Soil Microbiological Characteristics Research Articles

Microbiological and Chemical Modifications of Soil Cultivated with Grapevine Following Agronomic Application of Olive Mill Wastewater

The reuse of olive mill wastewater (OMW) by spreading on agricultural land is subject to a long-time debate since they supply to agricultural land both substances of undoubted positive influence on fertility and compounds that may adversely alter its chemical, physical and microbiological characteristics and/or cause negative effects on crops. In this study different amounts of OMW from 3-phases centrifugal decanter were spread in February on soil cultivated with grapevine in a research-farm located in central Italy for 11 consecutive years, with the aim to verify the long term effect on grape production, physico-chemical and microbiological characteristics of soil. In particular, the effect of the OMW spread in the largest amount (50 L m−2) was an increase of the weight of the grape-brunches and total grapes production and, in addition, an improvement of the soil characteristics due to the increase of the content of the organic reducing substances with humic-like properties. Moreover, it was also ascertained that in the short-medium period (2–8 months) the respiratory activity of the micro-organisms of the soil parcels, treated with different amount of OMW, was higher than that of the soil control parcels. The results obtained demonstrated that the controlled spreading of OMW helps to increase both the grapes crop and the fertility of the soil, recycling the organic matter and mineral nutrients, in this way allowing to reduce, or avoid, the use of chemical fertilisers.

Microbial Biomass Soil Content and Activity Under Black Alder and Sessile Oak in the Western Black Sea Region of Turkey

Tree species have a remarkable impression on the physical, chemical and microbial properties of the soil. Some tree species like alders create a favorable environment for microbes in their soil–root interface in addition to carrying out soil reclamation. This study, conducted in the Western Black Sea Region of Turkey, compared the N-fixing in the roots of the black alder [Alnus glutinosa (L.) Gaertn.] and the non-N-fixing in those of the sessile oak [Quercus petraea (Matt.) Liebl.] species in terms of physical, chemical and microbiological soil characteristics. Samples of topsoil (0–6.5 cm) were collected randomly from under the black alder and the sessile oak trees, respectively, at seven different sites in the study area. Soil microbial biomass C and N were established by the chloroform fumigation extraction method. Basal respiration of soil was retained by the sodium hydroxide (NaOH) trap method. Contrary to expectations, the average organic C (2.59%), total N (0.22%), microbial biomass C (738.48 µg g−1) and N (99.56 µg g−1) were higher under the sessile oak trees, demonstrating the positive effect of sessile oak on soil microflora. The black alder and sessile oak tree soils exhibited significant differences in their content of organic C (Corg), total N, microbial biomass C (Cmic), and N. In addition, significant positive linear correlations were found between organic C and microbial biomass C, and also between organic C and basal respiration; however, the correlation between the metabolic quotient (qCO2) and Cmic/Corg percentages was negative for the black alder and sessile oak (r = − 0.589 and r = − 0.474, respectively), likely due to the fact that relatively more C was being utilized for growth than for respiration. These results indicated that, compared to the sessile oak, the relatively lower organic C and total N and subsequently, the microbial biomass C and N content under the black alder were most likely due to shallow and deep groundwater flow and thus, the loss of plant nutrients was probably brought about by weathering.

Efeito da Utilização de Cama de Aviário como Adubo Orgânico na Qualidade Química e Microbiológica do Solo

A disposicao de cama de aviario no solo de maneira continua e descontrolada pode causar impactos ambientais. Esse estudo teve como objetivo avaliar a influencia da aplicacao de cama de aviario nas caracteristicas quimicas e microbiologicas do solo. A primeira coleta de solo foi realizada dois anos apos a ultima aplicacao de cama de aviario nas areas com cultivo de tifton, milho/aveia, olericolas e mandioca, e na mata nativa. A segunda coleta foi realizada noventa dias apos a aplicacao nos solos com cultivos anuais (tifton e milho/aveia) e na mata nativa. Os dados da primeira coleta foram constituidos de um experimento inteiramente casualizado, e os da segunda coleta por meio de um experimento fatorial 3x2 (usos do solo x tempo de aplicacao). As analises quimicas realizadas foram de macro e micronutrientes, pH, carbono orgânico e saturacao por bases, alem do nitrogenio mineral. As caracteristicas microbiologicas analisadas foram carbono da biomassa microbiana, respiracao basal, quociente metabolico, quociente microbiano e mineralizacao do nitrogenio. A aplicacao de cama de aviario atrelada aos demais fatores relacionados as culturas, teores de argila e manejos dos solos provocou um aumento da saturacao por bases e nas concentracoes de Ca, Mg, K, P e Zn, e reduziu o carbono orgânico e o nitrogenio mineral. O CBMS e a sua atividade diminuiram, e o quociente metabolico aumentou. Os solos da segunda coleta apresentaram valores maiores de RBS, qCO2, N mineral e mineralizacao do nitrogenio. A aplicacao de cama de aviario influenciou as caracteristicas quimicas e microbiologicas do solo.

Microbial and physico-chemical analyses of soil receiving cassava mill waste water in Umudike, Abia State, Nigeria

The microbiological and physico-chemical characteristics of soil receiving cassava mill waste water in five different cassava processing mill sites in Umudike, Abia State, Nigeria, were assessed. The mean bacterial counts of the assessed soil ranged from 3.72±4.51×10 5 cfu/g to 5.77±6.11 ×10 5 cfu/g for contaminated soil and 6.10±4.36×10 5 cfu/g to 8.79±4.51×10 5 cfu/g for pristine soil. The mean fungal counts ranged from 6.67±1.16×10 3 cfu/g to 11.00±1.00×10 3 cfu/g for the contaminated soil and 11.00±0.21×10 3 cfu/g to 17.33±1.01 x10 3 cfu/g for the pristine soil. The microorganisms isolated include; Klebsiella spp., Proteus spp., Bacillus spp., Escherichia coli , Enterobacter spp., Staphylococcus aureus , Pseudomonas spp., Streptococcus spp., Micrococcus spp., Aspergillus spp., Rhizopus spp., Penicillium spp., yeast, Mucor spp. and Fusarium spp. The physicochemical parameters assessed had different ranges for the contaminated soil samples and the control. The study thus reveals that the cassava mill effluent has some deleterious effects on soil structure, soil microbiota, and soil quality, and hence recommends that appropriate measures be put in place to enforce and regulate the treatment of such effluents prior to discharge to receiving soil and/or water bodies. Keywords: Microbial, Physicochemical, analyses, soil, cassava, waste water

BIOLOGICAL MANAGEMENT OF Pratylenchus brachyurus IN SOYBEAN CROPS

ABSTRACT The efficiency of biological products combined with biological fertilization for controlling Pratylenchus brachyurus in soybean crops, and effects of these treatments on soybean crops were evaluate. A greenhouse experiment was conducted at the Mato Grosso State University, in Brazil, using a randomized block design with a 10×2 factorial arrangement, and four replications. The treatments consisted of Trichoderma asperellum, B. subtilis, Purpureocillium lilacinum, B. subtilis + T. asperellum, B. subtilis + P. lilacinum, T. asperellum + P. lilacinum, B. subtilis + T. asperellum + P. lilacinum and abamectin, and Controls with, and without nematodes. Nematode population, plant height, stem base diameter, and soil microbiological characteristics (at 60 and 120 days after sowing - DAS), shoot dry weight (60 DAS), and number of pods per plant, and grain yield (120 DAS) were evaluated. The treatments were efficient for the control of phytonematodes at 60 DAS; the efficiency of treatments with biological products increased when combined with biological fertilization. The biological products were more efficient for controlling the nematodes than abamectin at 120 DAS; and the percentage of control were higher when they were combined with biological fertilization, in both growing periods. The biological treatments resulted in better agronomic characteristics, and higher number of pods per plant, and grain yield, affecting the plants in the first growing period, and significant interaction with the biological fertilizer for these variables in the second growing period. The interaction between treatments and biological fertilization was significant for soil microbiological characteristics in the second growing period.

Long-term fertiliser (organic and inorganic) input effects on soil microbiological characteristics in hydromorphic paddy soils in China

This study investigated long-term fertilisation effects on soil microbiological characteristics of hydromorphic paddy soils. The study was conducted in 30-year-old experimental plots with various treatments involving chemical fertiliser (nitrogen, phosphorus, and potassium) alone or in combination with manure in relation to a control in a rice–rice–fallow system at the farm at Jiangxi Academy of Agricultural Science. The soil microbial biomass carbon (SMBC) and nitrogen (SMBN), microbial enzyme activity, and microbial community structure were analysed. Changes in levels of SMBC and SMBN in response to combinations of organic–inorganic fertilisers were significantly higher than for inorganic fertiliser treatment. Furthermore, activities of microbial enzymes (sucrase, urease, proteinase, acid phosphatase, and catalase) were significantly higher in combined than in inorganic fertiliser and control treatments. Additionally, the richness and evenness of soil bacteria were decreased by long-term fertilisation, especially inorganic, whereas the Shannon–Weiner and richness indexes of soil fungi were higher. Long-term fertilisation with high doses of combined organic–inorganic input significantly increased microbial biomass, enzyme activity, and fungal community diversity. However, the same input decreased bacterial community diversity. This study will be useful for improving fertilisation management in hydromorphic paddy soils.

Microbiological Characteristics of Soils of the Upper Delta of the Selenga River under Arid Conditions (Baikal Region)

The abundance, ratio of ecologo-trophic groups of microorganisms, microbial biomass, and predominant members of the taxonomic composition of microbial complexes are indicators of the different ecological states of soils of the central floodplain and islands of the upper delta of the Selenga River under arid conditions. The highest coefficients of oligotrophy with an increased share of microorganisms growing on the nitrogen-free Ashby medium, as well as predominance of Arthrobacter bacteria, were determined in low-moistened soils of the islands. In general, low microbiological activity (in comparison with the soils of the central floodplain depressions), resulting from a lack of moisture, is observed in these soils despite the uncontrolled cattle grazing in the areas of the latter.

Characterization of coniferous forest soils in the arid zone

Abstract Arid zones are very harsh environments characterized by binding edaphic and climatic factors, their rainfall is low and irregular accentuated by high temperatures and their soils are fragile and vulnerable. In recent years, it has been noted that vegetation is regressing and that the majority of reforestation has been a failure. Our study aims to know the physico-chemical and microbiological characteristics of forest soils in the pinewoods of an area of the highlands of western Algeria (Naama). For this we analyzed several soil samples spread over five sampling stations in a forest of Aleppo pine. The results show that the forest soils of our study area are characterized by a generally sandy texture and an orange color for all the selected stations. They are characterized by: a very high C/N ratio that indicates a slow evolution of organic matter and a nitrogen deficiency that is necessary for carbon decomposition. The conductivity shows that the soil contains some salinity, its permeability is strong and its humidity fairly low with an alkaline pH (> 8) due to the increase in the limestone level in the area. Basal respiration is low compared to microbial biomass due to poor physico-chemical quality of soils and the effect of water stresses that slow down microbial activities. Soils in this arid forest are generally characterized by soil homogeneity sensitive to the influence of environmental factors mainly poverty into elements necessary for its proper functioning such as nitrogen and water that accentuate soil degradation of these forest formations, which results in the risk of degradation being triggered.

Microorganisms in soils with elevated heavy metal concentrations in southern Serbia

Soil chemical properties and total heavy metal concentrations (As, Cd, Cr, Cu, Ni, Pb, Zn, Fe and Mn) and their relationships with some soil microbiological characteristics (such as soil respiration and numbers of specific groups of microorganisms) were evaluated in agricultural soils in southern Serbia. In 42% of samples, slightly elevated concentrations of As, Ni and/or Pb were detected, with the highest values of 43.4, 64.4 and 184.1 mg/kg, respectively. No significant differences were observed in soil microbiological characteristics between soil samples with elevated heavy metals and heavy metals below the maximum allowed concentrations (MAC). There was no negative correlation between any of the heavy metals and any microbiological characteristics, except the total number of fungi and the concentration of Ni (r=-394). Positive correlations between most of the heavy metals and the number of Azotobacter were obtained. Correlation analysis and stepwise multiple regression analyses indicated that the chemical properties of the soil are the factors that affected the number of microorganisms the most. The content of CaCO3 significantly contributed to variations in soil respiration (39%), the total number of microorganisms was affected the most by humus (53%), oligonitrophiles by the total N content (49%), while the numbers of actinomycetes and fungi were affected by the pH (48% and 58% of the variation).

Growth Promotion of <i>Telfairia occidentalis</i> by Application of <i>Chlorella vulgaris</i> (Bioinoculant) Colonized Seeds and Soil under Tropical Field Conditions

The application of fertilizer is an essential factor for improving plant growth. This study was carried out to investigate the effect of Chlorella vulgaris (bio-fertilizer), NPK and poultry manure on the microbiological, biometric and biochemical properties of Telfairia occidentalis and its rhizosphere soil after forty days of planting. There were significant changes in the microbiological and physicochemical characteristics of soil in the various treatments administered. Maximum bacterial and fungal counts of 2.6 × 1010 and 3.8 × 105 cfu/g were obtained in soil treated with poultry manure and Chlorella vulgaris respectively whereas; maximum nitrogen (0.85%) and potassium (13.6 mg/ml) contents were obtained in NPK treated soil. Soil amended with Chlorella vulgaris showed maximum organic matter (9.48%) and phosphorus (8.55 mg/ml) concentrations. The amendment of soil with Chlorella vulgaris also speeded up germination of the Telfairia occidentalis to 5 days while, maximum plant length, number of leaves and fresh weight of the fluted pumpkin were obtained in Chlorella vulgaris amended soil and seed treatment pot. Total chlorophyll, carbohydrates, proteins and lipids were also increased on application of Chlorella vulgaris to soil or seed. Generally, application of Chlorella vulgaris to either seed or soil before planting resulted in increase in plant growth characteristics. Results of this study thus suggest that Chlorella vulgaris (bio-fertilizer) is a veritable biotechnological agent for improved cultivation of Telfairia occidentalis.

Evaluation of Fungal Growth on Olive-Mill Wastewaters Treated at High Temperature and by High-Pressure Homogenization.

Reuse of olive mill wastewaters (OMWWs) in agriculture represents a significant challenge for health and safety of our planet. Phytotoxic compounds in OMWW generally prohibit use of untreated OMWWs for agricultural irrigation or direct discharge into surface waters. However, pretreated OMWW can have positive effects on chemical and microbiological soil characteristics, to fight against fungal soil-borne pathogens. Low amounts of OMWW following thermal (TT-OMWW) and high-pressure homogenization (HPH-OMWW) pretreatments counteracted growth of some of 12 soil-borne and/or pathogenic fungi examined. With fungal growth measured as standardized change in time to half maximum colony diameter, Δτ, overall, HPH-OMWW showed increased bioactivity, as increased mean Δτ from 3.0 to 4.8 days. Principal component analysis highlighted two fungal groups: Colletotrichum gloeosporioides, Alternaria alternata, Sclerotium rolfsii, and Rosellinia necatrix, with growth strongly inhibited by the treated OMWWs; and Aspergillus ochraceus and Phaeoacremonium parasiticum, with stimulated growth by the treated OMWWs. As a non-thermal treatment, HPH-OMWW generally shows improved positive effects, which potentially arise from preservation of the phenols.

Long-Term Spreading of Olive Mill Wastewater on Olive Orchard: Effects on Olive Production, Oil Quality, and Soil Properties

ABSTRACTIn Italy, the law no 574 of 1996 permits and regulates the disposal of olive mill wastewater (OMW), the liquid by-product obtained in oil mill when olive fruits are processed to extract virgin olive oil, by its controlled spreading on cultivated soil. With the aim to verify the long-term effects of the practice on olive production, oil quality, and physical–chemical and microbiological characteristics of soil, different amounts of OMW were spread in February, for 9 years consecutively, on soil cultivated with olive trees. The results obtained confirmed that the controlled spreading of OMW is not harmful for the plant production. On the contrary, OMW spread on olive grove is useful for the fertility of soil and the growth of microflora for the important supply of nitrogen (N), phosphorus (P), potassium (K), and, above all, of organic matter. The evaluated biological properties indicated that OMW spreading stimulates the growth of soil fungal and fungus-like communities and aerobic N2 fix micro-organisms. With regard to the oil quality, the data indicate that no significant differences were ascertained on the analyzed parameters.

The Effects of Biochar and Its Combination with Compost on Lettuce (Lactuca sativaL.) Growth, Soil Properties, and Soil Microbial Activity and Abundance

Impacts of biochar application in combination with organic fertilizer, such as compost, are not fully understood. In this study, we tested the effects of biochar amendment, compost addition, and their combination on lettuce plants grown in a soil poor in nutrients; soil microbiological, chemical, and physical characteristics were analyzed, together with plant growth and physiology. An initial screening was also done to evaluate the effect of biochar and compost toxicity, using cress plants and earthworms. Results showed that compost amendment had clear and positive effects on plant growth and yield and on soil chemical characteristics. However, we demonstrated that also the biochar alone stimulated lettuce leaves number and total biomass, improving soil total nitrogen and phosphorus contents, as well as total carbon, and enhancing related microbial communities. Nevertheless, combining biochar and compost, no positive synergic and summative effects were observed. Our results thus demonstrate that in a soil poor in nutrients the biochar alone could be effectively used to enhance soil fertility and plant growth and biomass yield. However, we can speculate that the combination of compost and biochar may enhance and sustain soil biophysical and chemical characteristics and improve crop productivity over time.

Short–Term Effects of Young Landfill Leachates (LFL) on Chemical and Microbiological Properties of a Mediterranean Sandy Soil

Landfill leachates (LFL) constitute a serious environmental problem due to its high concentration of organic and inorganic compounds. However, landfill leachates can be also considered as fertilizer with respect to those substances. The present paper is an attempt to analyze the impact of application of municipal solid waste (MSW) landfill leachates on soil carbon, nitrogen and microbiological characteristics. Three doses of landfill leachates (0.5, 1 and 2%) were used corresponding to 10, 20 and 40 m3ha-1, respectively. The variation of the main physical, chemical and microbiological properties of soil was monitored. Temporary and permanent changes in several properties occurred after the application of LFL. These properties varied in sensitivity to the applied disturbance. Shortly, after the application of LFL the organic carbon and nitrogen (N) increased in soils amended. Simultaneously, an increase in the total number of soil bacteria, nitrifying populations and soil respiration (after two weeks of incubation) was occurred. But this effect disappeared after two months of treatment. The increase in microbiological activity accelerated the loss of soil organic carbon (SOC) and led to an increase of N at the end of incubation. The leachates treated soils exhibited elevated levels of electrical conductivity (EC) and lower levels of exchangeable Phosphorus (P).

EDAPHIC ATTRIBUTES OF A CROP-LIVESTOCK INTEGRATION SYSTEM IN THE CERRADO BIOME

ABSTRACT A significant increase in the use of integrated farming systems have been observed in the Brazilian Cerrado, such as crop-livestock integration (CLI), which combined with the no-tillage system (NTS) have shown significant influence on soil properties. Therefore, the objective of this work was to evaluate the influence of a CLI system on the chemical, physical and microbiological soil characteristics, in an area in the Cerrado biome, Montividiu, State of Goias, Brazil. The soil fertility, remaining phosphorus (Prem), total organic carbon (TOC), total nitrogen (Nt), aggregate stability (geometric mean diameter - GMD), microbial respiration (C-CO2) and easily-extractable glomalin-related soil protein (EE-GRSP) were evaluated. Soil samples were collected at depth of 0-5 and 5-10 cm in three areas with: CLI (13 years of annual rotation with Urochloa ruziziensis); Urochloa decumbens pasture (15 years of implementation); and native Cerrado vegetation. The CLI area had higher pH, Mg, P available (0-10 cm) and Prem (5-10 cm) values compared to the other areas, and equal values of TOC, Nt, EE-GRSP (0-10 cm) and aggregate stability (5-10 cm) compared to the pasture area. The CLI had no differences in C-CO2 emissions compared to the Cerrado, but had lower rates compared to the pasture. The P available and Prem were sensitive indicators to show the differences between the CLI and pasture systems, with higher contents in the CLI area. The TOC and Nt indicators had no differences between these two systems. The GMD results indicated a better aggregation in the pasture (0-5 cm) compared to the CLI area, while the EE-GRSP were similar in these areas. The total values of C-CO2 emission from the soil aggregates showed the stability of respirometry rates in the CLI and Cerrado areas.

A calorimetric assessment of the effects of sodium chloride and sodium bromide on the microbiological and thermokinetic characteristics of soil

Excess salinity may lead to degradation of arable land and exclusion from agricultural production by worsening of their properties. The evaluation of the characteristics of saline soils is very important from the point of view of the use of agricultural soil. The aim of this study was to determine changes in the physicochemical properties of soil, the content and activity of soil microbial biomass (SMB) and the thermokinetics of glucose biodegradation in soil samples containing different doses of sodium chloride and sodium bromide (0.0263; 0.0526; 0.1052; 0.1578; 0.2104; 0.2630mmolg−1 DM soil), and to compare the effects of both salts. The pH values of soil samples decreased (from 6.1 to 5.4 for NaCl and NaBr) and electrical conductivity increased (from 0.20dSm−1 to 2.61dSm−1for NaCl and 2.30dSm−1 for NaBr) with increasing doses of both salts. SMB content, determined based on substrate-induced respiration (SIR), decreased with increasing doses of NaCl and NaBr (from 737mg C to 348mg C for NaCl and 379mgCkg−1 DM soil for NaBr). Both salts inhibited glucose biodegradation processes in soil proportionally to their increasing doses (NaBr exerted a greater inhibitory effect). This was confirmed by lower values of the maximum rate of heat production (RHPmax) and the apparent growth rate constant (k), and by higher values of peak time (PT), generation time (tG) and the inhibitory ratio (I). Changes in pH, SIR-SMB and Qtmax (total heat production) were modeled based on the applied doses of NaCl and NaBr. The empirical data were well approximated by the proposed mathematical models representing relationships between soil pH, SIR-SMB and Qtmax vs. the applied doses of NaCl and NaBr. They can be used to reliably predict the effects of the analyzed salts on the tested soil parameters.

Comparative analysis of certain soil microbiological characteristics of the carbon cycle

In our researches, we examine the soil microbial parameters related to the carbon cycle. In this study, we compare the changes of microbial biomass carbon (MBC) and the soil CO2 production in soil samples which were taken in spring and autumn. The 30 years old long-term experiment of Debrecen-Látókép is continued in our experiments. The long-term fertilization experiment was set in 1983, and our sample was taken in spring 2014. The examinations of soil respiration processes and factors that influence soil respiration are required in optimal management. In our study, we interested to know how the growing levels of fertilization influence the soil respiration and microbial biomass carbon under non-irrigated and irrigated conditions in maize mono, bi, and triculture.

Organic plum cultivation in the Mediterranean region: The medium-term effect of five different organic soil management practices on crop production and microbiological soil quality

Organic farming practices recommended by European regulations offer an alternative to conventional soil management, but these practices should be analyzed in greater depth to assess their effectiveness on different plants and in different local conditions. Accordingly, this study evaluates the efficacy of five different organic management strategies on an organic plum farm in Southeastern Spain. This study was conducted for a period of six years and the five different organic treatments were applied in triplicate in 256m2 plots randomly distributed in three blocks (15 plots in total); each plot had 16 plum trees. Every year crushed pruning wastes were incorporated into the soil in all the experimental plots. One triplicated plot only received this aforementioned treatment (crop biomass treatment, CB). The rest of the plots also received one of the following treatments: (i) the addition of a commercial product for organic agriculture based on bacteria (biofertilizer), composed of Azospirillum brasilense (bacteria fixing N) and Pantoea dispersa (bacteria with a capacity for solubilising phosphates and stimulating plant growth) (biofertilizer treatment, B); (ii) the annual addition of 20t/ha of certified commercial organic compost (annual compost treatment, AC); (iii) the biennial addition of 20t/ha of certified commercial organic compost (biennial compost treatment, BC); and (iv) the sowing and subsequent incorporation of a mixture of 60% Avena sativa and 40% Vicia sativa (green manure treatment, GM). Each year the following indicators of ecosystem sustainability related to soil microbiological characteristics and carbon fixation were measured after harvest, in addition to plum yield: organic carbon (Corg), water soluble C, humic substances and humic acid C, microbial biomass C, respiration, ATP, dehydrogenase activity and hydrolase enzymes (alkaline phosphatase, urease and beta-glucosidase) activities. The two way ANOVA of the results indicated that all the above parameters were significantly affected (p≤0.001) by both, treatment and time. The interaction of treatment and time also significantly affected all of these parameters, except for yield and dehydrogenase activity. Composts not only produced better results than green manure cover crops and biofertilizer treatments in terms of plum yields, but they also brought about higher increases in the soil C pool and greater improvements in soil microbiological characteristics. In the six years of the study, compost-treated soils showed higher average plum yields and higher organic carbon, humic substance and humic acid contents than the rest of treatments. The size and activity of microbial population was also greater in the compost-treated soils, reflected in the higher values found in these soils for microbial biomass C, soil respiration, ATP (adenosine-tri-phosphate) content and dehydrogenase and hydrolases activity. Nevertheless, yields when compost was added biennially (BC) tended to be higher than in the annual compost treatment (AC) in most years as well as on average, although the differences were usually not significant. Yields in the sixth crop showed a high positive correlation with soil humic substances and humic C content (p≤0.01), as well as with Corg, microbial biomass C and phosphatase and urease activity (p≤0.05).

Effect of cassava mill effluent on biological activity of soil microbial community.

This study assessed the effect of cassava effluent on soil microbiological characteristics and enzymatic activities were investigated in soil samples. Soil properties and heavy metal concentrations were evaluated using standard soil analytical and spectroscopic methods, respectively. The microbiological parameters measured include microbial biomass carbon, basal soil respiration, catalase, urease, dehydrogenase activities and number of culturable aerobic bacteria, fungi and actinomycetes. The pH and temperature regime vary significantly (p < 0.05) throughout the study period. All other physicochemical parameters studied were significantly different (p < 0.05) higher than the control site. Soil organic carbon content gave significant positive correlations with microbial biomass carbon, basal soil respiration, catalase activity and dehydrogenase activity (r = 0.450, 0.461, 0.574 and 0.591 at p < 0.01), respectively. The quantitative analysis of soil microbial density demonstrates a marked decrease in total culturable numbers of the different microbial groups of the polluted soil samples. Soil contamination decreased catalase, urease and dehydrogenase activities. The findings revealed that soil enzymes can be used as indices of soil contamination and bio-indicator of soil quality.

Microbial biomass and cellulase activity in soils under five different cocoa production systems in Alto Beni, Bolivia

Cocoa is one of the most important crops of the “Alto Beni” region in Bolivia. This crop is produced in different systems, among them monoculture and agroforestry. In order to determine the effect of the production system on microbiological soil characteristics, we measured microbial biomass carbon, microbial biomass nitrogen and cellulase activity and we determined the microbial quotient in soil under five different cocoa production systems (conventional monoculture, organic monoculture, conventional agroforestry, organic agroforestry and successional agroforestry) and in fallow plots. The measurements were carried out in dry and rainy season. Soil from fallow plots and soil under agroforestry had higher microbial biomass than soils under monocultures, probably due to the effect of fresh organic matter input on microbial biomass. No significant difference for microbial biomass in soil from plots subjected to organic management and soil from plots subjected to conventional management was observed, possibly because of the short time elapsed from the initial establishment of the plots. In dry season, the microbial quotient showed a significantly higher value in soils under conventional agroforestry than in soils under organic monoculture, suggesting that besides the input of fresh organic matter, mineral fertilization may play a role on the fraction of available carbon. Cellulase activity was not affected by any of the factors tested, indicating that, under our assay conditions, it was not a good indicator of changes in soil.