This data package contains data on measured concentrations of mesquite-nodulating rhizobia on irrigated and non-irrigated dune plots at the Jornada Experimental Range from 1988-1989. Five mesquite dunes were irrigated by pumping water from a storage tank located 200 m from the site to the apex of each dune. Irrigation began in March with approximately 2.5 cm applied 2-3 times/week for 6 weeks to initially wet the dry soil. Thereafter, high water availability was maintained by weekly irrigation. Five non-irrigated dunes served as control. Five to 6 replicate soil samples were collected with hand augers under each mesquite shrub (Prosopis glandulosa) to three depths, 0-50 and 50-100, and 100-150cm. Concentrations of mesquite-nodulating rhizobia in field-moist soil samples were estimated using the plant-infection most probable number (MPN) technique. Data consists of the date of collection, treatment, mesquite dune number, depth, replicate, and number of nodules. This study is complete.