A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

Wood, soil-macrofauna and nutrients – a field experiment in central AmazoniaVerhaagh, Manfred 1 , Martius, Christopher 2 , Martins, Gilvan C. 3 , Medeiros, Lucilene G.S. 31 Staatliches Museum für Naturkunde, Erbprinzenstr. 13, D- 76133 Karlsruhe, Germanymanfred.verhaagh@smnk.de² Zentrum für Entwicklungsforschung – ZEF, Walter-Flex-Str. 3, D-53113 Bonn, Germany3 Embrapa Amazônia Ocidental, C.P. 319, 69.011-970 Manaus/AM, BrasilSlash-and-burn cultivation is the method commonly used in Amazonia to clear land for cropplants. Due to the normally highly weathered, nutrient-poor soils this practice has to be combinedwith shifting cultivation. In practice fields are often abandoned already after one or two years toallow the regeneration of the soil during the fallow period. Nevertheless, land degradation is acommon problem especially in densely populated areas like Manaus or Belém. Investigationsduring the SHIFT-Project ENV 25 in the Zona Bragantina, Pará (HÖLSCHER ET AL. 1997) haveshown very high element losses during burning (e.g. up to 98% of C, 96% of N, 48% of K or 47%of P) a major reason why this form of agriculture is not sustainable even under fertilization. In thesame project was shown, however, that fire-free land clearing by cutting and chopping thesecondary vegetation converting it into a mulch layer results in the preservation of organic matterand nutrients. Crop production can be adequate especially in the second year under theseconditions, too.In our field experiment as part of SHIFT-Project ENV 52/2 in Manaus (site of Embrapa AmazôniaOcidental) we aim to investigate the role of the soil macrofauna, with a special focus on woodconsuming termites, during the decomposition of wood and in the release of plant nutrients in firefreeland preparations. For this purpose, 9 areas of secondary forest (capoeira) were cut during thedrier season in 2001, each 30x40m sized. We prepared 3 replicates of 3 different land treatments:(1) traditional slash-and-burn as control; (2) arranging the cut wood in files inside the areas leavingthe litter layer intact; (3) creating a several centimeters thick mulch layer of chopped wood via acommercial wood chopper. Total wood biomass was at least 50 tons/ha (d.w.) in the selected areas,and all areas were planted in November 2001 with cassava.Wood decomposition and its colonization by fauna is monitored in wood bags of 70x40 cm filledeither with trunk pieces (about 4 kg d.w.) of two commonly encountered trees in the capoeiravegetation (Vismia cayennensis, Bellucia sp.) or with a mixture of chopped wood of both species(about 2 kg d.w.). Other methods used to compare macrofauna abundance and biomass in thedifferent areas are: extraction of fauna from the organic layer from 0,56 m² sized areas in Winklerbags;extraction from litter and soil cores (21 cm Ø, 7 cm depth) in a Berlese funnels; extraction ofearthworms from 4m² squares by diluted formol; direct counts of termites nests and galleries. Soilorganic matter, soil nutrients (N, P and major cations) and characters of soil physics aredetermined in the same intervals as the fauna, i.e. every 6 months so far until the end of the projectin September 2003. To compare the effect of fertilizer on root production of cassava we fertilizedone third of each area.Literature: HÖLSCHER, D., MÖLLER, M.R.F., DENICH, M., FÖLSTER, H. (1997): Nutrient input-outputbudget of shifting agriculture in Eastern Amazonia. – Nutrient Cycling in Agroecosystems 47: 49-57.