Soil Silt Content Research Articles

The influence of season, agricultural management, and soil properties on gross nitrogen transformations and bacterial community structure

The aim of this study was to assess the influence of season, farm management (organic, biodynamic, integrated, and conventional), and soil chemical, physical, and biological properties on gross nitrogen (N) fluxes and bacterial community structure in the semi-arid region of Western Australia. Moisture availability was the dominant factor mediating microbial activity and carbon (C) and N cycling under this climate. In general, microbial biomass N, dissolved organic N, and potentially mineralisable N were greater in organic and biodynamic than integrated and conventional soil. Our results indicate that greater silt and clay content in organic and biodynamic soil may also partly explain these differences in soil N pools, rather than management alone. Although plant-available N (NH4+ + NO3–) was greater in conventional soil, this was largely the result of higher NO3– production. Multiple linear modelling indicated that soil temperature, moisture, soil textural classes, pH, electrical conductivity (EC), and C and N pools were important in predicting gross N fluxes. Redundancy analysis revealed that bacterial community structure, assessed by denaturing gradient gel electrophoresis of 16S rDNA, was correlated with C and N pools and fluxes, confirming links between bacterial structure and function. Bacterial community structure was also correlated with soil textural classes and soil temperature but not soil moisture. These results indicate that across this semi-arid landscape, soil bacterial communities are relatively resistant to water stress.

Soil organic carbon in clay and silt sized particles in Chinese mollisols: Relationship to the predicted capacity

Soil organic carbon (SOC) associated with clay plus silt sized particles (< 20 μm) in uncultivated grassland soils has been proposed to have a maximum concentration that is referred to as the soil protective capacity. For cultivated soils, SOC is lost from the soil during various operations such as tillage, crop removal, lack of a crop cover between cropping seasons and as a result this SOC is typically lower than the maximum concentration. In this study, 28 surface soil samples (12 Black soils (Udolls) and 16 Baijiang soils (Albolls)) from long-term monoculture maize ( Zea mays L.) fields in Jilin Province, China, were analysed for SOC associated with the clay and silt particle fractions. Total SOC was significantly related to the clay plus silt content of soils. The correlation between the proportion of clay and silt sized particles and the amounts of SOC associated with this fraction was significantly greater in Black soils compared to Baijiang soils. Under the monoculture maize production, the SOC associated with clay plus silt fraction for Black soils was about half of the protective capacity estimated using the predictive model of Hassink (1997) [Hassink, J., 1997. The capacity of soils to preserve organic C and N by their association with clay and silt particles. Plant and Soil 191, 77–87.]. However, the SOC in clay plus silt fraction of Baijiang soils varied greatly, from ∼40% to 120% of the calculated protective capacity. The SOC contents in the fraction > 20 μm were relatively low and similar amongst all the Black soils. In contrast, SOC in the fraction > 20 μm varied considerably amongst the Baijiang soils. Soils which have the SOC associated with clay plus silt size fraction in amounts approaching or exceeding the protective capacity in general were those which had C accumulation in the > 20 μm size fraction. Since the SOC in Black soils has already decreased to about 50% of the protective capacity, there may be a greater potential for sequestering C in these Black soils than in the Baijiang soils.

Spatial Variability of Nitrogen in Soils from Land/Inland Water Ecotones

The variability of nitrogen (N) in soils from land/inland water ecotones of Yueliangpao wetland was studied in the horizontal and vertical directions. Nitrogen concentrations in topsoils vary obviously with soil moisture gradient, decreasing from water body to hillock, and the variability is higher compared with subsurface soils (except for -N). Spatial variability of N in subsurface soils is significantly controlled by N form. For example, the changing tendency of -N concentrations is opposite to that in topsoils; -N concentrations gradually decrease from the center zone to both sides; and the variability of K-N, OR-N, and TN is not only similar, but consistent in both soil layers. The surfacial variability of -N in soils is highest due to leaching loss and denitrification; but that of -N is lowest, since is easily adsorbed by soil colloids, and difficult to be leached. Similar to vertical variability, the surfacial variability, and distribution patterns of K-N, OR-N, and TN; and nitrogen concentrations in soils in this region are significantly correlated with SOM, TP, sand and clay content, but hardly influenced by soil pH values and silt content.

Soil Properties and Soil Nitrogen Dynamics of Prairie-like Forest Openings and Surrounding Forests in Kentucky's Knobs Region

Herbaceous communities located within forest openings increase plant species diversity of forests in the Knobs Region of Kentucky. Although these grass-dominated communities are protected and managed for rare plant species conservation, it is unclear how soil conditions may delineate the grassland-forest boundary. We compared soil chemical and physical properties and soil nitrogen pools and transformations of three forest openings with those in the surrounding forest and the wooded edge separating the grassland and forest communities. Soil pH, extractable cations, bulk density and silt content were higher in openings compared to forest soils and extractable phosphorus was lower. In forest-opening grasslands, total soil nitrogen and the availability and production of plant-available N were 25 to 50% of levels in adjacent forest. Soils of the woody edge were similar to the surrounding forest. Our results suggest that the presence of these calcareous glade openings is highly correlated with edaphic conditions, so that efforts to expand rare plant habitat may be constrained by the distinct soils of these forest openings.

Identification of Mapped Ice-Margin Positions in Western New York from Digital Terrain-Analysis and Soil Databases

Geographic Information Systems (GIS) are rarely applied to problems associated with Wisconsinan ice-margins. This study identifies inconsistencies in ice extent in the Salamanca Re-entrant in western New York as mapped using soil properties and surficial geology. In essence, previous studies have revealed a zone of disagreement between those areas that were clearly glaciated and those that were not. This study uses a raster-based approach to extract the soil pH, silt, and clay contents from digital soil databases; and the morphometric parameters of elevation, slope, terrain ruggedness, and planform and profile curvature from mosaiced 10-m digital elevation models. Two-way ANOVA indicates a close correspondence between the zone of disagreement and the glaciated area when soil information is used; however on the basis of morphometry, the area of disagreement is analogous to the unglaciated terrain. These results highlight both previous difficulties and the source of the mapped differences, suggesting that a GIS analysis of former ice margins is a productive preliminary step to their precise delineation.

Measurement of PM 2.5 emission potential from soil using the UC Davis resuspension test chamber

Human health effects have been linked to airborne concentrations of fine particulate matter. One source of fine particulate matter in the atmosphere is resuspended soil dust from a variety of activities, including agricultural operations. We have established a method to measure the potential of soil to emit fugitive dust in the PM 10 or PM 2.5 size range. The method is repeatable, and provides an index of PM 10 or PM 2.5 dust that is highly correlated to the soil texture. The ratio of the PM 2.5 Index to the PM 10 Index produced by this method is similar to field observations of ambient PM 2.5 and PM 10 concentrations downwind of agricultural operations in the San Joaquin Valley of California. The PM 2.5 or PM 10 Index will be a more useful parameter to estimate the potential of a soil to emit fugitive dust than the currently used dry silt content of soil. Research is currently underway to relate the PM 10 and PM 2.5 Index to measured emission factors, accounting for soil moisture and type of agricultural operation, so that a more reliable predictive equation can be developed for agricultural practices.

Formation and extraction of persistent fumigant residues in soils.

Fumigants are commonly thought to be short-lived in soil, but residues have been found in soils years following application. In this study, formation and extraction of persistent soil fumigant residues were investigated. Fumigants 1,3-dichloropropene (1,3-D), chloropicrin (CP), and methyl isothiocyanate (MITC) were spiked into Arlington, Glenelg, and Hagerstown soils and incubated for 30 d under controlled conditions. The incubated soils were evaporated for 20 h prior to extraction with a variety of organic solvents at different temperatures. Extraction with acetonitrile in sealed vials at 80 degrees C for 24 h was the most efficient method to recover persistent soil fumigant residues. At application rates of 1000-1700 mg (kg of soil)(-1), persistent residues of 1,3-D, CP, and MITC in the three soils ranged from 5 to 67 mg kg(-1). The residue content increased with application rate, correlated positively with soil silt content, decreased dramatically as indigenous organic matter (OM) was removed, and changed little with external OM addition. Adsorption to clay surfaces was not important in fumigant retention, while pulverization of soil aggregates significantly decreased persistent fumigant residues. The results suggest that persistent fumigant residues are retained in soil intra-aggregate micropores resulting from binding clay flocs and silt particles by humic substances.

Evaluation of carbon and nitrogen mineralization rates in meadow soils from dairy farms under transit to biological cropping systems

Mineralized soil N from meadow soils will become an important source of N to following crops in low-input biological cropping systems. The C and N mineralization rates of soils from 34 sites situated on dairy farms recently converted to biological cropping systems were evaluated in a 56-wk incubation at 25° C. Data on C and N mineralization were fitted to first-order kinetic models. Carbon and N generally presented similar patterns of mineralization. Total mineralized N (Nm) ranged between 88 and 235 mg N kg-1 soil, which represented 6.6 to 22% of total N. Carbon mineralization (Cm) rate was between 11 and 17 times greater than N mineralization (1523–2638 mg C kg-1 soil ) and C mineralized represented 9 to 19% of soil organic C. The rate constant was between 0.05 and 0.123 wk-1 for C (kC) and ranged from 0.032 to 0.088 wk-1 for N (kN). The half-life for C (TC0) and for N (TN0) varied, respectively, between 5.6 and 13.3 wk and between 15 and 28 wk. Results show that about 80% of total mineralized C and N were mineralized during the first 25 wk of incubation, corresponding to the mineralizable fraction of soil organic matter (OM). Data on C and N mineralization have been adjusted using a bicompartmental model (active and recalcitrant pools), which corresponded, respectively, to first-order and exponential equations. Total mineralizable C and N (Cm and Nm), and the C and N rate constants (kC and kN) were strongly related, whereas the rate constants of the recalcitrant pools (hc and hN) were negatively related to these parameters. This suggests that C and N mineralizable pools were independent of the humified stable OM (recalcitrant pool). Carbon and N mineralization parameters were positively related to the soil clay and silt contents, but inversely to the sand levels. This study indicates that when ploughed, meadow soils contain large mineralizable N pools, which could sustain following crops with N nutrition in low-input biological cropping systems. Key words: Meadow soils, C and N mineralization rates, low-input systems, dairy farms, soil particles sizes

Vegetation, soil, and flooding relationships in a blackwater floodplain forest

Hydroperiod is considered the primary determinant of plant species distribution in temperate floodplain forests, but most studies have focused on alluvial (sediment-laden) river systems. Few studies have evaluated plant community relationships in blackwater river systems of the South Atlantic Coastal Plain of North America. In this study, we characterzied the soils, hydroperiod, and vegetation communities and evaluated relationships between the physical and chemical environment and plant community structure on the floodplain of the Coosawhatchie River, a blackwater river in South Carolina, USA. The soils were similar to previous descriptions of blackwater floodplain soils but had greater soil N and P availability, substantially greater clay content, and lower soil silt content than was previously reported for other blackwater river floodplains. Results of a cluster analysis showed there were five forest communities on the site, and both short-term (4 years) and long-term (50 years) flooding records documented a flooding gradient: water tupelo community > swamp tupelo > laurel oak = overcup oak > mixed oak. The long-term hydrologic record showed that the floodplain has flooded less frequently from 1994 to present than in previous decades. Detrended correspondence analysis of environmental and relative basal area values showed that 27% of the variation in overstory community structure could be explained by the first two axes; however, fitting the species distributions to the DCA axes using Gaussian regression explained 67% of the variation. Axes were correlated with elevation (flooding intensity) and soil characteristics related to rooting volume and cation nutrient availability. Our study suggests that flooding is the major factor affecting community structure, but soil characteristics also may be factors in community structure in blackwater systems.

Impacts of off-road vehicles on nitrogen cycles in biological soil crusts: resistance in different U.S. deserts

Biological soil crusts are an important component of desert ecosystems, as they influence soil stability and fertility. This study examined and compared the short-term vehicular impacts on lichen cover and nitrogenase activity (NA) of biological soil crusts. Experimental disturbance was applied to different types of soil in regions throughout the western U.S. (Great Basin, Colorado Plateau, Sonoran, Chihuahuan, and Mojave deserts). Results show that pre-disturbance cover of soil lichens is significantly correlated with the silt content of soils, and negatively correlated with sand and clay. While disturbance appeared to reduce NA at all sites, differences were statistically significant at only 12 of the 26 sites. Cool desert sites showed a greater decline than hot desert sites, which may indicate non-heterocystic cyanobacterial species are more susceptible to disturbance than non-heterocystic species. Sandy soils showed greater reduction of NA as sand content increased, while fine-textured soils showed a greater decline as sand content increased. At all sites, higher NA before the disturbance resulted in less impact to NA post-disturbance. These results may be useful in predicting the impacts of off-road vehicles in different regions and different soils.

Modeling of fugitive dust emission for construction sand and gravel processing plant.

Due to rapid economic development in Taiwan, a large quantity of construction sand and gravel is needed to support domestic civil construction projects. However, a construction sand and gravel processing plant is often a major source of air pollution, due to its associated fugitive dust emission. To predict the amount of fugitive dust emitted from this kind of processing plant, a semiempirical model was developed in this study. This model was developed on the basis of the actual dust emission data (i.e., total suspended particulate, TSP) and four on-site operating parameters (i.e., wind speed (u), soil moisture (M), soil silt content (s), and number (N) of trucks) measured at a construction sand and gravel processing plant. On the basis of the on-site measured data and an SAS nonlinear regression program, the expression of this model is E = 0.011.u2.653.M-1.875.s0.060.N0.896, where E is the amount (kg/ton) of dust emitted during the production of each ton of gravel and sand. This model can serve as a facile tool for predicting the fugitive dust emission from a construction sand and gravel processing plant.

Sorption Studies of 2,4-D on Selected Soils

Adsorption/desorption characteristics of the herbicide 2,4-D on various types of soils were investigated. Batch equilibrium techniques were used in the laboratory experiments. Data were fitted to the linear and Freundlich sorption equations. K and Kf values ranged between 0.32–1.89 L- 1 mg and 2.6 × 10-3 – 7.4 mg kg- 1, respectively. Results showed that both for linear and Freundlich adsorption equations, for all soils, K and Kf were correlated to the organic matter content (r = 0.87 and r = 0.66, respectively). Adsorption was also positively correlated with silt and clay content of soils (r = 0.53) and negatively correlated with sand content.

The relationship between the amount of Verticillium dahliae in soil and the incidence of strawberry wilt as a basis for disease risk prediction

The incidence of wilt was recorded in runner and fruiting crops of 13 strawberry cultivars at 72 locations in southern England in 1989 and 1990, and soil samples from the sites were analysed for Verticillium dahliae. Linear regressions of wilt incidence on inoculum concentration in soil for runner crops of the susceptible cv. Elsanta in both years were significant whilst that for runner crops of the susceptible cv. Hapil in 1989 approached significance; the regression for cv. Elsanta fruiting crops in 1990 was not significant. The inclusion of sand content of soil in the regression model improved the fit for the cv. Hapil data but not for the cv. Elsanta data; neither clay nor silt content of soil significantly improved the fit of the models for any data set. There were insufficient data in either year for regression analysis for other cultivars, but the levels of wilt generally corresponded with the degree of soil infestation and broadly reflected known field resistance. The data were used to estimate an inoculum concentration which corresponds to 5% wilt incidence (IC5) for cv. Elsanta. It is suggested that this could be used as a yardstick for determining the risk of unacceptable levels of wilt in susceptible cultivars on the basis of pre‐planting soil analysis. For the 44 sites where the cropping history over the 15 years prior to soil analysis was available there was no clear association between any crop and soil infestation levels at or above the IC5. However, V. dahliae was more common at sites with a history of vegetatively propagated crops than at sites which had only supported crops grown from true seed.

Effect of Soil Characteristics on Adsorption and Mobility of (14C)Diazinon

The adsorption and mobility of diazinon (O,O-diethyl O-2-isopropyl-6-methylpyrimidin-4-yl phosphorothioate) in 25 soils of different physicochemical properties were studied. The adsorption isotherms were found to conform to the Freundlich adsorption equation. Freundlich's constant, K, and the distribution coefficient, K d , were found to be highly significantly correlated (p<0.001) with the organic matter (OM) content when all soils or only those with an OM content above 2% were considered. There was also a significant correlation (p<0.01) OF K AND K d with the silt plus clay content of soils with an OM content below 2%. On the basis of the R f values obtained by TLC, the pesticide was found to be slightly mobile in 80% and immobile in 20% of the soils studied

Relative stocking index: a proposed index of site quality

Site index is difficult to implement and interpret in multispecies, multiple-aged stands, and its relationship to site factors is obscure. Using data from the USDA forest inventory and analysis (FIA) for the Lake States, we developed log-log relationships between mean tree size and stand density for five cover types. Fits were good, with r2 from 0.96 to 0.98 and slopes from −0.948 to −0.995. We define an alternative index of site quality, the relative stocking index (RSI), as the ratio of a stand's measured density to that predicted using the log–log relationship for its cover type (the norm). We divided the range of RSI into three classes for each type (&lt;0.9 of norm, &gt;0.91 but &lt;1.1 of norm, and &gt;1.1 of norm). Based on analyses of the 1977 and 1990 FIA data from Minnesota, class assignments for individual stands remained constant over that 13-year period. Relationships between site factors and either RSI classes or analogous classes based on site index were examined in a subset of 169 stands. Temperature, precipitation, silt content of surface soil, and calculated annual water deficit all differed significantly among RSI classes, but not among site-index classes. The RSI is easy to apply, robust (resistant to change), and related to site factors. It merits additional examination as an index of site quality, especially in heterogenous stands.

A Statistical Exploration of the Relationships of Soil Moisture Characteristics to the Physical Properties of Soils

Stochastic modeling of soil water fluxes in the absence of measured hydraulic parameters requires a knowledge of the expected distribution of the hydraulic parameters in different soil types. Predictive relationships describing the hydraulic parameter distributions must be developed based on the common descriptors of the physical properties of soils (e.g., texture, structure, particle size distribution). Covariation among the hydraulic parameters within these relationships must be identified. Data for 1448 soil samples were examined in an evaluation of the usefulness of qualitative descriptors as predictors of soil hydraulic behavior. Analysis of variance and multiple linear regression techniques were used to derive quantitative expressions for the moments of the hydraulic parameters as functions of the particle size distributions (percent sand, silt, and clay content) of soils. Discriminant analysis suggests that the covariation of the hydraulic parameters can be used to construct a classification scheme based on the hydraulic behavior of soils that is analogous to the textural classification scheme based on the sand, silt, and clay content of soils.

ERZİNCAN OVASI TOPRAK VE SU KAYNAKLARININ SULAMA YÖNüNDEN PROBLEMLERİ VE GELİŞTİRİLME İMKANLARI ÜZERİNDE BİR ARAŞTIRMA

ERZİNCAN OVASI TOPRAK VE SU KAYNAKLARININ SULAMA YÖNüNDEN PROBLEMLERİ VE GELİŞTİRİLME İMKANLARI ÜZERİNDE BİR ARAŞTIRMA