Cocoa industrial debris composting in soil and earthworm breeding
Toasted husk, the main cocoa (Theobroma cacao L.) industrialization by-product, was added to pots in different husk doses with 1 kg of topsoil from a cocoa plantation (Umbrisol) and then treated with 5 earthworms (Pontoscolex corethrurus) during 60 days, in a greenhouse experiment. Amendment enhanced (p < 0.5) soil organic matter, water retention, bulk density. Best dose for earthworms breeding was 63.3 g·kg-1 (1,840 g·m-2). Husk was used to feed 10 earthwormsxm-2 in an Eutric Fluvisol at Villahermosa, Tabasco, Mexico; in 67 days, produced 58 worms on husk 920 g·m-2, or 54 worms on 1150 g·m-2 husk. Husk was then subjected to a conventional pile composting, and the compost was used to feed 10 earthworms m-2 in the Eutric Fluvisol; those fed with 920 g·m-2 yielded 300 worms·m-2. The product of this last experiment was used as amendment (dose 920 g·m-2) in a 30,000 plants·ha-1 maize crop on a highland Mollisol: yields were 954 kg·ha-1 without amendment, 1137 kg·ha-1 amended. As for humification, the main quality parameters from the materials and soils studied, and purified fractions of humic and fulvic acids were studied by visible and infrared (FTIR) spectroscopy. The major changes observed in the humic acid fraction suggest that the improvement in soil organic matter properties could be related to the increase in aromatic, oxygen-containing and amide functional groups, as could correspond to selective biodegradation process concomitant to incorporation of microbial products into oxidized, altered husk lignin fractions.