Why was human waste the main fertilizer in the Edo period?
The increasing population and urbanisation meant that the previous method of burying leaves and grasses as compost was not enough. The lack of horses (as only the upper classes were allowed to ride them) and other animals (as most people did not eat meat) meant that humans were the main alternative source. The fact that city dwellers lived in blocks with shared toilets must have also have made this system easier than in some countries and so have lead to its development.
Why are Japanese fields still so small and irregularly shaped?
Land was redistributed after the Second World War by the occupation authorities as a way of breaking down the feudal system that was thought to have led to the war.
Why do you still see people planting rice by hand?