The Senate is scheduled to vote this week on legislation to temporarily ban all agri-business mergers. Iowa Senator Chuck Grassley supports most of the plan but says the 18-month moratorium on mergers written into the bill by Minnesota democrat Paul Wellstone may be too strict.Grassley says the heart of the trouble with the mega-mergers may lie in a misunderstanding of farm life by Washington bureaucrats.The okay was given last week for farm machinery makers Case and New Holland to merge. Another merger still awaiting approval is the Smithfield purchase of Murphy Family Farms — that’s the nation’s largest hog producer trying to buy its number-one competitor.