Nitrogen release from differently aged Raphanus sativus L. nitrate catch crops during mineralization at autumn temperatures

• Published in: Soil use and management 2016-06, Vol.32 (2), p.183-191
• Main Authors: Thomsen, I. K., Elsgaard, L., Olesen, J. E., Christensen, B. T.
• Format: Article
• Language: English
• Subjects: Autumn; Crops; Fibre; fodder radish; incubation; Leaching; Lolium perenne; Mineralization; Nitrate catch crops; Nitrates; Raphanus sativus; Residues; ryegrass; Sinapis alba; Soil (material); white mustard
• ISSN: 0266-0032; 1475-2743
• DOI: 10.1111/sum.12264

In temperate climates with surplus precipitation and low temperatures during autumn and winter, nitrate catch crops have become crucial in reducing nitrate leaching losses. Preferably, the N retained by the catch crop should remain in the soil and become available to the next main crop. Fodder radish (Raphanus sativus, L.) has emerged as a promising nitrate catch crop in cereal cropping, although the course of remineralization of residue N following termination of this frost‐sensitive crucifer remains obscured. We incubated radish residues of different age (different planting and harvest dates) with a loamy sand soil; mineralization of residue N was determined after 1, 2, 4 and 7 months of incubation at 2 °C and 10 °C. Incubations with soil only and with residues of white mustard (Sinapis alba, L) and perennial ryegrass (Lolium perenne, L.) were included as references. Using linear regression, net N release was fitted to plant chemical characteristics (initial concentrations of N, fibre fractions, lignin and C/N ratio). Residue C/N ratio (ranging from 10 to 25) and N concentration (ranging from 17 to 40 mg N/g dry matter) showed superior fits to net N release at both temperatures (r2, 0.64–0.94) while fibre analyses provided inferior fits (r2, 0.12–0.64). This was true across planting date and plant age. Net N release after 7 months of incubation at 2 °C and 10 °C accounted for up to 40% and 50% of residue N, respectively. During most of the incubation period, nitrate dominated the mineral N pool at both temperatures. The N mineralization and nitrification potential at these low soil temperatures suggest that a considerable fraction of the N captured by nitrate catch crops may be remineralized, nitrified and thus available for plant uptake but also for loss by leaching and denitrification.