The accuracy of microhiitological techniques for analysis of herbivore diets was evaluated with cattle, sheep, and Angora goats fed grass, forb, and shrub mixtures of known botanical compositions. Two observers performed microhistological analyses on undigested diets as offered and on feces collected. Similarity indices and chi-square tests were used to determine if differences existed among actual diets, estimated diets, and fecal samples. Botanical compositions of diets fed to all 3 anhnal species generally were accurately estimated by fecal analyses. In some other studies, shrubs in ruminant diets have been inaccurately estimated by the microhistological technique. However, in our study, shrubs were accurately estimated with no differences between actual and observed compositions. We attribute this to the fact that shrub materials used in our study had a high proportion of current growth relative to woody materials. Woody plant parts had lower proportions of identifiable epldermal material than leaves and young stems. In grass-forb diets, forbs sometimes were overestimated and differentiation among grasses was difficult. However, In most cases, observers could precisely estimate diets of the 3 herbivore species.

On the Jornada Experimental Range in southern New Mexico, 2 belt transects, 30.5 cm in width and totnling 2,188 m in length, were established in 1935 on 2 areas where honey mesquite (Prosopis ghzndulosa Torr.) was spreading into black grama [Boutelouu eriopoda (Torr.) Torr.] grassland. Maps were made of the transects which portrayed the vegetation occurring in each of the 7,180 contiguous, O.OPm2 plots along the transect. The vegetation on the transects in 1980 was compared to that portrayed by the transect maps made in 1935. One transect had been read in 1950 and 1955. During the 45-year period mesquite attained complete dominance and many new mesquite dunes formed. Black grama had a relatively high frequency in 1935 but bad completely disappeared by 1980, both on an area grazed by livestock and on an area protected from grazing. Mesa dropseed [Sporobolus fZexuosus (Thurb.) Rydb.], fluffgrass [Erloneuronpu&hellum (H.B.K.) Tateokalbnd broom snakeweed [Xmthocephuhm sarottVae (Pursh) Shinners] increased in abundance, even during the drought period between 1950 and 1955. Only 25% of the perennial forb species encountered in 1935-55 were found in 1980. The spread of honey mesquite (Prosopis glandulosa Torr.) and other shrubs in the Southwest has been well documented, with heavy grazing, seed dispersal by domestic animals and periodic droughts being advanced as causes contributing to the increase in shrubs (Buffington and Herbel 1965; York and Dick-Peddie 1969). Mesquite has many features which enable it to exploit altered ecosystems. These include rapidly developing, deep taproots and long lateral roots, long-lived seeds, high germination rates over a wide range of temperature and moisture conditions, ability to withstand high negative water potentials, high water use efficiency, and the ability to regenerate from underground dormant buds following injury (Glendening and Paulsen 1955, Mooney et al. 1977). Mesquite has increased in abundance on a wide range of soil types but in southern New Mexico its greatest increase has been on sandy soils (Buffington and Herbel 1965). In arid areas mesquite typically grows as a low multi-stemmed shrub. These multistemmed plants entrap drifting sand, forming what has been called "coppice dunes" (Melton 1940). Vast areas of former desert grassland have been transformed into hummocky landscapes dominated by mesquite dunes. Dunes large enough to class as pedons have developed soils which are distinct from those of the interdunal areas (Giles 1966). Mesquite dunelands have an appearance of stability but considerable soil movement was found over a 45-year period (Gibbens et al. 1983). The transformation of desert grasslands into dynamic dunelands has resulted in the complete loss of Authors are respectively,. former graduate student, Department of Animal and

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.

An experiment was conducted to determine values for the mineralization potential (No), rate constant (k), and rate of mineralization for soils freshly amended with sewage sludge, and to determine the influence of soil type and sludge rate on these values. A secondary objective was to determine if the sum of two exponential functions could better model N mineralization than a single exponential functions, as is normally used. A clayey soil (Glendale, a Typic Torrifluvent) and a sandy soil (Latene, a Typic Calciorthid) were amended with three rates (0, 15, and 30 g kg−1) of gamma irradiated, dried, anaerobically digested sewage sludge. The Glendale soil was mixed with sand (1:1 by weight) to increase aeration. Triplicate 80‐g samples of each soil mixture were incubated aerobically for 32 weeks at 0.01 MPa moisture tension and 35°C. Before incubation and periodically during incubation, the soils were leached with 0.01M CaCl2 and the leachate analyzed for NH+4, NO‐2, and NO‐3. No and k were estimated by a nonlinear least squares iterative statistical method. Cumulative (NO‐3 + NO‐2)‐N at the end of 32 weeks was dependent on sludge rate, but not on soil type or the soil type‐sludge rate interaction. Cumulative (NO‐3 + NO‐2)‐N for the 0, 15, and 30 g kg−1 treatments were 60.9, 137.4, and 182.6 mg (NO‐3 + NO‐2)‐N kg−1, respectively. Mineralization rates decreased rapidly the first two weeks, followed by a slower decrease with time. Rates were higher in sludge‐amended soil than in unamended soil and averaged 0.6, 1.8, and 2.2 mg (NO‐3 + NO‐2)‐N kg−1 week−1 for the 0, 15, and 30 g kg−1 treatments, respectively, after 32 weeks. Several methods of estimating No and k were attempted. The best estimates for sludge‐amended soil were obtained by modelling N mineralization as the sum of two exponentials. Total N mineralization (organic N loss, x̄ (mean) = 63%) was more than twice that of net N mineralization (NO‐3 + NO‐2‐N accumulated, x̄ = 27%). Total and net mineralization were greater in the Glendale soil (x̄ = 68% and 30%, respectively) than in the Latene soil (x̄ = 58% and 24%, respectively). Total mineralization increased with sludge addition, but net mineralization decreased with sludge addition. Denitrification losses probably accounted for the discrepancies between total and net mineralization. Denitrification increased with sludge addition and was greater in the Glendale than the Latene soil.

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