Chemical dispersants and pre-treatments to determine clay in soils with different mineralogy

Knowledge of the soil physical properties, including the clay content, is of utmost importance for agriculture. The behavior of apparently similar soils can differ in intrinsic characteristics determined by different formation processes and nature of the parent material. The purpose of this study was to assess the efficacy of separate or combined pre-treatments, dispersion methods and chemical dispersant agents to determine clay in some soil classes, selected according to their mineralogy. Two Brazilian Oxisols, two Alfisols and one Mollisol with contrasting mineralogy were selected. Different treatments were applied: chemical substances as dispersants (lithium hydroxide, sodium hydroxide, and hexametaphosphate); pre-treatment with dithionite, ammonium oxalate, and hydrogen peroxide to eliminate organic matter; and coarse sand as abrasive and ultrasound, to test their mechanical action. The conclusion was drawn that different treatments must be applied to determine clay, in view of the soil mineralogy. Lithium hydroxide was not efficient to disperse low-CEC electropositive soils and very efficient in dispersing high-CEC electronegative soils. The use of coarse sand as an abrasive increased the clay content of all soils and in all treatments in which dispersion occurred, with or without the use of chemical dispersants. The efficiency of coarse sand is not the same for all soil classes.

Chemical and structural characterization of soil humic substances under agroforestry and conventional systems

Studies have proven that the agroforestry systems in the semi-arid region of the State of Ceará, Brazil, induce an increase in soil organic C levels. Notwithstanding, there is no information if this increase also results in qualitative changes in different pools of soil organic matter. The objective of this study was to verify the possible chemical and structural alterations in fulvic and humic acids of a Luvisol in areas adopting agroforestry, traditional intensive cultivation and native forest in a long-term experiment conducted in the semi-arid region of Ceará State, Brazil. The study was conducted in an experimental area of the National Goat Research Center (Embrapa) in Sobral, CE. The following treatments were evaluated: agrosilvopasture (AGP), silvopasture (SILV), intensive cultivation under fallow (ICF), and areas with native forest (NF). Soil fulvic and humic acids fractions were extracted from the 0-6 and 6-12 cm layers and characterized by elemental composition, thermogravimetry and infrared spectroscopy analyses. The elemental composition analysis of humic acids confirmed the data found for fulvic acids, showing reduction in the C, H and N levels, followed by an increase in O contents in the AGP and ICF treatments over SILV and NF. In all treatments, except to SILV in the 0-6 cm layer, the percentage of mass loss was highest (300-600 °C) for humic acids in the thermally most stable region. Despite the similarity between infrared spectra, soil fulvic acids in the SILV treatment extracted from 6-12 cm depth decrease the absorption bands at 1708 and 1408 cm-1 followed by an increase in the absorption band at 1608 cm-1 attributed to aromatic C=C groups. This behavior suggests an increase in the aromatic character of the structure. The AGP and ICF treatments, which increase the soil tilling, favored the maintenance of humic substances with a more aromatic character in the soil than SILV and NF. The less aromatic humic substances in the SILV treatment resulted in an increase of exchange sites of soil organic matter, indicating improved nutrient cycling and maintenance of productivity in the system.

Soil chemical properties related to acidity under successive pig slurry application

Pig slurry application as soil manure can alter the chemical properties of the soil and affect its acidity, modifying the environment for crop growth and development. The objective of this study was to evaluate the chemical properties related to soil acidity subjected to successive applications of pig slurry. The experiment was conducted in May 2000, in an experimental area of the Federal University of Santa Maria (UFSM) under no-tillage and lasted until January 2008. Nineteen surface applications of 0, 20, 40, and 80 m³ ha-1 of pig slurry were performed, during a period of 100 months and the soil sampled in the end (layers 0-2, 2-4, 4-6, 6-8, 8-10, 10-12, 12-14, 14-16, 16-18, 18-20, 20-25, 25-30, 30-35, 35-40, 40-50 and 50-60 cm). The application of pig slurry increased soil pH values, an effect that could reach the depth of 8 cm without affecting the potential acidity values. The applications also resulted in accumulation of Ca and Mg exchangeable levels in the surface layers, increasing base saturation and reducing Al saturation. Long-term applications induced an increase in organic matter in the deeper layers. However, the effect of this residue on the potential CEC was less significant and restricted to the surface layers.

Influence of organic-mineral fertilization of an oxisol on soil chemical properties and Bracharia brizantha production

The use of organic-mineral fertilizer produced by the manufacturing industry of lysine and threonine amino acids can improve the fertility of tropical soils. The objective of this study was to evaluate the influence of different doses of the organic-mineral fertilizer named Ajifer L-14 on chemical properties and on the response with increased production of a forage on a Red Latosol in the northwestern region of São Paulo State, Brazil. A randomized block design was used with seven treatments and four replications. The treatments consisted of: T1- control (without application of Ajifer L-14); T2- control (natural vegetation); T3- mineral fertilization according to crop requirements and soil analysis (application of 1.35 kg plot-1 of urea, 2.20 single superphosphate, and 0.51 KCl, corresponding to 60 of N, 40 P2O5 and 30 kg ha-1 of K2O); T4- fertilization with Ajifer L-14 according to the recommendation resulting from the soil chemical analysis (40 L plot-1, corresponding to 60 kg ha-1 N); T5- fertilization with Ajifer L-14, at a rate of 150 % of the recommended values (60 L plot-1, corresponding to 90 kg ha-1 N); T6- fertilization with Ajifer L-14 at a rate of 50 % of the recommended values (20 L plot-1, corresponding to 30 kg ha-1 N); T7- fertilization with Ajifer L-14 at a rate of 125 % of the recommended values (50 L plot-1, corresponding to 75 kg ha-1 N); T8- fertilization with Ajifer L-14 at a rate of 75 % of the recommended values (30 L plot-1, corresponding to 45 kg ha-1 N). The following soil chemical properties were evaluated (layers 0.0-0.1 and 0.1-0.2 m): P, organic matter, pH, K+, Ca2+, Mg2+, cation exchange capacity, potential acidity, and base saturation. The application of this organic-mineral fertilizer does not influence the soil chemical properties. Regression analysis indicated a polynomial relationship between the application rates of organic-mineral fertilizer and the production of dry matter and crude protein of Bracharia Brizantha.

Influence of liming on residual soil respiration and chemical properties in a tropical no-tillage system

Because of the climate changes occurring across the planet, especially global warming, the different forms of agricultural soil use have attracted researchers´ attention. Changes in soil management may influence soil respiration and, consequently, C sequestration. The objectives of this study were to evaluate the long-term influence of liming on soil respiration and correlate it with soil chemical properties after two years of liming in a no-tillage system. A randomized complete block design was used with six replications. The experimental treatments consisted of four lime rates and a control treatment without lime. Two years after liming, soil CO2 emission was measured and the soil sampled (layers 0-5, 5-10, 10-20, and 20-30 cm). The P, Ca2+ e Mg2+ soil contents and pH and base saturation were determined. CO2 emission from soil limed at the recommended rate was 24.1 % higher, and at twice the recommended rate, 47.4 % higher than from unlimed soil. Liming improved the chemical properties, and the linear increase in soil respiration rate correlated positively with the P, Ca2+ and Mg2+ soil contents, pH and base saturation, and negatively with H + Al and Al3+ contents. The correlation coefficient between soil respiration rate and chemical properties was highest in the 10-20 cm layer.

Soil uses in the sugarcane fallow period to improve chemical and physical properties of two latosols (oxisols)

Sugarcane production should be integrated with crop diversification with a view to competitive and sustainable results in economic, social and environmental aspects. The purpose of this study was to assess the influence of different soil uses during the sugarcane fallow period on the chemical and physical properties of eutroferric Red Latosol - LVef (Oxisol) and Acric Latosol - LVw (Acric Oxisol), in Jaboticabal, São Paulo State, Brazil (21º14'05'' S, 48º17'09'' W, 600 m asl). A randomized block design was used with five replications and four treatments, consisting of different soil uses (crops) in the sugarcane fallow period: soybean only, soybean/fallow/soybean, soybean/millet/soybean, and soybean/sunn hemp/soybean. After two soybean crops, the LVef chemical properties remained at intermediate to high levels; while those of the LVw, classified as intermediate to high in the beginning, increased to high levels. Thus, the different soil uses during the sugarcane fallow period allowed the maintenance of LVef fertility levels and the improvement of those of the LVw. Two soybean crops increased macroporosity in the 0.0-0.1 m layer of the LVef; reduced soil aggregates in the 0.0-0.1 and 0.1-0.2 m layers of both soils, and reduced aggregate stability in these two layers of the LVw. Planting pearl millet or sunn hemp between the two soybean growing seasons promoted the formation of larger soil aggregates in the surface layer (0.0-0.1 m) of the LVw.

Chemical properties of soils treated with biological sludge from gelatin industry

The impact of agro-industrial organic wastes in the environment can be reduced when used in agriculture. From the standpoint of soil fertility, residue applications can increase the organic matter content and provide nutrients for plants. This study evaluated the effect of biological sludge from gelatin industry on the chemical properties of two Ultisols (loamy sand and sandy clay) and an Oxisol (clay). The experiment lasted 120 days and was carried out in laboratory in a completely randomized design with factorial arrangement, combining the three soils and six biological sludge rates (0, 100, 200, 300, 400, and 500 m³ ha-1), with three replications. Biological sludge rates of up to 500 m³ ha-1 decreased soil acidity and increased the effective cation exchange capacity (CEC) and N, Ca, Mg, and P availability, without exceeding the tolerance limit for Na. The increase in exchangeable base content, greater than the effective CEC, indicates that the major part of cations added by the sludge remains in solution and can be lost by leaching.

Characterization and nutrient release from silicate rocks and influence on chemical changes in soil

The expansion of Brazilian agriculture has led to a heavy dependence on imported fertilizers to ensure the supply of the growing food demand. This fact has contributed to a growing interest in alternative nutrient sources, such as ground silicate rocks. It is necessary, however, to know the potential of nutrient release and changes these materials can cause in soils. The purpose of this study was to characterize six silicate rocks and evaluate their effects on the chemical properties of treated soil, assessed by chemical extractants after greenhouse incubation. The experimental design consisted of completely randomized plots, in a 3 x 6 factorial scheme, with four replications. The factors were potassium levels (0-control: without silicate rock application; 200; 400; 600 kg ha-1 of K2O), supplied as six silicate rock types (breccia, biotite schist, ultramafic rock, phlogopite schist and two types of mining waste). The chemical, physical and mineralogical properties of the alternative rock fertilizers were characterized. Treatments were applied to a dystrophic Red-Yellow Oxisol (Ferralsol), which was incubated for 100 days, at 70 % (w/w) moisture in 3.7 kg/pots. The soil was evaluated for pH; calcium and magnesium were extracted with KCl 1 mol L-1; potassium, phosphorus and sodium by Mehlich 1; nickel, copper and zinc with DTPA; and the saturation of the cation exchange capacity was calculated for aluminum, calcium, magnesium, potassium, and sodium, and overall base saturation. The alternative fertilizers affected soil chemical properties. Ultramafic rock and Chapada mining byproduct (CMB) were the silicate rocks that most influenced soil pH, while the mining byproduct (MB) led to high K levels. Zinc availability was highest in the treatments with mining byproduct and Cu in soil fertilized with Chapada and mining byproduct.

Chemical and biochemical properties of Araucaria angustifolia (Bert.) Ktze. forest soils in the state of São Paulo

Araucaria angustifolia, commonly named Araucaria, is a Brazilian native species that is intensively exploited due to its timber quality. Therefore, Araucaria is on the list of species threatened by extinction. Despite the importance of soil for forest production, little is known about the soil properties of the highly fragmented Araucaria forests. This study was designed to investigate the use of chemical and biological properties as indicators of conservation and anthropogenic disturbance of Araucaria forests in different sampling periods. The research was carried out in two State parks of São Paulo: Parque Estadual Turístico do Alto do Ribeira and Parque Estadual de Campos de Jordão. The biochemical properties carbon and nitrogen in microbial biomass (MB-C and MB-N), basal respiration (BR), the metabolic quotient (qCO2) and the following enzyme activities: β-glucosidase, urease, and fluorescein diacetate hydrolysis (FDA) were evaluated. The sampling period (dry or rainy season) influenced the results of mainly MB-C, MB-N, BR, and qCO2. The chemical and biochemical properties, except K content, were sensitive indicators of differences in the conservation and anthropogenic disturbance stages of Araucaria forests. Although these forests differ in biochemical and chemical properties, they are efficient in energy use and conservation, which is shown by their low qCO2, suggesting an advanced stage of succession.

Phosphorus transformation in poultry litter and litter-treated Oxisol of Brazil assessed by 31P-NMR and wet chemical fractionation

Large quantities of poultry litter are being produced in Brazil, which contain appreciable amounts of phosphorus (P) that could be of environmental concern. To assess the immediate environmental threat, five poultry litters composed of diverse bedding material were incubated for 43 days under greenhouse conditions. The litters consisted of: coffee bean husk (CH); wood chips (WC); rice husk (RH); ground corn cobs (CC) and ground napier grass (NG) (Pennisetum purpureum Schum.), in which the change in forms of soluble P was evaluated using 31P NMR spectroscopy. On average, 80.2 and 19.8 % of the total P in the extract, respectively, accounted for the inorganic and organic forms before incubation and 48 % of the organic P was mineralized to inorganic P in 43 days of incubation. Wide variation in the organic P mineralization rate (from 82 % -WC to 4 % - NG) was observed among litters. Inorganic orthophosphate (99.9 %) and pyrophosphate (0.1 %) were the only inorganic P forms, whereas the organic P forms orthophosphate monoesters (76.3 %) and diester (23.7 %) were detected. Diester P compounds were mineralized almost completely in all litters, except in the CH litter, within the incubation period. Pyrophosphates contributed with less than 0.5% and remained unaltered during the incubation period. Wood-chip litter had a higher organic P (40 %) content and a higher diester: monoester ratio; it was therefore mineralized rapidly, within the first 15 days, achieving steady state by the 29th day. Distinct mineralization patterns were observed in the litter when incubated with a clayey Oxisol. The substantial decrease observed in the organic P fraction (Po) of the litter types followed the order: CH (45 %) > CC (25 %) > RH (13 %) ≈ NG (12 %) > WC (5 %), whereas the Pi fraction increased. Incubation of RH litter in soil slowed down the mineralization of organic P.

Characterization of soil chemical properties of strawberry fields using principal component analysis

One of the largest strawberry-producing municipalities of Rio Grande do Sul (RS) is Turuçu, in the South of the State. The strawberry production system adopted by farmers is similar to that used in other regions in Brazil and in the world. The main difference is related to the soil management, which can change the soil chemical properties during the strawberry cycle. This study had the objective of assessing the spatial and temporal distribution of soil fertility parameters using principal component analysis (PCA). Soil sampling was based on topography, dividing the field in three thirds: upper, middle and lower. From each of these thirds, five soil samples were randomly collected in the 0-0.20 m layer, to form a composite sample for each third. Four samples were taken during the strawberry cycle and the following properties were determined: soil organic matter (OM), soil total nitrogen (N), available phosphorus (P) and potassium (K), exchangeable calcium (Ca) and magnesium (Mg), soil pH (pH), cation exchange capacity (CEC) at pH 7.0, soil base (V%) and soil aluminum saturation(m%). No spatial variation was observed for any of the studied soil fertility parameters in the strawberry fields and temporal variation was only detected for available K. Phosphorus and K contents were always high or very high from the beginning of the strawberry cycle, while pH values ranged from very low to very high. Principal component analysis allowed the clustering of all strawberry fields based on variables related to soil acidity and organic matter content.

Relationships between microbial activity and soil physical and chemical properties in native and reforested Araucaria angustifolia forests in the state of São Paulo, Brazil

Araucaria angustifolia (Bert.) O. Kuntze is the main component of the Mixed Ombrophilous forest and, in the State of São Paulo, it is associated with a high diversity of soil organisms, essential for the maintenance of soil quality, making the conservation of this ecosystem a major and pressing challenge. The objective of this study was to identify the physical and chemical properties that are most closely correlated with dehydrogenase enzyme activity, basal respiration and microbial biomass under native (NF) and replanted (RF) Araucaria angustifolia forests in three regions of the state of São Paulo, in winter and summer. The main differentiating factors between the areas were also determined. Each forest was represented by three true replications; at each site, from around the araucaria trees, 15 soil samples (0-20 cm) were collected to evaluate the soil physical, chemical and microbiological properties. At the same points, forest litter was sampled to assess mass and chemical properties. The following microbiological properties were evaluated: microbial biomass carbon (MBC), basal respiration (CO2-C), metabolic quotient (Q: CO2), dehydrogenase enzyme activity (DHA) as well as the physical properties (moisture, bulk density, macroporosity and total porosity), soil chemical properties [pH, organic carbon (org-C), P, Ca, K, Mg, Al, H+Al], litter dry mass, and C, N and S contents. The data were subjected to analysis of variance (TWO-WAY: ANOVA). A Canonical Discriminant Analysis (CDA) and a Canonical Correlation Analysis (CCA) were also performed. In the soil under NF, the values of K, P, soil macroporosity, and litter dry mass were higher and Q: CO2 and DHA lower, regardless of the sampling period, and DHA was lower in winter. In the RF areas, the levels of moisture, porosity and Q: CO2 were higher in both sampling periods, and DHA was higher in winter. The MBC was only higher under NF in the summer, while the litter contents of C, N and S were greater in winter. In winter, CCA showed a high correlation of DHA with CO2-C, pH and H+Al, while in the summer org-C, moisture, Mg, pH and litter C were more associated with DHA and CO2-C. The CDA indicated H+Al, available P, total porosity, litter S content, and soil moisture as the most discriminating variables between NF and RF, but moisture was the most relevant, in both seasons and CO2-C only in winter. The combined analysis of CCA and CDA showed that the contribution of the microbiological variables to a differentiation of the areas was small at both samplings, which may indicate that the period after reforestation was long enough to allow an almost complete recovery of the microbial activity.

Estimation of soil moisture in the root-zone from remote sensing data

Field-based soil moisture measurements are cumbersome. Thus, remote sensing techniques are needed because allows field and landscape-scale mapping of soil moisture depth-averaged through the root zone of existing vegetation. The objective of the study was to evaluate the accuracy of an empirical relationship to calculate soil moisture from remote sensing data of irrigated soils of the Apodi Plateau, in the Brazilian semiarid region. The empirical relationship had previously been tested for irrigated soils in Mexico, Egypt, and Pakistan, with promising results. In this study, the relationship was evaluated from experimental data collected from a cotton field. The experiment was carried out in an area of 5 ha with irrigated cotton. The energy balance and evaporative fraction (Λ) were measured by the Bowen ratio method. Soil moisture (θ) data were collected using a PR2 - Profile Probe (Delta-T Devices Ltd). The empirical relationship was tested using experimentally collected Λ and θ values and was applied using the Λ values obtained from the Surface Energy Balance Algorithm for Land (SEBAL) and three TM - Landsat 5 images. There was a close correlation between measured and estimated θ values (p<0.05, R² = 0.84) and there were no significant differences according to the Student t-test (p<0.01). The statistical analyses showed that the empirical relationship can be applied to estimate the root-zone soil moisture of irrigated soils, i.e. when the evaporative fraction is greater than 0.45.

Compaction of an Oxisol and chemical composition of palisadegrass

Compaction is an important problem in soils under pastoral land use, and can make livestock systems unsustainable. The objective of this research was to study the impact of soil compaction on yield and quality of palisade (UROCHLOA BRIZANTHA cv. Marandu). The experiment was conducted on an Oxisol in the State of Mato Grosso, Brazil. Treatments consisted of four levels of soil compaction: no compaction (NC), slight compaction (SC), medium compaction (MC) and high compaction (HC). The following soil properties were evaluated (layers 0-0.05 and 0.05-0.10 m): aggregate size distribution, bulk density (BD), macroporosity, microporosity, total porosity (TP), relative compaction (RC), and the characteristics of crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF) and dry matter yield (DMY) of the forage. Highly compacted soil had high BD and RC, and low TP (0-0.05 m). Both DMY and CP were affected by HC, and both were strongly related to BD. Higher DMY (6.96 Mg ha-1) and CP (7.8 %) were observed in the MC treatment (BD 1.57 Mg m-3 and RC 0.91 Mg m-3, in 0-0.05 m). A high BD of 1.57 Mg m-3 (0-0.05 m) did not inhibit plant growth. The N concentration in the palisade biomass differed significantly among compaction treatments, and was 8.72, 11.20, 12.48 and 10.98 g kg-1 in NC, SC, MC and HC treatments, respectively. Increase in DMY and CP at the MC level may be attributed to more absorption of N in this coarse-textured soil.

Chemical properties and mineralogy of soils with plinthite and petroplinthite in Iranduba (AM), Brazil

Large areas of Plinthosols with ferruginous materials such as plinthite and/or petroplinthite are fairly common in the Brazilian Amazon basin. This work was carried out to investigate the chemical behavior, mineralogical composition and weathering stage of four representative soil profiles with plinthite and petroplinthite, in Iranduba, AM (Central Amazon). Three well-drained soil profiles at high elevations were studied (P1, Plinthic Vetic Ferralsol; P2 and P3, Vetic Endopetric Plinthosol) and a contrasting poorly drained soil (P4 Haplic Plinthosol), located at low elevation. After profile descriptions, soil samples were collected from each horizon, air-dried, sieved (2 mm), and analyzed for particle-size distribution, pH, exchangeable cations (Al3+, Ca2+, Mg2+, K+, and Na+), as well as available P and total organic carbon (TOC) content. The minerals present in the clay and sand fractions, as well as in the ferruginous materials were identified by X-ray Diffraction (XRD). The weathering stage of these soils was assessed by means of Ki and Kr indexes, and the amounts of free and amorphous Fe and Al oxides by using dithionite citrate bicarbonate (DBC) and ammonium oxalate dissolution procedures, respectively. The results showed that all soils were extremely unfertile, with pH levels ranging between strong and moderate acidity, very low sum of bases and organic matter content, and of available P. The mineralogy of the soil profiles was very similar, mainly of the well-drained soils, with predominance of kaolinite and quartz in the clay and sand fractions, respectively. In the poorly-drained P4, 2:1 clay particles were also observed. These profiles can be considered highly developed according to the Ki index, however, the Ki value of P4 was higher, indicating that this soil was less developed than the others. In summary, these profiles with plinthite and petroplinthite can be characterized as highly developed and infertile soils and are, with exception of P4, well-drained.