for considerable depth into the subsoil. Once dried and rewet, they never regain the high water 

 content of undried samples. 



An organic soil such as Kenner (Fluventic Medisaprist) has water content in the organic layers 

 of about 590%-l,000%. Water content of 113% and 226% was measured in two thin mineral 

 layers that were present in the Kenner soil profile. The Lafitte soil (Typic Medisaprist) is also 

 organic and has a water content of about 763%-l,240%. When the organic soils are drained, they 

 shrink and large volume changes result (U.S. Department of Agriculture 1977, 1983, 1984, unpubl.). 



In general the organic soil material contains 2 to 8 times more water in the field state than 

 mineral soils. Mineral soils of clay texture that have never dried hold up to twice as much water 

 as clays that have undergone cycles of wetting and drying. 



Mineral content is defined as the percentage of ash remaining after ignition of an oven-dried 

 sample. The mineral content includes both mineral particles and ash residue from the organic 

 component. The material lost on ignition is considered as organic matter. The amount of ash 

 from the organic component contributes very little to the total mineral content. 



Mineral content is the distinguishing characteristic between mineral and organic soil materials. 

 Organic soil material contains more than 18% organic carbon (dry weight basis) if the mineral 

 fraction is more than 50% clay. If the mineral fraction has no clay, a soil with more than 12% 

 organic carbon may be classified as organic (Figure 1). In Louisiana, 18% organic carbon is 

 necessary to classify the soil material as organic since the mineral component is considered to be 

 more than 50% clay. 



The mineral content in the organic layers of Lafitte and Kenner soils ranges from 21% to 50%. 

 Mineral layers of the Larose and Sharkey soils range from 75% to 98% mineral (U.S. Department 

 of Agriculture 1984, unpubl.). 



Fiber content is used in classification of organic soils. A fiber is a piece of plant tissue large 

 enough to be retained on a sieve having 0.15-mm openings. The degree of decomposition of 

 organic material is related to content of fibers. If highly decomposed, fibers are nearly absent. 

 If only slightly decomposed, most of the volume normally consists of fibers. If the organic materials 

 are moderately decomposed, the fibers may be largely preserved, but are easily broken down by 

 disturbance. For this reason, the percentage of fibers that do not break down with rubbing gives 

 the most realistic field estimate of the degree of decomposition. Unrubbed-fiber percentage is 

 determined on undisturbed samples. 



As the percentage of fiber increases, there is only a slight decrease in bulk density of the soils 

 sampled in Louisiana. Except for the surface mat of live roots, most of the organic soil materials 

 have rubbed-fiber contents of less than 15% indicating a high degree of decomposition. Bulk 

 density is the mass of soil, exclusive of the liquid phase, per unit volume. It is calculated by the 

 general formula Db = weight of soil (exclusive of water) divided by volume of soil. Bulk density 

 of organic soils is lower than mineral soils. Bulk density is relatively constant at mineral contents 

 of 9%-70%. Above 70% mineral content, the bulk density increases markedly as the mineral 

 content increases (Figure 2). 



The attributes of soil material that are expressed by the degree and kind of cohesion and 

 adhesion or by the resistance to deformation or rupture are termed consistence. The consistence 

 of fluid mineral soils can be expressed as the n-value. The n-value can be calculated for mineral 



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