R. M. Palma

Exopolysaccharide of Nostoc muscorum (Cyanobacteria) in the aggregation of soil particles

The effects on a saline-sodic soil of exopolysaccaride isolated from Nostoc Muscorum or the addition of a cyanobacterial mass proliferation were evaluated in a greenhouse experiment. By day 180 exopolysaccharide increased soluble C by 100%, microbial activity by 366% and the amount of water-stable aggregates larger than 250μm by 12 times. Inoculation with living cyanobacterial mass increased at the end of 365 oxidizable C by 11%, soluble C by 66%, microbial activity by 73% and aggregates larger than 250 μm by66%. A slimy film 3–5 mm thick, with N. Muscorum predominating, covered all the surface of inoculated soils. The higher soil aggregate stability produced by both treatments is a consequence of increased microbial activity and concentrating the soil polysaccharide. The high percentage of clays favours the creation of firm and long-lasting slime-mineral joints. Addition of isolated exopolysaccharide produces a faster and higher increase in soil aggregate stability than cyanobacterial mass inoculation.

Changes in soil enzyme activities following additions of cyanobacterial biomass and exopolysaccharide

Abstract The aim of this research was to establish changes in the overall activity of extracellular enzymes: β-glucosidase, phosphomonoesterase, arylsulphatase, protease and urease and the intracellular enzyme dehydrogenase produced by the addition of Tolypothrix tenuis and Microchaete tenera (Cyanobacteria) exopolysaccharide (EPS) and biomass to a silty clay loam soil. Both biomass and EPS of M. tenera significantly (p

Chemical and biochemical properties as potential indicators of disturbances.

Abstract The response of a series of soil microbial, chemical, and enzymatic chacacteristics to two different tillage systems (conventional and no-tillage) and two crop rotations (continuous corn and soybean–corn) was evaluated in a long-term field experiment in the Rolling Pampas Region, Marcos Juárez, Córdoba, Argentina. The parameters studied included: oxidizable, soluble and respiration C, total and hydrolyzable N, microbial activity, ammonifiers, nitrifiers, cellulolytic and total microflora, protease and urease activities. After 15 years, oxidizable C, total N and hydrolyzable N showed no differences regarding no-tillage systems. However, differences were found regarding control soil. While soluble C did not exhibit any significant differences, respiration C and microbial activity were indicators sensitive to different treatments. Enzymatic activities, protease in particular, did reflect changes due to management. Fluctuation in microbial population counts were more related to plant residues than to tillage systems.

Effect of Cadmium, Copper, and Lead on Different Enzyme Activities in a Native Forest Soil

Abstract Heavy metals contamination has been reported to affect enzymatic activities in soils. The objectives of this work were (i) to study the effect of cadmium [Cd(II)], copper [Cu(II)], and lead [Pb(II)] at different doses and different incubation times on arylsulphatase, ß-glucosidase, acid phosphatase, protease, and urease activities in a noncontaminated native forest soil and (ii) to analyze the potential use of enzyme activity to detect contamination in soils by the studied metals. The study site was located in a subtropical forest of Argentine. A soil sample representative from the studied site was placed in plastic containers and contaminated with solutions containing Cd (20, 100, 200, and 500 mg kg−1 soil), Cu (50, 250, 500, and 2500 mg kg−1 soil), and Pb (40, 200, 400, and 1000 mg kg−1 soil) in a laboratory experiment. The metal influence on the enzymatic activity was studied at different incubation times (30, 60, 90, and 120 days). Results showed that, the metals studied inhibited the arylsuphatase, acid phosphatase, protease, and urease activities. Little or no effect was detected on the ß-glucosidase activity. The toxicity of the different metals evaluated through inhibition percentage of the enzyme activities was in the order Cd ≅ Cu > Pb. It may be concluded that protease was the enzyme more sensitive to indicate the soil pollution caused by the studied metals in this ecosystem.

β‐Glucosidase and Proteases Activities as Affected by Long‐Term Management Practices in a Typic Argiudoll Soil

The objective of the present study was to determine the effect of tillage systems on the activities of enzymes associated with the carbon (C) and nitrogen (N) cycles (β‐glucosidase and protease) on a Typic Argiudoll (Marcos Juárez Series). The experiment was performed in a randomized complete block design with three replications under no till, conventional tillage and native pasture used as control soil. The activities of β‐glucosidase and protease, total N and oxidizable C contents were determined at depths of 0–5 and 5–15 cm. Not only the activities of both enzymes, but also C and N contents were greater in the native soil at both depths, which shows the impact of land use on this soil. The enzymatic activities in the surface of no‐till soil were significantly higher than those for conventional tillage. At the 5–15 cm depth these variables did not present significant differences between tillage systems. The enzymatic activity was more sensitive to tillage systems than oxidizable C content in the first cm of the top layer. These results indicate that β‐glucosidase was a more sensitive index of management effects than protease.

Effect of cyanobacterial inoculation and fertilizers on rice seedlings and postharvest soil structure

Abstract The effect of soil inoculation with urea, Nostoc muscorum, and Tolypothrix tenuis on rice seedlings, nutrient contents, and structure of postharvest soil was studied. Tolypothrix tenuis and T. tenuis + urea produced the highest increase in oxidizable C (54.60% both) which resulted 7.63% higher than urea. Tolypothrix tenuis also produced the highest increase in soluble C (241.14%). Regarding nitrogen (N) soil content all treatments produced a positive difference. No treatment exerted any effect on soil available phosphorus (P). The percentage of aggregates >50 (m increased with all treatments from 6 to 12%, except N. muscorum. Tolypothrix tenuis produce the highest effect, with 50% more of these aggregates than urea. Seedling dry weight and shoot length were higher than control for all treatments. Shoots were longest with N. muscorum + urea being this treatment more effective than each Cyanobacteria alone. There was no effect on the number of leaves. Except for N. muscorum, all treatments increase...

Urease activity in Argentine soils: Field studies and influence of sample treatmenT

Abstract The effects of various treatments and seasonal variation upon urease activity were studied on surface samples of Argentine agricultural soils. Samples were selected to be representative of the zone covering a wide range of chemical and physical soil properties. Five sample treatments were selected: moist fresh; moist stored; air-dried; refrigerated; and frozen. It was shown that storage of soil at 4°C in sealed plastic bags maintained the natural moisture content and resulted in urease values most closely to those obtained at the time of sampling. Three Typic Argiudols under different vegetation covers were selected to elucidate the seasonal variation of urease activity. The highest enzymatic activities were found during the summer, whereas lowest values were encountered during the winter. The gradients of urease activity were different for the two types of vegetation studied (forest and natural grassland). As the values of urease activity also presented differences between soils under the two types of vegetation it may be presumed that the activity of this enzyme is related to the type of vegetation.

Seasonal variations of the light organic fractions in soils under different agricultural management systems

Abstract Annual dynamics of soil organic matter and seasonal evolution of total and light forms of carbon (CL) and nitrogen were studied for three series of soils in the humid Pampa of Argentina. Agricultural practice effects on the organic fraction of soil were also evaluated. Seasonal fluctuations in the light organic fractions of soils were confirmed, presenting each one of them its particular behaviour. In the Typic Argiudoll (Azul) and the Argiaguic Argialboll (Lujan) persistence of CL is related to low temperaure and moisture excess. Diferences between grasses and other crops are of small importance. In the Typic Hapludoll Pehvajo, soil texture and climatological conditions favour rapid mineralization. In this case, is very important that the maintenance of light carbon incorporation be made by pastures.

Cropping rotations: Effect on aggregate stability and biological activity

Abstract Growing crops and crop sequences over a period of 14 years leads to changes in soil properties. The effect of nine cropping rotations (wheat/soybean‐maize, wheat/soybean‐soybean, wheat/soybean, wheat‐wheat soybean‐soybean, maize‐maize, sunflower‐soybean, sunflower‐sunflower and soybean‐maize) on bulk density, structural stability, biological activity, and organic carbon (C) was investigated in experimental plots subject to conventional tillage. Type of soil used was a well‐drained Typic Argiudoll, with a silty loam texture and an easily alterable structure by cultivation and rainfall. Bulk density, structural stability and biological activity showed statistically significant differences between treatments, a high correlation between biological activity and stable aggregates was also found. Four of the crop sequences (wheat/ soybean‐maize, soybean‐maize, sunflower‐soybean, soybean‐soybean) were chosen because they represented extreme behaviour patterns as regards the effects of water. For these so...