C. García

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

Abstractu2002An 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.

Effect of plant cover decline on chemical and microbiological parameters under Mediterranean climate

Abstract The uses of many of the soils of Central Spain have changed and these changes have led frequently to the decline of natural plant cover. In this paper we report on the organic matter fractions and the microbial activity of soils developed from different substrates (limestone and granites) in relation to plant cover decline. Specific indicators of microbial activity (microbial biomass carbon (MBC), basal respiration, and some oxidoreductase and hydrolase activities) were measured. These indicators decreased in value in both limestone and acid soils where plant cover had declined (from climax, tree forest, to low bush); a similar effect was observed in the labile organic matter fractions (water soluble carbon (WSC), water soluble carbohydrates and polyphenolic compounds). For some measures of microbiological activity (e.g. MBC and soil respiration) the differences in acid soils were lower than in limestone soils. For example, MBC values in limestone soils ranged from 1426xa0ngCxa0g−1 in tree forest to 498xa0ngCxa0g−1 in low bush; while in acid soils, these values ranged from 428xa0ngCxa0g−1 in tree forest to 265xa0ngCxa0g−1 in low bush. Acid soils, unlike the limestone soils, showed no relationship between plant cover decline and hydrolase activities related to the N cycle (urease and protease). In general, soil microbial activity was negatively affected by plant cover degradation.

No-tillage, crop residue additions, and legume cover cropping effects on soil quality characteristics under maize in Patzcuaro watershed (Mexico)

Abstract Intensive maize ( Zea mays L.) cropping based on conventional tillage practices has resulted in soil quality degradation in the Patzcuaro Watershed in central Mexico. A field experiment with seven soil management treatments was implemented on a sandy loam Andisol to evaluate the impact on soil quality of maize cropping with conventional tillage, no-tillage with varying percentages of surface residue coverage (0, 33, 66 and 100%), and no-tillage with 33% residue coverage together with cover crops of either Vicia sp. or Phaseolus vulgaris L. The treatments of no-tillage under crop residue coverage were established in 1995 and the leguminous species were planted in 1998. By 2000, the alternative management treatments had increased soil enzymes, soil organic C, biodegradable C fractions such as water soluble C, water soluble carbohydrates, and microbial biomass C, and soil wet aggregate stability, compared to the CT treatment. Wet aggregate stability was increased by adopting no-tillage and even further by additional residue. Most soil quality characteristics improved in direct proportion to residue inputs. The use of no-tillage management together with a moderate amount of crop residue (33%) and planted to leguminous species rapidly improved some soil quality characteristics. We conclude that conservation tillage practices can provide an alternative technology contributing to sustainable agriculture in the Patzcuaro watershed of Mexico, which can be extrapolated to similar areas elsewhere in Latin America.

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.

Aggregate stability changes after organic amendment and mycorrhizal inoculation in the afforestation of a semiarid site with Pinus halepensis

Abstract The recovery of soil structural stability is a precondition for successful afforestation programmes in semiarid environments. A multifactorial field experiment was carried out in a semiarid rangeland in south-eastern Spain to evaluate the influence of a fresh organic residue addition (first factor), mycorrhizal inoculation with Pisolithus arhizus (second factor), and the rhizosphere of Pinus halepensis (third factor) on soil aggregate stability. A total of 6 years after planting, the addition of residue was seen to increase the levels of stable aggregates to a greater extent than the mycorrhizal inoculation. Both reafforestation methods increased C-fractions and enzyme activities measured (dehydrogenase and phosphatase). The rhizosphere also affected aggregate stability, particularly when P. halepensis was inoculated with P. arhizus. Aggregate stability in the rhizosphere of P. halepensis was strongly correlated (P

A study of biochemical parameters of composted and fresh municipal wastes

Three different groups of municipal organic materials (fresh city refuse, sewage sludge and the composted products of both) were characterized from a biochemical point of view, and ATP content and 5 hydrolase activities (total and extractable) determined. The highest ATP values were found in the sludges and the lowest in the composts demonstrating that this parameter is valid for following the degradation of organic matter in this kind of waste. The highest total urease activities were found in sewage sludges, while activities varied widely in the solid municipal wastes, suggesting the existence of some kind of inhibitor. Protease-BAA activity was low in all cases. The highest phosphatase and β-glucosidase activity occurred in the sewage sludges. With the exception of protease-casein, all the enzymes studied were positively correlated with ATP content. Protease-casein, β-glucosidase and phosphatase activities were correlated among themselves and with the different fractions of carbon contained in the wastes. As regards extracellular enzymes, only phosphatase was correlated with the carbon content of the Na4P2O7 extract. Extracellular protease-BAA activity was generally very low. Extracellular urease activity was higher in city refuse than in sewage sludge, while phosphatase activity was higher in the latter. All enzymatic activities decreased with composting.