Fertilizer use should not be a fourth principle to define conservation agriculture: Response to the opinion paper of Vanlauwe et al. (2014) ‘A fourth principle is required to define conservation agriculture in sub-Saharan Africa: The appropriate use of fe

•Fertilizer use is not required as a fourth principle to define Conservation Agriculture (CA)•Fertilizer use is a practice not a principle.•Adoption of CA in sub-Saharan Africa faces a number of challenges that are equally serious than fertilizer use.