Soil Erosion: A National Menace, Slides of Environmental Science

Download Soil Erosion: A National Menace and more Slides Environmental Science in PDF only on Docsity! UNITED STATES DEPARTMENT OF AGRICULTURE CIRCULAR No. 33 Washington, D. C. April, 1928 SOIL EROSION A NATIONAL MENAGE H. H. BENNETT . Soil Scieutist. Soil Investigations, Bureau of Chemistry and Soils and W. R. CHAPLINE Inspector of Grazing, Branch of Research, Forest Service UNITED STATES GOVERNMENT PRINTING OFFICE WASHINGTON 1928 ^^ SOIL EEOSION A NATIONAL MENACE 3, reduce its stiffness sufficiently to make it amenable to efficient cultiva- tion, to the establishment of a desirable seed-bed tilth. It bakes easier and, as a consequence, crops growing on it are less resistant to dry seasons, because of rapid evaporation from the hardened sur- face, and the many cracks that form deep into the subsoil to enlar<^e the area exposed to direct evaporation. Crops also suffer more in wet seasons because the material becomes more soggy or water-logged than did the original soil. On much of it both fertilizer and lime will be required for satisfactory yields. Certain piedmont areas whose records are known have, within a period of 30 years, lost their topsoil entirely, 10 inches or more of loam and clay loam having been washed off down to the clay subsoil ; and on this clay subsoil, substituted for the departed soil, from 400 to 600 pounds of fertilizer are required to produce as much cotton per acre as formerly was grown with 200 to 250 pounds of fertilizer of no better quality. While these difficulties of tillage and the lowered productivity are being attended to by the farmer in those fields not yet abandoned, the unprotected fields continue to wash. Unfortunately the farmers in many localities are doing little or nothing to stop the wastage and much to accentuate it. (PI. 1, A.) In many instances the farmer does not know just what to do to slow down erosion. In many other cases he does not even suspect that the waning productivity of his fields results from any cause other than a natural reduction of the plant-food supply by the crops removed. He does not recognize the fact that gradual erosion, working unceasingly and more or less equally at all points, is the principal thief of the fertility of his soil until spots of subsoil clay or rock begin to appear over the sloping areas. SOME WASTING AREAS The southern part of the great Appalachian Valley is an admirable place to see the evil effects of that gradual land washing known as sheet erosion. Here in thousands of areas of formerly rich limestone soil of loam, silt loam, and clay loam texture, the topsoil has been removed. The numerous galls or clay exposures that now splotch the slopes lose their moisture quickly in dry weather. The dam- aging effects of drought upon crops are felt much quicker than for- merly, according to those who have witnessed these changes in the soil. A much lighter rain than formerly now turns the Tennessee Kiver red with wash from the red lands of its drainage basin. Added to the severe impoverishment of a tremendous area of land throughout this great valley, and its extensions southward into Georgia and Alabama and northward into Virginia, are the gullied areas, which are severely impaired or completely ruined by erosional ravines that finger out through numerous hill slopes and even many undulating valley areas. Field after field has been abandoned to brush, and the destruction continues. Much erosion of the same type has taken place over the smoother uplands of south-central Kentucky; that is, in the rolling parts of the highland rim country; over much of the Piedmont region, and through many parts of the Appalachian Plateau. Land destruction of even worse types is to be seen in the great region of loessial soils that cover the uplands bordering the Mississippi and Missouri Kivers . 4 CIBCULAR 33, U. S. DEPARTMENT OF AGEICTJLTURE and many of their tributaries, from Baton Eouge, La., northward Numerous areas, small and large, have been severely impoverished and even ruined m the famous black lands of Texas. "^Even the drier Kh?NoAT^''^"''i^'^.'^TP'^^"*^^^^y smooth prairies and pTa^ns of the North-Central States have not escaped damage. Erosion is wasting the fertility of the soil and even the whole body of the soil doSfl ^iT' ^^''^ *^" '^'^' ^' '"'^'^''^ i«^ rain w^ater to rSn downhiU. Ihere are some exceptions to this, or rather some cartial exceptions, such as the nearly level lands, the loose, deep sandyTands the liighly absorptive gravelly areas, the loose gladal tfll anS moramic deposits m parts of the northern border of the countrv the peculiar red lands of the northern Pacific coastal region and a'few others Although the total area of these more or "less erosion-re sistant soils IS larg;e, the area of those lands which are susceSe to washing and which are being washed in a wastefuTway more dis^ astrously in some places than in others, is very much SJr Snv« when the fields are frozen or are covered with a bZiet ofTardeS tSr;-f«T • ^T ?" "P°" ^^''^ vulnerable lands during every rain ¿nîli '"^"^^^^^ly heavy to cause water to run downhilL S the gentle spring rains cause some erosion, and the surface water flow« ZZi:roÄZZufr^''^'t''i y^"«-' «^"„«rdinÎTo tne color ot the soils of the neighborhood. This color is cau-^PfThTT soil materials started en route to the sea. Most of this material comes from the surface layer, the richest part of the soil FIGURES ON SOIL WASTAGE The estimate of the quantity of plant-food elements annually lost SfscTar'o?|;oTo(?nrr ^ -;-™-,-timate based^^on a /eari? risers'fln.%w?Ä-*^^ *''"' ?* suspended material into the sea by rivers, plus twice tbis amount stranded upon lower slopes and de posited over flood plains, in the channels of^streams, anZeverin fh¡ basins of reservoirs, where it is not needed and not wan¿d Of en S SuX f^!ur'^ niore damage than good to the lands affVcted It gradually reduces reservoir storage capacity and makp=! wnf^r power plants dependent more and more upon the C S Se sTream rather than upon the impounded water It is obvious to all who are familiar with field conditions that the amount of erosional débris in transit to the sea, but îempomrily ttXactaSv t::?' '""ñr"' ^^/Z ^^''y ^^^•^'^'^^ twiLSmouS that actually passes out the mouths of rivers into tidewater Some soil scientists believe the amount thus annually washeTout of the fields and pastures and lodged on the way to the oceans is r^ore than a hundred times greater than that actually entering the Tea The uf;;n'wb?ol.i°Tf ^'' ^T ^^^? "^^^'y becLse no sftisfactory daía upon wh ch to base conclusively accurate estimates are available. 1 he estimates given do not include the dissolved matter which is annually discharged to the sea, a very considerable part of which obviously comes from erosional products. Furtherm^ore, it il not 27ÔZ%00°'to!?'',]rdAe'd'"rt*tfr I'rf tSÄSS?t^S°t*°îf. °* ^'^'^^'^ -^"«^^ «■>" Btrenms of the United States (« o SîT« ■?> r ^V.'^.Í^IO'Í,.*" tidewater every year by the more tons of " richest soil matter "are washed ?:ïï^^th" estimates that 1,000,000,000 or country every year (5) ""tier are >\asheä Into the oceans from the lands of this • Italic figures In parentheses refer to " Uterature cited," p. 35. SOIL EEOSIOïT A NATIONAL MENACE 5 known how much erosional detritus enters the ocean as drag mate- rial swept along the bottoms of streams. This material is exceed- ingly diihcult to measure. The débris thus swept along the bottoms o± many streams travels rather after the manner of waves or of sand dunes drifting before the wind. This characteristic of many river beds was brought out before a commissioner appointed by the Su- preme Court of the United States in the expert testimony relating to the recent Ked Kiver boundary dispute between Texas and Okla- homa. Gilbert {9, p. 11) makes the following interesting observa- tions regarding the process : Some particles of the bed load slide ; many roll ; the multitude make short skips or leaps, the process being called saltation. Saltation grades into sus- pension. When the conditions are such that the bed load is small, the bed is molded into hills, called dunes, which travel downstream. Their mode of advance is like that of eolian dunes, the current eroding their upstream faces and depositing the eroded material on the downstream faces. With any progressive change of conditions tending to increase the load, the dunes eventually disappear and the débris surface becomes smooth. The smooth phase is in turn succeeded by a second rhythmic phase, in which a system of hills travel upstream. These are called antidunes, and their movement is accomplished by erosion on the downstream face and deposition on the upstream face. Both rhythms of débris movement are initiated by rhythms of water movement. The amount of plant food in this minimum estimate of soil wast- age by erosion (1,600,000,000 tons of solid matter annually) amounts to about 126,000,000,000 pounds, on the basis of the average composi- tions of the soils of the country as computed from chemical analyses of 389 samples of surface soil collected by the Bureau of Soils (1.55 per cent potash, 0.15 per cent phosphoric acid^ 0.10 per cent nitrogen, 1.56 per cent lime, and 0.84 per cent magnesia). This is more than twenty-one times the annual net loss due to crops removed (5,900,- 000,000 pounds, according to the National Industrial Conference Board) \16). The amount of phosphoric acid, nitrogen, and potash alone in this annually removed soil material equals 54,000,000,000 pounds. Not all of this wasted plant food is immediately available, of course; but it comes principally from the soil layer, the main feeding reservoir of plants, and for this and for other reasons it is justifiable, doubtless, to consider the bulk of it as essentially repre- senting lost plant food, without any quibbling about part of it having potential value only. By catching and measuring the run-off and wash-off from a 3.68 per cent slope at the Missouri Agricultural Experiment Station, on the watershed of the Missouri Eiver, it was found that for an aver- age of six years 41.2 tons of soil material were annually washed from 1 acre of land plowed 4 inches deep, and that 68.73 per cent of the rainfall, the total precipitation amounting to 35.87 inches a year, was held back ; that is, 24.65 inches of the 35.87 inches of precipitation were temporarily absorbed as an average for the six-year period. From a grass-covered area of the same slope and soil type less than 0.3 ton of solid matter was removed each year (or a total of 1.7 tons in six years), while 88.45 per cent of the rainfall was retained. " In. 24 years this rate of erosion would result in the removal of a 7-inch layer of soil from the area tilled 4 inches deep; but for the removal of the same thickness of soil from the grassed area 3,647 years would be required. Circular 33, U. S. Department of Agriculture PLATE 2 A.—!?i\"-year-ol(l locust trees which have not only arrested washing on what was once a rather severely eroded area in western Tennessee but are also assisting in a gradual improvement of the soil B.—A cornfield almost obliterated by a blanket of infertile sand assorted and deposited by erosional waters of one heavy rain C—Typical erosion on dark Houston clay of the Alabama-Mississippi prairie region Circular 33, U. S. Department of Agriculture PLATE 3 A.—A field in northeastern Kansas, about 12 miles from Missouri River, that was eroded durina a single rainy spell B.—Highly productive Knox silt loam in northeastern Kansas, about 12 miles from Missouri River. severely damaged by incipient gullies, already 12 or 14 inches deep, which had their beginning ii 7J^ f T^^?/oi'^^Jl™'° '^ii '• V^'i,^^ •■'>'' ''«^"'* «f » ^ingle rainy period, after grain had been sown, fall of 1927. These will probably grow into deep gullies Circular 33, U. S. Department of Agriculture PLATE 4 ^¿W^ m/y' A.—stack of wheat straw dumped in Rully in field of Marshall silt loam, which durinc the fall rains 71 T^ Jnni/Ä' r-^ H$'^ *'"■ *''°'*,f ""i' ^°" «"»'""al washed from adjacent s?oVes B.-An apple orchard in the repon of loessial soils, in northeastern Kansas. The trunks of the SOIL EROSION A NATIONAL MENACE 9 SOIL EROSION NOT RESTRICTED TO THE SOUTH The experts who recently completed the soil survey of Doniphan County, in northeastern Kansas, found that an average of at least 6 inches of soil had been removed from the rich uplands of the county. Nearly all tilled slopes have suffered, some much more severely than others because of variations in the surface relief and in the kind of soil. In one place examined an area of original timber had through- out its extent from 12 to 24 inches of rich soil overlying clay subsoil. This surface layer was so rich in humus, so moist and mellow, that it was possible to dig down through the dark-colored permeable soil with the bare hand, even to the depth of the subsoil. Cultivated soil of the same kind, having the same degree of slope, lying in imme- diate contact with this forested area had in most places no topsoil at all, as the result of erosion, and in some places even the exposed subsoil clay had been eroded off to a depth of 6 inches or more. Indeed, both soil and subsoil, it was found, had been washed off some areas down to the basal limestone that at one time was 4 feet beneath the surface. These severe effects of erosion were found as a very common con- dition in a broad belt over the more rolling lands near the Missouri Kiver; indeed, this condition, or a close approximation of it, was found to be the rule, not the exception, through this more rolling belt, where the virgin soil, the Knox and Marshall silt loams, were among the very richest upland soils in the United States. Apple trees were dying on the eroded hilltops where, seemingly, the soil moisture con- ditions had been unfavorably upset by the removal of the surface soil layer. In the depressions and on the'gentler parts of the slopes and the bench positions some of the rich soil from above had lodged. In these places the apple trees were thriving. A farmer in this section said to the soil specialists : We have good apples on the deep soil of the flat places, but we have always had good apples In these places. These places did not need any more soil, they were already deep and rich. We want our soil to stay In the orchards and fields, but it is not staying there. In places 4 feet of soil has been washed off the land. The surface of the ground about our house has been gradually low- ered more than a foot I will show you washed places where not even weeds eucceeded this year. This terrific washing of the land has taken place in the memory of men living in the community. The wasted areas adjacent to the for- ested land referred to above were cleared about 40 years ago, accord- ing to the statements of men in the locality who said they had taken part in the clearing. Wheat, alfalfa, and sweet-clover fields seeded in the fall of 1927 had been severely damaged by the fall rains. (PI. 3, A.) In places each depression made by the seed drills had been converted into a small rill way or gully, and the wheel tracks of the seeder in some places had grown into ditches (pi. 3, B), which surely will expand rapidly into formidable gullies that will cause eventual abandon- ment of the areas affected. In small grain, alfalfa, and sweet-clover fields soil in excess of five tons to the acre was swept from the sur- face of numerous fields on these splendid soils, the Marshall and Knox silt loams, during a single period of rain last fall. In some fields of steeper slope the loss per acre as a result of this single rainy 88854°—28 ^2 10 CIRCULAB 33, U. S. DEPARTMENT Or AGRICULTURE spell was estimated as amounting to fully 40 tons. Much of this erosional débris passed down from the upland slopes into depressions and stream ways to be carried off in flood waters, although large quantities, as was readily determined, were deposited locally over depressional flats and the flood plains of small and large streams where none of it was needed. In one place a few miles south o^ lYoy, Kans., where newly planted grainfields had been severely dis- sected by the fall rains of last year a farmer had left a series of wheat-straw stacks in a depression at the foot of converging slopes Against the upper side of these large quantities of rich silt had lodged, building up small flood plains, or alluvial fans, 4 feet deep in places. (PI. 4, A.) One of these stacks had caught 430 tons of this rich soil matter during the single short rainy period referred to, even where vast quantities had been swept by to lower levels after the catchment basin formed by the straw bulwark had been ñlled Ihese straw stacks represented the sole attempt to check soil erosion that was observed through several Missouri and Kansas counties bordering on the Missouri River. Along the outer edge of the Missouri River bottoms, in the north- ern part of Doniphan County, a farmer had constructed an 8-foot embankment some distance out in the bottoms, approximately parallel to the foot of the upland, in order to intercept soil material that was being brought out of the hills by small local streams. This erosional material was covering the farmer's rich Missouri River alluvium (Wabash and Sarpy soils), causing a reduction in the yield of corn and was continually washing over the roadways, rendering them im- passable. Within 10 years eroded material from the uplands had lodged here level with the dikes, from 5 to 7 feet deep. Thus had been formed a terrace averaging 6 feet deep over 40 acres: and the intercepted soil was not so productive as the land it had buried The weight of this erosional placed material amounted to about 480,000 tons. It had accumulated at the approximate rate of 1,200 tons to the acre each year. It should be observed in this connection that ri/i: oV^e erosional detritus brought out of the uplands had been held by the dike. At first, part of it had escaped downstream in the conveying flood waters. Finally drainage had been blocked in that direction, whereupon the material began to escape in the transport- ing water around the upstream end of the diked area. *!, AÍ? sort of thing is taking place in varying degrees up and down the Missouri River and its tributaries, and along many other streams of the central West. Recently, it was necessary for the soil sur- veyors working m this great region to recognize a new soil type in order to classify and map material derived from the regional up- lands by erosion and freshly deposited over older stream alluvium. in an apple orchard near Lookout Mountain in northeastern Kansas the trunks of the trees had been completely buried by over- wash of silt from the adjacent uplands, and the level of the ground nZTf ^^iuTul' °* \^%*^^^'- (P^- 4' B-} The owner of this orchard stated that although the apple trees had not seemed to suffer by the hllmg in the uplands had suffered very greatly from the gradual erosion that gave rise to the transported soil. ..f -ifn} f orchard a gully is now advancing at a minimum rate ot 150 feet a year, according to local information. This ravine is SOIL EEOSION A NATIOÏTAL MENACB H 60 or 75 feet deep, nearly 300 feet wide in places and almost three- fourths of a mile lon^. It is destined to destroy all the farm land in this fertile valley, including the apple orchard, and it may, with its deploying prongs, cut through the local hills. Already in this new agricultural region fields (pi. 5, A) and even farms are beginning to be abandoned in the more rolling belts near the river, and land is being rapidly impoverished many miles back from the river. Indeed, all cultivated slopes are suffering to some extent. Nothing is being done to slow down the wastage, but con- siderable to accentuate it. In general, no effort is being made to cultivate along the slope contours; corn rows are run straight up and down hills as often as otherwise. It is a common practice in this region to plow furrows down the slopes in the spring, in order to allow water standing temporarily in corn " middles " to flow out. These furrows commonly develop into gullies that soon grow beyond control at anything like reasonable cost. . There are no terraces in this region; the farmers do not even know what they are. Erosion is gathering momentum. As the more absorptive topsoil is washed off down to the less absorptive subsoil, the rate of wastage increases. So, this region, which has already suffered seriously from rainwash, is really just upon the threshold of the most impoverishing kind of erosional wastage, and nothing is being done to conserve these splendid agricultural lands, the capital of the farmers living on them and a vital heritage to posterity. It is not to be understood from the above that erosion in the north-central part of the United States is restricted to the Missouri River region. The wastage is taking place generally throughout this great region, most violently, of course, on the sloping areas. Soil displacement by this process is slow on the very extensive flat areas of the prairie regions that formerly were covered by a most efficient soil-conserving mat of native grass; but even here there is a much greater gradual removal of the rich surface material than is commonly recognized. (PI. 5, B.) Since the clearing of the sloping and rolling areas and the destruction of the virgin sod, much costly washing has taken place in Missouri, Iowa, Nebraska, Illinois, Indiana, Ohio, Wisconsin, and other States. Eecent soil surveys in southwestern Wisconsin have shown that the problem of erosion is a most serious one in many localities. It was found that slopes, es- pecially on the Clinton and Boone soils, which were originally tim- bered or covered with brush, have been seriously gullied and damaged by sheet erosion from rain water and melting snow. Gul- lying was found even on bench lands of the valleys (Bertrand soils), and here as elsewhere the stream bottoms were being covered by overwash. These latter instances are mentioned to show that sou wash is a land menace even in parts of the northern border States. EROSION IN THE DRIER REGIONS Under the light rainfall of the western dry regions one might reasonably conclude, in the absence of the facts, that erosion is of negligible importance in comparison with that taking place in the humid regions. From the viewpoint of the extent of erosion, such a conclusion would be entirely contrary to the facts, at least for 14 OIBCULAß 33, TT. S. DEPARTMENT OP AGBICULTUBE frequent deposition of flood alluvium enriches the land, and that floods, therefore, are beneficial, in respect to the productivity of the overflowed alluvial plains. There is some truth'in this, of course • but m the main the conception is incorrect, and frequently the ffood accomplished is greatly overestimated. It has already been pointed out how disastrous overwash of inert sand has been to the alluvial lands ot the piedmont region and the "brown loam" belt of the lower Mississippi Valley. This same condition, or an approximation ot it, applies also to many other parts of the country. In the Ozark region, for example, the bottom lands of many farms, on which there was but little arable soil in the beginning, aside from the bottoms have been seriously impaired or ruined by overwash of chert eravel washed down from the regional hillsides. The November flood of 1927 in the New England States laid down upon many of the pro- ductive bottom lands a blanket of relatively infertile loose sand and gravel burying meadows and fields. In other parts of the bottoms the soil was ripped out and washed away by the swift, deep flood fl ^}^ h^T^^'t^ ^^tr^^ °* *^^ sediments deposited by the spring floods of the River Nile are often cited. It is not known preciself what the benefit amounts to in terms of money; but there is no doubt that sonie measure of soil enrichment does follow the floods of that river. It is obvious, also, that some enrichment of the soil is derived from the finer sediments laid down by the flood waters of the Mississippi. However, some damage is occasioned by the deposits ot comparatively inert coarse sand scattered about in the "sand blows, or by patchy deposits that take form locally with every flood ï«r,??^ T'' *^^^ f'^^ .^"^i^ ^"S^°°- However, the damage and destruction to property and planted crops occasioned by the Missis- sippi floods qmte obviously very greatly exceeds the net benefits accruing from sedimentation. When one thinks of possible benefits î,nf ilT'*- i!?'^i^!u'''^/ ^'■'*™ «imposition of flood-water silt, one should not lose sight of the damage done to upstream farm lands by the re- Znf.î the silt into the streams. Also the resultant increase in flood volume due to the additions of solid and dissolved products of erosion is dangerous, and one should not overlook the increased rapid- ity with which rain water flows off those areas denuded of their niore sSÄrÄ^ä The alluvial soils of the flood plain of the MS Ä ^t^Tñ '*^ tributaries are naturally so rich that most of :»!fi. ° be cropped probably for many generations, without severe impoverishment of the soil. These alluvial soils are deep many of them very deep, and exceptionally rich in plant food. The irn^^rA'"^''^^ composition of "buckshot" soil samples taken Í 9S r.P !"^i.^"'^J'?^'l"^.'\^ Counties, Miss., is as follows (3) : liSo qi Í! P^°?ho"« ^<^'à; 0.80 per cent potash; 0.81 per Ut lime; l.ál per cent magnesia. The phosphorus content of this soil, which is by far the most th^roTfh''^'^ "^ '^' ^^^^ Mississippi'flood plain, L nearly twLe that of the average surface soil of the country. It also exceeds the average soil considerably, in content of organic matter and nSogen Material of this exceptionally good fertility extends to a depth of rro/^h f""'*^ but slight change. The condition of fertiUty is so good that new sediments are not particularly needed, although, Circular 33, U. S. Department of Agriculture PLATE 5 A.—Land in northeastern Kansas formerly cultivated but now used for pasture because of gullying and sheet erosion. The gullies are constantly cutting deeper and Angering out over a wide area B.—Sheet erosion on almost flat rich black Iowa soil where the first evidence of erosion is the expo- sure of patches of the clay subsoil , j . ,. C—Area in western Texas representative of the destructive eflects of erosion on the dry lands of the West Circular 33, U. S. Department of Agriculture PLATE 6 ""•v^U St talLe' SrucUoi ¿?tteît^^TX^ofri^U so^S ''"'"• " ^'"'^'^ '" " "''''^' ™' "»""^ SOIL EROSIOK A NATIONAL MENACE 15 rccuracv wffíffo ,i^'' '""'"'^'f ^^'^ ^°* be estimated with much Îfltd'""'îtl5«*r'*"' '"í ~> r« '»■■ -veJ years follSl THE DANGER OF AVERAGES The effect of erosion is extremely variable from place to HIAPP and ShSd'of kn/''^'"^ «lopef with var^in^eSlVv: Ä Se dÄn^ tffhaTS c^ronl^^U^^S l^rivt X clay IS being p aned down at an equal rate. This is fa^ from the ^uth. The estimate so often read that erosion is loweriZ íhe Mississippi Basm at the insignificant rate of 0.0028 incTaSaílv IS not only too small as an average, but since erosion does not oüerÄ Zl \^'fr'^\^^ T^^"^ soils" according to any plan of averages centy ""* '' dangerous both for its inaccuracy and Iomp£ A most important thing to know about soil erosion is the ratP nf cutting away the topsoil, and after that the subsXf the individual soil types in those regions of the more vulnerable lands such althe K^r M K'T^ TH^ ^^Î ^^^^«^ «f the Susquehanna soils the t^r^oîir'^^? and related soil regions, the Cincinnati soil r^iom the Houston clay soil region, and the regions where Oraneefurï Decatur, Cecil, bekalb, leeves, Vernon, Putnam, FaiVmoS anj numerous other soils are important. t^J,tlf^^^^^^ already made in connection with soil-survey work show that there are many types of erosion, due to many variants, that hav^ to do with he process chief of whi'ch are, (1} soil type 2) degrle SoÄ/^^ '^r'*'' (4) vegetative cover ana (5) method of usfge! bome soils can be cropped with a fair degree of safety on slopes hiv ing a gradient up to about 20 per cent^ such as some of tS very unlfr'^'^Vif^^' °i.*^^ '^''^ "^g^^ i^ «^« southern par of S ^nî p J ^^ '^?.*^y ^^''^'''^ *^"® *° «^"^io"' even where the slope does sucn a soil. Un this soil erosion goes on in all tilled fields where there is any slope whatever. On some soils greatest erosinal damage is done by gullyine; on most soils, however, greater wastage results from that slow type of erosion called sheet erosion. On the Cecil soils of the piedmont region deep broad V-shaped gullies form and finger out rapidly, whereas on the Orangeburg soils, the sides of the ravines are more nearly perpendicular, and they extend by a process of caving, when the loose sand of the substratum is washed out, so that rapid widen- 16 CIBCtTLAE 33, tr. S. DEPARTMENT OP AGRICULTURE ing and head-on extension takes place. (PI. 7, A.) On the Grenada soils ot the "brown loam" belt, by reason of a compact subsoil layer peculiar to this group of soils, the washing extends more nearly eçiually in all directions, and rapidly invades broad areas of fine loes- sial land wherever the erosion has been neglected in its infancy. (PI. 7, B.) On gravelly red land in northern California, where smelter fumes have annihilated the forests and destroyed almost every vestige of vegetation, extremely deep, narrow ravines have de- veloped, which make travel over these areas difficult and even danger- ous. (PI. 8, A.) On soils like the Susquehanna, in which impervious heavy clay lies near the surface, the material of the cultivated soil IS converted quickly into an approximate liquid condition during rams. This causes the surface substance to flow away rapidly. Fof lowing this skinninff-off process, the exposed stiff clay is attacked by erosion and gradually cut to pieces by gullies that render the land absolutelj^ unfit for further cultivation. (PI. 8, B.) Numerous other variations of the manner by which soils erode could be given, but this will not be necessary for the purposes of this circular. Although there is some erosion on most tilled and bare areas, and probably always will be, wherever water runs downhill, provided the soil is not frozen or protected by hard snow, the damage is greatest m the southern and central parts of the Temperate Zone and in the Tropics. So long as the ground is congealed freezing gives practi- cally complete protection, save on those soils that "heave" badly. Slowly falling rains are everywhere much less destructive as an ero- smnal agent than hard, beating rains. For example, no important effect of surface wash is observable on cultivated slopes of the Fair- banks silt loam, a wind-laid soil, in the Tanana Valley in northern Alaska where the ground is frozen during eight or nine months and the light precipitation occurs almost entirely as drizzling rain and light showers. By simple and well-known laws of mechanics the erosive power of flowing wat«r increases enormously with increase of slope, but the destruction accomplished varies greatly with the soil type. Deep sandy soils, as a rule, do not wash severely, especially where the sub- soil does not consist of impermeable clay or hardpan. However some areas of sandy land, such as the Norfolk sand, do wash rather badly, and even gully on those slopes where there is impervious clay at a depth of 4 or 5 feet or less, as is true of areas in east Texas having a stiff subsoil like that of the Susquehanna clay. RELATION TO FLOOD CONTROL It is obvious that the erosional debris entering the streams adds to the volume of the water. It is equally obvious that those methods of soil conservation which have been found effective in slowing down or controlling soil erosion, chiefly terracing the land and the growing of trees, grass, and other soil-holding plants, are also methods which will cause more water to be retained in the surface soil and to be stored in the subsoil. Terracing.of fields and the growing of trees, grasses, and shrubs on idle lands and areas too steep for cultivation, and upon soils that are highly susceptible to washing, as a combina- tion of practices, will, it is believed, have considerable to do with flood reduction by decreasing the runoff and washoff from many SOIL EBOSION A NATIONAL MENACE 17 land areas. Soil conservation is somewhat synonymous with mois- ture conservation. Nothing will hold back all the water, of course, but enormous quantities can be held temporarily or stored for sum- mer-crop use, especially in the subhumid regions. At the same time the rich topsoil can be conserved by these proved implements of soil and water conservation. Soil conservation, therefore, should be an important adjunct of any long-continued system of flood control. To those who have seen the water from heavy rains rushing down unpro- tected cultivated slopes and bare areas, surcharged with soil matter, and carrying even gravel, cobbles, and bowlders, it is not necessary to argue about the effective contribution widespread use of these soil- conserving methods would make toward flood control as supplemen- tary measures to protection with levees, spillways, and reservoirs. Suspended material to the amount of 428,715,000 tons annually passes out of the mouth of the Mississippi River alone. This is but a part of the solid material that enters the river and its tributaries since much is left stranded somewhere along the pathway^ to the sea. In considering the relation of this water-transported erosional mate- rial to increased floods, it is necessary to take into account its full significance, along with that of a far greater amount stranded between the source of supply and the streams, in its relation to the increased amount of water flowing off the land areas which have contributed the material. So many tons of silt in the river stand, unmistakably, for so many denuded or partly denuded acres of sloping land some- Avhere upstream—land enabled by its denuded condition to contribute to the stream at a faster rate more of the rain that falls upon it. In discussing the relation of forest and other forms of vegetative cover to run-off water and floods, it is frequently contended that, although the methods may have value, the time required for a forest to grow up is too great for this means' of assistance to have any im- portant relation to flood problems requiring immediate attention. In this connection the fact should not be lost sight of that the roots of trees and of other plants begin to function as effective agents for holding soil against erosion very shortly after the seedling begins to grow. Greatest efficiency in this respect will come, of course, when the forest or other vegetative cover, as grass, bushes, and chaparal, has made sufficient growth to develop an absorptive, spongy coyer of vegetable litter. The immediate effectiveness of grass in holding both soil and water has been conclusively shown by results of the erosional test referred to above. It is said by those familiar with early conditions in the Prairie States that before the extensive culti- vation of the land the matted turf of the prairies, in many places, Inmg like canopies over the banks of streams that carried clear water throughout the year. With the breaking of the land this situation was changed. The streams are more frequently dry in summer and are more heavily laden with silt when the rains come. The following relates to the effects of rains on sloping areas in Orange County, Calif., following removal of a bush growth by fire : ' During the Orange County Farm Bureau Forestry Tour on November 19th, a remarkable demonstration of the effectiveness of chaparral cover In conserving water by preventing destructive erosion was seen at the Harding reservoir. 'Information furnished by C. F. Shaw. University of California, In a letter to tha writer. Data obtained from Extension Service Report, December, 1927. 888.'54°—28 3 20 CIRCULAR 33, U. S. DEPARTMENT OF AGRICULTURE methods of cultivation, but in their resistance to erosion and in the means necessary for checking erosion. Any other method of pro- -cedure in studying the problem will be, in no small degree, wasted «ffort, as methods that may apply to one soil may injure a soil of different character. As has already been pointed out, terraces must be adjusted care- fully, not only to soil type but to slope. If the protection embank- ment is given too much or too little slope, there is danger of breaks and intensified washing that may exceed that prevailing before the terrace was constructed. In one instance terraces built on Gran- Tille sandy loam, in the southern piedmont region, broke with the first heavy rainfall, causing almost complete destruction of the area involved ; whereas terraces of the same type made on the Wadesboro clay loam at about the same time and with the same slope withstood the rains that destroyed those on the other soil. In this connection it is pertinent to refer to a statement of G. E. Martin, of Oklahoma {14) '• A half finished job of terracing is likely to result in wasted time, wasted efCort, and wasted soil, and tends to bring into disrepute the most satisfactory means, so far determined, of preventing the enormous annual loss of soil fertility which now occurs. This loss constitutes a most serious drain upon the agricultural industry. It is very unlikely that any other industry could suffer such severe losses and survive. The importance of measuring the slope to determine the proi)er spacing of terraces can hardly be over emphasized. Too heavy a grade or too much fall along the terrace line, can defeat the moisture conservation objective and may result in hillside ditches instead of terraces. As an illustration of the important rôle soil character plays in determining the rate of soil erosion, comparisons might be made between the results obtained at the erosion station in subhumid west Texas and those obtained in the humid piedmont of North Carolina. On a 2 per cent slope of the Abilene clay loam at Spur, Tex., 41 tons of soil matter wore lost by erosion from 1 acre of land with 27 inches of rainfall ; whereas at the North Carolina station only 25 tons of soil matter were removed from 1 acre on a 9 per cent slope with 35.6 inches of rainfall. In other words, although the slope in the latter instance was more than four times steeper than that in the former instance, the eroded material was very much less on the steeper slope. It is not the purpose of this circular to go into the details of methods for preventing soil erosion, but rather to point to the evils of this process of land wastage and to the need for increased practical information and research work relating to the problem. Instructive bulletins have been published by the United States Department of Agriculture and by the States containing details relating to the best- known methods of checking soil erosion and of filling gullies. Bulle- tin No. 512, Prevention of the Erosion of Farm Lands by Terracing (i^), published by the United States Department of Agriculture, is especially instructive in connection with the theory and the practical side of terrace construction; and Farmers' Bulletin No. 1386, Ter- racing Farm Lands (19), is another useful bulletin relating to the subject. SOIL EBOSION A NATIOSTAL MENACE 21 THE WARNING OF A GEOLOGIST In his address before the Conference of the Governors of the United States, held at the White House in 1908, T. C. Chamberlin, of the University of Chicago, had the following to say in relation to erosion (5) : Let us turn at once to the basal factor in the problem, the rainfall, the soil, and the soil-wastage, the special theme of this hour. The rainfall is an inherited asset, the soil is an inherited asset . . . but reckless soil-wastage is a serious error. Soils are the product of the atmosphere and its waters modifying the rock surface. When the atmospheric waters have aided the air in producing soil by rock decay they may pass, on the one hand, into plants or back to the surface soil, and thence to the atmosphere by evaporation, or, on the other hand, they may pass on down to the ground-waters and thence into the streams. The alternative is to rush away as foul erosive floods on the surface, wasting soil and plant food, guUyiug the surface, choking the ravines, flooding the valleys, silting the pools, filling the reservoirs, sweeping out the dams, barring the streams and clogging the harbors. If it shall be found that all or nearly all the waters should go into the soil and thence into the underdrainage, coming out slowly and steadily by seepage and by springs into the streams, clear and pure, tlxese streams should present nearly ideal conditions for water-food, for power, and for navigation. The solution of the soil problems may therefore be, in large part, the solution of the whole complex of problems of which navigation is the last term. While soils are formed by the action of the atmosphere and its waters on and in the underlying rock (aided by plants and animals), their surfaces are carried away by wind and wash. At any instant, then, the depth of the soil measures the lag of removal behind production. We have as yet no accurate measure of the rate of soil production. We merely know that it is very slow. It varies obviously with the kind of rock. Some of our soils are derived from material already reduced to a finely pulver- ized condition. Such are the lowland accumulations from highland wash. Such also is the glacial drift, rockflour rasped from the face of the ledge by the glacial file, and ground up with old soils. On such a base of half-prepared material, soils may be developed with relative rapidity ; but even on these, when the slope is considerable, wind, wash and cropping remove the surface much too fast for stable fertility. . . . Without any pretensions to a close estimate, I should be unwilling to name a mean rate of soil-formation greater than one foot in 10,000 years on the basis of observation since the glacial period. I suspect that if we could positively determine the time taken in the formation of the four feet of soil next to the rock over our average domain, where such depth obtains, it would be found above rather than below 40,000 years. Under such an estimate, to preserve a good working depth, surface wastage should not exceed some such rate as one inch in a thousand years. If one chooses to indulge in a more liberal estimate of the soil-forming rate, it will still appear, under any intelligent estimate, that surface wastage is a serious menace to the retention of our soils under present modes of management. Historical evidence enforces this danger. In the Orient there are large tracts almost absolutely bare of soil, on which stand ruins implying former flourishing popu- lations. Other long-tilled lands bear similar testimony. It must be noted that more than loss of fertility is here menaced. It is the loss of the soil-body itself, a loss almost beyond repair. When our soils are gone, we too must go, unless we shall find some way to feed on raw rock or its equivalent. The immense tonnage of soil-material carried out to sea annually by our rivers, even when allowance is made for . . . material derived from the river channels, is an impressive warning, of the danger of negligent practices. Nor is this all ; the wash from one acre is often made the wastecover for another acre, or for several. Sometimes one's loss is another's gain, but all too frequently one's loss is another's disaster; and the 1,000,000,000 or more tons of richest soU- matter annually carried into the sea by our rivers Is the Nation's loss. Some of the soluble substances . . . formed at the base of soils are neces- sary plant food, while some are harmful; but what is more to the point, all are harmful if too concentrated. There is need therefore that enough water pass through the forming soil, and on down to the ground-water and 22 CIRCULAB 33, U. S. DEPABTMENT OF AGBIOTTLTTJBE out through the underdrainage, to carry away the excess of these products An essential part of the best adjustment is thus seen to lie in a. prlptaw^'-. ttonmentof the amount of water which goes through the soils. If this be not enough the plants will suffer from saline excess; if it be too much, the plants may suffer from saline deficiency. piauis foi^/'f^ *^®°,'^"® ^ series of possible excesses and deficiencies; between them falls the golden mean which gives best results. Thus the problem of soil management is a problem of proper balancings and adjustments, a problem to be solved by science and common-sense forced to their best by the enerev and intelligence of the American farmer. energy The key to the problem of soil conservation lies in due control of the water Ä/< KP^, °l T^ ^"^- ^^l^ ^''^^'^ *' *° ^^«et °i great possible value. It should be looked upon as such. It should be computed by every acre-owner as a possible value saved if turned where it will do good, lost if permitted to ^^n ^away. doubly lost if it carries also soil values and does destructive work Experimental studies have shown that, on the average within our domain crops can we to advantage all the rainfall durinff the growing season and that »n most cases crops are the better fw all the stmed supplies that can be carried over from the nwirgrowing seasons. This greatly simplifies the general prob- lem, for it justifies the conclusion—to which there are many local excentions of course—that the highest crop values will usually be secured when the soli Is made to absorb as much of the rainfall and snowfall as practicable In securing this maximum absorption and internal soil-work, the run-off ' and hence the surface wash, will be reduced to a minimum. It has already been seen that the wash of even this inevitable minimum is likely to be still too great to keep the proper slow pace with soil-generation, when the surface has much slope . . The practical problem then lies almost wholly in retalninff and passing into the soil the maximum of the precipitation. Obviously this gives the minimum of wash to foul the streams, to spread over the bottom lands to choke the reservoirs to waste the water-power, and to bar up the navigable rivers. The solution of the problem for the tiller of the sail essentiallv solv^ the whole train of problems running from farm, to river and from oroo-oro- duotion to navigation. ^yi^ti-t„u LOOKING FORWARD It must be stated that this circular does not undertake to tell the full story of the appalling wastage being caused by soil erosion. It merely refers briefly to some of the working processes of this greatest enemy to the most valuable asset of mankind (the agricultural lands), to some minimum estimates relating to the damage wrought and to the meagerness of fundamental data concerning the prob- lem. To visualize the full enormity of land impairment and devas- tation brought about by this ruthless agent is beyond the possibility of the mind. An era of land wreckage destined to weigh heavily upon the welfare of the next generation is at hand. Indeed, what has happened already and what is going on at an ever-increasing rate of progress is pressing upon many thousands of farmers now strug- gling to win subsistence from erosion-enfeebled soil. That the e^l process is gaming momentum is due to the wearing away of the topsoil, which was more productive and more resistant to rainwash than the subsoil that is taking its place. That some 15,000,000 acres or more of formerly tilled land has been utterly destroyed by erosion m this country is but an insignificant part of the story, for It IS the less violent form of erosional wastage, sheet erosion, that is doing the bulk of the damage to the land. Land depreciation by this slow process of planing off the surface is of almost incalculable extent and seriousness, and since the denudation does not cease when the subsoil IS reached, there must be in the near future, unless methods of land usage are very radically changed, an enormous increase in the abandonment of farm lands. Circular 33, U. S. Department of Agriculture PLATE II • • A.—Wind erosion, ( he rosuU. of druuglit and trampling, New Mexico. Excessive concentration of cattle near'permanent water during drought periods results in serious trampling. Wind has removed 5 or fi inches of soil, exposing the roots of the few remaining plants to desiccation B.—Fire has destroyed the vegetation, and the steep slopes are rapidly washing away (California) circular 33, U. S. Department of Agriculture PLATE 12 A.—A barren waste. Smelter fumes liave destroyed tlie vegetation (Arizona) B.—AH the herbaceous vegetation has been destroyed by overgrazing. The brush and timber are insufficient to prevent serious sheet and shoe-string erosion and excessive soil deterioration SOIL EEOSION" A NATIONAL MENACE 23 What would be the feeling of this Nation should a foreign nation suddenly enter the United States and destroy 90,000 acres of land, as erosion has been allowed to do in a single county ? Any American of live imagination knows that the people of the United States would willingly spend $20,000,000,000 or as many billions as might be necessary, to redress the wrong. Because rain water was the evil- doer in this instance, which is but one of many, is the act forgive- able and is there no occasion for concern about it ? It is not necessary to go to China or to some other part of the world for examples of what eventually happens to unprotected slopes of cultivated areas. There is an abundance at home, not yet so vast in area as in China, but just as bad, and by no means small. It is well to observe, however, that millions of human beings have been driven out of the wasted uplands of China into the valleys of the great rivers, where the population is so dense and the land so com- pletely used that even the roots of grain crops are dug for fuel. China cut the forests from the uplands and made no provision for protecting the bared slopes. Erosional débris sweeping out of these wasting highlands has rapidly extended the river deltas and made floods ever more difficult to control. After 4,000 years of building dikes and digging great systems of canals, the Yellow River broke over its banks and brought death to a million human beings during a single great flood. During one flood that great rirer, known in China as the " scourge of the sons of Han," changed its channel to enter the sea 400 miles from its former mouth. No one, of course, wants anything remotely Uke this to take place in this country, but " coming events cast their shadows before." That the greatest flood of which we have reliable records came down the Mississippi in 1927 was a prophetic event. G. E. Martin's statement (14) about erosion as an enemy to agriculture—" It is very unlikely that any other industry could suffer such severe losses and survive "— is prophetic. That bare land at the Missouri Agi-icultural Experi- ment Station was found to be wasting 137 times faster than land covered with bluegrass, on a slope of less than 4 per cent gradient, is prophetic. That many millions of acres of cut-over land lie bare and desolate and exposed to the ravages of fire and erosion, with but pitifuUy little done toward reforestation, is prophetic. That mini- mum estimates show that the rate of plant-food wastage by erosion is twenty-one times faster than the rate at which it is being lost in crops removed, is prophetic. These shadows are portentous of evil conditions that will be acutely felt by posterity. Shall we not proceed immediately to help the present generation of farmers and to conserve the heritage of posterity? -T • j The writer, after 24 years spent in studying the soils of the United States, is of the opinion that soil erosion is the biggest problem confronting the farmers of the Nation over a tremendous part of its agricultural lands. It seems scarcely necessary to state the perfectly obvious fact that a very large part of this impoverishment and wast- age has taken place since the clearing of the forests, the breaking of the prairie sod, and the overgi-azing of pasture lands. A little is being done here and there to check the loss—an infinitesimal part of what should be done. 26 CIECULAE 33, U. S. DEPARTMENT OF AGKICULTUEE grass land alone, they have burned over annually from 1916 to 1921 an average area of 336,000 acres. {15) In the southern Califor- nia brushfields, one may see a 1,000-acre burn wherein practically all of the vegetation, which required years to grow, was destroyed in a few hours. When one stands in several inches of ashes on an ex- tremely steep slope in the center of such a burn, knowing that the humus, "the life of the soil," has been consumed and that those ashes and the surface layer of soil will be washed down the slope with the first dashing rain, he realizes how great is the soil destruc- tion from fire and erosion. (PL 11, B.) MINING Hydraulic mining along streams throughout the West tore out the valleys and sides of gulches, leaving the débris in the creek beds for high water to carry down to fill the lower river channels or to spread like a wasting hand over fertile farm land. This destruc- tion has been especially severe in California but is now under regulation {16). Smelters, an adjunct to mining, depleted several hundred thousand acres of western range land and completely destroyed the vegetation on a considerable part of it. (PI. 12, A.) Bennett has already m this circular noted the excessive erosion on the denuded slopes. Damage is still being done, even though in some places recent abate- ment measures have reduced smelter-smoke injury materially. OVERGRAZING Following 1870 there was a rapid expansion of the range live- stock industry in the West, especially in sheep raising. By the late seventies the expansion in cattle was in full swing and pressed on with prospects for a rich harvest (i, 22,23). As numbers of livestock increased the palatable forage plants were grazed closer and closer and their vigor was sapped. Instead of thick grass knee high, of which the early stockmen speak, there were shorter and sparser grass blades and stems; finally many of the plants gave up the struggle, and the stand was thinned. The less valuable plants were then grazed more severely, until they too were practically eliminated. The hungry animals in their search for feed trampled the range, destroying plant roots and packing the soil. The ranges became dust beds. Eesidents of Utah tell of being able to count the herds of sheep on the mountains by the dust clouds rising as the sheep trailed through the country. Under such conditions there was nothing to check the rain as it fell; the more compact soil could not absorb the water, which ran off and was quickly converted to a slimy mass of flowing mud. Shoe-string gullies started and speedily gained depth, while the main drainage channels became raging torrents. The rich friable surface soil was washed away and the heavy clay subsoil exposed. Even before 1890 there were more livestock on the ranges than they could support satisfactorily. Oversupply brought a drop in values and caused a greater proportion of animals to be held on the range, until the drought of the early nineties, coupled with the greatly reduced feed supply, wiped out large numbers by starvation and forced stockmen to sell countless others at a loss. SOIL BBOSION A NATIONAL MENACE 27 Thus the stockmen have been, in part, victims of circumstance. Under " free," unregulated, and competitive grazing the range of any stockman who endeavored to have plenty of feed on his range vs^ould be eaten out by tramp stoclanen who were eager to find such " pick- ings." Then, too, with drought reducing the feed supply 40 per cent or more in a year, it was impossible without control to make the adjustments necessary to assure reserve feed. When prices were high everyone desired to hold stock in the hope of profiting by the rise, and when prices broke there was at times no market whatever for the surplus animals. All of these factors tending to overstock- ing and overgrazing developed conditions unusually favorable for soil destruction, and there were few ranges of the West which did not suffer severely from erosion in the nineties, a considerable part of which is not yet checked. The regulation of grazing within the national forests and the con- solidation of private holdings have greatly reduced the area of range overgrazed, but extensive areas throughout the West are still deteriorating through excessive or otherwise improper grazing use. (PL 12, B.) The most serious situation at present is that on the 196,000,000 acres of unappropriated and unreserved Federal lands with their unfenced, intermingled State and private lands, on which grazing can_ not now be legally controlled. Much of this public domain lies in the foothills and should furnish the abundant spring and fall feed essential to profitable livestock production. Drought and overgrazing, however, are seriously impairing the feed and watershed values of large expanses of these important Federal lands by robbing them, through erosion, of the soil material necessary to maintain a protective covering. OTHER AGENCIES Other agencies, such as the building of roads and trails, the culti- vation of steep slopes, the clearing of timber and brush from moun- tain-valley bottoms, the draining of wet meadows to facilitate cul- tivation, and the straightening or changing of stream channels, have come about with settlement and have caused erosion of range lands. These, with the exception of attempted hillside farming, have not as a rule caused sheet or shoe-string erosion of the slopes, but by cutting out the rich valley bottoms they have caused considerable damage. Rodents, mentioned earlier by Bennett, by denuding some range areas have thereby caused erosion. The early roads and trails followed the watercourses through the foothills and mountains. The sod was broken on the slopes, so that water might accumulate and start cutting runways. (PI. 13, A.) The natural beds of streams were altered to allow teams and wagons to pass, and the water was thus aided in its cutting process. Even to-day trie construction of mountain roads without proper drainage is a common cause of unnecessary erosion. Bates {£) found, in logging the timber from a mountam wastershed in Colo- rado, that the scar left by the logging road was largely responsible for an increase of 519 per cent over normal in the sediment eroded from the watershed during the fourth year after cutting. Her- baceous and shrubby vegetation quickly reclaimed the rest of the area, however, and protected the slopes from undue erosion, 28 OœCDLAB 333 V. s. DEPABTMEITT OF AQBIOUMUM valley was™ ou S toVarf í,„To,,??-° 'K»"-eam bed in thi «e/^lHes or ^^.^i^.tt SS^an'd 'd:^^?'"?^"'?^; Many of these arroyos are now 10 to 30 feet deen nnrl inn f ^. more in width whilp tho inr-^ûr. „^^ "" j.eet ueep ana lUO teet or wider drainage Tines On v fn ni^"'""" V''^ '".* ^^^P«'" ^"^ still accelerating the flow of water over fL fnl)/ f K^l^ ^""^^^ '^y SAS:St^¿tAAB¥!n^ ^^ZSSÍ ÄanlÄe!!^ Wa^^^^^^^^^ watershed of AdzoL^was destíoyíd bvT^J'"^''' *^' ^\' ^^^^^ age over this reIativelyTmaKrTtÄir$522%S^^^^^ *^^ '^^"^- THE SERIOUS EFFECTS OF THE EROSION the'^greSrqSütieTofiilÍTrri?; f^''''''\ "^^^^^-^d slopes, high^ater Lrt"iriïiL;r ¿to'toïSs'^Z^ FLOOD DAMAGE TO MOUNTAIN VALLEYS of the land to be protected was at that tim^ (1916) ."gpro„wX »;AT.',íS.Aí'=O;!. 'sîrîss ter ,SS,äT WATERSHED HAND- circular 33, U. S. Department of Agriculture PLATE 13 A.—Water accumulated in the wason tracks and cut these gullies (Montana) B.—Arroyo on Muddy Creek, Colo. The barn is about to be undermined Circular 33, U. S. Department of Agriculture PLATE 14 A.—Flood control fence constructed with iron posts to reduce velocity of flow, induce sUtinE. and prevent bank cutting in a large drainage (Arizona) B.—The establishment oí grass in a gully tended to check further cutting (Arizona) Circular 33, U. S. Department of Agriculture PLATE 15 A—Muck, driftwood, and otlier debris deposited in a young oranKO orcliard by flood from hills made barren by fire ^^ i. , ■ i.—Salt Kiver, in slight flood stage, undercutting silt banks i Keservolr basin and carrying the mud down nearer the dam B.-SaÍt''KÍve°r,''m"lf t l t , tti ilt in the upper part of the Koosevelt 32 CmCULAE 33, U. s. DEPARTMENT OF AGRICULTURE Station in Utah. After herbaceous vegetation had improved until It covered^ per cent of the soil surface, the run-off from summer rams was 55 per cent less, and sediment eroded 56 per cent less than when the vegetation covered but 16 per cent of the surface. Eun-off and erosion from melting snow appeared to be affected much less bv the change in herbaceous vegetation. Though approximately 95 per cent ot the annual run-off was from melting snow, it carried only 12 per cent of the sediment removed ; the 5 per cent of run-off from sum- mer rams carried 88 per cent of the sediment eroded annually Thus under the conditions prevailing in the experiment, the greatest need IS tor vegetation on the range to prevent the great erosion damage irom summer rains. Sometimes the range improvement is extremely slow, but everv bit o± progress helps not only in reducing erosion but in increasing the grazing value of the land. At the 1927 field day of the Great J^asin Jiixperiment Station it was shown that on an area on which the vegetation had been all but destroyed in 1903, the soil was so badly eroded and depleted that it had not yet built up to where it would support a stand of valuable forage species. Even so there had been a notable increase in carrying capacity. In 1927 7 4 acres were required to support a cow for a month. On another area on which the stand of vegetation had been badly depleted but on which the soil was not so wasted, and adjoining a hillside where grass plants still remained under the protection of brush so that seed was ^^ifr u ' * ^^^^^^ iisnse cover of valuable plants had become rees- tablished by 1927, and only 2.4 acres were required to support a cow a month. The greater part of this improvement has come in the last five years. The rate of improvement depends largely on the quantity of plants on the range which reseed or otherwise re- vegetate readily and on the methods of range management applied to aid recovery. In the Southwest rather badly depleted ranges can, with proper grazing, be reestablished, with three or four times as "auch forage as they are now supporting, in about five years. The value of trees, shrubs, and grass for bank protection along small stream courses should be better appreciated, so that efforts will be made to protect them or to reestablish the stand if it has been destroyed. REGULATE GRAZING Stockmen are recognizing that conservative grazing keeps their animals m a good, thrifty condition throughout the year, increases the number of young produced, reduces death losses, and increases the weight and finish of salable animals, thus affording top prices and profitable production. Conservative grazing implies placing no more livestock on the range than the feed will support, and allowing the palatable plants to get enough of a start in the spring so that grazing will not impair their vigor. It also implies removing the livestock m the fall before the soil becomes so wet that trampling would injure it, imless the range and soil are of a character that allows yearlong use. A certain reserve of feed as an insurance against the ever-recurring drought is essential to assure sustained livestock production and watershed protection. Also, distribution of livestock over the range so as to obtain as even a use as practicable without undue concentration or trampling is important. SOIL BEOSION A NATIONAL MENACE 33 There are areas on which erosion injury is now occurring that could be greatly improved if grazed by a different class of live- stock. This is true of certain rough mountain ranges where attempts to get full utilization of the feed on Äe range as a whole by cattle grazing is causing undue concentration in valleys and consequent erosion damage. Sheep would use the slopes to better advantage and could be more easily held off the damaged valley areas. Cer- tain brush areas could be grazed more profitably by Angora goats than by the cattle and sheep now grazing there, bringing about improvement in the watershed and erosion conditions. Likewise, on some areas a change from sheep to cattle would prove desirable. Deferred grazing or deferred and rotation grazing, which provides for reserving grazing from part or all of areas of range land until after seed maturity, although now widely applied, deserves more extensive use throughout the West. Other similar improved sys- tems adapted to specific soil and forage types need to be devised or further developed so as to improve range lands without loss of use of the range forage. Experiments at the Great Basin station and on the Jornada and Santa Rita Range Reserves in the Southwest indicate that, except where the vegetative stand has been practically eliminated and the exposed soil is seriously eroded, the native cover can ordinarily be restored under properly regulated livestock graz- ing almost as well and as quickly as under total protection from grazing. Furthermore, the range can more easily be maintained at its best with grazing than without. Some form of control of the unappropriated public domain is essential if it is to be restored. Most stockmen will agree that it should probably take the form of Federal regulation. PROTECT THE COVER AGAINST FIRE In recent years there has been a great awakening of the public to the need for fire prevention and quick suppression, especially in timber and brush lands. Most Western States have stringent laws regarding carelessness with fire, but, as brought out above, 336,000 acres of brush and grassland are burned yearly in California alone. The possible erosion danger should be carefully considered before fire is set with a view to improving the range. Under regulation, excessive grazing is sometimes practiced as a fire-prevention measure ; but this in turn causes erosion, reduced feed values, and usually uneconomic livestock production. With depleted vegetative stands thé fire danger is not great, but as the vegetation on range lands is improved for watershed protection it will be necessary to give more attention to fire protection. AID EROSION CONTROL BY ARTIFICIAL MEANS Artificial reseeding of range lands to known cultivated forage plants has not proved practicable except on areas with unusually favorable soil and moisture conditions. Tests are being made, how- ever, of a number of species that show some promise. These tests deserve considerable expansion. In the meantime, management of the native vegetation so that it may serve to best advantage will be the main means of revegetating depleted areas. Of course, on im- 34 CIBCULAE 33, TT. S. DEPABTMENT OF AGBICTILTUBB portant watersheds where the value of the stand is not alone deter- mined by Its grazing value it may pay to seed for erosion control, bampson and Weyl (21) &und terracing and planting of steep, barren, eroded, high-mountaffl? hillsides to native plants possible but costly Ihey urge such methods on areas that have eroded to such a point that natural revegetation is extremelv slow and the vegetation present noneffective in binding the soil and in preventing erratic run-oii. "^ Engineering works for the control of erosion have been used ex- tensivelv in the mountain regions of Europe. Large dams for hold- ing back flood crests or even for the catching of excessive silt have been established in a few places in the West. Check dams, small structures of rocks, logs, brush, or other materials, have also been constructed in the smaller stream channels, largely for the purpose ot reducing the velocity of the water and thereby its carrying and cutting power. Such works are usually costly and unless thev are supplemented with the maintenance of the highest type of vegeta- tion the land is capable of supporting are apt to prove ineffective As the importance of erosion control is recognized, however engi- neering works, especially check dams, will doubtless come into greater use. CONCLUSION With erosion losses on western grazing lands so great, corrective action must be taken soon if far gi-eater damage and more difficult control are to be obviated. Owners of range land should consider the use of their land not alone for immediate gain, but still more in the light of the future productivity of the range, the protection of water supply, and stream-flow regulation. Overgrazing should be stopped at once; control or regulation of the badly abused unappro- priated and unreserved public domain should not be longer delayed by the Federal Government. Arroyo cutting must be checked by engineering works and the establishment of vegetation in the bed j ?^ *o ® ^^^^^ °^ ^^^ arroyos. Range landowners, irrigationists, and the btate and Federal Governments should band together to use every available means for checking erosion, floods, and inadequate water supply at their source, on the slopes, in gullies, and on small drainages of the watersheds. The Federal Government has a direct responsibility since Federal lands occupy such a large part of the West. The main obstacle to action and one that has greatly delayed remedial measures has been lack of information as to the seriousness of the situation and as to concrete things which should be done under specific conditions. Without this information it is possible to work only m a broad way, rather than to attain a permanent control of erosion on range lands in a really constructive and economical man- ner. In view of the important part that herbaceous and shrubbv v-egetation play in controlling erosion of such lands it is essential that research determine just what is the optimum stand of vegetation that can be made to grow on the widely varying soil types and under the extreme climatic conditions of the'West and the influence of this vegetation on water supply. It is equally important to know more