Prairie Soils Research Articles

REGRESSIVE PEDOGENESIS FOLLOWING A CENTURY OF DEFORESTATION: EVIDENCE FOR DEPODZOLIZATION

After the logging and fires of the late nineteenth century, the upland stump prairies of Michigan's Upper Peninsula, which had previously supported dense forest, have remained deforested. Surrounding areas in similar geomorphologic settings have returned to forest. We investigated whether soil B horizon properties have degraded in response to the removal of podzolization-promoting vegetation by studying pedons under forest and stump prairie. Active soil processes were examined by analyzing ions sorbed on cation exchange resins and chelating resins that had been buried in the pedons, at three depths, for approximately 1 year. In both vegetation types, patterns of sorbed Fe and Al indicate that podzolization is on-going, with active translocation of sesquioxides into the B horizon. Larger absolute amounts of sesquioxides were sorbed on resins in forested pedons compared with stump prairie pedons, however, suggesting that podzolization processes are more active in forested than in stump prairie environments. The chemical and morphological properties of forested and stump prairie pedons were examined by analyzing the organic C and extractable Fe and Al content of horizon-based samples. Strength of podzol development was greater, in general, for forested than for stump prairie soils. The primary chemical difference between the two types was found in organic C content and in properties associated with organic C, including pyrophosphate-extractable Fe and Al. Differences between forested and stump prairie soils were much smaller for inorganic constituents. Depodzolization (the degradation of existing podzol features) in stump prairie B horizons is most evident in morphological properties associated with organic C, which are dependent on continued input of organometallic complexes. Depodzolization has occurred in the stump prairie soils because the balance between progressive development (podzolization) and regressive development (depodzolization) has been altered under stump prairie vegetation.

Air Pressure Fluctuations in a Prairie Soil

AbstractThe influence of air convection on soil aeration has not been investigated in great detail. A study was conducted to measure air pressure changes by depth in the first 2 m of a prairie soil that was known for its denitrification properties. An absolute air pressure probe was used to measure air pressure fluctuations at the soil surface and newly designed differential air pressure probes were placed at depths of 0.1, 0.2, 0.3, 0.4, 0.5, 0.75, 1, 1.5, and 2 m. A procedure of in situ recalibration was used every 6 or 7 wk for these probes. At the same depths, capacitive probes and thermocouples measured the volumetric water content and temperature, respectively. The bulk density profile, water table level, and rainfall amounts were recorded. The atmospheric pressure ranged between 97 000 and 101 000 Pa during the experiment. The signal drift of the air pressure probes was negligible for four of the probes and <50 Pa for the others. The accuracy of the measurements with signal drift compensation was superior to 10 Pa. Differences of air pressure between the soil at the surface and at depth may be >2000 Pa. These differences, which are not necessarily linked to the depth, are probably due to soil heterogeneities and generally to water infiltration. Air pressure seemed to level out quickly when the air‐filled pore space was continuous. This generally prevented “dephasing‐amortization” effects. When the air‐filled pore space was discontinuous, differential air pressures depended simultaneously on the atmospheric pressure and temperature fluctuations.

Nitrogen Cycling and Nitric Oxide Emissions in Oil-Impacted Prairie Soils

A remote site in the Tallgrass Prairie Preserve of Oklahoma (The Nature Conservancy) was contaminated with crude oil from a pipeline break and is being bioremediated using landfarming techniques. Landfarming is designed to stimulate microbial-based catabolism of petroleum through combined dilution/mixing and fertilization-based effects. To evaluate nitrogen-based effects during remediation, the site was sectioned and treated with urea, ammonium sulfate, or ammonium nitrate. Samples were obtained from prairie soil without chemical nitrogen addition and with or without hydrocarbon contamination. Nitrogen cycling dynamics were followed by measuring ammonium, nitrite, nitrate, and volatile nitric oxide (NOx) levels. Nitrifying and denitrifying bacterial numbers were estimated and compared to soil oxygen, carbon dioxide, and methane levels as well as to overall total petroleum hydrocarbon (TPH) reduction. For a prairie ecosystem of this type, a high level of fertilization, particularly with nitrogen, can have ecological effects almost as profound as the petroleum contamination itself. Fertilization of the oil-contaminated soil with the reduced and/or oxidized forms of nitrogen quickly resulted in elevated steady-state levels of both ammonium and nitrate, and exceptionally high levels of NOx released from soil. Although nitrogen fertilization increased microbial nitrogen metabolism and nitrogen cycling, it had minimal effects on the overall remediation efficiency.

Radiobrightness of prairie soil and grassland during dry‐down simulations

We present 60‐day summer dry‐down simulations for prairie grassland based upon a one‐dimensional hydrology and radiobrightness models for northern prairie. Our objective is to examine the effect of scaling upon the interpretability of mixed pixel radiobrightnesses. Even for relatively homogeneous regions like North American prairie, there are significant variations in land cover within the relatively large footprints of satellite microwave radiometers. In this paper we specifically address 1.4‐ and 19‐GHz brightness in the presence of subpixel variability in canopy density. Bare soil and a densecanopy grassland can be viewed as extreme examples of prairie land cover. If land cover within any pixel is viewed as a mixture of these two extremes, then the terrain within that pixel can be modeled as some combination of the hydrology and radiobrightness models for bare soil and dense‐canopy grassland. We examined two combination schemes: (1) a homogeneous combination where the dense‐canopy grasses are simply spread uniformly over the pixel to achieve a desired vegetation column density between that of bare soil and dense‐canopy grass, and (2) a tiled combination where the pixel is divided into a region of bare soil and a region of dense‐canopy grassland. We examined H‐polarized, 53° incidence angle, 19.35‐ and 1.4‐GHz pixel brightnesses and found the 19‐GHz brightness to be significantly greater for homogeneous pixels than for tiled pixels throughout the dry‐down period. For example, a 19‐GHz, 50% homogeneous pixel is 50 K brighter than a 50% tiled pixel at the beginning of the dry‐down and 40 K brighter at 60 days. In contrast, the 1.4‐GHz brightnesses are essentially identical for homogeneous and tiled pixels. Within the constraints of our simulation, subpixel variation in canopy density is a significant factor in the quantitative interpretation of the 19‐GHz brightness of prairie grassland but is not a factor in the interpretation of the 1.4‐GHz brightness.

Transport of Mercury in Three Contrasting River Basins

Total mercury (THg) concentrations and loadings in the Minnesota, Mississippi, and St. Croix Rivers were determined over a 2-year period. These rivers drain watersheds with greatly contrasting land use, soil, and hydrological characteristics. The Minnesota River basin is characterized by a vast artificial drainage network and fertile prairie soils that support the intensive cultivation of row crops. Mercury levels in this river are strongly correlated with total suspended solids concentrations, varying widely in response to precipitation and snowmelt runoff events. The St. Croix River and the headwater Mississippi River (above its confluence with the Minnesota River) drain watersheds characterized by more acidic and sandy soils, more forest and wetland areas, less artificial drainage, and less cultivation as compared to the Minnesota River watershed. Mercury concentrations and loadings in these rivers are much lower than those observed in the Minnesota River, vary over a much narrower range, and reflect a...

Environmental and social influences on calling effort in the prairie mole cricket (Gryllotalpa major)

Sexual advertisement in the form of acoustic display is energetically expensive. Calling effort, or metabolic energy expended specifically for advertisement, is adjusted in some species in response to competition from other males or to changes in climatic conditions. The prairie mole cricket (GrjUotatpa -major) is a rare insect of die south-central United States that produces its calling song, or advertisement rail, from a specially constructed burrow in taDgrass prairie soiL I found that prairie mole cricket males do not adjust their call amplitude with competition or female availability, nor do they vary amplitude with soil temperature or moisture within their established range of calling conditions. Chirp rate adjustments were made with social interactions and changes in soil temperature, but group size did not influence calling effort Males produced more complex calls in response to closer calling neighbors, but prairie mole cricket males may selectively respond to only the nearest one to two neighbors. Kty words: acoustic signaling, calling effort, Gryllotalpa major, prairie mole cricket, sexual advertisement. {Bthav Ecol 9:101108 (1998)]

CAMBIOS FLORISTICOS, FITOSOCIOLOGICOS Y EDAFICOS PROVOCADOS POR EXCLUSION DE PASTOREO EN UNA PRADERA VALDIVIANA, CHILE

In a farm prairie located 12 km west from San Jose de la Mariquina village, province of Valdivia (Chile) floristic, phytosociological and edaphic changes produced by grazing exclusion under a 10 years old electric fence are studied. The floristic analysis was made comparing plants lists obtained from partially tables made up by 7 and 11 vegetation samples taken with the phytosociological methods in the prairie and in the exclusion zone, respectively. Plant associations were determined with differential species. The soils comparison was made with physical and chemical analysis and using ecological indicators values. The resulte were analized with statistical multivariate methods of ordination and classification. The exclusion produced an impoverishment of the prairie flora and significative changes in frequency and cover of the species belonging to both conditions: in the grazing prairie dominated Dactylis glomerata, Lolium perenne, Bromus catharticus and Trifolium repens, in the exclusion zone on the other hand, dominated only Agrostis capillaris which is inhibited by grazing. The biological spectra are similar and only the annuals weeds are more abundant in the grazing prairie. Floristic changes in the exclusion zone are so extremely that a different plant association was formed, namely Hyperico-Agrostidetum capillariaeinst ead Bromo-Lolietumperennis of the grazing prairie. The prairie soil was more compactnees and the pH and mineral nutrients are highest. Ecological indicator values differentiated both conditions and characterized the prairie soil as eutrophic and the exclusion zone soil as oligotrophic.

Cation exchange and buffer potential of Saskatchewan soils estimated from texture, organic matter and pH

Cation exchange capacity (CEC) data provide information on important chemical attributes of soil (e.g., ability of soil to retain cations against leaching and to buffer pH). Measurements of CEC are expensive to perform. Further, since CEC is dependent on measurement pH, CEC data are difficult to interpret, especially in the case of soils whose field pH is far removed from measurement pH. We analyzed a large data set (n = 1622), collected in support of soil survey activities in Saskatchewan, to develop a method of estimating CEC as a function of pH and to establish relationships between soil buffer capacity and properties such as texture and organic matter content. A regression equation with organic C and clay as independent variables explained 86% of the variability in CEC measured using BaCl2 buffered at pH 8.2. The CECs (at pH 8.2) of organic matter and clay were estimated at 2130 and 510 mmol (+) kg−1, respectively. About 15% of exchange sites were not accounted for by organic matter and clay and were assumed to reside in the fine silt fraction. The CEC at field pH, i.e., effective CEC (ECEC), was described (R2 = 0.86***) by a function based on the assumption that the ECECs of organic matter and clay increase linearly as pH increases to 8.2, where their values are 2130 and 510 mmol (+) kg−1, respectively. This relationship is especially useful because it enables soil CEC to be estimated at any pH based solely on organic matter and texture. Soil buffer capacity values were obtained by estimating the change in soil ECEC (or titratable acidity) needed to produce a unit change in pH. Buffer strength of clay was low [∼30–50 mmol (±) kg−1 (pH unit)−1]. Our estimates of organic matter buffer capacity [∼400 mmol (±) kg−1 (pH unit)−1] were consistent with published values. The results suggest that prairie soils that are low in organic matter may be susceptible to acidification even if clay content is relatively high. Key words: Buffered CEC, effective CEC, pH dependence of CEC, buffer capacity, titratable acidity

Impacts of Rotational Grazing on Mixed Prairie Soils and Vegetation

In this study the impact of a rotation grazing system on the soil and vegetation of a Stipa-Bouteloua-Agropyron community in the mixed prairie ecoregion was compared with the ungrazed treatment in exclosures. At a low stocking rate, grazing had no effect on the vegetation but did alter soil quality. Grazing pressure was so light in the rotational grazing treatment that recovery of productivity, as measured by standing crop and litter, was not significantly different from the ungrazed treatment. Conversely, the species distribution was unchanged but was indicative of a lower seral state for this mixed prairie. The effect of grazing on this community was indirect, possibly by altering the microenvironment. The relationships observed among forage production, soil chemistry, and species composition raise questions on the importance of any one variable expressing range condition on the mixed prairie.

Vegetation Effects on Soil Resource Heterogeneity in Prairie And Forest

A current, widespread example of vegetation change is the invasion of grassland by woody plants. This is associated with an increase in soil heterogeneity, and it has been argued that woody plants both cause and benefit from high heterogeneity. We know of no experimental demonstrations of differences between grasses and woody plants in their effects on heterogeneity. Here we compare heterogeneity between mixed-grass prairie and aspen forest, and we report the results of a soil transplant experiment that tested for differences between these vegetation types in their effects on soil resource heterogeneity. We measured the heterogeneity of resources and plant mass along 10 transects in both prairie and aspen forest in spring and summer. Light and available nitrogen (N; sum of ammonium and nitrate) were significantly more variable in forest than prairie, as were root and understory shoot mass. The variability of soil moisture and topography did not differ between prairie and forest. In our experiment, N and water in cores of prairie soil moved to forest attained the relatively high variability of forest soils. Further, forest soils moved to prairie attained the relatively low variability of prairie soils. In summary, both the biomass heterogeneity measurements and the soil transplant experiment suggested that plant uptake contributed to greater heterogeneity in forests.

Biogeochemical Cycling following Planting to Red Pine on a Sandy Prairie Soil

Native prairies in the Lower Wisconsin River Valley provide a means of comparing nutrient cycling patterns across undisturbed and managed ecosystems. Bulk precipitation, throughfall, and soil solutions at three depths were collected from August 1991 to December 1993 at three study sites (native prairie and native prairie planted to 30 and 40-year-old red pine, Pinus resinosa Ait.). Elemental input-output balances were calculated from water chemistry data and from water balances using chloride as a tracer. Concentrations of cations and dissolved organic carbon (DOC) in soil solution were greater in the conifer plantations than in the prairie ecosystem. Inorganic acid concentrations were only slightly higher under pine than under prairie, suggesting that the greater cation leaching under pine vegetation was dependent on DOC contributed by throughfall and leaching from the forest floor. There was a small net gain in Mg and losses in Ca, K, and S in the prairie ecosystem. There was a net loss in all elements from the pine ecosystem, and losses were greater than from the prairie. The greater losses in Mg, K, and S from the pine ecosystem are attributed to interception of dry deposition by the tree canopy. Sulfur contributed by dry deposition to the pine ecosystem was mainly returned to the forest floor as organic S and oxidized to SO2−4 as solutions passed through the soil profile. In contrast, greater Ca losses under pine than under prairie are attributed to increased weathering due to afforestation.

Use of hot KCl-NH4-N to estimate fertilizer N requirements

We need an easy-to-use chemical index for estimating the amount of N that becomes available during the growing season, to improve N use efficiency. This paper discusses how producers may, in future, use crop growth models that incorporate indices of soil N availability, to make more accurate, risk-sensitive estimates of fertilizer N requirements. In a previous study, we developed an equation, using 42 diverse Saskatchewan soils, that related potentially mineralizable N (N0) to NH4N extracted with hot 2 M KCl (X), (i.e., N0 = 37.7 + 7.7X, r2 = 0.78). We also established that the first order rate constant (k) for N mineralization at 35°C is indeed a constant for arable prairie soils (k = 0.067 wk−1). We modified the N submodel of CERES-wheat to include k and N0 (values of N0 were derived from the hot KCl test). With long-term weather data (precipitation and temperature) as input, this model was used to estimate probable N mineralization during a growing season and yield of wheat (grown on fallow or stubble), in response to fertilizer N rates at Swift Current. The model output indicated that the amount of N mineralized in a growing season for wheat on fallow was similar to that for wheat on stubble, as we hypothesized. Further the model indicated that rate of fertilizer N had only minimal effect on N mineralized. We concluded that, despite the importance of knowing the Nmin capability of a soil, it is available water, initial levels of available N and rate of fertilizer N that are the main determinants of yield in this semiarid environment. The theoretical approach we have proposed must be validated under field conditions before it can be adopted for use. Key words: N mineralization, Hot KCl-NH4-N, potentially mineralizable N, CERES-wheat model

Effects of mycorrhizae on plant growth and Dynamics in Experimental Tallgrass Prairie Microcosms

Experimental microcosms (40 X 52 X 32 cm) containing an assemblage of eight tallgrass prairie grass and forb species in native prairie soil were maintained under mycorrhizal (untreated control) or mycorrhizal-suppressed (fungicide-treated) conditions to examine plant growth, demographic, and community responses to mycorrhizal symbiosis. The fungicide benomyl successfully reduced mycorrhizal root colonization in the fungicide-treated microcosms to only 6.4% (an 83% reduction relative to mycorrhizal controls). Suppression of mycorrhizas resulted in a 31% reduction in total net aboveground plant production and changes in the relative production of C4 and C3 plants. The C4 tallgrasses Andropogon gerardi and Sorghastrum nutans produced less plant biomass in the fungicide-treated microcosms, and had a greater ratio of reproductive to vegetative biomass. Cool-season C3 grasses, Koeleria pyramidata and Poa pratensis accumulated more biomass and were a significantly greater proportion of total community biomass in mycorrhizal-suppressed microcosms. Forbs showed variable responses to mycorrhizal suppression. The two legumes Amorpha canescens and Dalea purpurea had significantly lower survivorship in the fungicide-treated microcosms, relative to the controls. The results confirm the high mycorrhizal dependency and growth responsiveness of dominant prairie grasses, and indicate that differential growth and demographic responses to mycorrhizal colonization among species may significantly affect plant productivity and species relative abundances in tallgrass prairie.

Methane emission from Canadian prairie and forest soils under short term flooding conditions

Short term flooding of usually well-drained soils is a recurrent phenomenon in many regions of the world, particularly after snowmelt in the spring and after heavy and prolonged precipitation. Using incubation-leaching and static chamber techniques, we examined the impact of short term flooding on methane emission from Canadian prairie and forest soils. The laboratory study demonstrated that flooding caused significant methane evolution from incubated soils (13 to 184 mg kg-1 over 8 weeks). In contrast, 80–95% of the atmospheric methane in the incubation jar was absorbed by nonflooded soils in a week. The field data showed that after snowmelt in the spring, the methane emission rate was highest in soils and ranged from 7.8 (cultivated) to 10.5 mg m-2 d-1 (grassland). Methane emission was also observed from low slope positions after rainfall in the summer. Three days after 23 mm of precipitation, the rate of methane evolution was 0.03 (cultivated) and 0.02 mg m-2 d-1 (grassland) whereas it was 0.11 (cultivated) and 0.07 mg m-2 d-1 (grassland) one day after 48 mm of precipitation.

The Influence of Prairie and Forest Vegetation on Soil Moisture and Available Nitrogen

-Aspen clones have expanded into prairie during the last century at the northern edge of the Great Plains. Soil under aspen has more water and available N than that under adjacent prairie. We used a field experiment to test whether high resource availability in forest soil was attributable to the environment associated with forest vegetation. We collected 80 soil cores from prairie and forest and moved them to either prairie or forest. Neighboring roots were excluded from half the cores. Cores were moved in April and 10 samples were taken from each core in September. Cores from forest had significantly higher moisture and available N than those from prairie. Cores moved from forest to prairie had significantly less moisture than those moved from forest to forest, suggesting that the lower moisture in prairie soils depended partly on the environment associated with prairie vegetation. Available N did not differ between cores moved to prairie and forest. Both water and N were higher in cores with roots excluded, but the magnitude of this difference did not differ between prairie and forest, suggesting that there were no differences between prairie and forest in their abilities to take up these resources. The spatial variability of soil moisture was significantly higher in cores from forest than in those from prairie and tended to be highest in cores with roots present, which was consistent with the idea that uptake enhances resource heterogeneity.

Effect of Tillage and Rotation on Agronomic Performance of Corn and Soybean: Twenty-Year Study on Dark Silty Clay Loam Soil

In the U.S. Corn Belt, tillage without plowing was used on more than 50% of corn (Zea mays L.) and soybean (Glycine max (L.) Merr.] acreage in 1994, while no-till planting was used on about 30% of the acreage. Few research studies have evaluated these reduced tillage systems for 20 yr or more. This study includes plow, chisel, ridge, and no-till systems in continuous corn, corn after soybean, soybean after corn, and continuous soybean rotations. The experiment was conducted on Chalmers (fine-silty, mixed, mesic Typic Haplaquolls) silty clay loam soil in north-central Indiana for 20 yr. Objectives were to determine the effect of tillage and rotation on stands, growth, maturity, and yield of corn and soybean and to determine trends that develop with time for these variables. Major stand reductions occurred only in no-till continuous corn, 8% less than plowing. Compared with plowing, chisel and ridge tillage systems reduced growth and yield and increased harvest moisture by less than 3% in continuous corn. No-till reduced 4-wk height of continuous corn by 17%, yield by 14%, and increased harvest moisture by 2.1 percentage points compared with plowing. For corn following soybean, only no-till corn showed a yield reduction, 2.8%, compared with plowing. Twenty-year mean soybean yield reductions averaged 4 to 7% in both rotation and monoculture for chisel, ridge, and no-till systems compared with plowing. Relative yields for no-till continuous corn tended to be less than other tillage-rotation systems over time, while no-till soybean yields tended to improve with time, especially during the last 5 yr of the study. Both corn and soybean yields were better in rotation than in continuous cropping for all tillage systems. Of the tillage systems-rotation combinations in this study, only no-till continuous corn is likely to suffer major yield loss on a long-term basis on dark prairie soils of the Central and Northern Corn Belt.

Vegetation and Cropping Effects on Pedogenic Processes in a Sandy Prairie Soil

The presence of native prairies in the Lower Wisconsin River valley that have not been cropped affords a mean of comparison across undisturbed and managed ecosystems. A native prairie soil and a prairie converted to corn (Zea mays L.) and red pine (Pinus resinosa Aiton) plantations were studied to determine the influence of vegetation on soil-forming processes in the sandy landscape of the Lower Wisconsin River valley. Effects of afforestation and cultivation were determined by separating organic matter among particle-size and chemical fractions, differentiating among forms of extractable Fe and Al, and measuring dissolved organic carbon (DOC), Fe and Al in bulk precipitation, throughfall, and soil solutions at three depths. The soil under native prairie vegetation showed distinctive horizonation, including an umbric epipedon formed by melanization. Thickness of the A horizon was significantly less in the forested and cultivated soils than in the prairie soil. Greater amounts of the floatable fraction of organic C, fulvic acids, and Fe-organic complexes were present in the forested soils than in the prairie soil. Carbon concentration in the A horizon of the cultivated soil was significantly lower than in the prairie and forested soils, due to losses by erosion, decomposition, and DOC leaching. In the cultivated soil, the floatable and humin fractions showed the greatest decrease in C concentration compared with the prairie soil. Analysis of the solution data indicated leaching of soluble Fe-organic complexes under coniferous and corn vegetation, suggesting that afforestation and cultivation initiated incipient podzolization.

Acetogenic capacities and the anaerobic turnover of carbon in a kansas prairie soil

To assess the anaerobic capacities of a temperate grassland soil, a Kansas prairie soil was incubated anaerobically as either soil-water (1:2) suspensions or as soil microcosms at 78% soil water-holding capacity. Prairie soil formed acetate and CO(inf2) as the two main initial carbonaceous products from the anaerobic turnover of endogenous organic matter. Metabolic capacities of soil suspensions and microcosms were similar. Rates of acetate formation from endogenous organic matter in soil-water suspensions incubated at 40, 30, and 15(deg)C approximated 3.3, 2.4, and 1.1 (mu)g of acetate per g (dry weight) of soil per h, respectively. Supplemental H(inf2) and CO(inf2) were subject to consumption with the apparent concomitant synthesis of acetate in both soil suspensions and soil microcosms. In soil microcosms, rates of H(inf2)-dependent acetogenesis at 30 and 55(deg)C were nearly equivalent. The uptake of supplemental H(inf2) was not coupled to methanogenesis under any condition examined. These anaerobic activities were relatively stable when soils were subjected to either aerobic drying or alternating periods of O(inf2) enrichment. On the basis of the formation of nitrogen (N(inf2)), denitrification was engaged during anaerobic incubation periods; nitrous oxide (N(inf2)O) was also formed under certain conditions. Although extended incubation of soil induced the delayed methanogenic turnover of acetate, acetate was subject to immediate turnover under either O(inf2)- or nitrate-enriched conditions. These studies support the following concepts: (i) obligately anaerobic bacteria such as acetogenic bacteria are stable to periods of aerobiosis and are active in the anaerobic microsites of oxic soils, and (ii) acetate synthesized in anaerobic microsites of oxic terrestrial soils constitutes a trophic link to both aerobic and anaerobic microbial communities.

Biological Condition of an Agricultural Soil Six Years after Conservation Reserve

Microbial properties of Kenoma silt loam soil in Coffey County, Kansas, were investigated for a native tallgrass prairie, a field currently under cultivation, and a previously cultivated field that was reseeded to native grasses in 1986 as part of the Conservation Reserve Program (CRP). Soil samples were taken from the surface 10 cm and analyzed for soil respiration, microbial biomass carbon (C) and nitrogen (N), N availability, and dehydrogenase activity. In comparison to soils in native prairie, measures of microbial quality in soils under cultivation decreased as follows: microbial biomass C and N by 67%, nitrogen availability by 37%, dehydrogenase activity by 68%, and respiratory rate by 69%. When CRP land was compared with soils in cultivation, no significant differences could be detected in terms of microbial biomass N, N availability, and dehydrogenase activity. The CRP land showed lower values of microbial biomass C, but a significantly higher respiratory rate. These results led to three important conclusions: First, the results strongly confirm that cultivation has a profound impact on native prairie soils. Second, the levels of soil microbial quality parameters in the reseeded prairie were not similar to those in the native prairie after a period of 6 years. Third, a higher respiratory rate in the reseeded prairie indicates a response of the soil microbial community to the reestablishment of permanent prairie vegetation. The latter point also was supported by a greater proportion of active pools of C and N in the reseeded prairie.

PRAIRIE SOIL DEVELOPMENT IN NORTHWESTERN PENNSYLVANIA

Prairies have been noted in several areas of Pennsylvania since the time of European settlement. Because very little is known about the soils of these areas, a prairie area in northwestern Pennsylvania was studied. The A horizon of the soils of this area is thick (mean of 55 cm), and many areas have colors dark enough to qualify as mollic or umbric epipedons. The organic matter content for the top meter of the soils was greater than reported for midwestern prairie soils of similar texture and drainage and probably reflects greater plant growth and/or a lower rate of decomposition as a result of cooler and more moist climatic conditions in northwestern Pennsylvania. The average opal phytolith content for the top 15 cm of the prairie soils was 21.1 Mg ha -1 . The age of these soils, estimated from phytolith accumulation, is 2000 to 6000 years. This would indicate that prairie occupation and soil formation started during the late Hypsithermal (3000 to 7000 years ago) interval. The characteristics of these soils indicate an apparent developmental continuum, extending from the midwest to Pennsylvania, of increasing organic matter accumulation and leaching under prairie vegetation. Although developed under prairie grass, these soils do not meet the base saturation classification requirements of Mollisols and would be classified as Inceptisols (Umbrepts).