Rangeland Soils Research Articles

Does cultivation influence the content and pattern of soil proteins?

Proteins comprise one of the largest N inputs to soils. There is, therefore, a need to investigate the factors involved in the inputs and fate of proteins in soil. While land use management is expected to influence the amount and diversity of soil proteins, the responses of protein as a source of mineralizable N to land use changes have not yet been studied. We hypothesized that extractable soil protein could be a sensitive indicator in evaluating the effect of stress in ecosystem. Soil samples were collected in October of 2009 from a native forest (Typic Calcixerolls) and a native rangeland (Typic Calcixerepts) as well as adjacent cultivated fields in Zagros area, central Iran. Tris–HCl buffer (pH 6.8) containing 1% (w/v) SDS was used for soil protein extraction. The results showed that soil protein content decreased by 64% and 55% in cultivated sites, as compared with their corresponding native forest and native rangeland sites, respectively. To determine the effects of land use changes on soil protein pattern, SDS-PAGE was carried out. Electrophoretic patterns of soil proteins from agricultural soils were clearly different from those of native lands. Protein bands ranged from 17 to 90kDa and from 20 to 62kDa in native forest and in the adjacent cultivated soils, respectively. Protein bands were detected in the range of 17–57kDa for the native rangeland soil but in the range of 17–198kDa for the adjacent cultivated soil. Land use changes were found not only to decrease significantly the amount of soil proteins but also to influence the protein pattern. We achieved the objective of this paper which was to show the potential of the quantity and diversity of soil proteins as indicators of land use changes. The presented soil protein extraction method as well as soil protein content and pattern determination require further validation in a variety of soils types, climates and land use systems.

Physicochemical characteristics of communal rangeland soils along two defined toposequences in the Eastern Cape, South Africa

To proffer a sustainable solution to rangeland degradation, an understanding of the innate soil properties is vital. This study investigated the relative association of surface (0–20 cm) soil physicochemical properties, viz. electrical conductivity, cation exchange capacity (CEC), soil organic carbon, available phosphorus, particle size composition, soil aggregate stability and microbial respiration, along a toposequence in two vegetation types. The study sites and vegetation types were Magwiji (Lesotho Highland Basalt Grassland) and Upper Mnxe (Tsomo Grassland). In each site, we identified three experimental units along toposequence delineation, classified as crest, midslope and valley bottom. Vegetation type significantly (p < 0.05) affected sand fraction, aggregate stability under fast wetting, and mechanical disaggregation and CEC. Toposequence delineation significantly (p < 0.05) affected fast wetting, slow wetting, mechanical disaggregation, microbial respiration and CEC. There was significant variation and relationship between vegetation types, toposequence delineation and soil properties. The results suggest that toposequence delineation more than vegetation type influences soil property rangelands; therefore, in determining site-specific management techniques for communal rangelands it is important to consider the direction and magnitude of these relationships.

Land-Use Conversion Effects on Phosphate Sorption Characteristics in Soils of Forest and Rangeland Sites from Zagros Area, Western Iran

This study was performed to assess the effects of clearing and cultivation on phosphate sorption kinetics and equilibria as well as phosphate buffering behavior of soils in forest and rangelands from Zagros area, western Iran. Total phosphorus and its organic and inorganic fractions were also determined for the soils according to reference methods. The results showed that clearing and cultivation practices caused a significant increase in soil total and total inorganic phosphorus in the forest soils, but a decrease was observed in the rangeland study area. The concentration of soil organic phosphorus, however, decreased in both forest and rangeland soils after long-term cultivation. Phosphate sorption behavior of the soils was also affected by the land-use changes. The time-dependent sorption data for soils of both protected and disturbed sites were adequately fitted by Power function, Elovich and Parabolic diffusion equations. Kinetic parameters related to rate of phosphate sorption including “specific sorption rate at unit time” and “apparent diffusion coefficient” derived from the models were markedly increased after the land-use conversion. The equilibrium-based phosphate sorption on the soils was significantly described by Langmuir and Freundlich isotherms. Sorption capacity and buffering indices of phosphate, calculated from the isothermal equations, also increased in the cultivated soils as compared to the corresponding soils of the protected sites. The results demonstrated that land-use conversion from natural forest and rangeland to agriculture could significantly influence the distribution and sorption of phosphate in the studied soils which should be considered in sustainable land management in the Zagros area.

Factors Affecting Carbon Dioxide Release from Forest and Rangeland Soils in Northern Utah

Laboratory and field CO2 efflux measurements were used to investigate the influence of soil organic C (SOC) decomposability and soil microclimate on summer SOC dynamics in seasonally dry montane forest and rangeland soils at the T.W. Daniel Experimental Forest in northern Utah. Soil respiration, soil temperature, and soil moisture content (SMC) were measured between July and October 2004 and 2005 in 12 control and 12 irrigated plots laid out in a randomized block design in adjacent forest (aspen or conifer) and rangeland (sagebrush [Artemisia tridentata Nutt.] or grass–forb) sites. Irrigated plots received a single water addition of 2.5 cm in July 2004 and two additions in July 2005. The SOC decomposability in mineral soil samples (0–10, 10–20, and 20–30 cm) was derived from 10‐mo lab incubations. The amount of SOC accumulated in the A horizon (16 Mg ha−1) and the top 1 m (74 Mg ha−1) of the mineral soil did not differ significantly among vegetation type, but upper forest soils tended to contain more decomposable SOC than rangeland soils. The CO2 efflux measured in the field varied significantly with vegetation cover (aspen &gt; conifer = sagebrush &gt; grass–forb), ranging from 12 kg CO2–C ha−1 d−1 in aspen to 5 kg CO2–C ha−1 d−1 in the grass–forb sites. It increased (∼35%) immediately following water additions, with treatment effects dissipating within 1 wk. Soil temperature and SMC, which were negatively correlated (r = −0.53), together explained ∼60% of the variability in summer soil respiration. Our study suggests that vegetation cover influences summer CO2 efflux rates through its effect on SOC quality and the soil microclimate.

Potential and Challenges of Soil Carbon Sequestration in Iceland

Soils of Iceland are severely degraded and land resources desertified due to anthropogenic perturbations since AD. 875. Of the total area of 10.3 million hectares (Mha), the land area is 10.0 Mha. Land cover, at the time of settlement 1100 years ago comprised 6.5 Mha of vegetation cover, of which 3.0 Mha was birch (Betula pubescene) woodland and 3.5 Mha other vegetation. At present, the land area under some vegetation cover is only 2.8 Mha, of which highly productive birch cover is only 0.125 Mha. There are 3.7 Mha of severely eroded and barren lands in Iceland. The fossil fuel emission was 0.7 Tg C yr−1 in 1990, 0.82 Tg C yr−1 in 2000, and is projected to be 0.9 Tg C yr−1 in 2010 and 0.95 Tg C yr−1 in 2020. Afforestation and adoption of recommended management practices (RMPs) can lead to terrestrial C sequestration at the rate of 0.01 to 0.05 Mg C ha−1 yr−1 (1 Mg = megagram = 106 g = 1 tonne) in degraded rangeland soils by establishing native lyme grass (Leymus arenarius) and soil organic carbon (SOC) sequestration at the rate of 0.7 to 0.8 Mg C ha−1 yr−1 through N fertilization. Effective erosion control can lead to emission avoidance of 0.01 to 0.02 Tg C yr−1, and restoration of eroded soils to C sequestration of about 1 Tg C yr−1. Potential of terrestrial C sequestration in Iceland is 1.2 to 1.6 Tg C yr−1, which can effectively offset fossil fuel emission by 2025 and beyond, and make Iceland an emission-free nation.

Soil and runoff response to dairy manure application on New Mexico rangeland

Manure disposal is a major challenge for the fast-growing dairy industry in New Mexico. There are currently over 355,000 milking cows in the state and limited cropland on which to use the manure generated by these cows. On the other hand, 80% of the state lands classified as rangelands are suffering from a lack of organic matter and nutrients. Application of dairy manure to rangelands could serve a dual purpose: (1) manure disposal from dairies and (2) soil amendment to improve soil characteristics and promote herbaceous production. Manure was applied at two rates according to phosphorus (P) content: (1) a recommended (light) rate (54 kg P ha −1) to enhance blue grama growth and (2) a gross over-application (heavy) rate (493 kg P ha −1) to determine the effects on runoff and soil properties. Light applications enhanced soil properties including decreased sediment runoff, increased soil organic matter, increased extractable P, and increased soil moisture, whereas heavy applications increased soil salinity, sodium adsorption ratio, and runoff water. Dairy manure can be safely applied at light rates to conserve and enhance rangeland soil properties and their herbaceous productivity. Manure disposal at heavy rates are unsafe. Further study is required to find out if other safe disposal exists between the light and heavy treatments.

Water Treatment Residuals and Biosolids Co‐applications Affect Phosphatases in a Semi‐arid Rangeland Soil

Co‐application of biosolids and water treatment residuals (WTR) land has not been extensively studied but may be beneficial by sorbing excess biosolid‐borne or soil phosphorus (P) onto WTR, reducing the likelihood of off‐site movement. Reduction of excess soil P may affect the role of specific P‐cleaving enzymes. The research objective was to understand the long‐term effects of single co‐applications and the short‐term impacts of repeated co‐applications on soil acid phosphomonoesterase, phosphodiesterase, pyrophosphatase, and phytase enzyme activities. Test plots were 7.5 × 15 m with treatments consisting of three different WTR rates with a single biosolids rate (5, 10, and 21 Mg WTR ha−1; 10 Mg biosolids ha−1) surface co‐applied once in 1991 or reapplied in 2002. Control plots consisted of those that received no WTR–biosolids co‐applications and plots that received only 10 Mg biosolids ha−1. Plots were sampled to a 5‐cm depth in 2003 and 2004, and soil phosphatases and phytase enzyme activities were measured. Soil phosphodiesterase activity decreased in WTR‐amended plots, and pyrophosphatase activity decreased with increasing WTR application rates. In contrast, acid phosphatase and phytase activity increased with WTR addition, with WTR application possibly triggering a deficiency response causing microorganisms or plants to secrete these enzymes. Biosolids and WTR co‐applications may affect enzymatic strategies for P mineralization in this study site. Reductions in phosphodiesterase activity suggest less P mineralization from biomass sources, including nucleic acids and phospholipids. Increased acid phosphatase and phytase activities indicate that ester‐P and inositol‐P may be important plant‐available P sources in soils amended with WTR.

Edaphology Sorptivity and Bioaccessibility of Chromium in a Tropical Rangeland Soil

Edaphology Sorptivity and Bioaccessibility of Chromium in a Tropical Rangeland Soil

Nutrient Availability in Rangeland Soils: Influence of Prescribed Burning, Herbaceous Vegetation Removal, Overseeding with Bromus Tectorum, Season, and Elevation

Soil nutrient availability influences plant invasions. Resin capsules were used to examine soil nutrient bioavailability along 2 sagebrush–grassland elevation transects in the east Tintic Range (Utah) and Shoshone Range (Nevada). In the fall of 2001, treatments were applied to 3 replicate plots at each site, which included prescribed burning, herbaceous vegetation removal, and controls. Cheatgrass (Bromus tectorum L.) was overseeded in small subplots within each treatment. Following treatments in each plot, resin capsules were installed at 15-cm depth in a shrub interspace and a B. tectorum–overseeded area. Nutrient availability was integrated during late fall to spring and spring to late fall for 2 years. Herbaceous vegetation removal increased availability of nitrate (Nevada and Utah) and Ca and Mg (Nevada only) but only during the second sampling period (growing season). Availability of K and ortho-P (Nevada and Utah) and nitrate (Nevada only) was greater on prescribed burned plots. For Utah, availability of ortho-P, K, Ca, Mg, and Fe generally increased with increasing elevation. Availability of Ca, Mg, K, and Fe was greatest during late fall to spring integration periods for Nevada. Overseeding with B. tectorum interacted with the burn treatment to influence availability of Ca, Mg, and Fe (Nevada sites only). Patterns of nutrient availability can be explained by a combination of decreased root uptake in relation to mineralization, differences in soil water content with season and elevation, and nutrient release from vegetation and soil as a consequence of prescribed burning. Herbaceous vegetation removal and burning can raise nitrate availability and increase risk of invasion by nitrophilic species such as B. tectorum. Nutrient availability can be out of phase with plant growth; plants capable of taking up nutrients during cold periods may have a competitive advantage. Resin capsules have utility in quantifying the effects of treatments on the availability of many soil nutrients.

Establishment of Native Species in Soils From Russian Knapweed (Acroptilon Repens) Invasions

Russian knapweed (Acroptilon repens [L.] DC.), an exotic perennial forb, has invaded many native ecosystems in western North America. Russian knapweed's success is attributed to allelopathy, extensive tap rooting, zinc accumulation in soils, and a lack of North American predators. Revegetation following chemical control slows exotic reestablishment, but the impacts of Russian knapweed-invaded soils on the establishment of native forbs and shrubs have not been determined. In a greenhouse experiment, we monitored the establishment of two native forbs, Indian blanketflower (Gaillardia aristata Pursh) and purple prairie clover (Dalea purpurea Vent.) and two native shrubs, winterfat (Krascheninnikovia lanata [Pursh] A.D.J. Meeuse & Smit syn. Ceratoides lanata) and Wyoming big sagebrush (Artemisia tridentata Nutt. subsp. wyomingensis [Hook.] Nutt.) in soils obtained from three Russian knapweed invasions and adjacent noninvaded areas. We analyzed soils collected near Greybull and Riverton, Wyoming, and Greeley, Colorado, for cation exchange capacity, organic matter, electroconductivity, pH, and total nitrogen, carbon, and plant-available potassium, zinc, manganese, copper, and phosphate. We documented seedling emergence of the four natives and Russian knapweed every two days for 14–17 weeks, harvested seedlings biweekly to assess their growth, and determined their zinc accumulation. All species established in invaded soil and seedlings were larger in invaded than in noninvaded soils. Invaded rangeland soils had greater organic matter (8.6% and 1.1% in invaded vs. 2.5% and 0.4% in noninvaded soils) and lower pH (7.4 in invaded versus 8.0 noninvaded soils). Zinc concentrations in invaded soils (from 0.15 to 6.56 mg · kg-1) were not high enough to limit plant growth. Reports that Russian knapweed is a hyper-accumulator of zinc are not supported by our seedling data, which suggests that previously invaded soils may not limit native seedlings. “Russian knapweed” (Acroptilon repens [L.] DC.), una hierba perenne introducida, ha invadido muchos ecosistemas nativos del oeste de Norte América. El éxito del “Russian knapweed” es atribuido a alelopatia, su sistema radical pivotante extensivo, la acumulación de zinc en los suelos y la falta de predadores para esta especie en Norte América. La revegetación posterior al control químico hace mas lento el reestablecimiento de especies exóticas, pero los impactos de los suelos invadidos por “Russian knapweed” sobre el establecimiento de herbáceas y arbustos nativas no ha sido determinado. En un experimento en invernadero monitoreamos el establecimiento de dos herbáceas nativas “Indian blanketflower” (Gaillardia aristata Pursh) y “Purple prairie clover” (Dalea purpurea Vent.) y dos arbustos nativos “Winterfat” (Krascheninnikovia lanata [Pursh] A.D.J. Meeuse & Smit syn. Ceratoides lanata) y “Wyoming big sagebrush” (Artemisia tridentata Nutt. subsp. wyomingensis [Hook.] Nutt.) en suelos provenientes de tres sitios invadidos por “Russian knapweed” y tres sitios adyacentes no invadidos. Analizamos suelos colectados cerca de Greybull y Riverton, Wyoming y Greeley, Colorado para determinar la capacidad de intercambio catiónico, contenido de materia orgánica, conductividad eléctrica, pH, nitrógeno total, carbón, potasio disponible para la planta, zinc, manganeso, cobre y fósforo. Documentamos la emergencia de plántulas de las cuatro especies nativas y del “Russian knapweed” cada dos día durante 14 a 17 semanas, cosechamos plántulas cada dos semanas para evaluar su crecimiento y determinar su acumulación de zinc. Todas las especies se establecieron en suelos los invadidos por “Russian knapweed” y las plántulas fueron más largas que las de los suelos no invadidos. Los suelos de pastizal invadidos por “Russian knapweed” tuvieron más materia orgánica (8.6% y 1.1% en suelos invadidos vs. 2.5% y 0.4% en suelos no invadidos) y menor pH (7.4 en suelos invadidos versus 8.0 en los no invadidos). Las concentraciones de zinc en los suelos invadidos (0.15 a 6.56 mg · kg-1) no fueron lo suficientemente altos para limitar el crecimiento de las plantas. Reportes respecto a que “Russian knapweed” es un hiperacumulador de zinc no son soportados por nuestros datos de plántulas, sugiriendo que los suelos previamente invadidos pueden no limitar las plántulas nativas.

Macronutrient and Trace Element Leaching Following Biosolids Application on Semi-arid Rangeland Soils

The objective of this study was to quantify the leachate concentration of macronutrients and trace elements obtained through intact soil columns containing two rangeland soils with different texture and amended with biosolids. This was done to evaluate the possibility that surface application of biosolids could adversely affect subsurface water quality via leaching. Biosolids were applied on the surface of the soil columns at 0 (control), 7, 18, 34, or 90 Mg ha−1 in dry basis. Results indicated that biosolids did not increase NO3 − − N leaching, except for the application of 90 Mg ha−1 in the Stellar soil (Calciargid), the finer-textured soil. In the Armesa soil (Haplocalcid), the coarser-textured soil, all leachate NO3 − − N concentrations were higher than the maximum contaminant limit (MCL) for drinking water established by USEPA, irrespective of biosolids treatment. Orthophosphate leaching occurred mostly in the Stellar soil and was favored by biosolids application. Of the trace elements that are regulated by USEPA, Cd, Ba, Cr, and Be were found below the MCL for drinking water irrespective of the biosolids application rate or soil type. The application of 90 Mg ha−1 of biosolids represented a significantly higher potential of leaching for many elements and compounds (NO3 − − N, SO4 =, Cl−, Ca, K, Mg, Na, and Sr) than applications of 34 Mg ha−1 or lower. In general, the application of biosolids up to 34 Mg ha−1 did not pose potential adverse effects for subsurface water quality.

Digitally Mapping Gypsic and Natric Soil Areas Using Landsat ETM Data

Mapping salt‐affected soils in remote rangelands is challenging. We used Landsat 7 ETM data to facilitate digital mapping of gypsic and natric soil areas in the upper Colorado River drainage. Optimum index factor band combinations were used to explore the scene. Normalized difference ratio models and threshold values were developed by comparing spectral signatures with gypsic and natric soil areas verified in the field. Gypsic soil areas were mapped using the normalized difference ratio of Bands 5 and 7 with a threshold &gt;0.11, probably related to the spectral reflectance of gypsum within a few centimeters of the surface. All sites predicted to be gypsic soil areas were determined to be gypsic by field assessment, and 87% of the field‐observed gypsic soil areas were correctly predicted. Natric soil areas were mapped using the normalized difference ratio of Bands 5 and 4 with a threshold &gt;0.19, possibly related to the co‐occurrence of Fe‐bearing minerals with natric soil areas. Most of the sites predicted to be natric were determined in the field to be natric (82%), but only half of the field‐observed natric areas were correctly predicted, indicating that natric soils are harder to detect spectrally than gypsic soils. While the gypsic model may be transferred to other areas, particularly in the arid Colorado Plateau, transfer of natric models would be difficult. Normalized difference ratio models can be developed for other digital soil mapping areas where land surface features produce differences in Landsat spectral band reflectances.

Fertilizer-Derived Uranium and Sulfur in Rangeland Soil and Runoff: A Case Study in Central Florida

Fertilizer applications to rangeland and pastures in central Florida have potential impact on the nutrient–sensitive ecosystems of Lake Okeechobee and the Northern Everglades. To investigate the effects of fertilizer applications, three soil profiles from variably managed and improved rangeland, and four samples of surface runoff from both fertilized and unfertilized pasture were collected. In addition to determining nutrient concentrations, isotopic analyses of uranium (U) and sulfur (S) were performed to provide isotopic evidence for U derived from historically applied phosphate (P)-bearing fertilizer (234U238U activity ratio =1.0 ± 0.05), and Sderived from recently applied ammonium sulfate fertilizer(δ34S=3.5permil).The distribution and mobility of fertilizer−derived U in these samples is considered to be analogous to that of fertilizer−derived phosphate.Variations of U concentrations and234U/238U activity ratios in soils indicate contribution of fertilizer-derived U in the upper portions of the fertilized soil (15–}34 percent of total U). The U isotope data for runoff from the fertilized field also are consistent with some contribution from fertilizer-derived U. Parallel investigations of S showed no consistent chemical or isotopic evidence for significant fertilizer-derived sulfate in rangeland soil or runoff. Relatively abundant and isotopically variable S present in the local environment hinders detection of fertilizer-derived sulfate. The results indicate a continuing slow-release of fertilizer-derived U and, by inference, P, to the P-sensitive ecosystem, and a relatively rapid release of sulfate of possible natural origin.

The role of the native soil community in the invasion ecology of spotted ( Centaurea maculosa auct. non Lam.) and diffuse ( Centaurea diffusa Lam.) knapweed

Diffuse ( Centaurea diffusa Lam.) and spotted knapweed ( Centaurea maculosa auct. non Lam.) are damaging exotic plant invaders of North American rangelands. Although existing weed management techniques can successfully reduce negative impacts of knapweeds, these plants continue to spread in an unpredictable manner. The successful spread of knapweeds into native plant communities may be driven, in part, by interactions between these plants and native soil communities. This study was conducted to evaluate the relative benefit of native soil communities to two native plants and two knapweeds and to investigate the growth of these plants in soil from knapweed infestations and from adjacent native rangelands. Individual plants of bluebunch wheatgrass ( Pseudoroegneria spicata (Pursh) A. Löve), yarrow ( Achillea millefolium L.), spotted and diffuse knapweed were grown in a greenhouse in field collected soil. The relative benefit of the native soil community was determined by comparing emergence and production of native plants and exotic knapweeds in autoclaved versus unautoclaved native rangeland soil. Emergence and production were also determined in the greenhouse for native plants and exotic knapweeds grown in soil collected from the core and perimeter of knapweed infestations and in soil from the adjacent, uninvaded native rangeland. The native soil community had a negative effect on the growth of bluebunch wheatgrass ( P. spicata (Pursh) A. Löve) and diffuse knapweed, but a positive effect on spotted knapweed emergence. The interactions between yarrow ( A. millefolium L.) and the native soil community were variable. The native soil community appears to be more beneficial to spotted knapweed than to the other plants studied, including diffuse knapweed. Therefore, it appears that two closely related knapweeds have very different interactions with soil biota and perhaps different strategies for invasion. Soil from diffuse and spotted knapweed infestations did not prevent growth of two native plants. Diffuse knapweed growth was not promoted by soil from within a diffuse knapweed infestation, but soil from the core of a spotted knapweed infestation did increase emergence of spotted knapweed.

Soil carbon distribution and quality in a montane rangeland-forest mosaic in northern Utah

Relatively little is known about soil organic carbon (SOC) dynamics in montane ecosystems of the semi-arid western U.S. or the stability of current SOC pools under future climate change scenarios. We measured the distribution and quality of SOC in a mosaic of rangeland-forest vegetation types that occurs under similar climatic conditions on non-calcareous soils at Utah State University's T.W. Daniel Experimental Forest in northern Utah: the forest types were aspen [ Populus tremuloides] and conifer (mixture of fir [ Abies lasiocarpa] and spruce [ Picea engelmannii]); the rangeland types were sagebrush steppe [ Artemisia tridentata], grass-forb meadow, and a meadow-conifer ecotone. Total SOC was calculated from OC concentrations, estimates of bulk density by texture and rock-free soil volume in five pedons. The SOC quality was expressed in terms of leaching potential and decomposability. Amount and aromaticity of water-soluble organic carbon (DOC) was determined by water extraction and specific ultra violet absorbance at 254 nm (SUVA) of leached DOC. Decomposability of SOC and DOC was derived from laboratory incubation of soil samples and water extracts, respectively. Although there was little difference in total SOC between soils sampled under different vegetation types, vertical distribution, and quality of SOC appeared to be influenced by vegetation. Forest soils had a distinct O horizon and higher SOC concentration in near-surface mineral horizons that declined sharply with depth. Rangeland soils lacked O horizons and SOC concentration declined more gradually. Quality of SOC under rangelands was more uniform with depth and SOC was less soluble and less decomposable (i.e., more stable) than under forests. However, DOC in grass-forb meadow soils was less aromatic and more bioavailable, likely promoting C retention through cycling. The SOC in forest soils was notably more leachable and decomposable, especially near the soil surface, with stability increasing with soil depth. Across the entire dataset, there was a weak inverse relationship between the decomposability and the aromaticity of DOC. Our data indicate that despite similar SOC pools, vegetation type may affect SOC retention capacity under future climate projections by influencing potential SOC losses via leaching and decomposition.

Long-term impacts of infrequent biosolids applications on chemical and microbial properties of a semi-arid rangeland soil

A plot study was conducted to quantify long-term (>12 years) impacts of a single biosolids application, and short-term impacts (<2 years) of a repeated application, on semi-arid rangeland soil chemical and microbial parameters. In 2003 and 2004, plots which had received 0, 2.5, 5, 10, 21, or 30 Mg biosolids ha−1 once in 1991 (long-term plots), or again in 2002 (short-term plots), were sampled and analyzed for soil chemical parameters, microbial biovolumes, C and N mineralization activities, Biolog EcoPlate substrate utilization potential, and plant productivity and tissue quality. Repeated applications temporarily exacerbated differences in soil chemical properties among treatments, but after 2 years, soil chemistry trends were similar between short-term and long-term plots. Soils which received a repeated application of 21 or 30 Mg biosolids ha−1 had greater bacterial biovolumes and C and N mineralization activities. In long-term plots, mineralization activities were stimulated only at the highest rate. Biosolids-amended soil communities also utilized Biolog substrates more quickly compared to communities from control plots. Plant biomass increased, whereas plant diversity and plant C/N ratio decreased with increasing application rate for both short- and long-term plots. Infrequent biosolids application had positive ecosystem effects in terms of site management objectives, with relatively low extractable metal levels in soil and greater plant biomass and tissue quality despite reduced species richness.

Impacts of overgrazing and reclamation on soil resources in rangeland ecosystems in Huailai Basin, Heibei, China

The soil constituents and relations between the variation of soil resources and plant communities in three adjacent sites representing the overgrazing, reclamation and comparatively undusturbed communities respectively were quantified and examined in study are in Huailai Basin, Hebei Province, China. There have been significantly greater constituent of C, N, P in the soils of shrubland site. Corg, Ntotal, Navail and Paval were between 1. 18 and 3. 90 times more concentrated in the soils of shrubland site in comparison with the other two sites. Although the Ptotal concentration was lower in shrubland soils than in overgrazed rangeland soils, the Pavail concentration, however, was significantly greater in the soils of shrubland site comparing to those in the soils of rangeland and millet field sites. Among the three sites, CV exceeding 40% were found for SO4, Cl, and F ion. The CV of organic carbon also exceeded 40% but only in the soils of millet field site. The highest CV were found for F, SO4, ion in the soils of shrubland and overgrazed rangeland sites, while for Cl and SO4 ion in those of millet field site. The results also showed that the introductions of shrubs are of vital importance for the accumulation of soil nutrients and maintenance of soil fertilities, and also for the restoration and reconstruction of deseritified ecosystems.

Modeling soil CO2 emissions from ecosystems

We present a new soil respiration model, describe a formal model testing procedure, and compare our model with five alternative models using an extensive data set of observed soil respiration. Gas flux data from rangeland soils that included a large number of measurements at low temperatures were used to model soil CO2 emissions as a function of soil temperature and water content. Our arctangent temperature function predicts that Q10 values vary inversely with temperature and that CO2 fluxes are significant below 0 °C. Independent data representing a broad range of ecosystems and temperature values were used for model testing. The effects of plant phenology, differences in substrate availability among sites, and water limitation were accounted for so that the temperature equations could be fairly evaluated. Four of the six tested models did equally well at simulating the observed soil CO2 respiration rates. However, the arctangent variable Q10 model agreed closely with observed Q10 values over a wide range of temperatures (r2 = 0.94) and was superior to published variable Q10 equations using the Akaike information criterion (AIC). The arctangent temperature equation explained 16–85% of the observed intra-site variability in CO2 flux rates. Including a water stress factor yielded a stronger correlation than temperature alone only in the dryland soils. The observed change in Q10 with increasing temperature was the same for data sets that included only heterotrophic respiration and data sets that included both heterotrophic and autotrophic respiration.

Changes in soil carbon and soil nitrogen after tree clearing in the semi-arid rangelands of Queensland

Changes in soil carbon (C) and nitrogen (N) stocks following tree clearing were estimated at 32 rangeland sites in central and southern Queensland by using paired-site sampling. When corrected for soil bulk-density differences at each site, average soil C across all sites decreased after tree clearing by 8.0% for 0–0.3-m soil depth, and by 5.4% for 0–1.0-m depth; there were corresponding declines in soil C of 2.5 and 3.5tha–1, respectively. Mean soil C stocks (excluding surface litter, extractable roots and coarse charcoal) at uncleared sites were 29.5tha–1 for 0–0.3-m soil depth, and 62.5tha–1 for 0–1.0-m depth. Mean soil C stocks (0–0.3m) were 41% of the mean total C for the soil–plant system (soil + litter/woody debris + stand biomass) at uncleared sites. Soil C decline (0–0.3m) accounted for approximately 7% of the average total C lost because of land clearing across all sites. Soil C stocks at uncleared sites were correlated with tree basal area, clay content and soil phosphorus (P) content. Changes in soil C after tree clearing were strongly correlated to initial soil C contents at the uncleared sites, and were associated with particular vegetation groups and soil types. Changes in soil N were strongly correlated with changes in soil C; however, the average change in soil N across all sites was not significant. Given the size of the C and N pools in rangeland soils, the factors that influence soil C and soil N dynamics in rangeland systems need to be better understood for the effective management of C stocks in these soils.

A framework relating soil surface condition to infiltration and sediment and nutrient mobilization in grazed rangelands of northeastern Queensland, Australia

AbstractThe effect of grazing‐induced variation in soil surface condition on infiltration and runoff composition was studied at the small patch scale using a rainfall simulator. A range of sites was selected to represent soil surface conditions typical of the more widely distributed rangeland soils in northeastern Queensland. A simple soil surface condition classification scheme relates ground cover and a few easily recognizable surface features to mean infiltration, sediment and nutrient concentration data. Earthworm activity was identified as being a significant factor in recovery of soil hydrological function. A broader framework is proposed that encapsulates past, current and future trends in soil surface condition in relation to landscape hydrological response and that provides a basis for future research. Copyright © 2004 John Wiley &amp; Sons, Ltd.