INVESTIGADORES
ALVAREZ Roberto
artículos
Título:
A regional audit of nitrogen fluxes in pampean agroecosystems
Autor/es:
. R. ALVAREZ; H STEINBACH Y R ALVAREZ; J. DE PAEPE
Revista:
AGRICULTURE, ECOSYSTEMS AND ENVIRONMENT
Editorial:
ELSEVIER SCIENCE BV
Referencias:
Lugar: Amsterdam; Año: 2014 vol. 184 p. 1 - 8
ISSN:
0167-8809
Resumen:
Calculation
of nitrogen (N) budgets can help in the understanding of agroecosystem
functioning and in proposing more sustainable management strategies.
Changes in the main N fluxes of the pampean agroecosystems of Argentina
were calculated over time. The impact of management changes on regional N
budget and possible future trends were estimated. Changes in land use were
quantified using national censuses data. Biological N fixation of leguminous
forages was assessed using a regression model and local field experimental
data. Nitrogen fixation by soybean, the most extensive grain crop, was
calculated using an existing model. Fertilizer input was based upon farmer surveys,
and atmospheric N input estimated using local data. Nitrogen output by grain
harvest was estimated using national yield statistics and averaged grain N
concentration derived from many field experiments widespread over the region.
During the last 50 years cropped area has doubled as a result of the widespread
adoption of soybean as the main component of rotations. The agricultural
expansion included areas previously used for grazing on seeded pastures
and seasonal graminaceus forages. The historical N budget of the entire region
was positive but has dropped from 2.0 Mt y-1 in 1960 to 1.3 Mt y-1 at
present. This reduction implies that N fixation by soybean and fertilizer
application were lower than the previous livestock/pasture systems N input.
During the cropping phase of rotations the N budget was usually negative in the
past. Currently, in low yielding areas of semiarid environments, the N budget
turned positive; meanwhile in humid climates with high productivity scenarios
it remained negative. Fertilizer rates applied balanced N output in the former
case but not in the latter. Partial factor productivity of N inputs increased
from three- to six-fold during the last 50 years in the Pampas. Uncertainties
related to the estimations performed are discussed.