摘要:

Topsoil stratification in ridged soil and implications for the measurement of average wetness and estimation of change in profile wetness by the neutron probe method are discussed. Defining the topsoil of a Haplustalf as the ridge plus the 12.5 cm of soil below the furrow elevation, four strata in terms of bulk density and water retention were identified: ridge, ridge base, furrow, and 10-cm depth. The count ratio was sensitive to ridge geometry and density variables in addition to weighted average wetness. In terms of precision and simplicity, the best linear calibration model included wetness and ridge cross-sectional area as independent variables. The optimum depth of measurement was found to be 3 cm. Failure to recognize the importance of ridge geometry for the top-soil calibration, especially for shallow profiles in uniform soil, may introduce a bias in estimates of change in profile wetness and significantly increase the number of access tubes required for a given level of precision. It is concluded that tillage-induced stratification and geometry of the topsoil must be considered when investigating and modeling the water balance of ridged soil.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Models of soil temperature in the literature address several broad groups of variables: first, those that are site-specific such as latitude and soil series, second, those that directly or indirectly measure insolation by proxies such as cloud cover, cover crops, and the sun's relative position to the location, and third, daily weather variables such as air temperature and precipitation. Although each of the models reviewed was effective in predicting daily soil maximum and minimum temperatures, a simpler model was developed that shows equal or better predictability to existing models using easily obtainable data, such as minimum (Amin) and maximum (Amax) air temperature and day of year. Five locations in Arkansas with about 15 years of observations form the basis of the data set. Two general models were developed to predict daily soil minimum and maximum temperatures at 5 and 10 cm. All parameters were significant in the general model (for all locations), while 10 of the 12 terms in the site-specific model were significant. Values ofR2for the models ranged from 0.911 to 0.951, indicating that the parameters used in each model consistently accounted for at least 91% of the observed variation in soil temperature. Only minor differences existed in the values ofR2when comparing the site-specific with the general model, suggesting that including variables for location does not sufficiently increase the prediction capability of the model enough to warrant their inclusion. The general model provides adequate predictability with a greater degree of efficiency. Hence, the general model may be used with appropriate variables (Amax, Amin, and day of year) to predict soil minimum or maximum temperatures at either the 5− or 10-cm depth. Two applied examples are presented that use the kind of information generated by these models.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Infiltration into freshly tilled soils is influenced by the type and degree of surface roughness and plough layer porosity, both of which often change with time as a result of the impact of cumulative rainfall amount. This study was conducted to evaluate the effects of rainfall and tillage-induced surface roughness and total porosity on infiltration. This was done by simulating five 150-min rain storms, applied every 24 hours at a constant rate of 70 mm h-1, on micro-catchments taken from freshly ploughed, harrowed, and rolled soils and from an untilled soil. The results showed that infiltration into the freshly tilled soils was more strongly associated with the degree and stability of the initial tillage-induced micro-structure at the surface than the hydraulic conditions and properties of the underlying layers. The curve analysis of the infiltration data to six infiltration equations showed that infiltration into the freshly tilled soils was best described by exponentially decaying functions in which surface, rather than profile, conditions, and properties, control the process.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Density, viscosity, and surface energy properties of some industrial, municipal and soil (extract) effluents were experimentally investigated by their flow in horizontal capillaries of 0.0421 cm internal radius. Observance of the square root of time law for meniscus advancement in an unfilled capillary and linearity between velocity and hydraulic gradient in a filled capillary verified Poiseuille's law under unsteady and steady flow. Surface tension decreased linearly with organic carbon of the effluents. The wettability (Cos α) was found to increase linearly with the ratio of humic colloidal carbon fraction (HCC) to total colloidal carbon fraction (TCC) (Cos α = 0.3791 + 1.6686 (HCC/TCC). An appreciable decrease in the values of penetration coefficient, saturated hydraulic conductivity (Ks) and infiltration capacity (t4) with the application of liqueur distillery effluent (ELD) in sand indicated the practical utility of applying ELD for decreasing the percolation losses of water and nutrients in sandy soils.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The kinetics of initially nonexchangeable K released to H-resin were investigated on Gurdaspur loam (Udic Haplustalfs), Nihalkhera sandy loam (Typic Comborthids), and Tulewal loamy sand (Ustochrepts) representing three agroclimatic regions of the Punjab state. Calcium-saturated soil samples were equilibrated with H-resin for 0.25 to 96 h. The kinetics of K release were evaluated using Elovich, power-function, first-order diffusion, zero-order, and parabolic diffusion equations. Potassium release from nonexchangeable pool to H-resin on all three soils conformed well to the first-order (R2= 0.936–0.987; SE = 1.0–3.30 x 10-3) equations as evidenced by the highest values of coefficient of determination (R2) and lowest values of standard error (SE) of the estimate. The Elovich equation and power-function equation also described the data satisfactorily. The zero-order equation did not describe the data well as shown by higher SE and lowerR2values than those found with the Elovich, first-order, diffusion, and power-function equations. The values of rate constants or the nonexchangeable K release coefficients (kr) exhibited a great variation in their magnitude, which is attributed to the mineralogical differences among these soils. The kr values varied from 0.025 to 0.034 h-1in Gurdaspur, 0.030 to 0.049 h-1in Nihalkhera, and 0.018 to 0.036 h-1in Tulewal soil profiles. The magnitude of kr suggested the medium rates of nonexchangeable K release from the three soils.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Field experiments were conducted to measure CH4fluxes over the first and ratoon cropping seasons from a flooded Louisiana rice field. Treatment plots contained the semidwarf, early, long-grain rice cultivar Texmont, drill-seeded into a Crowley silt loam soil (Typic Albaqualfs). Main crop treatments were (i) urea (100 kg N ha-1) with rice plants, (ii) urea without plants and (iii) unfertilized plants; ratoon crop treatments consisted of (i) urea (84 kg N ha-1) with plants (ii) urea with plants plus rice straw (10 tons ha-1) and (iii) unfertilized plants. Methane emissions from the microplots were measured over the 77-day first crop and 73-day ratoon crop growing seasons. A closed-chamber technique was used to collect CH4gas samples in the morning and afternoon hours. Significant urea fertilizer and rice straw effects were observed, and CH4fluxes were highly variable over the two rice-cropping seasons. Over the main crop-growing season (77 days) approximately 50, 240, and 340 kg of CH4ha-1were released to the atmosphere from the urea without plants, unfertilized plants, and urea with plants treatments, respectively. Methane emissions from the ratoon crop (73 days) were 220, 520, and 1,490 kg ha-1for the unfertilized plants, urea with plants, and urea with plants plus rice straw treatments, respectively. Approximately 1,830 kg of CH4ha-1were emitted from the urea-treated planted plots over the 150-day collection period provided the first crop straw was left in the field after harvest.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The ketonic part of soil lipids was studied in a hydromorphic forest-podzol. The undecomposed forest litter layer (L) and the fragmented mycelium-invaded litter layer (F), and the soil A1horizon were sampled and analyzed for total lipid and total ketone contents. Total ketones were separated into methylketones and triterpenic ketones.Extractable ketones were not observed in the L layer, but were determined in the F layer of the soil litter. From the F litter layer to the soil A1horizon, the portions of the two types of ketones, mainly the methylketones, decreased sharply. These last components, which are not primarily plant substances, originated essentially from the β-oxidation of n-alkanes, and the amount of transformation of n-alkanes into methylketones was in inverse ratio to their carbon number.Triterpenic ketones were the dominant part of soil ketones, and all their identified components were of plant origin. An important decrease of the amount of triterpenic ketones was observed from litter to soil, but their decomposition processes were not clearly determined.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID