Effect of Tillage and Straw Returning on Nitrogen Reserves in Summer Corn Topsoil

A field experiment with six treatments was conducted to study the nitrogen reserves in summer maize topsoil on the north China plain. Results showed that topdressing significantly increased topsoil nitrogen reserves. Summer corn topsoil nitrogen reserves were affected by several management measures. Shallow tillage, wheat straw no-returning and deep intertillage at the corn seedling stage significantly decreased topsoil nitrogen reserves, while wheat straw returning, no-tillage and biogas residue application during the wheat planting season significantly increased topsoil nitrogen reserves. The topsoil nitrogen reserve of Treatment 5 (straw returning + biogas residue + no-tillage + no-intertillage at the corn seedling stage) (biogas residue applied in the wheat season) increased by 629.55 kg/ha in the corn season. In Treatment 2 (straw returning + no-tillage + no-intertillage at corn seedling stage), topsoil nitrogen reserve increased by 445.2 kg/ha. Topsoil nitrogen storage showed the largest decrease in Treatment 3 (straw returning + no-tillage + intertillage at corn seedling stage), with a reduction of 1283.85 kg/ha. The topsoil N storage of Treatment 4 (straw returning + shallow (spin) tillage + no-intertillage at corn seedling) stage, Treatment 1 (straw no-returning + no-tillage + no-intertillage at corn seedling stage) and Treatment 3 (straw returning + no-tillage + intertillage at corn seedling stage) decreased by 935.7 kg/ha, 399.3 kg/ha and 351.9 kg/ha, respectively.