SYDNEY, April 18 (Reuters) - Australia on Tuesday reaffirmed its commitment to improving agriculture ties with China after a ministerial meeting, as Canberra cheered progress made toward restoring trade in barley amid a thawing in diplomatic relations. Australia last week said it had reached an agreement with China to resolve their dispute over barley imports which followed Beijing in January resuming purchases of Australian coal after almost three years, and a ramping of up beef imports. Agriculture Minister Murray Watt said the resumption of normal trade was in the interests of both countries after a meeting with Chinese agriculture vice...