Comparison of laboratory methodologies to determine soil nitrogen mineralization from organic residues

Recycling organic waste for use as fertilizer requires prior knowledge of mineral nitrogen (N) availability for crops. Estimation of soil N release or potentially mineralizable N is an important tool for the design of fertilization strategies that aim to minimize the use of N fertilizer. The aerobic incubation method is considered a standard technique to measure soil potential to mineralize N. In this study, alternative methods of aerobic incubation were evaluated to help overcome its limitations (long time and equipment). In this regard, biological methods (anaerobic incubation at 7 and 14 days) and chemical extraction (hot KCl) procedures were examined. To determine potentially mineralizable N, a silty clay loam soil was fertilized with spent mushroom substrates and anaerobic digestates from different origins (C/N ratio of 4 to 38). Based on the results, chemical extraction emerges as a reliable alternative to the aerobic incubation method, particularly when the C/N ratio of the organic residues ranges from 12 to 15. Moreover, its implementation in routine soil laboratories is straightforward and faster, and it does not require any special equipment.

PSVI-14 Effects of saturated fatty acids of 6 to 12 carbons in length on spoilage microbes, zoonotic pathogens and antimicrobial resistant bacteria in air exposed corn silage

Aerobic exposure of silage during the feed-out phase promotes growth of spoilage as well as pathogenic and multi-drug resistant (MDR) microbes which can risk infection of food-producing animals and the foods they produce. Livestock producers are interested in finding effective yet environmentally friendly interventions to preserve the nutritional value of these spoiled feedstuffs. We investigated the antimicrobial activity of 6 to 12 carbon-containing saturated fatty acids (C6, C8, C10 or C12) added (0.03 g) individually or as 1:1 mixtures of C6:C8:C10:C12 or C8:C10 to 4 g of overnight exposed silage suspended in 10 mL water. Net changes in colony counts, determined as the difference between counts measured after 0 and 24 h aerobic incubation (22oC) of untreated and treated silage suspensions (n = 3/treatment), were subjected to an analysis of variance. Populations of wild-type total aerobes and experimentally-inoculated MDR-Staphylococcus aureus were unaffected by treatment (P > 0.05), decreasing on average (± SD) 0.64 ± 0.40 and 1.09 ± 0.39 log10 CFU/g silage, respectively. Treatment effects (P < 0.05) were observed against experimentally-inoculated Listeria monocytogenes, with the C8:C10 mix decreasing this foodborne pathogen by 0.64 log10 CFU/g compared to a 0.95 log10/g increase in controls. Indigenous yeast and mold, considered responsible for spoilage, were decreased 2.12 and 3.07 log10 CFU/g by the C8 and C8:C10 treatments compared to 0.40 log10 CFU/g increase in controls. Indigenous lactic acid bacteria, considered beneficial, were decreased most potently by the C8 and C8:C10 treatments compared to controls (1.28, 0.66 and 0.37 log10 CFU/g, respectively). Indigenous enterococci decreased in all incubations, including controls (3.03 log10 CFU/g), compared to 4.69 to 5.03 log10 CFU/g decreases in C6, C8, C10, C12 and C8:C10 treatments. Results reveal that some fatty acid treatments inhibited pathogenic and spoilage microbes, yet treatment optimization is needed to avoid adverse effects against beneficial microbes.

PbS biomineralization using cysteine: Bacillus cereus and the sulfur rush

Bacillus sp. Abq, belonging to Bacillus cereus sensu lato, was isolated from an aquifer in New Mexico, USA and phylogenetically classified. The isolate possesses the unusual property of precipitating Pb(II) by using cysteine, which is degraded intracellularly to hydrogen sulfide (H2S). H2S is then exported to the extracellular environment to react with Pb(II), yielding PbS (galena). Biochemical and growth tests showed that other sulfur sources tested (sulfate, thiosulfate, and methionine) were not reduced to hydrogen sulfide. Using equimolar concentration of cysteine, 1 mM of soluble Pb(II) was removed from Lysogeny Broth (LB) medium within 120 h of aerobic incubation forming black, solid PbS, with a removal rate of 2.03 µg L−1 h−1 (∼8.7 µM L−1 h−1). The mineralogy of biogenic PbS was characterized and confirmed by XRD, HRTEM, and EDX. Electron microscopy and electron diffraction identified crystalline PbS nanoparticles with a diameter <10 nm, localized in the extracellular matrix and on the surface of the cells. This is the first study demonstrating the use of cysteine in Pb(II) precipitation as insoluble PbS and it may pave the way to PbS recovery from secondary resources, such as Pb-laden industrial effluents.

Characterization of dissolved organic matter extracted from water treatment sludge

The characteristics of dissolved organic matter (DOM) that formed during the aerobic and anaerobic incubation of drinking water treatment sludge stored at different temperatures (5 °C, 20 °C, 40 °C) for long periods (7, 14, and 21 days) were investigated. Anaerobic incubation at high temperatures with prolonged storage was found to result in higher organic content than aerobic incubation (3.6–6.8 times at 40 °C). The high temperatures caused changes in the DOM fractions, with humic-like substances mainly formed in aerobic incubation and protein-like substances in anaerobic incubation. Results showed that the fluorescence intensity of humic-like and protein-like substances increased by 45% and 22%, respectively, at the end of the anaerobic incubation period. The UV-absorbing DOM constituents in aerobic incubation had lower molecular weights and were more heterogeneous than those in anaerobic incubation.

How does measuring methodology impact N mineralization in controlled conditions and relations to soil biological parameters: air dried versus fresh soil

<p>Predictions of N mineralization are still difficult but maybe this is due to the methodologies. Many soil tests have been proposed to predict N mineralization between field and laboratory experiment. Incubations of soil in the laboratory under controlled environmental conditions are most commonly used to assess N mineralization rates both from SOM and from added organic materials. However, predicting N mineralization due to the methods (the impact of using air-dried and fresh soil) has never been assessed before. If the results differ between the methods commonly used, there is a serious problem. Therefore, the objective of this study was to evaluate the influence of the incubation methods (air-dried vs fresh soil) to predict N mineralization. The N mineralization potential from fifteen agricultural soils in West and East Flanders – Belgium, were determined by aerobic incubation methods used air-dried and fresh soil at (20 – 25<sup>0</sup>C) for 84-days in the laboratory. The results indicated that total mineral nitrogen (NH4<sup>+</sup> + NO3<sup>-</sup>) concentrations and carbon content of microbial biomass (MBC) did not differ significantly between these methods. Nitrogen was mineralized in fresh soil incubations (0.36 mg N. kg<sup>-1</sup> soil day <sup>-1</sup>) while in air-dried soil (0.31 mg N kg<sup>-1</sup> soil day <sup>-1</sup>). Thus, the results generate that it may be conceivable to predict N mineralization by these two methods in controlled conditions.</p>

¿La incorporación de residuos de diferentes especies de Lupinus, como abono verde, afecta la actividad microbiana del suelo?

In the state of Jalisco, corn and tequila agave are the most important agricultural crops. The soils to cultivate these species are characterized by low content of organic matter and nitrogen. The amendments applied to the soil provide an important source of energy and nutrients for microorganisms; promotes the diversity of nitrogen-f ixing bacteria and nitrifying bacteria, which increases nitrogen availability in the soil. The aim of this study was to evaluate the use of two species of wild legumes: Lupinus exaltatus and Lupinus rotundiflorus as green manure (AV), and its effect on soil microbial biomass. An aerobic incubation experiment (14 days) was carried out on soil samples with green manure and without green manure (control). Under laboratory conditions, the microbial activity of soil was monitored through the response in basal respiration and the concentration of C and N in the microbial biomass. The CO2 production and C and N content in the microbial biomass showed significant differences (P < 0.05) due to the effect of green manure. The residues of Lupinus are considered better quality than the residues of Zea mays due to its nitrogen content and low C: N ratio. The response of microorganisms presented a positive primer effect with the input of AV. Therefore, we conclude that the input of L. exaltatus and L. rotundiflorus as a green manure to the soil increases the biological activity of the soil and promotes the enrichment of C and N of the microbial biomass.

Evaluation of Enzymes Production Activity of Trichoderma, Aspergillus and Rhizopus Species in Paraeforce (Herbicide) Degradation

The study aims to evaluate enzymes that facilitate fungal degradation of paraeforce. Soil samples for fungal isolation were collected from impacted sites and inoculated on potato dextrose agar (PDA). The isolates were screened for growth and tolerance to paraefoce in 50 mg/l concentration of the test herbicides. Trichoderma, Aspergillus and Rhizopus species were found to grow in paraeforce supplemented PDA. Qualitative and quantitative assay for different enzyme production in hydrogen peroxide, methyl red, guaiacol and hydrogen peroxide-pyrogallol complex proved potential for catalase, lignin peroxidase, laccase and manganese peroxidase production, respectively. The results showed that these three fungi have great potential for catalase, peroxidase and laccase production after six days aerobic incubation in paraeforce and these enzymes facilitated the utilization of the paraeforce.

PSV-41 Antibacterial activity of ferulic acid and sodium chlorate against Escherichia coli F18 and K88 during incubations with porcine fecal bacteria

The influence of ferulic acid (FA) and sodium chlorate (SC) was evaluated in two trials on the growth of Escherichia coli F18 and K88 (F18 and K88) incubated with porcine fecal bacteria. Treatments were 2 levels of FA (0 and 5 mg/mL) and 2 levels of SC (0 and 10 mM/mL). In trial one, ½-strength Mueller Hinton broth mixed with porcine feces (0.5% w/v) was inoculated with a novobiocin and naladixic acid resistant F18-strain. This fecal suspension was transferred to tubes (3/treatment) and anaerobically incubated at 39 oC for enumeration at 0, 6 and 24 h using MacConkey agar supplemented with novobiocin and naladixic acid with aerobic incubation at 37 oC. An interaction (FA x SC) at 6 and 24 h was observed (P &lt; 0.01). At 6 h of incubation, SC alone or combined with FA had the lowest counts (P &lt; 0.05); FA alone was lower than control but higher than SC or SC+FA (P &lt; 0.05). At 24 h, FA alone or combined with SC had the lowest counts (P &lt; 0.05); SC was lower than control but higher than FA or SC+FA (P &lt; 0.05). In trial 2 were used the same procedures of trial 1, except that K88 was used. There was an interaction at 6 h (P &lt; 0.01) where the lowest counts were in FA+SC (P &lt; 0.05). SC alone or FA alone were lower than control but higher than SC+FA (P &lt; 0.05). There was no interaction at 24 h (P = 0.16), where FA reduced the K88 counts (P &lt; 0.01), however it was not affected by SC (P = 0.12). In conclusion, SC reduced E. coli counts; however, at 24 h of incubation greater reductions were observed when FA alone or combined with SC was added into the incubation fluid with porcine feces.