Try the Bare Soil Index, since theoretically the agricultural land should have more exposed soil than a forest. Also I would suggest that you use band information only (no indices) it improved accuracy in one of my past projects related to water body monitoring.

Have you incorporated SAR?

Still need to figure out how I can make my "Discover" more hydrology and remote sensing oriented. And LinkedIn is trash, too many "influencers" and substandard cringe content that neither entertains nor provides anything of value