Tex. Agric. Code § 60.125

If the board determines the total cost of an assessment to finance a project or service, the board shall impose the assessment against each parcel of land or against the agricultural product against which an assessment may be imposed in the district. The board may impose an annual assessment for a service. The amount of an annual assessment may vary from year to year, but may not exceed the amount necessary to pay the costs and debts of a project to be financed by the assessment.