I managed to get AgriCraft working on BoP soils, with this farmland_soil.json file:

{ "enabled": true, "path": "vanilla/soils/farmland_soil.json", "id": "farmland_soil", "name": "Farmland", "varients": [ { "item": "minecraft:farmland", "meta": 0, "tags": "", "ignoreMeta": true, "ignoreTags": [ "*" ], "useOreDict": true }, { "item": "biomesoplenty:farmland_0", "meta": 0, "tags": "", "ignoreMeta": true, "ignoreTags": [ "*" ], "useOreDict": true }, { "item": "biomesoplenty:farmland_1", "meta": 0, "tags": "", "ignoreMeta": true, "ignoreTags": [ "*" ], "useOreDict": true } ] }

I think I'll hold off on adding BoP support until we have a better method of accounting for soil-cross compat.