RESUMO
Amazonian forests continuously accumulate carbon (C) in biomass and in soil, representing a carbon sink of 0.42-0.65 GtC yr-1 . In recent decades, more than 15% of Amazonian forests have been converted into pastures, resulting in net C emissions (~200 tC ha-1 ) due to biomass burning and litter mineralization in the first years after deforestation. However, little is known about the capacity of tropical pastures to restore a C sink. Our study shows in French Amazonia that the C storage observed in native forest can be partly restored in old (≥24 year) tropical pastures managed with a low stocking rate (±1 LSU ha-1 ) and without the use of fire since their establishment. A unique combination of a large chronosequence study and eddy covariance measurements showed that pastures stored between -1.27 ± 0.37 and -5.31 ± 2.08 tC ha-1 yr-1 while the nearby native forest stored -3.31 ± 0.44 tC ha-1 yr-1 . This carbon is mainly sequestered in the humus of deep soil layers (20-100 cm), whereas no C storage was observed in the 0- to 20-cm layer. C storage in C4 tropical pasture is associated with the installation and development of C3 species, which increase either the input of N to the ecosystem or the C:N ratio of soil organic matter. Efforts to curb deforestation remain an obvious priority to preserve forest C stocks and biodiversity. However, our results show that if sustainable management is applied in tropical pastures coming from deforestation (avoiding fires and overgrazing, using a grazing rotation plan and a mixture of C3 and C4 species), they can ensure a continuous C storage, thereby adding to the current C sink of Amazonian forests.
Assuntos
Sequestro de Carbono , Florestas , Solo/química , Biomassa , Brasil , Carbono , ÁrvoresRESUMO
This experiment evaluated a pensacola Bahiagrass pasture (Paspalum notatum Flüggeé). It was conducted near Gainesville, Florida, USA, to measure the effect of pasture management on biomass allocation (kg ha -1) of herbage, litter, root+rhizome, as well as forage quality. Treatments were three continuously stocked (low, moderate, and high, receiving 40, 120, and 360 kg N fertilizer ha-1 yr-1and with stocking rates of 1.2, 2.4, and 3.6 AU ha-1, respectively) and one rotationally stocked (RS; 7 -d grazing and 21-d rest periods; N rate of 360 kg ha-1 yr-1, 1 AU = 500 kg) pasture. The root+rhizome biomass was 4 to 12 times greater than herbage biomass. There was no effect of treatment on root+rhizome biomass. The root+rhizome biomass decreased during the grazing season. The greater manageme nt intensity imposed on high and RS pastures resulted in greater herbage biomass. The root/herbage ratio decreased with the intensification of management. The litter biomass turned to be greater than herbage biomass in the high and RS treatment, characteri zing the different cycling pattern that goes through the animal excretions. Treatments affected neither herbage NDF nor IVDOM, but increasing management intensity tended to result in high IVDOM.
Visando medir efeitos do manejo da Bahiagrass cv. pensacola (Paspalum notatum Flüggeé) na repartição de biomassa (kg ha-1) das folhas+colmos, serrapilheira, raízes+rizomas, e valor nutritivo da forragem, foi instalado um experimento próximo a Gainesville, Flórida, EUA. Tratamentos: três manejos contínuos (não intensivo, moderadamente intensivo, altamente intensivo, recebendo 40, 120, e 360 kg N ha -1 ano-1 e com lotação de 1,2; 2,4 e 3,6 UA ha-1, respectivamente) e um tratamento de manejo rotacionado (7 dias de pastejo e 21 dias de descanso), recebendo 360 kg N ha-1 ano-1 e 3,6 UA ha-1 (1 U A= 500 kg). A biomassa de raízes+rizomas foi superior a de folhas+colmos. Não houve efeito dos tratamentos na biomassa de raízes+rizomas. A biomassa de raízes+rizomas decresceu durante a estação de pastejo. A maior intensidade de manejo dos tratamentos altamente intensivo e rotacionado resultou em maior biomassa de folhas+colmos. A relação raiz/parte aérea decresceu com a intensificação do manejo. A biomassa de serrapilheira foi superior a de folhas+colmos nos tratamentos altamente intensivo e rotacionado, privilegiando a ciclagem de nutrienes via excreção animal. Os tratamentos não afetaram a FDN nem a DIVMO da forragem, mas intensificação do manejo tende a elevar a DIV MO da forragem.