Distribution of nitrogen storage in density and size fractions varied with tillage practices and cropping systems with residue return in black soil of Northeast China

Abstract Crop residue return can prevent the degradation of cropland caused by conventional tillage practice in Northeast China. Meanwhile, additional nitrogen (N) input from crop residue inevitably changes soil N pools. Our objectives were to evaluate soil N storage changes in soil physical fractions. The residue return treatments consisted of no‐tillage (NT) and moldboard plow (MP), combined with continuous maize ( Zea mays L.) (MM) and maize–soybean [ Glycine max (L.) Merr.] rotation (MS) cropping systems, that is, NTMM, NTMS, MPMM, MPMS; conventional tillage (removal of crop residue and deep plow) with continuous maize (CTMM) was included as a control. The concentration of total N (TN) in bulk soil and physical fractions (light fraction [LF], sand, silt, and clay) was measured. In 0‐to‐5‐cm layer, TN content was higher in NT than MP, whereas the result was opposite in 10‐to‐20‐cm layer. Thus, the stratification ratio (SR) of soil TN was greater under NT. The TN content in MM was greater than MS under both tillage practices with residue return. Residue return treatments increased soil N storage by 6.44–24.85% in 0–20 cm compared with CTMM. Continuous maize increased the N storage in all physical fractions, whereas the decrease of silt‐N storage was observed in MS. Overall, it was concluded that residue return could enhance soil N storage, whereas the distribution of N storage changes in LF and sand size fractions was influenced by tillage practice, and the distribution of N storage changes in silt size and clay size fractions was influenced by cropping system.