摘要:

Recent evidence suggests that crop roots in soil may significantly alter preferential flow processes and thus impact non-point source pollution from agricultural land. Therefore, the objectives of this study were to evaluate: (i) the effect of tillage practices on the leaching of surface applied chemicals, (ii) the spatial and temporal variations in preferential flow pathways under corn and soybean cropping during the growing season, and (iii) the effect of application method on solute leaching through field soil. On soil cropped to corn and soybean, two tracer solutes were applied, Br−by spraying and Cl−under ponded conditions, on two different dates (during vegetative and reproductive stages) during 2 different years to a total of 22 2 × 2-m2plots. Three days before chemical application, plants and surface residues were removed from each plot, a 2-cm simulated rainfall was applied, and the plot surface was covered. Sprayer application of Br−was followed by ponded applications of chloride and tracer-free water. Four days after chemical application, within the central 1 × 1-m2area of each plot, at least 10 core samples (7.6- or 11.5-cm diameter) were collected in 10-cm depth increments to a maximum depth of 1.5 m. Chloride, applied under ponded surface conditions, consistently moved deeper into the profile than bromide, even though the latter had been sprayed on the soil before ponding the Cl−application. With equal volumes of water infiltrating at the soil surface, solutes moved significantly deeper into the soil profile for between row (BR) than for in row (IR) positions for each tillage and crop treatment, despite the attempt to equalize initial conditions near the soil surface in the BR and IR positions by application of water 3 days before chemical application. This work shows that solute transport properties vary as a function of (a) position relative to the crop row, (b) tillage, (c) stage of growth, and (d) crop species. These factors should be considered when modeling is used to assess regional scale non-point source pollution and when determining best management practices.

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Clean air legislation has resulted in increased production of flue gas desulfurization (FGD) by-products by coal-fired boilers. Use of FGD by-products as substitutes for agricultural limestone represents a potential beneficial use alternative to landfill disposal of these materials. To determine the efficacy and potential for environmental impact of such use, an 8-month greenhouse study was conducted in which three dry FGD by-products were mixed with Wooster silt loam at rates of 0, 3.5, 7, 14, and 28 g kg−1. Separate pots were planted with alfalfa (Medicago sativa,L) and tall fescue (Festuca arundinacea,Schreb). Following a 3-month growth period, plants were harvested monthly for a total of six harvests. Pots were leached at the beginning and end of the experiment. All three FGD by-products increased soil pH from 4.5 to approximately 7.5. Leachate concentrations of Ca, Mg, and S were increased by FGD, indicating a potential for transport of these solutes to subjacent soil. Leachate Mn and Zn concentrations were decreased by FGD amendment of alfalfa, and leachate Al was decreased with both crops. Leachate trace element concentrations were not increased by FGD with the exceptions of B and Cu. Alfalfa yield was increased by FGD, although the largest amendments suppressed yields of the first two harvests. Fescue yield was also increased by FGD amendment although the response was less than with alfalfa. Plant tissue contents of Ca, Mg, and S were increased by FGD. There were no increases in tissue concentrations of any trace elements except B and Mo. Dry FGD by-products appear to be effective substitutes for agricultural limestone with little potential for adverse environmental impacts.

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

It has been speculated that arbuscular mycorrhizal fungi (AMF) produce extracellular compounds and that these are involved in soil stabilization. An unusual and abundant protein was found on hyphae of AMF, and it was hypothesized that the hyphal protein could be found in soil. The purpose of this work was to test extraction conditions for soil protein on a range of soils collected from undisturbed sites, to compare protein from hyphae with protein from soils, and to examine the relationship between soil protein and percent of total dry weight of soil made up of ca. 1 to 2-mm water stable aggregates. The A-horizons of 12 acidic soils collected from the midAtlantic area of the United States were used to develop a protocol for protein extraction. Protein was measured by the Bradford assay, with bovine serum albumin as the standard. Also, an indirect enzyme-linked immunosorbent assay (ELISA), using the monoclonal antibody that had been used to detect the protein on hyphae of AMF, was performed on 0.5 μg of protein from soil or hyphae. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of denatured protein was used to compare soil protein with hyphal protein. The extraction conditions that gave the best results for total protein were 0.25 g soil in 2 mL of 50 mMcitrate, pH 8.0, for 90 min at 121°C yielding a range of 4.4 to 14.4 mg protein/g of soil for these soils. Highest ELISA values were obtained by using 20 mMcitrate, pH 7.0, for 30 min at 121°C, but less protein was extracted under these conditions. Crude extracts of protein from hyphae and soil showed the same banding patterns and density of bands on SDS-PAGE gels. ELISA values for soils were between 60 and 107% of hyphal ELISA values. Total protein concentration was correlated linearly with organic carbon in soil (r2= 0.85,P≤ 0.001). The percent dry weight of soil composed of water-stable aggregates was correlated positively (P≤ 0.05) with silt and ELISA values and correlated negatively with sand. The possible contribution of this protein to soil stabilization is discussed.

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The proposed criteria for Andosol classification in the World Reference Base (WRB) of Soil Resources were evaluated using the Tohoku University World Andosol Database (TUWAD). The WRB proposal defines a diagnostic andic horizon comprised of vitr-andic, alu-andic, and sil-andic subtypes, and eight second level soil units. Several notable refinements to the WRB criteria were apparent from evaluation of soil properties from TUWAD and are proposed as revised criteria. Our analysis indicated that the most effective criteria for differentiating the andic horizon were glass content, phosphate retention, oxalate extractable Al and Fe, pyrophosphate-extractable Al, and bulk density. The vitr-andic horizon is distinguished by its low degree of weathering, evident from its low oxalate extractable Al and Fe, low P retention, and high glass content. The ratio of pyrophosphate to oxalate extractable Al is used to separate andic horizons dominated by Al-humus complexes (alu-andic, Alp/Alo≥ 0.5), from those dominated by allophanic materials (sil-andic, Alp/Alo< 0.5). When Alpdata are not available, the Siovalue of 0.6 could be used as an approximate criteria. We also propose revisions to the nine second level soil units based on the dominant pedogenic processes occurring in Andosols: noncrystalline material formation and organic matter accumulation. These soil units are based on the degree of weathering (oxalate extractable Al, Fe, glass content), the dominant weathering agent (organic acids vs. carbonic acid), type (melanic or fulvic) and quantity of organic matter, and high 1.5 MPa water-holding capacity. The revised criteria determined by this study effectively differentiate Andosols based on their dominant pedogenic processes, and the relationship of soil properties to productivity and utilization.

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The goal of this field study was to obtain a detailed account of wind erosion processes within a single agricultural field during a regional dust storm in the Southern High Plains of West Texas. The field, located in Wolfforth, Texas, was observed as the wind grew in strength, peaked, and later weakened. Sediment transport was monitored by an array of samplers spaced across the field, and meteorological information was obtained from a 10-m tower erected within the field. Erosion activity was monitored by a piezoelectric sensor that responded to the impact of saltating grains and provided a means for detecting the threshold of soil movement. Attempts were made to relate the observed temporal and spatial variations of sediment transport to meteorological factors and surface conditions. The results indicate that at the beginning of the storm, threshold was around 7 to 8 m/s. As the storm progressed, threshold appeared to slowly shift downward with time, suggesting a surface that was becoming increasingly erodible. Mass flux measurements showed substantial temporal variations that reflected changes of wind strength and changes in surface erodibility. The pattern of mass flux variation across the field was dependent on the height of measurement. The near surface flow of saltating grains (z < 0.25 m) was found to vary according to surface conditions, especially surface roughness. At greater heights, the flow of fine dust was less affected by surface conditions immediately beneath the point of measurement. Within the fully developed surface layer (z < 0.25 m), the mass flux profile was found to follow a modified powerlaw function. The near surface mass flux consisted of a broad range of particle sizes ranging from 50 μm to 300 μm, whereas farther from the surface the mode shifted distinctly toward smaller particle sizes with few particles larger than 100 μm. We show that it is possible to display graphically the relative contribution of the various grain sizes to the mass flux at each height in a way that makes it possible to visualize the zones of saltation and suspension, and the region of transition between these regimes.

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID