E. S. O. Bortolon

Caracterização, potencial agrícola e perspectivas de manejo de solos leves no Brasil

Light soils occupy 8% of the Brazilian territory and are especially expressive in the new and last agricultural frontier in Brazil: the Matopiba region – in the states of Maranhão, Tocantins, Piauí, and Bahia –, where they represent 20% of the area. These soils fit into the textural classes of sand and loamy sand or sandy loam, down to 0.75-m soil depth or deeper, and they are mainly represented by Neossolos Quartzarênicos (Quartzipsamments) and, partly, by Latossolos (Oxisols) and Argissolos (Ultisols). The understanding of soil functioning depends on the establishment of distinguishing criteria for: organic matter dynamics; content and mineralogy of the clay fraction; coarse sand and total sand contents, in relation to those of fine sand; mean diameter of the sand fraction; and water retention capacity. These criteria can contribute for the zoning and for the conservation and fertility management of light soils, as well as for the estimation of their agricultural potential. Integrated production systems, such as crop-livestock and crop-livestock-forestry integration, besides no-tillage with crop rotation, mixed forestry planting with legumes, and the use of green manure and cover crops are relevant for the proper management of these soils. The objective of this review was to characterize light soils and to highlight the main challenges regarding their agricultural potential and their conservation and fertility managements, in face of the expansion and consolidation of the new Brazilian agricultural frontier.

Simulações espacialmente explícitas dos estoques de carbono orgânico de um LATOSSOLO BRUNO por meio da integração do modelo century com GIS

Simulation models are useful tools for assessment of the impacts of agriculture on nutrient and soil organic C (SOC) dynamics. Results of simulation studies can be applied to develop sustainable agricultural systems. This study simulated SOC in clayey Humic Hapludox with Century model (version 4.0) in a subtropical climate, with support from historical soil and land-use surveys; GIS and remote sensing techniques. Major reductions in SOC stocks were observed after land under native vegetation was converted to agricultural use, especially under annual crops managed under conventional tillage. Simulations of these soils under current management to the year 2058 showed that soils under conservation systems (especially no tillage) can recover and in some cases even exceed the original SOC stocks under native vegetation.

Carbon Balance at the Regional Scale in Southern Brazil Estimated with the Century Model

Modeling of soil organic C (SOC) dynamics associated with GIS can be useful to estimates C emissions and sequestration as a function of the changes in the land use and soil management. A balance of C emissions and sequestration was made at the regional scale using the Century model and GIS. Santana district in Ijui, RS (28° 20′S and 53° 53′W) was selected where occur Hapludox, Orthents, Argiudolls, and Fluvents are common. We identified four homogeneous areas based on cropping systems, soil tillage systems, and native vegetation. These areas were converted into agriculture at different times. Soil samples were taken at 0–20 cm depth. The Century model was calibrated and validated based on the sampled areas and their estimates were generalized. We defined different simulation units that are similar zones in soil class, landscape elements (hilltops, slope, and depositional areas) and time of agricultural use (1901, 1957, 1965, 1976, and 1988). The agriculture use caused a 50 % reduction in SOC stocks from 1900 to 1986 (from 550.9 to 276.8 Mg × 103), by the end of most intensive soil management period, which corresponded to emissions of 2,277.5 × 103 Mg of CO2 into the atmosphere. Moreover the adoption of conservation agriculture management in 1987 enabled the recovery of C content of the soil. It is considered for 2007, compared with the original, recovery of the SOC stock in up to 60 % (337.7 × 103 Mg) when the soil C balance was positive in 276.5 × 103 Mg of CO2. These results shows the CO2 potential emission to the atmosphere by the forests removal and burning, as well as the potential of soil C sequestration by the adoption of soil conservation tillage systems. Century model adequately estimated the evolution of SOC stocks and CO2 balance due to the use, land use changes, and soil management.