Carl,
Some times the irrigation design contract comes under the gca and other times the owner pays separately. I would guess its a 50% proposition, maybe a little weighted to the gca paying as part of his fee.
Field time varies. I believe JN and TF put full or nearly full time field coordinators out, and have senior design associates visit once a week or more. Some gca's might only visit once a month and let the contractors have at it, but probably not in that group. As to design-builders, Tom Doak might answer better than I. But, I think that Pete Dye took whatever his fee was, and the Owner hired his people separately for on site field time in addition to the fee. In all cases, the expenses are extra, including any machinery, which is probably rented by the owner.
But, it can vary every time.