Rocio Vaca

Microbiological and biochemical properties of an agricultural Mexican soil amended with sewage sludge

The application of sewage sludge is a concern because it may affect the quality of organic matter and microbiological and biochemical soil properties. The effects of surface application of sewage sludge to an agricultural soil (at 18 and 36 t ha-1 dry basis) were assessed in one maize (Zea mays L.) growing season. The study evaluated microbial biomass, basal respiration and selected enzymatic activities (catalase, urease, acid and alkaline phosphatase, and β-glucosidase) 230 days after sewage sludge application and infrared spectroscopy was used to assess the quality of dissolved organic matter and humic acids. Sewage sludge applications increased the band intensity assigned to polysaccharides, carboxylic acids, amides and lignin groups in the soil. The organic matter from the sewage sludge had a significant influence on the soil microbial biomass; nevertheless, at the end of the experiment the equilibrium of the soil microbial biomass (defined as microbial metabolic quotient, qCO2) was recovered. Soil urease, acid and alkaline phosphatase activity were strongly influenced by sewage sludge applications.

Soil Organic Matter Quality and Zinc and Lead Sorption as Affected by a Sewage Sludge Or a Sewage Sludge Compost Application

Sewage sludge (SS) or sewage sludge compost (SSC) were applied to soil under controlled conditions, at rates of 0 or 200 Mg ha−1, to investigate changes in dissolved organic matter (DOM), humic acids (HA), and Pb and Zn sorption in the soil. Infrared spectroscopy, visible spectrophotometry, and sorption isotherms (mono-metal and competitive sorption systems) methods were used to assess the changer. The E4/E6 ratio (λ at 465 / λ at 665 nm) and the infrared spectra of DOM and HA showed aromatic behaviour in compost-soil (SSC-S); in contrast sewage sludge-soil (SS-S) showed an aliphatic behaviour. Application of either SS or SSC increased the Pb and Zn sorption capacity of soil. The Pb and Zn sorption increased in soil and soil mixtures with a competitive metal system. The metal affinity sequence for soil, SS-S, and SSC-S was compared with the predicted affinity sequences obtained from metal properties. Poor correspondence was observed between the metal affinity sequence and the metal affinity sequence predicted by ionic potential, indicating that metals bonding to soils were not predominantly electrostatic. An affinity sequence based on Pearsons theory agreed with the metal affinity sequences for soils. A statistical analysis showed that the bands assigned to esters (1080 cm−1) of DOM, phenolic OH (1420 cm−1), amide I (1650 cm−1), carboxyl and carbonyl C=O stretches of different nature, C=O stretch of aromatic esters, aliphatic cetone, aldehyde (1720 cm−1), ethers and esters (1230 cm−1), aliphatic alcohols (1125 cm−1), and lignin (1380 cm−1) of HA were correlated with Zn constants of Langmuir adsorption isotherm (P < 0.05).

Bactericidal effect of silver nanoparticles against the propagation of Clavibacter michiganensis infection in Lycopersicon esculentum Mill

This study explored the use of silver nanoparticle as a bactericidal against the propagation of Clavibacter michiganensis onto tomatoes (Lycopersicon esculentum Mill). In Mexico, tomato production covers about 73% of the total vegetable production but it is affected by outbreak of bacteria canker caused by Clavibacter michiganensis subspecies michiganensis (Cmm). Silver ions possess inhibitor properties, bactericides and high specter antimicrobials. In this study, 6 groups of culture were prepared using 6 different petri dishes where silver nanoparticles of varying concentrations (120, 84, 48, 24, 12 and 0 μg) were added. Furthermore, each group was observed for 20 min, 1, 2, 12 and 24 h. The optimum concentration is 84 μg, which shows an average of 2 Cmm colonies after 20 min. Further increase to 120 μg shows no significant change. However, the average colonies was observed for 48 μg after 1, 2, 12, and 24 h. The obtained results indicate that silver nanoparticles are a promising inhibitor, bactericide and high a specter antimicrobial for treatment or prevention of Cmm.

ABONO ORGÁNICO ELABORADO CON LODO RESIDUAL Y ESTIERCOL EQUINO A TRAVÉS DE VERMICOMPOSTEO: UNA PROPUESTA COMO MEJORADOR DE SUELOS

Human activities produce tons of organic solid waste causing problems to the environment, polluting soil, water and groundwater. In view of this, strategies such as vermicomposting —a process of organic solid waste stabilization— has been developed. This study aims to use the process of vermicomposting to test mixtures of sewage sludge and horse manure in different percentages in order to know its stability and to propose it as a soil improver. Four percentages for processing equine manure and sewage sludge were used: E 100 , E 85 -LR 15 , E 70 -LR 30 and E 55 -LR 45 , followed by a 90 day-period under greenhouse conditions. The product showed gradual decrease in the percentage of organic C, C: N ratio and pH. It increased in the total content of N after 30 days and electric conductivity after 75 days. The P increased in E 70 -LR 30 (57.3 ± 8.3 mg/kg a 1369.8 ± 114.8 mg/kg) towards the end. After a 45 days of vermicomposting, the stability in the C:N ratio, E 100 (11.4); E 85 -LR 15 (10.8); E 70 -LR 30 (12.6) y E 55 -LR 45 (11.2) was reached. The best relationship is E70-LR30, as it presents a balance in the supply of N and C and the concentration of heavy metals decreased for Cu, Zn, Ni and Cd. Furthermore, the pH (7.24 ± 0.1) was neutral, the P concentration increased significantly and the number of worms was higher (1790) in comparison to other treatments. Thus, this relationship is suitable as organic fertilizer.

EFECTOS DEL LODO RESIDUAL Y RESIDUOS ORGANICOS VERMICOPOSTEADOS SOBRE INDICADORES INORGÁNICOS Y CATALASA

En este trabajo se evaluaron indicadores inorganicos y actividad enzimatica de tres mezclas de vermicomposta hechas con estiercol bovino (EB), residuos domesticos (RD), lodo residual (LR) y suelo (Cambisol), para conocer su madurez. Los tratamientos fueron mezclas de estiercol de vaca y residuo domestico a una relacion 1:1 (T1), 3:1 (T2) y 100 % de estiercol de vaca (T3); ademas, a todos los tratamientos se les agregaron el equivalente a 40 Mg/ha de LR. Los analisis de laboratorio se hicieron siguiendo las NOM-004 (2002) y 021 (2000) de SEMARNAT. Los resultados antes de hacer el vermicomposteo para RD, EB y LR indican que los metales pesados no rebasaron la norma NOM-004 (2002). La relacion C/N fue apropiada y va de acuerdo con lo reportado por Yang et al. (2014). Para los tratamientos, la humedad fue adecuada (menor a 72 %) y el pH presento un comportamiento ligeramente alcalino (7.93). El Corg para T2 y T3 presentaron mayor contenido (12.88 y 12.84 %) respectivamente, con respecto a T1 (8.90 %). El N total vario de 0.73 a 1.03 % siendo el mayor valor para T1. La relacion C/N senala la estabilizacion de los tratamientos de acuerdo a la norma NMX-FF-109-SCFI (2007) siendo para T3 y T2 de 14.14 y 17.48 respectivamente y T1 de 8.78. La catalasa estuvo entre 0.61±0.15 a 0.81± 0.015 μmol H 2 O 2 g –1 h –1 donde la mayor actividad se mostro en T3, con estos datos, se concluye que T1 se considera la mejor opcion para uso agronomico.