As almost all my articles suggest, take the word EXEMPTION out of your lexicon when speaking about ag land.

The Texas agricultural exemption is not an exemption. It is a county appraisal district assessment valuation based on agricultural use.  

There is an Agricultural Sales Tax Exemption and the details can be found here.

There are 2 types of ag valuations when discussing land. 

One is the traditional Agricutural Valuation:  The land must be devoted principally to agricultural use. Agricultural use includes producing crops, livestock, poultry, fish, or cover crops. It also can include leaving the land idle while participating in a government program or for normal crop or livestock rotation. Land used for raising certain exotic animals (including exotic birds) to produce human food or other items of commercial value qualifies. Cutting wood for use in fences or structures on adjacent agricultural land also qualifies.

Second Ag use - is the wildlife management valuation. Using land for wildlife management is an agricultural use, if such land was previously qualified open-space land and is actively used for wildlife management. Wildlife management land must be used in at least three of seven specific ways to propagate a breeding population of wild animals for human use. This type of valuation does NOT require animals, crops or raising of exotics for food. Instead you are managing the habitat to benefit a native or migratory species of wildlife.