Five native tree species and manioc under slash-and-mulch agroforestry in the eastern Amazon of Brazil: plant growth and soil responses |
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| Authors: | Aaron H Joslin Daniel Markewitz Lawrence A Morris Francisco DeAssis Oliveira Ricardo O Figueiredo Oswaldo R Kato |
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| Institution: | (1) Warnell School of Forestry and Natural Resources, The University of Georgia, Athens, GA 30602, USA;(2) Institute of Agricultural Sciences (ICA), University of Agricultural Sciences of Amazonia (UFRA), 2501 Perimetral Avenue, PO Box 917, Belem, PA, 66077530, Brazil;(3) Embrapa Amazonia Oriental, Belem, Brazil; |
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| Abstract: | Throughout the Amazon of Brazil, manioc (Manihot esculenta) is a staple crop produced through slash-and-burn agriculture. Nutrient losses during slash-and-burn can be large and nutrient
demand by food crops so great that fields are often abandoned after two years. In recent decades, farmers have reduced the
fallow phase from 20 to ~5 years, limiting plant nutrient accumulation to sustain crop yields. Improved fallows through simultaneous
planting of trees with food crops may accelerate nutrient re-accumulation. In addition, slash-and-mulch technology may prevent
loss of nutrients due to burning and mulch decomposition may serve as a slow-release source of nutrients. This study in Pará,
Brazil, in a 7-year-old secondary forest following slashing and mulching of the vegetation, involved two main plot treatments
(with and without P and K fertilizers) and two sub-plot treatments (with or without a N2-fixer Inga edulis). A mixed-culture of trees and manioc was planted in all plots. P and K fertilizer increased tree mortality due to weed competition
but growth of surviving trees in four of the five tree species tested also increased as did biomass production of manioc.
In the N2-fixer treatment trends of greater growth and survival of four of five tree species and manioc biomass were also observed.
Fertilization increased the biomass of competing vegetation, but there was a fertilizer by N2-fixer interaction as I. edulis caused a reduction in competing biomass in the fertilized treatment. After one year, fertilization increased decomposition
of the mulch such that Ca, Mg, and N contents within the mulch all decreased. In contrast, P and K contents of mulch increased
in all treatments. No influence of the N2-fixer on 0–10 cm soil N contents was observed. Two years after establishment, this agroforestry system succeeded in growing
a manioc crop and leaving a well-maintained tree fallow after the crop harvest. |
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