U.S. manufacturing and trade companies kept their stockpiles nearly unchanged in March, U.S. Commerce Department reported on Monday. The March inventory figure of 1.6409 trillion U.S. dollars was nearly the same as that in the previous month, an increase of 4.5 percent from a year earlier, said the department. Combined sales by manufacturers, wholesalers and retailers dropped 1.1 percent from the prior month to 1.2696 trillion dollars in March. The total business inventories-to-sales ratio, which measures the time span of the inventories being sold, stood at 1.29 by the end of March, higher than the level of 1.28 in the prior month. It is normally interpreted as a positive sign of economy when businesses step up restocking. Companies need to order more goods to build their inventories, which generally would boost factory production.