Effects of straw and biochar addition on soil nitrogen, carbon, and super rice yield in cold waterlogged paddy soils of North China

The additions of straw and biochar have been suggested to increase soil fertility, carbon sequestration, and crop productivity of agricultural lands. To our knowledge, there is little information on the effects of straw and biochar addition on soil nitrogen form, carbon storage, and super rice yield in cold waterlogged paddy soils. We performed field trials with four treatments including conventional fertilization system (CK), straw amendment 6 t ha−1 (S), biochar amendment 2 t ha−1 (C1), and biochar amendment 40 t ha−1 (C2). The super japonica rice variety, Shennong 265, was selected as the test crop. The results showed that the straw and biochar amendments improved total nitrogen and organic carbon content of the soil, reduced N2O emissions, and had little influence on nitrogen retention, nitrogen density, and CO2 emissions. The S and C1 increased NH4+-N content, and C2 increased NO3−-N content. Both S and C1 had little influence on soil organic carbon density (SOCD) and C/N ratio. However, C2 greatly increased SOCD and C/N ratio. C1 and C2 significantly improved the soil carbon sequestration (SCS) by 62.9 and 214.0% (P<0.05), respectively, while S had no influence on SCS. C1 and C2 maintained the stability of super rice yield, and significantly reduced CH4 emissions, global warming potential (GWP), and greenhouse gas intensity (GHGI), whereas S had the opposite and negative effects. In summary, the biochar amendments in cold waterlogged paddy soils of North China increased soil nitrogen and carbon content, improved soil carbon sequestration, and reduced GHG emission without affecting the yield of super rice.