Showing papers in "Soil Science in 2004"

Soil Genesis And Classification, 5TH Edition.

Abstract: Description: Soils are natural bodies wherein inorganic components derived from geologic materials combine with organic materials produced by biological activity in ecosystems. The nearly infinite combinations of geologic materials and biological diversity of life on earth have produced a staggering array of chemical, physical, and biological reactions that over time have created the soils that we observe today. In the United States more than 23,000 kinds of soil are formally identified, and the number of soils in the world is not known. Soil Genesis and Classification, Sixth Edition builds on the strong foundations of this venerable soil science text to present the most current concepts on how soils are formed and sustained within the dynamic changes of ecosystem successions and climatic dynamics. The sixth edition has been fully revised and updated, incorporating more detailed data regarding specific examples of how soils have acquired various characteristics. Methods of communicating and analyzing spatial information have been expanded in light of the latest technological advances. Color plates have also been added to allow readers a better visualization of various soils. Soil Genesis and Classification, Sixth Edition is a comprehensive work that meets the diverse range of needs from soil science students professionals in fields ranging from agriculture and ecology to civil engineering. The well–established text will be a vital source of information for those with a need to better understand soils and their various impacts on ecosystem functions, on environmental quality, and on the multitude of human endeavors to sustain human life on earth.

Soil Erosion and Carbon Dynamics Under Simulated Rainfall

Abstract: Soil erosion affects soil organic carbon (SOC) dynamics by redistributing SOC within the watershed or ecosystem and by altering the C release rate into the atmosphere. Although the mechanism of this process is poorly understood it has the potential to influence global climate.Crosby loam soil (fine,

Increasing the phosphorus sorption capacity of southeastern coastal plain soils using water treatment residuals

Abstract: Long-term animal manure applications to many sandy Coastal Plain soils has resulted in the accumulation of excess soil phosphorus (P). When soils contain excessive P concentrations, dissolved phosphorus (DP) can be desorbed with water and transported into streams and rivers via runoff and leaching.

Copper distribution and dynamics in acid vineyard soils treated with copper based fungicides

Abstract: Vineyards often receive large amounts of copper salts as fungicide treatments. This study investigated the presence, form distribution, adsorption-desorption dynamics, and transport of copper in 20 acid vineyard soils from northwest Spain. Total copper concentration varied considerably but exceeded

Soil quality indicators for reclaimed minesoils in southeastern ohio

Abstract: Soil quality indices are useful for ascertaining temporal changes in soil properties in relation to land use and management, especially for drastically disturbed soils, and for designing the best management systems for minesoil reclamation. Soil quality indices were developed by analyzing physical and chemical properties of the minesoils in Jackson and Vinton counties, Ohio, reclaimed in 1975 and 1976. Soil properties were also assessed for the adjoining unmined soil and the spoil. The principle component analysis (PCA) was performed on 20 physical and chemical soil properties, separately for each experimental site, for 0- to 10-cm depth. The PCA performed with correlation matrix grouped 20 measured soil attributes into four distinct principle components (PCs) for each site. The PCs were related to measured soil properties, based on their communality estimates. The factors identified were (i) bulk density, (ii) water infiltration, (iii) aggregate size, and (iv) soil nitrogen for the Jackson site and (i) bulk density, (ii) water infiltration, (iii) organic carbon, and (iv) porosity for the Vinton site. These factors were assessed with respect to the specific soil functions and were designated as soil quality indicators. The discriminant analysis of retained PCs showed that the bulk density factor was the most discriminating and water stable aggregation the most dominating common measured soil attribute or the dynamic soil quality indicator for both sites. Other soil quality indicators varied in the order soil bulk density > field water capacity > clay concentration. These factors monitored over time are indicators of change in soil quality, whether aggrading, degrading, or stable. (Soil Science 2004;Volume 169:133–142)

Managing soil quality: Challenges in modern agriculture

Abstract: The editors of this book, P. Schjonning, S. Elmholt, and B.T. Christensen, have succeeded in compiling perhaps the most focused technically based book on soil quality published to date. The chapters they have brought together are predominately the work of European, Australian, and Canadian authors who, to a greater degree than in previous texts, have taken a data-based analytical approach to concept demonstration and testing. This is refreshing for a topic that has been largely dominated in the American literature by philosophical semantics and institutional proselytizing, more often than not in the absence of specific data collected or applied to the proposed conceptual framework. Even the nonempirical opening and closing chapters by Schjonning et al., which are intentionally philosophical, consider some new conceptual refinements and are at least somewhat open to the possibility that critiques of the soil quality concept offered to date have merit worth pondering. Nevertheless, as one of us communicated to Per Schjonning during the preparation of the book, we feel an opportunity was missed by failing to include more objective assessments of the concept directly from concept-skeptics. Although a few chapters cite the existence of concept criticisms superficially, none deal substantively with any of the twenty or more specific technical reservations about the soil quality concept that have been specifically and repeatedly articulated in several high-profile critiques in the literature. Fewer than ten sentences in Schjonning et al.'s book deal with these specific reservations, and none substantively.

X-ray photoelectron spectroscopy of nitrogen functional groups in soil humic acids

Abstract: The composition of nitrogen (N) species in 11 humic acids obtained from a wide variety of soils was investigated by X-ray photoelectron spectroscopy (XPS). The N1s spectra of the humic acids were fitted by three Gaussian curves with binding energy at 399.0 ± 0.1, 400.4 ± 0.1, and 402.4 ± 0.2 eV, whi

Principal component analysis for predicting corn biomass and grain yields

Abstract: Soil variability, a rule rather than an exception, necessitates site-specific management for optimizing the efficient use of inputs. Biomass and grain yields depend on complex interactions among spatially variable physical and chemical properties of soil. The objectives of this study were to determine (i) the variability in soil properties using coefficient of variation (CV) and range as indicators and (ii) the relationships between principal components (PCs) derived from measured soil attributes and corn (Zea mays) biomass and grain yields. Soil physical and chemical properties were determined for four treatments: no-till corn without manure (Field 1), no-till corn with manure (Field 2), no-till corn-soybean (Glycine max) rotation (Field 3), and conventional tillage corn (Field 4). The CV for saturated hydraulic conductivity (K s ) (0.59 to 1.43) and infiltration rate at 5 min (i 5 ) (0.38 to 0.86) was classified as most variable; for 3-h infiltration (i c ) (0.30 to 0.97) and cumulative infiltration (I) (0.27 to 0.76) as moderate to most variable; for SOC (0.21 to 0.02) and MWD (0.12 to 0.23) as moderate to least variable; and the CV for WSA (0.03 to 0.12), pH (0.1 to 0.2), and soil bulk density (ρ b ) (0.05 to 0.11) as least variable. The highest CV overall was obtained for soil properties in the conventional till treatment (Field 4), although mean values of K s , is, and I for this field were the smallest. The biomass and grain yields were also the lowest for Field 4. The principal component (PC) analysis showed that four PCs with eigen-values greater than one explained more than 78% of the variability in soil physical and chemical properties. The stepwise regression analysis showed that the grain yield (Y g ) was linearly correlated with PCs as Y g = 8.77 + 0.81 PC1 (r 2 = 0.19; P < 0.02) and biomass yield (Y b ) as Y b = 4.85 + 0.41 PC1 + 0.32 PC2 (r 2 = 0.36; P < 0.003). The coefficients on PC1 were positive and were the highest for both Y g and Y b . Therefore, PC1 was the most dominant yield determinant.

Soil carbon relationships with terrain attributes, electrical conductivity, and a soil survey in a coastal plain landscape

Abstract: Soil organic carbon (SOC) estimation at the landscape level is critical for assessing impacts of management practices on C sequestration and soil quality. We determined relationships between SOC, terrain attributes, field scale soil electrical conductivity (EC), soil texture and soil survey map units in a 9 ha coastal plain field (Aquic and Typic Paleudults) historically managed by conventional means. The site was composite sampled for SOC (0-30 cm) within 18.3 × 8.5-m grids (n = 496), and two data sets were created from the original data. Ordinary kriging, co-kriging, regression kriging and multiple regression were used to develop SOC surfaces that were validated with an independent data set (n = 24) using the mean square error (MSE). The SOC was relatively low (26.13 Mg ha -1 ) and only moderately variable (CV = 21%), and showed high spatial dependence. Interpolation techniques produced similar SOC maps but the best predictor was ordinary kriging (MSE = 9.11 Mg 2 ha -2 ) while regression was the worst (MSE = 20.65 Mg 2 ha -2 ). Factor analysis indicated that the first three factors explained 57% of field variability; compound topographic index (CTI), slope, EC and soil textural fractions dominated these components. Elevation, slope, CTI, silt content and EC explained up to 50% of the SOC variability (P ≤ 0.01) suggesting that topography and historical erosion played a significant role in SOC distribution. Field subdivision into soil map units or k-mean clusters similarly decreased SOC variance (about 30%). The study suggests that terrain attributes and EC surveys can be used to differentiate zones of variable SOC content, which may be used as bench marks to evaluate field-level impact of management practices on C sequestration.

Evaluation of soil phosphorus transformations by sequential fractionation and phosphatase hydrolysis

Abstract: Increased understanding is needed on the interconversion among P species when manure and fertilizer are added to soils. To assess changes in P species affected by manure and fertilizer addition, a sandy loam (no established soil series designation; coarseloamy, mixed, frigid, Typic Haplorthod) and a

Effects of Soil Cover and Land-Use on the Relations Flux-Concentration of Trace Gases

Abstract: Information regarding the impact of soil surface condition on soil-atmosphere exchange of gases is limited. In this study, fluxes and soil air concentrations of CO2, CH4, and N2O were monitored for 17 months at three central Ohio sites, including a bare (vegetation-free) soil, a mulch (covered with

Variable rainfall intensity effects on runoff and interrill erosion from two coastal plain ultisols in Georgia

Abstract: Predictions and understanding of runoff and soil loss could be improved if the effect of variable rainfall intensity during a storm were quantified. We quantified and compared effects of constant (Ic) and variable (Iv) rainfall intensity patterns on infiltration, runoff, soil loss, and interrill erodibilities (Ki) from a Tifton loamy sand (Plinthic Kandiudult) and a Greenville sandy clay loam (Rhodic Kandiudult). Each soil was air-dried, sieved (19 mm) and then placed in a 1.5-m2 stainless steel erosion pan (Tifton = 4% slope; Greenville = 7% slope). Simulated rainfall was applied for 70 min at a constant (57 mm h−1) and variable rainfall intensity patterns. The Ic event was determined from the statistical average of the Iv pattern; thus, total rainfall volume applied was the same for both patterns. Values for runoff (R), soil loss (E), splash water (Sw), and splash sediment (Ss) were measured at 5-min intervals throughout each simulation. Rainfall intensity patterns did not affect total runoff or infiltration, but they did influence Rmax values, when runoff occurred, and soil loss from each soil. Runoff curves for Iv events (peaks = 25–28 min) lagged intensity curves (peak = 20 min) by 5–8 min. Rmax values for Iv events were significantly (2 X) greater than those for Ic events and occurred 35–37 min before those for the Ic events. For the Tifton ls, Etot for Ic events was signficantly greater (2 X) than that for Iv events. Conversely, for the Greenville scl, Etot for Iv events was significantly greater (20%) than that for Ic events. For the Greenville scl, Emax for Iv events was significantly greater (3 X) than that for Ic events, whereas time to Emax for both soils was 16 min earlier for Iv events than for Ic events. Runoff and soil loss rates for Ic events increased gradually during the first 35–40 min before reaching steady-state conditions, whereas runoff and soil loss rates for Iv events increased sharply to a maximum at 25–29 min and then gradually declined to quasi-steady-state conditions. As a result, Iv events had about 28% more rainfall run-off and 32% more soil loss during the first 35 min of each event than for Ic events. Conversely, Ic events had about 28% more rainfall run-off and 32% more soil loss during the last 35 min of each event than for Iv events. For Ic events, capacity to transport sediment was limited by the lack of runoff during the first 35–40 min, whereas during the second half of each simulation event, runoff was well established at steady-state rates and able to transport sediment. Soil detachment was maintained or supplied at a constant or increased rate. R70 and E70 values were greater than R35 and E35 values. Greater r2 values were obtained for the R versus E relationship (r2 = 0. 98) than for the Ss versus E relationship (r2 = 0.28) on the Tifton ls, whereas relatively high r2 values were obtained for R versus E (r2 = 0. 99) and Ss versus E (r2 = 0.81) on the Greenville scl. For Iv events, there were detachment- and transport-limiting conditions, especially near the end of each event where capacity to detach soil and transport sediment decreased. R70, E70, and Ss70 values were less than R35, E35, and Ss35 values, and relatively high r2 values were obtained for R versus E (r2 = 0. 94–0. 99) and Ss versus E (r2 = 0.91–0.96). The Greenville scl was 75–97% more erodible than the Tifton ls. Kiq values were 16–30% larger than Kii values. Variable rainfall intensity causes problems, conceptually and mathematically, when calculating Ki. Ki values were not solely a property of the soil, were not constant, and did not increase as soil loss increased. Emax values were up to 13 times greater than steady-state soil loss values, yet Ki values for steady-state conditions were 3–5 times greater than those for maximum loss conditions. If Ki represents the susceptibility of a soil to erosional forces, and since rainfall intensity distributions, runoff, and soil loss within a rainfall event are not constant, then, according to our results, Ki distributions within the same event should not be assumed constant.

Desorption and plant availability of myo-inositol hexaphosphate adsorbed on goethite

Abstract: The specific adsorption and high affinity of inorganic phosphate for Fe oxides limit its desorption and, hence, its availability to plants. Organic P compounds such as inositol phosphate show even greater affinity for soil oxides. This may result in low desorption and, hence, poor bioavailabilty, ex

Increased plant growth, nutrient uptake, and soil enzymatic activities in a desertified mediterranean soil amended with treated residues and inoculated with native mycorrhizal fungi and a plant growth-promoting yeast

Abstract: The effectiveness of microbial inoculants with different and interactive metabolic abilities, native arbuscular mycorrhizal (AM) fungi and a plant growth-promoting yeast (PGPY) Yarowia lipolytica, were assayed in a natural semiarid soil. The soil was either amended or was not amended with microbiolo

Stability analysis of soil aggregates treated with anionic polyacrylamides of different molecular formulations

Abstract: Soil sealing and erosion on agricultural fields is a severe problem that often leads to increased runoff and decreased soil quality Much research has been conducted using polyacrylamide (PAM) to control soil sealing and reduce erosion, yet few studies have attempted to determine the most effective molecular formulation(s) of PAM Our objective was to examine the ability of a range of PAM formulations to stabilize soil aggregates We hypothesized that PAM would perform differently on an assortment of soil types with varying optimum formulations and effectiveness The PAM solutions studied included combinations of three molecular weights (MW: 6, 12, and 18 Mg mol-1) and three charge densities (CD: 20, 30, and 40% hydrolysis) The soils used varied in both texture and mineralogy: Heiden clay (fine, smectitic, thermic Udic Haplusterts), Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludults), and Fincastle silt loam (fine-silty mixed, superactive, mesic Aeric Epiaqualfs) Soil samples treated with PAMs of different formulations were analyzed using a fall velocity settling tube A slaking index (SI) and an aggregate stabilization index (ASI) were used to compare the treatments Polyacrylamide enhanced resistance to slaking of Fincastle silt loam but not Heiden clay or Cecil sandy loam Furthermore, differences among PAM treatments were observed only for the Fincastle silt loam When examining slaking and dispersion components together, PAM treated aggregates were more stable than the control for Heiden clay and Fincastle silt loam soils For Heiden clay, CD was the main factor influencing aggregate stability, whereas CD x MW controlled the stability of Cecil sandy loam Fincastle silt loam exhibited no preference to a specific PAM formulation factor Polyacrylamide was effective in enhancing the stability of aggregates; however, it may not be as important in controlling the slaking component specifically (Soil Science 2004;169:573-581)

Influence of management history and landscape variables on soil organic carbon and soil redistribution

Abstract: Controlled studies to investigate the interaction between crop growth, soil properties, hydrology, and management practices are common in agronomy. These sites (much as with real world farmland) often have complex management histories and topographic variability that must be considered. In 1993 an i

Nitrogen fertilization suppresses soil phenol oxidase enzyme activity in no-tillage systems

Abstract: Phenol oxidase is associated with the carbon cycle and its presence in soil environments is important to the formation of humic substances. Little effort has been made to integrate the response of phenol oxidases with soil management. We investigated phenol oxidase activity on a Maury silt loam (fin

Impact of manure application on soil phosphorus sorption characteristics and subsequent water quality implications

Abstract: For nutrient management purposes, it is important to understand the impact of manure application on soil phosphorus (P) sorption characteristics and what it means with regard to potential environmental problems. The objectives of this study were (i) to determine whether previous manure applications

Spatial Variability of Soil Properties and Potential Management Classification of a Chernozemic Field in Lower Austria

Abstract: Knowledge of the spatial variability of soil physical and chemical properties is important for precision agriculture. Fuzzy classification and geostatistical interpolation are useful tools for the simultaneous handling of continuous variation in both attributes and location. The objectives of this study were: (i) to classify data to capture optimally in-field variability and (ii) to delineate contiguous areas for site-specific management. Several soil physical and chemical parameters for a loam soil were measured in the 0- to 15-cm depth of a 50- X 25-m grid at the experimental farm of the University of Agricultural Sciences, Vienna, Austria. Using Variowin and ArcGIS, models were fitted to variograms, and continuous maps of individual attributes were generated by spline smoothing. The coefficient of variation (CV) for soil bulk density (ρ b ), pH, and silt and clay contents was 35%. The nugget:sill ratio showed moderate spatial dependence for silt content, ρ b , SOC, K s , Φ m , EC, clay content, and TC (from 38% for silt content to 59% for TC) and weak spatial dependence for TN and pH (>75%). The nugget:sill ratio from covariograms showed moderate spatial dependence for K and TC, TC and clay content, ρ b and pH, TN and clay content, K s and Φ m , and ρ b and 0 (38 to 62%). Four classes captured total within-field variability optimally. Despite a low level of actual statistical variation in data, contiguous areas of each class were present in the field. The study demonstrated that by careful collection of data, site-specific management zones can be created for soil management within the field.

Rapid water flow and transport of inorganic and organic nitrogen in a highly aggregated tropical soil

Abstract: ludox of central Amazonia, Brazil. The soil water percolated to a depth of 0.9 m within 2 h of a rainfall event of 48 mm. Water fluxes were significantly slower below 0.9 m (17% of infiltration at 0–0.9 m) due to higher bulk densities. Percolation not only started rapidly after a rainfall event when soil water suction reached a certain threshold (ca. 20–30 hPa) but was also reduced to background levels less than 1 h after the rain had ended. Traces of labeled N reached 5 m within a few days, and 15 N maintained high levels to a depth of 1.2 m throughout the rainy season. Organic N was a large proportion (36–44%) of the total N leaching and the proportion increased with depth. However, organic N percolated more slowly than nitrate. The demonstrated extreme short-term dynamics of water fluxes have implications for measurement design of water availability and solute leaching in microaggregated tropical soil that require correct time integrals of solution concentrations and soil water dynamics. Measurement intervals of 30 min or less were necessary in our study. Rapid water flows explain the observed high N losses from the topsoil of microaggregated tropical soil and the large nitrate accumulation in the deep soil to a depth of at least 5 m. (Soil Science 2004;169:330–341)

Soil Quality Indicators For The North Appalachian Experimentalwatersheds In Coshocton Ohio

Abstract: Identification of soil quality indicators (SQI) is important to sustainable management of natural resources. The objective of this project was to develop a technique for identifying SQIs for agricultural land use. Soil structure, water retention and transmission properties, and pH and electrical conductivity (EC) were measured and related to agronomic productivity for five land use and soil management treatments at the experimental farm of the North Appalachian Experimental Watersheds, Coshocton, Ohio. The five treatments were no-till corn without manure (NTWM), no-till corn with manure (NTM), no-till corn (Zea mays)-soybean (Glycine max) rotation (NTCSR), conventional tillage corn (CT), and meadow (M). Soil properties measured were bulk density (ρ b ), drainable porosity (f a ), available water capacity (AWC), steady state infiltration rate (i c ), saturated hydraulic conductivity (K s ), soil organic carbon (SOC) concentration, water stable aggregation (WSA), mean weight diameter of aggregates (MWD), and texture. The correlation analysis on the measured soil attributes reduced the number of key variables from 17 to 11. A rating index on a 1 to 5 scale was obtained for each of the key soil properties. The linear regression analysis was first performed with key soil attributes as independent variables and biomass or grain yields as dependent variables, with the rating factor later assigned to each measured key soil attribute. The multiple regression analysis showed that SOC and WSA explained more than 35% of variability in biomass and 33% in grain yields, respectively, and were identified as the major SQIs. Other important SQIs were ρ b , AWC, MWD, pH, and EC. The cumulative sustainability ratings (CR) for each land use showed that NTM was the most sustainable soil management treatment (CR = 20) and CT the least sustainable (CR = 30). The CR was also correlated significantly with grain yield (R 2 = 0.31, P < 0.002). The CR for different land uses suggests that soil management with NTM is the most sustainable and CT the least.

Influence of three weed species on soil nutrient dynamics

Abstract: The hypotheses that weeds increase soil nutrient availability and differentially alter soil nutrient dynamics were tested in the greenhouse by comparing and contrasting plant-soil relationships among Bromus tectorum L. (cheatgrass, downy brome), Lepidium latifolium L. (perennial pep-perweed, tall wh

Biosolids effects on microbial activity in shrubland and grassland soils

Abstract: Natural ecosystems in the western United States provide potential locations for recycling sewage biosolids. However, little is known about how this practice would affect soil microbial activity. Our objective was to determine whether one-time surface biosolids applications at 0 and 40 Mg ha −1 to a

The hydraulic properties of soil at root-soil interface

Abstract: Root penetration modifies the soil in the rhizosphere, which affects the transport of water. To study this phenomenon, we developed a soil microcosm for growing roots that allowed our infiltration measurements easy access to the soil. The infiltration of water through small circular areas into the rhizosphere, where roots had penetrated, and into bulk soil, was measured at negative pressures of -1, -2, and -3 hPa. The infiltration data were used to obtain sorptivity values and an estimate of the hydraulic conductivity of saturated soil. At a given negative pressure, the infiltration of water was less through soil that had been deformed by root growth than through bulk soil. To explain these differences we considered how changes in soil density and the effect of root mucilage might influence infiltration into the soil. Our data suggested that it is the increase in density of the rhizosphere soil that is responsible for the change in its hydraulic properties. In other works, root mucilage has been shown to make the soil water-repellent, but we were unable to confirm that finding in this work. The effect of mucilage on soil may depend on the organic matter content of the soil. Further research in this area is needed.

Biochemically Protected Soil Organic Carbon at the North Appalachian Experimental Watershed

Abstract: Land use and soil management affect the balance between labile and stable organic matter fractions in surface soils. This study was conducted to quantify the contribution of nonhydrolyzable carbon (NHC) to total soil organic carbon (SOC) and to identify the role of biochemical protection mechanisms in SOC sequestration by comparing the NHC fraction associated with aggregates from 0 to 5-, 5 to 10-, and 10 to 20 cm depths under forest, meadow, no-till (NT) and conventional tillage (CT) treatments. The NHC contribution to SOC declined from 53% under forest to 37% under CT and 39% under NT, implying that the conversion from forest to cultivation led mainly to a reduction in the NHC. Aggregate-associated NHC concentration increased with aggregate size (except for CT treatment). Conversion from CT to NT enriched NHC in all aggregate fractions, but even more so in the >250-μm fraction, underscoring the importance of macroaggregate fractions in encapsulating and thus protecting SOC from microbial processes. The formation of macroaggregates is coupled with the depletion of microaggregates, which can be quantitatively described by functions (for each aggregate class) expressed in terms of the aggregate mass and the proportion NHC/SOC. Both the NHC fraction and the nonhydrolyzable C:N ratio increased with the increase in SOC concentration in soils under meadow and forest, suggesting a large potential for SOC sequestration through biochemical protection mechanisms.

Soil Reflectance as a Tool for Assessing Physical Crust Arrangement of Four Typical Soils in Israel

Abstract: Investigation of soil structural crust reflectance across the NIR-SWIR spectral region was conducted to account for the possibility of remotely sensed soil crust-related properties such as water infiltration. The raindrop energy disintegrates the soil aggregates and rearranges soil particles within

Modeling the Impact of Ferrihydrite on Adsorption-Desorption of Soil Phosphorus

Abstract: Ferrihydrite is an Fe-oxide mineral with a high phosphorus (P) sorption capacity. Modeling the P adsorption and desorption mechanisms of soil amended with ferrihydrite is necessary to predict the movement of dissolved and sediment-bound P. The objective of this study was to model the multi-reaction

Soil phosphorus dynamics after ten annual applications of mineral fertilizers and liquid dairy manure: fractionation and path analyses

Abstract: Knowledge of phosphorus (P) dynamics in soil is essential for predicting its bioavailability and the risk of P transfer from soil to bodies of water. A comparative study was conducted to assess the changes in P fractions and pathways of P transformation in soil measured after 10 annual applications of mineral fertilizers (MIN) and liquid dairy manure (LDM). Fractionation and path analyses were performed to quantify inorganic P (P i ) and organic P (P o ) forms and the relationships between P pools in the 0 to 15-cm layer of a Labarre silty clay (fine, mixed, frigid, Humic Cryaquept) under barley monoculture. The MIN additions resulted in larger increases in P i fractions and smaller increases in the NaOH-P o compared with the LDM applications. The LDM, however, produced 1.9 times more total soil labile P than the MIN plot. Path analysis indicated that path coefficients between the source and recipient P pools were P-source dependent. The NaOH-P i was a primary sink of added P i and a source of NaHCO 3 -P i . The roles of P g pools were more important than the P i pools for P transformations. The NaHCO 3 -P o was sensitive to P sources and likely acted as a transitory pool rather than as a sink or source of soil P. The NaOH-P o constituted a sink for added P o and immobilized labile P i in the MIN plot; it was conversely mineralized and contributed to labile P i in the LDM plot. The results of this study stress that the pathways of P transformation in this Cryaquept can be revealed by the descriptive path analysis.

Soil silicon extractability with seven selected extractants in relation to colorimetric and ICP determination

Abstract: The importance of silicon (Si) in nutrition is currently being recognized by its beneficial effects in many crops. At present, various procedures are being used to extract Si and to determine soil Si status. This study was undertaken to evaluate the relationships among various extractants and to compare inductively coupled plasma (ICP) Si measurement with the molybdenum blue colorimetric method for possible incorporation of Si determination into existing routine soil and water testing procedures. Seven extractants were evaluated on 30 Louisiana soils. These were: deionized (D.I.) water, 0.5 M acetic acid, 1 M sodium acetate buffer (pH 4.0), 0.5 M ammonium acetate (pH 4.8), 0.1 M hydrochloric acid, 0.5 M citric acid, and Mehlich III. Soil-extractable Si determination by ICP correlated highly with that by colorimetric analysis in HCl, citric acid, acetic acid, acetate buffer, and ammonium acetate extractions (R 2 ≥ 0.972, P citric acid > HCl > acetic acid > acetate buffer > NH 4 OAc > D.I. water, as determined by colorimetry. Silicon extracted by different extractants was well correlated among citric acid, HCl, acetic acid, acetate buffer, and NH 4 OAc (R 2 ≥ 0.611, P < 0.001). Water and Mehlich III showed poor correlations with other extractants (R 2 ≤ 0.430). The results suggest that these seven extractants characterize different pools of Si-supplying capacity of the soil: extractable by water, extractable by any of HCI, citric acid, acetic acid, acetate buffer, and NH 4 OAc, and extractable by Mehlich III.

Soil bacterial community structure changes following disturbance of the overlying plant community

Abstract: The effect of plant species identity and diversity on the spatial and temporal differentiation in bacterial community structure in the active root zone was studied at a field site that was treated with herbicide, burned, and then reseeded with native grass species. Treatments were arranged in three blocks. The blocks corresponded to an elevational gradient that was used as a surrogate for moisture differences across the field. Samples were collected before and after devegetation, and eight times thereafter, over the subsequent year. The soil samples were examined for bacterial abundance (direct counts) and bacterial community structure by the genetic fingerprinting techniques randomly amplified polymorphic-DNA (RAPD) and denaturing gradient gel electrophoresis (DGGE) of whole-community DNA extracts. The bacterial abundance was relatively constant in both time and space. Discriminant function analysis and the Mantel test revealed clear temporal trends in community structure throughout the entire 2-year study that coincided with the overall development of the grasses in the field. Spatial differentiation of community structure was clear among the blocks, suggesting differences in community structure based on soil moisture content. Significant differences were also observed between control and treated plots. Spatial and temporal change in the bacterial community was evident, and bacterial and plant succession coincided temporally. Differences in the bacterial communities that developed were also affected by the soil moisture.