The Alberta investment manager, which invests some $70 billon on behalf of 26 pension, endowment and government funds in the province, praised the incumbent Agrium board and the company's new director nominees.
Jana advocates splitting up Agrium, a move that the incumbent board rejects, as it seeks to install its managing partner and four other nominees as directors at the company's annual meeting on April 9.
AIMCo said activist investors fulfil an important role when boards tolerate poor performance.
"That is not the case with Agrium. It has done well for its shareholders, both absolutely and relative to peers," AIMCo said in a statement.
"AIMCo considers the incumbent Agrium director roster to be robust in terms of composition, experience, and independence. The new Agrium director nominees offer superior agricultural market knowledge."
Jana has invested about $1.2 billion in Agrium since May of last year for a 7.5 per cent stake, making it the company's largest shareholder.
However, Agrium has won the support of several other large investors including British Columbia Investment Management Corp. and Montreal investment firm Letko, Brosseau & Associates Inc.