I have bad news for people who want to know why Japanese veggies are the best in the world and why they are many time better than the best in American farmer's markets. We already know why the fruit is so good; each fruit sprout is wrapped in paper while it grows.
The bad news on why Japanese veggies are so great is that the most fanatic home-grown-organic garden can never duplicate what Japanese farmers do on a large scale.
The information comes from my friend of 30 years, Murayama san, who has been head of the Japanese Organic Farmers Association for decades and on the boards of every major international organic farm organization. He and his brother created the largest organic farm in Japan and he still farms (his wife does most of the work).
When the Japanese are ready to expand a farm, they prepare the soil for 10 years with intense composting, no growing. The compost is made from local roughage and the excrement of the humans and animals that eat from the local farm. Nothing is planted until the 11th year. For the next ten years the amount of added compost is reduced annually until in year 20, and from there on, no compost is added.
One key ingredient, used in Japan and a very few places in the world, is local human waste (from family septic tanks) which is carefully treated and added to the compost. Called 'night soil'.
The only semblance of a theory about this highly local growth-regeneration farming practice is that it aims to: create and maintain a local and stable micro-organism world to nourish the vegetable crops; and it assumes that underground water-flows and rain include a significant volume of nutrients.
For the 'local/organic/foodie' crowd this is going to be hard to replicate. The whole methodology has been discussed at international meetings on agriculture and a few Japanese are showing farmers from other regions how to duplicate it.