It may be that Japanese soil husbandry over centuries has delivered a more fertile soil today. Which would fit the Cornell study's showing that soil fertility increases over years of organic farming.
This article suggests that Japanese farming today uses chemical fertilisers causing environmental damage, which recourse to traditional fish-meal use may help to limit.
I have to admit, I was surprised at the distinctly greater fertilizer usage by the Japanese, as I'd always thought Americans were the worst. But I suppose if you're out there, looking at every crop and spraying by hand, then maybe you'd end up using more than one would with an even spraying via plane.
With land and labour scarcer and more expensive, and more intensely subsidised food prices in Japan, fertiliser use is more profitable - thus Japanese farmers get their optimal return with a higher amount of fertiliser. It's also a product of much more intensive agriculture, too. Un roi sans divertissement est un homme plein de misères
