Soil nitrogen and its fractions between long-term conventional and no-tillage systems with straw retention in dryland farming in northern China

• Long-term tillage and residue significantly affect soil nitrogen pools.
• Significant positive correlations were observed between STN and its fractions.
• Greater soil N stocks were observed in NTR system than in CT system.
• NTR may be an appropriate farming practice for dryland farming.

Knowledge about the changes in soil nitrogen pools under different tillage managements is necessary to assess the feasibility of adoption of conservation practices for sustaining productivity and protecting the environment in dryland farming in northern China. We investigated the long-term effects (22 years) of no-till with residue retention (NTR) on total soil N and its fractions in a dry-land winter wheat (Triticum aestivum L.) cropping system in northern China. Compared with conventional tillage without residue retention (CT), significantly higher soil total N (STN) concentrations were observed in the surface soil layer (0–10 cm) under NTR. Meanwhile, more soil N accumulated for the whole soil profile (0 to 60 cm) in the NTR (3.38 Mg ha− 1) treatment relative to the CT (3.17 Mg ha− 1) treatment. The particulate organic matter N (PON), microbial biomass N (MBN), and water extractable organic N (WEON) levels in the NTR treatments were 52.3%, 116%, and 69.4% greater at a depth of 0–5 cm and 41.6%, 108%, and 44.9% greater at a depth of 5–10 cm, respectively, compared with the CT treatment. However, no differences were observed below the 10 cm layer. At a depth of 0–60 cm, the soil NH4-N content under CT was higher than that under NTR. However, the soil NO3-N contents in the NTR treatments were significantly greater at a depth of 0–10 cm and were not significantly different at a depth of 10–60 cm, relative to the CT treatment. Significantly positive correlations were observed between the STN and the labile organic N fractions. Overall, the results show that no-till coupled with residue retention is an effective management method for improving soil N stocks and increasing soil fertility. Nonetheless, other benefits associated with NT and residue retention present greater challenges regarding their popularization and application in the dryland farming areas in northern China.