No abstract

Scarification in sulfuric acid consistently increased germination of Opuntia edwardsii sp. nov, O. discata Griffiths, and O. lindheimeri Engelm. ♯ OPULI seeds over that of untreated seeds. Optimum constant temperatures for germination were generally 25 to 35 C and germination was not enhanced by alternating temperatures. There was a trend for increased germination following leaching in water for 12 h which suggested the presence of chemical germination inhibitors. Seeds passed through the digestive tracts of cattle exhibited average germination percentages that were 1.5 times greater than seeds removed from ripe fruits.

Establishment of shrubs and other forage plants on arid and semiarid rangelands and salt-contamhtated sites may be enhanced ifecotypes with ability to germinate and establish under moisture stress and high temperatures can be identified. The interactive effects of temperature, osmotic potential, and pH on germination were evaluated with seed from 4 populations of fourwing saltbush [Atr@lex canescens (Pursh) Nutt.] from western Texas. Predicted optimum temperature (15 to 18' C) from osmotic potential by temperature response surfaces for germination of 3 populations (Valentine, Grandfalls, and San Angelo) were similar to those reported for populations of fourwing saltbush from other western states. Germination of seed collected near Texon, Texas was significantly (JYO.01) affected by media pH range 6 to 9. Seed from the Texon population germinated under lower osmotic potentials compared to the other 3 populations. Total germination of all four populations was enhanced by osmotic potentials lower than 0 MPa. Seed from the Texon population may possess germination characteristics more suitable for arid-hmd seeding than those from populations near Valentine, Grandfalls, and San Angelo, Texas. Fourwing saltbush [Atriplex canescens (Pursh) Nutt.], a native, evergreen shrub, is absent or rare on most western Texas rangeland, probably because of the prevalence of continuous, yearlong grazing by cattle, sheep, and/or goats. The species has been successfully used for rehabilitation of oilwell reserve pits where high concentrations of soluble salts and sodium prevented acceptable establishment or growth of other species.1 Our preliminary grazing trials suggest that fourwing saltbush may be valuable for balancing the seasonal deficiencies of protein in native forages (D.N. Ueckert, unpublished data). Fourwing saltbush frequently grows on relatively dry, saline Authors are reseach associate, professor, and research associate, Texas Agricultural Experiment Station, 7887 N Hwy 87, San Angelo 76901 and Grounds Keeper, University Lands,

Fourwing saltbush [A tr@kx cmescens (Pursh) Nutt.] seedlings from 4 western Texas tetraploid populations were established in uniform nurseries at San Angelo, Barnhart, and Marfa, Texas, in 1981 to determine relative adaptability to these respective environments. Survival and canopy development of the ecotypes were similar at the site with the most favorable growing conditions (San Angelo), but the ecotype originating nearest the planting site tended to have greatest survival and canopy size where site conditions were less favorable. Additional shrub attributes evaluated at the !3an Angelo site included: leaf, current year's stem, and wood phytomass, seasonal nutrient concentrations, and floral develop ment and phenotype. prediction equations utilizing plant canopy measurements were used to estimate weights of plant components. Variation in canopy size and yields among individual plants within ecotypes masked detection of significant (PrO.05) differences among ecotypes, but ecotypes from arid environments tended to be larger and to have greater yields than those from more mesic environments. Concentrations of crude protein (CP), phosphorus (P), and digestible organic matter (DOM)of leaves and stems were similar among the 4 ecotypes. Floral development of the ecotype from the most mesic environment progressed at a faster rate than that of ecotypes from more xeric environments. Ecotypes from xeric environments tended to have fewer staminate plants, but more plants with no sex expression than ecotypes from more mesic areas.

Knowledge of the rate woody plant canopy cover increases is essential for understanding the ecology of rangeland plant communities, determining the economic feasibility of brush management practices, and for scheduling initial and maintenance control practices. We determined rates of change in redberry juniper (Juniperus pinchotii Sudw.) canopy cover from the mid 1950s through the late 1990s at 5 locations in western Texas on rangeland that had been chained or grubbed for juniper control and on adjacent untreated areas. Juniper cover was estimated from aerial photographs by the line intercept method using a 10-X monocular lens with a vernier. Juniper cover increased at 0.35 ± 0.06 percentage units year-1 on untreated sites and at 1.01 ± 0.07 percentage units year-1 following chaining or grubbing. Juniper cover returned to pre-treatment levels in an average of 20 years (range 11 to 25) following chaining or grubbing. Herbage production on untreated rangeland was predicted to decline slowly (2.4 to 5.0 kg ha-1 year-1) as juniper cover increased from 6 to 14% and rapidly (> 8 kg ha-1 year-1) as juniper cover increased from 30 to 38%. Herbage production was predicted to decline at a constantly increasing rate following mechanical control of juniper, from < 2 kg ha-1 year-1 in year 1 to 23 kg ha-1 year-1 in year 29. Potential additional livestock carrying capacity due to juniper control would be under estimated by more than 40%, assuming forage production without treatment remained constant during the entire planning horizon of an economic analysis. To avoid significant reductions in livestock carrying capacity, redberry juniper control should be implemented before its canopy cover exceeds about 20%.

Pricklypear (Opuntiaspp.) is a major constraint to rangeland livestock production in several resource areas of Texas. The phenological and physiological stages of pricklypear have heretofore been ignored in relation to timing of herbicide applications. The phenology, percent total nonstructural carbohydrates (TNC), and water content in Lindheimer pricklypear (Opuntia lindheimeriEngelm. # OPULI) were monitored biweekly for 2 yr in the southern Rolling Plains of Texas. TNC in cladophylls, crowns, and roots declined sharply from bud break (late March to late April) through the period of rapid development of new cladophylls and fruits, with minimum levels occurring during mid-July to early August. This depletion period coincides with the period when control has traditionally been attempted with broadcast applications of translocated herbicides with erratic results. Replenishment of TNC in cladophylls and basal crowns occurred during August through March or mid-April; major increases in root TNC occurred from early autumn through midwinter. Application of herbicide in late summer, autumn, or winter when TNC is being replenished in organs bearing meristematic tissue may be more effective for pricklypear control if the herbicide is translocated with photosynthates.

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Clones of superior pollen-and seed-producing plants of 4 fourwing saltbush (Atriplex canescens [Pursh] Nutt.) ecotypes were planted in a seed orchard in west-central Texas to determine if seed production and quality could be enhanced by irrigation and fertilization. Subplots of nitrogen (N) at 112 kg~ha À1 , phosphorous (P) at 112 kg~ha À1 , N þ P at 112 þ 112 kg~ha À1 , or no fertilizer were superimposed on irrigated or dryland main-plots. Neither irrigation nor fertilization affected estimated seed yields or utricle fill during the third growing season after planting. Fertilization did not affect seed germination of any of the saltbush ecotypes on irrigated plots or that of the 2 more xeric ecotypes (Grandfalls and Valentine) on dryland plots. Fertilizer N on dryland plots increased germination of the San Angelo ecotype, and N þ P increased germination of the Texon ecotype. Estimated gross value of the first seed crop was about $4 648~ha À1 even though the superior reproductive traits of parental pistillate plants were poorly expressed by the clones. Fertilization did not affect estimated seed yields in irrigated plots, but N and N þ P increased seed yields in dryland plots in the fourth growing season. Fertilization effects on seed weights varied among irrigated and dryland plots and among saltbush ecotypes. Mortality of the shrubs during the period extending from 1988 to 1990 was not affected by irrigation or fertilization but increased among ecotypes as the xeric nature of their sites of origin increased and as the distance of their sites of origin from the seed orchard increased. Evidence from this study did not strongly support cloning, irrigation, or fertilization for improving seed harvests of fourwing saltbush in west-central Texas. Resumen Clones de plantas superiores en la producció n de polen y semilla de 4 ecotipos de ''Fourwing saltbush'' (Atriplex canescens [Pursh] Nutt.) fueron plantados en un huerto para semilla en la parte centro-oeste de Texas para determinar si la producció n de semilla y su calidad pudiera ser mejorada mediante irrigació n y fertilizació n. Subparcelas de nitró geno (N) a 112 kg~ha À1 , fó sforo (P) a 112 kg~ha À1 , N þ P a 112 þ 112 kg~ha À1 y sin fertilizante fueron sobrepuestas en parcelas irrigadas y sin irrigar que constituyeron las parcelas principales. Ni la fertilizació n ni el riego afectaron los rendimientos estimados de semilla o el llenado del utrículo durante la tercera estació n de crecimiento después de la plantació n. La fertilizació n no afectó la germinació n de la semilla de ninguno de los ecotipos en las parcelas irrigadas o la de los dos ecotipos má s xéricos (Grandfalls y Valentine) en las parcelas sin irrigació n. En las parcelas sin riego, la fertilizació n N incrementó la germinació n en el ecotipo San Angelo y la fertilizació n N þ P incrementó la germinació n del ecotipo Texon. El valor bruto estimado de la primer cosecha de semilla fue aproximadamente $4 648~ha À1 aunque las características reproductivas superiores de las plantas paternales pistil...