Randal J. Southard

Role of pedogenesis in distribution of magnetic susceptibility in two California chronosequences

Abstract Pedons from two soil chronosequences from coastal terraces in northern California were examined and sampled and samples were analyzed to determine the contribution of normal pedogenic processes to the distribution of mass magnetic susceptibility (χ) in soils. Commonly, χ distribution in soils and the formation of susceptibility enhancement in near-surface soil layers are attributed in large part to the in situ conversion of nonferrimagnetic iron oxides and oxyhydroxides to microcrystalline ferrimagnetic minerals. Solubilization of Fe 2+ and subsequent precipitation also contribute to enhancement. We show that χ enhancement occurred throughout the eluvial and in some illuvial horizons to depths as great as 100 cm in these soils. Eluvial horizon χ and χ enhancement increased with increasing soil age. The enhancement of magnetic susceptibility resulted from the accumulation of pedogenic ferrimagnetics and the preferential accumulation of both inherited magnetite and pedogenic maghemite. We use the differential solubility of inherited magnetite and maghemite in citrate-bicarbonate-dithionite and X-ray diffraction to distinguish between the two minerals. Although magnetite is a relatively more durable soil mineral, it did weather and the total amount of magnetite decreased as soil age increased. Sonicated sand grains, free of clay or Fe coatings contributed to susceptibility enhancement. Silt- and clay-sized grains provided the larger part of illuvial horizon χ. Illuviation to or formation of clay-sized ferrimagnetic particles in illuvial horizons probably reduced the observed eluvial enhancement. Enhancement of eluvial horizons and χ distribution throughout the soil oprofiles can be explained by common soil forming processes.

Paleoenvironmental reconstruction from chemical and isotopic compositions of Permo-Pennsylvanian pedogenic minerals

Mineralogical and chemical analysis of Late Pennsylvanian and Early Permian paleosols from the eastern shelf of the Midland basin, north-central Texas, USA, are used to test hypothesized climate change in Late Paleozoic western equatorial Pangea, previously defined independently on the bases of sedimentologic and paleontologic proxies and climate models. The <0.2-μm size phyllosilicate fraction in the studied paleosols exhibits down-profile trends in mineralogy and chemical composition that are consistent with modern weathering profiles suggesting a dominantly pedogenic origin. A stratigraphic trend from kaolinite-dominated profiles in Upper Pennsylvanian paleosols to profiles dominated by smectite and hydroxy-interlayered 2:1 phyllosilicates in Lower Permian paleosols indicates a relatively rapid decrease in soil weathering and leaching in the latest Pennsylvanian followed by a more gradual decrease in leaching throughout the Early Permian. The chemical composition (cation ratios and exchange capacity) of these phyllosilicates further corroborates this shift toward less intensive leaching, presumably in response to climate change from humid to progressively more arid conditions. The phyllosilicates in the <0.2-μm size fraction and contemporaneous pedogenic calcites from the Permo-Pennsylvanian paleosols exhibit a long-term stratigraphic increase in their δ18O values of as much as ∼3.2‰ and ∼5.2‰, respectively. This long-term trend is consistent with a transition throughout the latest Pennsylvanian through Early Permian toward progressively more evaporatively enriched soil waters. Superimposed on the long-term trend is an apparent rapid enrichment (1.5 to 2‰) in phyllosilicate δ18O values immediately above the Pennsylvanian–Permian boundary. Observed oxygen isotope fractionation between the phyllosilicates and calcites within individual paleosols indicate isotopic disequilibrium between mineral pairs. This is attributed to a minor detrital component in the pedogenic clay-dominated phyllosilicate fraction coupled with the effects of seasonality of mineral formation. Inferred δ18O compositions of Late Paleozoic meteoric water (−2‰ to +4‰) are compatible with less intensive soil leaching under conditions of increasing aridity, possibly coupled with a shift in local precipitation from a continental source to a marine source.

Stratigraphy and genesis of Durorthids and Haplargids on dissected alluvial fans, western Mojave Desert, California

Abstract Presumed slow weathering rates in arid-region soils have given rise to the hypotheses that (1) the major carbonate source in most Aridisols is from eolian deposition, and (2) soil horizons cemented by carbonates and opaline silica are indicators of geomorphic surfaces of mid-Pleistocene age. To test these hypotheses we studied the stratigraphy and genesis of four soils, a Typic Durorthid (Alko series), two Typic Haplargids (Neuralia and Garlock series) and a Typic Torripsamment (Cajon series), found in close association on a dissected alluvial fan in the western Mojave Desert. The study area has a rolling topography with the calcareous Alko soil occurring on narrow summits and on the edges of broad summits, Neuralia (calcareous) on broad summits and on sideslopes, Garlock (noncalcareous) on sideslopes, and Cajon in the drainage ways. Soil stratigraphy in an excavated trench indicates that these soils are forming on deposits of differing ages. Paleomagnetic data indicate that at least four aggradational events have occurred in the past 783 ka (thousand years). The sequence of alluvial units in the area is similar to other sequences observed in the Mojave Desert and eastern San Joaquin Valley. The Garlock soil, with 5YR hues and a distinct carbonate-free argillic horizon, occurs on an older geomorphic surface, but younger deposit, than the Alko and Neuralia soils. Rodents are active in the profiles of Alko and Neuralia soils. Bioturbation of the upper soil mantle brings calcareous soil and duripan fragments to the surface, thus creating a pedogenically rejuvenated geomorphic surface on which profile development has been retarded. The occurrence of calcareous Haplargids adjacent to Haplargids that are noncalcareous to a depth of 65 cm, indicates that the atmospheric input of CaCO3 in the study area has been minimal during the Holocene. The rate of CaCO3 accumulation in soils of the study area is estimated to be 0.03 to 0.05 g cm−2 1000 yr−1 over the past 200 ka. A rate of accumulation of 0.27 g cm−2 1000 yr−1 is required to form the 2-cm-thick laminar cap of the upper Alko duripan during the Holocene. This amount could easily be added to the surface by bioturbation from calcareous duripan fragments in the profile. Thus, much of the laminar part of the duripan is probably a Holocene phenomenon.

Mineralogical comparison of agriculturally acidified and naturally acidic soils

SoilacidificationandacceleratedmineralweatheringasaresultofNfertilizationmayresultinasoil solution silica activity that favors the formation of short-range-order aluminosilicates, thereby sequestering Al. Furthermore, soils formed in alluviums of differing lithology may partition Al 3+ into different pools. We hypothesized that parent material silica content controls solution silica concentrations and short-range-order aluminosilicate formation, thereby controlling solution Al 3+ activity. As a result, we expected mineralogy to follow alteration pathways toward the minerals found in weathered naturally acidic (acidic) soils. To test this hypothesis, we compared the mineral assemblages in nonacidified (NA), agriculturally acidified (AA) and acidic soils formed in sialic, mafic, and mixed alluvium. X-ray diffraction analysis revealed that the clay fraction bulk mineralogy of AA soils is similar to their NA counterparts, but in every case, clay activity, as measured by CEC/ clay, was reduced by the acidification process, a trend consistent with mineral alteration trajectories toward the acidic, weathered soils. A combination of selective dissolution and CEC measurements suggested that precipitation of short-range-order hydroxy-Al and aluminosilicates were the dominant mechanisms that control solution Al. In the AA soil derived from sialic parent material, hydroxy-Al was the largest Al pool. In the agriculturally acidified soil derived from mafic parent materials, the short-range-orderaluminosilicatefraction wasthedominantAlpool.AluminumsinksinAAsoilswith mixed lithology were dominated by hydroxy-Al and exchangeable Al. We speculate that ‘‘free’’ (noninterlayer) hydroxy-Al may be a significant Al sink in the AA soils. Our results suggest that shortrange-order aluminosilicates playsome role in controlling soil solution Al activity, but the higher silica content of the parent material did not correlate directly with increased abundance of short-range-order aluminosilicate compounds in acidified soils. This research on soil acidification provides new information on how ammonium fertilization affects the chemical aspects of soil quality, in particular, the partitioning of Al to solid phases that may not be in equilibrium with the bulk clay mineralogy. D 2003 Elsevier Science B.V. All rights reserved.

Soil water content and soil disaggregation by disking affects PM10 emissions.

Row crop agriculture in Californias San Joaquin Valley is a major contributor of particulate matter <10 microm in aerodynamic diameter (PM10). The California Air Resources Board uses fixed PM10 emission values for various tillage operations to monitor and design attainment strategies. However, fixed emission values do not reflect emissions produced by a single implement operating under different soil conditions. This 2-yr study evaluated how PM10 mass concentrations (microg L(-1)) from disking change as a function of gravimetric soil water content (GWC), number of sequential diskings (D1, D2, D3), and the soils weighted mean ped diameter (WMPD). Results showed PM10 increased logarithmically as the soil dried from a GWC of 14 to 4%. Average PM10 values at the lower GWCs were six to eight times greater than at the higher GWCs. Number of diskings also increased PM10, especially in drier soil. Below a GWC of 7%, PM10 for D3 was about twice that for D1. Despite strong correlations between more disking and lower WMPD, a lower WMPD did not always result in an increase in PM10. This underscored the role soil water plays in reducing PM10 at high GWCs despite low WMPDs from multiple diskings. Three-way interactions between GWC, disking, and PM10 showed, on average, that the magnitude of PM10 produced by D1 was 1.3 to 1.6 times lower than by D3, despite having insignificantly different GWC. Therefore, a disking operation can yield two different PM10 values under similar GWCs if the amount of soil disaggregation is different. Our results show that inclusion of soil parameters in PM10 emission estimates is essential to describing agricultures role in air quality violations and to assess the value of proposed mitigation measures, such as conservation tillage.

LUNG INJURY AND FIBROGENIC RESPONSE TO DUSTS FROM CITRUS AND GRAPE HARVESTS

AbstractOusts were collected in citrus orchards and in vineyards from leaf surfaces in the area where harvest operations were ongoing. Six milligrams of each of the dusts was instilled intratracheally into the lungs of rats. All dusts contained approximately the same amounts of quartz. Three days later, the lung lavage fluid was assayed for protein and cell content. In animals that had been exposed to vineyard dusts, the percentage of polymorphonuclear leukocytes in the recovered cells was significantly higher than in control animals. This change was not seen in animals exposed to citrus orchard dusts. One of the vineyard and one of the citrus orchard dusts were instilled either once or four times into other animals, and lung hydroxyproline content, lung lavage composition, and incorporation of bromodeoxyuridine into cellular DNA was measured 1 wk later. Following a single instillation, vineyard dust produced signs of increased cell proliferation in the large airways and terminal bronchioles and, after fo...

Estimating Plant-Available Potassium in Potassium-Fixing Soils

Soil tests commonly used to develop potassium (K) fertilizer recommendations, such as extraction by 1 M ammonium acetate (NH4OAc) at pH 7, measure both soluble and exchangeable K. In soils that fix K so that it is no longer exchangeable, although a portion of it may still be available to plants, additional tests are required to understand the dynamics of soil K. The sodium tetraphenylboron method has been shown in some studies to provide a better measure of plant-available, nonexchangeable K. Two K-fixation-potential tests estimate the amount of K that a soil will fix in a nonexchangeable state. This study uses extractions with ammonium acetate and sodium tetraphenylboron along with the 1-h K-fixation-potential test to analyze the fate of K applied as potassium chloride (KCl) to K-fixing soil samples from the San Joaquin Valley of California. Samples were incubated moist for 1, 2, 4, 8, or 16 days to evaluate the effect of time on the K-test values. The effects of drying on K-fixation potential and NH4OAc-extractable K were also investigated. After application of K at a rate equal to the measured K-fixation potential and incubation for up to 16 days, soils continued to fix added K, though reduced as compared to initial amounts. Drying treated samples increased their subsequent K-fixation potential but had mixed effects on NH4OAc-extractable K. Over the range of incubation times, K-fixation-potential values remained stable for all soils. NH4OAc-extractable K and sodium tetraphenylboron–extractable K values, however, were affected variably by incubation time. The results of this work will be useful for determining K-fertilizer application requirements for K-fixing soils.

Soils of the Pacific Coast Region: LRRs A and C

Land Resource Region (LRR) A is located in the Pacific Northwest of the United States and is dominated by four major mountain ranges (Cascades, Klamath, Coast Range and the Olympics) and two main coastal areas (Puget Sound and Pacific Coast). The Region includes two large valley systems (Willamette Valley and the Puget Lowland) and the adjoining eastern and western mountain foot slopes. The region covers over 234,000 km2. It includes a rich agricultural area due to a mild coastal climate, deep soils formed in alluvium and adequate precipitation for crops. The parent material of the Cascade Mountains is mainly volcanic tephra and residuum, the valleys are primarily mixed alluvial sediments, and the parent materials of the Coast Range, Klamath and Olympic Mountains are mixtures of alluvium, residuum and colluvium derived from sedimentary rocks that are uplifted sea floors and volcanic rocks. Elevations range from sea level to over 4,400 meters in the Cascade Mountains.