s:2121:"TI Dynamics of soil physical properties under alternative systems to slash-and-burn 
AU Alegre, J.C. 
AU Cassel, D.K. 
AB 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. 
";