‘Without bamboo, the land dies’: nutrient cycling and biogeochemistry of a Javanese bamboo talun-kebun system

Abstract

The accumulation and removal of biomass, and the inventory of five major nutrients (N, P, K, Ca, and Mg) in plants, litterfall, forest floor, and in the mineral soil were quantified at various stages of a bamboo talun-kebun agroforestry system (West Java, Indonesia). Data were collected in order to explain the biogeochemistry of the system over an entire rotation cycle. This cycle consisted of 1 year of mixed species vegetable cropping ( kebun) after the removal of bamboo, followed by a year of cassava cropping, and 4 years of bamboo fallow ( talun): a total cycle length of 6 years. The accumulation of five major nutrients in live plant biomass during a complete talun-kebun rotation cycle was 787, 134, 692, 218, and 248 kg ha −1 for N, P, K, Ca, and Mg, respectively. The overall nutrient removals accounted for approximately 51%, 48%, 55%, 52%, and 56% of N, P, K, Ca, and Mg accumlated in the live plant biomass, respectively. Accumulation of N, P, K, Ca, and Mg in the forest floor peaked at the end of the mature talun stage, i.e. when the forest floor mass accumulation reached its maximum. Fertilization was an important input during the first year of cropping: it accounted for 63%, 145%, 100%, 188%, and 225% of N, P, K, Ca, and Mg output, respectively, during this period. Cassava cultivation decreased the content of exchangeable K in the mineral soil during the second year of cropping. Available P in the surface 5 cm of mineral soil increased slightly after clearing and hoeing, but decreased to 92% and 75% of its original value in the first and second year cropping stages, respectively. About 220 kg N ha −1 was lost from the system over the 6-year rotation, a difference between input and output to and from the system which reflected changes in the soil N compartment. Soil data on P, Ca, and Mg did not suggest a current problem of declining availability of these elements on the site, although the use of an NPK fertilizer does suggest concern over the availability of K. Finally, soil leaching losses were very small in comparison to losses in harvest removals.