'Without bamboo, the land dies': A conceptual model of the biogeochemical role of bamboo in an Indonesian agroforestry system

The Italun-kebun' system consists of a 6-7 year management cycle in which a 4-5 year fallow period of perennial clump bamboo is alternated with 2 years of food crop production, Clearcutting, raking the forest floor and slash into piles for burning, and hoeing the soil to a depth of 25 cm reduces the vigour of the bamboo to the point at which it poses no competitive threat to the first year of planted food crops. These crops are (typically) cucumber, bitter solanum and hyacinth (pole) beans, Ash from the burned slash piles, plus some animal manure and application of NPK fertiliser (only recently), are used to increase the production of these vegetables. In spite of these nutrient additions, the fertility of the upper soil layers declines during the first year, and the field is planted to cassava (a less nutrient-demanding root crop) the second year after clearcutting. After 2 years of cultivation, bamboo regrowth and declining soil fertility prevent continued food cropping, The field is abandoned and permitted to revert to an unmanaged stand of bamboo for 4-5 years. The historical success of the system appears to be based largely on the 'nutrient pumping' action of the bamboo, the slow decomposition of its silica-rich litter, and the extremely high biomass of bamboo fine roots. Studies reported earlier and in subsequent papers support the interpretation that the bamboo recovers much of the nutrients leached deeper into the soil profile during the 2 years of cropping and deposits them at or near the soil surface as above-ground litter and dead fine roots. The biogeochemical role of bamboo in sustaining the productivity of this agroforestry system reflects the rural farmer's saying: 'without bamboo, the land dies'.