ABSTRACT Soil nutrient availability and interpretations of nutrient contents are based on the results obtained from specific extraction methods used in routine testing laboratories. The development of new extraction methods and new extractants with better accuracy is particularly important to determine the correct fertilizer rates to be applied. For this purpose, this study aims to synthesize, characterize and evaluate the predictive capacity of cellulose acetate film containing calcinated layered double hydroxide (CAF-LDH-c), as a new extractant and a new method of P extraction in soils. Different analyses techniques were used to characterize the CAF-LDH-c sample, including X-ray diffraction, attenuated total reflectance Fourier transform infrared spectroscopy, and scanning electronic microscopy. Soils were collected from twelve areas with different management and initial availability of P. The soils were subjected to six rates of P and were cultivated with plants. The predictive capacity of CAF-LDH-c, as a new extractant of P in different soils, was evaluated and compared to Mehlich-1 (M-1), Mehlich-3 (M-3), and Mixed Exchange Resin (MER) extractants. Chemical analyses performed on CAF-LDH-c showed that LDH in powder form was incorporated into the cellulose acetate film. There was a linear relation between P uptake by plants and extractable soil P in the soil by CAF-LDH-c, M-1, M-3, and MER extractants. The significant correlations between extracted P in the soil and P uptake by plants for CAF-LDH-c showed the efficacy of the new extractor and the newly proposed method for different types of soils. The results from the present study confirm the possibility of using CAF-LDH-c extractant as a new methodology to evaluate the availability of P in the soil for plant cultivation.

ABSTRACT Studies aimed at mitigating environmental impacts have received attention in recent years. The use of biochar obtained from the pyrolysis is an alternative for the recovery of organic materials that usually are directly discarded in the environment. Biochar has the potential to recover nutrients from wastewater, and in the latter case, the reuse or recycling of biochar as a controlled-release fertilizer could be an option. However, the adsorption characteristics of the ions into different biochars have not been known. The aim of this study was to evaluate the ions adsorption in biochar derived from discarded potatoes, as well as to make physical and chemical characterization of the produced materials. The biochar derived from discarded potatoes was produced by pyrolysis at 450 °C under an N2 atmosphere. In order to define its ionic profile, the adsorption of HnPO4(3–n)–, Ca2+, Mg2+, and Al3+ was tested in pure biochar, as well as adsorption of HnPO4(3–n)–in biochar after it was doped with Al3+. The desorption of these ions was tested by washing with deionized water, and the KCl (1.0 mol·L–1) and Mehlich-1 extractors. In absolute values, the adsorption order of the ions was Al3+ (in acid pH value) = Ca2+ > Al3+ > HnPO4(3–n)–(biochar doped with Al3+) > Mg2+ > HnPO4(3–n)– (biochar without doping). The adsorption of HnPO4(3–n)– was positively influenced by the doping of biochar with Al3+. The biochar has preferential characteristics for cations adsorption, and the doping process can aid in adsorption of anions.

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 O2 (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.

ABSTRACT Given the increase in crop yields and the expansion of agriculture in low fertility soils, deficiency of micronutrients, such as iron, in plants grown in tropical soils has been observed. The aim of this study was to evaluate Fe availability and Fe uptake by corn (Zea mays L.) plants in 13 different soils, at two depths. Iron was extracted by Mehlich-1, Mehlich-3, and CaCl2 (Fe-CC) and was fractionated in forms related to low (Feo) and high (Fed) crystallinity pedogenic oxyhydroxides, and organic matter (Fep) using ammonium oxalate, dithionite-citrate, and sodium pyrophosphate, respectively. In order to relate Fe availability to soil properties and plant growth, an experiment was carried out in a semi-hydroponic system in which part of the roots developed in a nutrient solution (without Fe) and part in the soil (the only source of Fe). Forty-five days after seeding, we quantified shoot dry matter and leaf Fe concentration and content. Fed levels were high, from 5 to 132 g kg-1, and Feo and Fe-CC levels were low, indicating the predominance of Fe as crystalline oxyhydroxides and a low content of Fe readily available to plants. The extraction solutions showed significant correlations with various soil properties, many common to both, indicating that they act similarly. The correlation between the Mehlich-1 and Mehlich-3 extraction solutions was highly significant. However, these two extraction methods were inefficient in predicting Fe availability to plants. There was a positive correlation between dry matter and Fe levels in plant shoots, even within the ranges considered adequate in the soil and in the plant. Dry matter production and leaf Fe concentration and content were positively correlated with Fep concentration, indicating that the Fe fraction related to soil organic matter most contributes to Fe availability to plants.