Is the recitation of Al-Fatiha obligatory only in the third and fourth rak'ahs of prayer?

Reciting Al-Fatiha is a pillar (Rukn) in every unit (Rak'ah) of prayer. It is also recommended to recite whatever is easy from the Quran along with it in the first two Rak'ahs. As for the last two Rak'ahs, confining oneself to Al-Fatiha was predominantly the practice of the Prophet, peace and blessings be upon him, though it is permissible to add more occasionally.