Patrick E. Reece

Frequency of endomycorrhizal infection in grazed and ungrazed blue grama plants.

Highlight: The frequency of mycorrhizal infection in blue grama roots was determined from two criteria: (1) occurrence of any mycorrhizal element, and (2) occurrence of fungal vesicles. No significant differences were observed with respect to grazing using the first frequency criteria. However, roots of previously grazed plants had significantly higher frequencies of vesicles than those collected from exclosures. Frequency of vesicles was found to increase linearly with increase in rooting depth of blue grama. Significant grazing effects on the frequency of vesicles were observed primarily in the first sample depth, 0-10 cm.

Grazing date and frequency effects on prairie sandreed and sand bluestem.

A 5 year study was conducted during 1988-1992 to quantify the effects of grazing date and frequency on total organic reserves of prairie sandreed [Calamovilfa longifolia (Hook.) Scribn.] and sand bluestem (Andropogon hallii Hack.). Treatments consisted of mid-month grazing periods in (1) June, (2) July, (3) August, (4) October, (5) June and July, (6) June and August, (7) July and August, or (8) June, July, and August. Seasonal stocking rates were equal among treatments and divided equally over multiple grazing periods. Grazing treatments were applied to the same pastures during 4 consecutive years with yearling cattle and 4-7 day grazing periods. Mean tiller weight of etiolated initial-spring growth was used to estimate total organic reserves in the fifth year. Dormant season grazing in October was not different from 4 years of rest for either species. Total organic reserves in prairie sandreed decreased when paddocks were grazed in June or July regardless of the number of grazing periods per treatment. Reserves in sand bluestem were maintained by grazing once in June or August. Rotationally grazing pastures 2 or more times during June-August is least likely to maintain or increase total organic reserves in either species. Multiple grazing periods initiated in June reduced reserves by about 38% in prairie sandreed and 30% in sand bluestem. When stocking rates are similar to this study, deferment periods should be longer than 60 days after grazing in June to avoid measurable reductions in total organic reserves in both species. Periodic deferment of grazing until mid-August or later will be required to maintain simultaneously high levels of reserves in prairie sandreed and sand bluestem.

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 ...

Early summer grazing effects on defoliation and tiller demography of prairie sandreed.

Grazing strategies should be designed to maintain vigorous populations of plant species critical for livestock production, wildlife habitat, and/or ecosystem functions. Treatments consisting of 5- to 7-day, mid-month grazing periods in June or July at 16, 32, or 48 animal unit days (AUD) per ha, were replicated 3 times and applied to the same pastures in 1995 and 1996 to quantify cattle use and tiller recruitment and mortality of prairie sandreed [Calamovilfa longifolia (Hook) Scribn.], a rhizomatous species characterized by dispersed populations of tillers. Cumulative grazing pressure (AUD Mg -1 ) was used to quantify treatments because of differences in phytomass among pastures and dates. Grazing pressure ranged from 10 to 90 AUD Mg -1 and accounted for 69, 61, and 77% of the variation in percentage of tillers grazed, mean defoliation of grazed tillers, and use of prairie sandreed, respectively. As grazing pressure increased from 10 AUD Mg -1 , percentage of tillers grazed increased from 48 to 90%; defoliation of grazed tillers increased from 54 to 74%; and utilization of prairie sandreed increased from 27 to 67% at plateaus beginning at 50 to 60 AUD Mg -1 . When spring precipitation was above average, 45 to 55% use in June or July increased tiller densities, however, these increases were not sustained or repeated in the following year with average precipitation. Utilization was 50% at 28 AUD Mg -1 and 60% at 40 AUD Mg -1 . Relatively large increases in utilization per-unit-change of grazing pressure below 20 AUD Mg -1 indicated that yearling cattle selectively grazed prairie sandreed. The high degree of correlation between percentage of prairie sandreed tillers grazed and use of prairie sandreed (R 2 = 0.91 in June and 0.90 in July) suggests that percentage of grazed tillers can be used to monitor early-summer use of this species in the Nebraska Sandhills.

Spring Growth and Use of Cool-Season Graminoids in the Nebraska Sandhills

Abstract Upland sites in the Nebraska Sandhills are dominated by warm-season grasses, although cool-season graminoids often produce from 10% to 40% of the herbage. The grazing season on uplands traditionally begins when warm-season grasses have initiated rapid growth, which coincides with declining nutrient density of cool-season plants. Earlier initiation of grazing would improve the efficiency of use of cool-season plants. A study was conducted in 2001 and 2002 to characterize the growth of cool-season species on upland range and to determine the use and herbage production in response to spring grazing date and stocking rate. Grazing dates were 10 April, 1 May, and 22 May, combined with stocking rates of 3, 6, and 9 AUD (animal unit days)·ha−1. Needleandthread (Stipa comata Trin. & Rupr.) and sedges (Carex spp.) accounted for an average of 48% of the spring herbage yield. Amount of total current-year herbage ranged from 114 to 472 kg·ha−1 over the grazing dates. Overall, paddock use of needleandthread and sedges averaged 11% and 4%, respectively. Use on 10 April averaged 61% of that observed on 1 and 22 May, likely because of short plant height (5 cm). Residual (prior-year) herbage probably was a substantial component of animal diets on 10 April. Increasing stocking rate resulted in greater herbage use (% weight removed) and percentage of plants grazed (P < 0.1). Total herbage yield in mid-June (1 130 kg·ha−1) and mid-August (1 350 kg·ha−1) was greatest when paddocks were grazed in April, and it declined by approximately 20% when grazed in May (P < 0.1). Overall, upland grazing strategies that include a grazing period in early May will result in greater utilization of cool-season species, but summer yield will be reduced. However, utilization of cool-season species in the spring would be advantageous, because they are being consumed at a time when their nutritive value and palatability are greater.

Tiller recruitment patterns and biennial tiller production in prairie sandreed

Tiller recruitment is an essential process for ensuring the perenniality of grasses. The timing and extent of tiller recruitment and the role of biennial tillers must be documented for key range species. Prairie sandreed [Calamovilfa longifolia (Hook) Scribn.] is an important grass in the Nebraska Sandhills for both ecological functioning and as a forage. The objective of this study was to document tiller recruitment patterns and the occurrence and contribution of current year and biennial tillers to biomass production in prairie sandreed at 2 locations in Nebraska. Tiller recruitment was monitored at 2-week periods throughout the growing season during a 2-year period. Newly emerged tillers were classified as intravaginal, extravaginal, or rhizomatous tillers and marked with colored wire. Prairie sandreed has an unimodal pattern of tiller recruitment and over 50% of the current year tillers emerged by mid-May and 80% by mid-June. Rate of tiller emergence and absolute number of emerged tillers were poorly correlated with short- and long-term precipitation totals (r 0.20). The year after new tillers were marked, biennial tillers and tillers initiated during the current-year were counted and clipped in September for biomass determination Biennial tillers made up only 6 and 20% of the total tiller emergence at these locations and were generally only 30% as large as the new tillers. Extravaginal tillers composed over 78% of the biennial tiller population as a result of both their dominance in emerging populations and the higher percentage of tillers that survived the winter. Current year tillers contributed the most to prairie sandreed forage production and their emergence was largely completed by mid-June. The lack of a relationship between tiller recruitment and precipitation patterns, combined with previous studies of prairie sandreed, indicates that tiller recruitment involves a process that begins the previous growing season. DOI:10.2458/azu_jrm_v53i5_hendrickson

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.

Late-summer forage on prairie sandreed dominated rangeland after spring defoliation.

The potential of using spring defoliation to improve late-summer nutritive value of prairie sandreed [Calamovilfa longifolia (Hook.) Scribn.] on rangeland was studied with a factorial array of replicated 1-year treatments that included clipping plots at ground level or at a 5 or 10 cm height on 1 April, 26 April, 20 May, or 14 June. Vegetative tillers accounted for 83% of prairie sandreed herbage on unclipped control plots. After spring treatments, late-summer crude protein content (CP) in vegetative tillers of prairie sandreed ranged from 5.0 to 7.9% and in vitro dry matter digestibility (IVDMD) ranged from 45 to 52% compared to 5.0% CP and 45% IVDMD for unclipped plots. Reductions in mean weight of prairie sandreed vegetative tillers after April and May treatments were offset by 20 to 30% increases in tiller density. Treatments that increased tiller density had little or no effect on forage nutritive value when applied more than 90 days before herbage was sampled. Nutritive value of prairie sandreed and total yield from all species in mid-September were unchanged after April treatments. After sandreed tillers began to emerge in early May, late-summer nutritive value improved as clipping was delayed and degree of defoliation increased during May and June, however, yield was inversely related to nutritive value. While mid-September nutritive value of prairie sandreed was comparable to mid-summer values after June treatments, clipping reduced projected, late-summer stocking rates by 58 to 100% compared to control. It may be possible to improve mid-September forage nutritive value with moderate stocking rates in June with less reduction of total late-summer herbage because of selective herbivory. Measurable increases in prairie sandreed yield after complete defoliation of associated species in late April indicated prairie sandreed populations might be increased by concentrating cattle in selected pastures during late April.

Interactions Among Western Ragweed and Other Sandhills Species After Drought

Abstract Interannual differences in yield and species composition of herbaceous vegetation on semiarid rangelands are common and often related to variations in precipitation regime. Interspecific interactions that occur after drought-induced population fluxes of western ragweed (Ambrosia psilostachya D.C.) were evaluated by removing western ragweed or associated species from 1-m2 quadrats at weekly intervals beginning in early May, June, or July 1991 or 1992 on high-seral sandhills prairie in Nebraska. The composite of peak standing crops for ragweed and each group of associated species was 77% greater during May–October 1991 (2 252 kg·ha−1) compared with 1992 (1 275 kg·ha−1) when April and May precipitation was 98 mm below average and a late frost occurred. Mean levels of western ragweed herbage up to 436 kg·ha−1 had no effect on associated species in 1991 when above average precipitation occurred throughout the growing season. In contrast, when an unusually dry spring occurred in 1992, relatively small mean levels of ragweed (189 kg·ha−1) reduced end-of-season standing herbage of rhizomatous C4 grasses on control plots by about 21% (137 kg·ha−1) with little effect on other associated species, regardless of when treatments were initiated. Within a given year, western ragweed density was seasonally constant, similar among treatments, and independent of preceding-year species composition. Severe defoliation of western ragweed had little effect on subsequent-year populations, indicating an ability to maintain primordia for several years with limited plant growth. Because western ragweed is not a strong competitor in the presence of vigorous graminoids, deferring use of June- or July-grazed pasture until after July in the subsequent year can minimize increases in western ragweed.

Diet Composition of Cattle Grazing Sandhills Range During Spring

Abstract The grazing season on upland Sandhills range traditionally begins in mid-May when the dominant warm-season grasses have initiated growth. Initiating grazing earlier would improve efficiency of use of cool-season plants and reduce the time period during which hay is fed. A 2-year study was conducted to determine nutrient and botanical composition of cattle diets when grazing upland Sandhills range during spring. Diets were collected from esophageally-fistulated cows on 10 April, 1 May, and 22 May each year. Concurrently, current-year, and residual herbage was clipped to determine pasture composition and calculate preference indices for the primary plant species and groups. Averaged across dates, needleandthread (Stipa comata Trin. & Rupr.), bluegrasses (Poa spp.), and sedges (Carex spp.) accounted for 19% of the total herbage and 68% of the current-year herbage yield. These species constituted an average of 74% of cow diets. Diet composition of sedges was less on 10 April than on 22 May (P < 0.05), whereas similar amounts of needleandthread and bluegrasses were present on all dates. Preference indices indicated strong selection for species with abundant current-year growth and avoidance of residual herbage. Crude protein content of diets was less on 10 April (10.7%) than on 1 May or 22 May (13.9%, P < 0.05), likely because of a greater amount of residual herbage present in 10 April diets. Overall quality of diets would meet requirements of average spring-calving cows; however, grazing management strategies would need to account for the limited availability of current-year growth during spring, particularly April, to ensure that cattle are meeting their nutrient needs.