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This study evaluated the effects of organic acids on the diffusive flux of phosphorus (DFP) along time. Treatments were a factorial 2 × 2 × 2 × 2 × 5 design: two soils (clayey Red Latosol and a sandy-loam Red-Yellow Latosol), two organic acids (citric acid, CA, and humic acid, HA), and two phosphorus (P) sources [monopotassium phosphate (KH2PO4) and inositol hexaphosphate (IHP)] either with or without heating (100 °C) of the soil. The soil plus treatments, in all combinations, were placed in contact with an anion exchange resin and the P in the resin was measured after 2, 4, 6, 10, and 15 days. The DFP was greater when the soils were treated with CA than when treated with HA. Citric acid was more effective in increasing the DFP from KH2PO4, whereas HA was the organic ligand that promoted a larger DFP when the source was IHP. [ABSTRACT FROM PUBLISHER]

The objective of this study was to evaluate changes in distribution and quality of organic matter in light and heavy fractions of a medium-texture Red Latosol under different uses and management practices in Capinópolis, Brazil. Soil samples were collected from different layers in the profile (0–5, 5–10, and 10–20 cm). The following treatments were evaluated: NTs, no till (no tillage) for 4 years with maize (silage) / soybean in succession; NTg, no till for 4 years with maize/maize/maize/soybean in succession; NTtf, no till for 3 years with tifton (hay) and soybeans in the last year; CS, about 30 years with conventional cultivation system (maize/soybean) with only soybean in the past 4 years; and NF, native forest. The heavy fraction contributed 75–98% of total carbon and 94–99% of total nitrogen, indicating that most carbon and nitrogen in the soil are associated with the mineral fraction, which is fundamental for the maintenance of their stocks. Tifton grass in no tillage was efficient in increasing the amounts of light fraction (free and occluded). Increases of occluded light fraction in no-till systems were greater than in conventional cultivation system. The light fraction was shown to be sensitive to soil cultivation and can be considered indicative of soil degradation. Light-fraction analysis by Fourier transform infrared spectroscopy (FTIR) allowed the study of changes in the chemical structure of these fractions under different uses and management practices. Occluded light fraction was shown to be more recalcitrant and condensed than the free light fraction. The surface layer in the conventional cultivation system has a more aromatic and condensed free light fraction than in no-tillage system. In general, the upper layers were less aromatic than the deepest ones. [ABSTRACT FROM AUTHOR]

The effect of the introduction of an agrosylvopasture (SASP) system on the changes in the carbon (C) of the soil and its lability were studied. Since 1993, this system has been annually implanted in Paracatu, MG. It was planted under eucalyptus forest abandoned after three cuts, when the brachiaria grass was established. The eucalyptususes were planted at 10×4 m spacing, and the following crops have been grown between the lines: rice in the first year, soybean in the second, and brachiaria in the third. After the third year, pasture of the meat cattle begins on brachiaria and remains until the end of the system cycle that was foreseen for the 11th year. A savannah area and another one with eucalyptusus under a conventional system were used as references to natural condition and the way the area is used before plantation of the SASP, respectively. Some samples aged 1, 2, 3, 6, and 10 years were collected in SASP. According to the obtained results, the following conclusions were drawn: (i) the C contents and stocks were affected before and during the plantation of the SASP by the use and management of SASP, as they were reduced in the first years of the system establishment but improved at the 10th year; (ii) the C from the particulate free light fraction (CFLLP) that was extracted by potassium permangate (KMnO4) was sensitive to the use and management, and so reflected the changes in total organic C (TOC); (iii) the more labile fractions of C that were extracted at different concentrations of sulfuric acid (H2SO4) satisfactorily reflected the changes in both use and management, whereas the less labile fractions were just slightly affected; and (iv) the C management index (IMC) calculated from CFLLP was the most sensitive to the changes in use and management. However, when calculated from the C fraction 1 extracted by 3M H2SO4 (CF1), it showed better reliability. [ABSTRACT FROM AUTHOR]

Organic acids (OA) play an important role in phosphorus (P) availability in soils. They can be adsorbed with great energy by the soil mineral fraction, reducing P adsorption and increasing P availability to plants. The aim of this study was to evaluate the effect of different sources (acetic acid, AA; citric acid, CA; and humic acids, HA) and doses of OA on P uptake and dry-matter production by corn plants grown in highly weathered soils. Samples (2 dm3) of a clayey Red Latosol, RL (Rhodic Haplustox), and a sandy loam Red Yellow Latosol, RYL (Typic Haplustox), were accommodated in plastic pots located in a greenhouse. Phosphorus (K2HPO4) and/orOA were applied at different timings: organic acid added before (OABP) or simultaneously (OASP) to the phosphate application. The OA doses ranged from 0.0 to 8.0 mmol L-1. The doses of humic acids ranged from 0.0 to 12 g dm-3 and were equivalent to an organic compost addition of 0 to 80 t ha-1. The addition of OA influenced dry-matter production and P uptake by corn plants in both soils. The effectiveness of OA in increasing P uptake and dry-matter production of corn plants followed the order humic acids>citric acid>acetic acid. In both soils, the greatest dry-matter production and P uptake were obtained when OA were applied to the soil before P was added (OABP). [ABSTRACT FROM AUTHOR]

Soil organic matter (SOM) is the greatest carbon reservoir in the terrestrial ecosystem, reaching approximately 1.500 × 109 t of carbon (C). The knowledge of the size and dynamics of this compartment is essential for carbon stock evaluation, leading to a national inventory of carbon fluxes, as well as the modeling of tropical carbon cycles. Latosols (oxisols) cover approximately 40% of the Brazilian territory, being important with regard to SOM accumulation. This process can occur both at the surface and within minute aggregates at greater depths. The mean C stock values were calculated for Brazilian Latosols (Red Latosol—RL, Yellow Latosol—YL, Red Yellow Latosol—RYL, and Humic Latosols—HL); in addition, we evaluated the effects of climate, vegetation, and land use on C stocks. A database was used of organic carbon contents of A and B horizon of Latosols from different morphoclimatic regions (humid tropical northern Brazil, semi-arid, northeast, coastal Atlantic southeast, dry topical central, and subtropical southern) compiled from the extensive RADAMBRASIL and EMBRAPA soil surveys. The mean C stock values of Brazilian Latosols are: 6 and 13 kg m−2 for YL; 7.5 and 11 kg m−2 for RL; 6.8 and 8.8 kg m−2 for RYL; and 30.16 and 15.78 kg m−2 for HL, for A and B horizons, respectively. Carbon stock values were markedly influenced by regional climate, type of vegetation, and land use. The usually neglected pool of organic carbon in B horizons of deeply weathered Latosols accounts for between 42–76% of the total C stocks. [ABSTRACT FROM AUTHOR]