ISSN:0038-075X    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

We measured effects of variations in topsoil depth on finger millet yield, without and with fertilizer application, on a continuous in situ prepared gradient on an alfisol over two seasons. There was highly significant positive correlation between the yields and depth of topsoil under varying rainfall and fertilizer conditions. The data and a regression analysis showed that the rainfall effect was constant while topsoil showed an interaction with fertilizer. Rainfall effect was 67 and 53 kg/ha without and with fertilizer, respectively. Fertilizer application compensated for 15 cm of topsoil. Without fertilizer the rainfall dominates the topsoil effect while with fertilizer the topsoil dominates the rainfall effect in increasing the yields of this hardy crop. Thus, for sustainable production of finger millet in the agricultural watersheds, the fertilizer application is essential to mitigate the adverse effects of erosion and aberrant rainfall. The absolute payoff from the multiplicative technology is larger on deep than shallow topsoil.

ISSN:0038-075X    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

Organic matter was extracted from cultivated and uncultivated portions of two sandy loam soils using a mild pretreatment and chelation procedure. Soil organic constituents were separated into various molecular weight fractions by gel permeation chromatography. Molecular weight fractions were analyzed for peptide content using reverse-phase high performance liquid chromatography; isolated peptide fractions were acid hydrolyzed and analyzed in this manner for their amino acid content. Peptide amino acid composition of corresponding size fractions often differed between uncultivated and cultivated soils of the same series, but cultivation did not consistently influence the content or composition of soil peptides in molecular weight fractions. The contributions of peptide amino acid N to the total N pool of Queens sandy loam were 16.01% and 3.82% for the cultivated and uncultivated soil, respectively. The contributions of peptide amino acid N to the total N pool of a Pugwash sandy loam were 2.38% and 7.55% for the cultivated and uncultivated soil, respectively. Fifteen different amino acids were recovered from hydrolyzed peptides of the Queens soil whereas 16 different amino acids were recovered from the Pugwash soil. Some amino acids, notably serine and glycine, were more common in Queens than in Pugwash peptide fractions.

ISSN:0038-075X    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

Soil formation in loess/sandstone topo-sequences in west-central Kentucky is closely related to the stratigraphy of the parent materials and landscape position. Soils in summit positions have weakly developed modern argillic horizons underlain by a truncated paleosol with well developed paleoargillic horizons. The loess-derived modern argillic is separated from the fine-grained sandstone-derived paleosol by distinct partially cemented stone-lines in summit positions. Downslope, modern sola developed in mixed colluvium from loess and weathered sandstone are completely welded into the paleosol. Stone-lines are not well defined on these landscapes. Solum and argillic horizon thickness decrease with increasing slope gradient in summit, shoulder, and upper back-slope positions but increase downslope due to depositional processes and greater permeability of the coarser-textured paleosol. The comparable paleoargillic horizon development in the lower backslope and middle summit positions, as evidenced by fine/total clay ratios and free iron oxide data, suggests a more stable Pleistocence landscape position for the paleosols. Evidence from this study and extensive field observations suggests that all summit, shoulder, and upper backslope pedons could be classified as fine-loamy Hapludults in the range of the Riney series. Most mapping concerns should be associated with the lower backslope and foot-slope positions where variable colluvial accumulation, truncation depth, paleolandscape influence, or gravel content has formed a variety of soils ranging from clayey Hapludults to loamy-skeletal Paleudults.

ISSN:0038-075X    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

The reaction kinetics of hydrogen ions with gibbsite, goethite, kaolinite, and three electrodialyzed variable charge soils were studied by monitoring the decrease in H+ion concentration and the increases in soluble aluminum and positive surface charge. The H+ion concentration: dropped sharply within 5 s and then remained practically unchanged for goethite; showed a marked decrease after the rapid reaction stage for gibbsite; and changed only very slowly for kaolinite. For soils, there were also a rapid reaction stage and a slow reaction stage. The magnitude of the increase in positive surface charge was of the order Hapludox > Kanhapludult > Paleudult, while that of the increase in soluble aluminum was of the order Paleudult > Hapludox > Kanhapludult. These phenomena were interpreted in terms of the protonation of surface -Fe-OH groups (a rapid reaction) and the dissolution of aluminum-containing minerals (a slow reaction). The addition of iron oxides to the soil or the removal of free iron oxides from the soil affected the reaction kinetics markedly. The reaction kinetics can be described by parabolic diffusion equation, Elovich equation, and two-constant rate equation fairly well, with the degree of fitness depending on the initial concentration of H+ions.

ISSN:0038-075X    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

Chemical transformations that occur under flooded conditions in two limestone soils from flood-prone agricultural areas of south Florida were investigated. Redox potential and pH of Krome very gravelly loam and Chekika very gravelly loam soils were monitored over a 5-week submergence period. Within 2 days of flooding, redox potential decreased to −150 mV and −300 mV for the Krome and Chekika soils, respectively, and by day 21 it had stabilized at about −165 mV for all treatments. The initial pH values of the Chekika and Krome soils was 7.9 and 7.5, respectively, but after 3 weeks of flooding the pH of both soils had stabilized at about 7.25. Samples of both soils were subjected to aerobic (field capacity moisture content, nonflooded) or anaerobic (submerged in water under N atmosphere, flooded) incubation in serum bottles. After 0, 1, 3, 5, and 7 weeks of incubation, concentrations of K, Fe, Mn, Mg, Ca, NH4+, NO3−and P were determined. Before incubation, concentrations of Mn and Fe were about 1–2 μg/g soil for both soils. After 7 weeks of flooding, extractable Mn and Fe increased 50-fold and 30-fold, respectively, for the Krome soil and 7-fold and 15-fold, respectively, for the Chekika soil. With aerobic incubation, Mn decreased and Fe increased slightly in both soils. Extractable Mg and Ca increased in both soils regardless of incubation treatment, but flooding resulted in higher concentrations of Mg and lower concentrations of Ca than aerobic incubation by week 7. For both soils, K increased regardless of incubation treatment, whereas P decreased, but decreased more rapidly with flooding. Extractable NO3−decreased with flooding but increased with aerobic incubation, where NH4+decreased with aerobic incubation but increased with flooding. The data obtained from this study indicate that annual, cyclical flooding may have potential for alleviating crop deficiencies of minor elements which is a major production expense in these soils.

ISSN:0038-075X    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

Much of the mineral nitrogen loss during winter and early spring in central Alberta has been attributed to denitrification. However, the extent of this loss is site- and season-specific. In an attempt to use the results of more basic studies in the estimation of field denitrification, a simulation technique for denitrification was constructed as part of a more comprehensive agroecosystem model. As part of the larger model, the technique was fully coupled to submodels for carbon and nitrogen transformations and transport. In the technique, inter- and intra-horizon fluxes of oxygen in gaseous and soluble phases were simulated as oxygen moved from the atmosphere to sites of microbial respiration. A portion of the simulated demand for electron acceptors not met by oxygen at the microsites was met by nitrate, using a Michaelis-Menten function of rate versus nitrate concentration. The technique was tested against nitrate loss recorded under a range of controlled laboratory conditions. Recorded nitrate losses ranging from 0 to 3.0 μg N g−1soil h−1were reproduced by the technique across a range of temperatures, water contents, and nitrate concentrations. An interaction between temperature and water content on denitrification rate as observed elsewhere was also reproduced. However, the technique relies on an understanding of the distribution of soil organic matter among kinetic fractions in the simulated soil profile and upon the rates at which these fractions decompose. Thus, a process-based technique for the simulation of denitrification will require more detailed insight into soil carbon dynamics.

ISSN:0038-075X    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

The effect of low molecular weight aliphatic acids on aluminum and SO42−activity in the soil solution of two forested Cecil soils (typic Hapludult) was evaluated. A column study was conducted in which soils were selectively leached with malonic, or tartaric acid or with distilled water treatment. Leachate concentrations for SO42−were in the range 2 to 709 μmol·L−1, total aluminum 26 to 945 μmol·L−1, and pH 4.1 to 6.5. Stability diagrams using aluminum, SO42−and pH suggests that the aluminum and SO42−activities were regulated by solid phases with the chemical composition of jurbanite and alunite. The addition of organic acids to the soil resulted in shifts in the solid phases controlling both aluminum and SO42−activity. In the Cecil (South Carolina) soil, organic acids resulted in a shift from solution equilibrium with basaluminite to that of jurbanite, whereas the Cecil (Virginia) soil shifted in equilibrium from alunite to basaluminite as the controlling solid phase. The number of eluent pore volumes required for a solution to become saturated with respect to basaluminite varied with the organic acid source. For the Cecil (Virginia) soil 6, 10, and 14 pore volumes were required by the oxalic, malonic, and tartaric acid treatments, respectively, for the solution to become saturated with respect to basaluminite. Results from this study suggest the jurbanite provides an upper solubility limit for aluminum and SO42−activities in these soils, whereas alunite provides the lower solubility limit. Solid phase transformations between various basic aluminum sulfate solid phases resulted in increased solution pH and may serve as a secondary source for H+neutralization.

ISSN:0038-075X    

出版商:OVID    

年代:1991

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1991

数据来源: OVID