I don't know if this is bug or not but after turning to christianity in my vh Mori campaign I seem to have lost my ability to upgrade farms beyond improved irrigation. When I checked chi art trees all improvements beyond improved irrigation seem to have vanished too. I have teched to Chonindo which should give me land consolidation.

So is there some tech I must research to get newer farms available or am I doomed to stagnation as I cant build better roads or forts (to get other improvements like marketplaces/sake dens/dojos to get better troops) as they consume food.