Lowell E. Moser

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.

Stomatal variability of native warm-season grasses from the Nebraska Sandhills

Soil moisture deficit is usually the major limiting factor for herbage production in the Sandhills of Nebraska. We examined inter-population and interspecific variability in stomatal characteristics and drought tolerance in sand bluestem (Andropogon hallii Vitman), little bluestem [Schizachyrium scoparium (Michx.) Nash], prairie sandreed [Calamovilfa longifolia (Hook) Scribn.], and switchgrass (Panicum virgatum L.). Ramets were collected during the dormant season across an aridity gradient from east to west (ranging from 560 mm to 340 mm average annual precipitation) in the Sandhills of Nebraska. Plants were grown in individual pots under greenhouse conditions. Once plants were well established, stomatal characteristics were determined and stomatal conductance (gs) was measured through a dry-down period of no watering. Populations did not differ in stomatal characteristics across the gradient, except for stomatal density on the adaxial leaf surface of prairie sandreed and the abaxial leaf surface of sand ...

Prediction of leaf:stem ratio in grasses using near infrared reflectance spectroscopy.

Leaf:stem ratio of grass stands is an important factor affecting diet selection, quality, and forage intake. Estimates of leaf:stem ratios commonly are based on a labor intensive process of hand separating leaf and stem fractions. Near infrared reflectance spectroscopy (NIRS) has been used successfully to predict forage quality and botanical composition of vegetation samples. The objective of this study was to evaluate the use of NIRS to predict leaf:stem ratios in big bluestem (Andropogon gerardii Vitman), switchgrass (Panicum virgatum L.), and smooth bromegrass (Bromus inermis Leyss.). A total of 72 hand-clipped samples of each species was taken from seeded monocultures in eastern Nebraska throughout the 1992, 1993, and 1994 growing seasons. Leaf:stem ratio was determined first for each sample and then the entire sample was ground. Samples were scanned by a Perstorp model 6500 near infrared scanning monochromator. Three calibration equations were developed based on using 18, 36, and 54 (1/4, 1/2, and 3/4 of total samples, respectively) samples. These 3 calibration equations were used to determine the number of samples necessary to achieve an r2 of 0.70 or higher for each data set. Big bluestem and switchgrass had coefficients of determination (r2) of less than or greater than 0.69 for all calibration equations except for the equation using only 18 samples of big bluestem r2 = 0.60). Smooth bromegrass had a r2 ranging from only 0.06 to 0.14 for the calibration equations regardless of the number of samples used. Near infrared reflectance spectroscopy was a rapid means of estimating leaf:stem ratios in monocultures of big bluestem and switchgrass but it was not suitable for smooth bromegrass.

Carbohydrate and Organic Nitrogen Concentrations within Range Grass Parts at Maturity

Renner, F. G., and B. W. Allred. 1962. Classifying rangelands for conservation planning. U. S. Dep. Agr., Agr. Handbook 235. 48 p. Rogler, George A., and Howard J. Haas. 1947. Range production as related to soil moisture and precipitation on the Northern Great Plains. J. Amer. Sot. Agron. 39:378-389. Shiflet, Thomas N. 1970. Data acquisition, storage, and retrieval for range ecosystem planning. In Modelling and Systems Analysis in Range Science (Donald A. Jameson, ed.). Colo. State Univ., Range Sci. Dep. Sci. Series 5. p. 101-110. Blair, Robert M. 1959. Weight technique for sampling browse production on deer ranges. In Techniques and Methods of Mea&ring Understory vegetation. Southern and Southeastern Forest Exp. Stations, Forest Serv. U. S. Dep. Agr. p. 26-31. Dahl, B. E. 1963. Soil moisture as a predictive index to forage yield for the sandhills range type. J. Range Manage. 16:128-132. Hazell, Don B. 1965. The claypan range site in northern Osage County, Oklahoma. J. Range Manage. 18:94-96. Hilmon, J. B. 1959. Determination of herbage weight by doublesampling: Weight estimate and actual weights. In Techniques and Methods of Measuring Understory Vegetation. Southern and Southeastern Forest Exp. Stations, U. S. Dep. Agr. p. 20-25. Hulett, G. K., and G. W. Tomanek. 1969. Forage production on a clay upland site in western Kansas. J. Range Manage. 22:270-276. Rauzi, Frank. 1964. Late-spring herbage production on shortgrass rangeland. J. Range Manage. 17:210-212. Shoop, M. C., and E. H. McIllvain. 1963. The micro-unit forage inventory method. J. Range Manage. 16:172-179. Smoliak, S. 1956. Influence of climatic conditions on forage production of shortgrass rangeland. J. Range Manage. 9:89-91. Snedecor, George W., and William G. Cochran. 1967. Statistical methods (6th ed). Iowa State Univ. Press. Ames, Iowa. 593 p. Soil Conservation Service. 1971. National list of scientific plant names. U. S. Dep. Agr. Soil Conserv. Serv. Lincoln, Nebr. 281 p. (Litho).

Yield, Vigor, and Persistence of Sand Lovegrass [ Eragrostis trichodes (Nutt.) Wood] Following Clipping Treatments

Individual sand lovegrass [Erugrostis trichodes (Nutt.) Wood.] plants on a choppy sands range site in Nebraska’s Sandhills were clipped with 7 different harvest regimes for 3 years to determine critical defoliation times. After 3 years unclipped plants had the greatest survival rate and phnts harvested only once a year on June 10 or July 10 survived better than those with other harvest regimes. Top and root yields, new tiller counts, and total non-structural carbohydrate (TNC) levels were all reduced severely with multiple harvests within one year. Sand lovegrass plants cannot tolerate close defoliation at anytime of the year although a single June defoliation appeared to be less detrimental than August defoliation. Sand lovegrass is difficult to manage when it makes up a small component of a pasture. Sand lovegrass will probably persist and yield best in a rotational grazing program where it is defoliated only once a year and some leaf area remains at the close of the grazing period. Plants are normally short lived so they should be managed to allow seed production periodically. A grazing management program necessary to maintain small amounts of sand lovegrass in a mixture may not be practical. Sand lovegrass [Erugrostis trichodes (Nutt.)Wood.] is a warmseason perennial bunchgrass that is native to sandy soils in the central Great Plains. It is best adapted to north and east-facing slopes and in some instances can be prevalent on sands and choppy sands range sites (Vallentine 1967). Sand lovegrass is very palatable and highly preferred by livestock. Yearling steer gains per acre in Oklahoma were improved with sand lovegrass compared to other grasses (Smith 1947). Adding sand lovegrass to either big bluestem (Andropogon gerardii Vitman), switchgrass (Panicum virgatum L.) or sideoats grama [Bouteloua curtipendula (Michx.) Torr.] at Lincoln, Nebraska increased the average daily gain and beef production per acre although dry matter yield was generally not increased. In several seasons a relatively small amount of sand lovegrass in switchgrass pastures helped maintain animal performance’ late in the summer (Conard personal communication). Due to its palatability and bunchgrass growth habit it is often overgrazed by cattle. Sand lovegrass is difficult to maintain in stand even with good management and generally acts as a short-lived perennial. Recently, Vogel and Kindler (1980) have shown that a subterranean aphid (Geoicu urticularia Passerini) reduced yields of sand lovegrass. Severe clipping treatments reduced yield of range grasses (Owensby et al. 1974, Branson 1956, Stout et al. 1980, Perry and Chapman 1976). Tiller numbers are reduced with intensive clipping even though removal of the shoot apex should remove apical dominance and increase tillering if environmental conditions are favorable. Carbohydrate level is important in tiller initiation and continued development (Jameson 1963). Root production was more adversely affected than top production by The senior author is a professor and the ju@or avthor was an as

Tiller recruitment patterns and biennial tiller production in prairie sandreed

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

ceased), Department of Agronomy, Umvers~ty of Nebraska-Lmcoln, Ltncoln This report is published as Paper Number 6216, Journal Series. Nebraska Agricultural Experiment Station. 236; severe clipping treatments (Branson 1956, Crider 1955, Biswell and Weaver 1933). Adequate carbohydrate reserve is important in initial regrowth (White 1973). Close defoliation treatments, especially at critical stages in plant development, often deplete carbohydrate reserves in range grasses to a level that is not replenished readily (Kinsinger 1961, Perry and Chapman 1974, White 1973) and as a result future tiller production, yield, and plant persistence are adversely affected. A critical time to defoliate grasses was during shoot apex elevation (Branson 1953, Booysen et al. 1963, Pearson 1964, Vogel and Bjugstad 1968). Sand lovegrass begins growth earlier in the spring than most warm-season grasses (Vallentine 1967, Smith 1947) and elevates its shoot apex later than many other warmseason range grasses (Gilbert et al. 1979). Consequently, sand lovegrass should have a long vegetative period where it would be somewhat resistant to grazing. Once tillers of sand lovegrass begin elevation, the process is more rapid than wijh other grasses(Gilbert et al. 1979). The experimental objective was to determine if there was a time during the growing season when relative close defoliation was not especially detrimental to vigor and persistence of sand lovegrass. Materials and Methods A southeast facing slope with abundant sand lovegrass on a chdppy sands range site was selected for the study near Halsey, in Nebraska’s sandhills, in an area protected from grazing. The data from the Halsey, Nebr., weather station, which is approximately 6 km from the plots, indicated normal to above normal rainfall for all 3 years of the study. Precipitation averaged 95 mm, 20 mm, and 289 mm above the normal of 528 mm for 1975, 1976, and 1977 respectively. The plants were fairly widely spaced and there was little other vegetation for competition. In March 1975, 7 replications were marked out and 3 sets of individual uniform plants were selected within each replication for the 3-year study. Seven harvesting treatments were imposed on the plants. The harvesting dates were as follows: (A) unclipped; (B) June 10; (C) July IO; (D) August 10; (E) June 10 and July 10; (F) June 10 and August 10; and (G) June 10, July 10, and August 10. At the end of the growing season, around November 1, all plants were clipped again and the unclipped treatment was harvested. Plants were clipped at S-cm height, which represented a fairly close harvest especially on a southeast facing slope. Tillers were counted at first harvest and the new tillers, which would represent many of those that would be producing the following year, were counted on November 1. In the fall of 1975 1 set of plants were carefully dug to a depth of 18 cm and removed from the site in order to measure root yields and the carbohydrate level. The remaining 2 sets were subjected to the same harvest treatments in 1976 and one set of them was removed in the fall of 1976. In 1977 the last set was subjected to the harvest treatments for the third year and then removed in the fall. Yield and tiller data from 1975 were averaged JOURNAL OF RANGE MANAGEMENT 36(2). March 1993 T&b 1. Vigor and wrvivoi of nnd lovegram pia& with various huventfng tre~lrncdr at H&y, Nebr. V&WI are averages of 7.piants per treatment. Harvest dates First harvest date 1976 First harvest date 1977 November 1977 % alive % vigorous’ % alive %J vigorous % alive % vigorous Unclipped 86 86 86 43 June 10 71 71 57 43 57 43 July 10 86 86 86 71 57 29 August 10 71 43 43 43 43 43 June 10, July IO 57 43 43 I4 43 0 June IO, August IO 57 0 29 0 29 0 June IO, July IO, August IO 71 0 0 0 0 0 ‘Plants were considered vigorous if they had 5 or more tillers per plant. across ail 3 sets of plants and in 1976 data were averaged over the 2 remaining sets. Total nonstructural carbohydrates (TNC) were measured using a takadiastase enzyme and a copper iodimetric method (Smith 1969). The stem base material was used for TNC analysis (Perry and Moser 1974). The experiment was designed as a randomized complete block and Duncan’s new multiple range test was used to separate treatment means. only once, generally had more tillers than those plants clipped more than once. Significantly w.05) more tillers developed in the fall of 1976 on unclipped plants and those clipped once on June 10 than on the other treatments. At the conclusion of the study the same trend was evident except all of the plants were generally less