Ridge tillage is likely better than no tillage for 14-year field experiment in black soils: Insights from a 15N-tracing study

Abstract

Conservation tillage practices, such as no tillage (NT) and ridge tillage (RT), have been widely proposed for use in many countries to increase carbon sequestration. However, understanding of how conservation tillage affects soil gross N transformation is still very limited. In this study, a 15N-tracing experiment was carried out to investigate the effects of 14 years of RT and NT practices on the gross N transformation rates in black soils of northeast China. Based on the results for soil N transformations, soil organic carbon (SOC) sequestration, and crop yields, we propose suitable conservation tillage practices. The results showed that the NH4+ immobilization rates were significantly higher under RT than NT. The heterotrophic nitrification rate in RT was significantly higher than in either conventional tillage (CT) or NT, contributing more than 89% of the total nitrate production in RT. NO3− immobilization was negligible under NT and CT, but this process was significantly stimulated by RT. Consequently, relative to NT and CT, a long-term RT treatment can stimulate inorganic N retention capacity and thus provides greater capacity to supply available N for uptake by crop plants. In addition, the average concentrations of SOC and total nitrogen (TN) in the 0–15 cm soil layer under RT were significantly higher than those under NT and CT. The average maize yields (2011–2015) under RT were similar to NT, both of which were significantly higher than under CT. Therefore, RT is arguably a more suitable tillage practice than NT and CT for enhancing the N retention, maize yield, and C sequestration for the studied black soils.