The designation of a property for the Agricultural Exemption (Ag) relates to local property taxes and is not used for your Federal tax return.
If you use this property for business (farm, ranch, etc.), you can report expenses such as supplies and feed. Farm and ranch activities are reported on Schedule F.
The easiest way to find this section of TurboTax is to open your return, then use the Search box at the top right side of the TurboTax header. Click on the magnifying glass, type in "farm income", hit Enter, and click on "jump to farm income" to go directly to beginning of this topic.
Or go to My Account >> Tools >> Topic Search. Type in "farm income", then click the topic in the list to go directly to the start of this section.