摘要:

This paper describes the possibility of continuous remote sensing of the moisture content of soil using atmospheric neutrons produced by cosmic radiations near the ground surface. Using polyethylene-moderated BF3neutron counters at several different underground depths, we measured time variations of the neutron fluxes, to examine their responses to soil moisture changes quantitatively. From the close correlations between neutron fluxes and soil moisture contents, we show that the fluxes of the underground neutrons with energies from the cadmium threshold of 0.025 eV to about 106eV, measured at a depth of 20 cm, are affected most sensitively by the moisture content of the soil near the same depth. Their fractional change is represented by a regression coefficient of 1% per unit percent of soil moisture change for a range from 33% (∼2.8 pF) to 52% (∼1.9 pF) at the 20-cm depth. This neutron technique promises to be a simple and reliable measurement that depends on the counting statistics of neutrons.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

We attempted to determine if the clay mineralogy class of fine-textured soils in New York State could be reliably predicted using a total potassium (K2O) determination. Previous x-ray diffraction results have shown that the fine-textured soils in New York State are in the illitic clay mineralogy class, except for those found in the St. Lawrence Valley, which have a mixed clay mineralogy class. The total potassium method did correctly predict hydrous mica content and clay mineralogy of seven pedons that represented the lowland regions of New York State excluding the St. Lawrence Valley. Five pedons from the St. Lawrence Valley could not be correctly predicted due to the presence of significant quantities of K feldspars and inter stratified (2:1) minerals in the clay fraction. For the other lowland regions in New York State, the total potassium method does provide a sufficiently reliable method for predicting hydrous mica content and clay mineralogy class for soil series that are currently being surveyed and correlated.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

I conducted a laboratory study to determine the organic compounds present in the soil solution of a coarse-textured soil and the effect of these compounds on P adsorption. Solutions of KC1 at concentrations of 10−2and 10−4mol L−1were added to columns that contained 800 g of Valentine loamy sand (Typic Ustipsamment) after the surface application of either 0.3 or 0.72 g diammonium phosphate. The collected leachates were analyzed using gas chromatography (GC) and thin layer chromatography (TLC) to determine which organic compounds were present in solution. A subsequent adsorption study was conducted in which solutions containing 25 ppm inorganic P and 10 ppm organic anion were added to 10-g soil samples and equilibrated for 24 h, after which I determined the inorganic P concentration in solution. Results obtained from the TLC analysis indicated that phytic acid was the predominant organic P species present in the soil solution. Compounds of the cinnamic and benzole acid series did not influence P sorption, but phytic acid strongly inhibited P sorption. Inorganic P sorption was reduced to less than 14% of the control when the phytic acid concentration in_solution exceeded 8 ppm. Identification of phytic acid in the soil solution suggests that the phytic acid inhibition of inorganic P sorption may accelerate P leaching in coarsetextured soil.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

In laboratory studies we investigated the effect of initial soil water content and amount of water applied on the movement of surface (0 to 2 cm) and deep-placed (8 to 10 cm) P, under different potential evaporation rates (2.2 and 7.5 mm/d PE), in a sandy loam (Typic Ustochrept) soil. We applied phosphorus as diammonium hydrogen orthophosphate at the rate of 300 ppm P labeled with 10 μCi32P/g P. The distribution of P and water in soil columns was examined immediately after infiltration of water and after 15 d of redistribution, with and without evaporation.Initial soil wetness affected P displacement by affecting the time needed to leach the soil. Phosphorus mobility increased with the amount of water applied, but the P front lagged behind the water front. Increasing rates of evaporation did not affect the total depth of P penetration, but did affect the distribution of P in the displaced zone. Phosphorus peaks shifted upward, and their number increased from one under no-evaporation to two under evaporation conditions. The effect of PE was more pronounced-on the displacement of surface-placed P than on the deep-placed P. Even under higher PE, deep-placed P was better distributed in subsoil than surface-placed P, which showed a tendency to accumulate in the surface soil layers.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

We studied various properties of nonallophanic Andosols in Japan. Our results showed that, despite many similarities between nonallophanic and allophanic Andosols, significant dissimilarities also exist between the two groups of soils.The nonallophanic Andosols used for our study formed from rhyolitic, dacitic, or andesitic volcanic ash in a humid temperature climate. They had distinctive morphological properties common to allophanic Andosols in Japan: (1) very dark, thick humus horizons, (2) granular structure in the humus horizons, (3) friable to very friable consistence, and (4) abrupt or clear smooth boundaries between humus and nonhumus horizons.The clay mineralogy of the nonallophanic Andosols was very different from that of the allophanic Andosols. In nonallophanic Andosols the clay fractions are mostly dominated by chloritized 2:1 minerals and the active Al (acid-oxalate-ex-tractable Al) consists largely or wholly of Al complexed with humus (pyrophosphate-extractable Al).The nonallophanic Andosols had mostly medium to fine textures and considerable high water retention at 15 bars. We noted that these soils have characteristically low bulk density, which is closely correlated with the organic carbon content.A remarkable accumulation of humus took place in the nonallophanic Andosols and was closely correlated with the formation of Al-humus complex. The high CEC of these soils was ascribed to the high humus content. We noted that nonallophanic Andosols are strongly acid to very strongly acid, reflecting the abundance of chloritized 2:1 minerals and the very low base saturation. Therefore, they had high Al saturation and large amounts of KCl-exchangeable Al, which is a major deterrent to plant growth in the soils. The average values of Al saturation and KC1-ex-changeable Al were 74.4% and 5.51 meq/ 100 g for humus horizon soils and 59.8% and 3.50 meq/100 g for nonhumus horizon soils, respectively. Almost all the nonallophanic Andosol samples had pH (NaF) >10 and phosphate retention > 85%. These values were significantly correlated with the acid-oxalate-extractable Al (Alo). Soils containing > 1% Alo have pH (NaF) > 9.4 and phosphate retention >85%. Therefore, we noted that Al complexed with humus has a significant amount of OH groups and is highly reactive. The analysis of pyro-phosphate-soluble components indicated that the humus associating with Al and Fe consists largely or wholly of humic acid with the highest degree of humification.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

Using a Troxler surface gamma-neutron gauge, we measured soil bulk density and moisture content at field capacity 0 to 100 and 0 to 300 mm deep at 40 locations in a tilled wheat field and 20 locations in an adjacent native pasture on a silt loam soil (Udertic Paleustolls). Macroporosity at these sites was determined as total porosity minus field capacity. The bulk density of the 0 to 100-mm layer was lower than that of the 0 to 300-mm layer/The mean bulk density values were similar in both fields, but the field capacity was slightly higher, and the macroporosity lower in the grass field than in the wheat field, especially for the 0 to 100-mm layer. We compared four methods of calculating the above soil properties from gamma readings. These methods involved the use of measured gravimetric soil water contents versus the volumetric soil water contents determined by the back-scatter neutron meter and the use of soil-core calibrated attenuation constants for soil water versus a Troxler approximation of these constants. Differences found among the four methods of calculation were small, as were the differences between the results of these methods and the soil-core values from an earlier study. The volumetric soil water content, 2 d after the soil had been wetted, did not vary much with depth within the topsoil (0 to 300 mm). Then, the surface neutron meter provided an acceptable value for the average topsoil water content and for the average bulk density calculated using that water content. The results demonstrate the tremendous utility of a surface gamma-neutron gauge for rapid hydrol-ogic characterization of a variable field and for measuring the relative effects of tillage, cropping, and erosion depositions.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

We assessed the phosphate-buffering capacity of soils from the slope of an adsorption or desorption isotherm relating P quantity to P intensity. Although adsorption isotherms are readily assessed through solution P changes from P additions with a single soil, P desorption isotherms are not as conventionally determined. We conducted this research to compare P adsorption and desorption isotherms using various laboratory procedures with anion exchange resins. Resin desorptions were assessed on an Ascalon sandy loam and on an Apishapa silty clay loam. Desorption procedures involved (1) keeping the amount of resin constant while varying the equilibrating time, (2) keeping time and resin constant while varying soil quantity (surface P), and (3) keeping time constant and varying the amount of resin added to the soil.The results show that adsorption and desorption curves did not coincide under the experimental conditions. Phosphate was less soluble when subjected to desorption treatments. Slope values varied ninefold. Because the slope is generally used as a measure of the P diffusive characteristics, some consistent and standardized way to measure this parameter is needed.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

The Guelph permeameter method is used in 0.02-m- and 0.03-m-radius wells to measure in situ the field-saturated hydraulic conductivity (K10) and matric flux potential (&phis;m) of a heterogeneous, anisotropic, structured loam soil. TheK10, estimates, obtained using both Richards (GP-R) and Laplace (GP-L) analyses, are compared with saturated hydraulic conductivity (K.) estimates obtained using vertically and horizontally oriented, “undisturbed” soil cores. The&phis;mvalues, obtained using both GP-R and the Gardner (GP-G) analyses, are used in estimating soil sorptivity (S) and the α-parameter of the exponential hydraulic conductivity-pressure head relationship for infiltration.TheK10values are found to effectively average the vertical and horizontalK. values. In accordance with the theoretical prediction, the GP-L calculation ofK10, which neglects capillarity, significantly overestimates the GP-R calculation, which accounts for capillarity. This implies that earlier well permeameter analyses that neglect capillarity can also be expected to overestimateK10(in the absence of overriding factors, such as smearing of the well wall). The GP-G calculation of&phis;m, which neglects field-saturated flow, overestimates the corresponding GP-R estimate, which takes it into account. This also agrees with theoretical prediction.The meanSestimates are plausible for the soil type and condition, though the mean α values are high relative to some published values. It is speculated that the α values may, in fact, be appropriate considering that they apply to transient, 3-D infiltration into a structured soil.The 0.03-m-radius wells, which were dug using a “Riverside” bucket auger, tended to produce higherK10and&phis;mvalues than the 0.02-m-radius wells dug with a screw-type auger. The difference, however, is attributed to heterogeneity and the macroporous structure of the soil, rather than to auger type.TheK10and&phis;mestimates from the GP-R analysis are considered valid and accurate if they are both positive and both lower than their corresponding GP-L and GP-G estimates.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID