Does residue incorporation influence available nitrogen release from cereal rye and tillage radish cover crops under controlled conditions?

Abstract

Nitrogen (N) captured by cover crops can be recycled for use by the following crop via decomposition and net mineralization. This study assessed the magnitude of inorganic-N released from radish (Raphanus sativus L.) and cereal rye (Secale cereale L.) residue. The experiment was designed using a five by two factorial treatment structure with five cover crop residue treatments (radish shoots, radish roots, whole radish, cereal rye shoots, and no cover crop) and two levels of residue incorporation (incorporated and surface applied). Cover crop residues were applied to a silt loam soil on an equivalent N basis, incubated for 25 weeks and sampled periodically. Generally, NH₄-N concentration increased for 7–11 days after residue application, after which, NH₄-N concentration declined and NO₃-N concentration increased due to nitrification. Mineralization during the later days (42–179 days after residue application) was negligible from radish residue, but cereal rye shoots and radish roots released significant amounts of NH₄-N, which decreased over the last 137 d. Radish roots generated significantly more NO₃-N from day 42 through 141 than any other residue, while cereal rye shoots mineralized the least amount of NO₃-N from day 42 through 86. Incorporating cereal rye residue increases the occurrence of immobilization within the first 35 days after residue application; however, incorporation increases the rate at which NO₃-N is released from residues between 42 and 179 days after residue addition, regardless of cover crop species. Incorporation of residue can increase N mineralization rate, but the effect varies across cover crop species.