摘要:

Analytical solutions to the one-dimensional, linearized moisture flow equation are presented. The surface boundary condition is taken either as a time-varying flux, time-varying water content, or with the flux as a linear function of the water content. A semi-infinite, vertical flow medium is considered with arbitrary initial conditions. Calculations for a cyclic flux input are compared to the associated nonlinear, finite difference solution for five simulations using data from two soils. The results are encouraging in that the same general profiles are obtained. The solution is believed to have particular merit to describe moisture regimes resulting from a high frequency irrigation schedule.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

For total air pressure and oxygen partial pressure measurements a hydrophobic membrane probe is used. The probe consists of a small membrane-covered chamber and two teflon capillaries. The probe represents an artificial, permanently air-filled pore which connects the soil atmosphere at a certain depth with a pressure transducer or an oxygen electrode placed on the soil surface. The soil water is excluded from the artificial gas phase by a water-repellent membrane highly permeable to air. The hydrophobic membrane makes the gaseous phase between soil and sensor continuous. This instrument was used in the field to follow changes in total air pressure and oxygen partial pressure in the soil atmosphere during water infiltration and drainage processes. The total pressure in the soil atmosphere and the partial pressure of its components strongly depend upon the continuity of the gaseous phase. This effect is shown in an undisturbed soil profile after a heavy artificial rainfall of 75 mm was applied within 2 hr.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The effect of abrupt textural change on the shape of the steady-state potential profiles in a layered porous medium is examined both theoretically and experimentally. It is shown that a variety of shapes are possible, depending on the rate of flow, layering sequence, and the hydrologic properties of the layers. Three distinct shapes of the potential profiles and the requirements for their development in a two-layered system are discussed.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Two empirical methods of using soils as ionizing radiation dosimeters are presented. These methods were derived through the use of the thermoluminescence characteristics of soils. Method A was designed for irradiated soils for which preirradiation collection of the soils was available. This method is workable for maximum radiation exposure levels up to about 480,000 roentgens. Method B was designed for irradiated soils for which pre-irradiation collection of them was not available. This method is workable for maximum radiation exposure levels up to about 5,000 roentgens. Some of the reasons for the discrepancy in the sensitivity between the two methods are discussed. Various factors that influence the measurement of soil thermoluminescence are discussed also.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The quantity-intensity (Q/I) approach was applied to evaluate the effects of liming on K equilibria in four major agricultural soils of Rio Grande do Sul, Brazil. The amount of labile K estimated from the Q/I parameters ΔK° and Kc, decreased slightly with liming. However, the most pronounced changes in Q/I parameters following liming were an increase in the buffering capacity (BCk) and a decrease in the intensity factor (ARko). Double layer theory and effects of liming on exchangeable Al and polynuclear Al-OH complexes were used to partially explain these effects. It is apparent from this study that liming these soils leads to relatively lower amounts of K in solution at equivalent exchangeable levels. This results in lower leachability of native or added K, but it might also contribute to K deficiencies for crops if the intensity factor were lowered below the critical level.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

From the lime water extractive of a peat soil a variety of phenolic compounds has been isolated. The identity of the compounds has been established by chromatographic and spectroscopic techniques. It is suggested that, when peat is treated with lime, certain phenolic compounds become solubilized as calcium complexes and that the removal of these coupounds aids the decomposition of the peat.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Mechanical strength values were determined for dried briquettes formed from soil material taken from the surface horizons of 83 experimental cotton plots located in the North Carolina Coastal Plain and for which cotton stand data were available. A highly significant direct relationship was found between strength and content of clay. Greater strength values were also observed with increasing amounts of fine clay (<.2 μ). A significant inverse relationship between cotton stand and content of clay was also demonstrated. This appeared to be an indirect effect of clay operating through its effect on strength.The effect of clays separated from the above soils on mechanical strength of artificial soil samples was also studied. The relative concentrations of clay-size quartz and alkali-extractable alumina were the mineralogical properties most correlated with the strength of artificial soils. Quartz was negatively correlated whereas alumina was positively correlated with briquette strength.Enrichment of the clay fraction with negatively charged particles increased strength two- to threefold. This enrichment was accomplished by the selective dissolution of some of the noncharged clay components such as gibbsite, a portion of the quartz, and alkali-extractable silica and alumina.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Metal-organic complexes were extracted from six soil samples collected on the Caribbean island of Dominica and from a Canadian Podzol Bh horizon soil sample. Following extraction with dilute base, the metal-organic complexes were purified by dissolution in methanol and prolonged dialysis against distilled water. The complexes were characterized by chemical, IR-spectrophotometric, thermal, and X-ray methods.Between 22.8 and 70.4 percent of the soil C was found to occur in the purified complexes. The most prominent metal in all complexes was Al which constituted between 3.45 and 7.17 percent of the air-dry weights. Other major inorganic constituents were Fe and Si. The Al and Fe in the metal-organic complexes appeared to be present as Al(OH)2+and Fe (OH)2+, bonded to negatively charged carboxyl and phenolic hydroxyl groups on the ligands. X-ray analysis failed to show any crystallinity in the complexes. The ligands were identified after removal of most of the metals as fulvic acids.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

An experiment on a Spodosol (Alfic Haplaquods) was begun for a citrus scion-rootstock trial with three main soil treatments each one hectare in size, namely: shallow tillage (ST), deep tillage to 110 cm by a trenching machine (DT), and similar deep tillage with incorporation of 56 mt/ha of coarse grade dolomitic limestone applied on the surface. Soil samples were taken from narrow profiles of unmixed and those of deep-tilled soil on a DTL area upon opening of tenches for tile-drain installation. Saturated soil extracts were obtained from freshly taken samples and after incubation of subsamples with NH4-N. At depths below 10 cm, shallow lime incorporation resulted in different patterns of NO3distribution, pH, soluble Ca and Mg, and in nitrification efficiency than in corresponding DTL soil. Nitrification resulted in large increases in acidity, amounts of Ca and Mg in solution, and loss of pH-dependent cation exchange. Another set of soil profile samples was taken from the main treatments 2 years after deep tillage. Redistribution of organic matter in Al and Bh horizons in deep tilled profiles was within 25 percent variability of the expected mean values. Increase in P sorption capacity from near nil in A1 and A2 horizons of ST soil to mean values of 0.38 on 0.43 mM/100 g in DT and DTL soil was attributed mainly to Fe and A1 incorporated with the clay from the B21 horizon. Cation exchange capacity was nearly doubled in all depths of DTL soil compared to those in DT soil. About 25 percent of the applied dolomite was unreacted, 40 percent was present as exchangeable Ca and Mg, and 35 percent not accounted for, presumably lost by leaching and outflow in 2 years. Recyling of drainage water by irrigation use is suggested to increase nutrient use efficiency and reduce ground water enrichment.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The in situ soil gamma analyzer is an instrument constructed to measure the position of gamma-emitting trace elements in soil. It consists of a solid state scintillator, a lead shield with a 3-mm-wide horizontal window, and a portable analyzer. When the detector is lowered into a circular excavation dug vertically into the soil of interest, the gamma activity of the tracer is plotted as a function of depth thus yielding a profile of the tracer distribution. Because of a broad base profile in the original plotted data, which is due to soil attenuation and the lack of collimation, a computer program was written to replot the distribution pattern to within ± 1 mm of actual position. By making a series of time-related measurements, the rate of pollutant movement in soil is obtained.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID