摘要:

Reports on the effects of soil submergence on urea hydrolysis are divergent, and hydrolysis of urea in the components (floodwater; oxidized and reduced soils) of the wetland soil system is not completely understood. In laboratory experiments, we evaluated the effect of soil submergence on urea hydrolysis with time in the floodwater, the oxidized soil, and the reduced soil. In a submerged soil system with about 1 mm of floodwater and incubated for2O3, Fe2O3, and αFeOOH), which may be present in the floodwater and the underlying oxidized layer, did not seem to influence urease activity in the floodwater. It is apparent from these results that urease activity will show temporal and spatial variations in the wetland rice soils. The amount of urea hydrolyzed in a given time, therefore, will be an overall consequence of (1) the differences in the urease activities in the floodwater and in the underlying oxidized-reduced soil components of the system, and (2) the relative distribution of urea in those components as influenced by method of application used. We suggest that, for a better understanding of in situ urea hydrolysis in a wetland rice field, along with the effect of soil submergence time, the effects of rice plant rhizosphere and sunlight need to be considered.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

We measured the dissolution rate of gypsum particles (0.5− to 1.0-mm fraction) in distilled water and in aqueous salt solutions of NaCl, MgCl2, Na2SO4, MgSO4, and CaCl2at salt concentrations of 20, 40, and 60 mmol kg−1. Two gypsum samples were tested, one from a gypsum mine in Egypt and another from New Mexico, United States. We monitored the dissolution rate by measuring Ca concentrations in these solutions with and without shaking. The rate of gypsum dissolution increased with shaking and with increasing concentration of the salt solutions. Neither ion concentration nor species influenced the rate of gypsum dissolution when the rate was normalized by the solubility. The first-order reaction equation was unsuited for describing the dissolution process when Ca concentrations exceeded about 50% of gypsum solubility. The second-order reaction equation described the process well, providing a rate constant independent of ion concentrations or species.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

This paper reports optimal conditions for the reaction of aluminum (III) with chromeazophenol KS [also called trisodium 2-(2-hydroxy-3-carboxy-5-sulfobenzeneazo)-1, 8-dihydroxynaphthalene-3, 6-disulfonate, which will be abbreviated CAPKS] (Λmax= 585 nm, pH = 4,CR= 1.59 X 10−4M) and a new procedure developed for the spectrophotometric determination of exchangeable aluminum in soils.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

In a laboratory experiment we followed the dynamics of P availability in sludge-amended soil. A clayey soil (Glendale) and a sandy soil (Latene) were amended with three rates (0, 15, and 30 g kg−1) of gamma-irradiated, dried, anaerobically digested sewage sludge. Triplicate 300-g samples of each soil and sludge rate were incubated for 84 d at 35°C and 0.03 MPa moisture tension. Samples were periodically taken to determine NaHCO3- and H2O-extractable P. In subsequent experiments, Glendale soil was sterilized by either gamma irradiation (50 kGY) or autoclaving to study the effects of microbial activity on NaHCO3-P and H2O-P.Sludge amendment significantly increased NaHCO3-P levels in both soils throughout the 84-d incubation period. NaHCO3-P values for both soils were directly related to the amount of sludge added. A rapid rise in NaHCO3-P occurred in the 1st wk of incubation, but values remained fairly constant thereafter. For days 7 to 84, values of NaHCO3-P for the 0-, 15-, and 30-g kg−1treatments were 16, 35, and 50 mg P kg−1and 6, 27, and 44 mg P kg−1for the Glendale and Latene soils, respectively. Sludge amendment significantly increased H2O-P levels in only the Latene soil. However, in both sludge-amended soils, H2O-P significantly increased with time over the 84-d incubation period.Soil sterilization by irradiation had no effect on NaHCO3-P and H2O-P levels, compared to nonsterilized soil. Soil sterilization by autoclaving had a much greater effect on indigenous soil P than irradiation. Although data from the autoclave experiment were highly variable, no consistent differences were observed between the sterile and nonsterile soils.We conclude that NaHCO3-P and H2O-P increases in sludge-amended soil are the result of chemical rather than microbial transformations.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

We designed a laboratory incubation study to provide evidence that immobilization of fertilizer N occurs within a matter of hours after application. Labeled (NH4)2SO4-N and urea N were added to moist organic soils (MB18 and MC15), cropped sandy loamy soils (WI and WZ), and a forest sandy loam (F2), at a rate of 2 mg N to 20 g of oven-dry soil. Nitrogen immobilization was measured by the appearance of15N in the soil organic N fraction. Approximately 1, 6, and 10% of the applied (NH4)2SO4−15N was immobilized in the cropped mineral (sandy loam) soil, forest (sandy loam) mineral soil, and organic (muck) soil, respectively, after 12 h of incubation. After the same length of incubation, 2 to 3% and 9 to 10% of the applied urea15N was immobilized in cropped mineral soils and organic soils, respectively. A readily available carbon source appeared to be limiting immobilization, because, when soils were amended with 4000 μg glucose C per g soil, immobilization of added urea N increased from 2 to 18% in the cropped soil and from 20 to 25% in the organic soil.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

We studied a sequence of three soil types formed in different parent materials on different topographic positions. Soils in this sequence consist of sandstone-derived soils, soils from dominantly in shale, and last soils formed in colluvial/limestone soil materials sitting unconformably on limestone. The soils occupy the upland, midslope, and lower slope positions. Sandstone-derived soils are well drained and reddish brown, and the soils derived from lowland shale and limestone are gray or grayish brown. Mottling and concretionary materials are morphologic features of pedons in the lower hydromorphic positions. No cutans were readily observed on any of the examined pedons, though texture seemed to become increasingly clayey with depth for the sandstone-derived soils. The lower positions of the perched water table, as observed in one of the pedons, may be estimated by the horizon with the reddest hue. The soils formed in sandstone have a dominant clay mineralogy that consists of kaolinite, goethite, and quartz. Soils formed in shale materials have a mixed clay mineralogy of smectite and kaolinite with depth. Those formed in colluvial/limestone material have a dominant kaolinite clay mineralogy with some subsoil smectite. Parent material and soil moisture regime play dominant roles in the direction of weathering, as observed from chemical and mineralogical data. The distribution of exchangeable Al in addition attests to this. Soils derived from sandstone were classified as Typic Paleustult, those formed in colluvium over shale as Aeric Tropaquept, and those formed in colluvium over limestone as Plinthic Aeric Tropaquepts.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

Movement of the metals Ni, Co, Fe, Mn, Cr, and Hg in Dublin loam soil was studied after 6 yr of sludge addition. Sludges from two sources were added annually at rates ranging from 0 to 225 metric tons per hectare (t/ha) in increments of 45 t. Increasing rates of sludge addition resulted in almost no change in the concentration of metals in the surface soil, with the exception of Cr and Hg, where the metal concentrations in the added sludge were markedly greater than those found in the untreated soil. In these cases metal increased linearly with rate of sludge addition. Surface concentrations of HNO3-extracted Mn were less than those obtained at lower depths. The low values appeared to be due to the failure of HNO3to extract all the Mn from sludge-treated soils. Only Fe of all elements increased significantly in the profile with time. No element moved more than 5 cm below the zone of sludge incorporation in either the highly acid (pH 4.5) Oakland or the near-neutral (pH 7.3) Pacheco sludge-treated soils. Relative metal availability followed the same order for both sludges, i.e., Mn > Co = Ni ≫ Fe > Cr. Percentage of available metal in Oakland sludge-treated plots was nearly double that in Pacheco sludge-treated plots. Percentage availability of Fe and Cr was extremely low.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

We installed 99 tensiometers along a 76-m row planted with chile pepper and irrigated through trickle tubing placed 5 cm below the soil surface. We collected data on soil water tension after the plants had a leaf area index greater than 3. Readings were taken after the row was irrigated through the trickle line and also after rainfall. Additional readings were taken at the end of the growing season after surface flooding the row from both sides.There was extensive variability and little spatial dependence (distance of dependence was always less than 6 cm) in soil water tension measured along the row of chile peppers. We found variability and spatial dependence to be a function of the method of water application, time after water application, and the magnitude of the soil water tension. Variability was greatest and spatial dependence smallest for water application through a trickle line. Variability was the least and spatial dependence the greatest after rain or extensive flooding.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

In continuation of earlier examinations of the suitability of amending cultivated organic soils with moderate amounts of Cu for slowing down their decomposition and resultant subsidence, this greenhouse study revealed that the presence of 1060 ppm (μg·g−1) Cu in organic soilBhad no adverse effect on the yield and nutrition of flooded rice grown on it, compared with the same on soilAcontaining 136 ppm Cu. The rice had been preceded by five crops in the same plots.The long-term study also simulated an event where the organic soilB, enriched in Cu to three times the level required for mitigating the subsidence, was mixed individually with four mineral sublayers in 1:1 vol/vol ratio for argonomic convenience. The yields and nutrition of roots, straw, and grain (with husks) of the rice crop indicated that the Cu added to these mixtures through soilBwas not injurious to the crop. Similarly, data on the rice crop grown on the mineral sublayers specially amended with organic-bound Cu to possibly phytotoxic levels, and on fractionation of the soil Cu, revealed that with time the Cu in these soils was becoming less available to plants. Consequently, the rice grown on the soils did not suffer decreases in yield in spite of 600 to 1000 ppm of Cu in roots.The results confirmed earlier conclusions that the Cu needed for slowing down the subsidence by half would not be phytotoxic, even if the organic soil was mixed with certain mineral sublayers and the organic matter nearly dissipated, and extended the conclusions to include submerged culture of rice.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

We measured oxygen and carbon dioxide concentrations in the pore space of two waste rock dumps that are significant sources of acid and trace metal pollutants to a local river system. The release of these pollutants is a consequence of the oxidation of pyritic material within the dumps, which are at the abandoned Rum Jungle mine in the Northern Territory, Australia. Comparison of oxygen concentration distributions with heat source distributions indicates that oxygen supply is the oxidation-rate-limiting mechanism in most regions of the dumps. Gas transport into the dumps is by diffusion and advection due to both thermal effects and atmospheric pressure changes. The extent to which one transport mechanism dominates reflects the proximity of the edge of the dump and differences in the properties of the material in different regions. In some areas, at least two transport mechanisms determine the pore gas composition.Carbon dioxide levels, which are generally one to three orders of magnitude higher than atmospheric levels, indicate that the bacteria that catalyze pyritic oxidation have a plentiful supply of carbon dioxide, which is essential for their metabolism.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID