Response of nitrate leaching to no-tillage is dependent on soil, climate, and management factors: A global meta-analysis.

No tillage (NT) has been proposed as a practice to reduce the adverse effects of tillage on contaminant (e.g., sediment and nutrient) losses to waterways. Nonetheless, previous reports on impacts of NT on nitrate ( NO 3 - $$ {\mathrm{NO}}_3^{-} $$ ) leaching are inconsistent. A global meta-analysis was conducted to test the hypothesis that the response of NO 3 - $$ {\mathrm{NO}}_3^{-} $$ leaching under NT, relative to tillage, is associated with tillage type (inversion vs non-inversion tillage), soil properties (e.g., soil organic carbon [SOC]), climate factors (i.e., water input), and management practices (e.g., NT duration and nitrogen fertilizer inputs). Overall, compared with all forms of tillage combined, NT had 4% and 14% greater area-scaled and yield-scaled NO 3 - $$ {\mathrm{NO}}_3^{-} $$ leaching losses, respectively. The NO 3 - $$ {\mathrm{NO}}_3^{-} $$ leaching under NT tended to be 7% greater than that of inversion tillage but comparable to non-inversion tillage. Greater NO 3 - $$ {\mathrm{NO}}_3^{-} $$ leaching under NT, compared with inversion tillage, was most evident under short-duration NT (<5 years), where water inputs were low (<2 mm day -1 ), in medium texture and low SOC (<1%) soils, and at both higher (>200 kg ha -1 ) and lower (0-100 kg ha -1 ) rates of nitrogen addition. Of these, SOC was the most important factor affecting the risk of NO 3 - leaching under NT compared with inversion tillage. Globally, on average, the greater amount of NO 3 - leached under NT, compared with inversion tillage, was mainly attributed to corresponding increases in drainage. The percentage of global cropping land with lower risk of NO 3 - leaching under NT, relative to inversion tillage, increased with NT duration from 3 years (31%) to 15 years (54%). This study highlighted that the benefits of NT adoption for mitigating NO 3 - $$ {\mathrm{NO}}_3^{-} $$ leaching are most likely in long-term NT cropping systems on high-SOC soils.