摘要:

Studies to evaluate the effects on arylsulfatase activity of 21 trace elements showed that all elements inhibited the activity of this enzyme in soils. Results showed that the relative effectiveness of trace elements in inhibition of arylsulfatase activity depends on the soil. When the trace elements were compared by using 25 μmole/g soil, the average inhibition of arylsulfatase in the four soils studied showed that Ag(I), Hg(II), B(III), V(IV), and Mo(VI) were the most effective inhibitors (average inhibition>50 percent) and that Fe(II) was the least effective (average inhibition <10 percent). Other trace elements that inhibited arylsulfatase in soils were: Cu(I), Cd(II), Sn(II), Zn(II), Cu(II), Ba(II), Mn(II), Ni(II), Pb(II), Co(II), Cr(III), Al(III), Fe(III), As(III), Se(IV), Ti(IV), As(V), and W(VI). Among these elements, Cu(II) and Fe(III) were more effective than Cu(I) and Fe(II), respectively. But As(V) was somewhat less effective than As(III).Generally, the inhibitory effect of the trace elements studied decreased when the amount of trace element added per gram of soil decreased by 10-fold (from 25 μmoles to 2.5 μmoles). The inhibition by MoO42-, WO42-, AsO43-, and PO43-showed competitive kinetics. Related anions, such as NO2-, NO3-, Cl-,SO42-, did not inhibit arylsulfatase activity in soils.

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

The influence of mineralogical composition, saturating ions, and electrolyte concentration on the flocculation and dispersion behavior of various clay minerals was used to explain reductions in the hydraulic conductivity observed in many sodic soils containing little or no expandable clay minerals. Sodium-saturated clay minerals were found to differ in their sensitivity to flocculation by NaHCO3in the decreasing order: illite, vermiculite, smectite, and kaolinite. Critical salt concentrations (CSC) were 185, 58, 28 to 60, and 8 me/liter, respectively, for the above clays.Very low concentrations of CaCl2or MgCl2, on the order of 1 me/liter or less, were required to flocculate Ca- or Mg-saturated clays. At a sodium adsorption ratio of 15, CSCs were several times greater than those for CaCl2or MgCl2. A small amount of smectite, possibly deposited on positively charged edges of kaolinite, was responsible for large increases in CSC values of kaolinite. The flocculation behavior of soil clays extracted from four California soils was influenced by their mineralogical composition, similar to the patterns observed for reference clay minerals.

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

A novel approach was developed for assessing the degree of humification of peats at various stages of decomposition. The approach involves extraction of the peat with 0.5MNaOH for 1 h, removal of the insoluble residue by centrifugation, and determination of the free radical content of the clear supernatant solution. Heights of ESR signals were found to be directly proportional to the degree of humification, as measured by solubility of the peat in dilute Na4P2O7solution (the Na4P2O7index).The free radicals that are involved in humification are substituted semiquinones, whose concentrations increase as humification advances.

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

BASF's lysimeter facility at Limburgerhof was 50 years old in 1977. Approximately 130,000 percolate samples from 232 outdoor plots have been removed and measured there to date. About 1.5 million analyses of substances in soil and percolate have been carried out, as have about 190,000 analyses of substances in crops. Thirty-nine publications on the subjects of fertilization and crop protection provide evidence of the comprehensive work in agricultural chemistry, as well as in crop and environmental protection. These publications discuss nutrient supply and nutrient behavior in the soil and their relation to the most varied growing conditions. The speed with which the substances migrate in the soil and their degradation are of special importance when studying the active ingredients of crop protection. The numerous results at Limburgerhof allow the following conclusions to be drawn.1. The most accurate methodical aid for establishing nutrient balances for the plant-soil system remains the lysimeter trial, although great care must be taken in interpreting the results for practical conditions.2. The percolate is of decisive importance as a means for transporting the substances moving into the soil. The formation of percolate is influenced considerbly by weather, soil type, vegetative cover, and rooting intensity. More percolate is released into deeper levels when the soil is light, the crop cover thin, and porecipitation plentiful (especially if poorly distributed) than when the soil is heavy with vigorously growing vegetation. Crop type and cropping method (intercropping) have an influence on these relationships.3. Of the primary nutrients, nitrogen is most easily displaced in the soil. What the plants do not take up is leached into the soil or released by denitrification. The nitrogen removed with the percolate is almost completely in the form of nitrate. Most of this comes from the nitrogen reserves in the soil; only 5 to 7 percent comes from fertilizer. The nitrogen balances of the soils were negative; exceptions occurred only under extreme circumstances. High, unfavorably distributed precipitation increased the migration of nitrogen, especially in light soils; dense plant covers (intercropping) decreased it. The combined effect of nitrogen fertilization and irrigation helped to counteract leaching losses.4. Phsosphorus is the least mobile primary nutrient in the soil; most of it removed by the crop stands. The relatively small amount that is leached is largely independent of the crop type and the amount and form of phosphate fertilizer. It does vary, however, with the type of soil and the amount of water supplied. Therefore, increasing phosphate dressing frequently brings about a positive P balance in the soil.5. Potassium is more mobile in the soil than phsophorus, but it is less mobile than nitrate nitrogen. The quantities of potash removed by the plants and the percolate were relatively high in Limburgerhof, but they came from the fertilizer only when the potash dressings were heavy. The K balances of the soils were usually negative.6. In humid climates the amount of calcium leached considerably exceeds that extracted by the crops, even with crops that consume lime. In the long term, the percolation losses from applied fertilizer lime are distinctly influenced by the form of the fertilizer. Although the irrigaiton water partially counteracted the losses, the CaO balances of the soils were very negative.7. Magnesium behaves somewhat like calcium in the soil, but it is much less mobile. The amount taken up by the crop exceeds the amount leached. As sodium, sulfur, and chlorine are more subject to leaching, the soil balances for these nutrients are negative, except for areas close to industrial zones. In the case of micronutrients, the percolation losses were insignificant in comparison to the amounts extracted by crops.8. The nutrients from organic fertlizers have to be minieralized in the soil before they can be taken up by the plants. Since the course of this process does not necessarily correspond with the vegetative growth, the leaching losses, especially for nitrogen, are usually much more severe than from mineral fertilizers. Green manuring (intercropping), on the other hand, exerts a positive influence on the soil's nutrient status by creating a favorable rotation effect and increasing the mass of vegetation remaining in the soil.9. None of the hormone weedkillers (2,4-D, 2,4-DP, MCPA, CMPP, 2,4,5-T) were detected analytically (limit of determination 0.5 ppb) in any sample of percolate. The soil herbicides chloridazon (Pyramin) and fluchloralin (Basalin) were not measurable in the percolate either, at most, traces were discernible in the metabolite. Neither was it possible to detect the plant growth regulator chlormequat chloride (Cycocel) at a depth of 1 m with a limit of determination of 0.002 ppm.

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

Published data concerning the average OH/Al molar ratio (basicity) of Al adsorbed by smectite and by a sulfonic resin were reviewed and found to be in disagreement. The data available for the sulfonic resin were considered further and judged to be ambiguous because of the unaccounted-for possibility of Al hydrolysis during the preparation of Al resin. In order to resolve the conflict among the published data, the basicity of Al adsorbed by an Na resin from solutions of AlCl3and by a Ca resin from suspensions of acidified, x-ray amorphous Al(OH)3was investigated. These experiments were not subject to the possible hydrolysis effect that complicated the interpretation of the earlier published data on sulfonic resin.The data presented in this paper show that the average basicity of hydroxy-Al adsorbed by Na resin from a solution of AlCl3increases as the solution concentration decreases and is always greater than the average basicity of Al in a resin-free solution of the same total Al concentration. This effect would be expected, in particular, when an Al resin is leached to remove Cl-after treatment with aqueous AlCl3.The average basicity of Al adsorbed by Ca resin in the presence of acidified Al(OH)3was found to be 2.50 ± .06 in the measured pH range of 4.5–5.4, independent of the relative composition of the Ca resin-Al(OH)3system. The maximum basicity observed in these model experiments (OH/Al ≅ 2.5) agreed with the many available data on the average basicity of hydroxy-Al adsorbed by smectite but disagreed with the existing published data for Al resin which are systematically lower (OH/Al ≅ 2). The reason for the discrepancy is believed to lie with the presence of hydroxy-Al, which was adsorbed on the Al resin during its preparation, and which, if not taken into account, would result in a low estimate of the OH/Al molar ratio.

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

The chemical properties and nutrient status of an Alfisol under no-tillage and conventional plowing were investigated after 6 years of continuous maize. No-tillage with crop residue mulching resulted in higher concentrations of organic C, total N, available P, and exchangeable Ca and K than the plowed plots in the 0 to 10-cm layer. No-tillage treatment lead to stratification of soil pH in the 0 to 50-cm profile.Nutrient depletion in the conventionally tilled plots was mainly due to accelerated soil erosion. Grain yield was consistently higher from the no-till than from the plowed treatment at the same rate of N application.

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

An experiment was conducted to test the validity of a mechanistic simulation model describing the process of soil moisture extraction by root systems, and to assess the quantitative importance of root hydraulic resistance in this process. Close-growing stands of ryegrass were raised in tubes packed with sand and loam, with and without the presence of a water table. The pattern of water uptake was monitored by gamma-ray scanning and tensiometry. Correspondence between measured and independently predicted uptake patterns could be greatly improved by assigning a relatively high value of root resistivity. Further improvement of the mechanistic model's predictive capability may require explicit formulation of conductive (axial) resistance in addition to absorptive (radial) resistance, as well, perhaps, as such important subsidiary factors as aeration, mechanical impedance, and distribution of nutrients in the soil profile.

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID