Dear Muhammad,

Clay, silt and sand affect the soil porosity:

Sand particles are quite big. The pore spaces between the particles in sandy soils are also quite large. This allows water to drain quickly and air to enter the soil. Sandy soils tend not to get waterlogged in winter but can be subject to drought during summer.

Silt particles are too small to see. Silt soils have much smaller pore spaces but a lot more of them.

Clay particles are smaller than 0.002 mm in diameter. Clay soils are poorly drained and hold on to the water in their pore spaces for much longer. However, they can become very hard if they dry out.

The porosity order is sand>silt>clay.

http://sciencelearn.org.nz/Contexts/Soil-Farming-and-Science/Science-Ideas-and-Concepts/Soil-properties

Hoping this will be helpful,

Rafik

Soil porosity is determined by sand, silt and clay. Please check the links given below for more details.

http://www.earthsciweek.org/classroom-activities/soil-properties

http://www.education.com/science-fair/article/testing-porosity-of-soils/

Dear Muhammad, 

Interesting question, i should add that for me , the reason behind the dependance of soil clay and porositiy is the soil clay had colloidal properties ( attract other particle) and they had high surface area. 

Porosity is more a result of the clay particule, Organic matter, Calcium carbonate , Sesquioxydes of Iron and Al binding together to form aggregate in hierarchical manner and each step create in this processs create pores from nonopore to macropore. and of course once we arrive to the macropore formation, these kind of porosity are strongly affect by soil management pratices, and there are correlated with soil structure rather with soil texture . 

Kind regards Louadj Yacine

I really appreciate the answers by all members. I think the details of Rafik Karaman and Arvind Singh are more useful for understanding the soil porosity concept clearly.

Regards,

Muhammad Saeed

 Dear colleagues, we have recently discussed   a topic related porosity in researchgate 'how is bulk density of soil related to the soil texture'.

Porosity(P)=1-(BD/PD)

PD is Particle density, is simply the density of the individual particles themselves(not including pores),while BD is the relation between a soil's dry mass and bulk volume(the volume of soil solids and soil pores).So the BD is intimately related to porosity Smaller the BD,larger the pore space in soil.As explained by Mr. Yacine,the aggregated clay soils will have greater total porosity because of the abundance of very small pores (micropores).The sandy soils have large but fewer pore.Soil pores are grouped into three categories,macropores(>0.08mm,) mesopores,common in medium textured soils( between 0.08 and 0.03 mm) and micropores(