Microbiological studies of some typical Iowa soil profiles

The determination of the numbers of bacteria, actinomycetes and molds in various horizons of typical profiles of some Iowa soils was made during two seasons and the results compared with careful descriptions of the soil profiles by horizons. The Carrington loam was sampled in typical profiles several times thru the season of 1926 in Buchanan County. The Lindley sandy loam was also sampled at different dates. In 1927 the Carrington loam, the Clyde silty clay loam and the Dickinson fine sandy loam were sampled in the same county at several dates during the early part of the season. In the same season the Marshall silt loam and the Knox silt loam were sampled at several different dates in typical profiles in Crawford county. It is apparent from the results as a whole that the content of microorganisms decreased from the surface to the lower horizons in typical soil profiles of the various soil types. The largest numbers of bacteria appeared in either the A1 or the A2 horizon, and the largest numbers of actinomycetes likewise appeared in one or the other of these horizons. In the case of the molds, the largest numbers sometimes occurred in the third surface horizon. In all the soils, however, the most striking decreases occurred from the A3 to the B horizon. Further decreases occurred from the B1 to the B2 horizon, from the B2 to the C1 horizon and from the C1 to the C2 horizon, but these decreases were relatively smaller. In the case of the molds the decreases in the lower soil horizons were usually relatively insignificant. The total decrease in numbers of molds from the surface soils to the lowest depths was relatively smaller than in the case of the bacteria and actinomycetes. In some instances the variations in numbers of microorganisms in the three surface, or A horizons, were relatively small. In other cases, considerable decreases occurred from the A1 to the A2 or from the A2 to the A3 horizon. The variations in the moisture content of the different soil layers in the samples studied seemed to have no definite relationship to the numbers of bacteria, actinomycetes or molds. In some cases, decreases in numbers of microorganisms occurred between layers in which the moisture content was very much the same. Increases in numbers of microorganisms frequently occurred along with decreases in moisture. Hence, while in a number of cases decreases in numbers corresponded with decreases in moisture, apparently the decreases were occasioned largely by other conditions in the soil. The variations in moisture content seemed to be of the least significance in the lower soil layers, the numbers decreasing without regard to the variations in moisture content. In the surface soils there was sometimes an indication of a relation between the moisture content and the numbers of bacteria and actinomycetes. With the higher moisture content there was sometimes a higher content of bacteria. This was not uniform, however, and the general conclusion must be drawn that the variations in numbers occur with little or no regard to slight variation in moisture conditions. It should be emphasized that the differences in moisture conditions in the various soils compared were not very large and probably other factors were of greater significance. With extremes of moisture, either a high content or a low content, the effect would undoubtedly have been more significant. There were some indications of seasonal effect upon the numbers of microorganisms in the different soils studied, especially in Series I. The largest numbers of microorganisms, in general, seemed to occur in the early spring samplings and again in the early fall samplings. Low counts ordinarily appeared in the samples late in the fall. Indications of similar seasonal effects were noted in the soils studied in Series II and Series III, altho the samplings in these two cases were not carried over the entire season. The results, in general, do seem to confirm previous observations which have indicated larger numbers of microorganisms in the June and September samplings than in the samplings taken during the summer. It should be noted further that variations in numbers of organisms, as affected by seasonal conditions, occurred only in the surface layers and were chiefly confined to the A1, A2 and A3 horizons. No definite effect could be noted in the B or C horizon from seasonal variations. The seasonal effect appeared to be similar on the bacteria and actinomycetes, but there was little influence upon the mold content. It is quite possible that more extreme seasonal conditions than those which prevailed while these experiments were under way would have had a much larger influence on the numbers of microorganisms. The soil type differences were reflected in some cases in the content of microorganisms in the various soil layers. Apparently the characteristic of the most significance was the content of organic matter or the color of the soil. Obviously, however, the texture of the soil was also of very large importance. Topography, the character of the subsoil and all other characteristics which serve to distinguish the soil type may play a part. The most striking relationship between the numbers of organisms present and the soil types studied was found in Series II. The Dickinson fine sandy loam, which is lighter in color than the Carrington loam and the Clyde silty clay loam, showed a lower content of microorganisms, especially bacteria and actinomycetes. Undoubtedly this was due in large part to the lower organic matter content of the soil. In Series III, the Knox silt loam was, in general, lower in numbers of bacteria and actinomycetes than the Marshall silt loam, again a difference which is probably due in large part to the variation in content of organic matter. Other factors, however, may be of quite as large significance in individual cases. Heavy-textured types, such as the Clyde silty clay loam, may actually be lower in content of microorganisms even tho they are blacker in color than soils which are not so heavy in texture. This was noted in the case of some of the comparisons between the Clyde silty clay loam and the Carrington loam. When the texture is very heavy, aeration undoubtedly is limited. The development of microorganisms may be hampered because of a lack of air, while the content of organic matter and the color of the soil may be such that a large number of microorganisms would be expected to be present. The differences in content of microorganisms in the surface soil, as influenced by the type characteristics mayor may not continue into the lower soil layers. In general there seemed to be little relationship between the variations in conditions in the subsoil and the content of microorganisms. The coarse textured subsoil of the Dickinson fine sandy loam had a larger content of microorganisms than did the Clyde silty clay loam or the Carrington loam, which have much larger numbers in the surface soils. Larger numbers of microorganisms were noted in some cases in the lower layers of the Knox silt loam, while the surface soil was lower in content of microorganisms than the surface soil of the Marshall silt loam. Comparing the numbers of organisms in the subsoils of the loess types, the Marshall silt loam and the Knox silt loam, there seemed to \u27be many more bacteria and actinomycetes than in the case of the soils of drift origin, the Carrington loam, the Clyde silty clay loam, the Dickinson fine sandy loam and the Lindley sandy loam. The earlier studies on numbers of bacteria in the Missouri loess soils, compared with those in Wisconsin drift soils, are largely confirmed by these data. The difference is undoubtedly due to differences in the physical conditions of the subsoils of the loess types and of the drift types, which are ordinarily very heavy and even impervious in texture There is a possibility that the difference in the lime content of the drift soils may also be of significance, altho no definite evidence along this line is indicated by these results. This may be one reason for the higher content of microorganisms in the lower layers of the Knox silt loam as compared with the Marshall silt loam. Only one comparison gives any information regarding the effect of treatment on the numbers of microorganisms in the different soil layers. In Series I it appears that the cultivation of the Carrington loam had increased the numbers of microorganisms in the different layers to a considerable extent. The soil in virgin sod was found to be much lower in numbers of microorganisms thru the A horizon, and even down into the Band C horizons. At the lower depths, however, the effect of cultivation was not shown very distinctly. It is quite probable that differences in the characteristics of the lower soil layers would have more effect upon the content of microorganisms than the treatment of the surface soil. Extremes of soil treatment, such as applications of large amounts of farm manure, would undoubtedly very materially affect the content of microorganisms in the surface layers, and this difference might extend even down into the B horizon. Probably the texture of the soil would be of particular significance in determining the rapidity with which the lower soil layers are influenced by the treatment of the surface soil. The relationships between the numbers of bacteria and the numbers of actinomycetes and molds were usually very similar in the different soils. The numbers of actinomycetes seemed to be affected in a very similar way to the numbers of bacteria, but in many instances the numbers of molds were affected in quite the opposite direction. Large increases in numbers of bacteria and actinomycetes occurred when decreases in the number of molds were found. The mold content of the soils was very low and the differences in mold count were often hardly large enough to be significant. Large numbers of actinomycetes were found in all the soils, but the total numbers were very much smaller than the total numbers of bacteria. In general, the decreases in the lower layers from the surface layers, were relatively less in the case of the actinomycetes and much less in the case of the molds than was true of the bacteria, which confirms earlier results. In general, the results show striking decreases in the numbers of bacteria in the lower soil layers over those present in the surface soils. Variations in the decreases occurring between different horizons were often quite large, and they generally occurred without reference to differences in moisture. There is some evidence of seasonal effects, and there is some indication of an influence from long continuous soil treatment, but the chief factor which is probably responsible for these variations is the natural difference in the physical and chemical characteristics of the lower soil layers. Probably the most important is the difference in the organic matter content, which is reflected in the color of the soil. The texture, however, is also undoubtedly of large significance, particularly when fine textured types are compared with coarse textured soils. Probably all the characteristics which serve to distinguish the individual soil types have an influence on the content of microorganisms in the various soil layers. At least in two cases definite relationships between the soil types studied and the content of microorganisms are shown

Soil Survey of Iowa, Report No. 81—Marion County Soils

Marion County is situated in south-central Iowa in the third tier of counties north of the Iowa-Missouri line. Knoxville, the county seat and largest town, is located 38 miles southeast of Des Moines, the state capital, and 51 miles northwest of Ottumwa. With the exception of 55 square miles in the northeastern corner, all of the county lies within the drainage basin of the Des Moines River. The region is a part of a loess-mantled drift plain, once apparently level over extensive areas but now generally rolling because of the dissection of the older land surface by streams. Occasional flat upland divides still mark the level of the former plain

Soil Survey of Iowa, Report No. 82—Ida County Soils

Ida County is situated in the northwestern part of Iowa, lying in the second tier of counties east of the Missouri River and in the fourth tier south of the Iowa-Minnesota line. Ida Grove, the county seat and largest town, is 50 miles east and a little south of Sioux City, 80 miles northeast of Council Bluffs and 110 miles northwest of Des Moines. The county lies in the eastern part of a rolling, loess-covered plain which, in places, reaches a width of 100 miles along the western boundary of Iowa. All of Ida County lies within the drainage basin of the Missouri River, and the major part of the county is drained by the Maple River and its tributaries

Prediction of LDEF ionizing radiation environment

The Long Duration Exposure Facility (LDEF) spacecraft flew in a 28.5 deg inclination circular orbit with an altitude in the range from 172 to 258.5 nautical miles. For this orbital altitude and inclination two components contribute most of the penetrating charge particle radiation encountered - the galactic cosmic rays and the geomagnetically trapped Van Allen protons. Where shielding is less than 1.0 g/sq cm geomagnetically trapped electrons make a significant contribution. The 'Vette' models together with the associated magnetic filed models were used to obtain the trapped electron and proton fluences. The mission proton doses were obtained from the fluence using the Burrell proton dose program. For the electron and bremsstrahlung dose we used the Marshall Space Flight Center (MSFC) electron dose program. The predicted doses were in general agreement with those measured with on-board thermoluminescent detector (TLD) dosimeters. The NRL package of programs, Cosmic Ray Effects on MicroElectronics (CREME), was used to calculate the linear energy transfer (LET) spectrum due to galactic cosmic rays (GCR) and trapped protons for comparison with LDEF measurements

Minor degree of hypohydration adversely influences cognition: a mediator analysis

Background: The assumption that small changes in hydration statusare readily compensated by homeostatic mechanisms has been littlestudied. In this study, the influence of hypohydration on cognition wasexamined.Objectives: We assessed whether a loss of ,1% of body mass dueto hypohydration adversely influenced cognition, and examined thepossible underlying mechanisms.Design: A total of 101 individuals were subjected to a temperature of308C for 4 h and randomly either did or did not consume 300 mLH2O during that period. Changes in body mass, urine osmolality,body temperature, and thirst were monitored. Episodic memory, focusedattention, mood, and the perceived difficulty of tasks weremeasured on 3 occasions. The data were analyzed with the use ofa regression-based approach whereby we looked for variables that mediatedthe influence of hypohydration on psychological functioning.Results: Drinking water improved memory and focused attention.In the short-term, thirst was associated with poorer memory. Later,a greater loss of body mass was associated with poorer memory andattention (mean loss: 0.72%). At 90 min, an increase in thirst wasassociated with a decline in subjective energy and increased anxietyand depression, effects that were reduced by drinking water. At180 min, subjects found the tests easier if they had consumed water.Conclusions: Drinking water was shown, for the first time to ourknowledge, to benefit cognitive functioning when there was a lossof ,1% body mass at levels that may occur during everydayliving. Establishing the variables that generate optimal fluid consumptionwill help to tailor individual advice, particularly in clinicalsituations

Soil Survey of Iowa, Report No. 79—Franklin County Soils

Franklin County is located in the third tier of counties south of the Minnesota-Iowa line and lies approximately 35 miles northeast of the geographical center of the state. Hampton, the county seat and largest town, is 45 miles northwest of Waterloo and about 80 miles, slightly east of north, from Des Moines

Soil Survey of Iowa, Report No. 73—Crawford County Soils

Crawford County is located in western Iowa in the second tier of counties east of the Missouri River and in the middle tier between the north and south state boundaries. It lies entirely in the Missouri loess soil area and the soils of the county are, therefore, chiefly of loessial origin

Soil Survey of Iowa, Report No. 74—Poweshiek County Soils

Poweshiek County is located in southeastern Iowa in the fourth tier of counties north of Missouri and in the fifth tier west of the Mississippi River. It is partly in the Mississippi loess and partly in the Southern Iowa loess soil areas and hence the soils are mainly of loessial origin, only small areas of drift soils being exposed where the loessial covering has been removed by erosion

Soil Survey of Iowa, Report No. 76—Hancock County Soils

Hancock County is located in north central Iowa in the second tier of counties south of the Minnesota state line and in the middle tier of counties from east to west in the state. It lies entirely in the Wisconsin drift soil area, and hence its soils are all of drift or glacial origin

Soil Survey of Iowa, Report No. 67—Buchanan County Soils

Buchanan County is located in eastern central Iowa in the third tier of counties west of the Mississippi River. It is chiefly in the Iowan drift soil area and hence most of the soils of the county are of drift origin. There is a small area of loess soils, probably derived from the Mississippi loess deposit