INVESTIGADORES
ALVAREZ Roberto
artículos
Título:
Nitrogen fixation by soybean in the Pampas: relationship between yield and soil nitrogen balance
Autor/es:
C. DI CIOCCO; E. PENÓN; C. COVIELA; S LOPEZ; M DIAZ-ZORITA; F MOMO; R ALVAREZ
Revista:
AGROCHIMICA (PISA)
Editorial:
IST CHIMICA AGRARIA
Referencias:
Lugar: Pisa; Año: 2012 p. 305 - 313
ISSN:
0002-1857
Resumen:
Soybean (Glycine max
(L.) Merrill) is the major grain crop in the Pampas.
Its productivity strongly depends on soil nitrogen availability and biological
nitrogen fixation because nitrogen fertilizers are not usually applied. Scarce local
information has been generated about biological nitrogen fixation potential of
soybean crops or to the soil nitrogen balance during its growing season. A meta-analysis
was performed of locally published results from 10 field experiments in order
to estimate average values of nitrogen fixation from the atmosphere, crop yield
and soil nitrogen balance in the region and, also, to fit a regression model
relating yield and fixed nitrogen. Results were compared with a nitrogen
balance calculated using a model fitted to worldwide data. Nitrogen fixation in
aboveground biomass was assessed by isotopic methodologies in all the
experiments and an estimation of fixed nitrogen in roots was performed. Grain
yield varied from 662 kg of dry matter (DM) ha-1 for non nodulating
isolines to 4260 kg DM ha-1 for commercial varieties. Nitrogen
fixation accounted for 20 to 55 % of the plant nitrogen. In average, 40 % of the
soybean nitrogen was fixed from the atmosphere, rounding 109 kg N ha-1.
Shoot biomass and grain yield were positively correlated to fixed nitrogen (R2>
0.69, P = 0.05). The slope of the regression of the amount of fixed nitrogen
against yield showed that, in average, the crop fixed from the atmosphere 52 kg
of N t-1 DM grain produced. By harvest approximately 60 kg of N t-1
DM were extracted from the agricultural system. Consequently, the apparent soil
nitrogen balance was slightly negative and as higher the yield, the more
negative the nitrogen balance. For an average soybean yield in the Pampas (2600 kg ha-1, 14 % water) the soil
nitrogen balance can be estimated to be -18 kg N ha-1 yr-1.
Estimation of fixed nitrogen with the model adjusted to worldwide data was
higher than with the local model and the calculated nitrogen balance turned to positive,
so this later model seemed not to be applicable to pampean conditions. Future
research is needed for the evaluation and the development of management practices
and crop rotations for minimizing the negative soil nitrogen balance of the
region.