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doi: N/Apmid: N/A
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 (Kmand Vmax), 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.
MCDOWELL, WILLIAM H.; WOOD, TIMOTHY
doi: N/Apmid: N/A
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.
doi: N/Apmid: N/A
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.
doi: N/Apmid: N/A
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.
SCHRAMM, LAURIER L.; KWAK, JAN C. T.
doi: N/Apmid: N/A
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.
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