Methane Fluxes by dffhrtcv3


                                                                     Fluxes of methane from soils in the Central Amazon: The role of agroforestry systems
                                                                                                                                          Marco A. Rondón*, Erick C.M. Fernandes*, Elisa Wandelli‡ and Rubenildo Lima Da Silva‡
                                                                                  *Department of Crop and Soil Sciences, Cornell University, Ithaca, NY 14853; ‡Centro de Pesquisa Agroflorestal da Amazônia (EMBRAPA-CPAA), AM-10, km 29, Manaus, AM, 69011-970;

                                                                                                                                                                    2. OBJECTIVES                                                                                                                                                                                   Figure 3. Methane fluxes in agroforestry systems in the                                           Figure 4. Methane fluxes in managed pastures
   Forests soils have been found to be net sinks for atmospheric methane during most of the annual cycle in several                                                                                                                                                                                                                                                                     Central Amazon

   tropical regions (Davidson et al, 1995) and are considered to play an important role in global methane budgets (Dorr                                             *         To assess net fluxes of methane from soils under three agroforestry systems (AS1,AS2                                                                                              90

   et al, 1993). When primary forest is converted to agriculture or pastures, the methane sink is usually reduced and                                                          and ASP), primary rainforest and secondary forest (SF).                                                                                                                          60

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   eventually soils could become net sources (Keller et al, 1997).                                                                                                  *         To determine the effect of fertilization (P, Ca and Gypsum) on fluxes of methane from                                                                                             -30

                                                                                                                                                                               pastures.                                                                                                                                                                        -60
                                                                                                                                                                                                                                                                                                                                                                -90                                  Nov

   In the last three decades at least 30 x             106
                                               ha of Amazon forest has been converted to pasture. Poor management                                                   *         To make preliminary estimates of methane fluxes from termite mounds under                                                                                                        -120
                                                                                                                                                                                                                                                                                                                                                                        Aug/00    Sep     Oct
                                                                                                                                                                                                                                                                                                                                                                                                                          Jan/01                             -120
                                                                                                                                                                                                                                                                                                                                                                                                                                                                       Oct/00                            Nov                     Dec                   Jan/01

                                                                                                                                                                                                                                                                                                                                                                                              AS1    ASP     AS2                                                                                                 Control   Fertilized

   leading to a drastic decline in pasture productivity and invasions by persistent, herbaceous and woody weeds have                                                           agroforestry systems and secondary vegetation.
   led to most being abandoned within a few years of use. This provokes clearing of additional primary forest for new
   pasture establishment. Considering the vast area involved, net changes in fluxes of methane and other GHG                                                                                                                                                                                                               5. DISCUSSION
   associated with the continued conversion of Amazonian forest into pasture could have effects at regional and global
   scales.                                                                                                                                                                                                                                                                                                                 Due to its influence on gas diffusion, soil texture is an important factor associated with fluxes of
                                                                                                                                                                                                                                                                                                                           methane under native vegetation (Dorr et al, 1993). Campina forest located in a soil with 94% sand
   It is well known that termites emit methane to the atmosphere. In degraded lands in the Central Amazon, termite                                                                                                                                                                                                         (high gas diffusivity) showed higher sink fluxes compared to primary "terra firme" forest on a clayey
   mounds are abundant and they appear to negatively impact primary productivity by inhibiting re-colonization by                                                                                                                                                                                                          soil (75% clay). Native forest (campina and terra firme) are clearly the strongest methane sink (figure
   vegetation (see Fernandes et al, this session). They may also contribute to net methane fluxes.                                                                                                                                                                                                                         6), with an estimated annual oxidation rate of 4,5 to 6,9 g CH4.ha -1y-1 (Only the drier months have been
                                                                                                                                                                                                                                             ASP                                                                           evaluated so far). These estimates coincide with reported values for tropical rainforest (Keller et al,
   Our LBA project considers two strategies for regenerating degraded pasture land aimed at breaking the vicious                                                                                                                                                                                                           1997).
                                                                                                                                                                                                                                     AS 1                                                                                                                      Figure 5. Methane emission from termite mounds under                                                 Figure 6. Estimated methane oxidation during the dry
   circle of deforestation: Restoring productivity through modest inputs of P and Ca; and the establishment of                                                                                                                                                                                                                                                        various land uses in the Central Amazon                                                                   season in the Central Amazon
                                                                                                                                                                                                                                                                     AS 2
   agroforestry systems (AFS) [see McCaffery et al, this session]. Regenerated pastures are expected to enhance
   methane sinks, while AFS growing on formerly degraded lands have been proven to improve soil quality, increase                                                                                                                                                                                                                                              40                                                                                                                         9

                                                                                                                                                                                                                                                                                                                                                                                                                                                                         kgCH4 ha -1y-1
                                                                                                                                                                             Aerial View of the plateau with experimental sites. The 3 blocks are surrounded by secondary forest Systems studied
   soil faunal activity and diversity (Fernandes et al, 1995) and would likely also result in positive impacts on methane

                                                                                                                                                                                                                                                                                                                               mgCH4 m-2 h-1
                                                                                                                                                                             included: Palm -based (AS1), Fruit based (AS2), tree-grass-legume pastures (ASP), Secondary forest (SF). Plots of                                                                 20
   balances. However, data on methane fluxes between soils and the atmosphere from AFS in the tropics is notably                                                             Primary forest, control and fertilized pastures are located 1 km apart.                                                                                                                                                                                                                                      3

   scarce.                                                                                                                                                                                                                                                                                                                                                      0                                                                                                                         0




                                                                                                                                                                                                                                                                                                                                                                            AS1         AS2         Forest           SF            Pasture

                                                                                                                                                                                   4. PRELIMINARY RESULTS

                                                                                                                                                                        Precipitation: Figure 1 shows weekly rainfall distribution for the experimental area.                                                              Conversion of forest to pastures resulted in drastic net reductions in methane oxidation by soils, almost
                                                                                                                                                                        (data from McCaffery, 2001).                                                                                                                       eliminating net sinks during the sampled period. This is in agreement with findings for other rainforests
                                                                                                                                                                        Methane fluxes in primary and secondary forests: Figure 2 shows that in agreement                                                                  (Keller and Reiners, 1994, Goureau et al, 1993). Secondary forest also showed only negligible net
                                                                                                                                                                        with results from other tropical areas (Scharfe et al, 1990), forest soils in the Central                                                          methane sinks, comparable to those of degraded pastures. This could be attributed to "leaks"coming
                                                                                                                                                                        Amazon are net sinks of methane during the dry season. Sandy "Campina"soils                                                                        from abundant termite mounds that are found in this vegetation. (see Fernandes et al, this session)
    Millions of hectares of the Amazon rainforest
    are converted each year to pasture. Oxidation of
                                                       Because of poor management, pastures only                 Degraded pastures are soon abandoned and               constitute the largest sink within the land uses studied, although we only have late dry                                                           Figure 6 shows how AS1 and AS2 Agroforestry systems allowed a recovery of methane sinks to around
                                                       maintain their productivity for a few years before        secondary vegetation start to colonize the land.       season data evaluated for this ecosystem. Early wet season data are currently being
    methane by the soils is drastically reduced.
                                                       becoming degraded.
                                                                                                                                                                                                                                                                                                                           50% of forest values, but the pasture based ASP reached only nearly 25% of forest sink strength.
                                                                                                                                                                                                                                                                                                                           Initial data suggest that the application of modest levels of P and Ca to recover degraded pastures could
                                                                                                                                                                        SF soils exhibit small net methane fluxes during the early dry season, but later become                                                            enhance methane sinks in the region.
       3. METHODS                                                                                                                                                       a small sink again until the onset of rains. It is feasible that observed fluxes in SF are
                                                                                                                                                                        related to high termite populations and activity. Intense rainfalls in late December                                                               Fluxes of methane by termites. Though the proportion of the area covered by termite mounds is less
   Site: Three repetitions of four AFS were planted (3/92) at the EMBRAPA/CPAA Research station, km 54 on BR-174
                                                                                                                                                                        triggered a change in fluxes from sinks to small sources.                                                                                          than 2% of total area (Queiroz, 2001), methane fluxes in SF and in Pasture sites are at least two orders
   north of Manaus, on a Xanthic Hapludox in an area of abandoned degraded pastures: Palm-based (AS1);                                                                                      Figure 1. Weekly rainfall distribution                                   Figure 2. Methane fluxes in Primary and Secondary

   Fruit/Timber-based (AS2); Silvopastoral-High Inputs (ASP); were established after a slash and burn in 11/91 and                                                                                                                                                              forest in the Central Amazon               of magnitude higher than recorded sinks by soils in the same plots. This suggests that termites could

   three secondary forest (SF) control plots demarcated. Primary forest on the same soil type (Forest) and "Campina", a                                                                                                                                        30
                                                                                                                                                                                                                                                                                                                           control methane budgets in such areas. Our estimates resulted in higher emission rate from soil termite
                                                                                                                                                                                                                                                                                                                           mounds than reported data by Martius et al (1993) for above-ground termite mounds. Our data set is still

                                                                                                                                                                                                                                               ug CH4m-2h-1
   dwarf forest on a Quartzipsament were also studied. In the same area, 12 year old pastures of Brachiaria sp. were                                                          80
                                                                                                                                                                                                                                                                                                                           limited and therefore any extrapolation is cautioned. Studies will continue during 200.

   fertilized on 10/00 with P, Ca and gypsum (Welch, 2000). Twelve termite mounds from each land use were sampled                                                                                                                                              -60

   in early January 2001.
                                                                                                                                                                                                                                                               -90                                                         Data does not yet cover the full annual cycle thus net annual estimates are premature.
                                                                                                                                                                                                                                                                     Aug/00   Sep       Oct      Nov      Dec     Jan/01
   Gas sampling: Four closed vented chambers (25cm diameter) were used to sample gas in each of AS1, AS2, ASP,                                                                 0
                                                                                                                                                                                                                                                                                         SF    Forest   Campina

   SF, Forest and Campina, as well as in fertilized and control pastures. Weekly to bi-weekly measurements were
                                                                                                                                                                                   Aug/00       Sep      Oct       Nov        Dec    JAn01
   initiated on August 2000 and to date, they cover part of the dry season and the onset of the rainy season. Gas samples                                                                                                                                                                                                  Thanks to Antonio Nobre, Eleusa Barros, and INPA’s Agronomy laboratory personnel for allowing us
   were analyzed within 24 hours after collection using a Perkin Elmer model GC400 gas chromatograph. (FID                                                                                                                                                                                                                 to use their GC and for providing a friendly working environment. Thanks to all students and staff of the
                                                                                                                                                                        Methane fluxes in Agroforestry systems: As shown in figure 3, during the dry season                                                                LBA ND0-4 project for continued support and productive discussions. Photographs by E. Fernandes, K.
   detector, 3m Porapak Q column, 75C, carrier gas, He).
                                                                                                                                                                        all the AFS sites oxidized atmospheric methane. As the soil becomes more humid with                                                                McCaffery and M. Renjifo.
                                                                                                                                                                        the arrival of the rainy season, soils reduced their sink strength and became a net source
                                                                                                                                                                        of atmospheric methane. Both AS1 and AS2 were successful in enhancing methane sink
                                                                                                                                                                        compared to ASP which consistently showed reduced sink capacity. Temporal
                                                                                                                                                                        variability in flux estimates was high especially in pastures and was more homogeneous
                                                                                                                                                                        in AS2.
     Presence of termite mounds is
     abundant on degraded pasture land.                                                                                                                                 Methane fluxes in fertilized pastures: Figure 4 illustrates that fertilization appears to
     Mounds inhibit vegetation
     regrowth. Emission of methane by                                                                                                                                   slightly enhance methane sinks at the end of the rainy season. Fertilizer was applied in
     termites could surpass oxidation by                                                                                                                                September and therefore a time lag seems to exist before an effect is evident. Pastures,
     the termite impacted soils.
                                                                                                                                                                        including ASP, showed consistently lower methane sinks or higher sources. This is in                                                                                           Restoring pasture productivity with modest inputs and                                                   Agroforestry systems offer an alternative to regenerate
                                                                                       Heavily degraded pastures are covered by dispersed                               agreement with studies done in the region (Goreau et al, 1988).                                                                                                                selection of proper species, can reduce the necessity to                                                degraded land and to partially recover soil methane sinks.
                                                                                       earthworm casts. Surface sealing occurs limiting the                                                                                                                                                                                                            clear additional primary forest.
                                                                                       diffusion of methane from the atmosphere to the
                                                                                       soils.                                                                           Methane emissions from termite mounds: Figure 5 shows average fluxes from 12
                                                                                                                                                                        mounds sampled in each land use. All mounds sampled in SF were active (emitting                                                                                                                                                       6. REFERENCES CITED                                                                 see Handout

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