. Soils, their properties and management . or developing a favorable crumb structure is obviouslythe optimum moisture content for the development ofthe highest tilth. In fact, it can be stated with certaintythat the optimum moisture condition for plant growthis the optimum for all favorable soil activities, whetherphysical, chemical, or biological. Granulation, then,becomes the vital factor in placing the soil in a physicalcondition such that the highest tilth, that physical criterionwhich every farmer should strive for, may be developedin any soil. Until proper granulation is reached, no soil
. Soils, their properties and management . or developing a favorable crumb structure is obviouslythe optimum moisture content for the development ofthe highest tilth. In fact, it can be stated with certaintythat the optimum moisture condition for plant growthis the optimum for all favorable soil activities, whetherphysical, chemical, or biological. Granulation, then,becomes the vital factor in placing the soil in a physicalcondition such that the highest tilth, that physical criterionwhich every farmer should strive for, may be developedin any soil. Until proper granulation is reached, no soilcan be expected to yield maximum paying returns. 121. Granulation. — While it is possible to Hst thefactors that bring about granulation in a soil, it is diffi-cult to state specifically just why this phenomenon takesplace. It has been suggested that much of the granuleformation in the soil is due to the contraction of themoisture film around the particles when, for any reason,the moisture content is reduced (see Fig. 29). It is known. Fig. 29. — A puddled and a well-granulated soil. that the soil particles tend to be drawn together by this re-duction in the soil moisture, due to the pulling power of thethinned film. If to this condition is added a material whichtends to exert not only a drawing power on loss of mois-ture, but also a binding and cementing power when dry, all 186 SOILS: PROPERTIES AND MANAGEMENT the essentials for successful granulation are present. Thissecond force is found in the colloidal material present inconsiderable quantities in heavy soils. These are the sameforces that have already been shown to determine thecohesion and plasticity of the soil, except that in granu-lating operations they are localized at numberless foci,and clodding or puddling is thereby prevented. It isevident that if cohesion and jilasticity forces are to func-tion for granulation — or, in other words, locally in thesoil instead of generally and uniformly as when cloddingor pu
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