Gene Towne

Long-term effects of annual burning at different dates in ungrazed Kansas tallgrass prairie.

Ungrazed tallgrass prairie plots in the Kansas Flint Hills have been burned annually at 4 different dates since 1928. Time of burning markedly altered the physiognomy and was the crucial factor effecting vegetation change. Late-spring burning, coinciding with emergence of the warm-season perennial grasses, increased grass production and favored Andropogon gerardii and Sorghas- trum nutans. Burning in winter, early-spring, or mid-spring reduced herbage production and shifted vegetational composition by differentially favoring other species. Andropogon scoparius increased with mid- and early-spring burning, while perennial forbs and sedges increased with early-spring and winter burning. Amorpha canescens was favored by all burning treatments. Mulch buildup in unburned, undisturbed plots increased Poa pratensis and tree species and eventually reduced grass production. The long-term effects of annual late-spring burning, even in dry years, was not detrimental to herbage production, species composition, or total basal cover in tallgrass prairie. Tallgrass prairie is fire-derived and fire-maintained (Stewart 1951). Historically, fires were intermittent and occurred at nearly any time of the year (Jackson 1965). In the 1880s, cattlemen observed that transient steers gained more weight on burned than on unburned range, and as a result, grazing leases later mandated annual burning (Kollmorgen and Simonett 1965). Time of burn- ing, however, was of little concern, and most pastures were burned in January or February to stimulate earlier greenup. Although voluminous literature exists on vegetational effects from fire, few studies have acknowledged the importance of time of burning. Aldous (1934) initiated preliminary research on burning ungrazed tallgrass prairie at different dates. Subsequent reports on herbage production (McMurphy and Anderson 1963) and botani- cal composition (McMurphy and Anderson 1965) were nonrepli- cated, short-term studies in which the unburned control was mowed and raked annually, and included data from years when the plots were not burned. This paper compiles earlier research and adds recent data from undisturbed control plots to evaluate the importance of time of burning on herbage production and species composition in ungrazed tallgrass prairie over the past 56 years.

Cytokinins Effect on Protein and Chlorophyll Content of Big Bluestem Leaves

Four concentrations of the synthetic cytokinin benzyladenine (BA) were applied to ungrazed tallgrass prairie near Manhattan, Kans., in 1979 on 4 biweekly dates beginning in mid-June. Changes in chlorophyll and crude protein content of big bluestem (Andrepogon gerardi Vitman) leaves from the different treatments were monitored weekly from August until early October. BA did not significantly delay chlorophyll breakdown in big bluestem, but leaves sprayed with 5 ppm BA contained higher mean chlorophyll contents throughout the sampling period than leaves from other treatments. Big bluestem receiving 5,20, and 40 ppm BA applied in July had significantly more crude protein than untreated leaves, but 10 ppm BA had no effect on leaf protein content. Applying BA in mid-June was ineffective in maintaining. high crude protein levels, regardless of concentration. BA did not alter protein or total nonstructural carbohydrate content in big bluestem rhizomes, indicating that it had no deleterious effect on internal nutrient reserve cycles. Applying 5 ppm BA in either midor late-July significantly increased herbage yields the next year in comparison with yields of untreated plots. Forage quality of range plants rapidly decreases with increasing maturity. In tallgrass prairie, protein content falls below the subsistence level required for cattle about mid-July (Rao et al. 1973). At that time, organelles are being broken down and constituent materials exported from senescing leaves to other parts of the plant. Delaying translocation of metabolites from leaves could provide higher forage quality to grazing animals when nutritive values normally are declining. Richmond and Lang (1957) initially reported that exogenous cytokinins could delay senescence onset in detached leaves. Although plant senescence is a complex syndrome of biochemical and physiological changes, the antisenescent effect of cytokinins has generally been attributed, in whole or in part, to retarding chlorophyll loss, inhibiting protein degradation, preventing effluent carbohydrate translocation, and mobilizing metabolites. Most researchers who confirmed cytokinin-induced senescence deferral used excised leaves in the dark. The physiological response of cytokinins in vivo, however, are often less conspicuous and dramatic than in vitro, so the antisenescent role of cytokinins generally has been relegated to tissue cultures and post-harvest preservation of horticultural products. The potential for manipulating plant development was demonstrated by Fletcher (1969) when he discovered that exogenous cytokinins could retard senescence in intact bean (Phaseofus vulguris) leaves. Since then, other in vivo greenhouse studies have confirmed that phenomenon, but there is little diversity in plant species examined. We suspected that field applications of a synthetic cytokinin could delay senescence onset in perennial grasses. The senescent leaf becomes a major source of nitrogen following protein hydrolysis and and redistribution throughout the plant. In annuals, nutrients remobilized from senescing leaves are transrocated acropetally for seed development. Dalling et al. (1976) reported that 80% of the nitrogen in wheat (Triticum aestivum) Authors are research assistant and research range scientist, Department of Agronomy, Kansas State University, Manhattan. This report iscontribution No. 81-426-j Department of Agronomy, Kansas Agricultural Experiment Station, Manhattan 66506. Manuscript received June 8, 1981. JOURNAL OF RANGE MANAGEMENT 36(l). January 1983 grain originated from senescing leaves. But in perennial grasses, N and other metabolites are mobilized to storage organs for recycling (Weinmann 1942). McKendrick et al. (1975) reported that 18% of the total annual N requirement for growth in big bluestem (Andropogon gerardi Vitman) and indiangrass [Sorghastrum nutans (L.) Nash] came from an internal nitrogen reserve. Thus, manipulating senescence with exogenous cytokinins could alter internal nutrient cycling to the extent that it lowered overwintering survival and herbage production the next growing season. Study Site and Methods The study area is on Kansas State University pastures in the northern Flint Hills near Manhattan. Average annual precipitation is 85 cm. Rainfall during the 1979 May-September growing season was 39 cm, 30% below the 50-year average. Moisture in the 1980 growing season was 50% below average, and temperatures exceeded 38 ’ C on 35 days. Soil at the study site is a Benfield-Florence complex in the Udic Argiustolls subgroup of the Mollisols. That loamy upland range site has well-drained, moderately deep, silty clay loams and cherty silt loams overlying a heavy silty clay loam subsoil. Botanical census for the study area conducted in 1979 by the modified step-point technique (Owensby 1973) indicated typical vegetation for native tallgrass prairie, with big bluestem and indiangrass comprising over 50% of the total vegetation. The area has been burned annually in late-spring, and in 1978 the study site was fenced to exclude livestock. Benzyladenine (BA) was dissolved in 25 mL of 95% ethanol, heated, and mixed with distilled water. That cytokinin stock solution was diluted into 10 L aliquots of 5, IO, 20, and 40 ppm BA, each containing 10 ml (O.l’%) Tween-20 surfactant. All mixtures were formulated I day before being applied. The site was partitioned into 4.3 m X 6.4 m plots separated by 0.6 m alleys that were intermittently mowed throughout the growing season. Entire plots received approximately 3 L of one of the 4 concentrations of BA via pressurized handsprayer at biweekly intervals from mid-June until late-July 1979. Each treatment was replicated 3 times, and there were 6 untreated (control) plots in the completely randomized design. Beginning the first week of August, and every week thereafter until October, big bluestem culms within 15 cm on either side of a line through the width of each plot were clipped 2 cm above ground level. Each week the line was systematically moved in the plot to prevent sampling any previously clipped plants. One-third of the big bluestem harvested from each plot was placed into a plastic bag, cooled in an ice chest, and stored in a freezer for chlorophyll analysis. The remaining portion of the sample was dried in a forced-air dryer (600 C), ground through a l-mm mesh screen, and stored in sealed containers for nitrogen analysis. At least 10 big bluestem rhizomes from each plot were collected in December 1979, along previously unclipped transects. After cold-water washing, rhizomes were oven-dried for 5 days at 60” C, ground in a Wiley mill (l-mm mesh screen), and stored in sealed bottles for nitrogen and total nonstructural carbohydrate (TNC) analyses. Chlorophyll from the frozen leaf samples was extracted with acetone and measured spectrophotometrically (Arnon 1949). Micro-kjeldahl nitrogen (N) was determined calorimetrically for all leaf and rhizome samples, and crude protein estimated by N X 6.25. TNC concentration was measured for rhizome samples by enzyme extraction and copperiodometric titration (Smith 1969).

Ruminal microbial populations and fermentation characteristics in bison and cattle fed high- and low-quality forage.

Ruminal microbial populations and fermentation products were compared between two ruminally cannulated bison (375 kg) and two ruminally cannulated Hereford steers (567 kg) on alfalfa or prairie hay diets. Differential media were used to enumerate carbohydrate-specific bacterial subgroups. Voluntary dry matter intake was higher (P=0.006) for cattle than for bison fed alfalfa, but prairie hay intake was not different (P=0.16) between the two species. Volatile fatty acid concentrations, pH, and ruminal ammonia were similar between bison and cattle on both diets. Total anaerobic bacteria and xylanolytic bacterial counts were higher (P<0.02) in bison than in cattle fed alfalfa. However, with the prairie hay diet, no differences in bacterial counts on any medium were observed between ruminant species. Both bison and cattle possessed a mixed A-B protozoan population with nearly identical protozoan numbers and distribution of genera. The similarities between bison and cattle consuming either high-or low-quality forage suggest that any differences in putative forage digestibility between the species are not due to differences in microbial counts.

Particle size changes in rumens of cattle grazing Kansas Flint Hills range.

A ruminally fistulated Hereford steer and heifer grazing Kansas Flint Hills range were used with the objective of determining forage particle breakdown and distribution in different rumen sites over several hours post feeding during seasons of differing forage quality. During the first year, samples were taken after an overnight fast from 3 rumen sites and from feces early on the sample morning (AM sainple). The cattle were fed and sampled again 12 hours later (PM sample). During year two, the cattle were sampled immediately as they came from the native pasture (PRE sample) in addition to the 2 other sample times. Samples were wet-sieved through a series of 5 screens to separate particle sizes. Material from each screen was dried, weighed and expressed as a percentage of the total of all screens. In the rumen, relative amounts of coarse particles generally decreased while amounts of smaller particles generally increased with advancing season. Forage maturity had similar effects on fecal particle sizes. Particles in the feces were more uniform in size than particles in the rumen.

Annual broomweed (Gutierrezia dracunculoides (DC.) Blake) response to burning and mulch addition.

The influence of artfficial mulch additions and mulch removal with fall, winter, and spring burning on annual broomweed [Cutierrtwiu drucuuc&idcs (DC.) Blake] density hr the Kansas Flint Hills was studied. Removing mulch, either by fill and winter burning or by fall mowing, significantly increased (X.03) annual broomweed density compared to untreated plots. As mulch thicknees increased, the number of emerging broomweed plants decreased. Cyclic infeetntlons of annual broomwad appear to be favored by the lack of an overwintering mulch ln closely grazed or denuded areas.

Effects of supplemental tallow on rumen ciliated protozoa in feedlot cattle

Ruminal samples were collected at slaughter from 98 steers consuming a high-grain diet and receiving either no fat, or 2, 4, 6, or 8% supplemental tallow. Tallow supplementation tended (P = 0.11) to increase average ciliated protozoan numbers, however, the occurrence of defaunated animals was higher in the 8% fat treatment than in the control group. Entodinium spp. were the only protozoans that survived in all treatments, and total numbers ranged up to 3.2 x 10(6)/g of ruminal contents. Although increasing tallow supplementation induced a defaunating effect in many animals, the response was unpredictable and protozoa occasionally proliferated irrespective of fat level.

Evaluation of stocking rate, Compudose® implants,and Rumensin® ruminal delivery deviceswithin intensive-early stocking

This report is brought to you for free and open access by New Prairie Press. It has been accepted for inclusion in Kansas Agricultural Experiment Station Research Reports by an authorized administrator of New Prairie Press. Copyright 1987 Kansas State University Agricultural Experiment Station and Cooperative Extension Service.

Nutrient removal rates from ruminoreticula of cattle grazing Kansas Flint Hills Range.

A Hereford steer and heifer were used to compare rumen removal rates of forage nutrients from Kansas Flint Hills range over a 2-year period. Rumens were emptied after an overnight fast and the contents sampled, weighed, and returned to the mmen. The cattle were then fed a known amount of range forage and fasted for 12 hours, at which time the rumen evacuation procedure was repeated. Removal rate calculations were based on change in rumen contents during the It-hour fast. All nutrients studied passed the rumen more rapidly during spring and summer months than fall and winter months. Fibrous fractions were removed more rapidly than cell solubles and crude protein, which may indicate that optimum utilization of native Flint Hills range forage is not being achieved. Methods which increase microbial attack of plant cell wall contents may significantly improve livestock production on native rangeland.