摘要:

Unsaturated soil hydraulic conductivity (K) versus depth was measured in situ in five infiltration plots within a 0.01 hectare area on a soil developed from lacustrine materials in a glacial lake bed. Sufficient water was allowed to infiltrate each plot to wet the soil profile to 152 cm. The soil surface was covered to prevent evaporation and during the ensuing drainage period, soil water pressure was monitored with triplicate tensiometers at each depth of 15, 30, 45, 61, 91, 122, and 152 cm. Soil water characteristic data determined on triplicate cores taken from the same depth as the tensiometer cups, were used in conjunction with the soil water pressure head data to compute the hydraulic conductivity.Significant spatial variability of hydraulic conductivity at the 1 percent level was found. In addition,Ksignificantly varied with depth, at the 1 percent level, generally increasing, due to the heterogeneous nature of soil in the vertical direction.Hydraulic conductivity as a function of porosity was computed for each site by the modified Green and Corey method. Agreement of these theoreticalKvalues with those measured in situ depended on the soil water content at which the matching factor was selected. Agreement between methods was best when the matching factor was selected at the lowest water content at whichKwas measured in the field for that particular soil depth.

ISSN:0038-075X    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

Prometryne desorption from selected South Carolina soils (Lakeland s, Norfolk Is, Norfolk scl, Cecil sl, Cecil c, Okenee sl) by added water varies with soil organic matter and texture. Desorption is rectilinear for the prometryne/soil range 1–100 μmol/kg.Kb(desorption constant) values for 1/1 soil/water systems range from 0.86 for Lakeland s (0.22 percent organic matter) to 12 for Okenee sl (5.16 percent organic matter). Prometryne desorption from model soils (sand,Kb= 0.25; sand containing 20 percent kaolin,Kb= 0.76; and sand containing 5 percent peat,Kb= 99) illustrates the effect of diverse additives and tends to clarify interpretations.Kbis a nonlinear function of soil/water ratios: relative toKb 1/1= 1,Kb 1/0.5≈ 1.66,Kb 1/2≈ 0.76, andKb 1/4≈ 0.64.Prometryne movement in 1 m soil columns wet with 1 pore volume of water varies with soil organic matter and texture. 1/Zpdvalues (characterizing values based on prometryne distribution within the column at equilibrium) for 10 μmol/m prometryne treatment range from 0.64 for Lakeland s to 4.6 to Okenee sl.Kband 1/Zpdvalues are numerically different but highly correlated (r≈ .96). This suggests that prometryne movement in soil columns can be predicted from desorption data. Predictions based onKbvalues adjusted for cumulative column soil/water ratios approximate observed movement.

ISSN:0038-075X    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

The interaction of Ca and Mg in the nutrition of intact sugarbeets (Beta vulgarisL.) was studied in the greenhouse by the nutrient solution technique. Salts were supplied in nontoxic amounts to half-strength Hoagland's nutrient solution to provide Ca:Mg ratios of approximately 0.33, 0.63, 1.25, and 2.5, with Ca ranging in concentration from 0.33 to 20.0 and Mg from 1 to 16 me/1. Under these conditions the ionic ratio of nutrients within the physiological range of salt tolerance was defined as the physiological ionic ratio.Magnesium induced Ca deficiency symptoms at about the same plant age in treatments of a similar Ca:Mg ratio even though the amount of Ca and Mg added exceeded by far the amount needed for growth. This interference of Mg with the uptake of Ca by sugarbeets was again emphasized by the delay in the development of Ca deficiency symptoms when Mg was added frequently in small doses to the nutrient solution rather than as a single large dose. In contrast to the interference of Mg in Ca uptake, Ca interfered with Mg uptake but did not induce Mg deficiency symptoms.On the basis of our present and earlier results (Mostafa and Ulrich 1973), it is concluded that the ratio of Ca:Mg in the nutrient solution may be a limiting factor in the Ca nutrition of intact sugarbeets.

ISSN:0038-075X    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

Samples of bentonite, illite, and kaolinite clays were studied for their Mn fixation properties under various pH levels, alternate wetting and drying conditions, and incubation at moisture saturation. Bentonite and illite fixed significant quantities of Mn under wetting and drying. Fixation was directly related to pH and the amount of Mn added. Incubation of treated samples at moisture saturation resulted in considerably less than half the amount of Mn fixed as when subjected to repeated wetting and drying. Kaolinite fixed relatively small amounts of Mn as compared to bentonite and illite regardless of treatment.Since x-ray did not reveal a mineralogical change, it was concluded that Mn was fixed as a result of precipitation, physical entrapment in clay lattice wedge zones, or because it was oxidized to higher valence oxides and/or strongly adsorbed at the exchange sites. Cation exchange capacity (CEC) values were inversely related to Mn fixation.

ISSN:0038-075X    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

The effect of Mn and Zn on plants grown in salt-affected soil was studied. The soils were salinized with NaCl. The test plants were tomato, millet, and berseem. The growth of these plants decreased considerably as the degree of salinity increased. Addition of Mn to saline soil accelerated plant growth and significantly increased yields in saline soil. Under nonsaline conditions the plants did not respond to the addition of Mn. Application of Mn resulted in increased levels of this element in the plants, the values being considerably higher in plants grown in saline soil. Application of Zn enhanced the development of tomato plants at high salinity levels, but in nonsaline soil and at low salinity there was no response; this occurred in a soil which contained an appreciable amount of native zinc. In a soil poor in zinc, tomato plants responded to Zn application in nonsaline as well as saline soil. Application of Zn increased the zinc content of the tomato plants, generally to a higher degree in saline soil.

ISSN:0038-075X    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

Barley was grown in zinc-polluted soils in order to investigate zinc toxicity and the zinc-supplying ability of such soils, as well as to study the effects of high zinc content on the chemical composition of barley.The application of zinc increased the zinc content of barley from 320 to 737, 191 to 379, and 233 to 489 ppm in soils A, B, and C, respectively, but failed to produce severe toxicity. A high correlation (0.999) between “A” values and zinc determined by chemical method indicates that the “A” value is a good criteron for assessing the zinc-supplying ability of soils.Except for Mn (where the concentration in the barley plants increased with increased level of added zinc), the concentrations of Fe, Cu, P, K, Ca, and Mg were not affected by zinc application, which indicates that the interactions between Zn and other cations are governed by their relative concentrations in the growth medium.

ISSN:0038-075X    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

Analysis of zinc-polluted soils and the barley plants grown in these soils shows a relatively higher concentration of Cd, Hg, Pb, and As. The average values of Cd, Hg, Pb, and As in soils are 5.9, 0.36, 104, and 4.4 ppm, respectively, and those in barley plants are 1.65, 0.10, 1.20, and 0.12 ppm, respectively. The levels of Se, Cr, and V are, however, in the normal concentration range. Applied zinc has no real effect on the content and uptake of the trace elements concerned in barley.The results indicate that contamination of soils with Cd, Hg, Pb, and possibly As has occurred, and is presently occurring, in this area.

ISSN:0038-075X    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

Different soils were exposed to 2450 MHz microwaves in the laboratory and in the field. The effect of microwave radiation on soil microorganisms was assessed by classical microbiological techniques. It was found that soil bacteria, bacterial spores, actinomycetes, fungi, nitrogen-fixing bacteria, and nitrifying bacteria were resistant to 40,000 joules of microwave energy applied to each cm2of soil surface. Weed seeds exposed to much lower levels of radiation were uniformly inactivated in laboratory and field experiments. Bacteria became susceptible to microwaves when removed from their natural habitat but they were not affected by soil moisture. There appear to be no residual effects of microwaves in the soil and the effects on microorganisms seem to be nonselective except that fungi, as a class, were more susceptible. A “heat shock” activation of bacterial and fungal spores was observed. From the data presented, it is reasonable to assume that microwaves can be used to control field weeds without damage to the soil microorganisms.

ISSN:0038-075X    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

No toxaphene degradation was observed in a Crowley silt loam, either unamended or amended with alfalfa meal, and incubated aerobically in the laboratory for 6 weeks. There was little degradation in unamended soil incubated in a moist anaerobic environment under N2. However, extensive degradation occurred during anaerobic incubation, especially where the soil was amended with alfalfa meal as an energy source. The order of toxaphene degradation after 6 weeks of incubation was flooded anaerobic (stirred) > moist anaerobic > flooded anaerobic (unstirred) > moist aerobic. During this time, the extent of degradation was 98, 90, 50, and 0 percent, respectively. Microbiological involvement was demonstrated when no respiratory activity or toxaphene degradation occurred after the amended soil was autoclaved and incubated anaerobically. When these soils were reinoculated, rapid degradation resumed, and microbiological activity was evident. Rate of toxaphene degradation under soil anaerobiosis increased as the redox potential (Eh) decreased and became very rapid over the Eh range of 0 to −100 mV.

ISSN:0038-075X    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

A simple column experiment is proposed for the estimation of metal chelate stability under specified conditions such as soil type, pH, and Ca concentration. The metal chelate solution is passed through the soil column and the effluent concentration is measured in a steady state. Assuming a first-order reaction rate for the fixation of the metal (exchange of the metal under study followed by its precipitation) and a linear adsorption isotherm of the metal chelate, the effluent concentration in the steady state is simply related to the reaction rate and to the adsorption coefficient of the metal chelate.

ISSN:0038-075X    

出版商:OVID    

年代:1976

数据来源: OVID