Maria L. Silveira

Biosolids and heavy metals in soils

The application of sewage sludge or biosolids on soils has been widespread in agricultural areas. However, depending on their characteristics, they may cause increase in heavy metal concentration of treated soils. In general, domestic biosolids have lower heavy metal contents than industrial ones. Origin and treatment method of biosolids may markedly influence their characteristics. The legislation that controls the levels of heavy metal contents in biosolids and the maximum concentrations in soils is still controversial. In the long-term, heavy metal behavior after the and of biosolid application is still unknown. In soils, heavy metals may be adsorbed via specific or non-specific adsorption reactions. Iron oxides and organic matter are the most important soil constituents retaining heavy metals. The pH, CEC and the presence of competing ions also affect heavy metal adsorption and speciation in soils. In solution, heavy metals can be present either as free-ions or complexed with organic and inorganic ligands. Generally, free-ions are more relevant in environmental pollution studies since they are readily bioavailable. Some computer models can estimate heavy metal activity in solution and their ionic speciation. Thermodynamic data (thermodynamic stability constant), total metal and ligand concentrations are used by the GEOCHEM-PC program. This program allows studying heavy metal behavior in solution and the effect of changes in the conditions, such as pH and ionic strength and the application of organic and inorganic ligands caused by soil fertilization.

Carbono orgânico dissolvido e biodisponibilidade de N e P como indicadores de qualidade do solo

Soil quality has become an important issue in soil science. Considerable attempts have been made to define soil quality, but a general concept has not yet been accepted by the scientific community. The selection of quantitative indices for soil quality is extremely difficult, and a considerable number of chemical, physical, and biochemical properties have been suggested as potential indicators of soil quality. Because soil organic matter (SOM) can be associated with different soil chemical, physical and biological processes, it has been widely considered as one of the best soil quality indicator. Land use can significantly influence dynamics of organic carbon and N, P, and S cycle. However, changes in total soil organic carbon (SOC) contents in response to land use may be difficult to detect because of the natural soil variability. In the short to medium term, biological properties and readily decomposable fractions of SOC, such as dissolved organic carbon (DOC), are much more sensitive to soil management than is SOM as a whole, and can be used as a key indicator of soil natural functions. Despite the fact that labile C accounts for a small portion of the total organic matter in the soils, DOC is the most mobile and important C-source for microorganisms, and can easily reflect the effects of land use on soil quality. Although several methods are used to characterize DOC, the factors influencing mineralization and bioavailability of elements associated with organic matter (N, P, and S) remains unclear. Future research should focus on the processes that govern DOC and nutrient dynamics and how they affect soil quality.

COPPER ADSORPTION IN OXIDIC SOILS AFTER REMOVAL OF ORGANIC MATTER AND IRON OXIDES

Copper (Cu), despite being an essential micronutrient, may be toxic whenever it occurs in the soil solution at high concentrations. Chemical reactions that control copper availability in the soil–plant system are complex. Copper can be found in both organic and inorganic soil fractions. This work studied Cu adsorption into surface (0–0.2 m) and subsurface (in the B2 horizon) samples from three Brazilian soils, namely a heavy clayey-textured anionic Rhodic Acrudox (RA), a medium-textured anionic Xanthic Acrudox (XA) and a heavy clayey-textured Rhodic Hapludalf (RH), before and after the removal of organic matter (OM) and iron oxides. pH values were adjusted to 5 with either HNO3 or Ca(OH)2. In natural samples, when OM was not removed, Cu adsorption did not differ statistically among the surface samples. Cu adsorption, however, was significantly lower in the subsurface samples of XA and RA. Removal of OM influenced Cu retention only in XA and RA surface samples. In the subsoil, which had low OM contents, elimination of OM did not significantly affect adsorption. In RH, the amounts of Cu adsorbed were not significantly affected by OM removal, and the mineral fraction, basically constituted of kaolinite, contributed almost entirely to the adsorption reactions. When soil pH was below the zero point of salt effect (ZPSE), iron oxides removal increased Cu retention, likely due to a reduction in repulsion between the positively charged surface and the metal. For pH values above ZPSE, oxides effectively contributed for Cu adsorption, since their removal was followed by a decrease in Cu retention.

Environmental impacts and nutrient recycling on pastures grazed by cattle

Grasslands are being replaced by urbanization and more profitable agricultural activities around the world. Producers may be faced with land constraints and need to consider intensification of the remaining grasslands as a means of maintaining overall production on a decreasing land resource. However, intensification of the grazing system is usually associated with greater nutrient inputs, including those from commercial fertilizers and supplement fed to animals. Excessive loading of nutrients in intensive grazing systems via fertilizer and animal wastes can cause nutrient buildup in the soil and subsequent water quality problems. Surface runoff and leaching of nutrients are the two major process affecting water quality. Nitrogen and P represent major nutrient concerns as related to water quality. Increased nitrate concentrations render groundwater unsuitable for drinking and can cause serious health issues for humans. Excessive N and P concentrations may contribute to eutrophication of streams and lakes. Maximizing efficiency of nutrient recycling through the soil-forage-animal system minimizes off-site nutrient transport and decreases production costs by reducing the quantity of commercial fertilizer needed. Management strategies to reduce soil and water contamination include refining the balance of nutrient inputs from feeds and fertilizers as well as accounting for the nutrients recycled through the decomposition of plant litter and animal wastes. Current interest in the development and adoption of efficient and sustainable agriculture systems has led forage researchers to amplify the scope of grasslands research by increasing multidisciplinary efforts. There is an increased interest in quantifying the impacts of forage-animal management strategies on the environment, with the goal of developing economically viable best management practices that result in optimum forage production and profitability, while protecting the environment. Furthermore, these best management practices will supply reliable information for future environmental policies that may be adopted by governmental agencies.

Condicionadores químicos de solo e retenção e distribuição de cádmio, zinco e cobre em latossolos tratados com biossólido

Land application represents an efficient alternative for disposal of biosolids. However, depending on the origin (urban and/or domestic) and the treatment system, biosolids may contain high amounts of heavy metals, which can gradually build up in the soil. Soil chemical amendments in contaminated areas can reduce the bioavailability and mobility of heavy metals and, consequently, minimize the risks of their adverse effects on the environment. The objective of this study was to evaluate the effects of four chemical amendments [calcium carbonate (CaCO3), calcium sulfate (CaSO4), monobasic potassium phosphate (KH2PO4) and synthetic hydroxyapatite (HA)] on Zn, Cu, and Cd retention and distribution in Oxisols amended with biosolid. Due to the low solubility, HA was equilibrated at pH 4, 5, and 6. Surface soil samples (0-20 cm) of a Rhodic Acrudox (RA) and a Typic Haplorthox (HP) were used. Two grams of each soil sample were equilibrated in a dual- diffusion chamber with 2 g of heavily contaminated with heavy metals. The suspension was constantly stirred for a more uniform mixing of the solutions. When the equilibrium was reached (after approximately seven days), the solution was centrifuged, filtered and acidified. Copper, Zn, and Cd concentrations in solution were determined. The solid phases (soil and biosolid) were freeze-dried and sequential extractions of Zn, Cu and Cd were performed. The chemical amendments were efficient in Zn, Cd and, to a lesser extent, Cu immobilization. Calcium carbonate followed by HA (pH 6) was, in general, the most efficient treatment in reducing metal concentrations in solution. No heavy metal immobilization was obtained by HA equilibrated at pH 4 and 5. Chemical amendments markedly reduced the amounts of metals associated with the exchangeable fraction and increased the surface oxide/carbonate pool, especially in the treatments with CaCO3 and HA (pH 6).

USING TISSUE ANALYSIS AS A TOOL TO PREDICT BAHIAGRASS PHOSPHORUS FERTILIZATION REQUIREMENT

Tissue analysis in combination with soil testing has been recently incorporated in the fertilization recommendations for bahiagrass in Florida; however, limited research is available to validate the proposed critical tissue phosphorus (P) level. A greenhouse experiment was conducted to identify the critical minimum tissue P concentration below which bahiagrass dry matter (DM) yield is impacted. Treatments consisted of three nitrogen (N) rates (0, 50, and 100 kg N ha−1), four P rates (0, 20, 40, 60 kg P2O5 ha−1) and two clipping intervals (28 and 56 d). Bahiagrass yields and tissue P increased in response to P application. Phosphorus uptake showed a quadratic response to P rates when N was applied. Phosphorus recovery increased linearly as P rate increased. Root mass responded to P, even at the smallest (20 kg ha−1) rate. Data indicated that tissue P concentration of 1.3 (±0.2) g kg−1 can be used as an indicator of bahiagrass P deficiency.

Metal-associated forms and speciation in biosolid-amended oxisols

Abstract The objective of this study was to determine the effects of pH and ionic strength on the distribution and speciation of zinc (Zn), copper (Cu), and cadmium (Cd) in surface soil samples from two Brazilian Oxisols amended with biosolids. Soils and biosolids were equilibrated in an experimental dual‐chamber diffusion apparatus that permits the soils and biosolids to react through a solution phase via diffusion across a membrane. After equilibrium was reached, soil and biosolids samples were sequentially fractionated to identify various solid forms of Zn, Cu, and Cd. Metal concentrations in the solution phase were determined and mass balance calculated. Equilibrating pH had no major effect on Cu solubility from biosolids and, at pH range from 4 to 7, most Cu remained in the biosolids. Soluble Zn and Cd concentration increased with decreasing pH because of the increased solubility of the biosolids. Copper and Zn were primarily associated with the residual fraction and Fe oxides in one soil, but were primarily associated with chemically unstable fractions, or adsorbed to the surface of oxides, in the other soil. In both soils, Cd was primarily associated with readily bioavailable fractions. The effect of pH on the metal distribution was more evident than the ionic strength effect. Free ions were the predominant metal species in solution, especially at lower pH values.

Phosphorus management and water quality problems in grazingland ecosystems.

Phosphorus management in grazingland ecosystems represents a major challenge of agronomic and environmental importance. Because of the extensive acreage occupied by grazinglands, decisions concerning pasture fertilization and nutrient management in forage-based livestock systems are crucial to both farmers and regulatory agencies. The purpose of this paper is to provide an overview of the literature relevant to pasture P fertilization and the potential impacts on water quality. There continue to be uncertainties regarding interrelationships between pasture management and water quality issues. Despite the extensive body of literature on nutrient transport from grazinglands, limited information is available on the relationships between land use, transport potential, water management, and climatic conditions affecting nutrient losses at a watershed scale. As agriculture continues to modernize and intensify, public concerns about the impacts of plant nutrients on environmental quality will likely increase. Managing water quality protection and profitable agriculture will be a major challenge for the next generations.

Biochar Decreases Atrazine and Pendimethalin Preemergence Herbicidal Activity

Abstract Biochar and vinasse are by-products of biofuel production that can be used as soil amendments. However, their addition to the soil might affect PRE herbicide activity. Although studies have shown that biochar has a high herbicide adsorption capacity, there is little information available about biochar effect on weed control especially under field conditions. Therefore, the objective of this study was to determine the influence of biochar and vinasse application on atrazine and pendimethalin availability and herbicide activity under in vitro and field conditions. In vitro atrazine and pendimethalin herbicidal activities were not influenced by vinasse addition, but biochar application reduced atrazine and pendimethalin injury for all evaluated species. A sorption experiment confirmed high affinity of biochar for atrazine and pendimethalin. Linear regression analysis showed that the slope for atrazine and pendimethalin adsorption was 16 and 4 times higher in soil with biochar than in soil alone. Under field conditions, biochar at 0.5 kg m−2 reduced atrazine and pendimethalin weed control 75% and 60%, respectively. These results suggested that the use of biochar as a soil amendment in cropping system could decrease PRE herbicide efficacy. Therefore, mitigating practices such as the use of higher rates or reliance on POST herbicides and cultivation might be necessary to ensure proper weed control. Nomenclature: Atrazine; pendimethalin; biochar; vinasse. Resumen El biochar y la vinaza son subproductos de la producción de biocombustibles que pueden ser usados como enmiendas de suelo. Sin embargo, su adición al suelo podría afectar la actividad de herbicidas PRE. Aunque estudios han mostrado que el biochar tiene una alta capacidad de adsorción de herbicidas, hay poca información disponible acerca del efecto del biochar sobre el control de malezas, especialmente bajo condiciones de campo. Por esta razón, el objetivo de este estudio fue determinar la influencia de la aplicación de biochar y de vinaza sobre la disponibilidad y actividad herbicida de atrazine y pendimethalin in vitro y en condiciones de campo. In vitro, la actividad herbicida de atrazine y pendimethalin no fue influenciada por la adición de vinaza, pero la aplicación de biochar redujo el daño causado por atrazine y pendimethalin en todas las especies evaluadas. Un experimento de sorción confirmó la alta afinidad del biochar por atrazine y pendimethalin. Análisis de regresión lineal mostraron que las pendientes de las curvas de adsorción de atrazine y pendimethalin fueron 16 y 4 veces mayores en suelo con biochar que en suelo solo. Bajo condiciones de campo, el biochar a 0.5 kg m−2 redujo el control de malezas de atrazine y pendimethalin en 75% y 60%, respectivamente. Estos resultados sugirieron que el uso de biochar como enmienda de suelo en sistemas de cultivos podría disminuir la eficacia de herbicidas PRE. Por esto, prácticas de mitigación tales como el uso de mayores dosis o una mayor dependencia en herbicidas POST y labranza podrían ser necesarios para asegurar un control adecuado de malezas.

Management of Perennial Warm-Season Bioenergy Grasses. II. Seasonal Differences in Elephantgrass and Energycane Morphological Characteristics Affect Responses to Harvest Frequency and Timing

Elephantgrass (Pennisetum purpureum Schum.) and energycane (Saccharum spp. interspecific hybrid) are perennial C4 grasses with potential for use as bioenergy feedstocks. Their biomass production has been quantified, but differences in plant morphology and the relationship of morphology with biomass harvested and plant persistence are not well understood. The objective was to quantify monthly changes in morphological characteristics of elephantgrass (cv. Merkeron and breeding line UF1) and energycane (cv. L 79-1002) and relate these changes to biomass accumulation and plant responses to defoliation. All were evaluated monthly during full-season growth or when defoliated once in mid-season. Merkeron and UF1 elephantgrass generally showed similar morphological characteristics. Relative to energycane, elephantgrass had fewer tillers early in the growing season, less seasonal variation in tiller number, greater tiller mass and maximum leaf area index (LAI), and earlier spring development of LAI. Energycane showed slower leaf area development in spring, lower maximum LAI, and shorter period of increasing tiller mass and canopy height during the growing season relative to UF1. Elephantgrass had greater incidence of lodging than energycane when exposed to high wind, likely due to greater elephantgrass tiller mass. Morphological characteristics of tall-growing bioenergy grasses help to explain differences among them in biomass production and plant persistence responses to defoliation.