Sense subject of an infinitive

Dear folks,

Please teach me the sense subject of the infinitive in the

passage below:

"Getzin believes the Namibian and Australian fairy circles benefit

the surrounding plants in slightly different ways. The soil in Namibia's

fairy circles is sandy, allowing rainfall to penetrate and stored beneath

them to nourish the plants just outside the circles." [Source unknown]

I suppose the sense subject of the infinitive, from a semantic point of

view, is rainfall, but at the same time from a structural point, I suspect

that it would be the soil . If the former analysis of mine is correct -- if the

usage of the infinitive is allowed -- how would you explain its grammatical

function objectively?

In fact, I cannot decide in the least what the subject really is.

Of course, the passage as a whole makes complete sense to me, but

I would like to fully comprehend this kind expression both semantically and

grammatically.

Thank you very much for your time.

Ray