Reduced nitrate leaching from an Irish cropland soil under non-inversion tillage with cover cropping greatly outweighs increased dissolved organic nitrogen leaching

• Published in: Agriculture, ecosystems & environment Vol. 265; pp. 340 - 349
• Main Authors: Walmsley, David C., Siemens, Jan, Kindler, Reimo, Kaiser, Klaus, Saunders, Matthew, Fichtner, Andreas, Kaupenjohann, Martin, Osborne, Bruce A.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.10.2018; Elsevier BV
• Subjects: Agricultural ecosystems; Agricultural land; Agricultural practices; agroecosystems; Ammonium; Barley; Cereal crops; conventional tillage; Cover cropping; Cover crops; cropland; Cropping systems; Crops; Dissolved organic nitrogen; Drainage; fallow; Land use; Leaching; Management practices; Mustard; Nitrates; Nitrogen; Nitrogen balance; Nitrogen leaching; Nutrients; Organic nitrogen; reduced tillage; soil; Soil suction; spring; Tillage; Winter; Nitrogen balance; Cover cropping; Dissolved organic nitrogen; Tillage; Management practices; Nitrogen leaching
• ISSN: 0167-8809; 1873-2305
• DOI: 10.1016/j.agee.2018.06.031

•Non-inversion tillage + cover crop reduced nitrate leaching by over 80%.•Non-inversion tillage + cover crop increased DON leaching by 59%.•Consideration of DON losses can be crucial for cropland N balance assessments. Reduced tillage and cover cropping are common measures to minimize leaching losses of nutrients from cropland soils. While the efficiency of these measures for reducing inorganic N leaching has been studied intensively, their effect on dissolved, organically-bound nitrogen (DON) remains unclear. In this study, leaching of nitrate, ammonium and DON from spring barley-based cropping systems, subject to either conventional management (CT = inversion tillage with a winter fallow period), or non-inversion tillage with a winter mustard cover crop (NIT + CC), were assessed using suction cup sampling and modelled drainage volumes. Total dissolved nitrogen losses with drainage from the NIT + CC treatment (2.5 ± 0.2 g N m−2 yr−1) were considerably smaller than those from the conventional treatment with fallow (13.9 ± 0.7 g N m−2 yr−1). As drainage volumes were similar between treatments, differences in total N leaching were mainly associated with larger nitrate concentrations under CT (23.0 ± 1.1 mg N L−1) than under the NIT + CC treatment (5.1 ± 0.3 mg N L−1). The average contribution of DON to total dissolved nitrogen concentration was 3% within the CT treatment, but rose to 19% within the NIT + CC treatment, which was primarily due to the strong reduction in nitrate and to a lesser extent due to the higher concentrations of DON within the NIT + CC treatment (NIT + CC: 0.52 ± 0.04, CT: 0.33 ± 0.04 mg N L−1). Averaged over the two-year study period, the CT system showed a net loss of 9.4 g N m−2 yr−1 whilst an N surplus of 1.7 g N m−2 yr−1 was observed for the NIT + CC system. Here DON accounted for 11% of total N leaching, supporting the notion that it can be an important component of dissolved N losses in agroecosystems. By neglecting DON leaching the N-surplus under NIT + CC would have been overestimated by 18%. In conclusion, our results show that the capacity of winter cover cropping in combination with non-inversion tillage to reduce nitrate leaching far outweighed the higher leaching losses of DON observed. The quantification of DON losses, however, may be essential for a complete picture of the N balance of these and similar cropping systems.