Poland actually has some wide-gauge railways connecting Ukraine to Silesia region in Poland (originally for moving coal, steel and sulphur between Ukraine and i

Poland actually has some wide-gauge railways connecting Ukraine to Silesia region in Poland (originally for moving coal, steel and sulphur between Ukraine and industrial part of Poland, now used for various things including moving refuges out of Ukraine). See https://en.wikipedia.org/wiki/Linia_Hutnicza_Szerokotorowa https://en.wikipedia.org/wiki/Linia_Hutnicza_Szerokotorowa So it's not true that all the reloading has to happen on EU border. We also have trains that can move from standard to wide gauge and back with minimal delays. For example https://en.wikipedia.org/wiki/SUW_2000 https://en.wikipedia.org/wiki/SUW_2000 but there are also more modern versions. The main problem is simply too small capacity of railway transport compared to sea transport. We'd have to increase the number of cargo trains Poland and Ukraine owns by orders of magnitude to move all that grain in a reasonable time.