Μg NH4 Research Articles

Effect of Natural, Organic and Inorganic Farming Methods on Microorganisms and Enzymes Activity of Maize Rhizosphere

Continuous use of fertilizers decreasing the biological activity of the soil. Fertile soils teem with microorganisms, which directly contribute to the biological fertility of the soil. Microorganisms are responsible for the availability of nutrients to the plants which are already exist in the soil. Hence, the present study focused on to investigate the effect of natural farming on soil microorganisms and enzymes activity of maize rhizospherein comparison with inorganic and organic farming during the autumn season of 2016-17 at Agricultural College, Jagtial. The results of the investigation revealed that the population of microbes (bacteria and fungi) at 30, 60 Days After Sowing (DAS) and harvest was unaffected by variety (Aswini) or hybrid (DHM 117). But, among the different farming methods, organic farming recorded higher bacterial (19, 29 and 22.5 x 10-7 CFU{Colony Forming Unit} g-1 dry soil) and fungi (8.25, 14.67 and 10.25 x 10-5 CFU g-1 dry soil) population at 30, 60 DAS and harvest stage respectively and significantly superior to inorganic and natural methods. The microbial population in inorganic method was inferior to that in absolute control similar to microbial population, highest urease activity was recorded in organic method at 30, 60 DAS and harvest (52.92, 68.33 and 33.25 µg NH4+ g-1 2 h-1, respectively) and it was superior to inorganic and natural farming which were at a par with each other. Significantly higher activity of dehydrogenase was observed with organic farming at 30, 60 DAS and harvest (1.65, 2.29 and 1.72 µg TPF g-1 day-1) compared to natural farming and inorganic farming. The activity of urease and dehydrogenase remained similar with DHM 117 or Aswini.

Soil microbial properties influenced with long term application of manures and fertilizers

An ongoing long-term field experiment established in 1995 at CCS Haryana Agricultural University, Hisar (India) under pearl millet-wheat cropping system was selected to examine the impact of organic manures and fertilizers on soil microbiological properties. After 19 years of experiment, the samples were collected after wheat harvest in April, 2014. Under different combinations of treatments, the microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) content in soil ranged from 202–491 and 35.0–79.8 mg/kg, respectively. The lower content of MBC and MBN was observed in farmyard manure (FYM) treated plots as compared to pressmud or poultry manure. Soil microbial quotient (SMQ) ranged from 3.18– 5.61% and higher SMQ was observed with pressmud and poultry manure application as compared to FYM application. The highest dehydrogenase activity (DHA) was reported with FYM15 (63.71 μgTPF/g/24 hr) which was statistically at par with FYM15N150 (59.75 μg TPF/g/24 h) and pressmud7.5 (58.14 μg TPF/g/24 h). Among organic manures applied alone alkaline phosphatase activity (APA) followed the order: poultry manure>FYM>pressmud. The highest urease activity (97.6 μg NH4 +-N/g/h) was observed with pressmud7.5 and this may be attributed to higher N content (3.23%) in pressmud. The dehydrogenase and urease activity decreased in the plots where organic manures were applied in conjunction with NP fertilizers as compared to solitary application of organic manures. However, reverse trend was observed in case of alkaline phosphatase. Overall, pressmud applications exhibited favorable impacts on soil properties under pearl millet wheat cropping. Therefore, continuous application of pressmud could lead to long term maintenance of soil microbial properties in these sandy loam soils.

Effect on soil biological properties as influenced by different nutrient management approaches under pigeonpea cultivation in Vertisol

A study was conducted to know the effect of different nutrient management approaches along with FYM on soil biological properties in pigeonpea cultivation during 2016-17 and 2017-18 in farmer’s field of Raichur district. The experiment was laid out in Randomized Block Design with three replications and ten treatments. The results revealed that, application of 150% RDF approach with FYM at 90 DAS and at harvest stage of pigeonpea significantly increased the beneficial microbial load of bacteria (37.08 and 22.47 X 107 cfu g-1), fungi (37.08 and 22.47 X 107 cfu g-1) and actinomycetes (16.07 and 9.63 X 104 cfu g-1), microbial biomass (277 and 261 µg CO2-C g-1 soil for 24 hrs) and enzyme activities of dehydrogenase (21.09 and 15.73 μg TPF g-1 soil for 24 hrs), phosphatase (69.37 and 66.8 μg PNP g-1 soil for 1 hr) and urease (170 and 161 μg NH4- N g-1 soil for 2 hrs) in soil, respectively.

C and N cycle under beech and hornbeam tree species in the Iranian old-growth forests

Beech and hornbeam are two of the most common species in old-growth temperate forests. However, how these two species affect soil carbon (C), soil nitrogen (N) and soil microbial and enzymatic activities is still not well understood. Thus, the aim of the present study was to quantify the effects of beech and hornbeam on soil chemical, biochemical and biological features at Makarod forest, Northern Iran, by sampling either forest floor or mineral soil (30 × 30 × 15 cm) under individual trees of both species. Based on our data, hornbeam showed higher concentrations of N, phosphorous (P), potassium (K), calcium (Ca) and magnesium (Mg), but lower total thickness, C and C: N ratio in the forest floor. Top mineral soil under hornbeam had alkaline condition (pH > 7), higher electrical conductivity (EC), total N, N in micro- and macro-aggregates, N sequestration, available P, K, Ca, Mg, humic acid, fine root biomass, total earthworm (i.e. epigeic, anecic and endogeic) density and biomass, total nematode, acarina and protozoa densities. Hornbeam trees increased soil basal respiration and substrate induced respiration (0.50 and 1.47 mg CO2 g−1) compared to beech. The two studied species did not show any significant difference in soil microbial biomass C, metabolic quotient, microbial ratio, C availability index, particulate organic C and dissolved organic C, whereas, higher values of soil microbial biomass N, particulate organic N and dissolved organic N (66.97 mg kg−1, 0.52 g kg−1 and 38.53 mg kg−1, respectively) were again found under hornbeam. Except for arylsulfatase, all the other soil enzyme activities (i.e. urease, acid phosphatase and invertase) were almost two-fold higher under hornbeam (24.55 μg NH4+–Ng−1 2 h−1, 498.30 μg PNP g−1h−1 and 296.2 μg Glucose g−1 3 h−1, respectively). As well, higher values of ammonification rate were measured under hornbeam (0.38 mg kg−1 d−1), whereas beech significantly increased the nitrification rate (−0.16 mg kg−1 d−1). Net N mineralization rate was about three-fold higher under hornbeam (0.14 mg kg−1 d−1) than under beech. Our results indicate that differences in functional traits between beech and hornbeam caused changes in microbial community and in its activity, underlying a higher forest floor quality, higher soil fertility and more active microbial populations under the latter.

Ammonia emissions and dry deposition in the vicinity of dairy farms

We conducted the first research in the Czech Republic to measure ventilation and ammonia (NH 3 ) emission rates in a naturally ventilated animal building (dairy farm) during a five-day measurement period in June, combined with a three-month (May-July) monitoring of NH 3 concentration and dry deposition at 12 locations along horizontal gradients from the dairy farm up to the distance of 400 m. Passive diffusion-tube samplers were used to measure monthly NH 3 concentrations. Moisture (H 2 O) balance was used to determine ventilation rates of the dairy farm. Continuous measurements of gas concentrations (NH 3 ), temperature and relative humidity inside and outside the building were performed. The air exchange rate was 4.8 h –1 and the emission rate was 43.2 NH 3 g cow –1 d –1 for building. The emission rate was 126% of what was obtained using emission factors from the Czech national inventory (34.2 g cow –1 d –1 ). NH 3 concentrations and dry deposition fluxes decreased exponentially with distance from the dairy farm. Between May and July, mean predicted dry deposition fluxes ranged from 0.28 to 0.03 µg NH 3 m –2 s –1 at a distance of 50 and 400 m from the source, respectively. Dry NH 3 deposition over the nearest 400 m from the source accounted for 11.5% of daily emissions. The results confirm the short-range dispersion of NH 3 emitted from a point source found in other studies, but it may not be the same in other situations, since dispersion of NH 3 is dependent on the surrounding land-cover and on the number of animals in a barn.

Seasonal variation induced stability of municipal solid waste compost: an enzyme kinetics study

An investigation was carried out in laboratory to find out the effect of ambient temperature and different treatments on passive bin composting of municipal solid waste (MSW). A potent cellulase degrading inoculum (Bacillus subtilis, B. amyloliquefaciens, B. nakamurai and B. velezensis) sourced from dumpsite soil and cow dung slurry was used as addon to MSW composters. Treatments were tested during summer (26–45 °C) and winter (5–22 °C) season to profile the physio-chemical, enzymatic and microbial changes during 90-day study. In addition, a kinetics model for MSW composting was derived for the rate of organic load degradation deducing the first order kinetics rate (Kr), limiting velocity (Km) and dissociation constant (Kd). The results of the present investigation revealed that ambient temperature hastened the degradation of organic substrates in case of MSW amended with microbes and cow dung (60 days) as indicated by the achieved maximum kinetics reaction rate, 0.0131 day−1 (R2 = 0.993) and reduced C/N ratio (11.6%). Also, enzymatic profiles; dehydrogenase (170.1 µg TPF g−1 day−1), cellulase (96.1 µg glucose g dwt−1 h−1) and urease (539.1 μg NH4+–Ng dwt−1 h−1) with a high temperature profile (47–63 °C) in the finished summer compost, Cs4 supported the results. Whereas, winter composting could not attain the desired results and produced immature compost even after 90 days. Statistical analysis (proximal cluster analysis, hierarchical cluster analysis and ANOVA) and kinetics study showed that ambient temperature in collaboration with addons significantly influenced the compost maturity.

Effect of body size on the energetic physiology of the West Indian top shell Cittarium pica (Linnaeus, 1758)

Cittarium pica is an endangered Caribbean gastropod of ecological and economic importance. In order to provide the basis for the aquaculture development and/or population management of this species, the relationships among its body size and physiological variables associated with the energetic balance were assessed. Individual measurements of rates of egestion (ER), ingestion (IR), absorption (AR), oxygen consumption (OCR), ammonia excretion (UR), mucus production (MR), absorption efficiency (AE) and scope for growth (SFG), were carried out on specimens between 0.01 and 12.07 g of dry weight of the soft parts (DW) under controlled laboratory conditions. Most of the variables showed positive potential relationships with the DW of the animals (ER mg h -1 = 1.51 DW 0.37 , IR mg h -1 = 4.13 DW 0.32 , AR = 2.56 DW 0.30 , OCR mL O 2 h -1 = 0.38 DW 0.74 , UR μg NH 4 -N h -1 = 19.17 DW 0.78 , MR mg h -1 = 1.28 DW 0.14 and SFG = 36.92 DW 0.22 ). AE did not show any relationship with this variable. The large snails had faster input and output of energy compared to the small specimens, also having proportionally greater energetic expenditures, mucus production, and energetic balance.

Ammonium Transformation in 14 Lakes along a Trophic Gradient

Ammonia is a widespread pollutant in aquatic ecosystems originating directly and indirectly from human activities, which can strongly affect the structure and functioning of the aquatic foodweb. The biological oxidation of NH4+ to nitrite, and then nitrate is a key part of the complex nitrogen cycle and a fundamental process in aquatic environments, having a profound influence on ecosystem stability and functionality. Environmental studies have shown that our current knowledge of physical and chemical factors that control this process and the abundance and function of involved microorganisms are not entirely understood. In this paper, the efficiency and the transformation velocity of ammonium into oxidised compounds in 14 south-alpine lakes in northern Italy, with a similar origin, but different trophic levels, are compared with lab-scale experimentations (20 °C, dark, oxygen saturation) that are performed in artificial microcosms (4 L). The water samples were collected in different months to highlight the possible effect of seasonality on the development of the ammonium oxidation process. In four-liter microcosms, concentrations were increased by 1 mg/L NH4+ and the process of ammonium oxidation was constantly monitored. The time elapsed for the decrease of 25% and 95% of the initial ion ammonium concentration and the rate for that ammonium oxidation were evaluated. Principal Component Analysis and General Linear Model, performed on 56 observations and several chemical and physical parameters, highlighted the important roles of total phosphorus and nitrogen concentrations on the commencement of the oxidation process. Meanwhile, the natural concentration of ammonium influenced the rate of nitrification (µg NH4+/L day). Seasonality did not seem to significantly affect the ammonium transformation. The results highlight the different vulnerabilities of lakes with different trophic statuses.

Impact of management practices on soil microbial properties under wheat-cluster bean cropping system

A study of organic, integrated and inorganic plant nutrient management systems was conducted to determine the effect of management practices on soil microbiological properties after 10 years of continuous application. The rate of C mineralization and potentially mineralizable nitrogen were 6.8 and 41.5 mg/kg soil, respectively. Arginine ammonification and nitrification activities were 0.88 µg NH4+- N/g soil/h and 56.0 µg NO3--N/g/day, respectively. Microbial biomass C, N and P were 320, 40 and 12 mg/kg soil, respectively. Alkaline phosphatase, urease and cellulase activities were highest with application of VC@15t /ha.

Effect of moisture content on biophysical characteristics of chickpea cultivars

A study of organic, integrated and inorganic plant nutrient management systems was conducted to determine the effect of management practices on soil microbiological properties after 10 years of continuous application. The rate of C mineralization and potentially mineralizable nitrogen were 6.8 and 41.5 mg/kg soil, respectively. Arginine ammonification and nitrification activities were 0.88 µg NH4+- N/g soil/h and 56.0 µg NO3--N/g/day, respectively. Microbial biomass C, N and P were 320, 40 and 12 mg/kg soil, respectively. Alkaline phosphatase, urease and cellulase activities were highest with application of VC@15t /ha.

Contrasting response of two grassland soils to N addition and moisture levels: N2O emission and functional gene abundance

Nitrification and denitrification processes dominate nitrous oxide (N2O) emission in grassland ecosystems, but their relative contribution as well as the abiotic factors are still not well understood. Two grassland soils from Duolun in Inner Mongolia, China, and Canterbury in New Zealand were used to quantitatively compare N2O production and the abundance of bacterial and archaeal amoA, denitrifying nirK and nirS genes in response to N additions (0 and 100 μg NH4 +–N g−1 dry soil) and two soil moisture levels (40 and 80 % water holding capacity) using microcosms. Soil moisture rather than N availability significantly increased the nitrification rate in the Duolun soil but not in the Canterbury soil. Moreover, N addition promoted denitrification enzyme activities in the Canterbury soil but not in the Duolun soil. The abundance of bacterial and archaeal amoA genes significantly increased as soil moisture increased in the Duolun soil, whereas in the Canterbury soil, only the abundance of bacterial amoA gene increased. The increase in N2O flux induced by N addition was significantly greater in the Duolun soil than in the Canterbury soil, suggesting that nitrification may have a dominant role in N2O emission for the Duolun soil, while denitrification for the Canterbury soil. Microbial processes controlling N2O emission differed in grassland soils, thus providing important baseline data in terms of global change.

Influence of Inorganic Fertilizers and Organic Amendments on Plant Nutrients and Soil Enzyme Activities under Incubation

An incubation experiment was carried out in the department of Soil Science and Agricultural Chemistry, ANGRAU, Hyderabad, India during 2013−14 with 12 treatments including control to study the mineralization pattern and timely release of nutrients (N, P, K and soil enzymes) to plant from different sources and periods. Mineralization of nitrogen (NH4+-N and NO3−-N), phosphorus (P2O5) potassium (K2O) and soil enzymes (urease, acid and alkaline phosphatase and dehydrogenase) activities from different treatments were evaluated. During initial period 7 to 21 days after incubation (DAI), the recommended dose of fertilizer (RDF) had maximum release of NH4+-N and NO3−-N and later on decreased in the succeeding days but manures combination treatment has taken lead to release the N from 1 DAI to 70 DAI than control. Similar trends were followed in available P2O5 and K2O. The maximum quantity of urease and DHA were reached 203 to 227 μg NH4+-N g−1 soil h−1 and 10.6 to12.4 μg TPF g−1 soil h−1 from combination of poultry manure and neem cake at 70 DAI, respectively. Maximum released of acid and alkaline phosphatase were observed in 21 DAI and 35 DAI in RDF respectively. Among the manures treatment, PM+NC had superior in releasing of alkaline phosphatase over other, followed by poultry manure and FYM+PM. Correlation study between nutrients (N, P and K) and enzymes activity showed that a significant (p<0.05) positive relationship with each others.

The chemical quality of frozen Vietnamese Pangasius hypophthalmus fillets.

The aim of the present study was to evaluate the chemical quality parameters regarding frozen Pangasius hypophthalmus specimens from Vietnam. The proximate composition, pH, ammonia, biogenic amines (BAs), total mercury (Hg), malondialdehyde (MDA), and polyphosphate were determined. The moisture, protein, lipid and ash values were between 83.83–85.59, 12.51–14.52, 1.09–1.65, and 0.76–2.38 g 100 g−1, respectively. Fraud by excessive polyphosphate addition was detected in 30% of the samples whereas Hg above the recommended limit was observed in 50% of the samples. With regard to compounds from the degradation process, low concentrations of individual BAs and pH values were found in this study and ranged from 5.88 to 6.18, except for samples with polyphosphate >1 g 100−1 (pH > 7.00) were observed in the present study. However, ammonia concentration indicated that a degradation process initiated in 80% of the samples (0.12–0.34 NH 3 g−1) and 20% of the samples (1.87–1.94 μg NH 3 g−1) were in an advanced deterioration process. Furthermore, MDA values (1.21–7.88 mg kg−1) suggested some failures, mainly during transportation and/or storage. We concluded that quality control measures must be implemented on the Pangasius production chain to improve the quality of products provided to consumers worldwide.

Dynamics of microbiological parameters, enzymatic activities and worm biomass production during vermicomposting of effluent treatment plant sludge of bakery industry.

This paper reports the changes in microbial parameters and enzymatic activities during vermicomposting of effluent treatment plant sludge (ETPS) of bakery industry spiked with cow dung (CD) by Eisenia fetida. Six vermibins containing different ratios of ETPS and CD were maintained under controlled laboratory conditions for 15 weeks. Total bacterial and total fungal count increased upto 7th week and declined afterward in all the bins. Maximum bacterial and fungal count was 31.6 CFU × 10(6) g(-1) and 31 CFU × 10(4) g(-1) in 7th week. Maximum dehydrogenase activity was 1921 μg TPF g(-1) h(-1) in 9th week in 100 % CD containing vermibin, whereas maximum urease activity was 1208 μg NH4 (-)N g(-1) h(-1) in 3rd week in 100 % CD containing vermibin. The enzyme activity and microbial counts were lesser in ETPS containing vermibins than control (100 % CD). The growth and fecundity of the worms in different vermibins were also investigated. The results showed that initially biomass and fecundity of the worms increased but decreased at the later stages due to non-availability of the palatable feed. This showed that quality and palatability of food directly affect biological parameters of the system.

Microbial abundance and community structure in a melting alpine snowpack.

Snowmelt is a crucial period for alpine soil ecosystems, as it is related to inputs of nutrients, particulate matter and microorganisms to the underlying soil. Although snow-inhabiting microbial communities represent an important inoculum for soils, they have thus far received little attention. The distribution and structure of these microorganisms in the snowpack may be linked to the physical properties of the snowpack at snowmelt. Snow samples were taken from snow profiles at four sites (1930-2519 m a.s.l.) in the catchment of the Tiefengletscher, Canton Uri, Switzerland. Microbial (Archaea, Bacteria and Fungi) communities were investigated through T-RFLP profiling of the 16S and 18S rRNA genes, respectively. In parallel, we assessed physical and chemical parameters relevant to the understanding of melting processes. Along the snow profiles, density increased with depth due to compaction, while other physico-chemical parameters, such as temperature and concentrations of DOC and soluble ions, remained in the same range (e.g. <2 mg DOC L(-1), 5-30 μg NH4 (+)-N L(-1)) in all samples at all sites. Along the snow profiles, no major change was observed either in cell abundance or in bacterial and fungal diversity. No Archaea could be detected in the snow. Microbial communities, however, differed significantly between sites. Our results show that meltwater rearranges soluble ions and microbial communities in the snowpack.

Impact of biodynamic preparations andpanchgavyain organically managed cropping systems comprising legumes on soil biological health

Biological health of soil was assessed to understand the effect of varingly managed organic cropping systems under field conditions. Twelve treatment combinations comprised two cropping systems (CS1-Basmati rice-Chickpea-Sesbania green manure;CS2 -Basmati rice-Vegetable pea-Maize (green cob & Fodder) + Green gram (residues incorporation) and six organic nutrient manangement practices- T1: Farmyard manure + Vermicompost + Enriched Compost + Neem Cake, T2: Biodynamic Preparations, T3: Farmyard manure + Vermicompost + Enriched Compost + Neem Cake + Panchgavya, T4: Farmyard manure + Vermicompost + Enriched Compost + Neem Cake + Biodynamic Preparations, T5: Farmyard manure + Vermicompost + Enriched Compost + Neem Cake + Biodynamic Preparations + Panchgavya, T6: Control. The highest activity of different soil enzymes viz., dehydrogenase, acid, alkaline and total phosphatase; and aryl sulfatase was assessed to the tune of 1311.02 μg Tri Phenyl Formazan 24h−1g−1 soil at flowering in ‘spring’, 26.99 μg p-nitrophenol h−1g−1 soil, 35.19 μg p-nitrophenol h−1g−1 soil, 62.18 μg p-nitrophenol h−1g−1 soil and 77.75 μg p-nitrophenol h−1 g−1 soil at harvest of ‘rabi’ crop, respectively receiving the organic nutrient package through T5. Significantly enhanced microbial population and their biomass facilitating the enhanced mineralization of nitrogen to the tune of 150.10 μg NH4+-N g−1 soil with nutrient management practices employed through T5 was observed.

Parent material and vegetation influence soil microbial community structure following 30-years of rock weathering and pedogenesis.

The process of pedogenesis and the development of biological communities during primary succession begin on recently exposed mineral surfaces. Following 30 years of surface exposure of reclaimed surface mining sites (Appalachian Mountains, USA), it was hypothesized that microbial communities would differ between sandstone and siltstone parent materials and to a lesser extent between vegetation types. Microbial community composition was examined by targeting bacterial and archaeal (16S ribosomal RNA (rRNA)) and fungal (internal transcribed spacer (ITS)) genes and analyzed using Illumina sequencing. Microbial community composition significantly differed between parent materials and between plots established with tall fescue grass or pitch x loblolly pine vegetation types, suggesting that both factors are important in shaping community assembly during early pedogenesis. At the phylum level, Acidobacteria and Proteobacteria differed in relative abundance between sandstone and siltstone. The amount of the heavy fraction carbon (C) was significantly different between sandstone (2.0 mg g(-1)) and siltstone (5.2 mg g(-1)) and correlated with microbial community composition. Soil nitrogen (N) cycling was examined by determining gene copy numbers of ureC, archaeal amoA, and bacterial amoA. Gene quantities tended to be higher in siltstone compared to sandstone but did not differ by vegetation type. This was consistent with differences in extractable ammonium (NH4 (+)) concentrations between sandstone and siltstone (16.4 vs 8.5 μg NH4 (+)-N g(-1) soil), suggesting that nitrification rates may be higher in siltstone. Parent material and early vegetation are important determinants of early microbial community assembly and could be drivers for the trajectory of ecosystem development over longer time scales.

Effect of 7-year application of a nitrification inhibitor, dicyandiamide (DCD), on soil microbial biomass, protease and deaminase activities, and the abundance of bacteria and archaea in pasture soils

The nitrification inhibitor dicyandiamide (DCD) has been shown to be highly effective in reducing nitrate (NO3 −) leaching and nitrous oxide (N2O) emissions when used to treat grazed pasture soils. However, there have been few studies on the possible effects of long-term DCD use on other soil enzyme activities or the abundance of the general soil microbial communities. The objective of this study was to determine possible effects of long-term DCD use on key soil enzyme activities involved in the nitrogen (N) cycle and the abundance of bacteria and archaea in grazed pasture soils. Three field sites used for this study had been treated with DCD for 7 years in field plot experiments. The three pasture soils from three different regions across New Zealand were Pukemutu silt loam in Southland in the southern South Island, Horotiu silt loam in the Waikato in the central North Island and Templeton silt loam in Canterbury in the central South Island. Control and DCD-treated plots were sampled to analyse soil pH, microbial biomass C and N, protease and deaminase activity, and the abundance of bacteria and archaea. The three soils varied significantly in the microbial biomass C (858 to 542 μg C g−1 soil) and biomass N (63 to 28 μg N g−1), protease (361 to 694 μg tyrosine g−1 soil h−1) and deaminase (4.3 to 5.6 μg NH4 + g−1 soil h−1) activity, and bacteria (bacterial 16S rRNA gene copy number: 1.64 × 109 to 2.77 × 109 g−1 soil) and archaea (archaeal 16S rRNA gene copy number: 2.67 × 107 to 3.01 × 108 g−1 soil) abundance. However, 7 years of DCD use did not significantly affect these microbial population abundance and enzymatic activities. Soil pH values were also not significantly affected by the long-term DCD use. These results support the hypothesis that DCD is a specific enzyme inhibitor for ammonia oxidation and does not affect other non-target microbial and enzyme activities. The DCD nitrification inhibitor technology, therefore, appears to be an effective mitigation technology for nitrate leaching and nitrous oxide emissions in grazed pasture soils with no adverse impacts on the abundance of bacteria and archaea and key enzyme activities.

Positive effect of shredders on microbial biomass and decomposition in stream microcosms

Summary1. Animals play a major role in nutrient cycling via excretory processes. Although the positive indirect effects of grazers on periphytic algae are well understood, little is known about top‐down effects on decomposers of shredders living on leaf litter.2. Nutrient cycling by shredders in oligotrophic forest streams may be important for the microbial‐detritus compartment at very small spatial scales (i.e. within the leaf packs in which shredders feed). We hypothesised that insect excretion may cause local nutrient enrichment, so that microorganism growth on leaves is stimulated.3. We first tested the effect of increasing concentration of ammonium (+10, +20 and +40 μg NH4+ L−1) on fungal and bacterial biomass on leaf litter in a laboratory experiment. Then we performed two experiments to test the effect of the presence and feeding activity of shredder larvae. We used two species belonging to the trichopteran family Sericostomatidae: the Palaearctic Sericostoma vittatum and the Neotropical Myothrichia murina, to test the effect of these shredders on fungal and bacterial biomass and decomposition on leaves of Quercus robur and Nothofagus pumilio, respectively. All experiments were run in water with low ammonium concentrations (2.4 ± 0.34 to 14.47 ± 0.95 μg NH4+ L−1).4. After 5 days of incubation, NH4 concentrations were reduced to near‐ambient streamwater concentrations in all treatments with leaves. Fungal biomass was positively affected by increased ammonium concentration. On the other hand, bacteria abundance was similar in all treatments, both in terms of abundance (bacteria cells mg−1 leaf DW) and biomass. However, there was a tendency towards larger mean cell size in treatments with 20 μg NH4 L−1.5. In the experiment with S. vittatum, fungal biomass in the treatment with insects was more than twice that in the control after 15 days. Bacteria were not detected in treatments with insects, where hyphae were abundant, but they were abundant in treatments without larvae. In the decomposition experiment run with M. murina, leaf‐mass loss was significantly higher in treatments with larvae than in controls.6. Our hypothesis of a positive effect of shredders on fungal biomass and decomposition was demonstrated. Insect excretion caused ammonium concentration to increase in the microcosms, contributing to microbial N uptake in leaf substrata, which resulted in structural and functional changes in community attributes. The positive effect of detritivores on microbes has been mostly neglected in stream nutrient‐cycling models; our findings suggest that this phenomenon may be of greater importance than expected in stream nutrient budgets.

Short-term effects of ammonium nitrogen in upland pasture soil affected or not affected by cattle

The short-term effects of excessive NH 4 + -N on selected characteristics of soil unaffected (low annual N inputs) and affected (high annual N inputs) by cattle were investigated under laboratory conditions. The major hypothesis tested was that above a theoretical upper limit of NH 4 + concentration, an excess of NH 4 + -N does not further increase NO 3 − formation rate in the soil, but only supports accumulation of NO 2 − -N and gaseous losses of N as N2O. Soils were amended with 10 to 500 μg NH 4 + -N g−1 soil. In both soils, addition of NH 4 + -N increased production of NO 3 − -N until some limit. This limit was higher in cattle-affected soil than in unaffected soil. Production of N2O increased in the whole range of amendments in both soils. At the highest level of NH 4 + -N addition, NO 2 − -N accumulated in cattle-affected soil while NO 3 − -N production decreased in cattle-unaffected soil. Despite being statistically significant, observed effects of high NH 4 + -N addition were relatively weak. Uptake of mineral N, stimulated by glucose amendment, decreased the mineral N content in both soils, but it also greatly increased production of N2O.