No abstract

SUMMARYDespite the large number of studies addressing the quantification of phosphorus (P) availability by different extraction methods, many questions remain unanswered. The aim of this paper was to compare the effectiveness of the extractors Mehlich-1, Anionic Resin (AR) and Mixed Resin (MR), to determine the availability of P under different experimental conditions. The laboratory study was arranged in randomized blocks in a [(3 x 3 x 2) + 3] x 4 factorial design, with four replications, testing the response of three soils with different texture: a very clayey Red Latosol (LV), a sandy clay loam Red Yellow Latosol (LVA), and a sandy loam Yellow Latosol (LA), to three sources (triple superphosphate, reactive phosphate rock from Gafsa-Tunisia; and natural phosphate from Araxá-Minas Gerais) at two P rates (75 and 150 mg dm -3 ), plus three control treatments (each soil without P application) after four contact periods (15, 30, 60, and 120 days) of the P sources with soil. The soil acidity of LV and LVA was adjusted by raising base saturation to 60 % with the application of CaCO 3 and MgCO 3 at a 4:1 molar ratio (LA required no correction). These samples were maintained at field moisture capacity for 30 days. After the contact periods, the samples were collected to quantify the available P concentrations by the three extractants. In general, all three indicated that the available P-content in soils was reduced after longer contact periods with the P sources. Of the three sources, this reduction was most pronounced for triple superphosphate, intermediate for reactive phosphate, while Araxá phosphate was (1) REUSMO: FÓSFORO EXTRAÍDO COM RESINAS TROCADORAS DE ÍONS E MEHLICH-1 DE LATOSSOLOS SUBMETIDOS A FONTES E DOSES DE FÓSFORO E TEMPOS DE CONTATO

No abstract

the Mehlich-1 (M-1) extractant and Monocalcium phosphate in acetic acid (Mcpa) have mechanisms for extraction of available p and s in acidity and in ligand exchange, whether of the sulfate of the extractant by the phosphate of the soil, or of the phosphate of the extractant by the sulfate of the soil. in clayey soils, with greater p adsorption capacity, or lower remaining p (rem-p) value, which corresponds to soils with greater phosphate buffer capacity (pbc), more buffered for acidity, the initially low ph of the extractants increases over their time of contact with the soil in the direction of the ph of the soil; and the sulfate of the M-1 or the phosphate of the Mcpa is adsorbed by adsorption sites occupied by these anions or not. this situation makes the extractant lose its extraction capacity, a phenomenon known as loss of extraction capacity or consumption of the extractant, the object of this study. twenty soil samples were chosen so as to cover the range of rem-p (0 to 60 mg L -1 ). rem-p was used as a measure of the pbc. the p and s contents available from the soil samples through M-1 and Mcpa, and the contents of other nutrients and of organic matter were determined. for determination of loss of extraction capacity, after the rest period, the ph and the p and s contents were measured in both the extracts-soils. Although significant, the loss of extraction capacity of the acidity of the M-1 and Mcpa extractants with reduction in the rem-p value

The increase of the absorption efficiency of boron (B) by plants is essential for increasing crop productivity. The intercalation of B in MgAl layered double hydroxides (LDHs) is an alternative to evaluating how these materials can provide B to plants. In this work, a MgAl LDH intercalated with borate ions (Mg2Al-B-LDH) was synthesized by the constant pH coprecipitation method, and the material produced was evaluated as a matrix for storage and as a source of B for plants. The Mg2Al-B-LDH was characterized by XRD, ATR-FTIR, TGA-DTA, specific surface area, pore size and volume, and SEM. A bioassay was performed to verify the supply of B to plants from the two sources in the forms of H3BO3 and of Mg2Al-B-LDH to sunflower plants grown in pots. The LDH basal spacing value of 12.0 Å is characteristic of intercalation of tetraborate octahydrate ions [B4O5(OH)42−]·8H2O between the layers. There was an increase in the dry matter (DM) and B content of the plants relative to those treatments where no B was added. The lack of statistical difference for plant yield between the two sources of B suggests a lack of stability of the Mg2Al-B-LDH structure under the acidic condition of the soil.

Visual symptoms of Zn deficiency, induced by excessive P applications, have been observed in commercial orchid nurseries. The supply of other metallic micronutrients, such as Fe and Mn, may also be inadequate in the plant due to high application rates of P. The aim of this study was to investigate this interaction in the nutrition of Phalaenopsis plants. Experimental treatments consisted of three P rates . Dry matter production was evaluated, as well as the levels of P, Zn, Fe, and Mn in both shoots and roots. Higher P rates induced higher shoot dry matter production. However, symptoms of Zn deficiency were observed in plants treated with the highest P rate in the absence of Zn. With increasing P rates, Zn concentrations in the shoots decreased more markedly than in roots, with accumulation of the element in the roots, indicating low Zn translocation to the shoot. A much higher Mn content in shoots (661 mg kg ) suggested that the species is highly tolerant to this micronutrient. The Fe concentrations in the plant were much higher than those indicated in the literature as critical levels for this genus.

Increases in greenhouse gases (GHG) emissions, upon changes in land use and agricultural management, lead to a search for techniques that enhance carbon residence time in soil. Pyrolysis increases the recalcitrance of organic materials and enhances their activities as physical, chemical and biological soil conditioners. Emissions of CO 2 , CH 4 and N 2 O quantified from a sandy soil that was treated with three rates (12.5, 25 e 50 Mg•ha −1 ) of either non-pyrolysed poultry manure and sugarcane straw or biochars, pyrolysed at two contrasting temperatures (350˚C and 650˚C). Subsequently, the flux of the three gases was converted and compared in a standard unit (CO 2 eq). The added biochars, significantly reduced GHG emissions, especially CO 2 , relative to the non-pyrolysed materials. The greatest differences between applied rates of poultry manure, relative sugarcane straw, both to biochar and raw material, and the positive response to the increase of pyrolysis temperture, confirm the importance of raw material choice for biochar production, with recalcitrance being an important initial characteristic. Greater emissions occurred with intermediate rate of biochars (25 Mg•ha −1 ) amendment to the soil. These intermediate rates had higher microbial biomass, provided by an intermediate C/N ratio derived from the original soil and the biochar, promoting combined levels of labile C and oxygen availability, leading to an optimal environment for microbiota.

ABSTRACT:Vale do Rio Doce shoot dieback (VRDSD) is an anomaly whose cause seems to be associated with hypoxic conditions and their consequences (excess Mn and Fe) triggered by elevation of the water table in areas with poor drainage. Different plants have distinct survival strategies under this form of stress. The objective of this study was to understand the physiological responses involved in the differential tolerance of eucalyptus clones to VRDSD and their relationship to hypoxia and excess Mn. A hydroponic experiment was carried out using a 2 × 2 × 2 factorial arrangement, two eucalyptus clones with different levels of tolerance to VRDSD (sensitive Urograndis hybrid -1213; and the tolerant Rio Claro hybrid -Eucalyptus grandis x unknown -2719), two concentrations of O 2 (8 and 4 mg L -1 ), and two Mn concentrations (1.39 and 300 mg L -1 ) in a randomized block design (RBD) with three replicates. Forty-day-old clones were maintained in Clark nutrient solution for 30 days. After this period, the treatments were applied for 11 days. Plant gaseous exchange shoot and root production, and the quantity of enzymes related to oxidative stress in leaves and roots were evaluated. In the tolerant clone, reactive oxygen species (ROS) were produced under hypoxic conditions, accompanied by reduction in production of dry matter, malondialdehyde (MDA), and in activity of the enzyme alcohol dehydrogenase (ADH). However, this clone had greater production of superoxide dismutase (SOD) under these conditions, an enzyme responsible for detoxification of ROS, which acts as part of the Low Oxygen Quiescence Syndrome (LOQS). In contrast, sensitive clones did not exhibit expressive reductions in growth or changes in the leaf/root ratio. These clones formed large quantities of adventitious roots and had high levels of MDA and ADH and low levels of SOD. Therefore, sensitive clones appear not to be prepared for detoxification of ROS and other toxic metabolites, but rather adopt morphological escape mechanisms, the Low Oxygen Escape Syndrome (LOES), in response to hypoxia. Thus, the period of soil waterlogging may cause the death of large numbers of roots in sensitive clones, limiting their ability to absorb water and nutrients and culminating in the death of these plants. Excess Mn seems to aggravate the damage caused by hypoxia, but it is not the causal agent of VRDSD.