摘要:

First, here are reported some interesting data of cumulative evaporation observed in the drying process of soil columns without a water table and under a very low drying rate. It is a fact that there is a stage in which the drying rate is remarkably low, after the first stage of drying has finished, i.e., early in the second stage of drying. Second, approximate solutions of the unsaturated liquid water flow equation for the first stage of drying of moist soil have been derived under a constant rate of drying assuming that water movement during the first stage occurs under a total hydraulic head gradient which is not far from zero. Solutions are presented for finite soil columns under the isothermal conditions applying an empirical expression relating water content to tension for limited ranges of water content. The domain of validity of theoretical analysis is characterized by the ratio of drying rate to the unsaturated hydraulic conductivity at the soil surface. When this condition is met, the theoretical water content profiles are in good agreement with the experimental water content distributions.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

Temperature and relative humidity were monitored in a horizontal column apparatus at selected sites during infiltration into dry soil. As the wetting front approached a measurement site, the temperature was observed to rise; later the humidity was observed to increase, which was followed very closely by the wetting front. As the liquid front passed the measurement site, the temperature was observed to drop rapidly.These data show that the advance of a wetting front involves several processes: (a) as dry soil is wetted, a large amount of heat is evolved; (b) evaporation during the wetting process supplies a vapor phase; (c) as liquid moves into dry soil, the vapor phase moves as a front immediately ahead of the wetting front; (d) a large portion of the heat evolved moves as a front well in advance of both the vapor and liquid fronts; and (e) the heat evolved subsequently heats the liquid front; however, due to evaporation and the thermal conductivity of water, the wetted soil behind the liquid front is cooled.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

Four soils sampled at two depths were equilibrated with Mn solutions to test the conformity to the Langmuir isotherm and to relate the Langmuir coefficents to soil properties. The data conformed to the Langmuir isotherm over the entire Mn concentration range tested (2 to 64 μg Mn/ml) except where there was very low adsorption by sandy, low organic matter top soils. In those soils the isotherm was followed only up to 16 μg Mn/ml in the original solution. Adsorption capacities for Mn were higher for the finer-textured, high organic matter soils and generally followed the CEC of the soils. However, the Mn adsorption maximum was less than 40 percent in all cases and for the sandy top soils only 6 percent of the CEC. There was an inverse relationship between the bonding energies of the soils for Mn and the Mn adsorption capacities. For a relatively constant pH, clay and organic matter contents (and the subsequent CEC) were the soil properties more closely related to Mn adsorption by soils.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

A better classification of sodic soils within grasslands of north-central Oklahoma, based on quantitative data, was the objective of this report. The data matrix has 79 rows and 43 columns. Rows indicate the number of horizons which were sampled from seven sampling pedons. Columns indicate a total of 39 laboratory data, either measur-able or interpretative, together with hue, value, chroma, and the thickness of each horizon. A computer program was used to construct the dendrograph based upon the result of clustering, using the unweighted pair-group method. In order to use the program, the coefficient of similarity between every two horizons in the data matrix was computed. The lower triangle of the 79 x 79 symmetrical similarity matrix was punched on the I.B.M. cards. The 79 soil samples were clustered into 19 groups. A correlation-type similarity of .58 or more existed within each group. Soils were clustered disregarding their relative position within the pedons. Transition matrices with 19 rows and 19 columns were built for each pedon separately. The transition matrix approach was followed in order to separate the seven sampling pedons into groups. Five groups were recognized which were comparable to the subgroups in conventional taxonomy.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

In an experiment in the greenhouse, NH4+-(Ca2++ Mg2+) exchange equilibria were studied for two soils from the equilibrium soil solution. Activity ratios of ammonium,aNH4/aCa +aMg)1/2, when plotted against the changes (±ΔNH4ex) in the exchangeable NH4content of the soil, gave a linear relationship and obeyed Schofield's ratio law. Submergence markedly increased the equilibrium activity, AR0NH4, from 5.95 x 10-3to 6.9 x 10-3M1/2in Habbel Kher loam. Nearly constant buffering capacity (BCNH4) for Habbel Kher loam (52.5 ± 2.5 me 100–1 g soil M-1/2) and Saleempur sandy loam (68.3 ± 2.8 me 100–1 g soil M-1/2) showed that it is a characteristic property of soil and is independent of such management practices as flooding of paddy soils. A significant relationship between activity ratio and dry matter yield (r = 0.90) and N uptake (r = 0.98) by paddy shows that the ammonium activity ratio gives a fairly good measure of the N nutrition of rice grown under submerged soil conditions.A graphical method for determining forms of ammonium which are not water-soluble but are avdlaile to Icwlajid paddy is proposed. Equilibrium labUe ammonium (NH4EL) and activity ratios of ammonium,aNKH4+/(aCa +aMg)1/2, were calculated and plotted, and the intercept of the Q/I isotherm on the Q axis was determined. The negative value of the intercept showed the capability of the plants to utilize ammonical N even when the concentration of NH4+ in the soil solution is zero (ARNH4 = 0). The value of the intercept as 0.20 (me/100 g soil) can be used as a measure of the amount of these forms of ammonium.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

We estimated a water balance for irrigated and nonirrigated millet grown in a Varina sandy loam, which we harvested periodically during the 1970 growing season. Evapotranspiration (ET) was calculated using the water balance equation; all elements, except the subsurface drainage, were measured directly. The subsurface drainage was estimated, using the Darcy equation, to determine the net soil-water flux into and out of the root zone. The ET calculated from the irrigated plots agreed reasonably well with potential ET values computed using the combination equation. Hydraulic gradient data in nonirrigated plots showed that water moved upward for most of the season. During one drought, the upward flux accounted for about 34 percent of the calculated ET. Although the total amount of water moving upward was small, it provided enough water for the crop to subsist until rainfall was adequate.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

A mechanistic multistep model was developed using chemical kinetics and mass transport theory to describe transformations and movement of orthophosphate in soil. Soil phosphorus was assumed to occur simultaneously in any of four primary phases: water-soluble, physically adsorbed, immobilized (or chemisorbed), and precipitated. The kinetics of reactions which control the transformation of phosphorus between any two of the four phases were considered to be reversible and of Nth order. A range of values for the reaction rate coefficients were used in the model to describe the transport of applied phosphorus in the solution phase during steady water flow through a soil initially devoid of phosphorus.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

Surface soil samples from selected plots with varying rates of lime and N, P, and K fertilizers, collected from three locations in Illinois in 1935, 1945, 1955, 1965, and 1971, were analyzed for total Kjeldahl N. In most plots, total soil N declined during the 36-year period. The rate of decline was generally greater in the untreated plots than in plots where small amounts of lime, N, P, and K were added. Few significant changes in established trends in total N change with time occurred in the darker-colored soils when larger amounts of N, P, K, and lime were added after 1965. In the lighter-colored soil, substantial declines in total N occurred in both the untreated plot and in the plots receiving larger amounts of N, P, K and lime after 1965.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

The principle of hard soft acids and bases, HSAB, which can predict stable complex formation, is reviewed. In the soil system, cation exchange selectivity can be compared to complex formation, which can then be described in terms of HSAB theory. It is then demonstrated by comparing “softness” valves to observed cation exchange selectivity in soils, that the majority of soil exchange materials behave as relatively soft bases.

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1977

数据来源: OVID