Three soil-active herbicides: atrazine [6-chloro-N-ethyl]-N1-(1-methyethyl)-1,3,5-triazine-2,4-diamine]; propham (1-methylethyl phenyl carbamate); and pronamide [3,5-dichloro(N-1,1-dimethyl-2-propynyl)benzamide] were applied in the fall, postemergence to annual bromegrasses at 2 rates. These herbicides were evaluated for their efficacy in selective control of cheatgrass (Bromus tectorum L.) and Japanese brome (Bromus japonicus Thunb.) in perennial stands of crested wheatgrass (Agropyron cristatum [L.] Gaertn.), pubescent wheatgrass (Thinopyrum intermedium Host), Russian wildrye (Psathrostachys juncea [Fisch.] Nevski), and western wheatgrass (Pascopyrum smithii (Rydb.) Löve) and blue grama (Bouteloua gracilis) [H.B.K.] Lag. Ex Griffiths. Yields of annual bromegrasses and perennial grasses and crude protein (CP), phosphorus and total nonstructural carbohydrate (TNC) content of perennial grasses were measured 2 consecutive years after the single herbicide application. Yields of annual bromegrasses from the 3 herbicide treatments averaged 91 and 47% less than those of the control the first and second year posttreatment, respectively. Pronamide provided substantially better control the second year posttreatment than the other 2 herbicides. Yields of perennial grasses in the majority of the herbicide treatment-study site combinations were significantly increased the first year posttreatment (P<0.10). Crude protein of perennial grasses was increased in the atrazine treatment. Atrazine at 0.6 kg/ha was the most cost-effective herbicide for decreasing competition of annual bromegrasses and increasing yield of perennial grasses.

Use of livestock for biological weed control in timber plantations is gaining popularity in the United States and elsewhere. Efficient use of livestock to control unwanted brush relies upon knowledge of livestock feeding habits. A study was conducted during 1981 and 1982 to determine seasonal diets of herded sheep grazing cutover Douglas-fir (Pseudotsuga menziesii) forests in the Coast Range of Oregon. Study sites included both 4- to 6-year-old non-grass-seeded and 2-year-old grass-seeded plantations. Sheep grazing was monitored in spring, summer, and late summer. Forage on offer ranged from 764 to 2,459 kg/ha. Vegetational composition of sheep diets varied by year, season, and plantation age class. Averaged over the 2 years of grazing, graminoids and forbs were nearly equal, at approximately 40% each, in sheep diets in older plantations. In contrast, diets of sheep in young grass-seeded plantations averaged 70% graminoids and only 16% forbs. Ferns were a minor component (<2%) of sheep diets in both plantation age classes. Browse averaged 15 and 12% of sheep diets in old and young plantations, respectively. Douglas-fir was most palatable to sheep in spring soon after bud break. It was generally avoided, however, and never comprised more than 3% of sheep diets. Our data suggest that sheep can be most effectively used for biological control of unwanted brush species during summer and late summer when differences in relative preference indices for target brush species and Douglas-fir are greatest.

Profit maximizing combinations of livestock enterprises, plant control practices, and grazing management systems for ranches in the southern High Plains were examined. A typical ranch and a multi-period linear programming model were used to determine the combinations and timing of improvement practices and enterprises to maximize discounted net income with different investement capital constraints, cattle prices, and discount rates. All solutions included chemical control of sand shinnery oak (Quercus havardii) and a rotation grazing system. Timing of improvements and net income were affected by size of investment capital constraint.

The concept that low-temperature germination response is a population rather than a species characteristic has implications for range seeding. The success of a seeding could depend on the ability of the seed source to associate the appropriate degree of risk with germination in the cold at a particular site. Germination rate at 3 degrees C was determined for 27 seed collections of rubber rabbitbrush (Chrysothamnus nauseosus [Pall.] Britt) belonging to 9 subspecies and collected in 5 states. Marked differences in low-temperature germination rate were observed. Relative percentage of germination at 14 days varied from 0.4 to 100, while the period required to reach 50% relative germination varied from 5 to 96 days. Germination rate was negatively correlated with a climatic index of winter frost risk to seedlings at the site and seed origin. Warm desert collections germinated fastest, while montane and high latitude collections germinated slowest. Many collections from mid-elevation sites showed the bet-hedging strategy of asynchronous germination in the cold. Germination rate was not correlated with subspecific identity. Subspecies of wide ecological amplitude showed nearly the whole range of germination rate response. The possibility that other important range species might show similar patterns of variation in low-temperature germination response merits investigation.

Interspecific hybridization of grasses represents a valuable plant breeding procedure for developing new species with superior grazing value for livestock. Evaluations were made of the hybrid cross between quackgrass (Elytrigia repens [L.] Beauv.) × bluebunch wheatgrass (Pseudoroegneria spicata [Pursh.] Scribn and Smith) to determine how animal preferences for these hybrids were influenced by grazing season and year. Significant differences in the preference shown by steers as measured by bite counts in 1981 and percent utilization (P<0.01) in 1982 existed among the 46 clonal lines for each of the 2 successive years. Preference rankings for lines selected the first year were not identical to those selected a second year although lines with high preference rankings the first year were generally preferred the second year. A clonal line, designated line 30, was most preferred in 7 of 8 subtrials in 1981 and ranked in the top 3 preferred plants in all trials in 1982. There was a 4-week period in early summer when preference differences were minimal. It was attributed to the abundant regrowth on all lines at this time and was found to have a significant (P<0.01) effect on steers' dietary choices.

Kermes oak (Quercus coccifera L.) shrublands occupy more than 0.4 million ha in Greece and are the typical browse rangelands for 4.5 million goats. Five "range types" of kermes oak were identified based on morphological differences. Clipping of kermes oak improves growth rate of twig length, increases the production of new twigs, and alters the nutritive value of browse. Kermes oak can withstand very heavy (100%) clipping of twigs for 2 consecutive years, yielding the highest growth rate and twig number. Browse production varies among different forms of kermes oak shrublands. The low form (0.5-0.8 m height) yielded the highest production (3,467 kg ha-1). Goat liveweight gain of tall form (2 m height) of kermes oak shrubland was 25 kg ha-1 yr-1; improved shrublands, by topping, produced double liveweight gain when their form was altered. Liveweight gain was almost quadrupled when kermes oak shrublands were converted to grasslands.

Eight field trials [early August 1983 (EAUG83), late August 1983 (LAUG83), early November 1983 (ENOV83), early January 1984 (EJAN84), May 1984 (MAY84), late July 1984 (LJUL84), late August 1984 (LAUG84), late November 1984 (LNOV84)] were conducted on blue grama (Bouteloua gracilis) rangeland in southern rangeland in southern New Mexico to examine relationships among nitrogen (N) fertilization of forage, stage of plant growth, diet botanical and chemical composition, forage intake, digesta kinetics, and ruminal fermentation in beef steers. A fertilized pasture (45 kg N/ha) was evaluated during the year of and year after fertilizer application and compared with an adjacent nonfertilized pasture. Two esophageal- and 4 ruminally cannulated steers/pasture were used in a split-plot design. Dietary organic matter percentage was not affected by fertilization; however, fiber components increased as plants approached dormancy on both fertilized and nonfertilized rangeland. Dietary crude protein levels were numerically higher in the fertilized pasture within all trials. Fertilization had no consistent effect on rate or extent of in vitro organic matter digestibility. Fertilization increased (P<0.05) ruminal ammonia ( NH3) concentrations in all but one trial and levels were adequate for maximal microbial protein synthesis; however in the nonfertilized pasture, ruminal NH3 levels were potentially inadequate during periods of dormancy. Ruminal pH was numerically higher for steers on the fertilized pasture than for those on the unfertilized pasture each sampling trial except LNOV84. Fertilization had little effect (P>0.05) on total volatile fatty acid (VFA) concentration or molar proportion of individual acids. Total ruminal VFA concentration was highest in steers during periods of active plant growth. Voluntary organic matter intake was usually unaffected (P>0.05) by fertilization except in EJAN 84 when intake was higher (P<0.05) in the fertilized pasture and LNOV84 when intake was higher (P<0.05) for steers grazing the nonfertilized pasture. Organic matter intake by steers averaged 21.8 g/kg body weight (BW) and 21.6 g/kg BW across the 8 trials for fertilized and nonfertilized pastures, respectively. Intake in both pastures declined with advancing season. Particulate passage rate (PPR) was not different between treatments (P>0.05) during ENOV83, MAY84 and LNOV84. However, PPR was faster (P<0.05) for steers grazing the fertilized than in the nonfertilized pasture during the remaining 5 sampling periods. Correspondingly, retention time of digesta in the gastrointestinal tract was reduced for steers grazing the fertilized pasture during these 5 trials. Estimated gastrointestinal fill was unaffected (P>0.05) by treatment except during the EAUG83 and LAUG84 trials when steers grazing fertilized pasture had reduced (P<0.05) fill compared with steers grazing nonfertilized pasture. Fluid passage rate (FPR) did not differ (P>0.05) between treatments for any trials except in LAUG84 when steers in the fertilized pasture had a lower (P<0.05) FPR than steers in the nonfertilized pasture.

Linear programming ranch models were constructed for size of ranch and species of livestock operation within 5 regions of Colorado. Options to improve existing ranch resources and regional forage supply were included in each model. Parametric programming was used to derive shadow prices to approximate demand for USFS grazing in Colorado. Demand was derived under 3 livestock price scenarios and 2 herd management assumptions. USFS grazing demand was found to be very sensitive to livestock price changes. Variable herd management maximized profits and was able to capitalize on high livestock prices, increasing herds, thereby increasing the price of USFS forage for any given quantity. With herd size constant, ranches that could not cover variable costs ceased operation and demanded no USFS forage. Higher livestock prices could not induce increased USFS forage demand as with variable herd management. Regional differences in demand were also noted, reflecting differential transportation costs and ranch productivity.