IN INOCULANTS Nodulaid - 17th International Nitrogen Fixation ...

17 th International Congress on Nitrogen Fixation
Fremantle, Western Australia
27 November – 1 December 2011
Session Details: Thursday 1 December 2011
Plenary Session
0900 – 1030
Authors: Robert M. Boddey 1 , Lincoln Zotarelli 2 , Natalia P. Zatorre 3 , Segundo Urquiaga 1 , Claudia
P. Jantalia 1 , Julio C. Franchini 4 , Bruno J. R. Alves 1
1 Embrapa Agrobiologia, Seropédica, 23890-000, Rio de Janeiro, Brazil.
2 Horticultural Sciences Dept., University of Florida, Gainesville, FL 32611-0690, USA.
3 Departamento de Solos, Universidade Federal Rural do Rio de Janeiro, Seropédica,
23890-000, RJ, Brazil.
4 Embrapa Soja, Rod. Carlos João Strass , Warta, 86001-970, Londrina, PR, Brazil.
Presentation Title: Legume N2-fixation inputs preserve soil organic C stocks in no-till agriculture
Presentation Time: 0900 - 0930
In Brazil, no-tillage is widely adopted for soybean-based cropping systems. In the Southern region, soybean
alternates with maize in the summer, and oats or green-manure legumes in the winter to break the continuous
use of wheat in this season. Results from long-term experiments comparing conventional plough tillage (CT) and
no-till (NT) in this region have shown that if the only legume in the rotation is soybean there is very little increase
in soil C stocks, which has been attributed to lack of significant residual N in the system to build soil organic
matter owing to the large export of N in soybean grain. Here we present the results of a study with different crop
rotations of soybean, maize, wheat, oats and lupins managed under NT or CT which differed from each other in
the frequency of soybean and lupins in the crop sequences. Soil C and N stocks to a depth of 80 cm were
evaluated and the contributions of N2 fixation (BNF) to all the legumes in the systems were quantified using the
15 N natural abundance technique. Reliance on BNF of both soybean and lupins was higher under NT than under
CT. The use of lupins as a green manure represented an extra contribution to soil N of up to 300 kg N ha -1 , which
allowed high maize yields, comparable to N-fertilized maize following oats, and was essential to maintain a
positive cropping system N balance. Comparison of soil C stocks between 1997 and 2009 revealed almost no
gain in soil C under no-tillage, but a C loss of 19 Mg C ha -1 after 12 years of conventional till. The results highlight
the value of green manure legumes as a significant source of N for cropping systems which are a key aid to
preserving or increasing soil C stocks under NT.
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