Plastic film mulching and gravel mulching in combination with fertilization are widely used to increase crop yields and water use efficiency (WUE) in arid and semi-arid areas, but soil surface mulching may stimulate soil organic carbon (SOC) mineralization, therefore, film mulching with manure amendment was proposed to improve soil fertility. However, the combined effects of these practices on yield, WUE, and the stocks of SOC and total nitrogen (TN) need to be better understood. This study investigated the long-term effects of different practices on crop yields, WUE, and SOC and TN stocks in the 0-20, 20-40 and 40-60 cm layers based on a 12-year spring maize (Zea mays L.) field experiment on the Loess Plateau. The treatments included no mulching + NPK (CK), gravel mulching + NPK (GM), film mulching + NPK (FM), film mulching + NPK + cow manure (FCM). In 2019 and 2020, compared with the contral, both FM and FCM significantly increased crop yields, WUE, N uptake efficiency (NupE) and N fertilizer productivity (NfP). Compared with CK, the FCM treatment significantly increased SOC and TN stocks by 44.10% and 39.51% on average, and the C input of ≥ 0.67 Mg ha−1yr−1 could maintain soil C balance on the Loess Plateau. Over the 12 experimental years, compared with the initial value in 2009, the trends of SOC and TN contents in the FM treatment were downward, while those in the FCM treatment increased by 41.61% and 30.27%, respectively, but year after year of manure inputs lead to SOC saturation. Compared with CK, the FCM treatment significantly decreased SOC and TN sequestration potential by 33.38% and 19.59% on average in topsoil (0-20 cm), but it had less effect on those at 20-40 and 40-60 cm soil depth. The reasons of SOC saturation in the FCM treatment were analyzed, and periodic subsoiling was proposed to break the saturation state to further improve SOC and TN sequestration from the perspective of soil physics. In conclusion, film mulching with manure amendment was recommended as a long-term strategy to improve soil productivity and SOC and TN sequestration in semiarid farmland
