This will be the final season of “Knots Landing,” the long-running serial currently in its 14th year on the web, CBS and Lorimar TV have confirmed.Both were in on the decision, based on diminishing ratings for the show and the cost of maintaining its ensemble cast. Regular episodes will air through March, with a two-hour finale in May. “We though it was better to go out a winner than to go on one year too long,” said exec producer Michael Filerman. “Knots” was the last of an extremely successful CBS-Lorimar stable of prime time soaps that included “Dallas” and “Falcon Crest.” The show had averaged a 17 .2 rating, 29 share over its lengthy run but faded in recent years and was down to an 11.3/19 average in Nielsen for the eight episodes to air this season. One replacement candidate for the fall would seem to be another hour from Lorimar and exec producer David Jacobs, “Bodies of Evidence,” that performed well in the same slot last summer and received a midseason pick-up. “Knots” premiered in December 1979 and will conclude its run with 344 episodes, ranking as the third longest-running drama series in history, according to Lorimar, behind “Gunsmoke” (406 segments) and “Dallas” (356).