J. L. Boettinger

Soil development along an elevational transect in the western Sierra Nevada, California

Soil development along an elevational transect on the western slopes of the the central Sierra Nevada was investigated to assess the effects of climate on soil properties and processes. The transect of seven soils formed in granitic residuum spans elevations from 198 to 2865 m with mean annual temperature and precipitation differences of 13°C (3.9–16.7) and 94 cm (33–127), respectively. Soil pH decreased by about two units and base saturation decreased from 90 to 10% with increasing elevation. Concentrations of organic C in the solum increased with elevation, with the largest single increase occurring between the oak woodland (5–6 kg C/m2) and mixed-conifer sites (10–15 kg C/m2). Clay mineralogy showed a general trend of desilication and hydroxy-Al interlayering of 2:1 layer silicates with increasing elevation. The degree of chemical weathering, based on clay and secondary Fe oxide concentration in the solum, showed a maximum (clay = 536 kg/m2 and Fe oxides = 24 kg/m2) at mid-elevations having intermediate levels of precipitation and temperature. While some soil properties show a continuous progression (e.g., organic carbon, base saturation, clay mineralogy) with elevation, other properties (e.g., pH, soil color, clay and secondary Fe oxide concentrations) show a pronounced change (threshold-type step over a short distance at about 1600 m. The explanation for the abrupt nature of this shift is not known; however, it coincides with the approximate elevation of the present-day average effective winter snow-line.

Canopy vs. soil effects of shrubs facilitating tree seedlings in Mediterranean montane ecosystems

Abstract Question: Is the facilitative effect of nurse shrubs on early recruitment of trees mediated by a ‘canopy effect’ (microclimate amelioration and protection from herbivores), a ‘soil effect’ (modification of soil properties), or both? Location: Two successional montane shrublands at the Sierra Nevada Protected Area, SE Spain. Method: Seedlings of Quercus and Pinus species were planted in four experimental treatments: (1) under shrubs; (2) in open interspaces without vegetation; (3) under shrubs where the canopies were removed; (4) in open interspaces but covering seedlings with branches, mimicking a shrub canopy. Results: Both effects benefited seedling performance. However, microclimatic amelioration due to canopy shading had the strongest effect, which was particularly pronounced in the drier site. Below-ground, shrubs did not modify soil physical characteristics, organic matter, total N and P, or water content, but significantly increased available K, which has been shown to improve seedling water-use efficiency under drought conditions. Conclusions: We propose that in Mediterranean montane ecosystems, characterised by a severe summer drought, pioneer shrubs represent a major safe site for tree early recruitment during secondary succession, improving seedling survival during summer by the modification of both the above- and below-ground environment. Nomenclature: Castroviejo et al. (1986–2001) for Quercus and Pinus species, and Molero-Mesa et al. (1992) for shrub species.

Digital soil mapping: bridging research, environmental application, and operation

Digital Soil Mapping is the creation and the population of a geographically referenced soil database. It is generated at a given resolution by using field and laboratory observation methods coupled with environmental data through quantitative relationships. Digital soil mapping is advancing on different fronts at different rates all across the world. This book presents the state-of-the art and explores strategies for bridging research, production, and environmental application of digital soil mapping.It includes examples from North America, South America, Europe, Asia, and Australia. The chapters address the following topics: - exploring new environmental covariates and sampling schemes - using integrated sensors to infer soil properties or status - innovative inference systems predicting soil classes, properties, and estimating their uncertainties - using digital soil mapping and techniques for soil assessment and environmental application - evaluating and using legacy soil data - protocol and capacity building for making digital soil mapping operational around the globe.

Landsat Spectral Data for Digital Soil Mapping

We propose that Landsat remotely sensed spectral data represent useful environmental covariates for digitally mapping soil distribution on the landscape, especially in arid and semiarid areas. Based on the common conceptual model that unique soils are the products of unique sets of soil-forming factors, Landsat spectral data can represent environmental covariates for vegetation (e.g., normalized difference vegetation index, fractional vegetation cover) and parent material and/or soil (e.g., band ratios diagnostic for gypsic and calcareous materials). In areas with sufficient relief, topographic data (e.g., slope, compound topographic index) derived from digital elevation models (DEMs) can be combined with Landsat-derived data to quantitatively model soil distribution on the landscape. These digital data can by analyzed using commercially available image processing software. Various classification and analysis methods (e.g., optimum index factor; principle component analysis; unsupervised and supervised classification) can be used to recognize meaningful soil-landscape patterns. . Training sites can be selected from existing soil surveys or from areas that have actual field data collection points. Accuracy assessment with independent field observation can be performed, and various classification methods can be used to generate estimates of prediction error. Landsat scenes are spatially explicit, physical representations of environmental covariates on the land surface. While the 30-m spatial resolution and fairly coarse spectral resolution may limit some applications, the wide availability and low expense should facilitate the utility of Landsat spectral data in digital soil mapping.

Ammonium-loaded clinoptilolite : A slow-release nitrogen fertilizer for sweet corn

Abstract Nitrogen (N) loss from irrigated cropland, particularly sandy soils, significantly contributes to nitrate (NO3 ‐) contamination in surface and ground waters and increases N applications to crops. Ammonium‐loaded clinoptilolite (A‐Cp) may reduce N leaching from sandy soils while sustaining plant productivity. We conducted two greenhouse plant growth experiments with sweet corn (Zea mays L.). Pots containing a sandy soil planted with sweet corn were fertilized with either ammonium sulfate (AS) or one of three size fractions of A‐Cp, small (<0.25 mm), medium (0.25 to 2 mm), or large (2 to 4 mm), at rates of 112, 224, or 336 kgN ha‐1 (Experiment #1) and 112 or 224 kg N ha‐1 (Experiment #2). We compared ammonium (NH4 +) and NO3 ‐ leaching from these pots and compared corn relative growth rates (RGR), leaf area ratio (LAR), and net assimilation rate (NAR) among all N fertilizers. Soil amended with AS leached 10 to 73% of the added N, depending on N rate, whereas <5% of the added N leached from the A‐Cp...

Soil depth assessment of sagebrush grazing treatments using electromagnetic induction.

Depth to a root restricting layer affects both soil moisture and nutrient availability, resources strongly correlated to plant cover and production. We evaluated the potential of 2 electromagnetic induction meters (EM38 and EM31) for non-destructively assessing soil depth to bedrock in 2 long-term seasonal sagebrush steppe sheep grazing treatments with different vegetational compositions. Apparent conductivity readings, measured with the EM38 and EM31 in both the horizontal (H) and vertical (V) dipole orientations, were positively related to soil depth. Apparent conductivity measured with the EM31H (r2 = 0.78) and EM38V (r2 = 0.75) were the best predictors of depth. Soil depth distributions were similar between grazing treatments based on Kolmogorov-Smirnov (K-S) tests of the EM38H apparent conductivity (P = 0.47) and EM38V apparent conductivity (P = 0.56). In constrast, K-S tests for the EM31H apparent conductivity (P = 0.09) and EM31V apparent conductivity (P < 0.01) indicated the fall-grazed treatment had a larger area in which soil depth exceeded 150 cm. Because less than 2% of each grazing treatment was predicted to have soils deeper than 150 cm, however, overall site differences between the 2 treatments appeared to be minor. Therefore, the vegetational differences between the treatments have probably resulted more from differences in the seasonality of grazing rather than ecological site characteristics as reflected in soil depth. Maps of soil depth indicated both treatments consisted of intermittent shallow and deep soils, created by several parallel basalt pressure ridges. Results suggest electromagnetic induction can effectively assess the spatial variability of soil depth and could aid in selecting sites for rangeland monitoring or manipulation.

Remotely-Sensed Regional-Scale Evapotranspiration of a Semi-Arid Great Basin Desert and its Relationship to Geomorphology, Soils, and Vegetation

Abstract Landsat thematic mapper data are used to estimate instantaneous regional-scale surface water and energy fluxes in a semi-arid Great Basin desert of the western United States. Results suggest that it is possible to scale from point measurements of environmental state variables to regional estimates of water and energy exchange. This research characterizes the unifying thread in the classical climate-topography-soil-vegetation relation —the surface water and energy balance— through maps of the partitioning of energy throughout the landscape. The study was conducted in Goshute Valley of northeastern Nevada, which is characteristic of most faulted graben valleys of the Basin and Range Province of the western United States. The valley comprises a central playa and lake plain bordered by alluvial fans emanating from the surrounding mountains. The distribution of evapotranspiration (ET) is lowest in the middle reaches of the fans where the water table is deep and plants are small, resulting in low evaporation and transpiration. Highest ET occurs in the center of the valley, particularly in the playa, where limited to no vegetation occurs, but evaporation is relatively high because of a shallow water table and silty clay soil capable of large capillary movement. Intermediate values of ET are associated with large shrubs and is dominated by transpiration.

Nondestructive assessment of rangeland soil depth to petrocalcic horizon using electromagnetic induction

The distribution of soil depth to cemented subsoil horizons is important for land evaluation and management, particularly in arid and semiarid rangelands, where plant growth is limited by soil depth. Traditional methods of quantifying soil depth distribution are destructive, time‐consuming, and costly. Therefore nondestructive, efficient, and inexpensive methods for assessing soil depth are needed. We investigated the effectiveness of electromagnetic induction for nondestructively assessing the distribution of soil depth to petrocalcic horizon in a semiarid rangeland landscape in central Utah. Apparent conductivity was measured with the EM31 and EM38 electromagnetic induction meters in an 11.5‐ha survey area and in four 0.1‐ha plots. Soil depth was measured in hand‐excavated pits or in hand‐augered holes. Rangeland soil depth was positively and significantly correlated with apparent conductivity. Apparent conductivity measurements made by different operators were not significantly different, indicating th...

Environmental Covariates for Digital Soil Mapping in the Western USA

Unlike most of the USA, the western region still lacks initial soil mapping on many private and public lands. Spatially explicit soil data are needed to support a variety of land uses including energy development, mining, grazing, agriculture, forest products, recreation, wildlife habitat, species conservation and urban development. The wide diversity of lithology, geomorphology, climate, and vegetation and the vast, difficult-to-access terrain of western landscapes facilitated the development of digital soil mapping. Environmental covariates used in digital soil mapping in the western USA include derivatives of digital elevations models (DEM) and remotely sensed spectral data (RS). DEM-derived data are often used to represent climate and relief (geomorphology, microclimate). The low vegetation cover of arid, semiarid, and seasonally dry climates typical of the West facilitates the use of RS data and its derivatives. Landsat and ASTER data are the most common sources of RS data, and are used to represent organisms (vegetation type and density), parent material (lithology, mineralogy), and soil (mineralogy, wetness, other surface characteristics). Spatially explicit, digital environmental covariates have improved several aspects of soil survey in the western USA including pre-mapping, developing efficient and targeted field sampling plans, and implementation of spatial prediction models.

Biogenic opal as an indicator of mixing in an Alfisol/Vertisol landscape

Abstract Boettinger, J.L., 1994. Biogenic opal as an indicator of mixing in an Alfisol/Vertisol landscape. In: A.J. Ringrose-Voase and G.S. Humphreys (Editors), Soil Micromorphology: Studies in Management and Genesis. Proc. IX Int. Working Meeting on Soil Micromorphology, Townsville, Australia, July 1992. Developments in Soil Science 22, Elsevier, Amsterdam, pp. 17–26.