Variabilidade de atributos do solo em um transecto entre os biomas Pantanal Mato-grossense e Cerrado

Abstract

The carbon contained in soils of natural environments is highly susceptible to changes due to land use. This is of great importance, since carbon has a close relationship with climate change of the earth system. This work was performed in the transition area between the Pantanal and Cerrado biomes in a landscape characterized by high pedological complexity due to the contributions of different factors of soil formation in each environment. The aim of this study was to evaluate the variability of carbon and some soil properties along a ~ 210 km transect which encompassed different soil classes and land uses. In the course of the transect, soil samples were collected with a Dutch auger every 1.4 kilometers, approximately, in the depths of 0 to 0.10 m, 0.10 to 0.20 and 0.20 to 0.30 m. For collecting soil samples at three depths, steel rings were used in mini-trenchs dug at the midpoint of each site. In landscapes selected for the study, samples were collected in the depths of 0 to 0.20 m, using the following sampling schemes: regular grid, irregular grid, and hierarchical grid. The collection sites were georeferenced with GPS to obtain coordinates and altitude. The soil attributes determined were: total carbon (TC) of soil, sand, silt, clay, bulk density and redness index (RI). The analysis of the clay content values by semivariogram and kriging allowed the identification of different associations of soil classes in mapped units by SEPLAN / MT. About 41% of the variance of the attributes studied occurred in the smaller spacing (2 m) of the nested sampling. Soil TC (0 to 0.20 m) of the landscapes under various uses, according to their soil classes were: Aquic Ustifluvents (69.7 Mg ha-1 ) statistically equal to Aquic Quartzipsamments (65.9 Mg ha- 1 ) > Typic Haplustox (52.6 Mg ha-1 ) > Typic Quartzipsamments (23.5 Mg ha-1 ) > Haplic Plinthustults (20.2 Mg ha-1 ) statistically equal to Typic Albaquults (19.2 Mg ha-1 ). RI proved a valuable indicator for identifying reducing and oxidizing environments. The particle size, in turn, had a close relationship with the soil carbon in landscapes both from the Pantanal biome as in the Cerrado. We identified the major environmental systems represented by Vereda and Gallery Forest in Aquic Quartzipsamments that maintain a high TC stock despite having low clay content in its soil profile, but a great risk of loss of soil carbon in case of drainage or conversion of these areas to agricultural use was evident. In general, we observed the occurrence of soil carbon sequestration in cultivated Oxisols. Moreover, in Typic Quartzipsamments, conversion of native vegetation for agricultural systems caused losses of carbon from the soil in all land uses. This carbon emitting behavior indicates that sandy soils must undergo different handling in relation to Oxisols due to differing characteristics.