An accord was signed in Abuja to mark the end of campaign on Thursday.
Analysts have expressed worry about hate speech that has characterized campaigns as they reach a climax.
Saturday’s elections, which pundits predict will end in a photo finish, was originally scheduled to have been held on February 14.
President Jonathan leads the People’s Democratic Party (PDP) – which has ruled the West African country since military rule ended in 1999 – while former military ruler Buhari leads the All Progressives Congress (APC).
Borders of Africa’s most populous nation have been closed and planned to open midnight Saturday after the votes.
The major bane to the elections, which was one of the reasons for the postponement from February 14, is the insurgency of militant group Boko Haram.
They have described the elections as un-Islamic and have forced states of emergency in Borno, Yobe, Adamawa, where they are strongest.
By Emmanuel Kwame Amoh|3news.com|Ghana]]>