Abstract
Agronomically significant N yield responses of cereals following grain legumes
compared with cereal monoculture are frequently measured. The positive N
response of the cereal has been attributed to the transfer of biologically
fixed N, to N-sparing under the antecedent legume, and to less immobilisation
of nitrate during the decomposition of legume residues. Methods for estimating
the transfer of biologically fixed N in rotations, and for separating the N
benefit into fixed N and non-fixed N components, are reviewed. Available data
indicate that both sources of N contribute to the N benefit. The role of the
grain legume in the gain or drain of soil N is evaluated by considering the
balance between symbiotic dependence and N harvest index, as well as long-term
changes in total soil N. Several 15N-based techniques
for direct estimation of inputs of biologically fixed N to the soil N pool are
reviewed. N balances in grain legume-cereal rotations may be positive or
negative depending on the legume species, symbiotic performance, and agronomic
factors.
Subject
General Agricultural and Biological Sciences
Cited by
175 articles.
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