Potentialities and limitations of agricultural use in soils of semi-arid region of the state of Bahia.

The objective of this study was to evaluate the potentialities and limitations of the agricultural use of representative classes of semi-arid regions of the state of Bahia, based on the pedological and evaluation of their soil characteristics. Five areas were selected where trenches were opened to collect samples for the analyses: Eutric Haplustept which presents vulnerability to physical and chemical degradation due to poor drainage with risks of erosion, waterlogging, salinization and compaction but having good natural fertility; Abrupt Kandiustalf with high vulnerability to physical degradation due to the presence of gravel and pebbles which may limit the development of deep rooting plants and mechanization but also with good natural fertility; Typic quartzipsaments and Typic Eutrustalf with no limitations related to drainage as low risk of compaction but featuring limitation of low moisture-holding capacity and nutrients; and Arenic Haplustulf wose characteristics are high vulnerability to degradation due to the drainage limitation related to the Btx horizon cementing in addition to low natural fertility and therefore is not recommended to agricultural use. However, in general, they feature no serious impediments for agricultural use. The amounts of OM is low in all soils but the use of management systems aiming at their accumulation and maintenance in appropriate levels will contribute to the CEC increase as well as to improve the chemical and physical properties.

Physical attributes of Ultisol of Brazil's northeastern semiarid under organic farming of wine grapes.

The purpose of this study was to evaluate the effects of organic farming of wine grapes under physical and chemical characteristics of Ultisol Brazil's northeastern semiarid region. The samples of soil were collected from the row and interrow of the farming and from the fallow area, at the depths of 0.0-0.10, 0.10-0.20, 0.20-0.30 and 0.30-0.60 m. The samples were collected at six and twelve months after the culture implementation to evaluate the state of aggregation, bulk density and total soil porosity, flocculation index and organic matter contents, calcium, magnesium, and sodium. The results were submitted to statistical analysis. The adoption of organic farming contributed to the soil aggregation process. The bulk density and total soil porosity did not differ significantly between the evaluations, but were within the critical limits for sandy soils. The index flocculation did not have a great influence on the aggregates formation, being this process influenced by organic matter. The period of one year was considered short to obtain conclusive results in improving the soil quality by organic farming, since there are difficulties in tropical soils in promoting significant increases in organic matter content in short time.

Studies of the compositions of humic acids from Amazonian Dark Earth soils.

The compositions of humic acids (HAs) isolated from cultivated and forested "Terra Preta de Indio" or Amazonian Dark Earth soils (anthropogenic soils) were compared with those from adjacent non-anthropogenic soils (control soils) using elemental and thermogravimetric analyses, and a variety of solid-state nuclear magnetic resonance techniques. The thermogravimetric index, which indicates the molecular thermal resistance, was greater for the anthropogenic soils than for the control soils suggesting polycyclic aromatic components in the former. The cultivated anthropogenic soils were more enriched in C and depleted in H than the anthropogenic soils under forest, as the result of the selective degradation of aliphatic structures and the possible enrichment of H-deficient condensed aromatic structures. The combination of variable amplitude cross-polarization (VACP) and chemical shift anisotropy with total suppression of spinning sidebands experiments with composite pi pulses could be used to quantify the aromaticity of the HAs from the anthropogenic soils. From principal component analysis, using the VACP spectra, it was possible to separate the different constituents of the HAs, such as the carboxylated aromatic structures, from the anthropogenic soils and plant derived compounds. The data show that the HAs from anthropogenic soils have high contents of aryl and ionisable oxygenated functional groups, and the major functionalities from adjacent control soils are oxygenated functional groups from labile structures (carbohydrates, peptides, and with evidence for lignin structures). The anthropogenic soils HAs can be considered to be more recalcitrant, and with more stable reactive functional groups which may, in part, explain their more sustainable fertility due to the organic matter contribution to the soil cation exchange capacity.