The Conservation Reserve Program (CRP) has been the largest land retirement programme, and the largest US conservation programme of any kind. CRP is a voluntary programme that offers annual rental payments, incentive payments for certain activities, and cost-share assistance to establish approved cover on eligible cropland. As of June 2004, there were 34.8 million acres enrolled in CRP, with 2.8 million of those acres in partial-field enrolments under the continuous signup, Conservation Reserve Enhancement Program (CREP), and the Farmable Wetland Program (FWP). More than 660 000 contracts were in force with more than 390 000 farmers covering this acreage. The annual rental cost was almost USD 1.7 billion, and the average rental cost per acre was USD 48. About 60% of CRP acreage was planted to grasses, 16% to trees or woody vegetation for wildlife, and 5% was dedicated to wetland restoration. The programme is authorized at 39.7 million acres for enrolments under 10-15 year contracts through 2007. The current CRP program targets land retirement to increase the cost-effectiveness of the programme, and adjusts the payment to closely match the market value.