Friability of soil refers to its crumbly texture, which is somewhere between sand and clay, not so fine and grainy like sand, or so thick and mushy like clay.A handful of friable soil when pressed hard, should form a lump,but the lump can be easily disintegrated.
Friable soil also will drain water very well, but also retain moisture like a wrung out sponge.Soil which is friable, is usually rich in carbon, minerals and organic will have sufficient porosity to allow oxygen to reach the roots.
The need for friable soil:
Plants grown in friable soil will be healthier, will have lush foliage, strong root systems and resistant to diseases and pests. Friable soil has tons of micro-organisms which will keep replenishing the fertility over time.
How to make clay soil friable :
Mix dried and powdered clay soil with equal volumes of coarse river sand and matured compost to retain its texture, keep mulching it with dry leaves, wood chips etc and maintain its moisture.Friable soil will not get hardened in the sun or become a slush in the rain ,the advantage being it also require less watering than clay.