Silvana A.M. Critter

Microbial biomass and microcalorimetric methods in tropical soils

The type of organic matter (OM) plays an essential role in nutrient cycling in agricultural soil systems. Microbial activity in tropical soils was calorimetrically followed as a useful tool in this investigation. Tropical soil samples with different textures: Rhodic eutrudox (R), Typic eutrudox (V) and a Quartzipsamment (Q) from Brazil were amended with 25% cattle manure (E), municipal refuse compost (L), earthworm casts (H), the agrochemical trifluralin (T); (23 g, equivalent dose of 1.25 kg ha −1 ) were explored. The microbial activity was determined by calorimetry and simultaneously by fumigation–extraction (microbial biomass carbon, C) to compare both methods. The results for R, Q, and V soils were: (212.04 A , 195.99 B , 204.47 A ) for microbial biomass C and (0.692 B , 0.714 B , 0.784 A ) for thermal effect with P< 0.05, respectively, over a period of incubation of 91 days. The microbial activity of the modified soils decreases in the order: E, H, L and T. Both methods showed a coefficient of correlation r = 0.7443 and the statistical probability of occurrence of the event, P< 0.0001. From this correlation the utility of both methods for measuring the microbial activity in soils could be deduced.

Microcalorimetric study of glucose degradation in some brazilian soils

Abstract Latosol soils, red, dark red, red-yellow, and red-yellow treated with vinasse, were studied by microcalorimetry. Microbial activity was stimulated by the addition of identical masses of glucose with ammonium sulphate, varying from 3.0 to 12.0mg per 1.5 g of soil (glucose being a limiting energy source) under controlled humidity at 298 and 306 K. After dosing all the soil samples (1.5 g) with 6.0mg of each nutrient and 0.8cm 3 of water, the power-time curves were recorded. These curves showed that red soil gave the largest power output (240μW) at a peak time of 35.2 h (the point of maximum amplitude of the experimental curve). Yellow soils, however, did not show any response to addition of nutrients. The power-time curves are all similar in shape, with the thermic effect and the peak time for both temperatures being directly dependent on the amount of nutrient. The peak time decreases with increasing temperature; values of 29.2–43.8 h at 298 K and 17.3–23.8 h at 306 K, were obtained.

The inhibitor effect of copper sulphate on microbial glucose degradation in red latosol soil

Abstract Microcalorimetry has been used in a series of experiments to study the inhibitory effect caused by copper sulphate on soil microbial activity. This activity was stimulated by addition of 6.0 mg of glucose and 6.0 mg of ammonium sulphate under a controlled humidity of 53% in a red Latosol soil sample of 1.50 g. Power-time curves were recorded for increasing amounts of the inhibitor, varying from zero to 6.19 mg. The curves showed a decrease of the maximum amplitude of the experimental curve, which shifted to longer times. Increasing masses of copper sulphate caused a decrease of the original thermal effect to reach a null value at 6.19 mg of inhibitor. The results relating the dependence of the maximum amplitude of the peak time with the considered pollutant mass, were fitted to a kinetic model in an attempt to establish the inhibitory effect of copper sulphate. In this conditions, the data were adjusted to a first power order model for the degradation of glucose. In the absence of inhibitor the consumption of glucose by the microorganisms is about 10% of the initial mass and decreases with the increase of the copper added to the soil sample.

Adsorption–desorption processes of calcium on Brazilian soils

Abstract Thermodynamic data on ion-exchange equilibrium were obtained on the heterogeneous cationic red or red–yellow latosol soil/aqueous solution interface. The equilibrium with the attached acidic functional groups can be represented by a general equation: SH n + M n+ ⇌ SM +n H + where SH is the soil surface containing H+ ions available for exchanging and Mn+ is the cation exchanged. After exchanging, the desorption process, which depends on the natural structure and properties of soil, presents reversibility expressed by: SM ⇌n S − + M n+ . The thermodynamic data related to the coefficient of distribution, Kd, equilibrium constant, K, and Gibbs free energy, ΔG, provide information about adsorbent–adsorbate interactions in the soil surface. K and ΔG values were calculated by the linearization of the Langmuir equation, to give a constant KL (Langmuir constant), with the values being compared with an absorption method, KR (adsorption constant). The equilibrium time for surface saturation was established as 2 h for both soils. The number of moles adsorbed, Nf, on red latosol, (30.17±1.51)×10−5 mol g−1, is five times higher than that found for red–yellow latosol, (6.07±0.30)×10−5 mol g−1. Nf for lead saturation and calcium/lead equilibrium were (7.09±0.35)×10−5 and (4.59±0.23)×10−5 mol g−1, respectively. The desorption process on red latosol soil occurred to the extent of 37.5% with nitric acid, after the soil surface was saturated with calcium as the index ion. The adsorption of the index cation caused a decrease in the adsorption curve of lead on the surface. The values obtained for red latosol and red–yellow soil for exchanging with calcium are: Kd, (3.35±0.17 and 0.77±0.04)×10−2 dm3 g−1; KL, (1.04±0.05 and 7.10±0.36)×102; KR, (39.20±1.96 and 6.91±0.35)×102; −ΔGL, 11.51±0.58 and 16.27±0.81 kJ mol−1; and −ΔGR, 20.50±1.03 and 16.20±0.81 kJ mol−1, respectively. Based on Gibbs free energy values, a spontaneous exchange process for cations on soils is easily detected.

Thermal analysis of brazilian tropical soils originating from different sources

Brazilian tropical Latosol soil samples were thermally analyzed associating thermogravimetric (TG) and differential scanning calorimetric (DSC) techniques under synthetic air or argon atmospheres. Rhodic eutrudox soils with forest vegetation, from unburnt and burnt cane plantations and that of a sandy phase having cerrado vegetation were investigated. From the organic soil fraction humic acids were extracted that decompose similarly to the commercial product, following the steps: i) adsorbed water, dehydrations, decarboxylations and release of organic molecules, ii) thermolabile decomposition fraction, iii) macromolecular organic matter and iv) residues. The DSC curves gave the corresponding peak for water release near 100 oC and exothermic peaks at temperatures higher than 300 oC, attributed to the combustion of thermolabile organic matter. The TG curves for all soil samples are more complex than those of the humic acids due to the inorganic components, being characterized by stages i) dehydration process, ii) thermolabile organic matter, iii) macromolecular organic domain and iv) oxide residues. These steps of decomposition correspond to three endothermic DSC peaks and one exothermic peak clearly shown under a synthetic air atmosphere, being attributed to the combustion of the macromolecular organic fraction near 300 oC. The DSC curves from burnt and unburnt red Latosol soils from sugar cane cultivation showed more intense endothermic peaks than those of the forest. These thermal results show the influence of both the type and the organic matter contents on curve profiles, which are highly influenced by the soil mineral compositions and land-use activities, as well as the burning processes.

Enzymatic activity measured by microcalorimetry in soil amended with organic residues

Enzymatic activity is an important property for soil quality evaluation. Two sequences of experiments were carried out in order to evaluate the enzymatic activity in a soil (Rhodic Eutrudox) amended with cattle manure, earthworm casts, or sewage sludges from the municipalities of Barueri and Franca. The activity of commercial enzymes was measured by microcalorimetry in the same soil samples after sterilization. In the first experiment, the enzyme activities of cellulase, protease, and urease were determined in the soil samples during a three month period. In the second sequence of experiments, the thermal effect of the commercial enzymes cellulase, protease, and urease on sterilized soil samples under the same tretaments was monitored for a period of 46 days. The experimental design was randomized and arranged as factorial scheme in five treatments x seven samplings with five replications. The treatment effects were statistically evaluated by one-way analysis of variance. Tukey´s test was used to compare means at p < 0.05. The presence of different sources of organic residues increased the enzymatic activity in the sampling period. Cattle manure induced the highest enzymatic activity, followed by municipal sewage sludge, whereas earthworm casts induced the lowest activity, but differed from control treatment. The thermal effect on the enzyme activity of commercial cellulase, protease, and urease showed a variety of time peaks. These values probably oscillated due to soil physical-chemical factors affecting the enzyme activity on the residues.

Microbial enzymatic activity and thermal effect in a tropical soil treated with organic materials

Bacteria and fungi are the most active decomposers of organic materials in soil. They directly affect plant nutrient availability, and chemical and physical properties of soils. This investigation aimed at quantifying the effect of several organic materials on microbial activity of a Rhodic Eutrudox. Soil samples were incubated over a period of 91 days with the following organic materials: cattle manure (CM), earthworm humus (HM), and city sewage sludge from Barueri (BA) and Franca (FR). The activities of cellulase, protease and urease enzymes, the soil microbial carbon content (by fumigation-extraction method) and the exothermal effect were evaluated. Experimental design was randomized and arranged as factorial scheme five treatments × seven samplings with five replications. Organic materials promoted oscillations in m icrobial carbon (mg C g -1 soil), and enzyme activities - cellulase (μg glucose g -1 soil 24 h -1 ), protease (mg Tyr g -1 soil 2 h -1 ), urease (mg NH 4 + -N g -1 soil 2 h -1 ) - and the total thermal effect (J g -1 soil),