[nradov]

You don't have a realistic understanding of the situation. Rail links are limited, and don't have the same capacity as ships. China has been trying to address that through the "Belt and Road" initiative but with limited progress so far.

It's not so much the fertilizer itself that China needs to import, but rather the natural gas needed to manufacture fertilizer. Beyond natural gas, China is also a huge importer of coal for power, heating, and steelmaking. They have no realistic path to energy independence and will remain dependent on maritime imports for decades at least. Reducing petrol use won't allow them to keep their economy running or feed the populace.

In a crisis, China could perhaps find alternative sources of food imports at very high costs. But that is not a rational approach to long term national survival.

There was never any possibility for the Japanese empire in 1941 to live off the land in the territory they had conquered. They were already being cut off from crucial raw materials including oil and rubber. Without a secure supply of those their situation was simply untenable.