Elimination approach: Consider each name against the movement they are actually associated with.
Bill Mollison - co-founder of permaculture, not the term "organic farming".
Rudolf Steiner - founder of biodynamic agriculture (1924 lectures), a distinct but related movement.
Masanobu Fukuoka - proponent of natural farming ("do-nothing farming"), again a related but separately named philosophy.
Only Lord Northbourne, in his 1940 book Look to the Land, explicitly used the phrase "organic farming" to describe the farm as a living, holistic organism. Eliminating the other three confirms Northbourne as the correct answer.