Land Use and Changes in Soil Morphology and Physical-Chemical Properties in Southern Amazon

Abstract

Many Amazonian farmers use the slash-and-burn method rather than fertilization for crop production. The aim of the present study was to evaluate changes in the morphological, physical, and chemical properties of naturally fertile Inceptisols after conversion from native forest to different uses in southern Amazonia, Brazil. Land covered by dense native forest (NF) was split into four areas of 1.0 ha each. Three areas were slashed and burned and then cultivated for 11 years with coffee (CO), secondary forest (SF), and pasture (PA). Four soil profiles were sampled in each treatment (four uses × four replicates). The mean value distribution of each physical and chemical analysis was determined for different depths, and standard error bars were placed to display significant differences among treatments. Results showed that morphology and physical properties were negatively affected after the establishment of PA and CO: a reduction in the thickness of the A horizon and in aggregate stability, a decrease in total porosity and macroporosity, and an increase in aggregate size and bulk density. Soil bulk density (SBD), geometric mean diameter of water-stable aggregates (GMD), and microporosity (SMi) were higher in soil under pasture as a consequence of more intense soil surface compaction. Native and secondary forests were the only treatments that showed granular structures in the A horizon. Significant differences between native forest and secondary forest were mainly found in the top soil layer for total porosity (STP) (NF>SF), macroporosity (SMa) (NF>SF), SBD (NF>SF) and GMD (SF>NF). Phosphorus contents in the A horizon increased from 6.2 to 21.5 mg kg -1 in PA and to 27.2 mg kg -1 in SF. Soil under coffee cultivation exhibited the lowest levels of Ca 2+ and sum of bases in surface horizons. In all slash-and-burn areas there was a reduction in the C stock (Mg ha -1 ) of the A horizon: native forest 6.3, secondary forest 4.5, pasture 3.3, and coffee 3.1.

Ponds, puddles, floodplains and dams in the Upper Xingu Basin: could we be witnessing the ‘lentification’ of deforested Amazonia?

“…Soil compaction, as indicated by increased bulk soil density or soil penetration resistance, and/or by decreased soil porosity, infiltrability or hydraulic conductivity, were consistently observed in all 19 studies we could find conducted in four basins (Coastal South Atlantic, Tocantins, Amazon, Orinoco), including five of six Amazon sub-basins (Xingu, Tapajós, Madeira, Solimões and Negro) [37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48; 5; 49; 50; 51; 52; 53; 54; 55] (Table 1). Importantly, soil compaction was observed in every type of land use including secondary and logged forests, deforested land, pastures, and in soybean, maize, oil palm, coffee, and teak plantations (Table 1).…”

Long fallows allow soil regeneration in slash‐and‐burn agriculture

“…) because the TOC in the surface layer is the main cementing agent for soil aggregation. Melo et al . evaluated changes in the morphological, physical and chemical properties of inceptisols after conversion from native forest to different uses with slash‐and‐burn agriculture in southern Amazonia, Brazil.…”

Soil enzyme responses to land use change in the tropical rainforest of the Colombian Amazon region

“…In the Amazon region, intensive deforestation of native rainforest for expansion of livestock and agricultural activities has led to significant changes of soil C stocks, and degradation of soil physico-chemical properties in many regions [ 12 – 15 ]. Particularly, soil health degradation and soil C declines were substantial in pasture systems with low-fertility soils [ 14 – 16 ].…”