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 (NO) loss remain controversial. We conducted a meta-analysis to compare NO 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 NO concentration, but similar runoff NO load. In contrast, leachate NO load was greater under NT than under CT, although leachate NO concentration was similar under both tillage practices, indicating that the effect of NT on NO 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 NO concentration and similar (instead of elevated) NO 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.