An agricultural irrigation system and method for irrigating a field includes a water supply pipe supported by a wheeled support or tower. The irrigation system can move in an oscillating fashion across the field while dispersing water. The irrigation system is advanced in a forward direction a first distance, reversed in a backward direction a second distance that is less than the first distance, then readvanced in a forward direction. The system can include a manifold connected to the water supply pipe. The manifold includes drop lines to supply water to a crop below the manifolds. Existing irrigation systems can be retrofitted with the manifold and drop lines.