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

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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 yr1 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.

Original languageEnglish
JournalAgriculture, Ecosystems and Environment
Pages (from-to)340-349
Number of pages10
Publication statusPublished - 01.10.2018

    Research areas

  • Cover cropping, Dissolved organic nitrogen, Management practices, Nitrogen balance, Nitrogen leaching, Tillage
  • Ecosystems Research