Jorge Lugo

Erosion significantly decreases the depth of a soil, the nutrients available for plants, the organic matter and, consequently, the productivity of the edaphic environment. Due to the above considerations, the objective of this study was to evaluate, through various properties, the quality of two eroded soils, one eroded by water and the other by mining activity, amended with biosolids. The quality for both soils was estimated through the selection of a minimum set of data by means of principal component analysis (PCA) and the subsequent realization of correlations, multiple regressions and finally calculations of normalized values (Vn) of those properties considered as indicators of soil quality. According to the results, inorganic nitrogen (NI) and respiratory activity (RA) were the properties selected as indicators to assess quality. For soil eroded by water and by mining activity, NI presented a low and very low quality, respectively (class 4 and 5 of quality according to the calculation of Vn). The quality of RA in soil eroded by mining extraction was very high (quality class 1 according to Vn), and thus it can be considered an ideal indicator for the evaluation of soil quality due to its sensitivity to anthropogenic changes (mining) in soil.

Phosphate-solubilizing bacteria (PSB) transform precipitated inorganic phosphorus into soluble orthophosphates. This study evaluated the efficiency of tricalcium and iron phosphate solubilization in Pikovskaya medium using five bacterial strains (A1, A2, A3, A5, and A6) cultured in acidic and alkaline pH levels. The bacterial strain that proved to be more efficient for P solubilization and was tolerant to pH variations was selected for assessing bacterial growth and P solubilization with glucose and sucrose in the culture medium. The bacterial strains were identified through 16S rRNA gene sequencing as Pseudomonas libanensis A1, Pseudomonas libanensis (A2), Bacillus pumilus (A3), Pseudomonas libanensis (A5), and Bacillus siamensis (A6). These five bacterial strains grew, tolerated pH changes, and solubilized inorganic phosphorus. The bacterial strain A3 solubilized FePO₄ (4 mg L⁻¹) and Ca₃(PO₄)₂ (50 mg L⁻¹). P solubilization was assayed with glucose and sucrose as carbon sources for A3 (Bacillus pumilus MN100586). After four culture days, Ca₃(PO₄)₂ was solubilized, reaching 246 mg L⁻¹ with sucrose in culture media. Using glucose as a carbon source, FePO₄ was solubilized and reached 282 mg L⁻¹ in six culture days. Our findings were: Pseudomonas libanensis, and Bacillus siamensis, as new bacteria, can be reported as P solubilizers with tolerance to acidic or alkaline pH levels. The bacterial strain B. pumilus grew using two sources of inorganic phosphorus and carbon, and it tolerated pH changes. For that reason, it is an ideal candidate for inorganic phosphorus solubilization and future production as a biofertilizer.

Agriculture is in a constant state of change. Its new practices and technologies represent impacts that are difficult to predict. The transition from animal traction to tractors and the substitution of manure for synthetic fertilizers are changes that are taking place particularly in developed countries, yet they are increasing in developing ones. However, the effect of these changes on agriculture and soil CO₂ emissions remains controversial. The objective of this study was to measure the effects of two tillage systems and fertilization on the CO₂ emissions from the soil under maize cultivation. Therefore, it consisted of two tillage systems, namely tractor (T) and animal (A) traction, and four fertilization methods. The fertilization treatments tested were: (CH) application of N, P, K chemical fertilizer; (HM) application of horse manure; (CM) application of chicken manure; and (CT) unfertilized control. We found that the soil CO₂ emission rates in the maize growing season was higher than those in the tillage before the harvest season. Soil respiration peaked in June after the second fertilizer application (9394.59–12,851.35 mg CO₂ m⁻² h⁻¹ at tractor and 7091.89–12,655.86 mg CO₂ m⁻² h⁻¹ at animal traction). The production of corn grain only presented differences between the treatments with and without application of fertilizers.

We investigated changes in biochemical activity of a soil cultivated with Ocimum basilicum L. plants and in the oxidative stress of plants caused by the addition of biosolids and inorganic fertilizer. A greenhouse experiment was set up; it consisted of pots containing basil plants to which different treatments with biosolids and fertilizers were added. After 10 and 210 days of the incorporation of the treatments, both the biochemical properties and oxidative stress of the plants were evaluated. Mineralization of nitrogen (N) and respiratory activity increased with a higher dose of biosolid after 10 days of application. After 210 days, there were no changes in the mineralization of N and respiratory activity, catalase showed an increase, while microbial biomass carbon decreased. In relation to the oxidative stress, there was a decrease in the anthocyanin antioxidant capacity, and 2,2-diphenyl-1-picrylhydrazyl (DPPH), total flavonoids, and phenolic compounds were observed in soils treated with biosolids. The results indicated that the biochemical properties of the soil were favored in the presence of biosolids because they increased, especially after 10 days of application. The antioxidant capacity decreased in the presence of biosolids, which suggests that the amendment does not affect such capacity, and therefore oxidative stress could be reduced.

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

Mexico is the world's fourth most important maize producer; hence, there is a need to maintain soil quality for sustainable production in the upcoming years. Pumice mining is a superficial operation that modifies large areas in central Mexico. The main aim was to assess the present state of agricultural soils differing in elapsed time since pumice mining (0–15 years) in a representative area of the Calimaya region in the State of Mexico. The study sites in 0, 1, 4, 10, and 15 year old reclaimed soils were compared with an adjacent undisturbed site. Our results indicate that gravimetric moisture content, water hold capacity, bulk density, available phosphorus, total nitrogen, soil organic carbon, microbial biomass carbon and phosphatase and urease activity were greatly impacted by disturbance. A general trend of recovery towards the undisturbed condition with reclamation age was found after disturbance, the recovery of soil total N being faster than soil organic C. The soil quality indicators were selected using principal component analysis (PCA), correlations and multiple linear regressions. The first three components gathered explain 76.4 % of the total variability. The obtained results revealed that the most appropriate indicators to diagnose the quality of the soils were urease, available phosphorus and bulk density and minor total nitrogen. According to linear score analysis and the additive index, the soils showed a recuperation starting from 4 years of pumice extraction.

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.