Soil nitrogen cycling following montane forest conversion in Central Sulawesi, Indonesia
2006
Corre, M.D. | Dechert, G. | Veldkamp, E.
The lower montane forest zone of Indonesia is undergoing rapid conversion of indigenous forests to agriculture. In this tropical region, however, the effects of forest conversion on soil N processes have not been investigated. Corn (Zea mays L.) and cacao (Theobroma cacao L.)-coffee (Coffea canephora Pierre ex Froehner) agroforestry are the main land use types in cleared lower montane forests in Central Sulawesi, Indonesia. Our main objective was to compare the soil N dynamics under agroforest systems and corn cultivation with indigenous forest. We measured the gross rates of N transformation processes using 15N pool dilution. The agroforest systems and indigenous forests had higher gross N mineralization rates and faster turnover rates of NH4(+) and microbial N pools than the long-term cultivated corn sites. Faster soil N turnover rates in agroforest systems suggest a more dynamic soil N cycling. Leguminous shade trees, which are important components of these agroforest systems, may have influenced the fast microbial N cycling through release of N-rich root exudates and plant residues. Our results show that compared with corn, agroforestry is a better option in terms of sustainability in the N-supplying capacity of the soil. In addition, we measured higher 15NH4(+) recoveries than 15NO3(-) recoveries after 15 min of 15N addition in all our sites. Our measured rates of gross nitrification were very low to negligible, due to rapid disappearance of added 15NO3(-). Such fast reaction of NO3(-) warrants further investigation, especially in tropical areas where 15N studies are very few.
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