摘要:

We discuss the hydrolysis in pure water of montmoriilonite in various homoionic forms. During normal preparation procedures nominally homoionic alkali metal and alkaline earth metal montmorillonite hydrolyzes to an extent governed by the nature of the counterions. The hydrolysis during preparation may remove as much as 16 percent of the initial counterions. The remaining capacity is taken up by exchangeable magnesium and aluminum. Long-term water leaching experiments indicate that eventually not only hydrolysis but also decomposition reactions take place, with the result that the ion exchange capacity becomes reduced.

ISSN:0038-075X    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

Phosphatases catalyze reactions important in P cycling in soils and for plant nutrition. We carried out this study to compare the type, pH optima, kinetic parameters (KmandVmax), and activation energies (Ea) of phosphatases in soils and organic waste materials. Results showed that plant materials (oat, alfalfa, corn, and soybean leaves) and sewage sludges do not contain alkaline phosphatase and phosphodiesterase, respectively, and evidently they are not sources of these enzymes in soils. The optimum pH value of acid and alkaline phosphatases in soils was 1.5 units higher than those of these enzymes in the organic waste materials. The optimum pH value of phosphodies; terase in soils and animal manures was at pH = 8, but that of the same enzyme in plant materials was at pH = 5.5. The optimum pH of pyrophosphatase was 2.5 units higher than that of the activity of this enzyme in animal manures and plant materials.The averageKmvalues of acid and alkaline phosphatases in soils and in plant materials, animal manures, and sewage sludges were similar. The averageKmvalue of pyrophosphatase in soils (37.8 mM), however, was much higher than theKmvalues of this enzyme in plant materials (10.1 mM) and in animal manures (6.3 mM). Comparison of the relative concentration of the phosphatases in soils and various organic waste materials showed that, expressed on 1 g of oven-dried materials, the averageVmaxvalues of the various phosphatases were much greater in plant materials than those in soils, animal manures, and sewage sludges. TheVmaxvalues, however, varied considerably among the materials studied, indicating the degree of enrichment of the various materials with the phosphatases studied.Expressed in kilojoules/mole, the averageEaof acid phosphatase in four soils (42.3) was higher than those of alkaline phosphatase (32.3), phosphodiesterase (37.0), and pyrophosphatase (37.6). In general, theEavalues of phosphatases in soils were in the same order of magnitude as those of phosphatases in the waste materials studied.

ISSN:0038-075X    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

Through field experiments conducted at three locations over several years I sought to determine the effect of B and lime on crop yields and tissue B concentrations in alfalfa (Medicago sativaL.), red clover (Trifolium pratenseL.), and timothy (Phleum pratenseL.). Boron applications increased alfalfa yields by 8 to 32% in half of the cuts and red clover yield by 15% in one cut at one location only. Liming proved to be most important for increasing yields of alfalfa, red clover, and timothy in that order. Tissue B concentrations of less than 30 ppm in alfalfa and of less than 20 ppm in red clover were related to B deficiency symptoms (yellowing of young leaves and tops in alfalfa and reddish coloration of young leaves in red clover). I found timothy to be insensitive to B deficiency; tissue B concentrations as low as 4 ppm were not related to any B deficiency symptoms on the foliage. Tissue B concentrations of 108,92, and 95 ppm in alfalfa, red clover, and timothy, respectively, were related to B toxicity symptoms on the foliage in the form of burning of older leaf edges, but were not related to any appreciable yield decreases. Large decreases in B concentrations occurred between the first and second samplings in B-treated samples. Liming decreased the plant tissue B, most decreases occurring in the earlier samplings. The results indicate that applying 2 kg B/ha should maintain sufficient B for alfalfa and red clover for 2 years.

ISSN:0038-075X    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

We measured dissolved organic carbon (DOC) in soil solutions collected from the A and B horizons of a Spodosol in central New Hampshire. DOC averaged 33 mg/L in the A2 horizon and declined to 2 to 3 mg/L, similar to stream water concentrations, in the B horizon. DOC concentrations in A2 horizon lysimeters were inversely related to the volume of water collected per day; we observed maximum concentrations (approximately 55 mg/L) during September. In the B horizon lysimeters, DOC levels were relatively constant, as were levels in stream water. In laboratory experiments, DOC in A2 horizon soil solution was rapidly absorbed by B horizon soils. The equilibrium DOC concentrations predicted by adsorption isotherms agreed to within 1 to 2 mg/L with lysimeter results. Our results suggest that coprecipitation of iron and organic matter in the upper B horizon, a process central to podzolization, largely controls the concentration of dissolved organic carbon in stream water at Hubbard Brook.

ISSN:0038-075X    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

Using the Ottawa Texture Measuring System, equipment developed by Agriculture Canada, we propose to call the moisture content at which remolded soils compact to their maximumcritical mositure content, instead of the termoptimum moisture contentused by various other agricultural scientists.Our data indicate that for a certain soil the resultant bulk density is a function of the soil's moisture content and the compactive force used. This relationship of bulk density with mositure content and compactive force can be expressed in a third-order polynomial equation. At a given compactive force, the critical moisture could be calculated from the first derivative of the equation.Soehne's (1958) approach is used to define and calculate compactibility indexes of some New Brunswick soils. We also project future practical use of the work presented.

ISSN:0038-075X    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

We determined the physical, chemical, and mineralogical properties of six clay to heavy clay soils developed from lacustrine material in Abitibi, Quebec. Maximum clay content occurred in the B horizons, which generally also had the highest dry bulk density. Quartz, feldspar, and hornblende were present in the clay fraction of all samples in association with illite, chlorite, and vermiculite, which were the dominant clay minerals. Cation exchange capacity values ranged from 16 to 46 meq/100 g of soil and were significantly related to the clay content. The effect of organic matter on CEC was also evident in some Ap horizons.

ISSN:0038-075X    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

Between 1970 and 1982, soil temperature data were collected on the Bridger-Teton, Caribou, Payette, and Salmon National Forests of the Intermountain Region, U.S. Forest Service. I grouped the data into northern and southern slope aspect classes for analysis and performed linear regression of elevation with soil temperature to determine elevational ranges of the cryic, frigid, and mesic soil temperature regimes for the study area. The coefficients of determination for the regressions ranged from 0.49 to 0.68. Cryic soils were dominant, occurring at elevations greater than 1950 m on southern aspect slopes and at greater than 1080 m on northern aspects. Frigid soil temperature regimes were not extensive, assuming a 15°C mean summer soil temperature limit for cryic regimes at all sites. Sampling duration requirements for soil temperature regime determinations are 5 years for obtaining ± 10 percent precision at the 95 percent confidence level.

ISSN:0038-075X    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

Soils in northern Idaho are exhibiting a rapid decline in pH. In undertaking this study, we sought to determine the relative effects of common northern Idaho cultural practices—tillage methods, crop rotations, and N fertilizer rates—on the acidification of a northern Idaho soil. The plots were established north of Moscow, Idaho, in 1974 and evaluated no-till, minimum tillage, and conventional tillage treatments and three-crop rotation systems: (1) a 2-year winter wheat (Triticum aestivumL. cv. Nugaines)-spring pea (Pisum sativumcv. Alaska) rotation; (2) a 3-year winter wheat-spring wheat (Triticum aestivumL. cv. Fieldwin)-spring pea rotation; and (3) a 3-year winter wheat-alfalfa (Medicago sativaL. cv. Ladak) red clover (Trifolium pratensecv. Kenland) peaalfalfa red clover rotation. The plots were split by N application rates and sampled by depth.When sampled by 300-mm increments, depth was the only factor that affected soil pH. Soil pH increased with increasing depth. There was a statistically unique calcium chloride pH at each sampling depth down to 1500 mm.When the surface 300 mm was sampled by 75-mm increments, the interaction of crop rotation x tillage x N rate x depth was significant. It was apparent that N rates were the major influence on pH differences. Crop rotations influenced the amount of N fertilizer required for crop production and consequently affected the magnitude of the pH decline. Tillage influenced the placement of N fertilizer and consequently the location and depth of acidification in the soil profile. The greatest acidification under no-till management occurred in the surface 75 mm, under minimum tillage at the 75-to 150-mm depth, and under conventional tillage in the surface 250 mm. A significant decrease in pH was observed in all treatments over the 8-year period.

ISSN:0038-075X    

出版商:OVID    

年代:1984

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1984

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1984

数据来源: OVID