Sewage Sludge Compost Application Research Articles

Biological remediation treatments improve the health of a mixed contaminated soil before significantly reducing contaminant levels.

The remediation of mixed contaminated soil is challenging as it often requires actions to minimize metal-induced risks while degrading organic contaminants. Here, the effectiveness of different bioremediation strategies, namely, rhizoremediation with native plant species, mycoremediation with Pleurotus ostreatus spent mushroom substrate, and biostimulation with organic by-products (i.e., composted sewage sludge and spent mushroom substrate), for the recovery of a mixed contaminated soil from an abandoned gravel pit was studied. The combination of biostimulation and rhizoremediation led to the most significant increase in soil health, according to microbial indicator values. The application of composted sewage sludge led to the highest reduction in anthracene and polychlorinated biphenyls concentrations. None of the strategies managed to decrease contamination levels below regulatory limits, but they did enhance soil health. It was concluded that the biological remediation treatments improved soil functioning in a short time, before the concentration of soil contaminants was significantly reduced.

Compost promotes biocrust and plant growth in greenhouse cocultures for dryland restoration

Biocrusts and plants are the main ground cover and provide multiple ecosystem functions in arid and semiarid areas. As land degradation worsens and waste management is ever more pressing, the use of composted waste appears as a sustainable restoration practice to enhance vegetation reestablishment, but its effects on biocrusts still remain largely understudied. Moreover, developing appropriate methods for the co‐introduction of plants and biocrusts can be an emerging approach to reconstruct the biocrust/plant interaction and their associated functions. We evaluated the effect of different compost types on biocrust and plant cocultivations. We performed a greenhouse mesocosm experiment using urban organic solid waste and sewage sludge composts to grow a moss‐dominated biocrust and seedlings of two pioneer shrubs (Senecio filaginoides and Acaena splendens) in the Patagonian steppe. Both compost types successfully enhanced biocrust cover and chlorophyll a development, with cultured biocrusts being compositionally similar to the natural inoculum. Only the addition of composted sewage sludge enhanced seedling growth, and biocrusts had significant but opposite effects (positive/negative) on the two plant species we used for experimentation. This difference in the biocrust/plant interaction outcome was likely mediated by the significant influence of biocrusts on the relative availability of ammonium and nitrate and possible plant species‐specific preferences for different inorganic nitrogen forms. We conclude that the application of sewage sludge compost effectively improves the success of biocrust and plant cocultures, but species‐specific differences in the performance of seedlings growing in biocrusted soils impose limits on attempts to promote biocrust and plant joint restoration.

Common Bean Productivity and Micronutrients in the Soil-Plant System under Residual Applications of Composted Sewage Sludge.

Composted sewage sludge (CSS) is an organic fertilizer that can be used as a source of micronutrients in agriculture. However, there are few studies with CSS to supply micronutrients for the bean crop. We aimed to evaluate micronutrient concentrations in the soil and their effects on nutrition, extraction, export, and grain yield in response to CSS residual application. The experiment was carried out in the field at Selvíria-MS, Brazil. The common bean cv. BRS Estilo was cultivated in two agricultural years (2017/18 and 2018/19). The experiment was designed in randomized blocks with four replications. Six different treatments were compared: (i) four increasing CSS rates, i.e., CSS5.0 (5.0 t ha-1 of applied CSS, wet basis), CSS7.5, CSS10.0, CSS12.5; (ii) a conventional mineral fertilizer (CF); (iii) a control (CT) without CSS and CF application. The available levels of B, Cu, Fe, Mn, and Zn were evaluated in soil samples collected in the 0-0.2 and 0.2-0.4 m soil surface horizons. The concentration, extraction, and export of micronutrients in the leaf and productivity of common beans were evaluated. The concentration of Cu, Fe, and Mn ranged from medium to high in soil. The available levels of B and Zn in the soil increased with the residual rates of CSS, which were statistically not different from the treatments with CF. The nutritional status of the common bean remained adequate. The common bean showed a higher requirement for micronutrients in the second year. The leaf concentration of B and Zn increased in the CSS7.5 and CSS10.0 treatments. There was a greater extraction of micronutrients in the second year. Productivity was not influenced by the treatments; however, it was higher than the Brazilian national average. Micronutrients exported to grains varied between growing years but were not influenced by treatments. We conclude that CSS can be used as an alternative source of micronutrients for common beans grown in winter.

Environmental risks of organic fertilizer with increased heavy metals (Cu and Zn) to aquatic ecosystems adjacent to farmland in the northern biosphere of Japan

In Abashiri, Hokkaido, northern Japan, composted sewage sludge (CSS) containing a large amount of zinc (Zn) and copper (Cu) is used as fertilizer in agriculture. The local environmental risks of Cu and Zn from such organic fertilizers were studied. The study area, especially the brackish lakes located near the farmlands, is important for inland fisheries. The risks posed by heavy metals to the brackish-water bivalve, Corbicula japonica, was therefore investigated as an example. First, the long-term effect of CSS application in agricultural fields was monitored. Second, using pot cultivation, factors influencing Cu and Zn availability in the presence of organic fertilizers were evaluated under different scenarios of SOM content. In addition, the mobility and availability of Cu and Zn in organic fertilizers were evaluated in a field experiment. In the pot cultivation, both organic and chemical fertilizers increased the availability of Cu and Zn with a decrease in pH, possibly caused by nitrification. However, this decrease in pH was inhibited by higher SOM content, i.e. SOM mitigated the heavy metal risk from organic fertilizer. In the field experiment, potato (Solanum tuberosum L.) was cultivated using CSS and pig manure (PM). As observed in the pot cultivation, the applied chemical and organic fertilizers increased the soil-soluble and 0.1 N HCl-extractable Zn with increased nitrate. Considering the habitat and the LC50 values of C. japonica that were lower than the concentration of Cu and Zn in the soil solution phase, there is no significant risk from heavy metals in the organic fertilizers. However, the Kd values for Zn were significantly lower for CSS or the PM-applied plot in the field experiment soil, indicating a higher Zn desorption rate from organically fertilized soil particles. The potential risk of heavy metals from agricultural lands under changing climate conditions must therefore be monitored carefully.

Composted Sewage Sludge Sustains High Maize Productivity on an Infertile Oxisol in the Brazilian Cerrado

Mato Grosso do Sul State in Brazil is characterized by the ‘Cerrado’ ecoregion, which is the most biologically rich Savannah globally. In agricultural terms, the region produces several commodities that are exported around the world. This level of productivity has been achieved through the large-scale use of synthetic fertilizers, which has created several economic and environmental concerns. New approaches in soil fertility management are required to avoid environmental degradation, pollution, and socio-environmental damages. A field experiment, lasting two years, was conducted to investigate the composted sewage sludge (CSS) effects on an infertile acidic soil (Oxisol) planted to maize (Zea mays L.). The following complete randomized complete block design with a 4 × 2 + 2 factorial scheme (four replications) was applied: four CSS increasing rates (from 5.0 to 12.5 Mg ha−1, w.b.) following two application methods (whole area and between crop rows). A control, without CSS or synthetic fertilizers, and conventional synthetic fertilization without CSS were also investigated. Evaluated parameters were: (i) soil and leaf micronutrient concentrations; (ii) maize development, yield, and production. The CSS application increased: (i) the concentration of micronutrients in both soil and leaves; and (ii) the crop yield. Both were particularly true at the higher CSS applied rates. Such organic fertilizer can be safely used as a source of micronutrients for crops as an important low-cost and environmentally friendly alternative to mineral fertilizers, thus safeguarding soil health.

Fertilizer Potential of Organic-Based Soil Amendments on cv. Sangiovese (V. vinifera L.) Vines: Preliminary Results

The intensification of highly specialized viticulture has led to a dramatic decrease of soil fertility that can be restored by increasing soil organic matter using organic fertilizers. The aim of the present experiment was to evaluate the effect of different organic amendments on vine vegetative growth and nutritional status, soil N availability and microbial biomass, as well as on yield and grape quality. The experiment was carried out in 2020 and 2021, on cv. Sangiovese (Vitis vinifera L.) vines grafted on 110 Richter (V. berlandieri × V. rupestris) planted in February 2019. Plants were fertilized yearly in spring with (1) mineral fertilization (MIN), (2) municipal organic waste compost (MOW), and (3) sewage sludge compost (SS). The application of SS increased nitrate availability in both years, while the supply of organic matter (no matter the source) enhanced soil microbial biomass content. Plant nutritional status was in the optimal range for all treatments, with an increase of N in SS and K in MOW. Fruit yield in 2020 was not influenced by treatments, while in 2021 it was enhanced by MIN and MOW, which also induced a higher berry quality. Plant vegetative growth was stimulated by the application of SS. In conclusion, from these preliminary results we observed a higher N availability as a consequence of SS supply that resulted in a higher plant biomass, but reduced yield and berry quality, supporting the theory that for vineyards, N should be carefully managed to reach an equilibrium between vegetative and reproductive activity.

Composted Sewage Sludge Application Reduces Mineral Fertilization Requirements and Improves Soil Fertility in Sugarcane Seedling Nurseries

Sugarcane demands large amounts of nutrients to reach a high level of productivity. Nutrients are generally supplied by mineral fertilizers, but their high costs and negative environmental impacts have generated interest in greater use of organic nutrient sources such as composted sewage sludge (CSS). In this study, we evaluated changes in soil chemical properties after the application of CSS or CSS/mineral fertilizer (MF) combinations to soil containing sugarcane seedlings under nursery conditions. Treatments included: T1: conventional mineral fertilization (MF) without application of CSS, T2: 100% of the recommended MF (06–30–24); T3: application of 2.5 Mg−1 CSS; T4: 5.0 Mg−1 CSS, T5: 7.5 Mg−1 CSS, T6: 2.5 Mg−1 CSS and 50% MF, T7: 5.0 Mg−1 CSS and 50% MF, T8: 7.5 Mg−1 CSS and 50% MF, T9: 2.5 Mg−1 CSS and 100% MF, T10: 5.0 Mg−1 CSS and 100% MF, T11: 7.5 Mg−1 CSS and 100% MF. Soil chemical properties were evaluated from the soil surface (0.0–0.25 m) and subsurface (0.25–0.50 m) horizons. The results showed that the increase in CSS application did not affect soil organic matter content at either depth, while Zn concentrations increased in the soil subsurface horizon. The application of CSS at 5.0 Mg ha−1 with or without 50% MF resulted in the highest pH values, sum of bases, cation-exchange capacity, P, K, Ca, Mg, Cu, and Zn in surface horizons. The use of CSS as an organic fertilizer in sugarcane nurseries improves soil fertility, reduces mineral fertilizer requirements, and, thus, facilitates the sustainable disposal of sewage sludge.

Composted Sewage Sludge Application in a Sugarcane Seedling Nursery: Crop Nutritional Status, Productivity, and Technological Quality Implications

Composted sewage sludge (CSS) contains large amounts of organic matter and nutrients and can be used as an organic fertilizer to improve growth, yield, and quality of sugarcane. However, there is a lack of information regarding the impact of CSS application on sugarcane seedling performance in nursery environments. A field study was conducted using a randomized complete block design to evaluate the development, nutritional status, productivity, and technological quality of sugarcane seedlings after CSS application with or without mineral fertilizer. Morphological variables (stem height, diameter, and number, as well as leaf area), technological attributes (total recoverable sugar: ATR; quantity of sucrose in sugarcane juice: Pol; Brix: percentage (weight/weight) of soluble solids contained in juice; TAH: tons of sugar per hectare), nutritional status, and sugarcane productivity were evaluated. Treatments did not influence morphological and technological variables except for TAH but did positively alter nutritional status and seedling productivity. The application rates of 5.0 and 7.5 Mg ha−1 of CSS with or without mineral fertilizers (MF) provided the greatest increase in crop productivity. Our results indicate that CSS can be a sustainable nutritional management option in sugarcane seedling nurseries, resulting in greater crop productivity at lower mineral fertilization rates.

High Nitrogen Addition after the Application of Sewage Sludge Compost Decreased the Bioavailability of Heavy Metals in Soil

High Nitrogen Addition after the Application of Sewage Sludge Compost Decreased the Bioavailability of Heavy Metals in Soil

Effect of Sewage Sludge Compost Application on the Taste of Fruit Vegetables Compared with Chemical Fertilizer Application

Effect of Sewage Sludge Compost Application on the Taste of Fruit Vegetables Compared with Chemical Fertilizer Application

Composted Sewage Sludge Enhances Soybean Production and Agronomic Performance in Naturally Infertile Soils (Cerrado Region, Brazil)

Naturally infertile soils require large amounts of mineral fertilizers to obtain the desired crop yield. In the Cerrado region of Brazil, there is a need to investigate the potential of organic fertilizers to sustainably increase crop productivity and food security. A field study was conducted over two experimental seasons to evaluate the agronomic effectiveness of composted sewage sludge (CSS) as a fertilizer for soybean cultivation in infertile tropical soils. A 4 × 2 + 2 factorial randomized complete block design was applied with the following treatments: (i) CSS: 5.0, 7.5, 10.0, and 12.5 Mg ha−1 on a wet basis applied according to two different methods: whole area (WA) or between rows (BR); (ii) comparison with two alternative treatments: a control with no CSS and mineral fertilizer application, and an area treated with conventional fertilizers only. All the treatments were compared in terms of micronutrient concentrations in surface soil and plant leaves, plant development, crop productivity, and yield. Bi- (ANOVA, correlation matrix, and polynomial regression analysis) and multivariate (PCA, principal factor analysis) statistics were applied to determine statistical differences and relationships/observed variability among the treatments. Results showed that at higher CSS-WA rates: (i) soil and leaf micronutrient concentrations increased; (ii) there was an increase in soybean yield by 12 and 20%, respectively, as compared to control and conventional fertilization; (iii) soybean yield was 67% higher than the mean soybean yields for Brazil. Research outcomes confirm the benefits of CSS application on infertile agricultural soils in the Cerrado region, representing a strong alternative source of micronutrients in the CSS with respect to conventional fertilizers.

Short-Term Effects of Sewage Sludge Compost Amendment on Semiarid Soil

The adoption of sewage sludge as an agricultural management strategy to improve soil properties and crop production is attracting great interest. Despite many positive effects on soil inorganic and organic components reported for different soil types, little information is available on sewage sludge application on Mediterranean soils, as well as on its use at different dose rates. The objectives of the present research was to evaluate, through an integrated approach, the effects of sewage sludge compost from urban wastewater on physicochemical, hydrological, biochemical parameters, and microbiota composition in soil pots under a three-year crop rotation system. Four different doses of sewage sludge compost (C3, C6, C9, C12) from municipal wastewater and a dose of them in combination with mineral fertilizer (C6N) were used. We have used 3-6-9-12 Mg/ha of sewage sludge compost for the treatments C3, C6, C9 and C12, respectively, and 6 Mg/ha of sewage sludge compost in combination with 60 kg/ha of ammonium nitrate for the treatment C6N.The effects were compared to non-fertilized (C0) and mineral fertilized (Min) sets of controls. The electrical conductivity, soil pH, stability of soil aggregates, percent of moisture of the dry soil both at the field capacity and at the wilting point, available P, and exchangeable K were all positively affected by increasing the amounts of composted sludge. The organic carbon and total N increased up to 66% and 39%, respectively. Increased enzymatic activities and microbial biomass were also observed in soil after the application of sewage sludge compost when compared to un-amended control. A higher richness and evenness among the soil plots amended with sewage sludge compost was observed, with no significant differences among the application dose rates, when compared to the un-amended soil control and soil treated with a mineral fertilizer. A three-year amendment was able to separate soil plots amended with high doses of sewage sludge compost from the low dose amended and control samples. Among the microbial groups responsible for such marked separation, bacteria belonging to Actinobacteria, Acidobacteria, Cyanobacteria and Bacteroidetes contribute the most, with a shift from oligotrophic to copiotrophic taxa. Significant changes in bacterial composition and taxonomic structure should be considered in order to properly balance agronomic and economic advantages with environmental concerns. After all, our results have evidenced the effects of sewage sludge amendment on different soil properties, microbial activity, and composition already after a short period of application. The findings are particularly relevant in semiarid soils, where an immediate restoration of soil fertility by short-term compost application is needed.

Composted Sewage Sludge Influences the Microbiome and Persistence of Human Pathogens in Soil.

Composted sewage sludge (CSS) gained attention as a potential fertilizer in agriculture. Application of CSS increases soil microbial activity and microbial biomass, however, it can also lead to increased chemical and microbiological risks. In this study, we performed microcosm experiments to assess how CSS reshapes the microbial community of diluvial sand (DS) soil. Further, we assessed the potential of CSS to increase the persistence of human pathogens in DS soil and the colonization of Chinese cabbage (Brassica rapa L. subsp. pekinensis (Lour.) Hanelt). The results revealed that CSS substantially altered the prokaryotic community composition. Moreover, addition of CSS increased the persistence of Salmonella enterica serovar Typhimurium strain 14028s and S. enterica serovar Senftenberg in DS soil. However, the enhanced persistence in soil had no impact on the colonization rate of B. rapa grown on soil inoculated with Salmonella. We detected Salmonella in leaves of 1.9% to 3.6% of plants. Addition of CSS had no impact on the plant colonization rate. The use of sewage sludge composts is an interesting option. However, safety measures should be applied in order to avoid contamination of crop plants by human pathogens.

High yield of protein-rich forage rice achieved by soil amendment with composted sewage sludge and topdressing with treated wastewater

Aiming to promote low-cost production of protein-rich forage rice and resource recycling from wastewater treatment plants, a pot experiment was conducted to assess the possibility to substitute mineral fertilizers with composted sewage sludge (CSS) with/without top-dressing with treated municipal wastewater (TWW). Results indicated that a basal application of CSS at 2.6 g N pot−1 replaced conventional mineral fertilization of 1.3 g N pot−1 to produce comparable yields with the same rice protein content, although there might be a risk of increased As concentration in rice grains. Interestingly, CSS application at a reasonable dose of 1.3 g N pot−1, followed by a topdressing with TWW resulted in 27% higher yield and 25% superior rice protein content relative to the mineral fertilization, with no risk of heavy metal(loid) accumulation in grains and in paddy soils. Here we demonstrated an appealing fertilization practice with zero use of mineral fertilizers in paddy rice cultivation, expectedly contributing towards sustainable rice farming and animal husbandry in Japan.

Microelement Variability in Plants as an Effect of Sewage Sludge Compost Application Assessed by Different Statistical Methods

This research deals with the effects of soil amendment with sewage sludge compost (SSC) on the accumulation of microelements (Cu, Zn, Mn, Ni, Fe) in plants—white mustard (Sinapis alba), triticale (Triticale) and white lupine (Lupinus albus)—cultivated on two contrasting soils (light vs. medium agronomic class). Additionally, the influence of experimental factors on variability of the harvest index (HI) was determined for individual plants and micronutrients. A 3-year pot experiment was conducted and SSC at the rate of 6 t·ha−1 was applied into the soils. These changes were determined by ANOVA and subject to regression analysis and subsequently visualized. The study clearly demonstrated that SSC as an organic fertilizer had a significant, but weak effect on the microelements level variability in the shoots and grains of plants cultivated in crop rotation. Regardless of the experimental factors, on average, the plants accumulated higher amounts of Cu, Zn and Mn in the grains, and Fe and Ni in the shoots. Harvest index values confirmed the significance and variable translocation of microelements within plant organs. The influence of SSC on micronutrient contents in plant organs was more significant in the case of medium soil.

Effects of consecutive application of composted sewage sludge on active organic nitrogen fractions in the sandy fluvo-aquic soil.

A field experiment was conducted with sandy fluvo-aquic soil under wheat-maize rotation system during 2012 to 2016 in Henan Province, with four treatments: Chemical fertilizer (CK), composted sewage sludge (CS) 15 t·hm-2(CS1), 30 t·hm-2(CS2), 45 t·hm-2(CS3). We investigated the effects of CS on soil active organic nitrogen and its allocation ratio. Results showed that CS significantly enhanced soil water content, decreased soil pH, increased contents of soil organic carbon and total nitrogen (TN) and available nutrients. Soil TN was increased by 93.1%-284.3%. The CS3 treatment significantly improved the content of light fraction organic nitrogen (LFON), particulate organic nitrogen (PON) and microbial biomass nitrogen (MBN). CS treatments promoted the allocation of PON/TN and MBN/TN. with an enhancement of 12.3% and 539.9% in the CS2 treatment, respectively. The distributions of LFON/TN and DON/TN were decreased by 17.3%-40.1% and 38.5%-71.3%, respectively. The contribution of soil active organic nitrogen fractions to TN was: PON>LFON>DON>MBN. Results from the principal component analysis showed that organic nitrogen and their distribution had high load value in CS2 and CS3 treatments. Results from redundancy analysis showed that positive correlations existed between the soil physicochemistry, enzymatic activity and soil active organic nitrogen as well as their distribution. In summary, CS had positive impacts on soil organic matter, soil properties, and the formation of active organic nitrogen. The rates of 30 and 45 t·hm-2 CS application had significant effects on soil fertility, which could be an effective way to improve sandy fluvo-aquic soil quality.

Leaching characteristic of toxic trace elements in soils amended by sewage sludge compost: A comparison of field and laboratory investigations

A 3-years field test and laboratory leaching test have been conducted to assess the environmental impact of land application of sewage sludge compost in conjunction with wheat and rice crops. Considering the complexity and variability of field conditions, we compared the result of laboratory test with the field test to understand the accuracy and uncertainty associated with using the laboratory test to evaluate the field scenario. The laboratory test with cycling of compost additions and water percolation was a high time-efficient and feasible method to simulate the annually repeated additions of compost in the field application scenario. The results of laboratory test were congruent to the 3-years field test regarding the leaching characteristics and geochemical speciation of toxic trace elements. Both the laboratory and the field test showed that repeated additions of compost to soils can increase leaching concentrations of toxic trace elements at neutral to alkaline pH. Increased toxic trace elements leaching was caused by the increase of organic matter from compost application and organic matter dissolution at alkaline pH. Uncertainties of the laboratory test mainly included the negligibility of crop growth and the strongly reducing condition formed with continuous percolation procedure.

Municipal sewage sludge compost promotes Mangifera persiciforma tree growth with no risk of heavy metal contamination of soil

Application of sewage sludge compost (SSC) as a fertilizer on landscaping provides a potential way for the effective disposal of sludge. However, the response of landscape trees to SSC application and the impacts of heavy metals from SSC on soil are poorly understood. We conducted a pot experiment to investigate the effects of SSC addition on Mangifera persiciforma growth and quantified its uptake of heavy metals from SSC by setting five treatments with mass ratios of SSC to lateritic soil as 0%:100% (CK), 15%:85% (S15), 30%:70% (S30), 60%:40% (S60), and 100%:0% (S100). As expected, the fertility and heavy metal concentrations (Cu, Zn, Pb and Cd) in substrate significantly increased with SSC addition. The best performance in terms of plant height, ground diameter, biomass and N, P, K uptake were found in S30, implying a reasonable amount of SSC could benefit the growth of M. persiciforma. The concentrations of Cu, Pb and Cd in S30 were insignificantly different from CK after harvest, indicating that M. persiciforma reduced the risk of heavy metal contamination of soil arising from SSC application. This study suggests that a reasonable rate of SSC addition can enhance M. persiciforma growth without causing the contamination of landscaping soil by heavy metals.

Parâmetros biométricos de trigo na terceira aplicação de lodo de esgoto compostado e irrigação com água residuária

Os esgotos domésticos e lodos de esgoto, por conterem elevado teor de matéria orgânica e nutrientes, tornam-se uma alternativa promissora de uso na agricultura, principalmente quanto à substituição ou complementação dos fertilizantes agrícolas tradicionais que muitas vezes possuem custo elevado. Nesse sentido, objetivou-se com este estudo avaliar a resposta de plantas de trigo (Triticum aestivum) mediante a aplicação de lodo de esgoto compostado como adubo nitrogenado no solo sob a irrigação com água potável (AP) e residuária de esgoto tratado (AR). Utilizou-se o delineamento inteiramente casualizado, no esquema de parcelas subdivididas, com 10 repetições. Avaliaram-se sete níveis de adubação nitrogenada (subparcela) distribuídos em duas parcelas experimentais, representadas pela irrigação com AP e AR, sendo assim definidos: T1 = sem adubação nitrogenada no solo; T2 = 100% de adubação nitrogenada química; T3 = 50% de adubação nitrogenada química + 50% de adubação nitrogenada via lodo de esgoto compostado (LEC); T4, T5, T6 e T7 corresponderam à 100, 150, 200 e 250% de adubação nitrogenada via LEC, respectivamente. Os resultados indicam a possibilidade de substituição da adubação nitrogenada química, 80 kg ha-1 de N, pelo equivalente em LEC, sem prejuízos à cultura. Em solo não adubado com N, a irrigação com AR de esgoto tratado foi benéfica ao trigo, proporcionando incremento de 60% no número de grãos por planta.

Responses of absolute and specific enzyme activity to consecutive application of composted sewage sludge in a Fluventic Ustochrept.

Composted sewage sludge (CS) is considered a rich source of soil nutrients and significantly affects the physical, chemical, and biological characteristics of soil, but its effect on specific enzyme activity in soil is disregarded. The present experiment examined the absolute and specific enzyme activity of the enzymes involved in carbon, nitrogen, and phosphorus cycles, the diversity of soil microbial functions, and soil community composition in a Fluventic Ustochrept under a maize—wheat rotation system in North China during 2012–2015. Application of CS led to increase in MBC and in its ratio to both total organic carbon (TOC) and microbial biomass nitrogen (MBN). Absolute enzyme activity, except that of phosphatase, increased in CS-treated soils, whereas specific activity of all the enzymes declined, especially at the highest dose of CS (45 t ha−1). The diversity of soil microbial community also increased in CS-treated soils, whereas its functional diversity declined at higher doses of CS owing to the lowered specific enzyme activity. These changes indicate that CS application induced the domination of microorganisms that are not metabolically active and those that use resources more efficiently, namely fungi. Redundancy analysis showed that fundamental alterations in soil enzyme activity depend on soil pH. Soil specific enzyme activity is affected more than absolute enzyme activity by changes in soil properties, especially soil microbial activity and composition of soil microflora (as judged by the following ratios: MBC/TOC, MBC/MBN, and TOC/LOC, that is labile organic carbon) through the Pearson Correlation Coefficient. Specific enzyme activity is thus a more accurate parameter than absolute enzyme activity for monitoring the effect of adding CS on the activities and structure of soil microbial community.