摘要:

Through both laboratory and field experiments, we studied the effects of soil moisture content on ammonia (NH3) volatilization from urea, surface-applied to bare Hagerstown silt loam (fine, mixed, mesic Typic Hapludalf). In the laboratory trial, urea fertilizer treatments were applied to cylindrical cores of soil in a flow-through apparatus. Volatilized NH3was measured by passing humid air through the head space and into boric acid traps for 12 d. Total loss from urea on soil with 0.15 kg kg−1moisture content was 30.7% and on soil with 0.22 kg kg−1moisture content, 18.3%. Nitrogen-15-enriched urea was applied to the surface of soils at 0.15 and 0.22 kg kg−1moisture content in confined cylindrical microplots in a field site in May and July 1985. Soil in the microplots dried during the 14-d trials, because the site was covered during periods of rainfall. Samples were analyzed 0, 3, 7, and 14 d after urea after urea application. The mean air temperature was 15.0°C in May and 20.5°C in July. After 14 d,15N recovery from 0.22 kg kg−1moisture soil was 71.9% in May and 60.0% in July. Recovery from 0.15 kg kg−1moisture soil was 95.5% in May and 84.9% in July. We concluded that under drying conditions greater volatilization occurs in soil with a greater initial moisture content, but when soil moisture conditions remain essentially constant, as occurred in the laboratory experiment, there is less volatilization from the soil with the greater moisture content. Also, there are greater NH3volatilization losses at higher temperatures, given adequate moisture to ensure complete and rapid urea hydrolysis.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Changes in nitrogen, tillage, and residue management influence N dynamics, soil moisture availability, soil temperature, and corn (Zea maysL.) yields. The magnitude of the effect of these parameters on the soil/crop system is determined by initial soil and climatic conditions and can be described by field and simulation experiments. The objectives of this research were to determine the influence of depth to gravel and autoclave-extractable N on corn yields within a nitrogen-tillage-residue field experiment and to compare field data with simulated results. Several techniques were used to evaluate the corn/soil system including: a field experiment consisting of N rates, tillage and residue treatment combinations, spatial variability analysis of pertinent soil parameters, and computer simulation of the corn/soil system. Spatial variability analysis enabled weighting of initial parameter values on an area basis for each of the experimental units within the field experiment. These weighted values were then used to determine the influence of the initial conditions on corn production. This study showed that benefits derived for the corn plant from deeper soil depths depended on the interaction between available water, microbial activity, and the ability of the plant to avoid drought. Corn yields for the simulation system were comparable to observed yields, and the NCSWAP model predicted many of the observed responses.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

We studied morphological, physical, chemical and mineralogical properties of six Costa Rican Andepts to elucidate the problems of classification, productivity, and management of ash-derived soils. The soils were formed on volcanic ash, predominantly andesitic, during Pleistocene and recent times. These ash-derived soils are found at elevations higher than 600 m, with model profiles occurring at elevations between 1000 and 1800 m. The climate is cool (15 to 22°C, mean annual temperature) and humid (1170 to 3534 mm, mean annual rainfall), and the original vegetation was a humid forest. These Andepts have a fairly uniform morphology, and the amorphous materials have become strongly stabilized with the soil organic matter to give the dark color, loamy texture, granular-fluffy structure, friable-smeary (thixotropic) consistence, acid reaction, good internal drainage, low bulk density, high porosity and water retention, and high cation exchange capacity that are unique and diagnostic in Andepts. One soil is a Hydric Dystrandept and five are Typic Dystrandepts.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

We examined soils along a transect across a submerged upland tidal marsh on the Eastern Shore of the Chesapeake Bay in Maryland. The soil was classified as a Terric Sulfihemist and was underlain by silty mineral sediments. Total S in the soil was partitioned into organic S, pyrite S, and soluble SO42−components. In the organic horizons, the ratio of pyrite S to total S was variable, ranging from 10 to 60%. The high levels of SO42−and organic matter in the peat, as well as the presence of free S2−, suggest that Fe is limiting pyrite accumulation in these horizons. Pyrite was identified in thin section by its spherical, framboidal habit and was confirmed in thin section and in grain mounts of heavy minerals using an electron microprobe. Individual or small clusters of framboids appeared to be randomly distributed through the organic horizons with few zones or pockets of high concentration. This was consonant with the low input of reactive (easily reducible) Fe (III) adsorbed to mineral sediments added to this isolated marsh. In the underlying mineral substratum, organic matter was thought to be limiting pyrite accumulation by controlling available energy for reduction. In this zone pyrite was concentrated in root channels where there had been some organic substrate for microbial sulfate reduction. The factors controlling pyrite reduction. The factors controlling pyrite accumulation in these tidal marsh soils may differ dramatically over distances as short as a few centimeters.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Mathematical relationships and an analytical apparatus to quantify electron flow through a soil suspension were developed and discussed. Suspensions of two soils, synthetic ferrihydrite and partridgeite, and naturally occurring manganite-hematite mineral were titrated with electrons in this study. The Eh, pH, and current flow through the suspensions were continuously monitored. A portion of the suspensions was drawn after every 24 h, filtered, and the concentrations of Fe and Mn were measured using an atomic absorption spectrometer.The electron titration of the experimental soils did not depict buffering regions that could be assigned to a thermodynamically known Mn solid phase. Maghemite and goethite minerals in the experimental soils reduced between pe+pH of 13.6 and 13.2. Reduction of the synthetic partridgeite mineral poised pe=pH approximately at 14.7. The suspensions of manganite-hematite mixture buffered pe+pH first approximately at 14.8 and later at 13.2. Redox potential of freshly prepared ferrihydrite suspensions poised approximately at pe+pH of 14.5 and decreased with aging.The concentrations of Fe and Mn in the experimental soils and manganite-hematite mineral suspensions were increased with the passage of current.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

The termbirefringencehas a specific meaning in mineralogy, but it has been misused constantly in soil micromorphology as being synonymous with interference colors. This paper is an attempt to discuss its correct use in describing certain soil features.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

We investigated the ability of an immobilized fungal laccase fromTrametes versicolorto transform 2,4-dichlorophenol (2,4-DCP), an intermediate of pesticide degradation. Immobilization supports were a silt loam soil and several clays, kaolinite, and two types of smectite, referred to as montmorillonite 1 and montmorillonite 2. The majority of the added laccase activity was immobilized to these supports, using 3-aminopropyltriethoxysilane and glutaraldehyde. The catalytic properties of these laccase-clay and laccase-soil complexes toward the substrate, 2,4-DCP, were assessed using radiolabeled tracer and chromatographic techniques. Incubation of 2,4-DCP with laccase caused the formation of oligomers, which are insoluble in aqueous solutions and can, therefore, be removed. The efficiency of the laccase immobilized on kaolinite and soil to remove 2,4-DCP from solution was similar to that of the free enzyme (approximately 95% of the added14C-2,4-DCP was removed) and greater than that of the enzyme immobilized on montmorillonites 1 and 2 (69 and 42%, respectively). For these last two supports, however, enzymatic removal may not have been responsible for the entire loss of 2,4-DCP, as adsorption on montmorillonites 1 and 2 also contributed to the observed decreases in 2,4-DCP. A noteworthy advantage of the immobilized laccase over the free enzyme was that it could be separated from the reaction mixture and used repeatedly. After repeated 2-h incubation cycles of the immobilized enzyme with14C-2,4-DCP, the laccase-kaolinite, laccase-montmorillonite 1, and laccase-soil complexes exhibited only a slight decrease in the ability to remove 2,4-DCP. The possibility of nonenzymatic removal of 2,4-DCP was excluded in experiments performed under anaerobic conditions, in which laccase activity was completely inhibited. The effect of a proteolytic enzyme on the free and immobilized laccase was also tested, and, as a result of their resistance to proteolysis, the immobilized enzyme catalyzed the removal of greater amounts of 2,4-DCP than the free enzyme. This stability and certain other characteristics, such as their reusability and their ability to transform xenobiotics as efficiently as the soluble enzyme, should make these laccase complexes useful catalysts of detoxification reactions in soil.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

In an ongoing field experiment comparing the effects of contrasting methods of soil cultivation, we studied the uptake by winter wheat (Triticum aestivumL.) of15N-labeled fertilizer, split-applied in three dressings, in microplots treated by either conventional plowing (CP), shallow cultivation (SC), shallow cultivation + subsoiling (SS), or minimal tillage (MT) in 1987. Results indicated that the percentage utilization (PU) of fertilizer N for each of the three dressings was similar between cultivation systems with total fertilizer N recovery ranging from 71.0% for MT to 73.8% for SC. However, farming systems significantly affected the relative contributions of fertilizer N and soil N to uptake into the aerial portion of the wheat; for example soil N uptake was 104.7 kg N ha−1for CP, 93.0 for SC, 94.1 for SS, and 99.2 for MT. For each treatment, soil N uptake was directly related to the rate of mineralization determined in a fallow soil. As in the previous year, the rate of mineralization was greatest for CP treatments.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

With any method for measuring soil water content it is useful to know the spatial sensitivity of the measurement, i.e., what volume of soil is measured and what the distribution of sensitivity is within that volume. We determined this information for the method of time-domain reflectometry (TDR), using a laboratory procedure in which the distribution of water surrounding the waveguides was controlled to give different spatial arrangements of water around the waveguides. The sensitivity is largely confined to a region with a cross-sectional area of approximately 1000 mm2surrounding the waveguides, although a limited sensitivity extends much farther, enclosing 3500 to 4000 mm2. The width of the region of sensitivity normal to the plane containing the wave-guides is approximately 30 mm, indicating that the method should allow excellent depth resolution when the waveguides are installed horizontally, and that it should be possible to place such waveguides within 20 mm of the surface. Finally, there was no discernible variation in sensitivity longitudinally (along the length of the wave-guides).

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID