Background and aims Reliance on nitrogen (N) fertilizers to maintain crop productivity requires a thorough understanding of the transformation of this nutrient within the soil-plant system. Organic matter input from a mixture of crop residues, such intercrop systems, influence N transformations differently compared to sole crops. We tested the hypothesis that N mineralization and immobilization differ between cereal-legume intercrops and sole crops. Methods A short-term experiment using 15 N isotopic pool dilution was conducted in 2007 and 2012 in maize (Zea mays L.) and soybean (Glycine max L. Merr.) sole crops and 1:2 (1 row maize:2 rows soybean) and 2:3 (two rows maize:3 rows soybean) intercrops. Soil characteristics, gross mineralization and immobilization, and net immobilization to a 10 cm depth were quantified. Results Soil characteristics (pH, bulk density, soil organic carbon (C), total N, and C:N) were not significantly different (P<0.05) among treatments, but differed significantly (P<0.05) between years (2007 vs. 2012). Soil NH 4 + -N was significantly lower (P<0.05) in the maize sole crop. Gross N mineralization, immobilization and net immobilization, were significantly different (P<0.05) among treatments and between years. Relative NH 4 + -N immobilization was significantly different (P<0.05) among treatments and between years, showing the lowest values in the intercrops. The amount of NH 4 + -N mineralized per day was significantly greater (P<0.05) in the 2:3 intercrop and was significantly different (P<0.05) between years in the 2:3 intercrop. Residence time of NH 4 +-N was significantly longer (P<0.05) in the soybean sole crop and 1:2 intercrop followed by the 2:3 intercrop and the maize sole crop. Conclusions Intercropping contributed to the long-term immobilization of N and therefore was a more sustainable land-management practice than sole cropping. The adoption of cereal-legume intercrops will curb our currently growing reliance on N fertilizers.

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Using process‐based models to predict changes in carbon (C) stocks enhances our knowledge on the long‐term dynamics of soil organic carbon (SOC) in various land management systems. The objective of this study was to apply the Century model to evaluate temporal SOC dynamics in two temperate intercrop systems [1:2 (one row of maize and two rows of soybeans); 2:3 intercrop (two rows of maize and three rows of soybean)] and in a maize and soybean sole crop. Upon initiation of intercropping, SOC increased by 47% after ≈ 100 years, whereas SOC in the maize sole crop increased by 21% and 2% in the soybean sole crop. The quantity of crop residue input was sufficient to increase the active (turnover time of months to years) SOC fraction in the intercrops and the maize sole crop, but not in the soybean sole crop. The slow fraction, with a turnover time of 20 to 50 years, increased in all crop systems and was the major driver of SOC accumulation. A 3 to 15% loss of SOC from the passive fraction, with a turnover time of 400 to 2000 years, in all crop systems showed the long‐term impact of land‐use conversion from historically undisturbed native grasslands to intensive agricultural production systems. This study provided an example of the potential of process‐based models like Century to illustrate possible effects of cereal–legume intercropping on SOC dynamics and that the model was able to predict SOC stocks within –7 to +4% of measured values. We conclude, however that further fine‐tuning of the model for application to cereal–legume intercrop systems is required in order to strengthen the relationship between measured and simulated values.