Wilbert H. Blackburn

Water budget for south Texas rangelands.

Understanding hydrologic processes is essential to determine if water yield augmentation is possible through vegetation manipulation. Nine large non-weighing lysimeters, each 35 m2, were installed on the La Copita Research Area, 20 km south of Alice, in the eastern Rio Grande Plain of Texas. The non-weighing lysimeters were used to test the hypothesis that honey mesquite (Prosopis glandulosa var glandulosa Torr.) shrub clusters have greater evapotranspiration rates than grass interspaces. Annual evapotranspiration rates of shrub clusters and grass interspaces were found to be similar, and both were significantly greater than evaporative losses from bare soil. Surface runoff and deep drainage of water (> 2 m) from the bare soil were significantly greater than from the grass interspaces and shrub clusters. There was no drainage of water below 2 m from the shrub clusters. A total of 22 mm of water percolated below 2 m from the grass interspace during the 18 month study period. These results indicate that no net change in the water budget would occur if shrub clusters were replaced with grasses in years with below average or normal rainfall. Increasing water yield from converting shrub-dominated rangelands to grass-dominated rangelands in south Texas is marginal in this area and limited to years when winter and spring rainfall exceeds potential evapotranspiration. There is little evidence to suggest that the minimal (non-significant difference) increase in percolation and surface runoff from the grass interspaces could be reliably captured and dependably made available off-site.

Vegetation and soil responses to cattle grazing systems in the Texas rolling plains.

The influence of erttle gr8zing on selected veget8tion 8nd soil p8rrmeters were eV8lU8ted on 8 clay Bat range site with shrub zon81, midgrass, and shortgr8ss communities in the Rolling Plrins ne8r Throckmorton, Texur. Measurements were mide on one prsture of each trertment during 1977 following 4 to 20 yerrs of gr8zbtg tre8tments. He8vy, continuous c8ttie yaxing hrd more 8re8 occupied by the shortgr8ss community th8n midgrass community. He8vily gnzed pastures were genenlly dominrted by the shortgrass community, with midgmsses, depending on the degree of utilization, restricted to the shrub zonal community. Conversely, cattle exclosures h8d no shortgrass community, 8nd deferredrotrtion and moderrtely stocked continuously grazed systems hrd much midgrass community with the shortgross community occup ylng only 30% of the area, thus increasing mnge productivity. Veget8tion 8nd soil parameters within the high intensity, low frequency md heavily stocked, continuously gr8xed prstures tended to be similar for the midgrass 8nd shortgmss communities, but the shrub zonal community was generally different. Vegetation md soil parameters in the midgrass community of the moderrrtely stocked, continuously grazed treatment were gener8lly simil8r to shrub zonnl 8nd different from shortgrass communities. Vegetation and soil Vlriables in the exclosures and deferred-rotation treatments were generally similrr among the midgrass md shrub zonal communities; however, they differed from the shortgr8ss communities.

Influence of Crusting Soil Surfaces on Emergence and Establishment of Crested Wheatgrass, Squirreltail, Thurber Needlegrass, and Fourwing Saltbush

Crusting soil surfaces with vesicular pores occur in arid and semiarid regions of the world where herbaceous vegetation is sparse. Morphological properties of crusting surfaces can impair seedling emergence and plant establishment. This study evaluated site preparation and seeding methods and species useful for encouraging successful stand establishment in such soils. Plowing to prepare a seedbed reduced seedling emergence on some soils but increased plant establishment on all soils. More seedlings emerged and established on non-crusting coppice soil beneath shrubs than on crusting interspace soil between shrubs. Crested wheatgrass was the most successful species followed closely by squirreltail and distantly by Thurber needlegrass and fourwing saltbush. Fourwing saltbush seedlings became established and grew well in some treatments. Seedling emergence and establishment were highest with the deep-furrow seeding technique on the non-crusting coppice soil. The standard-drill technique gave the best stand on the site with the largest surface cover of bare, crusting interspace soil. Soils with crusting surfaces occur in many arid and semiarid regions of the world. Various features of these soils in the western United States were described by Hugie and Passey (1964) and Schlatterer (1968). In the Great Basin these soils commonly are associated with northern-desert shrub and salt-desert shrub plant communities that have sparse herbaceous vegetation. In northern Nevada, such soils are found in the Humboldt Loess Belt, an &million-ha area of shallow, windblown silt and very fine sand deposition. These soils are on gently sloping fan piedmonts and nearly level alluvial flats. They include both typic and xerollic Durargids, Haplargids, Nadurargids, and Natrargids and have moderately fine and fine textured B2t horizons. These soils generally are crusted between shrubs (interspace soil) and are noncrusted beneath the shrubs (coppice soil) (Stuart et al. 1971, Blackburn 1975). The microtopographic positions, surface physiognomy, and morphological characteristics of the A horizon were presented by Eckert et al. in 1978. These surficial features are not mapped or measured even in detailed soil surveys, but must be determined on a site by site basis. The crusting interspace surfaces commonly are sandy loam, loam, or silt texture high in very fine sand or silt, with low organic matter content, are massive, and have vesicular pores. These factors contribute to the unfavorable behavThe authors are presently assistant professor of watershed management, Department of Animal and Range Sciences and Range Improvement Task Force, New Mexico State University, Las Cruces, 88003; range scientist, U.S. Dep. Agr., Agr. Res. Serv. Renewable Resources Center, University of Nevada, 920 Valley Road, Reno, 89512; professor of watershed management, Range Science Department, Texas A&M University, College Station, 77843; and professor of Soil Science, Plant, Soil. and Water Science Division, University of Nevada, Reno, 89512. This study was a cooperative investigation among U.S. Dep. Agr., Agr. Res. Serv., Bureau of Land Management, and Agr. Exp. Sta., Univ. of Nevada, Reno. Journal Series No. 483. Plant nomenclature follows Plummer et al. (1977). Manuscript received August 20, I98 I. 282 ior of this surface: unstable and slakes when saturated, dries to a crust that can reduce seedling emergence (Wood et al. 1978), and has a low water infiltration rate and high sediment production (Blackburn 1975). Wood et al. (1978) stated that rangelands with these kinds of soils have higher potential productivity than their present fair to poor condition suggests. These authors postulated that theareas of crusting interspace soil increase with overgrazing, loss of herbaceous cover, and lowered range condition at the expense of noncrusting coppice surface soil. They also stated that revegetation of these problem soils through grazing management alone would be difficult, if not impossible, in a reasonable time and that artificial seeding methods are required to establish forage species. Therefore, we evaluated seedling emergence and plant establishment of various species seeded by different techniques on soils with crusting and non-crusting surfaces.

Infiltration and runoff water quality response to silvicultural and grazing treatments on a longleaf pine forest.

The impacts of intensive vs. extensive silviculture, and moderate continuous livestock grazing vs. no livestock grazing as they relate to infiltration and runoff water quality were evaluated using rainfall simulation. Study sites were located in the Vernon District of the Kisatchie National Forest, Louisiana. Infiltration was greater, and interrill erosion, suspension-solution phase total nitrogen concentrations, and suspension-solution phase total phosphate concentrations were less from areas under extensive silviculture and no livestock grazing than from areas under intensive silviculture and livestock grazing, respectively. Intensive silviculture exposed more bare soil than extensive treatments. Litter cover and litter biomass were significantly reduced by the intensive silvicultural treatment. Livestock grazing also exposed more bare soil mainly resulting from a removal of grass cover and biomass.