摘要:

In a series of experiments, we studied the effects of Al concentrations, OH:Al and P:Al ratios, and ionic strength on soybean root length after 4 days' growth in nutrient solutions approximating soil solutions. Additions of NaOH and NaH2PO4.2H2O solutions decreased the concentrations of monomeric Al species in solution, Al polymers being formed with Al concentrations ≤50 μMoriginally in solution but not at concentrations ≥100 μMAl. In nutrient solutions with ionic strengths ≤900 μM, the Al polymers formed remained in solution, but were not detected in solutions with higher ionic strengths. Soybean root elongation was reduced severely with Al concentrations of ≥10 μM. The toxic effect of Al was ameliorated by the addition of OH or P through the reduction of monomeric Al species in solution. A close curvilinear relationship was observed between relative root length (%) (y) and Σ activities (μM) of the monomeric Al species in solution (x) (y= 14.9972 + 99.163 exp(-0.130605x);R= 0.950***), irrespective of the initial Al concentration, the concentration of polymeric Al species in solution, ionic strength, solution nutrient composition, P concentration, or pH. It appeared that one or more of the monomeric Al species was responsible for the toxic effect of Al on soybean root growth, and that the ameliorating effect of OH and P resulted from the reduction in the concentration of monomeric Al in solution, either through polymerization or precipitation of Al.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

摘要:

We took samples of six surface soils, two subsurface soils, and one organic soil from the Menomonee River Watershed, Wisconsin, and dispersed them by (1) shaking with water to simulate natural water erosion and particle transport conditions, and (2) ultrasound to provide complete dispersion. The shaking treatment consists of end-over-end agitation of a 1:10 wt:vol soil:water mixture for 0.5 to 128 hours, and the ultrasound treatment was for a 15-minute period. The ratio of the amount of clay-sized particles dislodged by shaking to the amount of clay-sized particles obtained by ultrasound treatment was used to measure ease of dispersibility of soils. Samples with clay-sized particles that disperse readily under the shaking treatment have a higher dispersibility ratio than samples with clay-sized particles that remain intact as aggregates. If a 4-hour shaking treatment simulates the onset of soil erosion conditions in the field, as much as 90 percent of the primary clay-sized particles remain intact as silt-sized or larger aggregates. The clay dispersibility ratio was significantly correlated with organic carbon content in an inverse relationship. We also investigated the logarithmic and linear relationships.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

摘要:

This paper describes a simple microcomputer simulation model that calculates changes in the vertical distribution of water beneath a crop from weather, plant, and soil physical data. Simulated patterns of water extraction by soybeans in western Iowa agreed well with measured patterns. The model requires only about 10K of memory, so the simulation can be adapted readily to form part of a more complex model.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

摘要:

We added nine 1000-milligram portions of catechol to nine 250-milliliter, conical flasks, each containing 100 milliliters of distilled water, and divided the flasks into three groups. Within each group, we added 1000 milligrams of aluminum oxide to one flask, 500 milligrams to another, and none to the third. After the three groups of flasks had been adjusted to pH 7.0, 6.0, and 5.0, respectively, and shaken for 18 days, we found that yields of polymer were significantly greater in the presence of aluminum oxide than in the blank and that they increased with pH. In the respirometer study, oxygen absorption byMpyrogallol solution was significantly greater in the presence of silica, alumina, and silicoaluminas than in the blank. All these findings confirm once again that aluminum oxide is an oxidative catalyst that accelerates the polymerization of catechol.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

摘要:

Many Italian soils over which fire has passed are intensely eroded. To clarify the effect of fire on some factors associated with the soil erodibility, such as soil organic matter content, aggregate stability, and hydrophobic and cementing substances, we performed an experimental burning in a selected watershed characterized by surface layers of soil that repel water slightly.After the fire had passed, we noted a decrease in soil organic matter content in the upper soil layers, connected with the disappearance of the resistance to wetting and with the lowering of the aggregate stability.The upper part of the underlying B horizons showed an accumulation of organic matter and an increase in aggregate stability. Contrary to previous findings, no evidence for soil hydrophobicity was detected, but the discrepancy may be explained by the fine texture of the soil tested.The deeper horizons were practically unaffected by the fire.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

摘要:

Using Fourier-transform infrared (FTIR) spectroscopic techniques, we examined a series of whole sewage sludges and extracts obtained from the various samples. Sludges were fractionated by three different, chemically mild techniques: (1) direct solvent extraction, (2) two-phase ether/water extraction in which the pH of the aqueous layer was adjusted from 1.5 to 11.5, and (3) dry-column chromatography. The FTIR spectra provide a qualitative assessment of the types of constituents and functional groups found in the sludges and extracts. The spectra also allow a comparison of the differences and similarities of both the whole and fractionated samples.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID

摘要:

We describe improvements in the theory and practical application of the constant head well permeameter method for field measurement of saturated hydraulic conductivity above the water table.The theoretical improvements result in a new analytical solution and a numerical solution that produce increases in the calculated value of the hydraulic conductivity of approximately 48 and 60 percent, respectively, over the commonly used Glover solution given in most standard drainage manuals. Using the numerical solution, the constant head well permeameter method produced estimates of the saturated conductivity of a structureless sandy soil that were statistically equivalent to the estimates produced by the air entry permeameter method. This improvement thus eliminates, at least within the limits of the tests, the previous tendency of the constant head well permeameter method to underestimate the hydraulic conductivity.The improvements in practical application, which result from refinements in apparatus design, increase the efficiency and range of operation of the method.

ISSN:0038-075X    

出版商:OVID    

年代:1983

数据来源: OVID