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I-VDUSTRIAL AND ENCINEERI-VG‘ CHEMISTRY
lose industries, is more largely dependent upon mechanical operations, it nevertheless deals with a complex chemical material and a wider recognition of this fact in the industry might well result in notable advances. This is the more true since rayon has been finding its way into cotton textiles in increasing amounts. For example, every cotton man knows how the strength of cotton varies with the moisture content, yet the reason for this is not fully understood. It would be very helpful to have a thorough knowledge of the relationship between the physical properties of cotton and the character of the soil on which it was raised. Such a study might lead to ways of controlling certain desirable properties and possibly even of varying them a t will, and might perhaps also throw light o n the perplexing problem of “neps.” The work might well be extended to include a study of the effect of chemical properties on the various physical characteristics on which depends the successful use of cotton fiber in the various textile operations. It is recognized that certain natural impurities in fibers seem to have an effect on these properties and the study of these impurities and their effects might well yield valuable results.
Vol. 18, No. 10
Mercerization is an example of what the treatment of cotton as a chemical material has done for the textile industry, and it is not inconceivable that further application of this same point of view might produce even more valuable results. Perhaps the one development which would bring the textile chemist to realize this more quickly than any other would be the appearance of an inexpensive, strong synthetic fiber, and this is by no means beyond the range of possibility. Conclusion
Regardless of whether the future shows that the trends which have been noted above develop as anticipated or whether some now unforeseen discovery changes the course of cellulose chemistry into quite other channels, one fact at least should persist. The recognition of cellulose in its various forms as a chemical raw material has resulted in great advances both in industry and in science during the past fifty years. The continued study of cellulose from this standpoint and the application of the results of these studies to industry should combine to maintain cellulose, not only as the most common chemical raw material from the vegetable kingdom, but also. in the aggregate, the most valuable one.
Future Trends in Soil Conservation1 By Jacob G. Lipman &?EW JERSEYAORICULTURAL EXPERIMENT STATION, NEWBRUNSWICK, N. J.
OOD-EXPORTING as well as food-importing countries compete with one another in the world’s markets. It is a competition of soils, of climates, of farmers, and of selling organizations. No small part is assigned in this competition to soil-fertility factors, including soil deterioration and soil maintenance and improvement. The advantage possessed by land of virgin fertility is a transitory one, but while it lasts, and as long as there are reserve areas to be brought under the plow, it often goes hard with the tillers of older soils. At best there is but a small margin of profit in the growing of staple crops such as wheat, oats, and cotton. It is easy to change profit into loss when untoward seasonal conditions, or attacks by insects and fungi, seriously reduce the yield. It is no less easy to reach low levels of production and to encounter years of adversity when the plant-food capital of the soil begins to shrink, when physical soil deterioration takes place, when the biological machinery of the soil no longer functions a t its best. After all, we cannot regard the soil resources of our country, or those of any other country, as a matter of purely local concern. Food surpluses are in effect soil surpluses, and food surpluses will flow in the direction of a partial food vacuum. The meaning of this comes clearly to us as we think of seed time and harvest in the far-flung regions of the northern and southern hemispheres, of the desperate efforts in many countries to wrest a maximum yield of human and animal food from the soil. Is there not ample reason, then, for our asking the chemist and biologist to tell us something about our soil resources and their bearing on our present and potential supply of food?
F
Our Soil Resources
The authors of the excellent essay on “The Utilization of Our Lands for Crops, Pasture and Forests”2 note with much justice that: 1 Paper No. 299 of the Journal Series, New Jersey Agricultural Ex periment Station, Department of Soil Chemistry and Bacteriology 2 Yearbook, U. S. Dept. Agr., 1929, p. 415.
The dominant characteristic of American economic life has been abundance of land resources. The assumption of this abundance has colored our habits of thought and become the essential foundation for our economic policy, both individual and public. This national tradition was iirst seriously challenged by the conservation movement, which caused our people to pause and consider whether our amazing population growth and two centuries of exploitation of natural resources might have altered the outlook.
Since this was written the post-war adjustments have gone somewhat farther. It has become more evident that our present methods of land and soil utilization are to be held accountable, in part a t least, for the economic depression in some of our agricultural regions. 4 s a basis for our consideration of the soil resources of the United States, we should note that the continental land area of the country is equivalent, in round figures, to 1,903,000,000 acres. The census returns of 1919 show that this area was used as follows: Crop harvested Humid grassland and pasture Farmland not in harvested crops pasture or forest Forest, including cut-ovez and burnt-over land pastured Semi-arid and arid pasture Forest, including cut-over and burnt-over land not pastured L-rhan, desert, marsh, roads, and railroad TOTAL
Acres 385,000,000 23 1,000,000 115,000,000 237,000,000 587,000,000 248,000,000 122,000,000 1,903,000,000
The present or future value of the different areas for agricultural uses must be determined primarily by climatic conditions. East of the one hundredth meridian the annual precipitation ranges from 20 to 60 inches. The corresponding amounts in the Great Plains area are 12 to 20 inches, while in portions of the Rocky Mountain Plateau states it is usually less than 10 inches. I n some localities in the Gulf states the annual precipitation is from 55 to 60 inches, while portions of the Pacific Coast states receive as much as 80 to 120 inches. Furthermore, it is not alone the total amount of precipitation, but also its seasonal distribution,
October, 1926
IiVD USTRIAL A N D ENGINEERING CHEMISTRY
that may become an important factor in the developing of policies of soil conservation. Temperature is another of the important factors that affect soil conservation policies and practices. According to the authors of "Weather and Agriculture:"3 Two significant values of daily mean temperature for agriculture may be mentioned, those of 50' and 68" F., and the duration of these for l, 4, and 12 months has been made a basis of certain classifications. The polar limit of trees and the more hardy food crops is fairly well outlined by the isotherm of 50' F. for the warmest month of the year. Near this line are found the last groups of trees in the tundras. A temperature of 50' F. for 4 months closely coincides with the polar limit of the oak and of wheat cultivation.
In general, the following classification of temperature in relation to plant life may be made: (1) Tropical belt, with all months warm-that is, the temperature averaging over 68" F. (2) SFbtropical belts, with 4 to 11 months warm-averaging over 68 F. (3) Temperate belts, with 4 to 12 months of moderate temperature, 50" t o 68' F. (4) Cold belt, with 1 t o 4 months temperate, and the rest cold, below 50" F. (5) Polar belt, with all months averaging below 50" F.
Aside from precipitation and temperature, light and the intensity of sunshine become factors in the utilization of solar energy. For instance, of the possible amount of sunlight the North Pacific coast receives 40 per cent, while the far Southwest receives 90 per cent. But since the plant is in a sense an engine operated by solar energy, it becomes evident that the soil, rainfall, temperature, and the amount of direct and diffused sunlight all participate in determining the amount of plant growth. The latter, in its turn, influences the accumulation or dissipation of carbon and nitrogen in the surface soil, the extent of erosion and leaching, the translocation of the mineral constituents of plant food, and the nature of the soil fertility reserves. The combined effect of soil and of the different climatic factors serves to determine the extent of forest, steppe, and desert. It likewise determines the nature and success of agricultural operations. To quote again from ''Weather and Agriculture:" Where farming operations are conducted in the drier regions larger farms are necessary. In Nebraska it has been found t h a t in some of the table-lands in the western portion of the state, where the rainfall is less than 20 inches, about six times as much land is required, under natural conditions, t o produce a given amount of plant matter as is needed in the southeastern portion, where the rainfall exceeds 30 inches.
As a result of unlike climatic conditions we find striking differences in the character of the plant cover and its ability to support animal life in different regions, as shown in Table 1.4
It must suffice here to call attention to the scantiness of the vegetation on much of the grazing area, and to note that over-grazing, a fairly common evil of the present day, easily leads to serious soil deterioration. By way of contrast it may be observed that an animal unit is carried on only 4.22 acres of humid pasture in the United States, while the average acre of pasture in Germany will carry a cow on less than 1 acre. In view of the fact that "livestock consume about three-fourths of the product of the improved land and practically all the product of the unimproved pastures and grazing lands within and without farms," the inference is obvious that policies of soil conservation affecting rnore than one billion acres of land must reckon with the reciprocal relation of soils and animals. 8 4
Yearbook, U. S Dept. Agr., 1924, p. 457. I b i d . , 1921, p. 251.
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Table I-Character
of F o r a g e and E s t i m a t e d C a p a c i t y of W e s t e r n G r a z i n g Areas of the U n i t e d S t a t e s Len t h Area to 0% support season a cow Areas Chief forages Months Acres Northern Great Plains Grama, mama-buffalo, 5 to 8 15 to 25 wheat grass 5 t o 10 15 t o 25 Grama-buffalo Southern Great Plains 3 to 5 25 to 30 Grama. short grasses Black Hills 20to25 Central Rocky Mountains Mountain weeds and grass 3 to 5 New Mexico-Arizona Grama grass, browse 6 to 12 25 to 30 mountains West Central-Northwest35 to 40 3 to 7 Pine grass ern Montana 3 to 6 20 t o 2: Short grasses Southwestern Montana h'orthern Rocky Moun3 to 6 60 to 150 Bunch grass, browse tains Bunch grass, weeds, browse 3 to 7 2.5 to 30 Central Idaho Wasatch, Uinta, and Wyo3 to 7 20 to 25 Grass, browse ming Mountains Northeastern Nevada, Southern Idaho, and Bunch grass, sagebrush 4 to8 35to40 Central Oregon East Central Nevada 4 to 6 25 to :0 Bunch grass, browse mountains Sagebrush, shadscale, Wyoming semideserts grease-wood, short 80 to 100 2 to 4 bunch grasses 2 to 5 75 to I50 Browse Utah-Arizona deserts New Mexico-Arizona footBrowse, tobosa, grama hills 4 to 8 30 to 60 mass San Luie Valley of Colorad0 Greasewood, salt and short grass 7 to 9 30 t o 4 0 Saaebrush. bunch, salt, and Utah foothills and valleys June grasses 5 to 7 25 to 30 Mohave Desert of California Annual weeds, browse 640 Nevada semideserts Shadscale, greasewood browse 1 to 4 75 to 150 Southeastern Oregon and Sagebrush and bunch Snake River plains grass 2 to 5 50 t o 100 Columbia River basin Bunch grass 7 to 9 10 to 30 Eastern California mounBrowse and bunch grass 3 t o 6 25 to 35 tains Western Oregon mountains Browse 3 to 7 75 to 100 Southwestern California Browse 6 to 12 40 to 60 mountains California-Oregon mounGrass and weeds 6 to 8 10 to 25 tain valley
...
Granting, then, that our soil conservation policies must take into account factors external to the soil itself, among them climate, topography, and certain economic and social factors, we may proceed with the examination of the soil as a mine and as a laboratory. It is a mine in the sense that it contains varying amounts of the raw materials needed for the production of plants. It is a laboratory in the sense that it is the seat of chemical and biological changes whereby mineral and organic substances become a part of the soil solution and ultimately find their way into growing plants. As a source of raw materials for plant building, soils are extremely variable in character. Many thousands of analyses have been made of soil samples derived from widely different regions. We are in possession, therefore, of reasonably accurate data concerning the amounts of carbon, nitrogen, phosphorus, potassium, sulfur, magnesium, and calcium present not only in the surface soil but also in the subsoil. Moreover, we have a sufficient number of determinations of iron and aluminum as major constituents, and of manganese, titanium, barium, strontium, and others as minor constituents to permit of our drawing more or less definite conclusions concerning the part played by each of these ingredients in the chemical changes taking place in the soil. Without going far afield for illustrations, let us examine, more or less critically some of the soil analyses reported by the Illinois Experiment Station (Table 11). In the upland soils there was found in the plowed depth a minimum of 5 tons of organic carbon and a maximum of more than 43 tons. Roughly speaking, the organic carbon represents one-half the weight of organic matter in the soil. I n other words, the soils in question contained 10 to 86 tons of organic matter per acre to the ploughed depth. I n the swamp and bottom-land soils the average mas much higher, up to 150 tons of organic matter per acre. The quantity of
INDUSTRIAL A N D ENGINEERING CHEMISTRY
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organic carbon found in the 13*/2 inches of subsurface soil was, if anything, less than that found in the 62/3 inches of surface soil. Hence, it would seem the surface soil is twice as rich in organic matter as the same depth of subsurface soil. Moreover, as has been shown repeatedly, the organic matter of the surface soil is much more easily decomposed
Vol. 18. No. 10
more. In this instance the relative concentration is in the subsoil rather than in the surface soil. When the maximum rather than the minimum amounts are considered the range in the surface soil is usually above 20 tons per acre, and in the subsoil above 40 tons per acre. The swamp soils are ordinarily relatively deficient in potassium.
of Illinois Soils POUNDS PEB ACRE Organic carbon Nitrogen Phosphorus Sulfur Potassium 36,000 t o 87,000 3000 to SO00 600 to 1600 300 to 1600 27 000 to 45 000 35,000 to 78,000 3000 t o 7000 1000 t o 2500 400 to 1600 55:OOO to lOb,OOO 16,000 to 36,000 1500 to 3300 500 to 1200 400 to 700 16 000 to 38 000 11,000 t o 23,000 1000 to 2700 400 t o 2000 400 to 1000 3d,000 to Si,OOO 10,000 to 80,000 1200 to 7000 700 to 1500 500 to 1200 23,000 to 40,000 16,000 to 70.000 2000 to 6000 1200 to 2300 500 to 2000 45,000 to 82,000 22,000 to 300,000 2000 to 27,000 1000 to 2000 500 to 2500 8000 to 46,000 20.000 to 740,000 3000 t o 57,000 1800 t o 3000 800 to 52,000 10,000 to 90,000 Subsurface, 6 2 / 3 to 20 inches. Table 11-Analysea
Depth of Character of soil sample Upland prairie Surfacea Subsurfaceb Upland timber Surface Subsurface Terrace Surface Subsurface Swam and bottom- Surface tanasails Subsurface Surface, 0 to S*/s inches. b
I
by microorganisms. The bearing of all this on the maintenance of soil fertility will be considered later. Soil nitrogen occurs largely in organic residues. For this reason soils rich in organic matter are also rich in nitrogen. There is a certain ratio of nitrogen to carbon. In the surface soil this may range from one part of nitrogen to ten or twelve parts of carbon. I n the subsoil the ratio is a narrower one, usually seven to ten parts of carbon to one part of nitrogen. I n soils impoverished by excessive tillage the nitrogen-carbon ratio may be substantially narrower both in the surface soil and in the subsoil. Under conditions favorable for the accumulation of large amounts of organic matter, as in muck or peat soils, the nitrogen-carbon ratio is usually fairly narrow. As to the nitrogen content of soils and subsoils, it will be observed that in the upland soils of Illinois there is a range of 1200 to 3000 pounds per acre. I n the peat and muck soils the relations between soils and subsoils are somewhat different. There is also present in them a much larger quantity of nitrogen. The phosphorus content of these soils is much smaller than that of nitrogen. I n the upland soils we find a range of 500 to 700 pounds per acre, and in the corresponding subsoils a range of 400 to 2500 pounds per acre. Since phosphorus is of rock origin in contradistinction to carbon and nitrogen, which are of atmospheric origin, we should expect to find a t least as much phosphorus in any given quantity of subsoil material as is found in the same quantity of surface soil material. Evidently there is a relative concentration of phosphorus in the surface soil. The significance of this will be discussed later.
Calcium Magnesium 6000 to 25,000 3500 to 12,000 12,000 to 40,000 12,000 to 40,000 4000 to 9000 3000 to 7000 7000 t o 17,000 7000 to 20,000 6000 to 11,000 3000 to 9000 12,000 to 25,000 7000 to 20,000 4000 to 14,000 2000 t o 40,000 16,000 to 85,000 8000 to 40,000
Finally, we may note that in the upland prairies soil calcium is relatively more abundant than magnesium, as compared with the upland timber soils. In the other soils the differences are not so great, even though calcium is usually more abundant than magnesium. We may also note that neither calcium nor magnesium is as plentiful in the Illinois soils as potassium and that there are differences in the relative concentration of potassium on the one hand and of calcium and magnesium on the other, in the soils and subsoils. These differences, together with the ratios of the several plant-food ingredients, have a direct bearing on the lasting quality of the soils. The soils of New Jersey differ from the Illinois soils both as to the origin of the mineral material and the conditions under which it was gradually changed into soil. The rainfall of New Jersey is approximately 50 per cent greater than that of Illinois. There are also marked differences in the range of summer and winter temperatures, in the topography of some of the area, and in the crop history of the several soils. Hence a comparison of the analyses of soils derived from the two states should bring out some interesting points (Table 111). The soils of the heavier type in New JerSey-that is, the Glacial, Appalachian, and Piedmont-show certain similarities to the upland prairie, upland timber, and terrace soils of Illinois. Both groups are well supplied with organic matter, nitrogen, and potash. There are also marked dissimilarities. The Illinois subsoils contain relatively more organic matter and nitrogen than the New Jersey soils. The latter contain more phosphorus in the surface soil and less in the subsoil than do the Illinois soils. There are likewise
of New Jersey Soils POUNDSPER ACRL? Nitrogen Phosphorus Potassium 2000 to 3500 900 to 2200 21 000 to 62 000 500 t o 2500 700 to 1900 21:OOO to 62:OOO 2000 to 6000 1100 to 3500 33 000 to 46 000 1000 to 3500 900 to 3500 33:OOO to 46:OOO 2000 to 3500 800 to 1500 20 000 to 50 000 500 to 2500 500 t o 900 20:OOO to 62,’OOO 600 to 2500 6000 to 25,000 800 to 3000 300 to 800 200 to 1300 5500 to 25,000 58,000 1500 2500 to 3500 10,000 to 54,000 1200 1200 to 2000
Table 111-Analyses Character of soil Glacial Appalachian (residual material of shale, sandstone, and gneiss) Piedmont Coastal plain Limeftone
Depth of sample Surface Subsoil Surface Subsoil Surface Subsoil Surface Subsoil Surface Subsoil
r
Organic carbon 20,000 to 40,000 3000 to 30,000 20,000 to 75,000 6000 to 45,000 20,000 to 45,000 2000 t o 25,000 11,000 t o 31,000 4000 to 9000 25,000 to 40,000 10,000 to 20,000
The content of sulfur is not large either in the soils or subsoils. It is partly of rock and partly of atmospheric origin, and the losses caused by leaching and cropping are, in part at least, offset by the combined sulfur brought down in rain and snow. The average Illinois prairie and timber soil is rich in potassium. There is usually present more than 10 tons of potassium per acre in the plowed depth. As a rule the corresponding subsoil, for any given depth, contains as much, if not
7
Magnesium Calcium 3500 to 9000 6600 to 18,000 1400 to 9000 8600 to 21.000 7000 t o 18 000 15 000 to 30 000 5000 to 14:OOO 15:OOO to 30:OOO 12,000 to 21,000 5700 3500 to 5700 18,000 to 27,000 1400 to 5700 2400 to 5400 1400 to 6400 1200 to 5400 7000 to 11,000 9000 to 18,000 3500 to 8600 9000 to 30,000
differences in calcium-magnesium ratio both in the surface and subsoil of the two groups. Moreover, there are interesting differences in the surface and subsoil content of potassium. The coastal plain soils are very much poorer than are the others in the content of organic matter, nitrogen, potassium, and the other mineral ingredients of plant food. Naturally, this has a direct bearing on the lasting qualities of the soil, its fertilizer requirements, and the size and quality of the crops.
INDUSTRIAL A-VD ENGINEERING CHEAIISTRY
October, 1926
Losses of Plant Food Constituents
Having considered the extent of plant-food reserves in some of the prominent types of soil, we are now ready to measure the losses against the reserves. It is well known that erosion, leaching, decay, and cropping are more or less responsible for the removal of plant food. As to erosion, the case is put clearly by Van Hise5 when he says: At the present time the average rate of denudation in the United States, based upon estimates as to the amount of sediment the streams carry to the sea, varies from one inch in 440 years to one inch in 3900, with an average of one inch in 760 years. This rate of erosion may seem extremely small, but the amount of material involved in it is enormous. I t s total each year is 783,000,000 tons or 610,000,000 cubic yards of surface soil, and this estimate is not more than half of the estimates of others. Before land is cleared there is a close balance between the agencies of manufacture of the soil and its removal by erosion, since originally the soil of the country varied from a few inches to a few feet in thickness. Had the rate of manufacture upon the average been much faster than the processes of erosion, the soil would have been thicker.
The actual effects of erosion and the havoc that it has spread are seen over many millions of acres of land surface once the site of splendid forests or of cultivated fields, but now gullied and eroded into a state of uselessness. Areas thus gullied are often known locally as “bad lands.” “Chemical denudation” is a phrase used by Clarke6 to describe large-scale leaching of the land. He says: To sum up, the crude figures for chemical denudation are as follows: North America South America Europe Asia Africa
Tons per square mile 79 50 100 84 44
Square miles 6,000,000 4,000,000 3,000,000 7,000,000 8.000.000
-
-__.
25,000,000
-
68.4
Total tons 474,000,000 200,000,000 300,000,000 388,000,000 352.000.000
1,914,000,000
Clarke assumes, therefore, that for the 40,000,000 square miles of land which drains into the ocean there is an annual loss of dissolved salts equivalent to 2,491,555,000 tons. This would correspond to 62.3 tons per square mile or about 195 pounds per acre. From the standpoint of soil fertility and soil coiiservation it is essential that we know not only the amount but also the kind of salts that are removed from the soil by leaching. Such information may be had through the gaging of streams and the analysis of surface waters and of the effluent from tile drains. Information thus obtained is more or less incomplete, however, since a portion of the dissolved matter is assimilated by bacteria, protozoa, and algae, and more particularly because the amount of drainage from any given T a b l e IV-Amounts Crop Corn Wheat Oats Cotton Potatoes Alfalfa
Portion of crop Grain and stover Grain and straw Grain and straw Entire crop Tubers only Hay
6
from fields of known history and treatment, furnish fairly accurate information concerning the quantities of the different plant-food constituents lost by leaching. It has been shown that calcium is removed in larger amounts than any of the other constituents. At times it exceeds in quantity all of the other constituents combined. Soils of the better sort lose an equivalent of calcium oxide at the rate of 200 to 500 pounds per acre per annum. Where fertilizer is used the loss may be even greater. In general, the amounts lost will be influenced not only by the soil type, but also by the amount and distribution of rainfall and the cropping methods employed. Nitrogen is also removed in considerable quantities in the drainage. Losses of 20 to 60 pounds of nitrate nitrogen per acre are not uncommon in humid regions. The amount of potassium removed in the drainage is not large, usually less than 10 pounds per acre. Where potassium salts are applied, or where rainfall is abundant and tillage thorough the amounts removed in drainage may be substantially larger. It is stated by Van Slyke’ that the loss in drainage of potassium from the soils in the United States is equivalent to 3,500,000, and of phosphorus to 400,000 tons annually. There are also substantial losses of sulfur, magnesium, and sodium. I n addition, there may be marked losses of nitrogen in very open sandy soils and in arid and semi-arid regions, thanks to the intensive oxidation of the soil organic matter. I n their entirety, therefore, the losses of plant food caused by erosion, leaching, and the decay of organic matter are quite large. Crops removed from the land carry away with them the material that they had taken up from the soil. Everything being equal, the larger the crop the more there is carried away. There are, however, also qualitative differences, for plants grown on rich soils may contain relatively more of certain plant-food ingredients than is contained in similar plants produced on poor soils. Analyses showing the average composition of crops will show us to what extent soil fertility may be depleted by the different crops. A few examples taken from Van Slyke7 will suffice (Table IV). To the amounts of plant food removed by crops there should be added those detached from the soil by leaching and the destruction of organic matter either in processes of burning or of rapid decay. It may be assumed for the purpose of our discussion that the average yield of corn in the Cnited States is between 26 and 27 bushels per acre, of wheat between 14 and 15 bushels per acre, of oats 30 bushels per acre, and of potatoes 100 bushels per acre. The average production of lint cotton is somewhat less than 200 pounds per acre. The yields of alfalfa hay are relatively large and
of C e r t a i n C o n s t i t u e n t s R e m o v e d by Crops
Yield per acre 25 bu. and 1750 Ibs. stover 2
