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Clearing brush from rangeland and seeding it to buffelgrass (Cenchrus ciliaris L.) is a popular range improvement practice in Mexico, but no data are available on the effects of these practices on soil properties. Twenty-nine study sites were randomly selected across 3 major climatic regions in Mexico: 13 in the northwest, 11 in the northeast, and 5 in the southeast. Soils under buffelgrass stands more than 10 years old and on adjacent virgin rangelands were sampled at 0-10, 10-20, and 20-30 cm depths to quantify sand, silt, clay, organic C, total N, pH, EC, CEC, available P, and exchangeable Ca2+, Mg2+, Na+, and K+.Because soil variables were not significantly (P 0.05) different among depths, only data from the surface horizon received further analysis. Soils in the northwest had higher (P 0.05) sand content and were particularly low in total N (0.08%), Ca2+, and K+, while soils of wetter and warmer southeast Mexico were significantly (P 0.05) higher than the other two regions in measures of soil fertili...

Prescribed burning of vegetation may increase the potential for surface runoff and erosion. Changes in surface runoff and sediment production were evaluated with time following fall and spring burns at two different soil and vegetation type locations in southeastern Arizona. Rainfall simulations were conducted immediately after prescribed burns on four replicate areas and 1 yr later following a repeat burn on the same areas, and compared with paired unburned areas. The burn treatment and evaluation sequence was repeated in a second year on new areas to evaluate differences in years. After the first burn, runoff and sediment production on unburned and burned areas were similar within locations, and were greater at one location than the other. One location showed significantly more runoff and sediment production in the fall season on both unburned and burned areas after the first burn treatment. There was significantly greater runoff and sediment production from the burned areas after the second burn and the burned areas were now similar between locations. Runoff and sediment production for the fall season and for the second year on the 1-yr-old areas was higher at both locations, regardless of treatment. The increases in runoff and sediment production were greater from the burning than the season or year effects after 1 yr. The management implications for these locations and conditions are that, immediately after a rangeland burn, runoff and sediment production maybe unchanged, but within 1 yr significant increases can occur and significant seasonal and yearly differences may occur irrespective of a burn.

Greater seed burial has been suggested as a way to increase the time of water availability to seeds and seedlings in revegetation of semiarid rangelands. The effects of sowing depth on seedling emergence and root development of 'Vaughn' side-oats grama [Bouteloua curtipendula (Michx.) Torr.), 'A-130' blue panic (Panicum antidotale Retz.), and 'Cochise' atherstone lovegrass (Eragrostis lehmanniana Nees × E. tricophora Coss. & Dur.) were measured in relation to water availability on a sandy loam soil in the greenhouse. Side-oats grama and blue panic were sown at depths of 0, 10, 20, and 30 mm, while Cochise lovegrass was sown at 0, 5, 10, and 15 mm. Pots were subirrigated every 3 d, on Days 1 and 7 after sowing, or on Day 1 only [...]

Arizona cottontop (Digitaria californica), a bunchgrass native to the Chihuahuan and Sonoran Deserts in North America, and Lehmann lovegrass (Eragrostis lehmanniana), a bunchgrass introduced to the southwestern USA from southern Africa, were defoliated and examined for above‐ and below‐ground productivity, nitrogen and phosphorus allocation, and photosynthetic potential. Stems plus sheaths from which leaf blades have been removed may be important to Lehmann lovegrass because this tissue is photosynthetically active and contains nitrogen and phosphorus reserves. After defoliation, Arizona cottontop re‐established a canopy more quickly than Lehmann lovegrass but differences were due to greater numbers and growth rates of Arizona cottontop leaves. Rapid Arizona cottontop leaf growth was followed by a 50% decline in below‐ground biomass. Lehmann lovegrass had a lower investment in above‐ and below‐ground biomass, nitrogen and phosphorus per plant. Grazing tolerance associated with Lehmann lovegrass may be rel...

Summer burning was used to reduce spittlebug (Aeneolamia albofasciata Lall.) populations in buffelgrass [Cenchrus ciliaris (L.) Link] on the Carbo Livestock Research Station in Sonora, Mexico. Five treatments included (1) an untreated control; (2) burning 7-14 days before the summer rains when the insect and the plant were inactive; (3) burning after the accumulation of 50 mm of summer precipitation during insect egg hatch or the second leaf stage; (4) burning between the second and third instars or early culm elongation; (5) and burning between the fifth instar and adult stages or active plant growth during the summer growing season. Summer burning after the accumulation of 50 mm of precipitation and between the egg hatch and the third instars or between the second leaf stage and early culm elongation reduced spittlebug nymph and adult populations by 100% and appeared to stimulate buffelgrass growth for 3 and 4 years post treatment. Burning at the peak of buffelgrass live biomass production effectively controlled spittlebug populations but reduced plant production by almost 50% for 4 years post-treatment. Equally detrimental was the untreated control where nymph and adult spittlebug populations killed more than 50% of the buffelgrass population. Summer fires conducted after 50 mm of precipitation were easier to control than fires conducted before the growing season when plant material was dry.

T-4464 buffelgrass (Cenchrus ciliaris L.), a perennial bunchgrass from Africa, has been extensively seeded throughout Mexico. After establishment and grazing, T-4464 either persists with time and actively invades surrounding areas (spreads), persists with time but does not increase (persists), or declines with time and all plants die (dies). To help land managers select high-potential seeding sites, we classified 139 seeding sites in three survival regimes : (i) spreads, (ii) persists, and (iii) dies. In previous research, we identified a relationship between plant survival and organic C. This research was designed to identify relationships between organic C and soil color. Single comparisons between organic C and Munsell hue, value, chroma, and reflectance in dry and moist soils were poor predictors of plant survival. To predict buffelgrass survival among the three survival regimes and between spreads and dies, we used discriminant function analyses. In dry soil, a model including value and chroma correctly classified 53% (Wilke's λ = 0.8) of the seeding sites in the three survival regimes, while in moist soils, value and reflectance components correctly classified 61% (Wilke's λ = 0.7) of the seeding sites. A dry soil model including value, chroma, and reflectance correctly classified 81% (Wilke's λ = 0.7) of the seeding sites between spreads and dies, while a moist soil model, including the same components, correctly classified 83% (Wilke's λ = 0.6) of the seeding sites. Survival regime selection with multiple soil color components prior to brush control and sowing will reduce adverse economic and environmental consequences and enhance long-term beef production.

This research was designed to identify relationships between T4464 buffelgrass (Cenchrus ciliaris L.) survival and climatic and soil characteristics. At 167 buffelgrass seeding sites in North America we collected climatic and soils data where the grass: 1) persisted over time and increased in area covered (spreads), 2) persisted over time but does not increase in area covered (persists), and 3) declined over time and all plants eventually died (dies). At 30 sites in Kenya we collected climatic and soils data in the area where T4464 seed was originally collected. Only total soil nitrogen and organic carbon differed among survival regimes. Total soil nitrogen and organic carbon concentrations were least where buffelgrass spreads, intermediate where the grass persists and greatest where the grass dies. To predict buffelgrass survival among the 3 survival regimes, and between areas where the grass spreads or dies, we used discriminant function analyses. A model including organic carbon, total soil nitrogen, sand, clay, potassium and cation exchange capacity correctly classified 78% (r2=0.8) of the seeding sites in the 3 survival regimes. A model including sand, total soil nitrogen, calcium, mean minimum temperature in the coldest month, annual precipitation and winter precipitation correctly classified 88% (r2 = 0.8) of the seedling sites between spreads and dies. Survival regime selection prior to brush control, seedbed preparation and sowing will reduce planting failure probabilities, soil erosion and economic losses, and enhance long-term beef production.

Buffelgrass (Cenchrus cilaris L.), a perennial bunchgrass from northcentral Kenya has been successfully seeded on 400,000 ha in northwest Mexico. To determine if carrying capacity increased after buffelgrass introduction we measured live, recent-dead standing, old-dead standing and litter at 2-week intervals for three years. Live biomass was produced throughout the year but peak production, over the 3 years was in August. Peak live biomass production varied from 46S kg/ha in a summer of below-average precipitation to 3,045 kg/ha in a summer of above-average precipitation. Recent- and old-dead standing quantities were highly variable among years and transfers among components were dependent on temperature and precipitation. Buffelgrass annually produces about 3 times more green forage than native grasses.

Over the past century woody plants have increased in abundance on sites formerly occupied by grasslands in the Sonoran Desert. Woody plant invasion has been associated with a multitude of biological and physical factors. This study was conducted to determine temperature, soil, fire, rodent, and livestock effects on the germination and establishment of whitethorn acacia (Acacia constricta Benth.) and velvet mesquite (Prosopis velutina (Woot.) Sarg.). Optimum termination temperatures for both shrubs ranged from 26 to 31 degrees C, and seedling emergence was greatest from seed sown at 1 to 2 cm depths in sandy loam soil. Merriams kangaroo rats (Dipodomys merriami) fed seeds in the laboratory removed seed coats and planted embryos at 2 to 4 cm depths in a sandy loam soil. Prescribed fire killed 100% of seed placed on the soil surface but had no measurable effect on the germination of seed planted at 2 cm. After passage by sheep, about 6% of the A. constricta and 13% of the P. velutina seeds germinated while after passage by cattle, only 1% of the A. constricta and 3% of the P. velutina seed terminated. Embryo planting by rodents may improve survival efficiencies for these legunminous shrub seedlings, but seed consumption and passage by sheep and cattle appear to adversely affect seed germination. Dipodomys merriami, rather than domestic livestock, may be responsible for the spread of these shrubs in the Sonoran Desert.

Lehmann lovegrass (Eragrostis lehmanniana Nees), a perennial bunchgrass from southern Africa, is replacing native grasses in Arizona. After the invasion, biomass production and quality may change. This study was conducted to determine the production and chemical composition of live Lehmann lovegrass leaves, culms, and seedheads during wet and dry years. During 3 years, green leaf biomass peaked at 78 +/- 14 g m-2 (mean +/- SE) in early August, green culms peaked at 103 +/- 21 g m-2 in mid October, and green seedheads peaked at 18 +/- 12 g m-2 in mid August. Leaf and culm growth peaks correspond with low crude protein (2.5%) and moderate phosphorus (0.23-0.25%) levels while seedhead growth peaks correspond with high crude protein (7-10%) and moderate phosphorus (0.19-0.29%) levels. There were no crude protein and phosphorus peaks in green culms. In Lehmann lovegrass forage, crude protein should meet animal requirements for about half the year while phosphorus should be adequate throughout the year. In native forages, crude protein is adequate throughout the year because animals selectively graze forbs, grasses, and shrubs but phosphorus does not meet animal requirements except in mid-summer.

Fire on rangelands used as a management tool or as an unwanted wildfire removes vegetation cover. Vegetation cover is thought to be a dominate factor controlling surface runoff and erosion. Vegetation removal by a burn should have an immediate effect on runoff and erosion. Surface runoff and sediment production were evaluated immediately after fall and spring season burns at 2 locations with different soil and vegetation types for 2 years in southeastern Arizona. The evaluations were conducted with a rainfall simulator at 2 precipitation intensities. Immediately after a burn there was not a significant change in runoff and erosion, therefore, vegetation cover by itself was concluded not to be a dominate factor controlling surface runoff and erosion. The increase found in surface runoff and sediment production from the burn plots was not significantly greater than the natural variability for the locations or seasons. Significantly higher surface runoff and sediment production was measured in the fall season compared to the spring at 1 location.

Successful germination and establishment of grass seedlings from surface-sown seeds requires a microsite which provides adequate soil water and temperature conditions, among other species-specific requirements. The microsite where these requirements are met has been termed a "safesite". Safesites may occur naturally as cracks and depressions in the soil surface, gravel, and plant litter, or be prepared by seedbed equipment and livestock trampling. A greenhouse study was conducted to determine the influence of seedbed microsite characteristics and soil water treatments on seedling emergence of 'Vaughn' sideoats grama (Bouteloua curtipendula (Michx.) Torr.), 'A-130' blue panic (Panicum antidotale Retz.), and 'Cochise' Atherstone lovegrass (Eragrostis lehmanniana Nees X E. tricophera Coss and Dur.). Although there were several interactions, in general, emergence of all 3 species was highest from gravel, followed by litter, cracks, and finally the bare soil surface. Bare surface sites decreased in water content more quickly than the other sites. Cochise lovegrass had high emergence in gravel under all water treatments. Small-seeded species such as Cochise lovegrass broadcast on coarse-textured surface soils may establish with minimal seedbed preparation, provided summer precipitation is adequate.

Eragrostis lehmmniana (Lehrnann lovegrass) is a warm-season bunchgrass native to South Africa which dominates many desert grassland sites in southern Arizona. To determine why fire results in high seedling recruitment of this species, we measured germination of seeds in the seedbank and field seedling emergence following 1) no treatment, 2) burning, 3) clipping and herbicide and 4) herbicide d y . Treatments were designed to compare the effects of initial fire heat treatment with those of canopy removal, as affecting seedbed temperatwe, light and water availability, on seedling emergence. Treatments were replicated over 2 years on a stand of Lehrnann lovegrass at the Santa Rita Experimental Range. Canopy removal, by either clipping or burning, increased seedling emergence in seedbank samples taken prior to summer rains and greatly increased field seeding emergence. High seedling emer- gence after canopy removal was not the result of greater seedbed water availability but probably the result of a greater range in diurnal soil temperatures and increases in red light reaching the seedbed, both of which stimulate germination. The ability of E. lehmanniana to persist after fire indicates that prescribed burning could be used to control associated woody plants and improve forage palat- ability of E. lehmanniana dominated grasslands.

Soils were collected to 15 cm along the four cardinal directions at three locations around 10 creosotebush (Larrea tridentata) plants at five sites in the southwestern United States. The sampling locations were: (i) at the canopy center, (ii) along the outer canopy edge, and (iii) in open areas between plant canopies. A portion of the soil from each sampling location was analyzed for particle size distribution, pH, EC, CaCO3, Ca, K, Na, Mg, NO3--N, organic C, available P, and Mn. The remaining soil from each sampling location was seeded with either Lehmann lovegrass (Eragrostis lehmanniana) or blue panicgrass (Panicum antidotale). Grass seeds were germinated and grown for 42 d in a greenhouse. Nitrate was significantly lower in open areas between creosotebush canopies than near the shrub canopy center at all sites. Grass seedling growth decreased with increasing distance from the canopy center and seedling growth was highly correlated with nitrate concentrations. Spatial distribution patterns for the other measured soil properties did not occur in a consistent fashion across all sampled sites. The action of mechanical tillage to limit creosotebush competition, and corresponding dilution of NO3--N in the soil volume, may reduce the probability of establishing perennial grasses.

Climatic and edaphic conditions at Eragrostis lehmanniana Nees sites in south-eastern Arizona, USA were compared with those in the Cape Province, RSA to determine a range of conditions under which the species might be expected to establish and persist in southern Africa. Mean annual precipitation amounts and temperature extremes were highly variable where Lehmann lovegrass predominates, but in most summers precipitation accumulations ranges from 150-220 mm and temperature extremes ranges from 20-35 °C in 30-40 days. Soils at Lehmann lovegrass sites in the Cape Province were more coarse textured and nutrient concentrations were usually less than at sites in south-eastern Arizona; but trends in particle-size distributions and measured chemical concentrations were generally equivalent. Climatic and edaphic conditions in central Botswana and north-eastern Namibia generally range between those in south-eastern Arizona and the Cape Province, RSA and we expect that seeded Lehmann lovegrass stands in these areas would enhance semi-desert grassland productivity. Keywords: arizona; botany; botswana; cape province; climate; distribution; eragrostis lehmanniana; grassland; kalahari desert; productivity; range; seeding; semi-desert; soils; sonoran desert; south africa; southern africa; temperature

Nine week old perennial grass seedlings were transplanted to coincide with the occurrence of summer and winter precipitation during 3 years at a study site in the Sonoran Desert. Six groups of similar grasses were evaluated biannually for 32 months to compare survival. Average survival over the 3 years of this study were 73% at 2 months and 39% at 32 months after summer transplanting. Summer transplant survival after 32 months for the Lehmann (Eragrostis lehmanniana Nees) and Boer (E. curvula var. conferta Nees) lovegrass groups averaged 64%, the weeping lovegrasses [E. curvula (Schrad.) Nees] averaged 22%, the large bunchgrasses [Anthephora pubescens Nees, Panicum antidotale Retz., P. coloratum L. and Pennisetum setaceum (Forssk) Chiov.] averaged 29%, the old world bluestems (Bothriochloa spp.) averaged 41%, and the gramagrasses [Bouteloua gracilis (Willd. ex H.B.K.) Lag. ex Griffiths and B. curtipendula (Michx.) Torr.] averaged 21%. Winter transplant survival of Cochise lovegrass (Eragrostis le...

Climatic and edaphic conditions at Eragrostis lehmanniana Nees sites in south-eastern Arizona, USA were compared with those in the Cape Province, RSA to determine a range of conditions under which the species might be expected to establish and persist in southern Africa. Mean annual precipitation amounts and temperature extremes were highly variable where Lehmann lovegrass predominates, but in most summers precipitation accumulations ranges from 150-220 mm and temperature extremes ranges from 20-35 °C in 30-40 days. Soils at Lehmann lovegrass sites in the Cape Province were more coarse textured and nutrient concentrations were usually less than at sites in south-eastern Arizona; but trends in particle-size distributions and measured chemical concentrations were generally equivalent. Climatic and edaphic conditions in central Botswana and north-eastern Namibia generally range between those in south-eastern Arizona and the Cape Province, RSA and we expect that seeded Lehmann lovegrass stands in these areas would enhance semi-desert grassland productivity.Keywords: arizona; botany; botswana; cape province; climate; distribution; eragrostis lehmanniana; grassland; kalahari desert; productivity; range; seeding; semi-desert; soils; sonoran desert; south africa; southern africa; temperature

The annual pattern of above-ground live biomass, recent dead standing biomass, old dead standing biomass, and standing crop of big sacaton (Sporobolus wrightii Monro) grassland community in semiarid Arizona was studied over a 3-year period. Live biomass was produced throughout the year but peak production, over the 3 2 years, was in August. Peak biomass production was 296 g m in 1 wet summer and averaged 133 g mover 2 dry summers. Recent dead standing biomass was greatest in spring and least in summer, over the 3 years. Transfer of recent dead standing biomass to old dead standing biomass was precipitation and temperature dependent. Old dead standing biomass was greatest in summer, least in winter, and was primarily composed of dead seed stalks. Livestock management of big sacaton grasslands should possibly be distinct from adjacent upland areas. Big sacaton (Sporobolus wrightii Monro) is a robust perennial warm-season bunchgrass that begins growth in early spring and usually produces a limited amount of green herbage in winter (Haferkamp 1982). The species grows on low alluvial flats and flood plains (Wooten and Standley 1912). It usually is excluded from alkaline and saline playas and lowlands dominated by alkali sacaton [Sporobolus airoides (Torr.) Torr.]. Big sacaton is distributed from southeastern Arizona to central Texas and Author is range scientist, Arid Land Ecosystems Improvement, USDA, Agricultural Research Service, 2000 East Allen Road, Tucson, Ariz. 85719. Appreciation is extended to R.M. Madrigal and B.B. Buck for field assistance; Drs. H.L. Morton and T.N. Johnsen, Jr., for technical assistance; the Donaldson family at the Empire Range for their cooperation; and ANAMAX Mining Company for permission to use their land. Manuscript received August 17, 1983. south into the northern Mexican Frontier States; however, stand development is greatest in southeastern Arizona (Kearney and Peebles 1960). Dense stands of big sacaton formerly dominated alluvial flats and bottomlands along the Santa Cruz and San Pedro Rivers in Southeastern Arizona and supported more than a million cattle in 1890 (Humphrey 1958). Big sacaton bottoms have been, and continue to be burned and grazed (Bock and Bock 1978), plowed and sown to agricultural crops (Griffiths 1901), channelized to provide irrigation water and drainage (Cooke and Reeves 1976), and covered with houses and asphalt (Renard et al. 1983). Today the species occupies less than 5% of its original area (Humphrey 1960). Big sacaton stands were usually associated with perennial, surface water and new growth was readily consumed by livestock in spring when upland grasses were dormant (Thornber 1910). Dead standing big sacaton biomass is coarse and stands have been burned or mowed in either late fall, winter, or early spring for at least the past 100 years (Thornber 1910, Humphrey 1970). The animal-carrying capacity of semiarid grazing lands is dependent on net primary production and the amount of plant biomass which is available to be converted into animal biomass. Previous investigators have been interested in big sacaton production after natural and man-caused fires (Humphrey 1960, Bock and Bock 1978, Gavin 1982). However, net primary production rates under nonburned conditions have not been measured. The first step in a program to evaluate carrying capacity should be to quantify the annual accumulation and decomposition characteristics of live biomass and standing litter in big sacaton grassland communities. JOURNAL OF RANGE MANAGEMENT 37(4), July 1984 377 This content downloaded from 157.55.39.223 on Wed, 24 Aug 2016 05:07:16 UTC All use subject to http://about.jstor.org/terms This paper reports on studies in which the above-ground live biomass production, recent dead standing biomass, and old dead standing biomass were examined over 3 years. The relative differences in yield accumulation and decomposition in response to climate were also studied.

Live and standing dead biomass, standing crop, and total nitrogen, within each component, were measured in a big sacaton (Sporobolus wrightii Monro) grassland in southeastern Arizona for 3 years to determine annual fluctuations in above-ground biomass and nitrogen. Mean live biomass varied from 150 kg/ha in February to 2,000 kg/ha in August. Standing dead biomass accumulated after the summer growing season and rapidly disappeared following either fall, winter, or summer moisture, but was the predominant vegetative component for about 49 weeks of each year. Standing crop (live plus standing dead) was greatest in August and averaged 4,450 kg/ha. Total nitrogen varied from 2 to 31 kg/ha in live biomass, from 5 to 15 kg/ha in standing dead biomass, and from 9 to 40 kg/ha in standing crop. The rapid disappearance of standing dead suggests that stocking rates should be based on standing crop just prior to the grazing period rather than peak standing crop after the summer growing season. Big sacaton (Sporobolus wrightii Monro) grasslands produce abundant forage in summer (Gavin 1982) and pure stands once existed along the channels and tributaries associated with the San Pedro and Santa Cruz Rivers in southeastern Arizona (Griffiths 1901). These grasslands, which are located on low alluvial flats or flood plains (Wooten and Standley 1912), naturally spread flood waters, trapped sediments (Hubbell and Gardner 1950), limited soil erosion (Humphrey 1958), and provided a forage resource for one million cattle before 1890 (Cox et al. 1983). Range managers and researchers have assumed for more than 100 years that the standing dead biomass of big sacaton disappears slowly, and this assumption has been used to justify the need for burning and mowing. Data to support this slow disappearance hypothesis is not available in the literature. Some work has been reported on the response of big sacaton following burning (Bock and Bock 1978) and mowing (Haferkamp 1982). However, information on the cycling of above-ground biomass and nitrogen in undisturbed big sacaton grasslands is currently unavailable. The objectives of this study were to (1) investigate the seasonal dynamics of live and standing dead biomass and nitrogen of big sacaton grasslands under natural conditions, and (2) to interpret biomass and nitrogen dynamics in relation to annual climate.

Around 1900 temperate and semidesert grassland productivity declined, soil erosion increased, and drought destabilized the livestock industry in the northern and southern hemispheres. As government leaders throughout the world began to recognize the importance of grassland productivity and soil conservation, a massive experiment began to evolve. Government and private individuals collected seed from every continent, and planted seed at experimental stations and ranches in their respective countries. Hundreds of individuals who conducted thousands of seeding trials observed that buffelgrass (Cenchrus ciliaris L.), weeping lovegrass [Eragrostis curvula (Schrad.) Nees], kleingrass (Panicum coloratum L.), and Lehmann lovegrass (Eragrostis lehmanniana Nees) plants from seed collected in Africa were easier to establish and persisted longer than other grasses. Between 1930 and 1986 scientists in many countries evaluated the establishment and persistence of these grasses, but no attempt was made to synthesize the data base and determine the effects of climate and soil on plant establishment and persistence. Our objective was to: (1) determine the climatic and edaphic characteristics of areas where the seed of each grass was collected in Africa, and where each grass has been successfully established in both hemispheres, and (2) identify characteristics which influence long-term persistence. Where buffelgrass predominates and spreads, summer rainfall varies from 150 to 550 mm, winter rainfall is less than 400 mm, mean miminum winter temperatures rarely fall below 5? C, and soil texture is loamy. Weeping lovegrass can be established and plants persist when spring, summer, and fall rainfall varies from 400 to 1,000 mm on deep sandy soil and mean minimum winter temperatures rarely fall below -5? C. The invasion of adjacent nonplanted sites occurs only in Africa where growing season rainfall infrequently cycles between 750 and 1,000 mm and soils remain wet in mid-summer. Kleingrass can be established where mean maximum daily summer temperatures are above 30? C, mean minimum daily winter temperatures rarely fall below 0" C, summer growing season rainfall varies from 400 to 990 mm, and soils are clayey or silty. Kleingrass, like weeping lovegrass, spreads to nonplanted sites only in Africa where a mid-summer drought does not occur. Lehmann lovegrass predominates and spreads only in southern Africa, southeastern Arizona, and northern Mexico when summer rainfall in 30 to 40 days exceeds 150 mm, and soil textures are sandy or

Perennial grasses were seeded by drilling or broadcasting on 4 mechanical and 3 herbicidal weed control and/or seedbed preparation treatments at 4 semidesert grassland sites invaded by creosotebush (Zarrea tridcnutu) in the Chfuahuan and Sonoran Deserts. The cultivars ‘Cochise’ Atherstone lovegrass (Eragrostis lehmanniana X Eragrostis trichophera) and ‘Catalina’ Boer lovegrass (Effrgrostis curvuIo var. coqferta) lovegrasses were initially established and persisted in 6 of the 8 plantings on disk plowed and disk plowed plus contour furrowed seedbeds. These grasses were established and persisted in 2 of the 5 plantings made in creosotebush stands treated with tebuthiuron [JV-(S-(l,l-dimethylethyl)1,3,4-thiadizol-2-yl)imethylurea] at 0.5, 1.0, and 1.5 kg a.i/ha rates. Grasses established initially on two-way railed and land imprinted areas usually died within 3 or 4 years. Creosotebush (Larrea tridentata), a woody perennial shrub, has invaded the semidesert grasslands within the Chihuahuan and Sonoran Deserts of North America (Humphrey 1958, Buffington and Herbel 1965, Hastings and Turner 1965). As creosotebush densities increase, perennial grass densities decline (Anderson et al. 1957). Therefore, it is desirable to replace creosotebush with perennial grasses to reduce soil erosion, increase infiltration, and provide forage for domestic livestock. Jerry COY. and Howard Morton are range scientist and supervisory plant physiologist, respectively; USDA, Agricultural Research Services Aridland Watershed Management Research Unit, 2000 E. Allen Road, Tucson, Artz. 85719, Martha Martin-R. and Fernando Ibarra-F. are head of the Department of Range Management and Technical Director, respectively, CIPES, Periferico OTS S/N, Conjunto UGRS, Postal 1754, Hermosillo, Sonora, Mexico. When this study was initiated Martha Martin-R. and Fernando Ibarra-F. were graduate students, School of Renewable Natural Resources, University of Arizona, Tucson. Appreciation is extended to Consejo National de Ciencia y Tecnologia (Mexico) for financial support; Elanco Products Company for the herbicide and fencing materials at the Mexican sites; Drs. Luis Carlos Fierro, Thomas N. Johnsen, Jr., and Gilbert L. Jordan for technical assistance; personnel at Rancho Experimental La Campana, Chihuahua, Mexico, and Aridland Watershed Management Research Unit, Tucson, Aria., for setting up plots, applying treatments, and collecting data; and ranchers Eloy Morales, Sergio Mendora, and Gilbert0 Valdez for permission to use their land and housing facilities. The Rocky Mountain Forest and Range Experiment Station gave permission to use land at the Santa Rita Experimental Range. Lovegrass seeds were provided by U.S. Dep. Agr., Soil Conservation Service, Plant Materials Center, Tucson, Arizona. Kleingrass and sideoats grama seeds were provided by Rancho Experimental La Campana. Buffelgrass seeds were provided by Centro de Investigations Pecuarias de1 Estado Sonora, Garbo, Sonora, Mexico. Manuscript accepted 5 May 1986. 540 For the past 90 years creosotebush management has consisted of mechanical tillage to reduce creosotebush competition and prepare a seedbed for seeding perennial grasses (Cox et al. 1982). Mechanical tillage disturbs surface soils and aids in rainwater infiltration (Jordan 1981), but seedings at creosotebush site were seldom successful and the treated area is usually reinvaded by creosotebush or annual forbs and grasses (Cox et al. 1984a). Pelleted tebuthiuron [N-(5-(1,ldimethylethyl)-1,3,4-thiadiazol2-yl)-WWdimethylurea] effectively controls creosotebush (Jacoby et al. 1982) and perennial grasses can be established if grass seeds and pellets are applied at the same time (Baur et al. 1977). Grass seedlings, however, may not survive if pellets are applied after seeds germinate because seedling roots encounter the herbicide as it moves through the upper soil profile (Baur 1979). The semidesert grasslands of the southwestern U.S.A. and northern Mexico are of great importance to the livestock industry, but the chances of reestablishing forage grasses are low because of erratic precipitation in summer. Therefore, it is important to address the effects of precipitation on plant establishment, persistence, and forage production. More than 300 forb, grass, and shrub species have been sown at 400 locations in the southwestern U.S.A. and northern Mexico during the past 90 years (Cox et al. 1982). A successful seeding was more likely to occur if seed of the following species were sown prior to the summer rains: (1) ‘A-68’ Lehmann lovegrass (Eragrostis lehmanniana), (2) ‘A-84’ and (3) ‘Catalina’ Boer lovegrass (E. curvula var. conferta), (4) ‘Cochise’ Atherstone lovegrass (E. lehmanniana X E. trichophera), (5) ‘S-75’ Kleingrass (Panicum coloratum), (6) ‘Premier’sideoats grama (Bouteloua curtipendula), and (7) ‘common’ buffelgrass (Cenchrus ciliaris). Researchers have evaluated either the relationships between mechanical seedbed preparation and grass establishment or chemical seedbed preparations and grass establishment, but have not attempted to directly compare both seedbed preparations. The purpose of this study was to compare establishment potential and persistence of 7 perennial grasses sown in mechanically and chemically prepared seedbeds.

Land managers have recommended burning or mowing big sacaton (Sporobolus wrightii) grassland in either fall or winter for 100 years. The greatest potential for natural flre would have occurred when lightning strike frequency peaked in summer. The objective of this study was to determine how burning and mowing in fall (October), summer (July) and winter (February) influences big sacaton forage quantity and quality. Plants defoliated in fall produced leaves within 215 to 245 days, those defoliated in summer within 3 days, and those in winter within 20 days. Green and dead forage that accumulated after the burning and mowing in the same seasons were similar, but differences occurred among seasons. Green and dead forage following summer treatments were similar to that on untreated areas within 2 or 3 summer growing seasons, but were reduced on fall and winter treatments. Crude protein in green forage was 3 to 5% greater in treated plants than in untreated plants for 6 weeks after treatment, but forage quality increases were temporary. Burning or mowing at any season removes green forage available to livestock and reduces the amount of green forage that may accumulate for at least 2 summer growing seasons.

Accessions A-68, L-11, L-19, L-28, and L-38 of Lehmann lovegrass (Eragrostis lehmanniana Nees); P-15608 Cochise lovegrass (E. lehmanniana Nees X E. trichophora Coss & Dur.); A-84 and Catalina boer lovegrass (E. curvula var. conferta Nees); Palar Wilman lovegrass (E. superba Peyr.) and P-15630 blue panicgrass (Panicum antidotale Retz.) were seeded at a study site near San Simon, Ariz., in spring 1970 and 1971. Seedbeds were prepared by root plowing and furrow pitting immediately before planting. Growing season precipitation was 136 mm in 1970 and 218 mm in 1971. Mean accession densities in the fall after the initial growing seasons were 18 plants/M2 for both the 1970 and the 1971 plantings. Between fall 1971 and 1972 mean accession densities declined 44% and forage production was unchanged on the 1970 plantings. Accession densities declined 22% and forage production increased 250% on the 1971 plantings. Between fall 1972 and 1982 the majority of seeded plants died and forage production declined 90% on the 1970 plantings. Accession densities declined 78% and forage production declined 84% on the 1971 plantings. Southeastern Arizona and southwestern New Mexico rangelands were overutilized and deteriorated rapidly between 1880 and 1900. Griffith (1901) documented the deterioration and corresponding livestock losses. Cooperative studies to restore these rangelands were initiated in the early 1900's by the Division of Agrostology (USDA) and State Experiment Stations at Tucson, Ariz., and Las Cruces, N. Mex. Blount (1892), Griffith (1907), Keefer (1899), and Thornber (1905) seeded native and introduced grasses on irrigated and rangeland sites and evaluated emergence and survival. Teff [Eragrostis abyssinica (Jacq.) Link.] emerged on irrigated and nonirrigated sites, but long-term survival occurred only at irrigated sites. Native grass either failed to emerge or to survive at southwestern revegetation sites between 1910 and 1934 (Barnes et al. 1958, Cassady 1938, Glendening 1937, and Hendricks 1936). Numerous grass, forbs, and shrub species were introduced after 1930 (Cox et al. 1982). These introduced species were screened for germination, drouth tolerance, and seed production potential at Soil Conservation Service Plant Materials Centers, and a few promising grasses were released for rangeland plantings. Among these were A-68 Lehmann lovegrass and A-84 boer lovegrass; both were introductions from southern Africa. Lovegrass species and newly developed accessions were sown in summer (Bridges 1941 and Herbel et al. 1973) and fall (Bridges 1941) at desert sites in southern New Mexico. A-68 Lehmann and A-84 boer lovegrasses emerged in moist summers, and A-68 emerged in wet winters at lower elevations. Jordan (1970) conducted studies for 9 years to determine the best combinations of mechanical brush control, seedbed preparation, The authors are range scientist, USDA, Agr. Res. Serv., Arid Land Ecosystems Improvement, 2000 East Allen Road, Tucson, Ariz. 85719; and professor, range management, School of Renewable Natural Resources, University of Arizona, Tucson 85719. This paper is published with approval of the Director, University of Arizona College of Agriculture, Agricultural Experiment Station, as Paper No. 3705. The paper reports on work supported by the U.S. Department of the Interior, Bureau of Land Management, and is a cooperative investigation of Agr. Res. Serv., USDA, and the Arizona Agr. Exp. Sta., University of Arizona. Manuscript received January 20, 1983. and time of seeding for emergence and survival of forage grasses at 3 sites in southeastern Arizona. A-68 Lehmann lovegrass emergence and survival was optimized when root plowing and pitting were used to control brush and prepare the seedbed in spring, and when seed were sown immediately after a mechanical treatment. Comparative seedling trials were conducted to select adapted lovegrass and blue panicgrass accessions at a study site near San Simon, Ariz., in 1970 and 1971. The purpose of this paper is to quantitatively document and compare initial and long-term plant densities and forage production for these seeding trials. Study Site and Methods The study site is located 25 km southwest of San Simon, Ariz., near the Arizona-New Mexico State Line in southeastern Arizona. Average annual precipitation is 280 mm, and 30 to 40% occurs in winter. Winter months (November to March) are cold, dry, and windy, and typical of the Chihuahuan Desert (Mabry et al. 1977). Winter precipitation is either evaporated or transpired by shrubs, and apparently not used by seeded grasses (Jordan 1970). Effective summer precipitation falls in late July through October and varied from 98 to 230 mm at San Simon between 1972 and 1982 (National Oceanic and Atmospheric Administration, Annual Climatological Data Summaries 1972-1982). Mean summer precipitation was 165 mm over the 10 years. Figure 1 shows the departure of annual summer precipitation from the 10-year average. Average annual air temperature is 17?C and the frost-free period is 220 days. Soils are deep, well drained, and formed in old alluvium from mixed sources. Soils are classified as Eba gravelly sandy loam, mixed, thermic Typic Haplargids (Vogt 1980). Native perennial grass forage production was 2.5 to 5.0 g/ m2 on

We studied the emergence of 4 lovegrass accessions planted at 0.0,0.5,1.0,1.5, and 2.0 cm depths in Pima silty clay loam, Sonoita silty clay loam, and Comoro sandy loam soils in a greenhouse. Catalina boer lovegrass (Erugrostis curvulu var. confertcr Nees) emergence was superior to A-84 boer lovegrass, A-68 Lehmann lovegrass (Eragrostis lehmanniana Nees) and Cochise lovegrass (Eragrostis lehi however, the clay fraction of the Pima was 60% montmorillionite and the Sonoita was 80% Authors are range scientist, USDA, Agr. Res. Serv., Arid Land Ecosystems Improvement, 2000 E. Allen Road, Tucson, Ark 85719; and graduate student, range management, School of Renewable Natural Resources, University of Arizona, Tucson. Ark. 8572 I. Manuscript received April I, 1983. 204 kaolinite (USDA-Soil Conservation Service, personal COmmUnications). Soils were screened to 5 mm, thoroughly mixed and added to 15 X 15-cm tapered plastic pots to 12.7, 12.2, 11.7, 11.2, and 10.7 cm depths above the pot base. Twenty-five pure live seed of one lovegrass accession were sown on the soil surface on each pot. Soils were added to 12.7 cm depths in all pots; thus, seed were planted at 0.0, 0.5, 1.0, 1.5, and 2.0 cm depths below the soil surface. Pots were subirrigated with distilled water to insure that the soil surfaces were moist and undisturbed during the 1Cday study. Emergence was considered complete when the first leaf was 1.5 cm above the soil surface in those pots planted at depths of 0.5 to 2.0 cm, or when the first leaf was 1.5 cm above the soil surface and the seed radicle had penetrated the soil in those pots in which seed were sown on the surface. Seedlings were counted daily and summed for the 14day experiment. The study was a completely randomized block design, with 6 blocks. Each block contained 60 pots, 4 accessions, 3 soils, and 5 planting depths. Data were subjected to analysis of variance and a Duncan’s new multiple range test (Steel and Torrie 1960) used to separate means (B.05). Results and Discussion Germination of the lovegrass accessions on soil surfaces ranged between 92 and 96%. The emergence of Catalina boer lovegrass was greatest, Cochise lovegrass was intermediate, and A-68 Lehmann and A-84 boer lovegrass were least on soil surfaces (Table 1). Table 1. Mean’ emergence (%) of four lovegrass accessions sown at five soil depths (cm). Emergence from depths Accession 0.02 0.5 1.0 1.5 2.0

A glassbouse study was conducted to dtttrmint how nonftrtillztd and ftrtlllztd solls collected ln crtoto~tbutb [Lunta Mdcntou (DC.) Cov.] communitlts would influence seedling ltaf gowtb and shoot production of Lebmann lovtgrass (Erugrostis Mmadana Nees) and blue pa&grass (Pdcum untidotde Ritz.). Soila were collected at 3 locations around creosottbusb plants: (1) at the crown base (Basal), (2) along tbt outer canopy tdgt (Drip), and (3) ln areas between plants (Open). Ltafltngtbs and shoot production were greatest on nonftrtillztd soils collected at the plant base, inttnntdiatt at the canopy edge, and least in open areas. Leaf lengths and shoot production significantly increased on ftrtilized solls collected in open areas.