Discussion and Conclusions

1
Carbon and Nutrient Stocks in Roots of
Agroforestry Systems and Secondary Forests in
Central Amazônia
Jorge Gallardo-Ordinola,1, Flavio J. Luizão,
Erick C.M. Fernandes, and Elisa
V.Wandelli Instituto Nacional de Pesquisas da
Amazônia, Rua Nelson Batista Sales 114, Cj
Petro-Aleixo, Manaus, AM, Brazil. Department of
Crop and Soil Sciences, Cornell University,
Ithaca, NY 14853 USA. Centro de Pesquisa
Agroflorestal da Amazônia da Embrapa
(EMBRAPA-CPAA), AM-10, km 29, Manaus, AM, Brazil
69011-970 1 Correspondence ilego_at_inpa.gov.br

• Results
• Carbon Stocks
• Based on three repetitions within each area, the
  secondary forest (SF) had the highest total
  coarse root biomass (18.3 t/ha) compared to the
  palm-based (AS1) (5.2 t/ha) and
  Silvopastoral-High Input system (ASP) (3.9 t/ha)
  (Figure 1).
• The AS1 and SF have a greater proportion of root
  biomass in the 10 mm diameter class than the
  ASP system, while ASP root biomass is
  characterized with a greater percentage of root
  biomass in the 0.5 - 10 mm diameter class.
• The SF contains higher carbon stocks within
  coarse roots than the two agroforestry systems.
  Of the two agroforestry systems, coarse root
  carbon stocks were higher in AS1 than the ASP
  system.
• Root distribution
• The majority of coarse roots were concentrated in
  the first 30 cm of soil for all species and
  land-use systems.
• Nutrient Stocks
• Concentrations for all nutrients were generally
  higher in fine roots than in coarse roots in the
  three systems.
• Vismia, a secondary forest species, had the
  greatest species-specific carbon concentration
  compared to other secondary forest and
  agroforestry species.
• Nitrogen concentrations within roots were
  greatest in Gliricidia and Desmodium
  (nitrogen-fixing legumes).
• Phosphorus concontrations within roots were the
  lowest of all analyzed macronutrients
  furthermore, root P concentrations were highest
  in cupuaçú, Gliricidia and Columbrina.

Objective To determine carbon and nutrient
stocks in fine and coarse roots in two 9-year-old
agroforestry systems established on abandoned
pastures in central Amazônia.

• Discussion and Conclusions
• Carbon
• The secondary forest and AS1 have more trees,
  denser vegetation, and greater aboveground
  biomass than the ASP system, which probably
  contributes to higher coarse root carbon stocks
  within those systems.
• Root distribution
• For the systems in general, the distribution of
  the roots, and nutrient quality depends on plant
  species, climate, age of the tree, planting
  density, management practices, among other
  factors (Szott et al., 1991 Froufe et al.,
  1997).
• The dominance of root biomass in the first 30 cm
  is probably a result of several physical and
  chemical soil properties
• 1) soil compact limits root development to
  greater depths.
• 2) nutrients are concentrated at the soil
  surface. Low sub-soil nutrients concentrations
  do not promote root develop to greater depths.
• Nutrient Stocks
• In AS1, the species Columbrina is contributing
  more to total coarse root biomass than other
  species within the same system, as a result of a
  large diameter tap root and deep rooting nature
  (Figure ___).
• The development continued development of
  agroforestry system which aim to increase
  resource capture will increase carbon
  sequestration reduce soil nutrient losses.
  Furthermore, agroforestry systems have the
  potential to provide for the well being of the
  people.

Introduction The maintenance of an adequate
level of soil organic matter (SOM) is one of the
main components of soil fertility management in
low-input land-use systems in the tropics (Young,
1989) Maintenance of soil organic matter
requires the input of crop residues and organic
fertilizers to the soils in sufficient quantities
to compensate for the rapid decomposition of
organic matter. One of the major aims of
agroforestry is to increase the availability of
biomass for soil amendment by the introduction of
highly productive tree species into cropping
systems. Plant root systems play a central role
in the development of soil fertility. They are a
source of carbon inputs into the SOM pool.
Furthermore, root systems take up mobile
nutrients from the soil solution, thus protecting
them from begin leached and, roots contribute
significantly to the maintenance of soil biomass,
among other functions. The creation of closed
nutrient cycles and increase of carbon inputs
into the soil through perennial root systems are
among the major reason for integrating trees into
cropping systems in agroforestry (Young, 1989).
Methods Study Sites The research was conducted
in central Amazônia, AM, Brazil at the
EMBRAPA/CPAA research station, km 54 on BR-174.
Three repetitions of two types of agroforestry
systems were planted in 1992 in abandoned
degraded pastures. The Palm-based (AS1)
Silvopastoral-High Inputs (ASP), were established
after a slash and burn in late 1991 and three
secondary forest (SF) control plots demarcated
(Fernandes et al., 2001). The soils are
well-structured, fast draining nutrient poor
Xanthic Hapludox Oxisol with more than 75
clay. Carbon Stocks and nutrients
evaluation Coarse roots in three classes (0.2 -
0.5 mm, 0.5 - 10 mm, and 10 mm) were measured
in AS1, ASP and SF to study inter- and
intra-specific species root interactions and
compare root biomass and nutrient stocks between
land-use systems. Roots were sampled with an
auger to 50 cm depth. Coarse roots were excavated
from trenches in 10 cm layers to 150 cm depth.
Soil pits were 3 x 3 m (AS1) and 0.5 x 3 m (ASP,
SF) and all were 1.5 m deep. Fine (also collected to compare nutrient concentrations
between species and systems. Roots were weighed
fresh, sub-sampled, washed, dried, re-weighed and
analyzed for C and nutrients.
Site study
Roots tn/há-1
Acknowledgements and References We the staff of
EMBRAPA/CPAA for facilitating fieldwork and
laboratory analysis. Research was financed in
part by the NASA - Long-term Biosphere-Atmosphere
Experiment in the Amazon.