Why cash crops cannot become food overnight

Could China quickly replace cash crops with food crops after losing access to modern global supplies?

No. Planting seasons, field requirements, and the industrial uses of cash crops prevent an immediate switch.

Changing the crop in a field can cost an entire growing season. Cotton, corn, and soybeans also supply materials for polymers, lubricants, and other products needed by wartime industry. A Mid-Atlantic farming example shows why a war starting in April would come too late for the preceding winter-wheat planting and require further waits for other crops. Rice presents another difficulty because its growing arrangements differ from those of many cash crops. Modern food supplies also draw on different harvest seasons around the world, so losing those flows creates a storage problem as well as a production problem.