeding trial was conducted to investigate the effect of supplementation with browse foliage or medic ( Medicago sp.) pods on wheat ( Triticum aestivum L.) straw intake and ewe lamb live weight. Diets were wheat straw (WS), WS plus alfalfa ( Medicago sativa L.) hay, WS plus oldman saltbush ( Atriplex nummularia Lindl.) foliage, WS plus blue wattle ( Acacia cyanophylla Lindl.) foliage, and WS plus medic pods. Alfalfa and urea feeding levels were set to provide a crude protein (CP) concentration of 90 g kg −1 DM in the diet. Shrub foliage and medic pods were offered ad libitum. Atriplex and Acacia foliage supplementation resulted in the highest and lowest straw intake increases, respectively. These findings would contribute to explain why animals receiving Atriplex foliage in addition to wheat straw were the only ones to maintain weight over a 14-week period. Medic pod supplementation resulted in an insignificant weight loss. These results showed that foliage from palatable shrubs and medic pods can be effective protein supplements for livestock consuming wheat straw. Implementing such strategies would require that farmers plant oldman saltbush ( Atriplex nummularia Lindl.) shrubs on their private land and manage medic pasture to produce enough pods to be grazed in summer.

Renovation of seeded warm-season pastures with atrazine

Numerous warm-se8son p8stures b8ve been established in the last 30 years in the centr81 Great Plains. Some of these p8stures 8re old enough to verify that they can be 8bused by overgrizing 8s easily 8s native t8llgms.s prairies. Overgrazed warm-season pastures are invaded 8nd domirurted by cool-tuason grasses such 8s smooth brome (Bromus inermis Leyaa.) and Kentucky bluegrass (Poaprate~ L.), which diminishes the pasture productivity during the hot summer months. Since established warm-season grasses have greater tolennce to the herbicide ntrazine than coolseason grasses, the effectiveness of atrrzine applications in renovating invrded warm-season pastures was evaluated. A single, early spring application of atrazine (3.3 kg/ha) killed or suff~Gently suppressed the cool-season grasses so that surviving warmseason remnants were able to effectively re-establish the warmseason pasture in a single growing season without any loss in total pasture forage production. Lower rates of atrazine were not as effective, particularly if smooth brome ~8s the primary coolseason gr8ss. The single rtrazine application cost was 8pproximutely 25% of the seed cost associated with more conventional renovation. Pastures should not be grazed the treatment year but c8n be hayed rt the end of the growing season. The success of the practice is dependent on the presence of warm-season grass remnants. Spraying test strips in small fenced areas would be advisable before treating entire pastures. The eastern one-third of Nebraska was historically warm-season dominated True Prairie (Weaver 1965). Much of this land was plowed when the area was homesteaded for production of grain crops. Many of these areas have been seeded into warm-season pastures during the last 30 years. Usual seed mixtures consist of big bluestem (Andropogon gerardii Vitman), switchgrass (Panicurn virgatum L.), indiangrass (Sorghastrum nutans Nash.), sideoats grama [Boureloua curripendula (Michx.) Torr.], and little bluestern [Schizachyrium scoparium (Michx.) Nash]. These pastures and native rangeland are used primarily for spring and summer grazing for cow-calf herds. Some of the seeded pastures are old enough to verify that overgrazing is a factor on seeded pastures as well as on native tallgrass prairies. This results in invasion and dominance by smooth brome (Bromus inermis Leyss.) and Kentucky bluegrass (Pea pratensis L.). Recently Samson and Moser (1982) demonstrated the effectiveness of a spring application of atrazine [2chloro+(ethylamino)-6(isopropyl amino)-s-triazine] in shifting the composition of native rangeland dominated by Kentucky bluegrass to warm-season remnant big bluestem and sod-seeded switchgrass in a single growing season. Waller and Schmidt (1983) also shifted species composition in native rangeland from a Kentucky bluegrass and smooth brome dominated mixture to one dominated by remnant warmseason grasses, primarily big bluestem, by a single spring applicaAuthors are county extension agent, Cooperative Extension Service, Stapleton, Neb.; professor, Dep. of Agronomy; supervisory research geneticist, USDA-AR% graduate research assistant, Dep. of Agronomy; and associate professor, Biometrics and Information Systems Center, Univ. of Nebraska, Lincoln, 68583. Gates is currently assistant professor Iberia Research Station, Louisiana State University Agricultural Center, Jeanerette 70544. Research is based on a thesis presented by T.O. Dill to the faculty of the Graduate College of the Univ. of Nebraska in partial fulfillment of the requirements of the M.S. degree. This paper is published as Journal #7680 of the Nebraska Agricultural Experiment Station. The authors express appreciation to Mr. LaMoine Brownlee, (retired) supervisory agronomis!, Roman L. Hruska, U.S. Meat Animal Research Center, Clay Center, Neb., for his assistance in this research. Manuscript accepted 14 May 1985. 72 tion of atrazine. The purpose of this study was to determine if the seeded warmseason pastures could be renovated by using atrazine to suppress cool-season competition. A second objective was to evaluate the use of atrazine in stands dominated by smooth brome rather than Kentucky bluegrass. Materials and Methods Study Area This study was conducted in south central Nebraska 6.5 km west of Clay Center, on the Roman L. Hruska U.S. Meat Animal Research Center (MARC). The area is located within the True Prairie region of North America (Weaver 1965). The topography is gently rolling to nearly level. Soils are formed in deep windblown Peorian loess, with a subsoil of glacial outwash and till. The study site is mapped as Crete silt loam (fine, montmorillonitic, mesic, Pachic Arguistoll) thick solum, with 0 to 1% slope. Average annual precipitation is 69 cm with 80% occurring from April through September. Average growing season is 148 days and the normal grazing period on range is from 1 May to 3 1 October (Hammer et al. 1981). Pasture History There are 4,450 ha of seeded, warm-season grasses at MARC. The study areas were formerly cultivated areas with grasses seeded into milo [Sorghum bicolor (L.) Moench.] stubble in the spring of 1967. Seed mix species were ‘Pawnee’ big bluestem, ‘Nebraska 54’ indiangrass, ‘Trailway’ sideoats grama, ‘Nebraska 27’ sand lovegrass, [Eragrostis trichodes(Nutt.) Wood]; and a legume, ‘Empire’ birdsfoot trefoil (Lotus corniculatus L.). Annual spring and summer grazing was initiated in the spring of 1969 (L. Brownlee 198 1, personal communication). Spring applications of 73 kg/ ha ammonium nitrate (NHdNOs) were made in alternating years. The overgrazing required to maintain herd size in beef cattle genetic studies allowed smooth brome to dominate the pastures. Kentucky bluegrass and annual brome (Bromus spp.) also appeared. The study area had been in smooth brome for many years and buried seed and rhizomes may have contributed to its occurrence. Additionally, roadside vegetation at MARC is a mixture of smooth brome and Kentucky bluegrass, providing a potential seed source. These cool-season grasses could exploit the wet springs when the seeded warm-season grasses were dormant. A grazing exclosure in one pasture was used to statistically define treatment effects over a 2-year period following a single herbicide application, The grazed portion of the pasture was used to determine the magnitude of treatment response. Additional pastures were sprayed in 3 different years to qualitatively evaluate the year effect and provide evidence of repeatability of treatment response. Grazing Exclosure Treatments, an unsprayed control and 1.1 2.2, or 3.3 kg (ai)/ ha atrazine (AAtrex 4L), were applied on 2 April 1981 within the exclosure using a conventional pressurized boom (3 m) sprayer. The herbicide solution was mixed for the low rate using a carrier volume of 200 1 /ha. Multiple passes were used to achieve the 2 higher treatments. Prior to growth initiation and before treatment application, the dormant standing crop was removed by mowing and raking. This is a common practice when dormant vegetation restricts the ease and efficiency of herbicide application. For easier data collection and to reduce the effect of shading from previous JOURNAL OF RANGE MANAGEMENT 39(l), January 1966 year’s growth, standing crop was also removed prior to the 1982 growing season. The experimental design was a randomized complete block with 4 replications. Plots (experimental unit) were 3 X 6 m and separated by 3-m alleys. Species composition data were obtained in May and October 198 1 and 1982. Warm-season species were at the 2 to 5 leaf stage and easily distinguishable in May of both years. Stand density and potential production eliminated the use of more conventional line transects or ten-point frames. Ten l-m rods used as line transects were randomly placed at right angles on either side of a line running lengthwise through the center of each plot. Relative species composition was estimated by counting basal culms of each species that intercepted the line (sampling rod). At the end of the second growing season, species composition was also determined in a similar manner outside the exclosure in the grazed portion of the pasture. Five randomly located transects (100 m) radiated away from the grazing exclosure and ten l-m rods were randomly located perpendicular to each transect. The area immediately adjacent to the fencing was excluded. Yield (above-ground biomass) was estimated by hand clipping individual species within 3 quadrats at ground level on 3 harvest date in 1981 and 1982. Quadrats (0.2 m*) were randomly located in each plot on each harvest date. Quadrats clipped in a previous sampling were not resampled. Samples were ovendried in a forced air oven for 48 hours at 68O C and weighed. Preplanned, orthogonal contrasts were used to compare treatment responses (Steel and Torrie 1980). Analyses were on plot means of above-ground biomass for warm-season grasses, coolseason grasses, and total herbage. Warm-season herbage was the sum of individual yields of the key species: big bluestem and indiangrass. Cool-season herbage was the sum of the individual yields of the prominent species: smooth brome, annual bromes, and Kentucky bluegrass. Total herbage was the sum of yields for warm-season grasses, cool-season grasses, and all other aboveground vegetation. Regression analysis was used to evaluate consistency of response. A multivariate analysis was used to determine significant treatment by time interactions for shifts in relative species composition (Stroup and Stubbendieck 1983). Pasture Demonstration During the 3 years following treatment of the grazing exclosure, I1 entire pastures (approximately 65 ha each) received a single spring application of atrazine. Each pasture selected was characteristic of the grazing exclosure. In 1982,3 pastures were sprayed 10 April with 2.2 kg/ ha atrazine. Five pastures were similarly treated in 1983. Three pastures were sprayed in 1984 with 2.8 kg/ha. Pas

Canopy analysis as a technique to characterize defoliation intensity on Sandhills range.

Characterization of relationships between grazing and vegetation responses is difficult. Rapid and accurate measurement of pasture canopy characteristics would help clarify these relationships if canopy changes are directly related to grazing variables. The objectives of this study were (1) to evaluate use of the LI-COR LAI-2000 for quantification of changes in canopy density and architecture in response to defoliation by cattle, (2) to determine if changes in leaf area index (LAI) measured with the LAI-2000 are related to stocking rate, and (3) to determine advantages and drawbacks of the LAI-2000 for monitoring grazing impacts on canopy density and architecture. Leaf area index and mean foliage tilt angle were measured before and after defoliation by cattle (Bos taurus L.) in June, July, and August under 9 grazing treatments on Nebraska Sandhills range. Differences in LAI could be attributed to certain grazing treatments at various points throughout the season. Grazing treatment had little impact on mean foliage tilt angle. Change in LAI (delta LAI) had a significant negative relationship with stocking rate (P < or = 0.0001). The relationship detected for delta LAI versus stocking rate predicted LAI reductions of between 0.14 and 0.40 for the range of stocking rates studied; stocking rate accounted for 62% of the decrease in LAI caused by grazing. When configured for the Sandhills canopy, the LAI-2000 provided a rapid and precise method for quantification of the degree of defoliation associated with grazing.

Weed suppression with grazing or atrazine during big bluestem establishment

Weed competition is a major factor causing warm-season grass seeding failures in rangeland and cropland. With a limited number of herbicides available for weed control, grazing may reduce competing vegetation in seedings and serve as an alternative to herbicides. Many immature needy forbs and grasses are palatable to cattle and contain high nutrient levels. Research was conducted (RCBD, 4 reps) comparing grazing by yearling cattle with chemical suppression [atrazine (6-chloro-N-ethyl-N’(methylethyl)-1, 3, S-triazine-2, 4-diamine)] for weed control in big bluestem (Andropogon

Leaf nutritive value related to tiller development in warm-season grasses.

Assessing nutritive value of key grass species in relation to plant development is essential for producers to efficiently manage livestock enterprises. Changes in nutritive value for tiller populations of 2 common Nebraska Sandhills grasses, prairie sandreed [Calamovilfa longifolia (Hook.) Scribn.] and sand bluestem [Andropogon gerardii var. paucipilus (Nash) Fern], in response to morphological development was evaluated at the Gudmundsen Sandhills Laboratory (GSL) during the 1990 and 1991 growing seasons. Morphological development was determined on a 40 to 60-tiller sample from each block (12 blocks in 1990 and 8 blocks in 1991) at ten-day intervals using a comprehensive staging system. In vitro dry matter digestibility (IVDMD), crude protein (CP), neutral detergent fiber (NDF) and lignin were determined for leaves and correlated with the morphological index (Mean Stage by Count), growing degree days and day of the year. Leaf NDF values of both species remained constant while leaf IVDMD declined throughout the summer indicating that decline in leaf IVDMD was caused by declining cell wall digestibility. Leaf IVDMD was influenced more by tissue aging than advancing morphological stage. Leaf CP was significantly different between years but not between species indicating leaf CP was largely influenced by environmental factors. In both species and for both years, leaf CP initially declined rapidly to low levels and then stabilized during the vegetative phase. Nutritive value of a single vegetative morphological stage over the growing season was similar to the leaf tissue of the tiller populations. Management decisions by producers depend on accurate assessment of changes in nutritive value during the growing season in tiller populations of these 2 important grasses.