Apparently, if rationing was introduced, Germany could produce enough food to feed itself. The problem is that WW1 was the learning experience that showed these things to all combattants. By the time the blockade really started to bite, from 1916 onwards, it was probably too late to do anything about it. However, as a result of WW1 the British rationing system of WW2 was an absolute marvel and was a significant factor in British victory.