A soil conditioner including, as an active ingredient, a compound represented by general formula (1), a salt thereof or a solvate of the same. In general formula (1), R1 to R6 independently represent an optionally substituted hydrocarbon group having 1-5 carbon atoms, an optionally substituted alkoxy group having 1-5 carbon atoms, an amino group, a hydroxy group, a halogen atom or a hydrogen atom