Agriculture Reference
In-Depth Information
Warmer climates or warmer winter temperatures allow temperate species
to persist during the winter, and tropical species are more adapted to the
summer months. It is the intra- and inter-specifi c genetic variability that
partly explains why some legumes grow more and accumulate more N
than others. However, it is mainly the soil and climatic conditions that are
the predominant factors that restrict the selection of the best performing
legumes species. For example, Brandsaeter et al. [84] showed in a recent
study that the biochemical quality of the plants differed between species
and dates of harvesting, and that this was refl ected in the dynamics of net
N mineralization. A number of reviews have focused on selection criteria,
breeding methods and genetic modifi cation approaches and have covered
future improvements in legume crops that will be benefi cial not only to
the environment and farmers but also to consumers in both developed
and developing countries [85-87]. Studies using quantitative genetics ap-
proaches to improve NUE in legumes are scarce. However, it seems that
both root and nodule traits are important for effi cient N assimilation for
further translocation to the seeds [88].
N production from legumes is a key benefi t of growing cover crops and
green manures. The amount of N available from legumes depends on the
species of legume grown, the total biomass produced, and the percentage
of N in the plant tissue. Cultural and environmental conditions that limit
legume growth, such as a delayed planting date, poor stand establishment,
and drought will reduce the amount of N produced. Conditions that en-
courage good N production include getting a good stand, optimum soil
nutrient levels and soil pH, good nodulation, and adequate soil moisture.
The portion of green-manure N available to a following crop is usually
about 40% to 60% of the total amount contained in the legume [76]. Inter-
estingly, it has been demonstrated that leguminous cover crops were also
able to replace 60% of the chemical N fertilization for cotton production,
although the quantity of available N derived from the cover crop was not
synchronized with the requirements of the cotton plant [89]. In turn, one
has to consider that NUE is strongly affected by the organic residues re-
maining from the preceding crop and the application rate of both synthetic
N or organic fertilizers applied to the next crop [90].
Both raw and composted manures are useful in organic crop produc-
tion (for a review see [91]). Used properly, with attention to balancing soil
