The Effect of Charcoal in Banana (Musa Sp.) Planting Holes – An On-Farm Study in Central Amazonia, Brazil

Agricultural production in the tropics is frequently limited by low soil fertility. Many tropical soils are rich in kaolinite and iron (Fe) and aluminium (Al) oxides, but relatively poor in soil organic matter (SOM), they frequently have a low cation exchange capacity (CEC), low pH, low calcium (Ca), and phosphorus (P) contents (Zech et al. 1990). In strongly weathered tropical soils, SOM plays a major role in soil productivity because it represents the dominant reservoir of plant nutrients (Tiessen et al. 1994; Zech et al. 1997). Generally SOM contains 95% or more of the nitrogen (N) and sulphur (S), and between 20% and 75% of the P in surface soils (Duxbury et al. 1989). Rapid mineralization of organic matter after clearing of forests and during continuous farming explains low fertility levels of many tropical soils under permanent cropping systems (Tiessen et al. 1994; Zech et al. 1990).

Conventional fertilization with mineral fertilizer (mainly N applied as urea or ammonium sulphate) is not very efficient on soils with low nutrient retention capacity (Alfaia et al. 2000). Heavy tropical rains leach easily available and mobile nutrients into the subsoil where they are unavailable for most crop plants (Giardina et al. 2000; Hölscher et al. 1997; Renck and Lehmann 2004). To overcome the poor nutrient supply the common agricultural practice in the tropics is slash and burn agriculture. Practiced by about 300 to 500 million people worldwide, (Giardina et al. 2000; Goldammer 1993) slash and burn contributes significantly to global warming (Fearnside 1997). This traditional agricultural practice is considered sustainable if adequate (up to 20 years) fallow periods follow a short time of cultivation (Kleinman et al. 1995). Long fallow periods make this technique land demanding and hardly any other crop than manioc can be cultivated by shifting cultivation in Central Amazon, without access to fertilizers.