Elimination by contribution: Nicholas Lampkin is a modern agricultural economist known for authoring textbooks on organic farming practice, not for founding the movement. Lord Northbourne only coined the term organic farming in 1940, decades after the foundational scientific work had begun. Masanobu Fukuoka pioneered natural farming in Japan, a related but distinct philosophy developed later.
The pioneering figure was Sir Albert Howard, whose Indore composting method and holistic soil-health research in the early twentieth century laid the scientific foundation of the organic movement, which is why he is honoured with this title, and in question banks his surname Howard is sometimes listed on its own.
Eliminating the other three by chronology and scope of contribution leaves the option naming Howard as correct.