Soil-plant-microbial relations in hydrothermally altered soils of Northern California

Soils developed on relict hydrothermally altered soils throughout the Western United States present unique opportunities to study the role of geology on above and belowground biotic activity and composition. Soil and vegetation samples were taken at three unaltered andesite and three hydrothermally altered (acid-sulfate) sites located in and around Lassen Volcanoes National Park in northeastern California. In addition, three different types of disturbed areas (clearcut, thinned, pipeline) were sampled in acid-sulfate altered sites. Soils were sampled (0 to 15 centimeters) in mid-summer 2010 from both under-canopy and between-canopy areas within each of the sites. Soils were analyzed for numerous physical and chemical properties along with soil enzyme assays, carbon and nitrogen mineralization potential, microbial biomass-carbon and carbon-substrate utilization. Field vegetation measurements consisted of canopy cover by life form (tree, shrub, forb, grass), tree and shrub density, and above-ground net primary productivity of the understory. Overall, parameters at the clearcut sites were more similar to the unaltered sites, while parameters at the thinned and pipeline sites were more similar to the altered sites. We employed principal components analysis to develop two soil quality indices to help quantify the differences among the sites: one based on the correlation between soil parameters and canopy cover, and the second based on six sub-indices. Soil quality indices developed in these systems could provide a means for monitoring and identifying key relations between the vegetation, soils and microorganisms

Mechanisms responsible for soil phosphorus availability differences between sprinkler and furrow irrigation

From a historical perspective, human-induced soil erosion and resulting soil phosphorus (P) losses have likely occurred for thousands of years. In modern times, erosion risk and off-site P transport can be decreased if producers convert from furrow to sprinkler irrigation, but conversion may alter nutrient dynamics. Our study goal was to determine soil P dynamics in furrow- (in place since the early 1900s) versus sprinkler-irrigated (installed within the last decade) soils from four paired producer fields in Idaho. Furrow- and sprinkler-irrigated soils (0–5 cm; Aridisols) contained on average 38 and 20 mg/kg of Olsen-extractable P (i.e., plant-available P), respectively; extractable P values over 40 mg/kg limit Idaho producers to P application based on crop uptake only. Soil samples were also analyzed using a modified Hedley extraction. Furrow-irrigated soils contained greater inorganic P concentrations in the soluble+aluminum (Al)-bound+iron (Fe)-bound, occluded, and amorphous Fe bound pools. Phosphorus K-edge X-ray absorption near-edge structure (XANES) spectroscopy was unable to detect Feassociated P but indicated greater amounts of apatite-like or octacalcium phosphate-like P in furrow-irrigated producer soils, while sprinkler-irrigated fields had lower amounts of apatite-like P and greater proportions of P bound to calcite. Findings from a controlled USDA-ARS sprinkler- versus furrow-irrigation study suggested that changes in P dynamics occur slowly over time, as few differences were observed. Overall findings suggest that Fe redox chemistry or changes in calcium (Ca)-associated P in flooded conditions altered P availability under furrow irrigation, even in aridic, calcareous soils, contributing to greater Olsen extractable P concentrations in long-term furrow-irrigated fields

Development of vegetation based soil quality indices for mineralized terrane in arid and semi-arid ecosystems.

Soil quality indices are often management driven and attempt to describe key relationships between above- and below-ground parameters. In terrestrial systems, indices that were initially developed and modified for agroecosystems have been applied to non-agricultural systems in increasing number. We developed a soil quality index in arid and semi-arid ecosystems of the Western US impacted by different types of geologic mineralization using the relationship between vegetation community parameters and soil abiotic and biotic properties. We analyzed these relations in soils associated with three different mineralization types: podiform chromite, Copper/Molybdenum porphyry, and acid-sulfate gold vein systems at four different sites in California and Nevada. Soil samples were collected from undisturbed soils in both mineralized and nearby unmineralized substrates as well as from waste rock and tailings. Aboveground net primary productivity, canopy cover and shrub density were measured for the vegetative communities. Minimum data sets were developed based on correlations between the soil and vegetation parameters, refined using principal components analysis, scored using non-linear functions, and combined into an overall soil quality index. The indices are comprised of one or two microbial parameters and three to six abiotic parameters, the latter consisting of nutrients and metals. Given the preliminary development of this approach, the parameters and combinations to arrive at a soil quality index for a given site cannot at this time be correlated or compared with that of another site. This soil quality index approach provides a means of quantifying disturbed ecosystem recovery resulting from mining, and could be applied to other disturbances in a way that readily distills the information for potential use by land managers

Phosphorus Biogeochemistry Across a Precipitation Gradient in Grasslands of Central North America

Soil P transformations and distribution studies under water limited conditions that characterize many grasslands may provide further insight into the importance of abiotic and biotic P controls within grassdominated ecosystems. We assessed transformations between P pools across four sites spanning the shortgrass steppe, mixed grass prairie, and tallgrass prairie along a 400-mm precipitation gradient across the central Great Plains. Pedon total elemental and constituent mass balance analyses reflected a pattern of increased chemical weathering from the more arid shortgrass steppe to the more mesic tallgrass prairie. Soil surface A horizon P accumulation was likely related to increased biocycling and biological mining. Soluble P, a small fraction of total P in surface A horizons, was greatest at the mixed grass sites. The distribution of secondary soil P fractions across the gradient suggested decreasing Ca-bound P and increasing amounts of occluded P with increasing precipitation. Surface A horizons contained evidence of Ca-bound P in the absence of CaCO3, while in subsurface horizons the Ca-bound P was associated with increasing CaCO3 content. Calcium-bound P, which dominates in water-limited systems, forms under different sets of soil chemical conditions in different climatic regimes, demonstrating the importance of carbonate regulation of P in semi-arid ecosystems

Soil-plant-microbial relations in hydrothermally altered soils of Northern California

Soils developed on relict hydrothermally altered soils throughout the Western United States present unique opportunities to study the role of geology on above and belowground biotic activity and composition. Soil and vegetation samples were taken at three unaltered andesite and three hydrothermally altered (acid-sulfate) sites located in and around Lassen Volcanoes National Park in northeastern California. In addition, three different types of disturbed areas (clearcut, thinned, pipeline) were sampled in acid-sulfate altered sites. Soils were sampled (0 to 15 centimeters) in mid-summer 2010 from both under-canopy and between-canopy areas within each of the sites. Soils were analyzed for numerous physical and chemical properties along with soil enzyme assays, carbon and nitrogen mineralization potential, microbial biomass-carbon and carbon-substrate utilization. Field vegetation measurements consisted of canopy cover by life form (tree, shrub, forb, grass), tree and shrub density, and above-ground net primary productivity of the understory. Overall, parameters at the clearcut sites were more similar to the unaltered sites, while parameters at the thinned and pipeline sites were more similar to the altered sites. We employed principal components analysis to develop two soil quality indices to help quantify the differences among the sites: one based on the correlation between soil parameters and canopy cover, and the second based on six sub-indices. Soil quality indices developed in these systems could provide a means for monitoring and identifying key relations between the vegetation, soils and microorganisms

Mechanisms responsible for soil phosphorus availability differences between sprinkler and furrow irrigation

From a historical perspective, human-induced soil erosion and resulting soil phosphorus (P) losses have likely occurred for thousands of years. In modern times, erosion risk and off-site P transport can be decreased if producers convert from furrow to sprinkler irrigation, but conversion may alter nutrient dynamics. Our study goal was to determine soil P dynamics in furrow- (in place since the early 1900s) versus sprinkler-irrigated (installed within the last decade) soils from four paired producer fields in Idaho. Furrow- and sprinkler-irrigated soils (0–5 cm; Aridisols) contained on average 38 and 20 mg/kg of Olsen-extractable P (i.e., plant-available P), respectively; extractable P values over 40 mg/kg limit Idaho producers to P application based on crop uptake only. Soil samples were also analyzed using a modified Hedley extraction. Furrow-irrigated soils contained greater inorganic P concentrations in the soluble+aluminum (Al)-bound+iron (Fe)-bound, occluded, and amorphous Fe bound pools. Phosphorus K-edge X-ray absorption near-edge structure (XANES) spectroscopy was unable to detect Feassociated P but indicated greater amounts of apatite-like or octacalcium phosphate-like P in furrow-irrigated producer soils, while sprinkler-irrigated fields had lower amounts of apatite-like P and greater proportions of P bound to calcite. Findings from a controlled USDA-ARS sprinkler- versus furrow-irrigation study suggested that changes in P dynamics occur slowly over time, as few differences were observed. Overall findings suggest that Fe redox chemistry or changes in calcium (Ca)-associated P in flooded conditions altered P availability under furrow irrigation, even in aridic, calcareous soils, contributing to greater Olsen extractable P concentrations in long-term furrow-irrigated fields

Development of vegetation based soil quality indices for mineralized terrane in arid and semi-arid ecosystems.

Soil quality indices are often management driven and attempt to describe key relationships between above- and below-ground parameters. In terrestrial systems, indices that were initially developed and modified for agroecosystems have been applied to non-agricultural systems in increasing number. We developed a soil quality index in arid and semi-arid ecosystems of the Western US impacted by different types of geologic mineralization using the relationship between vegetation community parameters and soil abiotic and biotic properties. We analyzed these relations in soils associated with three different mineralization types: podiform chromite, Copper/Molybdenum porphyry, and acid-sulfate gold vein systems at four different sites in California and Nevada. Soil samples were collected from undisturbed soils in both mineralized and nearby unmineralized substrates as well as from waste rock and tailings. Aboveground net primary productivity, canopy cover and shrub density were measured for the vegetative communities. Minimum data sets were developed based on correlations between the soil and vegetation parameters, refined using principal components analysis, scored using non-linear functions, and combined into an overall soil quality index. The indices are comprised of one or two microbial parameters and three to six abiotic parameters, the latter consisting of nutrients and metals. Given the preliminary development of this approach, the parameters and combinations to arrive at a soil quality index for a given site cannot at this time be correlated or compared with that of another site. This soil quality index approach provides a means of quantifying disturbed ecosystem recovery resulting from mining, and could be applied to other disturbances in a way that readily distills the information for potential use by land managers

Development and application of a soil organic matter based soil quality index in mineralized terrane of the Western US

Soil quality indices provide a means of distilling large amounts of data into a single metric that evaluates the soil’s ability to carry out key ecosystem functions. Primarily developed in agroecosytems, then forested ecosystems, we set out to develop and apply an index using the relation between soil organic matter and key soil abiotic and biotic properties in more semi-arid of the Western US arid systems impacted by different geologic mineralization types. We studied these relations in three different mineralization types: serpentine, acid sulfate and Cu/Mo porphyry systems at four different sites in California and Nevada. Soil samples were collected from undisturbed soils in both mineralized and nearby unmineralized terrane as well as waste rock and tailings. We measured eight different microbial parameters (carbon substrate utilization, microbial biomass-C, mineralized-C, mineralized-N and enzyme activities of acid phosphatase, alkaline phosphatase, arylsulfatase, and fluorescein diacetate) along with a number of physicochemical parameters. We developed multiple linear regression models between these parameters and both total organic carbon and total nitrogen, and used the ratio of predicted to measured values as our soil quality index. In most instances, pooling unmineralized and mineralized soil data within a given study site resulted in lower model correlations. Enzyme activity was a consistent explanatory variable in the models across the study sites, while carbon substrate utilization rarely occurred in the models. Though similar indicators were significant in models across different mineralization types, pooling data across sites inhibited model differentiation of undisturbed and disturbed sites. This procedure could be used to monitor recovery of disturbed systems in mineralized terrane and to help link scientific and management disciplines