using a texture instead of weight painting

Hi,

 I want to have grass sprout of the cracks and crevices of cracked soil, in cycles. So instead of weight painting and using that for the density, is there a way to just use a texture instead? I'd like to use an ambient occlusion of the texture or something similar so that only the black areas(crevices) have particles / grass sprouting.
 Suggestions?

Thanks in advanced

Add a particle system for the grass.
Add a particle texture and set it to influence density
Black = zero density
White = full density
To reverse this set the density influence to a negative value

Awesome. Thanks a bunch!