Scientist Traces Background of Holt’s Soil Prehistoric Waters Account for Varied Soil Deposits and Help Determine Productivity By Lloyd Mitchell, State Soil Scientist The soils of Holt county are the result of millions of years of gelogical activity and soil forming processes. In order to properly understand them, it is necessary that we think about the county as a whole and how many different types of materials are present within its boundaries on which the soils have developed. The present surface is part of what was once a nearly level to gently rolling plain. It was later cut into by headward erosion of the streams and drainages until in parts of the county the topogra phy is quite rough and broken. The establishment of the drainage system has exposed many ! different kinds of parent materials in the older lime rock and shale formations. These formations are the oldest sources of soil mate- { rial. The younger toil materials have been brought in by wind and flowing streams. The mate rials t^ary from gravel that wai washed in from adjacent areas and deposited over the old sur face. to sills and sands that have been blown in and depot tied. Another type of deposit that has furnished the material tot part of the soils in the county is the river sediments such as oc cur along the Niobrara. In order that we understand the various parent materials ot the soils and the soils them selves, it is advisable that each of them be described. Begin ning with the materials of the oldest geological ages up through the youngest, there is a definite sequence and type of soil devel oped. They are as follows. Parent Materials and Soils PIERRE SHALE — The Pierre shale is the oldest geological formation on which the soils of the county have de veloped. Typically it Is a dark gray to black shale that has oc casional thin brown colored zones in it. These latter zones are the result of weathering of material that contains a high percentage 'of iron. The formation is ex posed along the Niobrara river A typical example is near the Spencer dam. The Pierre shale is quite thick in Holt county. It varies from about 200 feet in the northeast (Mr. Mitchell is Nebraska soil scientist for the Soil Conserva tion Service, headquartering at Lincoln. This article w$s writ ten especially for The Fron tier’s Soil Conservation issue.) part of the county to about 700 feet in the northwest. It repre sents a period of deposition of | clay in a large sea that at one j time in past geological ages cov ered most of the central portion of the United States. Because the deposit is made up of fine sediments, the deposition proon- ; j bly took place during a time when the water was quite calm. , Geologists believe that this de position was largely from sedi ments brought into the inland sea from land areas outside and around this sea. The soils that : have developed on the Pierre 1 shale have one characteristic in common, namely, their heavy subsoil. > The surface soils are for the most part very dark, and may range in texture from a loose, silty material that is easy to cul tivate to one that is quite hea vy, and difficult to plow. Much ' of the land occupied by these j soils is too steep to cultivate and 'for this reason has been left in grass. There are, however, some ar eas where these soils are found on gently rolling slopes or near ly level stream terraces that are now 25 to 50-feet above the val ley floor. Where there is a suf ficient depth of surface soil (18 to 24-inches) over the heavy shale subsoil and rainfall is plentiful, good yields can be ob tained. Where erosion has been severe, and the surface soil has been removed, cultivation is dif- j ’ ficult. Crop yields are reduced to a minimum chiefly because ! water cannot be stored in them and the plants die due to the drouthy condition. These eroded soils take up rain very slowly and as a result much of it runs off. For this reasor farmers who cultivate this son of land should use every means possible to keep their surface soils in place and maintain them in condition to absorb all the moisture that falls. This can be done by saving the crop residue and working them into the sur face. OGALLALA FORMATION — The next younger formation or which many of the soils of Holl county have developed is the Og allala formation. It is the bed rock that underlies much of the area north of O’Neill on the Holt table and is exposed in many places in the county. It rests di rectly on the Pierre shale. One of the most extensive exposures occurs along the valley slopes of Eagle creek. __ Here, it has a light gray to white color and it is made up chiefly of sand that is loosely cemented with lime. Several other types of materials are in cluded in this formation but for the most part the limey sand stones predominate. The Ogallala formation repre ients a deposit of comparatively :oarse material eroded from the *ocky Mountains to the west and ;pread over the plains by streams hat once covered this area. Va rious divisions of this formation :an be traced from Texas to south Dakota. Some of the limey ieposits are the result of lime ... w .. 1 n,Vsi/.Vs in ** - - * — — — ponds or lakes on the surface of the landscape during that time. Other limey deposits are "cal iche” that is formed by the evap oration at or near the surface of ground water that carries consid erable quantities of lime in solu tion. Thq sandy and gravelly horizons that are found in this formation were brought in by eastward or southeastbound flowing streams. The soils that have developed on the Ogallala have moderate ly dark, silty, or slightly sandy surface soils that are about 10 or 12 inches thick under native veg etation. The next 8 to 10 inches below the surface soil is usual ly a light gray to almost white I when dry silty material. This is the material which some farmers call “sugary" be cause of its behavior when ex posed to water. It appears to melt away like sugar as water runs over it in the small gully heads. Below this latter zone or horizon are materials that may be quite variable. It may be quite sandy or gravelly or it may be solid "caliche.” The soils developed on the Og allala are variable as to depth. In places where there is 24- to 36-inches of relatively loose soil material over the unweathered parent material and erosion has not been sereve, good crop yields can be expected in years of ade quate moisture supply. Past ex perience has proven that where the underlying rock is within 6 to 12-inches of the surface, crop production is quite hazardous. Most of the land of this type has been left in grass for this reason. The conservation measures re ! quired to protect this type of soil are also variable. Where erosion is severe the crop yields are low. On the steeper slopes | this land is best suited to perma nent grass. Where the sloping land is not severely eroded, ter races, grasses, waterways, and good rotations that include fre quent legume crops arp advisa ble. Where this soil occurs on nearly level areas, protection from wind erosion is necessary along with good crop rotations, j PLEASTOCENE GRAVELS — Resting directly on top of the light gray or nearly white Oga llala formation is a deposit of sand and gravel that varies in thickness from 0 to 60 feet. It will average around 40 feet These sands and gravels were deposited in this area by north eastward flowing streams. The streams >vere partially blocked to the east by glaciers, causing them to deposit their gravel loads over the tableland areas. The surface of these deposits was ! comparatively level. Their vari ation in thickness is due largely to the uneven surface of the un derlying Ogallala formation. The establishment of a drain age system and valleys by head ward erosion of streams on the nearly level tableland has left ! extensive exposures in many places in the county. The soils that have developed on the grav el deposits are mostly too shal- j low and porous to hold moisture, j For this reason, there are large areas on the Holt table that have remained in grass. On the basis of observations it appears that where there is less than 16- to 18-inches of soil material ov,vr the gravel, the soils are too droughty for cul tivation. When there is 24- to 36-inches there seems to be sufficient mois- 1 ture holding capacity to produce 1 fair crop yields when the mois ture supply has been favorable. Only the nearly level or gently sloping areas are cultivated. The conservation program on them should include pilictices that con serve moisture, such as residue management, stubble mulch till age, strip cropping and protect the surface from wind erosion. I'wind-laid deposits — The wind deposits in Holt county are the principal parent materials of the soils and are of three general types. They are (1) silty (loess) deposits that are the parent materials of the good, deep, dark farming soils of the county; (2) the mixed silty and sandy deposits, also deep and quite dark, that are farmed ex tensively; and (3) sandhills. The dark silty soils are not ex tensive in the county. The larg est areas are east and northwest of Town Hall in Shields town i ship and north and east of Page in the easteni part of the coun ty. The topsoils are dark brown or dark giayish-brown • and are about 10- to 14-inches thick where erosion has not been ac | tive. There is enough sand mix ed with the silt on these soils to make cultivation quite easy. For the most part these soils occur on nearly level to gently rolling areas and are subject to only mi nor wind erosion losses. The conservation treaimient on these soils should include protection from wind erosion by use of strip cropping, stub ble much tillage, and crop res idue management. Crop rota tions that maintain a high level of fertility and soil structure should be used. The soils that have developed on mixed silts and sand depos its are good agricultural soils. They are found extensively in the area north of the Elkhorn river. They are closely associat ed with the soils that have silty parent materials and produce nearly as good crop yields. The topsoils are about the same thickness as the silty soils. Be cause of the fact that there are some variations that include sandy profiles in this group of -soils, they are subject to more severe wind erosion. Also, since the relief is undulating to rpll ing, there is an additional haz I ard from water erosion. The conservation treatment re quired for these soils should in clude adequate protection from wind erosion by the use of cover crops, strip cropping, contouring, terraces, windbreaks, and care ful management of crop residues. Moisture conservation and main tenance of fertility should also be used. SANDHILLS — The major portion of the sand hills area of the county is locat ed south of the Elkhorn riv er. The soils in this area have thin (4- to 6-inch) topsoils that are very sandy. Past experience has proven that this area is best adapted for the production of hay and pasture. The tall grasses grown in the area are one of the finest crgps produced in Holt county. There are three major sandy soils that can be described in the area. These are closely associated with the surface relief and are separ ated on the basis of the quanti ty of finer material mixed with the sand and the dark colored humus content. The dune sandy or “choppy hills” are almost de void of topsoil and are subject to severe losses by wind. In some instances the instability of the dunes has been caused by over-grazing the sparse grass cover. The conservation treat ment of this type of land is a matter of adjusting the number | of livestock so as to attain and I maintain a mixture of grasses that will give the maximum pro ductivity of forage on these soils with the moisture available. It also involves cautious grazing practices and ample livestock watering places. When this land is over-graz ed and the sand commences to mov^, the problem of reestab lishing grass stands end stabil izing them again is very diffi cult. Damage to the adjoining (Continued on page 15.) LYNCH NEWS Mr .and Mrs. Don Allen re turned home Thursday, February 15, after a week’s visit in Omaha. Mrs. Albert KalkNorwp«w«r GRAVELY Engine ★ TWO SPEEDS FORWARD and REVERSEI , , . Na tugging or pulling ★ AU. GEAR DRIVE1 . .. 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