Impacts of no-tillage management on nitrate loss from corn, soybean and wheat cultivation: A meta-analysis

Although no-till (NT) has been promoted as an alternative land management practice to conventional tillage (CT), its impact on water quality, especially nitrate (NO₃^-) loss remain controversial. We conducted a meta-analysis to compare NO₃^- concentration and load in NT and CT systems via two major transport pathways: runoff and leaching. Rainfall variability, aridity, soil texture, tillage duration, crop species, and fertilizer type were used as co-varying factors. In comparison to CT, NT resulted in an overall increase of runoff NO₃^- concentration, but similar runoff NO₃^- load. In contrast, leachate NO₃^- load was greater under NT than under CT, although leachate NO₃^- concentration was similar under both tillage practices, indicating that the effect of NT on NO₃^- load was largely determined by changes in water flux. Some deviations from these overall trends, however, were recorded with different co-varying variables. In comparison to CT, NT, for example, generated lower leachate NO₃^- concentration and similar (instead of elevated) NO₃^- leachate load from soybean fields (no N fertilizer applied). These results suggest NT needs to be complemented with other practices (e.g., cover crops, reduced N rate, split N application) in order to improve soil N retention and water quality benefits.