Long-term effects of different tillage practices on total nitrogen in black soils

Soil total nitrogen content is closely related to agricultural production and food security.Conservation tillage affects the distribution of total nitrogen in soil profiles due to crop residue returning and the reduction of soil disturbance.However, few studies concerning the conservation tillage's impacts on the total nitrogen of black soil are reported.Based on a long-term field experiment, soil total nitrogen's dynamics and its vertical distribution were studied under no-tillage, ridge tillage (reduced tillage with crop residue returned) and mouldboard plough.Results showed that, soil total nitrogen significantly increased in top soils and decreased in sub-surface layer after 13-year no tillage.Both ridge tillage and mouldboard plough increased total nitrogen in surface and subsurface soils, but the increment of total nitrogen with mouldboard plough was lower than that with ridge tillage.Overall, under three tillage practices, ridge tillage facilitated nitrogen keeping in soil layer and accumulating in soil, and thereby it would be an effective approach to reduce nitrogen fertilizer application in black soils of Northeast China.