Effects of fertilization with urban and agricultural organic wastes in a field trial – Waste imprint on soil microbial activity

In the past decades a significant change in composition of urban organic waste products has occurred in many first world countries, due to cleaner technologies as well as outsourcing of heavy industries. However, the societal perception of organic urban waste has become increasingly negative, leading to widespread advocacy of incineration. Therefore we established the ‘CRUCIAL’ long-term field trial in 2003, with the rationale that by approaching the known limits for a number of heavy metals below which no profound disturbance should be observed on key soil ecological functions, it should be possible to discern if some of the many unknown components in the composite urban waste as well as agriculturally based fertilizers have measurable impacts. The following treatments were established: human urine, sewage sludge (normal N-level and accelerated level aiming at three times normal N-level), degassed and subsequently composted organic municipal waste (normal and accelerated level), deep litter, cattle slurry, cattle manure (accelerated level), NPK fertilizer, unfertilized but with clover undersown and an unfertilized control. After 4 years the soil organic matter (SOM) C content, basal CO₂ respiration and soil microbial biomass (SMB) C was significantly affected by treatments. All soils having received organic fertilizer had higher SMB C than those with no added fertilizer (unfertilized and unfertilized with clover undersown) and inorganic fertilizer. The treatment effect on qCO2 (CO₂/SMB C) was not significant, but the unfertilized treatments showed the highest values. Treatments with accelerated levels of composted household waste and sewage sludge had the highest number of colony forming heterotrophic bacteria. Sole carbon source utilization in EcoPlates indicated a very robust microbial community in the treatments. Cumulative input of heavy metals was less than that required for reaching the heavy metal ecotoxicological limits, even after accelerated loading with sewage sludge corresponding to approximately 55 years of normal application. This could indicate that it is possible use organic urban waste for an extended period on a given site, without compromising soil functioning as long as ecotoxicological guidelines for heavy metal content are observed.     

Effect of herbicide used with years (8 + 1) on soil enzymic activity and microbial population diversity

Purpose

Soil microbes play important roles in plant nutrition and soil conservation, and the diversity and population of soil microbe are influenced by abiotic and biotic factors associated with different soil managements. However, the information concerning soil microbe diversity and population structure and its relation with soil fertility and enzyme activities are scarce in crop rotation under different soil management system.

Materials and methods

This paper reports the effects of three weeding managements (herbicide (2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl) acetomide, C1₄H₂₀ClNO₂), manual weeding, and no weeding (CK)), on soil microbial diversity, population structure, and its relationship with soil active organic matter (AOM) and pH, and the activity of soil enzymes like sucrase, catalase, and urease activities from long-term test area in red soil upland field in southeast China, which was set up since 2006. Soil samples at 0–20-cm depths were collected before (8 years) and after (8 + 1 years) weeding management in April 2014.

Results and discussion

Soil enzymes (sucrase, catalase, and urease activity) and soil microbial populations had no significant difference (P > 0.05) under the three weeding treatments. Based on richness of microbial population up to 0.10%, the phyla Proteobacteria and Actinobacteria highly dominated the three soil treatments, averagely accounting for 21.76 and 21.44%. Chloroflexi was the next phylum, about accounting for 6.84%. Firmicutes, Verrucomicrobia, and Planctomycetes phylum accounted for 4.98, 4.78, and 4.23%, respectively. The percentage of Gemmatimonadetes was 2.76%, and that of Bacteroidetes was about 1.45%. Armatimonade and Nitrospira were the lowest, with 0.69 and 0.26%, respectively. Among the 20 phyla, only 5 had significant correlation with some of the soil properties. Twenty-one in 46 classes had significant correlation with some of the soil properties. Armatimonadetes and Fusobacteria had positive correlation with moisture. Acidobacteria_Gp3, Deltaproteobacteria, Chthonomonadetes, Armatimonadetes_gp4, and Euryarchaeota also were positively correlated with moisture. Negative correlation between Armatimonadetes, Chloroflexi, Chthonomonadetes, and Armatimonadetes_gp5 and AOM exists, and Armatimonadetes, Chthonomonadetes, Clostridia, Armatimonadetes, and pH were negatively correlated. Fusobacteria was positively correlated with catalase. Acidobacteria_Gp10 and Armatimonadia were positively correlated with catalase. Chthonomonadetes, Clostridia, and Armatimonadetes_gp5 were correlated with urease. Gammaproteobacteria and Flavobacteria were correlated with sucrase.

Conclusions

For long-term herbicide experiment conducted on the Dongxiang upland site, no significant effect of herbicide on soil microbial community composition and enzyme activities was found. Further work is needed to relate microbial community structure and function in different herbicide systems or season sampling, even to detect herbicide effect on community structure during the growing season.

     

Responses of soil microbial biomass and activity for practices of organic and conventional farming systems in Piauí state,Brazil

The aim of this work was to investigate the response of soil microbial biomass and activity to practices in organic and conventional farming systems. The study was carried out at the Irrigation District of Piauí, Brazil. Five different plots planted with “acerola” orchard (Malpighia glaba) and established at the following management were evaluated: (1) under 12 months of soil conventional management (CNV); (2) under six months of soil organic management (ORG6); (3) under 12 months of soil organic management (ORG12); (4) under 18 months of soil organic management (ORG18); and (5) under 24 months of soil organic management (ORG24). Soil microbial biomass C (C_mic), basal respiration, organic carbon (C_org), C_mic-to-C_org ratio and metabolic quotient (qCO₂) were evaluated in soil samples collected at 0–10 cm depth. The highest C_org and C_mic levels occurred in organic system plots ORG18 and ORG24 compared to the conventional system. Soil respiration and C_mic-to-C_org ratio were significantly enhanced by the organic system plots. The qCO₂ was greater in conventional than in organic system. These results indicate that the organic practices rapidly improved soil microbial characteristics and slowly increase soil organic C.     

Method for 14C‐labeling maize field plots and assessment of label uniformity within plots

Abstract

There is increasing interest in use of isotopic tracers to study nutrient liberation and transformation in plant tissues and soils. We developed a technique for pulse‐labeling plants in the field with ¹⁴C. Spatial distribution of radioactivity was measured in plots of maize (Zea mays L.) plants exposed to ¹⁴CO₂. Two clear polyvinyl chambers measuring 1 m wide × 2 m long × 1 m high were used to ¹⁴C‐ label maize plants in conventional tillage and no‐tillage treatments. A closed loop in‐line with a pump allowed injection of ¹⁴CO₂ and unlabeled CO₂, and subsampling through an infrared gas analyzer. Cooling and mixing of the air within the chambers was achieved through the use of a free‐standing automobile radiator with fan placed in the center of each plot. The specific activities of leaf tips differed by an order of magnitude among maize plants within the plot. Tillage and time after labeling within the first 48 h had no significant effect on specific activity of maize plants. Plant activity significantly differed by row. The row closest to the inlet and along the edge of the chamber was significantly lower in several plots. Despite differences among leaf tip specific activities, total aboveground activity was uniform within the plot. Plant allometry and plant sampling immediately after labeling would help in correcting for within chamber variability in future field labeling studies.     

Carbon uptake by a microbial community during 30-day treatment with 13C-glucose of a sandy loam soil fertilized for 20 years with NPK or compost as determined by a GC–C–IRMS analysis of phospholipid fatty acids

To investigate the uptake by the microbial community of easily decomposable exogenous organic C and the proportion of this organic C remaining in soils under long-term fertilization schemes, ¹³C-glucose was supplied to arable soils (aquic inceptisol) following a 20-year (1989–2009) application of compost (CM) or inorganic NPK (NPK), along with a control (no fertilizer). Phospholipid fatty acids (PLFAs) were used as biomarkers for actinobacteria, bacteria and fungi. Gas chromatography–combustion–stable isotope ratio mass spectrometry (GC–C–IRMS) was used to determine the incorporation of ¹³C into individual PLFAs. The concentrations of soil microbial PLFAs significantly (P < 0.05) increased in all three soils after the addition of ¹³C-glucose. Over a 30-day incubation period, the highest PLFA concentrations were on day 7 (control) or day 15 (NPK and CM) for bacteria, and on day 30 for both fungi and actinobacteria. The added ¹³C-glucose was incorporated into bacterial PLFAs first, whilst an increase of ¹³C in fungal and actinobacterial PLFAs was measured on day 7 and 15, respectively. The mean amounts of ¹³C in bacterial, actinobacterial and fungal PLFAs in CM-treated soil during the 30-day incubation period were 0.589, 0.030 and 0.056 μg g⁻¹ soil, respectively, which were significantly (P < 0.05) higher than levels measured in the NPK and control soils. Among the bacterial groups, the amount of ¹³C in Gram-positive (G⁺) bacteria over the entire incubation ranged from 0.326 to 0.440 μg g⁻¹ soil in the CM scheme, which was significantly (P < 0.05) higher than levels detected in the NPK and control regimes. In contrast, ¹³C concentrations in monounsaturated PLFAs (aerobic microorganisms) in the CM-treated soil were 0.030–0.045 μg g⁻¹ soil, which was significantly (P < 0.05) lower than in the NPK schemes. The proportion of glucose-derived ¹³C remaining in soils was ranked as follows: CM (53%) > NPK (41%) > control (28%) after 30 days of incubation. Easily decomposable exogenous organic C was thus more effectively maintained under the CM regime, primarily because, after 20 years, CM had altered the microbial community by reducing the ratio of aerobic to anaerobic microorganisms whilst increasing levels of G⁺ bacteria in soil compared to the control and NPK soils. This study aids our understanding of the transformation and maintenance of easily decomposable organic C in soil over long-term fertilization regimes.     

Pore-scale view of microbial turnover: Combining 14C imaging, μCT and zymography after adding soluble carbon to soil pores of specific sizes

The location of microorganisms and substrates within soil pore networks plays a crucial role in organic carbon (C) processing, and its microbial utilization and turnover, and has direct consequences for C and nutrient cycling. An optimal approach to quantify responses to new C inputs from microorganisms residing in specific pores is the addition of new C to pores of target sizes in undisturbed soil cores. We used the matric potential approach to add ¹⁴C-labelled glucose to small (< 40 μm, root free) or large (60–180 μm, potentially inhabited by roots) pores of undisturbed soil cores. Localization of glucose-derived C via ¹⁴C imaging was related to pore size distributions and connectivity, characterized via X-ray computed microtomography (μCT), and to β-glucosidase activity, characterized via zymography. After 2-week incubations, 1.3 times more glucose was mineralized (¹⁴CO₂) when it was added to the large pores; however, more ¹⁴C remained in microbial biomass when glucose was added to the small pores. Consequently, although utilizing the same amounts of easily available C, the microorganisms localized in the large pores had faster turnover compared to microorganisms in small pores. Stronger associations between β-glucosidase activity and glucose-derived C were observed when glucose was added to the large pores. We conclude that (a) the matric potential approach allows placing, albeit not exactly, of soluble substrates into pores of target diameter range, and (b) microorganisms localized in large pores respond to new C inputs with faster turnover, greater growth and more intensive enzyme production compared to those inhabiting the small pores.     

Ecological studies of root-nodule bacteria introduced into field environments—6. Antigenic and symbiotic stability in Lotononis rhizobia over a 12-year period

Rhizobia suited to Lotononis bainesii do not occur naturally in Australia. Two serologically distinct strains of African origin were introduced into an isolated field station where perennial Lotononis-pangola grass pastures are grazed. Paddocks varied in the period of rhizobial occupancy from 5–12 years. Stability of four rhizobial characters: colony colour, effectiveness, cell antigens and antibiotic sensitivity were assessed from nodules on persisting Lotononis. Both strains became established throughout the 782 ha. No changes were observed in colony colour or serological reaction. Symbiotically, 8.5% of isolates had a lower N fixing capacity than stock cultures held in the laboratory although there were no ineffective isolates. Change in effectiveness was unrelated to serotype or to time of occupancy. There was also little change in antibiotic sensitivity although one isolate was tolerant to 15 parts/10⁶ streptomycin. The red bacterium Protaminobacter rubra was recorded for the first time as a cohabitant of Lotononis nodules. It is concluded that colony colour, serological and symbiotic properties are sufficiently stable to be of use in long-term ecological studies although antibiotic sensitivity appears less stable.     

Effects of fertilization with urban and agricultural organic wastes in a field trial – Prokaryotic diversity investigated by pyrosequencing

The impact of different fertilizer treatments on prokaryotic diversity in a Danish urban waste field trial was investigated using tag-encoded amplicon pyrosequencing. The field trial was established in 2003 to investigate the application of urban organic waste as fertilizer in agriculture and to identify the effects on soil quality. The fertilizers (e.g. composted organic household waste, sewage sludge and human urine) contain a large amount of nutrients but possibly also undesirable toxic compounds that may influence the bacterial flora in the soil. A 561 bp fragment of the 16S rRNA gene flanking the V4, V5 and V6 regions, was amplified from each soil sample, tagged and sequenced using pyrosequencing. The major classified bacterial phyla and proteobacterial classes for all treatments were Actinobacteria, Acidobacteria and Betaproteobacteria, while the Crenarchaeota was the most frequent phylum of Archaea. No major changes in the community composition due to different fertilizer treatments were found, demonstrating a high robustness of the soil microbiota. However, some differences were observed e.g. Cyanobacteria were most frequent in the unfertilized soil, in comparison to the soils treated with nitrogen containing fertilizers and Firmicutes had higher occurrence in the soil with the composted household waste compared to all other treatments. Additionally, we used quantitative PCR (qPCR) to quantify specific bacterial groups, and used these numbers to convert the relative abundances of all bacteria obtained by pyrosequencing, to the actual numbers present in one gram of soil. All treatments resulted in a total number of bacteria between 1.99 × 10⁹ and 4.11 × 10⁹ gram⁻¹ soil.     

Variation of soil microbial biomass C and hydrolytic enzyme activities in a rangeland ecosystem: are slope aspect and position effective?

This study was conducted to investigate the effects of slope aspect and position on microbial biomass C (MBC) and some hydrolytic enzyme activities involved in soil N, P, and S cycles in a rangeland ecosystem of west central Iran. Soil samples were collected from three slope positions (summit, backslope, and footslope) of contiguous north- and south-facing slopes. Results indicated higher silt and clay content, soil organic C (SOC), total N (TN), and C/N ratio on the north-facing slope. Furthermore, MBC, alkaline phosphomonoesterase (ALP), acid phosphomonoesterase (ACP), arylsulfatase (ARS), urease (URS), L-asparaginase (LAS), and L-glutaminase (LGL) activities were greater by 46.1, 65.9, 58.6, 59.6, 52.6, 62.8, and 65.7%, respectively, on the north-facing slope compared to the south-facing one. Higher ratios of enzyme activities to MBC were observed on the north-facing slope. In contrast, per cent of inorganic N and microbial quotient were greater on the south-facing slope. The activity of ALP, ACP, ARS along with SOC, TN, and MBC values decreased from summit to footslope. Overall, our findings indicate that north-facing slope and summit position support greater microbial biomass and hydrolytic diversity.     

Effects of fine bubble aeration at the sediment‒water interface on distributions of organic phosphorus fractions and related microbial activity in a heavily urban river

Journal of Soils and Sediments - Effects of aeration on distribution and release potential of organic phosphorus in sediments are of great significance. The aim of this study was to investigate...     

Microbial activity,organic C accumulation and <Superscript>13</Superscript>C abundance in soils under alley cropping systems after 9 years of recultivation of quaternary deposits

The impact of alley cropping on post-lignite mine soils developing from quaternary deposits after 9 years of recultivation was evaluated on the basis of microbial indicators, organic C and total N contents, and the isotope characteristics of soil C. Soils were sampled at the 0 to 3, 3 to 10, and 10 to 30 cm depths under black locust (Robinia pseudoacacia L.), poplar (Populus spp.), the transition zone and in the middle of alley under rye (Secale cereale). There was no significant effect of vegetation on microbial properties presumably, due to the high variability, whereas organic C and total N contents at the 0- to 3-cm layer were significantly higher under black locust and poplar than in the transition zone and rye field. Organic C total N contents, and basal respiration, microbial biomass, and microbial quotient decreased with soil depth. Soil organic C and total N contents were more than doubled after 9 years of recultivation, with annual C and N accretion rate of 162 g C _org m⁻² year⁻¹ and 6 g N _t m⁻² year⁻¹. Microbial properties indicated that the soils are in early stages of development; the C isotope characteristics confirmed that the sequestered C was predominantly from C3 plants of the alley cropping.     

Application of a quantum cascade laser-based spectrometer in a closed chamber system for real-time δC and δO measurements of soil-respired CO2

Laser spectroscopy is an emerging technique to analyze the stable isotopic composition of soil-respired CO₂ (δ¹³C_resp, δ¹⁸O_resp) in situ and at high temporal resolution. Here we present the first application of a quantum cascade laser-based spectrometer (QCLS) in a closed soil-chamber system to determine simultaneously δ¹³C_resp and δ¹⁸O_resp. In a Swiss beech forest, a total of 90 chamber measurements with 20 min sampling time each were performed. The instrument measured the δ¹³C and δ¹⁸O of the CO₂ in the chamber headspace at every second with a precision of 0.25‰, resulting in Keeling plots with 1200 data points. In addition, we calculated δ¹³C_resp directly from the flux ratio of ¹³CO₂ and ¹²CO₂. The flux-ratio values were 0.8‰ lower than the Keeling plot intercepts when the flux rates were derived from quadratic curve fits of the CO₂ increase. The δ¹⁸O-Keeling plots showed a significant bending very likely due to the equilibration of chamber CO₂ with the ¹⁸O of surface soil water. Therefore, we used a quadratic curve fit of the Keeling plots to estimate δ¹⁸O_resp. Our results also revealed that δ¹³C_resp was not constant throughout the CO₂ accumulation in the closed soil chambers: there were significant but non-systematic variations in δ¹³C_resp for the first 10 min, and systematic shifts in δ¹³C_resp of on average 1.9 ‰ in the second part of the 20-min measurements. These biases were probably caused by non-steady-state conditions in the soil-chamber system. Our study illustrates that the high temporal resolution of QCLS measurements allows the detection of non-linearities in the isotopic effluxes of CO₂ from the soil due to soil-chamber feedbacks. This information can be used to improve the estimates for δ¹³C_resp and δ¹⁸O_resp.     

Evaluation of biochar applications combined with alternate wetting and drying (AWD) water management in rice field as a methane mitigation option for farmers’ adoption

ABSTRACT

Biochar application and alternate wetting and drying (AWD) are emerging as promising technologies recommended for reducing CH₄ emissions and water consumption in rice cultivation. In this study, we hypothesized that both technologies could be practiced in combination and this could further reduce CH₄ emissions and water consumption when compared to practicing alone. The effects of biochar application and its co-application with chemical fertilizer or compost under conventional or AWD water management on CH₄ emissions, productivity of rice, water use, and SOC stock, as well as cost and income were investigated. The experiment was carried out in an irrigated paddy field in the central plain of Thailand during both in the wet and dry seasons. Relative to control (CT), biochar application (BI), its co-application with compost (BC) or chemical fertilizer (BF) reduced seasonal CH₄ emissions by 40.6%, 29.5%, and 12.3%, respectively. BI and BC significantly (p < 0.05) reduced grain yield by 19.9% and 10.8%, respectively, while BF significantly increased grain yield by 3.70%. In addition, BI, BC, and BF significantly enhanced soil organic carbon (SOC) stock by 21.2%, 21.4%, and 18.3%, respectively. Compared to the CT, higher production costs were found in BC and BF, but the farmer’s net incomes were also higher in BF because of its higher grain yield. On the other hand, water management in all amendment treatments under AWD was resulted in the reduction of CH₄ emissions by the average of 18.8% as compared to the conventional system. AWD decreased rice yield by an average of 2.29%. It significantly reduced irrigation water use by an average of 11.9%, resulting in reducing production cost for water pumping. The results show that the practice that combined biochar application, AWD and chemical fertilizer are feasible for CH₄ emission mitigation, SOC stock increase and irrigation water saving without significant effects on yield and farmer income.     

Introduced earthworm species exhibited unique patterns of seasonal activity and vertical distribution,and <Emphasis Type="Italic">Lumbricus terrestris</Emphasis> burrows remained usable for at least 7 years in hardwood and pine stands

It is difficult to obtain non-destructive information on the seasonal dynamics of earthworms in northern forest soils. To overcome this, we used a Rhizotron facility to compile 7 years of data on the activity of anecic (Lumbricus terrestris) and endogeic (Aporrectodea caliginosa complex) earthworms in two contrasting soil/plant community types. We hypothesized that L. terrestris burrows would be used for longer than a typical L. terrestris lifetime, and that the distribution and activity pattern of the two earthworm species would respond differently to changes in soil moisture and temperature. For 7 years we recorded earthworm distribution and activity state bi-weekly to a depth of 1.5 m, tracked L. terrestris burrows using images captured annually, and measured soil temperature and moisture. Activity and vertical distribution of earthworms was closely linked to earthworm species and soil temperature in the fall, winter and spring. Lumbricus terrestris typically remained active through the winter, whereas the A. caliginosa complex was more likely to enter an aestivation period. Activity of all earthworms decreased substantially in July and August when soil temperature was at its highest and soil moisture at its lowest for the year. Most L. terrestris burrows were used continuously and moved very little during the 7-year study, likely creating spatiotemporally stable hotspots of soil resources. The different patterns of response of these species to soil temperature and moisture suggests that endogeic earthworms are more likely than anecic earthworms to adjust activity states in response to climate change mediated shifts in soil moisture and temperature.     

Effects of a ‘one film for 2 years’ system on the grain yield,water use efficiency and cost-benefit balance in dryland spring maize (Zea mays L.) on the Loess Plateau,China

‘One film for 2 years’ (PM2) has been proposed as a practice to control the residual film pollution; however, its effects on grain-yield, water-use-efficiency and cost-benefit balance in dryland spring maize production have still not been systematically explored. In this study, we compared the performance of PM2 with the annual film replacement treatment (PM1) and no mulch treatment (CK) on the Loess Plateau in 2015–2016. Our results indicated the following: (1) PM2 was effective at improving the topsoil moisture (0–20 cm) at sowing time and at seedling stage, but there was no significant influence on soil water storage, seasonal average soil moisture or evapotranspiration; (2) PM2 induced significantly higher cumulative soil temperatures compared to CK, and there was no significant difference between PM2 and PM1; (3) no significant differences were identified in grain-yield and water-use-efficiency between PM1 and PM2, and compared to CK, they improved by 16.3% and 15.5%, respectively; (4) because of lower cost of plastic film, tillage, film laying and remove in PM2, economic profits improved by 21% and 70% compared to PM1 and CK. This research suggested that PM2 was effective at alleviating the spring drought and was beneficial in reducing poverty traps in dryland.