A global project on `Alternatives to Slash and Burn’ agriculture was initiated by a consortium of international and national research institutes to facilitate intensification of the use of converted forest land, in order to help alleviate poverty and protect the remaining forest areas for their biodiversity values and their role in mitigating greenhouse gas emissions. Data for the Indonesian benchmark areas in the lowland peneplain, piedmont and mountain zone of Sumatra are presented. A significant amount of forest land, especially in the lowland peneplain, has been converted in the last ten years into agricultural use, usually following logging concessions. Soils on the peneplain are poor (oxi-and ultisols) and current intensive crop based production systems are not sustainable. In the piedmont zone on better soils (inceptisols), rubber agroforests (still) characterize the area. Agroforests have emerged during the 20th century as the major alternative to slash-and-burn agriculture, based on a shift of emphasis from food crops to cash-earning tree crops. Emphasis on food crops, however continues in government resettlement schemes. Differences in organic C content of the topsoil between forests and crop land are about 0.5% C, with agroforests and tree crop plantations in an intermediate position. A new size-density fractionation scheme for soil organic matter demonstrated larger changes in light and intermediate fractions. Forest soils can be significant sinks for methane and thus partly compensate for the methane emissions in lowland rice production. Overall, the Sumatra benchmark areas demonstrate the need to combine intensification of land use at the field/household level with effective protection of remaining forest areas at the community level and reducing other driving forces of deforestation at the national level.
Tag: land clearing
Dynamics of soil physical properties under alternative systems to slash-and-burn
A change from slash-and-burn to continuously cropped agricultural systems is occurring in heavily populated areas in the humid tropics. Well managed alternative systems to slash-and-burn can reduce soil structure deterioration, maintain soil fertility, and promote long-term productivity. The objectives of this paper are to describe the dynamics of soil physical properties under slash-and-burn and some alternative systems. Different land-clearing methods and post land-clearing management systems were evaluated on Typic Paleudults at Yurimaguas, Peru, for their effects on soil physical properties such as: bulk density, soil water characteristic, infiltration rate, aggregate stability, and penetrometer cone resistance. Mechanical clearing reduced the infiltration rate from 420 mm h1 before clearing to 35 mm h1 for the straight blade and 95 mm h1 for the shear-blade bulldozing. Straight-blade clearing damaged soil structure the most as indicated by a decrease in the percentage of larger soil aggregates. The practice of planting on raised beds prevented foot compaction of soil near the plants; bulk density was 1.14 and 1.29 Mg ha1 for bedded and flat planted soil, respectively. Of the various agroforestry systems evaluated (multistrata, peach palm production, shifting agriculture low input and high input continuous cropping) bulk density was lower after 4 years for the systems with trees or cover crops. Mean annual soil loss for alley cropping on sloping soils was 0.2 Mg ha1 year1 compared with 53 Mg ha1 year1 for two annual crops per year. The infiltration rate after 5 years of intensive grazing on five associations of legumes with grasses was reduced from 127 to 41 mm h1. Overgrazing caused severe soil compaction and reduced earthworm biomass. Research indicates that the greatest change in soil physical properties occurs during mechanical land clearing. Agroforestry systems improved soil physical properties when cover crops and trees were included in the system.