. Soil physics and management. ng-con-tinued application of certainfertilizers, such as ammoniumsulfate or sodium nitrate, bringsabout a puddled condition. Someclay and clay loam soils are pud-dled naturally. This is likelyto be the case if they are stronglyacid and low in organic in a soil acts as a lubri- -Cracks in black clay loam after Caut and mOVCmCUt takeS place period. Photographed August, j^-^ readily bctwecn the par-ticles. It also softens thecementing material so that the granules are easily broken the soil is turned by the plow a shearing, slipping moveme
. Soil physics and management. ng-con-tinued application of certainfertilizers, such as ammoniumsulfate or sodium nitrate, bringsabout a puddled condition. Someclay and clay loam soils are pud-dled naturally. This is likelyto be the case if they are stronglyacid and low in organic in a soil acts as a lubri- -Cracks in black clay loam after Caut and mOVCmCUt takeS place period. Photographed August, j^-^ readily bctwecn the par-ticles. It also softens thecementing material so that the granules are easily broken the soil is turned by the plow a shearing, slipping movementis produced as it curves over the mold board. This will pulverize itif in good condition, but puddle it more or less if wet. \ATien aheavy animal steps on the dry soil it is compacted, but if wet thefoot sinks into the soil, causing a movement which breaks downmany granules, thus puddling the soil. Wlien puddling is produced in a heavy soil it may be almostworthless for a time, but the natural agencies of freezingr and thaw-. FiG. long dry1916. MINERAL CONSTITUENTS 137 ing and wetting and drying will gradually restore the soil to itsgranular condition. The time required for this depends somewhatupon the organic matter and lime content of the soil. It is never awise plan to permit stock to run on a moderately heavy soil whenwet so late in spring that its granular condition will not be restoredagain by freezing and thawing. In the corn belt considerable dam-age is done to the soil by pasturing the cornstalks too late in thespring. (e) Coagulation or Flocculation.—The examination of a claysoil usually shows it to be made up of fine particles cemented intogranules, crumbs, or grains. If a few grams of clay soil be pul-verized and put into a liter of water and stirred and allowed tostand for several weeks, some material will be found still in suspen-sion. If some mineTal acids or certain salts or lime water are addedto this liquid coagulation will occur and floccules may be
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