Sewage Sludge Application Rates Research Articles

Application of sewage sludge and sewage sludge biochar to reduce polycyclic aromatic hydrocarbons (PAH) and potentially toxic elements (PTE) accumulation in tomato.

The effects of sewage sludge (SS) and its derived biochar (SSBC) on the availability and uptake of polycyclic aromatic hydrocarbons (PAHs) and potential toxic elements (PTEs) by Solanum lycopersicum (tomato) fruits grown in contaminated urban soil were investigated. Increasing application rates of SS and SSBC (2, 5, and 10%) decreased PAH availability and, correspondingly, PAH accumulation (22-39 and 48-62%, respectively) into tomato. SSBC was more effective in this regard. The available concentrations of PAHs (Σ16PAH) in the SSBC treatments were significantly reduced (from 30.0-47.3%) as compared to the control treatment. The availability of high-molecular-weight PAHs (containing four to six benzene rings) was greatly affected, while low-molecular-weight PAHs (containing two to three benzene rings) was less affected by SSBC amendments. The addition of SSBC showed the least effect on bioaccumulation of naphthalene (two-ring PAH; 24.5-32.6%), while the highest effect was observed for benzo(b)fluoranthene (five-ring PAH; 3.1-86.8%) and benzo(g,h,i)perylene (six-ring PAH; 51.8-84.2%). In contrast, increasing application rates of SS successively increased PTE (As, Cd, Cu, Pb, and Zn) availability and accumulation (15-139%) into tomato while SSBC successively decreased PTE availability and accumulation (17-91%). Changes in accumulation varied with PTE and the extent to which PTE concentrations in soil was elevated.

Micropollutants in Sewage Sludge: Elemental Composition and Heavy Metals Uptake by Phaseolus vulgaris and Vicia faba Seedlings

Sludge is a major economic and environmental concern, and it can be reused for agricultural purposes. The germination success of seed and early growth regulation of plants treated with sludge requires more attention. The study evaluated the influence of municipal sewage sludge (0 and 5%) containing Cd, Co, Cu, Ni, Pb, and Zn, obtained from several sites and sampling dates, on germination and growth of bean (Phaseolus vulgaris L.) and Faba bean (Vicia faba L.) incubated at 25°C in the dark. Water uptake, reserve mobilization, and mineral nutrition in germinating P. vulgaris and V. faba seedlings were analyzed. Among studied heavy metals, zinc concentration was highest in sewage sludge (450 ± 5 mg kg−1 DW), while cadmium concentration was lowest (0.54 ± 0.1 mg kg−1 DW). The contents of Co, Cu, Ni, and Pb in the sewage sludge were about 5 ± 0.5, 104 ± 4, 17 ± 0.4, and 35 ± 0.5 mg kg−1 DW, respectively. Heavy metal concentrations were relatively similar independent of sewage sludge site (S1; S2; S3). Concentration of Zn is 85 ± 2 and 124 ± 2 μg g−1 dry weight in P. vulgaris and V. faba controls, respectively, to about 127 ± 2 and 148 ± 2 μg g−1 in both plants treated with sewage sludge. Metal amounts in this sewage sludge application rate (5%) are not toxic for germination process and growth of two tested leguminous plants. In this context, we shall try to use the 5% sewage sludge for seed germination. It appears that treatment of seed with the 5% sewage sludge was beneficial to germination and early plant development.

Sewage sludge fertilization in larch seedlings: Effects on trace metal accumulation and growth performance

The spreading of sewage sludge (SS) among forest plantations may provide interesting results for firewood production. While sludges are good fertilizers, they may nevertheless contain trace metals, which can reduce productivity and lead to environmental risks. We investigated the effects of SS application on nutrient uptake and growth parameters in larch seedlings (Larix decidua) and determined trace metal and mineral distribution. Without incorporation into the soil, sludge was applied to the soil surface at three rates (0, 30 and 60t dry weight DW ha−1). The plants were harvested after 12 months. The results showed significantly increased nitrogen and phosphorus concentrations in the top soil layer in pots amended with sludge, whereas no changes appeared in the lower layers. Similar results were obtained for the Cu, Zn and Cd concentrations. However, no differences were observed for the other measured soil mineral elements. Nitrogen concentrations in needles increased with rising sewage sludge application rates, yet the sludge had no effect on the P, Mg, Zn, Pb and Cd concentrations. In addition, Cu accumulated only in the lateral roots of seedlings that received the highest sludge loading rate. Sludge application improved the net photosynthesis, which resulted in higher chlorophyll contents in the needles. Following application, the dry matter accumulation rate increased due to the excessive availability of N, whereas available mineral elements in the plant tissues were diluted. Furthermore, amending the soil with sewage sludge can promote a higher biomass yield which may result in an increased trace metal bioaccumulation capacity in plants. Though this investigation has established the benefits of municipal SS application, further studies are needed to assess the potential transfer of TM to groundwater and through the food chain.

Field study on the uptake and translocation of PBDEs by wheat (Triticum aestivum L.) in soils amended with sewage sludge

Field experiments were conducted to explore the effects of different sewage sludge amendment strategies on the accumulation and translocation of polybrominated diphenyl ethers (PBDEs) in soil–wheat systems. Two types of application methods (single or annual application) and four annual application rates (5, 10, 20, and 40tha−1year−1) were investigated. BDE 209 was detected in all of the sewage sludge amended soils and different parts of wheat plants collected from the contaminated soils. However, the other seven PBDE congeners (BDE 28, BDE 47, BDE 99, BDE 100, BDE 153, BDE 154, and BDE 183) were not detected or were only observed at very low levels. A single application of sewage sludge in large quantities would likely increase accumulation of BDE 209 in soil and its subsequent uptake and translocation by wheat. The concentrations of BDE 209 in soils, wheat roots and straws increased with the increasing sewage sludge application rate. There is a negative correlation between the root accumulation factors (the ratios of concentrations in wheat roots to those in soils) and soil total organic carbon (R2=0.84,P<0.05), demonstrating that the bioavailability of BDE 209 was controlled by the soil total organic carbon. BDE 209 concentrations in the grains from the sewage sludge amended soils were not significantly different from those of the control soils, suggesting that atmospheric deposition was the main source of BDE 209 detected in the grains.

Growth, grain yield and nitrogen use efficiency of Mediterranean wheat in soils amended with municipal sewage sludge

The application of sewage sludge (SS) to agricultural land can improve soil fertility and physical properties, and enhance crop production. This field study was conducted for two consecutive growing seasons to investigate the influence of SS application on winter wheat growth, grain yield, N accumulation, translocation and use, and on trace elements concentrations in soil and wheat plants under Mediterranean conditions. Treatments consisted of three rates of SS, i.e. 20, 40, and 60 Mg dry weight ha−1 year−1, one rate of inorganic fertilizer (IF, 120 kg N ha−1 year−1 plus 80 kg P2O5 ha−1 year−1), and an unamended control. The application of SS resulted in tall plants with high early dry matter and N accumulation similar to or significantly higher than those obtained with IF. The lowest SS application rate resulted in grain yield similar to that obtained with IF. Nitrogen use efficiency (NUE) in SS treatments was mainly determined by uptake efficiency, which decreased with increasing SS application rate. Values of NUE and biomass production efficiency with the lowest SS rate were similar to those obtained with IF. SS application resulted in increased concentrations of total and DTPA-extractable trace elements in the soil after the first year, but concentrations were much lower than the regulation limits. Concentrations of Cu, Mn and Zn in wheat plants did not exceed those obtained with IF. Overall, SS could be considered for use as a fertilizer in wheat production systems in the area, serving also as an alternative method of SS disposal.

Influence of sewage sludge on yield and mineral contents of rice grain

Sewage sludge at the rate of 0, 40, 80, 120 and 240 t/ha showed that the number of filled grains per panicle, dry weight of grains and weight of 1000 grains of rice (Oryza sativa L.) were the significantly highest where 240 tons of sewage sludge per hectare was added. The contents of N, P, K, Ca, Mg, Fe, Cu, Zn and Pb in rice grains increased significantly with increasing rate of sewage sludge application, while that of Mn decreased significantly. Chromium, cadmium and nickel contents in the rice grain were below detection limit. DOI: http://dx.doi.org/10.3329/bjsr.v26i1-2.20231 Bangladesh J. Sci. Res. 26(1-2): 57-60, December-2013

Long-term effects of sewage sludge application on sour cherry (Prunus cerasus L.)

This study describes the long-term effects of different sewage sludge application rates on vegetative parameters, morphological characteristics, yield, and chemical properties of fruit and leaves of sour cherry (Prunus cerasusL.) cv. “Kütahya.” A three-year field experiment was set up in a completely randomized block design with six sewage sludge application rates (0.0, 2.5, 5.0, 7.5, 10.0 and 12.5 kg of dry matter per tree) and three replications. One-year-old Kütahya sour cherry trees grafted onPrunus mahalebrootstock were evaluated. In all application rates, sewage sludge altered vegetative growth parameters, morphological characteristics, and yield. The most effective application rate was 7.5 kg per tree, it increased cumulative yield more than twofold. The results obtained in this study demonstrate that application of sewage sludge to light-textured soil is an effective means for improvement of vegetative growth and yield, and that a single application of sewage sludge sustains its effects for at least 7 years.

Utilization of Biosolids in Production of Bioenergy Crops II: Impact of Application Rate on Bioavailability and Uptake of Trace Elements by Canola

Amendment of agricultural soils with municipal sewage sludge (SS) provides a valuable source of plant nutrients and organic matter but it may create a risk of trace-element pollution of the environment. Utilization of SS in cultivation of oil- and biofuel-producing crops such as canola (Brassica napus) may be useful for safe management of biosolids. The aim of this study was to examine the influence of SS application rate on bioavailability and phytoextraction of trace elements by canola. To achieve this goal, a greenhouse pot experiment was established in a Typic Xerfluvent from Greece amended with various rates of sewage sludge: 20 Mg ha−1 (SS1), 50 Mg ha−1 (SS2), and 100 Mg ha−1 (SS3). Furthermore, a soil sample without any amendment was cultivated and used as a control (C). After a planting period of 2 months, the whole plants and soils were removed from the pots. One kg from the soils was selected for analyses and the rest of the soil was cultivated again for 2 more months with the same crop. Soil samples were analyzed for total and available forms of trace elements [iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), nickel (Ni), lead (Pb), and cadmium (Cd)] and the same elements were measured in plant tissue. The results showed that increasing SS application rate increased significantly the total amounts of all the studied trace elements compared to the control except for Fe and Ni. However, the total concentrations of all the studied elements were less than the critical concentrations in soils. Diethylenetriaminepentaacetic acid (DTPA)–extractable element concentrations increased significantly with increasing the biosolid application rate, especially in the case of SS3. However, no significant differences were recorded between control and SS1 for Fe, Mn, Pb, Ni, and Cd. Plant tissue element concentrations for all elements except for Fe increased significantly compared to the control with increasing sewage sludge application rate, especially with SS3, whereas no significant differences were found between the control and SS1 in the cases of Cu and Pb. Iron showed the opposite trend, where it decreased significantly with increasing SS rate. The ability of canola in phytoextraction of the studied elements was measured by bioconcentration ratios (BCR) (plant tissues concentration / DTPA-extractable elements). Values of BCR differed widely between the elements. Iron and Zn BCR values decreased significantly with increasing the SS application rate in both planting periods. The BCR values of Cd, Cu, Mn, Ni, and Pb increased in the SS-treated soil compared to the control with a relative increase in SS1 and SS2 treatments compared to SS3. Data from this result convinced us that there is no risk from utilization of biosolids in production of noneaten plants like canola. The recommended rate was 20 Mg SS ha−1.

Utilization of Biosolids in Production of Bioenergy Crops I: Impact of Application Rate on Canola Biomass, Soil Properties, and Nutrient Availability

Amendment of agricultural soils with municipal sewage sludge (SS) or biosolids may provide a valuable source of plant nutrients and organic matter. Utilization of SS in cultivation of oil- and biofuel-producing crops such as canola (Barassica napus) has not been adequately studied. The aim of this study was to compare the influence of biosolid application rates on biomass production of canola and on soil properties and nutrient availability measured both by conventional methods and a new technique involving plant root simulators (PRS probes). For this purpose, a greenhouse pot experiment was established in a Typic Xerfluvent (5 kg) from central Greece amended with various rates of SS [0 Mg ha−1 (C) 20 Mg ha−1 (SS1), 50 Mg ha−1 (SS2), and 100 Mg ha−1 (SS3)] and cultivated with canola. After a 2-month planting period, the whole plants and soils were removed from the pots. One kg of the soils was selected for analyses, and the rest of the soil was cultivated again for 2 more months with the same crop. Bioavailability of phosphorus (P) and potassium (K) was measured using the conventional methods (Olsen and ammonium acetate method respectively) as well as by PRS probes. Results showed that application of SS significantly increased canola biomass only in the treatment SS1 compared to the control in the first planting period. However, in the second period, SS application significantly increased canola biomass in the treatments SS2 and SS3 compared to the control and SS1. Soil pH decreased significantly from 7.9 in the control treatment to 6.9 in the treatment SS3. Furthermore, soil organic matter, nitrate nitrogen, and hot water–extractable boron were significantly increased with increasing SS application rate. Olsen P increased significantly with SS application in both planting periods but its increase was greater in the second planting period compared to the first one. Phosphorus-supplyrate (PSR) as assessed by the PRS probes increased significantly with SS application rate in both planting periods but it decreased significantly in the second planting period as compared to the first one. Plant tissue concentration P showed a trend similar to P supply rate (PSR). A strong relationship was recorded between PSR and Olsen P while plant tissues P concentration was strongly correlated with PSR and Olsen P (R2 0.93*** and 0.87*** respectively), indicating that probe method estimates better bioavailability of P to the grown plants compared to the Olsen method. Application of SS decreased significantly available K and potassium-supply rate (KSR) compared to the control, especially in the second planting period. Potassium-supplying rate decreased significantly in the second period compared to the first one. No relationships were recorded among KSR, ammonium acetate K, and plant tissue K concentration.

Short-term usage of sewage sludge as organic fertilizer to sugarcane in a tropical soil bears little threat of heavy metal contamination

A field experiment was carried out to study the effect of application rates of sewage sludge and mineral nitrogen and phosphate fertilizers on As, Ba, Cd, Cr, Cu, Ni, Pb, Se, and Zn concentration in soil, cane plant, and first ratoon (residual effect) in a Typic Hapludult soil. To allow an analysis by means of response surface modeling, four rates of sewage sludge (0, 3.6, 7.2 and 10.8 t ha−1, dry base), of N (0, 30, 60 and 90 kg ha−1) and of P2O5 (0, 60, 120 and 180 kg ha−1) were applied in randomized block design, in a 4 × 4 × 4 factorial scheme, with confounded degrees of freedom for triple interaction, with two replications. To evaluate the residual effect of the sludge applied to cane plant on the cane ratoon growth, mineral NK fertilizers were applied at the rates of 120 kg ha−1 N and 140 kg ha−1 of K2O, on all treatments. The application rates of mineral nitrogen and phosphate fertilizers did not affect statistically the heavy metal concentration in the soil and in the sugarcane plants. Sewage sludge application increased As, Cd, Cu, Ni, Pb, and Zn concentrations in soil, but values did not exceed the quality standard established by legislation for agricultural soils. Although the concentrations of metals in the plants were very low, the uptake of heavy metal by sugarcane plants was generally increased by sewage sludge doses. The use of sewage sludge based on N criteria introduces a small amount of heavy metal into the agricultural system, however it poses no hazard to the environment.

Changes in chemical properties of soil and sour cherry as a result of sewage sludge application

This study, aimed at assessment of the effects of different sewage sludge application rates on heavy metal accumulation in the soil and in sour cherry leaves was carried out in the years 2005&amp;ndash;2007. The rates applied were 0.0, 2.5, 5.0, 7.5, 10.0 and 12.5 kg of dry matter per tree. Eighteen uniform one-year-old K&amp;uuml;tahya sour cherry trees on Prunus mahaleb rootstock were used. Sewage sludge not only improved soil chemical properties but also resulted in an increase of nutrient content in cherry leaves. Sewage sludge application increased heavy metal content of soils. However, this increase did not exceed the critical values and was not reflected in the leaf contents of heavy metals. The most effective application rate was 7.5 kg per tree. Studies should be continued to evaluate the effects of sewage sludge on vegetative and generative growth, yield and fruit quality parameters.

Phytoavailability of Copper, Zinc and Cadmium in Sewage Sludge-Amended Calcareous Soils

The toxicity of trace elements (TEs), such as copper (Cu), zinc (Zn), and cadmium (Cd), often restrict land application of sewage sludge (SS) and there was little information about soil-plant transfer of TEs in SS from field experiments in China. In this study pot and field experiments were carried out for 2 years to investigate the phytoavailability of TEs in calcareous soils amended with SS. The results of the pot experiment showed that the phytoavailability of Zn and Cu in the SS was equal to 53.4%–80.9% and 54.8%–91.1% of corresponding water-soluble metal salts, respectively. The results from the field experiment showed that the contents of total Zn, Cu, and Cd in the soils increased linearly with SS application rates. With increasing SS application rates, the contents of Zn and Cu in the wheat grains initially increased and then reached a plateau, while there was no significant change of Cd content in the maize grains. The bioconcentration factors of the metals in the grains of wheat and maize were found to be in the order of Zn > Cu > Cd, but for the straw the order was Cd > Cu > Zn. It was also found that wheat grains could accumulate more metals compared with maize grains. The results will be helpful in developing the critical loads of sewage sludge applied to calcareous soils.

Effect of long-term organic amendments on chemical and microbial properties of a luvisol

We studied the long-term effect (about 45 years) of farmyard manure, sewage sludge and compost application in two increments on organic carbon (C&lt;sub&gt;org&lt;/sub&gt;), the amount (C&lt;sub&gt;mic&lt;/sub&gt;) and activity of the microbial biomass (soil respiration, dehydrogenase activity), total N content and N delivery of soils as compared to manuring with mineral fertilizers. The application of both increments of compost and the high sewage sludge application rate resulted in an increase in C&lt;sub&gt;org&lt;/sub&gt; while soils treated with both compost application rates and the high farmyard manure application rate showed a significant increase in C&lt;sub&gt;mic&lt;/sub&gt;. C&lt;sub&gt;mic&lt;/sub&gt;/C&lt;sub&gt;org&lt;/sub&gt; ranged between 1.7 and 3.3. Dehydrogenase activity and soil respiration were the greatest in the soil with the highest compost and farmyard manure application rates. Total soil N content was significantly higher in both compost treatments and in the treatment with the high sewage sludge application rate. This was accompanied by the highest N uptake of ryegrass. &amp;nbsp;

Bário, cádmio, cromo e chumbo em plantas de milho e em latossolo após onze aplicações anuais de lodo de esgoto

A presença de metais pesados no lodo de esgoto é uma das restrições quanto ao seu uso em áreas agrícolas. Este estudo teve por objetivo avaliar os efeitos da aplicação de doses de lodo de esgoto por 11 anos consecutivos em um Latossolo Vermelho distrófico sobre as concentrações de Ba, Cd, Cr e Pb em três profundidades no solo (0-10, 10-20 e 20-40 cm), bem como quantificar os mesmos metais na folha diagnose e nos grãos de milho. O experimento foi conduzido em condições de campo, utilizando-se o delineamento experimental em blocos casualizados com quatro tratamentos (0, 5, 10 e 20 t ha-1 de lodo de esgoto, base seca) e cinco repetições. As amostras de folha diagnose, solo, plantas inteiras e grãos foram obtidas, respectivamente, aos 60, 68, 80 e 123 dias após a emergência das plantas. A aplicação de doses de lodo de esgoto de 10 e 20 t ha-1 aumentou os teores de Ba, Cr e Pb na camada superficial do solo (0-10 cm), mas não alterou os de Cd. As doses do lodo de esgoto testadas não proporcionaram incrementos nas concentrações de Cd, Cr e Pb na folha diagnose e de Ba, Cd, Cr e Pb nas plantas de milho. A concentração de Ba na folha diagnose reduziu com a aplicação do resíduo. Os teores de Cd e Pb em grãos de milho permaneceram abaixo dos limites estabelecidos para o consumo humano, a concentração de Cr não pôde ser avaliada e nenhuma referência foi encontrada para comparar as concentrações de Ba.

Effect of different sewage sludge applications on growth and yield of Vigna radiata L. field crop: Metal uptake by plant

The aim of this study was to assess the suitability of sewage sludge use for mung bean { Vigna radiata L. cv. Malviya janpriya (HUM 6)} plants by evaluating the growth, and yield responses, nutritional quality and heavy metal accumulation at different sewage sludge amendment (SSA) rates. Sewage sludge amendment modified the physico-chemical properties of soil by decreasing pH and increasing organic carbon, total iron and heavy metals. Plants showed increments in shoot length, leaf area and total biomass at all SSA rates, but root length increased only up to 9 kg m −2 SSA rates. Plants grown at different SSA rates showed higher nutrients and heavy metals in seeds, but protein content declined. Sewage sludge application caused about 39, 76 and 60% more yield at 6, 9 and 12 kg m −2 treatments, respectively. Concentrations of Pb and Ni in grains were higher than the Indian permissible limits at and above 9 kg m −2 and of Cd at 12 kg m −2 SSA rates. The study suggests that SSA at a rate lower than 9 kg m −2 may be recommended due to better fertilizing value for soil and promoting mung bean yield. Higher rate of sewage sludge application leads to elevated accumulation of heavy metals in seeds, which limits the suitability for human consumption.

Sewage sludge as nitrogen and phosphorus source for cane-plant and first ratoon crops

The use of sewage sludge in Brazilian agriculture was regulated by the resolution no. 375 Conama, in 2006. However, there is a lack of research to adequate the mineral N and P fertilizer doses to be applied in agricultural fields treated with this residue. In a field experiment, the effects of application rates of sewage sludge and mineral N and P fertilizers on the productivity and technical characteristics of the cane-plant and first ratoon (residual effect) crops were evaluated. Four doses of sewage sludge (0, 3.6, 7.2 and 10.8 t ha-1, dry base), of N (0, 30, 60 and 90 kg ha-1) and of P2O5 (0, 60, 120 and 180 kg ha-1) were combined in a factorial and laid out on randomized block design, a with two replications. To evaluate the residual effect of the sludge, 120 kg ha-1 N and 140 kg ha-1 of K2O were applied in all plots. Sludge application at cane planting, with or without N and/or P fertilizer increased the stalk yield from 84 up to 118 t ha-1, with no alteration in the sugarcane quality, compared with the application of NPK fertilizer alone, resulting in a stalk yield of 91 t ha-1. The study of the response surface for stalk yield on lowfertility soil was the basis for a recommendation of mineral N and P fertilizer doses for sugarcane implantation as related to sewage sludge application rates. It was also concluded that a sludge application of 10.8 t ha-1, which is the sludge dose established based on the N criterion according to the resolution Conama nº 375, could a) reduce the use of mineral N by 100 % and of P2O5 by 30 %, with increments of 22 % in stalk yield, as a direct effect of sludge application to cane plant crop, and b) increase the stalk yield in the second harvest (first ratoon) by up to 12 % and sugar yield by up to 11 %, by the residual effect of sludge application to sugar cane.

BIOACCUMULATION OF Cd, Pb AND Ni IN Eucaluptus SPP. AS AFFECTED BY SPECIES AND SLUDGE CONCENTRATION

The work was carried out at the Experimental Farm of El-Kassassin Horticulture Research Station, Horticulture Research Institute to study the effects of various sewage sludge application rates (0, 10%, 20%, 30% and 40%) on growth and Cd, Pb and Ni content in the roots, stems and leaves of two Eucalyptus species, Eucalyptus citriodora and E gomphocephala . Also, to study the possibility of using specific transplants for bioaccumulation some heavy metals on new reclaimed soils in semi arid areas using treated municipal sewage sludge. The highest value of plant height and stem diameter obtained from Eucalyptus gomphocephala with 30% or 40% of sewage sludge application. High amount of Ni was observed in leaves of the studied plants

Chemical Changes and Heavy Metal Partitioning in an Oxisol Cultivated with Maize (Zea mays, L.) after 5 Years Disposal of a Domestic and an Industrial Sewage Sludge

The need for solutions to minimize the negative environmental impacts of anthropogenic activities Fhas increased. Sewage sludge is composed of predominantly organic matter and can be used to improve soil characteristics, such as fertility. Therefore, its application in agriculture is an adequate alternative for its final disposal. However, there is a lack of information on its long-term effects on soil changes in tropical areas. Thus, the objectives of this study were to determine (i) the effect of sewage sludge application on heavy metal build-up in soil and maize grains and leaves, and (ii) the effects of soil amendment with sewage sludge on the chemical properties of a Brazilian oxisol. Besides the increasing levels of Zn, Cu, Ni, and Cr, amending soil with sewage sludge also alters the distribution of these metals by increasing the mobile Phases, which correlated significantly with the increase in metal extraction with two single extractants, Mehlich 1 and DTPA (Diethylene triamine pentaacetic acid). The levels of Fe, Mn, Zn, and Cu in maize grains and leaves increased with the type and rate of sewage sludge application. Nevertheless, metal build-up in soil and plants was within the allowed limits. Significant differences were also found in soil characteristics like humic fractionation with the applied sewage doses. The data obtained does not indicate any expressive drawbacks in the use of sewage sludge as a soil amendment, as the heavy metal concentrations observed are unlikely to cause any environmental or health problems, even overestimated loadings, and are in accordance with the Brazilian regulations on farming land biosolid disposal.

Mineralização de compostos nitrogenados após aplicações de lodos de esgoto em quatro cultivos de milho

O teor de N disponível em solos tratados com lodo de esgoto é um dos fatores restritivos à aplicação do resíduo em grandes volumes na agricultura, e deve ser utilizado nas normas que regulamentam seu uso agrícola com o fim de evitar a contaminação ambiental do solo e corpos d'água com nitrato. Quando se aplica o resíduo pela primeira vez em um solo, a disponibilização de N mineral a partir de compostos orgânicos naturais do solo não é diretamente considerada no cálculo da taxa de aplicação máxima, e este procedimento é comum também nas recomendações de adubação mineral. Porém, a aplicação continuada desses resíduos pode causar efeitos residuais acumulativos na geração de N mineral, o que implicaria recomendações específicas para reaplicações em uma mesma área. O objetivo deste trabalho foi avaliar a disponibilidade potencial de N mineral em um Latossolo previamente tratado com lodos de esgoto e com quatro cultivos sucessivos de milho. Amostras de solo da camada de 0-20 cm foram coletadas em subparcelas de um experimento realizado em campo, entre 1999 e 2002, em Jaguariúna (SP), onde foram aplicados 0, 14.716, 29.432, 58.864 e 117.728 kg ha-1 de lodo de origem urbana (Franca, SP) e 0, 22.700, 45.400, 90.800 e 181.600 kg ha-1 de lodo produzido a partir de esgotos urbanos e industriais (Barueri, SP). As doses foram parceladas em quatro aplicações anuais consecutivas. Em laboratório, essas amostras foram incubadas durante 15 semanas. As análises iniciais dos solos evidenciaram que houve efeito residual das aplicações prévias dos lodos sobre o acúmulo de N orgânico e de nitrato. No final da incubação, houve acúmulo de N inorgânico no solo e diminuição do pH em função da maior geração de nitrato com as doses crescentes dos lodos de esgoto. O potencial de mineralização estimado pelo modelo exponencial simples foi de 28 mg kg-1 de N no tratamento sem lodo, e crescente, de 28 para 100 mg kg-1 de N, nos tratamentos com lodo de Franca, e de 40 para 113 mg kg-1 de N tratamentos com lodo de Barueri. Concluiu-se que os efeitos residuais acumulados no solo devem ser considerados quando se pretender fazer novas aplicações de lodos de esgoto num mesmo local. Os potenciais de mineralização de compostos de N do solo e do lodo que será utilizado, além do acúmulo de nitrato no perfil do solo, devem ser determinados e considerados para o cálculo da dose da próxima aplicação.

Contributo para a melhoria de solos marginais destinados a pastagens pela aplicação de lama residual urbana, sem riscos ambientais

Sewage sludge (SS) application to soils reserved for pastures, still scarcely used in the country, often contributes to improve organic matter (O.M.) and some plant nutrient contents and to reduce the erosion risk, by increasing the soil vegetation cover. However, the occasional occurrence in SS of high levels of heavy metals, organic pollutant compounds, and pathogenic organisms restrict the SS rate to apply and makes indispensable their control in the soils to which they were applied. Also, the high nitrogen concentration often present in SS can inhibit the symbiotic rhizobium activity, with sequent damage in the leguminous species survival in grassland. In this work, dry matter yield, floristic composition, and copper (Cu) concentration in the plant biomass were evaluated, in two successive years of a field experiment with a sown pasture mixture, established in a poor Haplic Luvisol in the Mertola region. A biologically treated SS from Evora, rich in Cu, was applied. The evolution in the topsoil of the O.M., some plant nutrients, and aqua regia extractable Cu concentrations, was also examined for the same period. The magnitudes of the Rhizobium population (Rhizobium leguminosarum biovar trifolii) and of some indicators of faecal contamination (coliform bacteria and enterococcus) were evaluated too. Moreover, the evolution in the soil superficial layer of 11 polychlorinated biphenyls (PCBs), 13 organ chlorine pesticides, and 16 polycyclic aromatic hydrocarbons (PAHs) concentrations was examined for the 1st year following the SS application. The experiment, with a randomised block design, had three SS application rates (L0 = 0, L1 = 12, and L2 = 24 t/ha) as treatments and two replicates. The sown mixture consisted of Italian ryegrass, cocksfoot, five clover species, bird’s foot, and biserrula. Besides much higher biomass production, induced by higher soil available phosphorus concentration, the added SS neither polluted the soil with the analysed organic compounds, one year after application, nor increased the pathogenic microbial flora in two consecutive years. However, at the highest SS rate, soil aqua regia extractable Cu (0-10 cm depth) exceeded the maximum Portuguese legislated level in soil (100 mg kg-1), the rhizobium population was also reduced at the beginning of the 1st growing season, and legume percentage decreased at the 2nd growing season. The plant Cu concentrations were much lower than the maximum tolerable levels (25 mg kg-1) for the small ruminant’s diet, strongly suggesting that the SS application will not have damaging effects on the animal nutrition. Due to the undesirable effects of the L2 application rate, the L1 rate (12 t/ha) would be recommended for fertilizer purposes.