ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

This paper describes soils developed on calcareous bedrock with up to 60 cm of humus-rich A horizons from the Ogilvie Mountains in the Yukon Territory. These soils are of interest because they do not fit well into soil classification schemes and results from conventional analytical techniques are unreliable. Some of the unusual characteristics of these soils are: well-developed Ah horizons with high organic carbon contents, and high Ch/Cf ratios, on well-drained sites in a dry permafrost environment. We postulate that these soils are of polygenetic origin. They have developed under conditions where humic acid accumulation is greater than decomposition as a result of the limestone-rich environment, and where a portion of the organic component might be derived from residues of bedrock weathering.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

Having observed freezing fronts and liquid inclusions in liquid-saturated glass beads, I describe a simple technique for making these direct observations. The ice-water interface at the freezing front was concave when viewed from the ice side, because the glass beads were preferentially wetted by the liquid. The size and number of liquid inclusions decreased with distance behind the freezing front. More liquid is trapped by smaller glass beads. The liquid inclusions are probably enriched in soluble impurities. No tendency for pressure buildup or ice lense formation was observed, perhaps because large particles were used. It is very important to extend these observations to other conditions, especially to smaller particle sizes.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

Tidal marsh soils of New Jersey are divided into two varieties, protected coastal and estuarine. The soils have an average of 14% organic matter, indicating that they are not organic in a strict sense. Particle-size distribution indicates that the estuarine marsh types have formed under much higher energy conditions than protected coastal types; also, the latter are more saline than the former. Humification in tidal marsh soils increases with depth. Sand grain morphology indicates that surfaces of the grains from the saline tidal marshes are more spherical and chemically weathered than nearby terrestric counterparts. Tidal marshes in New Jersey are estimated to be about 3000 years old and, due to coastal subsidence, are currently migrating landward. Carbon/nitrogen ratios in the tidal marshes range from about 14 to 21. Estuarine sites have greater percentages of expanding clay minerals than the protected coastal marshes. Various plant species in the tidal marshes are associated with different levels of salinity.Phragmites australisandPanicum virgatumare associated with low levels,Spartina alternifloraandSpartina patenswith high and moderate levels, andSalicornia europaeawith high levels of salinity.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

Managing the water status of soil for crop production and waste disposal requires knowledge of the oxygen avilability in the profile. In this study a Captina silt loam (Typic Fragiudult) was nearly saturated and allowed to dry by drainage and evaporation. We measured oxygen flux and soil water tension simultaneously on two bare plots during three drying cycles. At the end of the study, we took undisturbed cores at three depth intervals in two plots and determined aeration porosity characteristics. The functional relationships between oxygen flux and aeration porosity determined from tensiometer data in the field and between tension and aeration porosity determined from the undisturbed cores were used to derive the mathematical relation between oxygen flux and soil water tension for the Captina profile.For the Captina soil, aeration porosity increased linearly with the natural logarithm of soil water tension. Similarly, the natural logarithm of oxygen flux was linearly related to aeration porosity. The combined equation describing oxygen flux as a function of soil water tension in the Captina soil constituted a power function. The description of the field data by the derived equations was excellent at all depths, and we found close agreement between the derived and the regression parameters of the power function relating oxygen flux and soil water tension.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

This study was part of a larger effort to identify and test field and laboratory analyses useful in evaluating soil chronose-quences. We extracted five phosphorus fractions from six soil profiles formed on mixed alluvium of a chronosequence that ranges in age from 300 to 250 000 years. When expressed as a percentage of total phosphorus (PT), the content of occluded phosphorus (Poc) generally increased, and the content of nonoccluded phosphorus (Pnoc) generally decreased in B horizons. The content of calcium-bound phosphorus or apatite (PCB) tended to decrease over time in A horizons, but to change little in B horizons. The content of organically bound phosphorus (Po) did not change systematically with time.Horizon ratios of the various fractions were the most useful weathering indicators. Ratios of Pnocfor the A/B and B/C horizons had highly significant correlations with deposit age. Comparisons between horizon-ratio P percentages (PTbasis) of various fractions indicated (1) that transformations from Pcato Poor Pnocwere similar in A and B horizons and (2) that rates of transformation to Pocwere more rapid in B than in A horizons.The results of P fractionation for these soils formed on transported, previously weathered parent material were less clearly useful as wethering indexes than they were shown to be on soils formed by in situ weathering.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

We conducted a pot experiment to study the utilization of three phosphatic fertilizers (monocalcium phosphate, diammonium phosphate, nitrophosphate) at three levels of sodicity (0.2, 29.3, 50.2 ESP) by wheat (Triticum aestivumL.). Diammonium phosphate and monocalcium phosphate were on a par in alkaline nonsodic soil. At 29.3 ESP, diammonium phosphate was a better source of P than monocalcium phosphate, but at 50.2 ESP monocalcium phosphate outyielded diammonium phosphate. Nitrophosphate having 57.5% water-soluble phosphate was only 51.5% efficient, compared with diammonium phosphate. The utilization of P decreased with increasing level of P. At higher levels of P, wheat plants exhibited copper deficiency, and the concentration of P and Cu followed a log-log linear relationship.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

We studied the magnitude and rates of dissolution of Ca and Mg from alkaline earth carbonates and of desorption of Ca and Mg from the cation exchange complex of Mancos shale. Samples of surficial, partially weathered Mancos shale were selectively preconditioned prior to leaching. Selective preconditioning treatments included removal of readily soluble ions, removal of calcite, and exchange saturation with Na, Ca, and Mg, respectively. Preconditioned samples were leached by a continuous, constant-rate, flow-through system, and Ca and Mg were measured in incremental leachates.The rates of release of Ca and Mg indicate that both emanate from more than one source. Selective removal of calcite resulted in an increase in Mg release to a rate approximately 2.7 times higher than when calcite was present.The rate of release of Ca from Ca-saturated shale was remarkably constant over the 8-h leaching period. Only a slight deviation from linearity was observed for release of Mg from Mg-saturated shale. Rates of release of Mg from Ca-saturated shale and of Ca from Mg-saturated shale both increased perceptibly with leaching duration. These data demonstrate a significant influence on ion release rates by the cation exchange complex and interactive relationships between the exchange complex and alkaline earth carbonates in the system.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

Plinthite is a subsurface soil feature that perches water during periods of excess soil moisture. Water movement in a plinthic soil in the Southern Coastal Plain was monitored over an 8-week period using a bromide tracer. Field investigations conducted on a Tifton loamy sand (Plinthic Paleudult) with a 4% slope indicate that much subsurface flow under saturated conditions occurs above and within plinthite. Results also indicate that movement through the plinthic horizons is slow and occurs primarily in low-chroma bodies associated with plinthite that are interconnected in dendritic patterns. Water does not readily penetrate the dense plinthic bodies.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID

摘要:

The objective of this study was to determine the influence of crop rotation and tillage methods on the level and distribution of extractable boron in northern Idaho soils.Plots were established north of Moscow, Idaho, in 1974 using no-till, minimum tillage, and conventional tillage treatments with three crop rotations. Rotations included: (1) a 2-year winter wheat (Triticum aestivumL. cv. Nugaines)-spring pea (Pisum sativumcv. Alaska) rotation (1:1 cereal/legume ratio), (2) a 3-year winter wheat-spring wheat (Triticum aestivumL. cv. Fieldwin)-spring pea rotation (2:1 cereal/legume ratio), and (3) a 3-year winter wheat-alfalfa (Medicago sativaL. cv. Ladak), red clover (Trifolium pratensecv. Kenland), pea-alfalfa, red clover rotation (1:2 cereal/legume ratio). Soil samples were collected by depth in all plots, and boron was determined by hot water extraction.Tillage × depth and rotation × depth interactions characterized extractable boron distribution in the northern Idaho soil studied. When parameters were considered individually, extractable boron levels in the sampled soils decreased with increasing depth. Extractable boron in the surface 30 cm of the soil profile was greater in conventional than in minimum and no-till treatments. Lower extractable boron levels found in soils with no-till and minimum tillage treatments may be attributed to greater B leaching potential, or greater B tie-up by organic matter, or both.The crop rotation with the greatest cereal/legume ratio (2:1) had highest levels of extractable soil B. It is probable that the greater demand of B by legumes, more specifically alfalfa, peas, and red clover in this study, resulted in lower extractable soil B levels in rotations with smaller cereal/legume ratios.

ISSN:0038-075X    

出版商:OVID    

年代:1985

数据来源: OVID