© 2015 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. Soil N mineralization is critical for designing appropriate N management strategies, though it has been seldom studied in plasticmulched croplands. We evaluated plastic mulch e ect on N mineralization in urea-amended furrow-ridge plots with and without maize (Zea mays L.) planting at a semiarid rain-fed site, China. Clear film covered all soil surfaces in the mulched treatments and maize was seeded in furrows in the cropped treatments. Mulch increased daytime soil temperature in the 0 to 15 cm throughout the season without maize but only in the seedling and elongation stages with maize, compared with no mulch. Mulch increased soil moisture in the whole season without maize but only in the early growth with maize, compared with no mulch in 2011. However, the mulch in uence on soil moisture was independent on the presence of maize in 2012. Compared with non-mulched soils, N mineralization rate increased in mulched soils throughout the season in 2011 and 2012. By harvest, in 2011 total N mineralized averaged 112 kg ha–1 in mulched soils, contrasting to 54 kg N ha–1 immobilized in non-mulched soils; in 2012 total N mineralization was 348 kg ha–1 in mulched soils whereas it was 116 kg ha–1 in non-mulched soils. Maize increased N mineralization in the tasseling and silking stages compared with no maize. However, the mulch e ect on N mineralization rate was independent on the presence of maize. We concluded that plastic mulch increased N mineralization in urea-amended soils by increasing soil temperature and moisture.