WASHINGTON — A diverse group of agribusiness companies and trade associations, as well as related groups, have jointly signed a letter to Secretary of Agriculture Tom Vilsack urging modification of the rules governing the Conservation Reserve Program. The group, the Alliance for Agricultural Growth & Competitiveness, wants growers to be able to remove land that is non-highly environmental sensitive from the program before contract expiration. The 105 entities signing the letter described a pressing need to make C.R.P. rules more flexible and allow growers to respond to market conditions. The statement was submitted in response to a U.S. Department of Agriculture request for comments ahead of a new environmental impact assessment of the C.R.P. The A.A.G.C. represents a diverse collection of groups focused on baked foods; meat; livestock and poultry; agricultural inputs; grain marketing, handling and processing; feed manufacturing and exports. The 105 signatories ranged from the American Bakers Association and the North American Millers’ Association to Zen-Noh Grain Corp.