Massachusetts Pension Reserves Investment Management Board, Boston, on Monday will issue an RFP for natural resources managers, including renewable energy, farmland, minerals and coal, said Michael Travaglini, executive director. The $53.7 billion system plans to invest 2% of its assets, or $1.1 billion, in natural resources, all of which will be allocated through the RFP. The new investment will be funded from the sale last year of half the systems timber assets. PRIM had about $2 billion invested in timber until the fourth quarter of 2007 when the fund got a hefty return by selling about $1 billion in timber assets managed by The Campbell Group, Mr. Travaglini said. Campbell Group has not been terminated and will be used in the future if timber valuations become attractive again. Becoming a timber buyer right now is hard because of (high) valuations, he said. Alternative investment consultant Cliffwater is assisting. The deadline for submissions will be March 24. The RFP will be listed on the pension funds website, www.mapension.com. Staff will recommend one or more managers to the board at its June 3 meeting.