Assessments shall be levied upon potatoes sold on a field run or ungraded basis as follows:

(1) If payment to the grower for said potatoes is based upon the gross weight of potatoes sold and not upon the yield of any particular grade of potatoes as determined by any type of sorting or inspection, then upon 90% of the gross hundred weight of potatoes so sold.

(2) If payment to the grower for said potatoes is based upon the net weight of potatoes intended for human consumption derived from the potatoes so sold as determined by any type of sorting or inspection, then upon the total net weight of such potatoes intended for human consumption.