Converting alfalfa (Medicago sativa L.) into cropland (rotation cropland, RC) is a common way of land use to reuse degraded alfalfa pasture. However, it is a big challenge for RC to achieve high productivity and maintain high soil organic carbon (SOC) achieved by previous alfalfa. Here, we conducted a nine-year field experiment, with continuous cropland (CC) under plastic film mulching as reference, to evaluate soil moisture restoration, crop productivity, and SOC in RC also under plastic film mulching, in the case of fertilization and non-fertilization, respectively. SOC and total soil N in the alfalfa pasture before conversion were 12.3% and 7.7% higher, but the available P and inorganic-N were 59.2% and 71.5% lower than in CC, respectively. The crop yield and biomass were not significant between RC and CC following the second year of conversion in both fertilization and without fertilization cases. The SOC and total soil N in RC with fertilization were similar to the previous alfalfa pasture throughout the nine-year experiment, while decreased in RC without fertilization by 8.3% and 7.5% after the nine years. Soil moisture in RC at 0-0.6 m restored to the level of CC only one year after the conversion, and restored from 77.6% and 56.2% of CC to 95.3% and 69.2% at 0.6-2 and 2-5 m through nine-years after conversion. These findings help to dispel the worries about the long-term low production and rapid decline of SOC in RC and support for sustainable high-productivity and high SOC sequestration in dryland farming.

The long-term planting of alfalfa (Medicago sativa L.) gradually reduces the yield and causes severe soil desiccation in semiarid areas. Converting alfalfa pasture into cropland (rotation cropland, RC) is a common way of land use to restore soil moisture. However, it is a challenge for RC to achieve high productivity and maintain high soil organic carbon (SOC) achieved by previous alfalfa. Here, we conducted a nine-year field experiment, with continuous cropland (CC) under plastic film mulching as reference, to evaluate soil moisture restoration, crop productivity, and SOC in RC also under plastic film mulching, in the case of fertilization and non-fertilization, respectively. After the long-term alfalfa pasture was converted to RC, Soil moisture at the upper 2 m profile, especially the upper 0.6 m, restored rapidly to the levels like the CC. The crop yield and biomass were not significant between RC and CC following the second year of conversion in both fertilization and without fertilization cases. The SOC content in RC without fertilization decreased gradually with the conversion years. However, it had no significant difference in RC with fertilization with the previous alfalfa pasture throughout the nine-year experiment. These findings imply that fertilization allowed the RC under plastic film mulching to keep similar productivity to CC and maintain SOC continuously the same as the previous alfalfa pasture while gradually restore soil moisture. This study provided promising adaptive management for increasing agricultural carbon sequestration and crop productivity in semi-arid Loess Plateau and other similar areas.