The load looks suspiciously like the barrel of a 42-cm Dicke Berta! I've attached a flipped photo, so it's not strictly accurate (the breech ring was asymmetrical and protruded more on the left hand side) for comparison.
The barrel is indeed of the Dicke Bertha. The tractor pulling it is a 80hp Lanz 3 wheeled tractor. This tractor was not built for the German, but for the Austrian army. The Prussian foot artillery confiscated the 20 built vehicles when war broke out, and they were sent to Krupp where they were used to pull the first battery (2 guns) of the Dicke Bertha. They were suplemented by the few 80hp Podeus tractors (the vehicle originally intended to pull the guns) that were built by then. The tractors were later rebuilt into 4 wheeled FWD vehicles.