Abstract
Data collated from around the world indicate that, for every tonne of shoot dry matter produced by crop legumes, the
symbiotic relationship with rhizobia is responsible for fixing, on average on a whole plant basis (shoots and nodulated
roots), the equivalent of 30-40 kg of nitrogen (N). Consequently, factors that directly influence legume growth (e.g. water
and nutrient availability, disease incidence and pests) tend to be the main determinants of the amounts of N2 fixed.
However, practices that either limit the presence of effective rhizobia in the soil (no inoculation, poor inoculant quality),
increase soil concentrations of nitrate (excessive tillage, extended fallows, fertilizer N), or enhance competition for soil
mineralN (intercropping legumes with cereals) can also be critical. Much of the N2 fixed by the legume is usually removed
at harvest in high-protein seed so that the net residual contributions of fixed N to agricultural soils after the harvest of
legume grain may be relatively small. Nonetheless, the inclusion of legumes in a cropping sequence generally improves the
productivity of following crops. Whilesome of these rotational effects may be associated with improvements in availability
ofN in soils, factors unrelated to N also play an important role. Recent results suggest that one such non-N benefit may be
due to the impact on soil biology of hydrogen emitted from nodules as a by-product of'N, fixation.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:tut/oai:encore.tut.ac.za:d1001480 |
| Date | January 2009 |
| Creators | Peoples, MB, Brockwell, J, Herridge, DF, Rochester, IJ, Alves, BJR, Urquiaga, S, Boddey, RM, Dakora, FD, Bhattarai, S, Maskey, SL, Sampet, C, Rerkasem, B, Khan, DF, Hauggaard-Nielsen, H, Jensen, ES |
| Publisher | Symbiosis |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Text |
| Format | |
| Rights | ©2009 Balaban, PhiiadelphialRehovot |
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