Showing papers in "Soil Science Society of America Journal in 1988"

Controls on Natural Nitrogen-15 and Carbon-13 Abundances in Forest Soil Organic Matter

Abstract: We used δ 15 N and δ 13 C measurements to study formation and decay of soil organic matter in surface soils of two oak (Quercus spp.) forests in Wisconsin. There were two controls of soil isotopic compositions: new litter inputs and overall isotopic fractionation during decomposition. Litter inputs lowered soil δ 15 N and δ 13 C values while decomposition increased δ 15 N and δ 13 C values. Leaf and root litter inputs averaged −3.8 and −1.6‰ δ 15 N and −27.3 and −28.2‰ δ 13 C, respectively. Field experiments showed that low surface soil δ 15 N and δ 13 C values resulted when litter inputs were high. Laboratory experiments showed that overall isotopic fractionation during decomposition left residual soil N and C enriched in 15 N and 13 C, and could explain the high δ 15 N and δ 13 C values observed in deeper forest soils (+5.9‰ δ 15 N and −23.6‰ δ 13 C for 10 to 20 cm soils)

Designs for disc permeameters

Abstract: Disc permeameters are designed to measure hydraulic properties of field soils containing macropores and preferential flow paths and are particularly useful in soil management studies. We present here designs for disc permeameters for both positive and negative water supply heads. The effects of the water supply membrane and soil contact material on permeameter performance are examined using approximate quasi-analytic solutions to the flow equation. This analysis provides approximate criteria for the selection of membrane and soil contact materials. Limitations to performance caused by restricted air entry are considered and design criteria are given also. We present in situ tests of the disc permeameter for the early stages of one-dimensional infiltration and an example of the deterministic variation of sorptivity of a field soil with supply potential. Finally, we use ponded and unsaturated sorptivities measured in situ with disc permeameters to find the saturated hydraulic conductivity and flow-weighted mean characteristic pore dimension of a field soil. View complete article To view this complete article, insert Disc 5 then click button8

Using Texture and Other Soil Properties to Predict the Unsaturated Soil Hydraulic Functions

Abstract: Rather than measuring the hydraulic properties directly, we followed a different approach by fitting analytical expressions for the soil water retention and hydraulic conductivity functions to experimental data for a wide range of soils in the Netherlands. (...) Regression analyses are used to relate the estimated model parameters to more easily measured soil properties, such as bulk density and percentages silt, clay and organic matter.

Anion sorption on a calcareous, montmorillonitic soil-arsenic

Abstract: Arsenic sorption on a calcareous, montmorillonitic soil was investigated as a function of solution pH (2-11) at two initial As concentrations (2.0 and 20 mmol m '). Arsenite sorption could not be determined because oxidation of arsenite occurred during the experiment. Arsenate sorption increased with increasing pH, exhibited a maximum near pH 10.5, and decreased at higher pH. Arsenate sorption as a function of pH was studied oh reference minerals representative of the dominant inorganic constituents of the soil: montmorillonite, kaolinite, and calcite. Arsenate sorption on the two clay minerals increased at low pH, exhibited a peak near pH 5, and decreased at higher pH. Arsenate sorption on the calcite increased from pH 6 to 10, peaked between pH 10 and 12, and decreased above pH 12. The constant capacitance model was able to describe arsenate sorption on kaolinite over the entire pH range studied and on montmorillonite and soil below pH 9. The soil sorption maximum near pH 10.5 was much reduced after removal of carbonates, indicating that carbonates play a major role in arsenate sorption above pH 9. Arsenate sorption on soil and calcite was unaffected by the presence of equimolar selenite concentrations.

Infiltration, macroporosity, and mesoporosity distributions on two forested watersheds

Abstract: Macro- and mesopore processes substantially control the subsurface flow in forested watersheds. Limited field scale information is available on spatial variability of macropore infiltration and associated porosity of the hydrologically active macro- and mesopores. The double-ring and tension infiltrometer methods were employed at 37 and 39 locations, respectively, on two contrasting forested watesheds. The spatial variability of infiltration under ponded-flow (macropore-flow) and under 2-, 5-, and 14-cm water tension (mesopore-flow) conditions was determined. The frequency distributions were tested for lognormality with the Shapiro-Wilk ω-statistic and with isopleth probability analysis, and the spatial dependence of these data was tested with semivariogram analysis. The infiltration rates were found to be lognormally distributed, with the mesopore infiltration rates as variable (coefficients of variation of 102-184%) as the macropore infiltration rates (coefficient of variation of 107%). Macropore flow constitued 85% of the ponded flux; however, the mesopore fluxes were large (~ 2 × 10-5 m s-1) and were considered sufficient to infiltrate rainfall without macropores filling and contributing to the flow. The large measured infiltration rates were associated with exceedingly small macroporosities of 0.0003 m³ m-3 and 0.0002 m³ m-3 for the two watersheds. The reduction in infiltration rate with increased tension was described as an exponential function of the diameter of the largest effective pore. Semivariograms revealed no spatial dependence for separation distances >4 m at one watershed and weak spatial dependence for separation distances <15 m at the other. Infiltration into these forested watersheds can be considered a stochastic process for hydrologic modelling

Long-term annual manure applications increase soil organic matter and nitrogen, and decrease carbon to nitrogen ratio

Abstract: The effects of long-term annual applications of cattle (Bos taurus) feedlot manure on the accumulation, decomposition (amounts and rates), and movement of organic matter (OM) and Kjeldahl-determined N (total N) in soil were determined. Manure was applied annually since 1973 at three different levels to nonirrigated and irrigated Dark Brown Chernozemic (Typic Haploborolls) clay loam soil. Significant increases in soil OM and total N content in the first 8 and 6 yr, respectively, as affected by the level of manure application, were limited to the surface 30 cm of soil of the nonirrigated and irrigated land. Tillage did not affect the amount of OM and total N accumulated in the soil, but it did affect their distribution within the 0 to 30-cm depth, which is attributed to placement during incorporation. The accumulation of OM and total N were similar under nonirrigated and irrigated conditions. Manure (C/N ratio of ca. 10.2) lowered the C/N ratio of the soil (ca. 8.2) by small amounts. The accumulation of OM and total N was described by a Michaelis-Menten type of function. A response surface was generated for the accumulation of OM and total N with increasing levels and years of manure application, from which the rates of accumulation and decomposition were derived. The rates of accumulation decrease with years of application such that after two or three decades increases will be small. The model can be used to develop general guidelines for use and disposal of feedlot manure under similar conditions.

Spatial variability of wheat yield and soil properties on complex hills

Abstract: Surface soil and wheat yield were sampled on a 400by 250-m grid to determine the relationship between wheat yield and soil properties influenced by erosion. The study, located in the Dunnigan Hills northwest of Sacramento, CA, began in October 1983. Five transects over complex slopes were made 50 m apart. Every 20 m, along each transect, depth to parent material, surface soil thickness, depth to carbonates, landscape position, and percent slope were recorded. In addition, soil samples were collected to determine particle size, percent organic C, water retention at 33 and 1500 kPa, and pH. One meter square plots of wheat were harvested at each of the 100 sites previously sampled. Subsoil samples were taken at select sites to determine organic C and particle size. Every meter along a 50-m transect, surface soil thickness and percent sand in the surface soil were determined to assess the nugget effect of these variables. Standard regression analyses showed no correlation between percent slope and yield or soil properties. Semivariograms and cross-semivariograms showed a strong spatial dependency between soil properties and wheat yield. Total above ground biomass increased from the knolls to the swales, while harvest index increased in the reverse direction. Particle size distribution varied by landscape position as a result of both mechanical and water erosion. Harvest index was shown to be positively correlated with percent clay <2 but not correlated with percent sand. Surface soil thickness was not found to be spatially correlated with crop growth. View complete article To view this complete article, insert Disc 5 then click button8

Colorimetric determination of oxidizable carbon in acid soil solutions

Abstract: A simple and sensitive method is described that determines, colorimetrically, oxidizable organic matter in solutions from acid soils. It relies on measuring the loss of color by a Mn(III)-pyrophosphate complex as Mn(III) becomes reduced by organic C in the presence of concentrated H2SO4. The method is applicable to 1-mL samples containing 0.08 to 4.0 micromol of organic C and is practically free of interferences in aerobic solutions

Soil Cohesion as Affected by Freezing, Water Content, Time and Tillage

Abstract: This study was developed to determine whether there are substantial annual changes in soil cohesion and to identify major factors causing those changes. Aggregate stability was measured throughout the year on soils in Utah and Idaho using wet sieving techniques. Stability generally increased during spring and summer months. Major decreases of cohesion, found when minimum daily air temperatures fell to or below 0 °C during winter and early spring months, were attributed to pressures and associated shearing forces caused by freezing at high water contents. Equivalent disruption occurred when confined soils were frozen in controlled laboratory studies. Disruption also increased as water content at the time of freezing increased for all soils studied. Disruption of soil by rototilling and compaction significantly decreased soil cohesion.

Denitrification Hysteresis During Wetting and Drying Cycles in Soil

Abstract: Denitrification response to soil moisture was studied in soils undergoing either wetting or drying cycles to determine if denitrification-soil water relationships were independent of antecedent moisture conditions. Intact, field moist soil cores were brought into the laboratory and subjected to either wetting or drying phase treatments. In the drying phase treatment, soils were wet to saturation and then progressively dried to field capacity, 60% water-filled porosity and 20% water-filled porosity with denitrification measured at each moisture condition. In the wetting phase treatment, soil cores were first dried to 20% water-filled porosity and were then progressively wet to 60% water-filled porosity, field capacity and saturation. Denitrification showed a hysteretic response to soil moisture when drying and wetting phases were compared

Estimating Soil Nitrogen and Carbon Pools in a Northern Hardwood Forest Ecosystem

Abstract: An intensive soil sampling design was evaluated to determine what resolution could be obtained in N and C pool size estimates in a northern hardwood forest soil. Pits of measured volume were excavated by horizon in the forest floor and in three depth strata in the mineral soil. Future comparisons should be able to detect differences in N and C pool sizes ranging from 8 to 25% of the observed mean values depending upon the element and depth strata. Future sampling should detect changes of 230 and 130 kg N ha⁻¹ in the forest floor (combined O horizons) and 0- to 10-cm stratum in the mineral soil respectively. Similarly, changes of 5.9 and 2.4 Mg C ha⁻¹ should be detectable for forest floor and 0 to 10 cm pools respectively. Soil N content for the forest floor was 1300 kg N ha⁻¹. For the mineral soil depth strata (0–10 cm, 10–20 cm, 20 cm to the bottom of the B horizon), N contents were 1600, 1200 and 3100 kg N ha⁻¹ respectively. Total solum N content was estimated to be 7200 kg N ha⁻¹. Soil C contents for the combined O horizons, 0- to 10-, 10- to 20- and ≥ 20-cm strata were 30, 32, 27 and 73 Mg C ha⁻¹ respectively. The total solum C content was estimated to be 160 Mg C ha⁻¹. Concentrations of soil N and C were positively correlated with elevation over the 240 m range studied, but soil pools of N and C were not correlated with elevation or soil mapping unit. Contribution of the Morris Arboretum.

Factors Influencing the Dispersibility of Clay in Worm Casts

Abstract: Factors affecting the contribution of casting activity to aggregate stability were assessed by measuring clay dispersibility in casts produced by Lumbricus terrestris L and Lumbricus rubellus Hoff in laboratory cultures when provided alfalfa (Medicago sativa L), bromegrass (Bromus inermis Leyss), red clover (Trifolium pratense L), or corn (Zea mays L) leaves or no food Fresh, moist casts were 26 to 41 % more dispersible than uningested, moist soil

A Comparison of Gas Diffusivity Models for Unsaturated Porous Media

Abstract: The effective gas diffusivity in a porous medium decreases rapidly with increasing water content Comparisons are made between experimental diffusivity data for different materials at various moisture contents, and estimation methods from the literature The estimation methods proposed by RJ Millington and RC Shearer in 1971 give the best predictions of the effective diffusivity The methods are extended here to account for the contribution of diffusion in the water-filled pores The method for aggregated media should be used for undisturbed clayey soils, and the method for nonaggregated media may be used for sandy soils and for other materials that are not aggregated, eg laboratory packed clayey soils The experimental data show that very low effective diffusivities may be obtained in practice in soils with high moisture content

Microbial Biomass and Soil Enzyme Activities in Compacted and Rehabilitated Skid Trail Soils

Abstract: Microbial biomass C and soil enzyme activities (dehydrogenase, phosphatase, arylsulfatase, and amidase) were measured in soil profiles of a silty clay loam from a 4-yr-old clearcut located in west-central Oregon. The treatments that were imposed after logging were: (i) control (uncompacted soil) (CONT), (ii) compacted skid trail (COMP), (iii) subsoiled skid trail (SB), and (iv) subsoiled and disked skid trail (SD). In the 10- to 20-cm depth, the COMP soil of the skid trail had significantly lower biomass C (38% decrease) and lower enzyme activities for all the enzymes assayed (decreases ranging from 41–75%) than the CONT. The SD treatment significantly increased biomass C, phosphatase activity, and total N content over the COMP treatment at depths from 10 to 60 cm. Both the SD and SB treatments restored the biological activities, organic C concentrations, and total N concentrations to levels that were equal to the CONT at depths from 10 to 60 cm. Significant positive correlations (P < 0.05) were found among enzyme activities, organic C content, and total N content, whereas bulk density had significant negative correlations (P < 0.05) with enzyme activities, biomass C, organic C, and total N. Biomass C showed a significant positive correlation (P < 0.05) with enzyme activities (except amidase).

Dry matter yield and nitrogen-15 uptake by tomatoes under sodium chloride stress

Abstract: An absorption study was conducted in nutrient solution with seedlings of tomato (Lycopersicon esculentum Mill.; cv. Columbia) to observe the effects of NaCl on (¹⁵N) uptake and distribution in plant roots and shoots. The 14-d-old seedlings were grown for 16 d (14 d as group of 6 plants per container and 2 d after the final transfer of 2 plants per container) in complete Hoagland solution no. 1, then salinized (except the controls, −0.03 MPa) to −0.3, −0.6, and −0.9 MPa osmotic potentials with NaCl. Nutrient solutions were sampled daily for N loss after addition of ¹⁵NH₄¹⁵NO₃ to the pots. The cumulative ¹⁵N loss was considered to be absorbed by plants. Lowering the osmotic potential of the culture solution decreased total N uptake at all salinity levels, and ¹⁵N uptake of the plants at medium (−0.6) and high (−0.9 MPa) salinity levels. A low level of salinity (−0.3 MPa) did not affect ¹⁵N uptake compared with the control (−0.03 MPa). Water uptake and dry matter yield were affected to a greater extent than ¹⁵N absorption. Nitrogen-15 concentration was slightly higher in roots than in shoots. Contribution of Dep. of Soil and Water Science.