1999-02-05_GENERAL DOCUMENTS - M1977493 (7)

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50 PHYSICAL PROPERTIES OF MINERAL SOILS Ch. 3 Sec. 3:7 BULK DENSITY OF MINERAL SOILS 1 centimeter. Thus, ' uhicceDt�meter—of_soil.solids weighs 2.6 grams, the In the field, ffMutardensity is .6 grams per cubic centimete>� one cubic centimeter If all the solids to Although considerable range may be obser ed in the density of the of a certain soil were compressed u g Y �t- the bottom,the cube individual soil minerals, the figures .for_most mineral soils usually vary appears as below: would look like this: between the narrow limits c f_2.60._and 2.75. This occurs because quartz, feldspar, and the colloidal silicates with densities within this range usually make up the major portion of mineral soils. When u d PORE SPACES nusual amounts of SOLIDS AND s PORE SPACES heavy minerals such as magnetite, garnet, epidote, zircon, tourmaline, an 1 33g � hornblende are present, the particle density may exceed 2.75. It should be z SOLI DS �1.33 gr y emphasized that the fineness of the particles of a given mineral and the p ..__—.___.___ _ __ ___ _ To calculate bulk density of the soil: arrangement of the soil solids_have nothing to do with the particle density. To calculate solid particle density: Organic matter weighs much less than an equal"volulhe of minecai Solids 3 g g _ __ Volume=1 cm Weight= 1.33 g Volume=0.5 cm3 Weight= 1.33 g erisity o 1.2 having a art_T_Z_ f� to 1.5: Consequentlyy—the amount of this constituent in a soil markedly affects the particle density. This accounts for Bulk density= Weight of soil Volume Weight of solids the fact that surface soils usually possess lower particle densities than do olume of soil Solid particle density=Volume of solids sub P soils. Some mineral to soils high in organic matter may drop as low as Therefore Therefore 2.4 or even below in particle density. Nevertheless, for general calculations the average arable surface soil may be considered to have a particle density Bulk density= 1'�33= 1.33 g/cm3 Solid particle density= 1. 5=2.66 g/cm3 of about 2.65. FIGURE 3:7. Bulk density and particle density of soil.Follow the calculations through *w carefully and the terminology should be clear. In this particular case the bulk density 3:7. BULK DENSITY O F MINERAL SOILS is one half that of the particle density and the percentage pore space is 50. BULK DENSITY. This is a second and different method of expressing soil weighC In t Is case, the total soil space (space occupied by solids and pore Silt loam surface soil is sure to be lower than that of a representative sandy la { spaces combined)is const ere . ulk densitys de niZ' ed-a ( g ) as the mass wei ht loam. E ----- of a unit volume of dry soil.This volume includes both solids and pores.The The bulk densities of clay,clay loam,and silt loam surface soils normally comparative calculations of bulk density and particle density are shown in .,,,,may range from 1.00 to as high as 1.60 grams per cubic centimeter,depending -}. Fig. 3:7. A careful study of this figure should make clear the distinction on their condition. A variation from 1.20 to 1.80 may be found in sands and f'? between these two methods of expressing soil weight. sandy loams. Very compact subsoils, regardless of texture, may have bulk 6 densities as high as 2.0 grams per cubic centimeter or even greater. The y g relationship among texture, compactness, and bulk density is illustrated in FACTORS AFFECTING BULK DENSITY. Bulk density tS a weight measurement l by which the entire soil volume is taken into consideration. Unlike particle Fig. 3:8. density, which is concerned with the solid particles only, bulk density is Even in soils of the same surface texture,great differences in bulk density determined by the quantity of pore spaces as well as soil solids. Thus, soils ;are to be expected when similar horizon levels are compared. This is clearly _-, that are loose and porous will have low weights per unit volume (bulk ! 3shown by data on Wisconsin silt and clay loams in Table 3:3. Moreover, densities an t ose that are more compact will have high values.. Since the there is a distinct tendency for the bulk density to rise with profile depth.This particles of sandy soils generally lie in close contact,such soils have high bulk ' ,apparently results from a lower content of organic matter, less aggregation s.. '- densities. The low organic matter content of sandy soils further encourages '1 and root penetration,and a compaction caused by the weight of the overlying this.On the other hand,the particles of the finer-textured surface soils,such layers. ` as silt loams,_.clay foams,an c ays,ordinar liZ- not rest so close`together. The system of crop and soil management employed on a given soil is This occurs because these surface soils are comparatively well granulated, frkely to influence its bulk density, especially of the surface layers. The a condition encouraged by their relatively high content of organic matter. l dition of farm manure in large amounts tends to lower the weight figure t low ak. Ofsurface soils, as does a bluegrass sod. Intensive cultivation operates in the Granulation encourages a fluffy, porous condition which results in 4 bulk-density values. Consequently, the bulk density of a well-granulated posite direction.