JLJLU. 



g. Area of surface of soil particles. 



The surface area of soil particles bears fin important relation 

 to the capillary action of that soil; the greater th<: area of the sur- 

 face of the particles, the icore i.:oisture is held on their Burfaces. A 

 large surface nlso increases the rate of chemical solution, by which the 

 food constitutes contained in the mineral particles become available for 

 tho plant's use. Another important property of an ir-'Tnonse surface area 

 of soils is to retain food materials in a. semi- available form,. In ca- 

 Tull'Ty wter the wter is practically held between two plates, and the 

 larger t plates the more v/ter v/ili be held. Consequently the more 

 surface per pouna of dirt holds more \mter; dry t;oil& absorb water. 



There art.- here two classes of soil... 



1) Crystalloids: sand. 



2) Colloids: clay, iron hydrates, zeolites, hun'us. 



e crystalloid has only the outside surface; the colloid has 

 particles composed of smaller particles (It JOG} ^nd a lot of inside 

 surfaces 11 accessible to water. Those inside surfaces of immeasurable 

 surfaces (particle*?) <;re greater than the outuide surfaces of measurable 

 particles . 



.rface may be measured by its hydroseopicity. 

 Given 1 gm. soil: area of particles in metres is: 

 moderate fine sand 1.3 square metres 

 loamy sand ~j6. 



sandy loam 8>. '* 



mi la clay 120. * 



heavy clay 2o^. 



extreme: heavy potter 's900 * " 

 clay, Fe hydrate 



A few standard figures (or stocjt figures) may be given: 



so il surface 



1 sand jiPO square yards 



1 loam 20,000 r< , raoro than 4 acres. 



1 hesvy clay M rt 20 acres. 



ood 



e surface area of a fine-textured soil is greater than the first 

 thought indicate. This immense area exposed by oolls is slgovrn by 

 the following table, which gives: (1} The area in square feet of one 

 gram of the soil; (2) The surface area per pound of the same soils; 

 J3) The approximate weight per cubic foot of the material in the field; 

 (4) The approximate are-i of surface in one cubic foot of these soils as 

 tlie^JL- o cciir in thf> *' i eld . , 



