Teresa Hernández

Potential use of dehydrogenase activity as an index of microbial activity in degraded soils

Abstract Soils from many portions of the Mediterranean region are subjected to progressive degradation as a result of erosion by wind and water. As a consequence, the fertility level of these degraded soils is declining. This report studied the dehydrogenase activity of 18 soils, all of which were subjected to processes of erosion, in order to ascertain whether such activity could serve as a marker of the microbial activity of a degraded soil. The dehydrogenase activity of the soils studied was not correlated with their organic matter content, indicating that total organic matter was not representative of the microbial activity of degraded soil. An analysis of principal components showed a similar behavior between other indices of microbial activity (basal respiration and biomass carbon) and the dehydrogenase activity values. This data confirmed that dehydrogenase activity can be used as a sensitive marker of soil degradation and soil microbial activity.

Microbial activity in soils under mediterranean environmental conditions

Thirty-six soils from twelve different arid zones from SE Spain under Mediterranean environmental conditions were characterized by a range of measurements indicative of soil microbiological activity. Our aim was to relate the degradation undergone by these soils with their microbiological and enzymatic characteristics. In general, the soils studied had a low microbiological activity. These soils showed similar values of pH and low total organic-C (TOC) and available nutrient content. The behaviour of dehydrogenase activity was similar to that of CO2 emission and biomass-C, with values ranging from 4 to 148 μg iodo-nitrotetrazolium formazan g−1 of soil. A positive correlation was found between the above indices which, in turn, were negatively correlated with the metabolic quotient values. No correlation was found between these measurements and physical variables such as clay content, pH and WHC of the soils. However, there was a negative correlation with electrical conductivity. The values of urease, protease which hydrolyses N-α-benzoil-l-argininamide, protease which hydrolyses casein, phosphatase and β-glucosidase were, in general, low. There was a positive correlation between the hydrolases of the soils studied. A positive correlation was also found between hydrolases and measurements such as CO2 emission, biomass-C, biomass-C-to-TOC ratio and dehydrogenase.

Changes in the microbial activity of an arid soil amended with urban organic wastes

Abstract Changes produced in the biological characteristics of an arid soil by the addition of various urban wastes (municipal solid waste, sewage sludge and compost) at different doses, were evaluated during a 360-day incubation experiment. The addition of organic materials to the soil increased the values of biomass carbon, basal respiration, biomass C/total organic C ratio and metabolic quotient (qCO2), indicating the activation of soil microorganisms. These biological parameters showed a decreasing tendency with time. Nevertheless, their values in amended soils were higher than in control soil, which clearly indicates the improvement of soil biological quality brought about by the organic amendment. This favorable effect on soil biological activity was more noticeable with the addition of fresh wastes (municipal solid waste or sewage sludge) than with compost. In turn, this effect was more permanent when the soil was amended with municipal solid waste than when it was amended with sewage sludge.

Short-term effect of wildfire on the chemical, biochemical and microbiological properties of Mediterranean pine forest soils

Abstract The short-term effects of wildfire on the characteristics of Mediterranean pine forest soils, exposed to semiarid climatic conditions, were evaluated by measuring different chemical, biochemical and microbiological parameters 9 months after the fire. Soils in which the fire had been intense showed higher electrical conductivity values than unburnt soils. All burnt soils had higher contents of nitrates, exchangeable NH4+ and available P and K while their contents of total organic C, extractable C, humic acids, water-soluble C and total and water-soluble carbohydrates were, in general, lower than those of unburnt soils. Microbial biomass-C in burnt soils represented from 50% to 79% of that of unburnt soils; basal respiration and dehydrogenase activity were also negatively affected by fire. In general, fire decreased urease and N-α-benzoyl-l-argininamide hydrolysing protease activities. Alkaline phosphatase activity in burnt soils was 29–87% that of the respective unburnt control soil. Arylsulphatase activity was also lower in burnt soils as was β-glucosidase activity, although in this case the differences from values of unburnt soils were not always statistically significant.

Effects of a cadmium-contaminated sewage sludge compost on dynamics of organic matter and microbial activity in an arid soil

Abstract An incubation experiment lasting 120 days was carried out to ascertain the effect on the soil microbial activity and organic matter mineralization of adding a sewage sludge compost contaminated with two different levels of Cd to an arid soil. Two composts, with a low (2 mg kg–1) and high (815 mg kg–1) Cd content, respectively, were used in this experiment. Both composts increased the total organic C, humic substance and water-soluble C contents, the beneficial effects still being noticeable after 120 days of incubation. The most labile C fraction (water-soluble C) was the most sensitive to the high Cd content. The high Cd concentration decreased soil microbial biomass C and stimulated the metabolic activity of the microbial biomass, the metabolic quotient (qCO2) revealing itself to be a very sensitive index of the stress that the incorporation of a Cd-contaminated sewage sludge compost causes in a soil. The effect of Cd contamination on enzyme activities (urease, protease that hydrolyse N-α-benzoil-l-arginamide, phosphatase, and β-glucosidase) depended on the enzyme studied.

Enzymatic activities in an arid soil amended with urban organic wastes : Laboratory experiment

This work studied the changes in soil oxidoreductase and hydrolase activities during 360 days of incubation of an arid soil amended with different amounts of organic materials (fresh and composted urban organic wastes). The enzymatic activities were stimulated by such amendments. The soil receiving sewage sludge showed the highest overall activity. The different enzymatic activities rose after amendment then decreased rapidly with time; 360 days after organic amendment, the soil receiving the highest dose showed significantly higher enzymatic activity than the unamended soil. The soil amended with compost showed lower, though more stable, overall enzymatic activity than the soils amended with fresh wastes (municipal solid waste and sewage sludge). The soil receiving organic material to raise its organic matter content by 0.5% did not generally show significant differences from the unamended soil, while the differences produced in the soils receiving organic material to raise their organic matter content by 1.5% were still significant 360 days after amendment.

Influence of salinity on the biological and biochemical activity of a calciorthird soil

Irrigation of agricultural land with saline waters can lead to soil degradation. In this paper the effect of the irrigation with water containing different concentrations of NaCl or Na2SO4 (0.1 M, 0.3 M, 0.6 M, 0.8 M, 1 M, and 1.3 M) on the biological and biochemical characteristics of a calciorthid soil was studied. In general, the increase of scil electrical conductivity caused by the addition of saline solutions had a negative effect on soils biological and biochemical fertility, (that related directly with the soils microbiological activity) this effect being more noticeable with NaCl than with Na2SO4. Soil microbial respiration was inhibited as much as 57% by a 1.3 M solution of NaCl. The activity of hydrolases such as protease, β-glucosidase and phosphatase was more negatively affected by salinity than that of oxidoreductases (dehydrogenase and catalase). Soil NO3- content decreased with salinity while NH4+ content increased. Carbohydrate content, which is closely connected with soil aggregate stability, was also negatively affected by salinity.

Lasting microbiological and biochemical effects of the addition of municipal solid waste to an arid soil

Abstract This paper reports the effect of the addition of the organic fraction of municipal solid waste at two different rates on the microbiological and biochemical properties of an arid soil after 8 years. The vegetation that appeared spontaneously just after the amendment was still present 8 years later. The organic matter fractions were higher in the amended soil than in the control soil. Amended soil showed higher values of microbial biomass C, soil basal respiration and dehydrogenase activity than control soil, which reached values near to those of the natural soils in the area. The organic amendment had a positive effect on the activity of enzymes related with C, N, P cycles, particularly when the amendment was at the highest dose. This effect could be also observed on the activity of extracted enzymes. The results indicated that the addition of urban waste could be a suitable technique with which to restore soil quality.

Study on water extract of sewage sludge composts

Abstract Quantitative changes in the components of the water extracts from the mixtures of sludge and organic residues during the composting and maturation processes were studied in order to identify parameters that can be used as indicators of compost maturity. The pH of the water extracts increased during the first 40 days of composting and then decreased. The EC increased in almost all the samples during composting. There was a significant decrease in the water soluble organic matter, water soluble C, organic N, and carbohydrate contents during composting and maturation. These processes were also responsible for a decrease in the amount of phytotoxic substances such as ammonium, phenols, and organic acids of low molecular weight. The organic matter content of the water extract, the water soluble carbon/water soluble nitrogen ratio, the sugar content and the biodegradability index can all be used as indices of maturity since, in addition to the decrease of the values with time, similar values were obtai...

Evaluation of the maturity of municipal waste compost using simple chemical parameters

Abstract Changes in different chemical parameters of the mixtures of several organic residues during composting were studied in order to establish simple parameters that can be useful as indices of compost maturity. Circular chromatography test and the study of the colour in solid samples of compost cannot be considered sufficiently reliable for determining the degree of maturity in composts. Similarly, parameters such as ash, C/N ratio, CEC, total organic carbon (TOC), and total nitrogen (TN) must be ruled out. Other parameters such as water soluble carbon (WSC), water soluble carbohydrates, the C/N ratio of the water soluble extract, and the ratios WSC/TN and CEC/TOC, can be used as indices of compost maturity.