Cultivation of <i>Erianthus</i> and Napier Grass at an Abandoned Mine in Lampung, Indonesia

Abstract

The production of cellulosic bioethanol from non-edible plants is drawing increasing attention, as it potentially avoids food-fuel competition. Because growing such plants on farmland indirectly reduces food availability, the plants should be grown on marginal, non-arable lands. In this study, we evaluated the growth of cellulosic energy crops at a former mining site in Indonesia. This mine was abandoned because it contained few mineral deposits, and exposed subsoils rather than toxic soils prevented revegetation. In the first trial, growths of two energy plant species Erianthus spp. and Napier grass ( Pennisetum purpureum ) were compared with that of maize ( Zea mays ) at the mine site and a nearby degraded farm. Erianthus and Napier grass produced 11.7 and 22.5 t·ha -1 of shoot dry matter at 8 months after planting (MAP) in the farm respectively while maize plants failed to establish, but none of the three species grew at the mine. In the second trial, two-week-old seedlings of Erianthus and Napier grass rather than stem cuttings as used in the first trial were planted at the mine site. Erianthus and Napier grass produced 16.3 and 24.0 t·ha -1 of shoot dry matter over the course of 18 months, respectively. Application of organic fertilizer significantly increased shoot dry matter to 18.9 and 39.6 t·ha -1 in Erianthus and Napier grass, respectively. During the 18-month growth period, both of the energy plants significantly increased soil carbon at the 0 - 0.3 m depth from 0.33% to 1.15% - 1.23% when chemical fertilizer was applied and to 0.67% - 0.69% when both chemical and organic fertilizers were applied. From 0 - 5 MAP, soil surface level dropped by 28.0 - 34.7 mm in plots without plants due to soil erosion. In contrast, both of the energy plants significantly reduced the drop of soil surface level to 16.0 - 19.3 mm in plots with chemical fertilizer alone and to 18.0 - 20.7 mm in plots with chemical and organic fertilizers. Proportions of small soil particles, that would be easily detached and transported by water flow compared with large particles, were larger in the planted plots than the no-plant plots at 16 MAP. The results suggest that successful cultivation of energy plants on abandoned mine sites is possible, particularly if seedlings are transplanted and the crops are fertilized with organic fertilizer. In addition, the cultivation of Erianthus and Napier grass has positive impacts on soil quality that may contribute to their sustainability as crops and to the conservation of the local ecosystem.