Effect of land-clearing methods and postclearing management on aggregate stability and organic carbon content of a soil in the humid tropics
1986
Alegre, J. C. | CASSEL, D. K.
The objective of this study was to evaluate the effects of land-clearing methods and subsequent soil management on aggregate stability and soil organic carbon (OC) content in the 0− to 15-cm depth. The 2-yr-long study, beginning in July 1980, was conducted on Yurimaguas soil (fine-loamy, siliceous, isohyperthermic Typic Paleudult) in the Amazon jungle of Peru. The site was initially covered with a 20-yr-old secondary evergreen forest. Land-clearing methods were: (1) slash-and-burn, with logs removed by hand, but stumps remaining in place; (2) mechanical clearing with a bulldozer with a straight blade; and (3) mechanical clearing with a bulldozer with a shear blade. Soil samples were taken before clearing and at 3, 8, and 23 mo after clearing. After the second soil sampling, various land-preparation techniques were superimposed upon the three clearing methods to give a total of six land clearing-soil management treatments. Each treatment was split in three subtreatments: (1) flat-planted with no fertilizer or lime, (2) flat-planted with recommended rates of fertilizer and lime, and (3) bedding with fertilizers and lime. The third and fourth sets of soil samples (8 and 23 mo after clearing) were taken prior to harvesting the first and fifth consecutive crops, respectively. Straight-blade clearing reduced mean weight diameter (MWD) and OC by 39 and 21%, respectively. The least change in these two soil properties occurred for slash-and-burn clearing, with an 11 % reduction in MWD and no change in OC. No significant changes in the percentages of five water-stable aggregate size classes occurred between 8 and 23 mo after clearing. Soil-management practices, such as bedding and lime application, tended to maintain aggregate stability and OC levels of newly cleared land during the first 2 yr of continuous cropping.
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