We measured the grazing preference of 3 castrated male Rocky Mountain elk (Cervus elaphus nelsoni) for 2 crested (Agropyron desertorum [Fischer ex Link] Schultes), 5 thickspike (Elymus lanceolatus ssp. lanceolatus [Scribner &J.G. Smith] Gould), 3 Snake River (proposed name E. lanceolatus ssp. wawawaiensis), and 2 bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Love) entries. Number of bites and visits were highly correlated in early May (r2=0.77) and late May (r2=0.83). 'Critana' and 'Elbee' thickspike and 'Hycrest' and 'Nordan' crested wheatgrasses can be recommended for seedings for elk spring grazing where these grasses are adapted.

Selaginella densa Ryd. is a shallow-rooted spikemoss that grows on sparsely vegetated short and mid-grass prairie. It covers a proportion of bare soil which may rival that covered by grasses. Not a forage plant, it is treated in agronomic research as background to the edible plants. Even when it appears to the eye as dry and without active chlorophyll, its spectral reflectance resembles more closely that of forage plants than that of soil background. It is distinguishable from dense stands of chlorophyll-rich fortes and grasses using the normalized differential vegetation index, but S. densa in all cases resembles sparse grasses. Its presence must be considered when estimating range condition using remote sensing techniques.

Old World bluestems (Bothriochloa spp.) are extensively used throughout the Southern Plains. Interseeding these stands with persistent nitrogen-fixing legumes could reduce N fertilizer input, extend the grazing season, and enhance diet quality. The objective of this study was to evaluate production and persistence of 'Overton R18' and TXR20 rose clover (Trifolium hirtum All.) and hairy vetch (Vicia villosa Roth) when interseeded into Old World bluestem. Treatments included these interseeded annual legumes and bluestem + 100 kg/ha N fertilizer. Both rose clover and vetch produced a measurable quantity of forage by early spring before bluestem began to grow. Crude protein and in vitro dry matter digestibility were higher in legume treatments when legumes were actively growing. Total season forage production was similar (6,460 kg/ha; P > 0.05) between rose clover and bluestem + N treatments except during 1991 when production under the Overton R18 treatment was less than bluestem + N or TXR20 rose clover. Average rose clover seed production (26 kg/ha) was greater than vetch (2 kg/ha; P < 0.05) resulting in greater rose clover forage compared to vetch during natural reseeding years. Rose clover plant counts 4 years after the original seeding showed an average of 22 plants/m2. Both rose clover entries appear to have excellent potential over previously available germplasm because of improved cold tolerance and the ability to produce substantial quantities of seed for natural reseeding even after close defoliation.

Cattle exclusion induced dramatic changes in the plant community and modifications in nutrient cycling in grazed native grasslands of the Flooding Pampa (Argentina). The study was carried out to analyze the effect of grazing on the status and spatial variability of soil organic matter, nitrogen and phosphorus. Sampling was performed in the late summer and early spring. Geostatistical methods were used to study the spatial dependence of these soil properties. Organic carbon (OC) and total nitrogen (TN) showed spatial structure only in the ungrazed area with a similar range of dependence (39 m and 36 m respectively). The occurrence of litter in this area lead to a large and spatially homogeneous C input to the soil, which would be the key factor of the spatial structure of organic carbon and total nitrogen. Mineral nitrogen content 1(NO3(-1)-N + (NH4+)-N] was higher in the ungrazed area on both sampling dates. The mineral N content showed a large short-range variability (nugget variation) independent of grazing history. A significant decrease in the extractable P (Bray & Kurtz #1) in the grazed area was found. The extractable P exhibited spatial structure only in the ungrazed area. However, its spatial pattern was different from those of organic carbon and total nitrogen: the range of dependence was higher (57 m) and the spatial structure exhibited a great irregularity. The differences between C, N, and P variability were possibly related to their dynamics in the soil. No evidence of effects of animal excrete on nutrient content or spatial variability was found.

Fifteen collections of 10 native and exotic grasses were germinated at constant 25 degrees C, and at gradual and abruptly alternating temperature regimes characteristic of wet seed bed temperatures in the southwest desert grassland in summer, winter, and spring. All species but bristle grass (Setaria macrostachya H.B.K. and S. leucopila Schum.) had high total germination under summer and spring temperatures (mean- 60% and 67%, respectively) and all but bristlegrass and bush muhly (Muhlenbergia porteri Scribn.) had relatively high total germination under winter temperatures (mean-53%). In general, total germination percentage was similar for gradual and abruptly alternating temperature regimes within a season. Constant 25 degrees C and abruptly alternating temperature germination percentages were similar enough to those at more realistic gradually alternating temperatures for most species to permit use of these tests to calculate estimates of summer bulk seeding rates. Time to 50% germination (D50) was slightly less for gradual than abruptly alternating summer temperatures, but was generally similar for these regimes under winter and spring temperatures. To determine if germination responses to constant temperatures could be used to estimate responses to dynamic temperatures, 12 collections of 8 species were tested for germination at constant temperatures of 5.4,10, 20, 25, 30, 35, 40, and 45 degrees C. Total germination and rate of germination (1/D50) increased and decreased as third-order polynomial functions of temperature. Polynomial regression estimates of 1/D50 were used to calculate estimates of D50 for diurnally alternating temperature that were within an average of 0.6 and 13 days of measured values for summer and spring temperatures respectively. Linear regression estimates of 1/D50 for suboptimal to optimal temperatures were similarly used to estimate D50 for dynamic winter temperature regimes that averaged within 3.6 days of measured values for most of the species. Differences between estimated and measured D50 for bush muhly under winter temperatures, and for Lehmann lovegrass (Eragrostis lehmanniana Nees) collections under winter and spring temperatures, indicate sensitivity of these species to extreme temperature in addition to accumulated heat. Similar measured and estimated D50 for most of the collections for summer, winter, and spring temperatures indicates that these species are primarily responding to cumulative heat effects. Even though most of the species have high germination percentages for winter or spring temperatures, field seedling emergence is much less likely in winter and Possibly less likely in spring than in summer. Slower germination rates during these cooler seasons would require long periods of soil water availability at the surface to allow germination.

Grass shoots after defoliation can be supplied with the nitrogen required for regrowth by either root uptake or remobilization of stores. Whilst it is accepted that after a single defoliation inhibition of root uptake and remobilization from root occurs, it has not been established how the capability of roots to supply nitrogen by uptake and from storage is affected with differing severities of regular defoliation, as experienced by grazed swards. The objective was to examine this question using Agrostis castellana Boiss et Reut., Festuca rubra L., Lolium perenne L. and Poa trivialis L., grasses associated with sites of differing fertility, grown in sand culture and defoliated weekly at a height of either 4 or 8 cm. Nitrogen was supplied as NH4NO3 in a complete nutrient solution. The use of 15N as a tracer allowed the nitrogen supplied to the shoot by root uptake and remobilization to be discriminated over a 35 day period. An increased severity of defoliation resulted in decreased root mass, and increased nitrogen uptake per unit root weight for all species. Increased severity of defoliation did not affect uptake on a per plant basis for A. castellana, 0.54 mg N (plant)-1 (week)-1 and P. rubra, 0.40 mg N (plant)-1 (week)-1, whilst mg N (plant)-1(week)-1 decreased from 0.54 to 0.14, and 0.54 to 0.34 for L perenne and P. trivialis respectively. For plants clipped at 4 or 8 cm, over 88% and 77% respectively of uptake appeared in the shoot. Nitrogen was remobilized from roots to the shoot for A. castellana and F. rubra when clipped at 4 cm, and for A. castellana, L. perenne and P. trivialis when clipped at 8 cm. Uptake by roots was more important than remobilization from roots in supplying nitrogen to the shoot. The ability to maintain the supply of nitrogen by uptake and remobilization to the shoot with increased severity of defoliation was species dependent.

Decision support software has evolved in a number of disciplines to facilitate efficient allocation of resources. Such tools are especially useful where the response of complex systems to human activity are difficult to predict. Decision support systems empower managers to rapidly analyze the ecological and economic implications of alternative management strategies. The Grazingland Alternative Analysis Tool (GAAT), has been developed to estimate the economic efficiency of a wide range of grazingland production systems. Systems that can be analyzed, either individually or in combination, include livestock, wildlife, leased grazing, grain and forage crops, wood products and other nonforage crops. The planning horizon, discount rate, available forage, consumption by class of animal, herd management practices, product yields, product and input prices, and improvement investments must be specified by the user. The GAAT program calculates the resulting annual forage balance for all enterprises being analyzed and the net present value and internal rate of return for the specified management interventions during the planning period. Two examples are presented to demonstrate the flexibility of GAAT for analyzing the economic efficiency of grazingland production systems. The first example analyzes the use of prescribed burning to control Ashe juniper (Juniper ashei Buckholz) and the second determines the economic effect of changing a dairy from a concentrate-dependent to a grazing-dependent system.