Soil Biological Parameters Research Articles

A classification of major natural habitats of Amazonian white-water river floodplains (várzeas)

Most countries sharing the Amazon basin have signed the Ramsar Convention on Wetlands of International Importance but still lack complete wetland inventories, classification systems, and management plans. Amazonian wetlands vary considerably with respect to hydrology, water and soil fertility, vegetation cover, diversity in plant and animal species and primary and secondary productivity. Here, we propose a classification system of major natural habitats of Amazonian white-water river floodplains (varzeas) based on hydrological, water and soil chemistry and biological parameters. The Amazonian varzea is one of the largest Amazonian wetlands. It is exceptionally rich in plant and animal species and plays important roles in landscape history, evolution, hydrology and biogeochemical cycles of the Amazon basin. Most of Amazonia’s rural population lives in or along the varzea, emphasizing the economic importance of its natural resources. Our classification indicates five major systems, which are subdivided into 10 main habitats and up to 40 functional (vegetation) units of which the most important mesohabitats are described. We understand this classification as a dynamic system, as it is open to the inclusion of future research attempts and habitats without affecting the entire classification system. Our classification may be used for scientific purposes, such as comparative studies on biomass, productivity, biogeochemical cycles and biodiversity. Also, because the classification builds on habitat types and/or vegetation and functional units already distinguished by the local population it may be especially useful in guiding intelligent use of varzea habitat for specific management activities, such as agriculture, animal husbandry, forestry, fisheries, and conservation.

The impact of organic and mineral fertilizers on soil quality parameters and the productivity of irrigated maize crops in semiarid regions

Pig slurry (PS) is widely used as a fertilizer for the production of maize in Spain. Field testing was carried out over a ten-year period to compare the performance of maize fertilized with PS (45 m3 ha-1, equivalent to 315 kg nitrogen (N) ha-1 year−1) (PS45) and mineral fertilizer (300 kg N ha-1) (N300) along with a N-free control (N0). Grain yield, biomass at physiological maturity, plant N uptake and soil nitrates (NO3−–N) were measured as agronomic properties. Soil physical, chemical and biological parameters (as acid-phosphatase activity, earthworm abundance, CO2 Flux, Shannon H′ diversity index (H’), number of utilized substrates (NUS), microbial biomass carbon (MBC), resistance to penetration (RP) and organic matter (OM) among others) were measured at harvest in the last two years of the experiment. The mineral fertilizer promoted the highest grain yield and N uptake by the plants, but also resulted in the highest residual NO3−–N levels in the soil. Interestingly, most of the indicators revealed no statistically significant differences between the treatments in either test years, although a general trend was observed (N0 < N300 < PS45). The repeated application of PS had a beneficial impact on the soil quality over time but did not improve grain yields.

Soil Carbon Dioxide Emissions from Sorghum–Sunflower Rotation in Rainfed Semi-arid Tropical Alfisols: Effects of Fertilization Rate and Legume Biomass Incorporation

The long-term effects of plant legume [horse gram (Macrotyloma uniflorum)] biomass incorporations were assessed in terms of carbon dioxide (CO2) emissions, soil quality parameters, and climatically influenced soil parameters in a dryland Alfisol under varying soil fertility conditions. Six selected treatments consisted of off-season legume incorporation (I) and no incorporation / fallow (F), each under three varying nitrogen and phosphorus fertilizer levels (viz., N0P0, N25P30, and N50P30). Soil moisture, soil temperature, soil surface carbon dioxide emission, soil dehydrogenases, and microbial biomass carbon (MBC) were monitored at three different crop situations [viz., Kharif period (KP), legume/fallow period (LP), and no crop period (NP)] at 14 different periods of the year. Incorporation practices resulted in greater rates of CO2 emission over fallow conditions during the Kharif and legume periods, whereas the emission rate was greater in fallow soils during the end of the legume and no crop periods. The increased rates of fertilizer doses also significantly increased the soil CO2 flux during the majority of the measurements. Beneficial effects of incorporation practices were observed in terms of high soil moisture (5–11%), low soil temperature (3–7%), and high content of MBC over without incorporations. Correlation studies indicated that the soil property MBC was found to be the greatest significant variable with CO2 emission in all the fertilizer treatments under biomass-incorporated soils. These results indicated the undesirable (in terms of CO2 fluxes) and desirable (soil biological and other parameters) effects of legume biomass incorporation and fertilizer application and their significance in improving soil quality and greenhouse gas (GHG) emissions in dryland Alfisols of semi-arid tropics.

Significance of litter layer in enhancing mesofaunal abundance and microbial biomass nitrogen in sweet corn-white clover living mulch systems

Living mulch is a type of sustainable farming system that consists of cover crops planted either before or with a main crop; a living mulch is maintained as a living ground cover throughout the growing season of the main crop. Microbial biomass and abundance of mesofauna (microarthropods and enchytraeids) are important soil biological parameters in relation to soil function, plant productivity, and nutrient cycling; however, the effects of living mulch on these parameters are not fully understood. In this study we examined the effects of living mulch treatment with nitrogen fertilizer (0, 40, 160, or 200 kg ha−1) on the abundance of soil microarthropods (Oribatida, Mesostigmata, Prostigmata, and Collembola) and the effects of living mulch treatment on the dynamics of the soil biota (mesofauna, microarthropods, enchytraeids, and microbial biomass nitrogen) from spring to autumn. Our results showed that living mulch treatment significantly (p < 0.05) increased the grain weight of the main crop in both experiments. Generally, living mulch treatment had a positive effect on the abundance of mesofauna and microbial biomass nitrogen, despite pesticide usage. Nitrogen levels did not affect the number of microarthropods. The litter layer in living mulch significantly (p < 0.05) enhanced microbial biomass nitrogen and the abundance of Oribatida, Prostigmata, and Collembola. We conclude that living mulch enhances mesofaunal abundance and microbial biomass nitrogen and that the production of a litter layer by living mulch is one of the major mechanisms for this enhancement.

Tree Species Effect on Litter Decomposition and Nutrient Release in Mediterranean Oak Forests Changes Over Time

Tree species can affect the decomposition process through the quality of their leaf fall and through the species-specific conditions that they generate in their environment. We compared the relative importance of these effects in a 2-year experiment. Litterbags containing leaf litter of the winter-deciduous Quercus canariensis, the evergreen Q. suber and mixed litter were incubated beneath distinct plant covers. We measured litter carbon loss, 9 macro- and micronutrients and 18 soil chemical, physical and biological parameters of the incubation environment. Tree species affected decay dynamics through their litter quality and, to a lesser extent, through the induced environmental conditions. The deciduous litter showed a faster initial decomposition but left a larger fraction of slow decomposable biomass compared with the perennial litter; in contrast the deciduous environment impeded early decomposition while promoting further carbon loss in the latter decay stages. The interaction of these effects led to a negative litter–environment interaction contradicting the home-field advantage hypothesis. Leaf litter N, Ca and Mn as well as soil N, P and soil moisture were the best predictors for decomposition rates. Litter N and Ca exerted counteractive effects in early versus late decay stages; Mn was the best predictor for the decomposition limit value, that is, the fraction of slowly decomposable biomass at the later stage of decomposition; P and soil moisture showed a constant and positive relation with carbon loss. The deciduous oak litter had a higher initial nutrient content and released its nutrients faster and in a higher proportion than the perennial oak litter, significantly increasing soil fertility beneath its canopy. Our findings provide further insights into the factors that control the early and late stages of the decomposition process and reveal potential mechanisms underlying tree species influence on litter decay rate, carbon accumulation and nutrient cycling.

Effect of tillage systems and nitrogen application rates on selected physical and biological properties of a clay loam soil in KwaZulu-Natal, South Africa

The effects of agricultural management practices on soil physical and biological parameters provide fundamental information for assessing sustainability. Tillage (annual conventional tillage and no-till) and nitrogen fertiliser (limestone ammonium nitrate at rates of 0, 100 and 200 kg N ha−1) were evaluated for their effects on bulk density, water retention characteristics, saturated hydraulic conductivity, soil penetration resistance and microbiological activity (hydrolytic and cellulolytic) on a clay loam soil (Typic Haplustox) at a field experiment initiated in 2003 and planted to dryland maize. Tillage regime and nitrogen application rate significantly (p < 0.05) affected soil physical properties and microbial activity in the 0–5 cm layer. Under no-till the saturated water content and saturated hydraulic conductivity were significantly lower than under annual conventional tillage while plant available water was greater under no-till. Penetration resistance, bulk density and microbial activity were greater under no-till than annual conventional tillage. At 200 kg N ha−1 microbial activity, bulk density, water retention and saturated hydraulic conductivity were significantly lower than at the lower rates of application, especially under no-till. These results indicate that no-till improved soil physical properties and suggest there is a need to re-evaluate the sustainability of using high rates of nitrogen to increase maize yields, especially under a no-till system.

Effects of transgenic Bt cotton on soil fertility and biology under field conditions in subtropical inceptisol

Although there is large-scale adoption of Bt cotton by the farmers because of immediate financial gain, there is concern that Bt crops release Bt toxins into the soil environment which reduces soil chemical and biological activities. However, the majorities of such studies were mainly performed under pot experiments, relatively little research has examined the direct and indirect effects of associated cover crop of peanut with fertilization by combined application of organic and inorganic sources of nitrogen under field conditions. We compared soil chemical and biological parameters of Bt cotton with pure crop of peanut to arrive on a valid conclusion. Significantly higher dehydrogenase enzyme activity and KMnO(4)-N content of soil were observed in Bt cotton with cover crop of peanut over pure Bt cotton followed by pure peanut at all the crop growth stages. However, higher microbial population was maintained by pure peanut over intercropped Bt cotton, but these differences were related to the presence of high amount of KMnO(4)-N content of soil. By growing cover crop of peanut between Bt cotton rows, bacteria, fungi, and actinomycetes population increased by 60%, 14%, and 10%, respectively, over Bt cotton alone. Bt cotton fertilized by combined application of urea and farm yard manure (FYM) maintained higher dehydrogenase enzyme activity, KMnO(4)-N content of soil and microbial population over urea alone. Significant positive correlations were observed for dry matter accumulation, dehydrogenase enzyme activity, KMnO(4)-N content, and microbial population of soil of Bt cotton, which indicates no harmful effects of Bt cotton on soil biological parameters and associated cover crop. Our results suggest that inclusion of cover crop of peanut and FYM in Bt cotton enhanced soil chemical and biological parameters which can mask any negative effect of the Bt toxin on microbial activity and thus on enzymatic activities.

Microbial Characteristics of Vertisol Under Different Fertilization Systems

The present study evaluates the effect of increasing rates of mineral nitrogen (90; 120; 150 kg×ha-1), liquid manure (80 t×ha-1) and solid manure (45 t×ha-1) on the microbial properties of vertisol (total number of microorganisms, numbers of actinomycetes and cellulolytic microorganisms) under maize. The research results showed dependence of the number of the test groups of microorganisms on the type and rate of fertilization, as well as on the date and zone of sampling. Namely, lower nitrogen fertilization rates (90 and 120 kg×ha-1) induced a significant increase in the total number of microorganisms, whereas the high rate (150 kg×ha-1) had a depressive effect, especially in maize edaphosphere. However, the numbers of actinomycetes and cellulolytic microorganisms were not reduced under these treatments. The organic fertilizers applied had a stimulatory effect on the above soil biological parameters.

Plant Cover and Soil Biochemical Properties in a Mine Tailing Pond Five Years After Application of Marble Wastes and Organic Amendments

Tailing ponds pose environmental hazards, such as toxic metals which can contaminate the surroundings through wind and water erosions and leaching. Various chemical and biochemical properties, together with extractable and soluble metals were measured five years after reclamation of a polluted soil affected by former mining activities. This abandoned mine site contains large amounts of Fe-oxyhydroxides, sulphates, and heavy metals. As a consequence, soils remain bare and the soil organic matter content is low (< 3 g kg −1). Marble waste, pig manure and sewage sludge were applied in 2004. Plant cover and richness, and soil chemical, biochemical and biological parameters were analysed five years later. Results showed that all soil biochemical properties as well as vegetation cover and richness were higher in treated soils than in the untreated contaminated plots (control), although organic matter, pH values and extractable metals concentrations were similar among treatments. Soluble cadmium and zinc were lower in the amended plots than in control. As a general pattern, soil amended with pig manure showed higher values of most biochemical properties compared to sewage sludge application, while the doses did not have a great effect, being only significant for β-glucosidase, phosphodiesterase and arylsulfatase. Significant correlations were found between vegetation cover, richness and soil biochemical properties, suggesting a high interdependence between plant colonization and reactivation of biogeochemical cycles during five years. This study confirms the high effectiveness of an initial application of the amendments tested to initialize the recovery of ecosystems in bare mine soils under Mediterranean semiarid conditions. This research also shows the high sensitivity of certain biochemical properties in order to evaluate soil quality and reactivation of nutrients cycles in reclaimed mine soils.

Oxidation of a PAH polluted soil using modified Fenton reaction in unsaturated condition affects biological and physico-chemical properties

A batch experiment was conducted to assess the impact of chemical oxidation using modified Fenton reaction on PAH content and on physico-chemical and biological parameters of an industrial PAH contaminated soil in unsaturated condition. Two levels of oxidant (H 2O 2, 6 and 65 g kg −1) and FeSO 4 were applied. Agronomic parameters, bacterial and fungal density, microbial activity, seed germination and ryegrass growth were assessed. Partial removal of PAHs (14% and 22%) was obtained with the addition of oxidant. The impact of chemical oxidation on PAH removal and soil physico-chemical and biological parameters differed depending on the level of reagent. The treatment with the highest concentration of oxidant decreased soil pH, cation exchange capacity and extractable phosphorus content. Bacterial, fungal, and PAH degrading bacteria densities were also lower in oxidized soil. However a rebound of microbial populations and an increased microbial activity in oxidized soil were measured after 5 weeks of incubation. Plant growth on soil treated by the highest level of oxidant was negatively affected.

Soil biological quantity and quality parameters of grasslands in various landscape zones

In three landscape zones of a permanent grassland catchment (discharge zone, D; transient zone, T; and recharge zone, R; Crystallinicum, Czech Republic), soil moisture by volume (&amp;theta;) and soil biological quantity and quality parameters, e.g. oxidizable C (C&lt;sub&gt;ox&lt;/sub&gt;), hot water soluble C (C&lt;sub&gt;hws&lt;/sub&gt;), microbial biomass C (C&lt;sub&gt;mic&lt;/sub&gt;), nitrification (NITR), aerobic N mineralization (MIN) and basal respiration rates (R&lt;sub&gt;bas&lt;/sub&gt;), metabolic quotient (qCO&lt;sub&gt;2&lt;/sub&gt;: R&lt;sub&gt;bas&lt;/sub&gt;/C&lt;sub&gt;mic&lt;/sub&gt;) and microbial quotient (C&lt;sub&gt;mic&lt;/sub&gt;/C&lt;sub&gt;ox&lt;/sub&gt;) were estimated in the surface soil layer. We found out positive correlation of C&lt;sub&gt;mic&lt;/sub&gt; and C&lt;sub&gt;mic&lt;/sub&gt;/C&lt;sub&gt;ox&lt;/sub&gt; with &amp;theta;, or NITR, MIN, R&lt;sub&gt;bas&lt;/sub&gt; and C&lt;sub&gt;mic&lt;/sub&gt; with C&lt;sub&gt;hws&lt;/sub&gt;, but no relationship between &amp;theta; on the one hand and NITR, MIN, R&lt;sub&gt;bas&lt;/sub&gt; or C&lt;sub&gt;ox&lt;/sub&gt; on the other. The wettest zone D with extremely low pH displayed the highest C&lt;sub&gt;mic&lt;/sub&gt; and C&lt;sub&gt;mic&lt;/sub&gt;/C&lt;sub&gt;ox&lt;/sub&gt; (1081&amp;nbsp;mg/kg, 5.29%) and the lowest qCO&lt;sub&gt;2&lt;/sub&gt; (31 &amp;micro;gC/day/mgC&lt;sub&gt;mic&lt;/sub&gt;). Soil drought in zones T and R reduced C&lt;sub&gt;mic&lt;/sub&gt; and C&lt;sub&gt;mic&lt;/sub&gt;/C&lt;sub&gt;ox&lt;/sub&gt; (939, 1029, and 3.72, 3.83, respectively) and augmented qCO&lt;sub&gt;2&lt;/sub&gt; (42; 51). Rainfall following a prolonged dry period reduced MIN and NITR in permeable zone R as a result of fast microbial regeneration (average in D: 2.24; 2.48 kg N/ha/day, T: 2.62; 2.82 kg N/ha/day, R: 1.51; 1.95 kg N/ha/day).

Soil biological attributes in pastures of different ages in a crop-livestock integrated system

The objective of this work was to evaluate the effect of the pasture (Urochloa brizantha) component age on soil biological properties, in a crop-livestock integrated system. The experiment was carried out in a Brazilian savannah (Cerrado) area with 92 ha, divided into six pens of approximately 15 ha. Each pen represented a different stage of the pasture component: formation, P0; one year, P1; two years, P2; three years, P3; and final with 3.5 years, Pf. Samples were taken in the 0-10 cm soil depth. The soil biological parameters - microbial biomass carbon (MBC), microbial biomass respiration (C-CO2), metabolic quotient (qCO2), microbial quotient (q mic), and total organic carbon (TOC) - were evaluated and compared among different stages of the pasture, and between an adjacent area under native Cerrado and another area under degraded pasture (PCD). The MBC, q mic and TOC increased and qCO2 reduced under the different pasture stages. Compared to PCD, the pasture stages had higher MBC, q mic and TOC, and lower qCO2. The crop-livestock integrated system improved soil microbiological parameters and immobilized carbon in the soil in comparison to the degraded pasture.

Effects of tillage and crop rotation on chemical phosphorus forms and some related biological activities in a Chilean Ultisol

AbstractThe effect of tillage systems and crop rotation on microbial biomass phosphorus (MBP) and acid phosphatase (P‐ase) activity, and the amount of different phosphorus (P) forms measured by 31P‐NMR spectroscopy were studied on a field experiment carried out in a temperate Ultisol from southern Chile. Two tillage systems, no tillage (NT) and conventional tillage (CT) and two crop rotations, oat–wheat (OW) and lupine–wheat (LW) were evaluated 4 yr after the start of the experiment to determine the effects of such management on some soil biological parameters and P forms at three depths (0–5, 0–10 and 10–20 cm). Microbial biomass P ranged from 6.5 to 22.6 mg/kg, whereas the mean total P (PT) was 1995 mg/kg for all treatments (OW and LW). Microbial biomass carbon (MBC) and surface P accumulation (at 0–5 cm depth), including Olsen P, MBP, orthophosphate monoesters (monoester‐P), were larger under NT than CT. Tillage effects were greater than crop rotation effects in enhancing P availability. The LW rotation showed enhanced P‐ase activity and increased monoester‐P forms (57 vs. 30% of the total integral area of the spectra, in average) compared with OW. Nevertheless, OW rotation increased orthophosphate (ortho‐P), especially at 10–20 cm. Microbial biomass carbon ranged from 532 to 2351 mg/kg, which represented 1.2–4.5% of total organic C (Co). Furthermore, MBP correlated positively with MBC (r = 0.80), Olsen P (r = 0.77), Co (r = 0.77), pH (r = 0.65), PT (r = 0.65) and P‐ase activity (r = 0.57), suggesting the importance of the microbial biomass on soil P availability.

Soil enzyme and microbial activities in a grazing ecosystem of Patagonian Monte, Argentina

Grazers exert important effects on the plant–soil system influencing the structure and functioning of the ecosystems. The effect of grazing on soil enzyme and microbial activities in arid ecosystems of the Patagonian Monte (Argentina) was studied by assessing the cover of plant life forms (grasses, shrubs and dwarf shrubs) at five modal plant-covered patches at three sites across a grazing gradient. We hypothesized that grazing mostly affects negatively soil enzyme and microbial activities through its effect on vegetation and on soil chemical and physical parameters. Soil cores were extracted from plant-covered patches and associated inter-canopy areas and analyzed the chemical (organic-C, total-N and pH), physical (bulk density), microbial (microbial biomass-C, and heterotrophic microorganism counts), and enzyme (dehydrogenase, ß-glucosidase, protease, alkaline and acid phosphatase and the geometric media for these activities) soil properties. Grass and dwarf shrub covers declined, and soil pH and bulk density increased with increasing grazing intensity at plant patches and inter-canopy areas. Soil organic-C and soil-N decreased at plant patches and, were positively correlated to grass cover. Soil organic-C was also positively correlated with ß-glucosidases and phosphatases, indicating that a reduction in soil organic-C could be associated with low enzyme activity and consequently with low soil organic matter turnover and nutrient release. Negative effects of grazing on enzyme activities were also detected on protease activity at inter-canopy areas and geometric media of the enzyme activities at plant patches. Increasing grazing intensity was associated with increasing values of microbial biomass-C and heterotrophic microorganism counts mostly at inter-canopy areas, suggesting that inputs of labile N by urine and dung may partially counteract the negative grazing effects. We concluded that grazing mostly affected soil physicochemical and biological parameters through direct and indirect effects of trampling and urine and changes in perennial grass cover, respectively.

Changes in soil quality following poplar short-rotation forestry under different cutting cycles

In the last decade, the change of energy concept induced by global warming and fossil fuel depletion together with the advances in agriculture towards a multifunctional and a more sustainable use of rural areas promoted the development of biomass crops. In this regard, Populus is largely utilised in short-rotation forestry (SRF), as it is known to be a fast-growing tree, producing large yields and having a high energy potential. Most studies focused on economic-productive and energetic aspects of Populus plantations, whereas their impact on soil quality and health have been poorly investigated. In this study, the main soil chemical parameters, microbial biomass and activity were assessed aiming at evaluating the impact of Populus SRF under one, two and three-year cutting cycles (T1, T2 and T3) in comparison with an intensive food cropping system (wheat-soybean rotation, WS). In addition, arbuscular mycorrhizal (AM) fungal inoculum potential was measured using root colonisation (RC) and number of entry points (EP). In the 0-10 cm soil depth, pH, phosphorus (P), total nitrogen (N) and soil organic carbon (SOC) were significantly affected by the management. In comparison with WS, Populus SRF treatments produced significant pH decreases together with N and SOC increases, these last ones ranging from 11 to 34% and from 21 to 57%, respectively. Under T3 soil pH decreased of 0.25 units, while P, N and SOC increased of 10, 34 and 57%, respectively, in comparison with WS. Microbial biomass and soil respiration under SRF showed also mean increases of 71 and 17%, respectively. Under SRF treatments, Lolium perenne, commonly observed in all field plots, was more than twofold colonised by AM fungi in comparison with WS, while the number of EP, observed on Lactuca sativa used as a test plant, showed values ranging from 8 to 21 times higher. The present study shows the potential of a Populus SRF to improve soil chemical, biochemical and biological quality parameters in comparison with an intensive food cropping system.

Response of Pecan Orchard Soil Chemical and Biological Quality Indicators to Poultry Litter Application and Clover Cover Crops

Little information is available regarding the activity of soil quality biological indicators in southeastern U.S. pecan [Carya illinoinensis (Wangenh.) K. Koch] orchards. The objectives of this study were to examine the effect of poultry litter application and the use of crimson clover (Trifolium incarnatum L.) as a cool-season cover crop on soil chemistry and soil quality biological indicators, including mycorrhizal inoculum potential (MIP), microbial biomass carbon (MBC), and phosphatase activity in a southeastern U.S. Coastal Plain pecan orchard system. The use of clover as a cool-season cover crop between tree rows provided multiple benefits for pecan orchard soil quality, including increased MIP and MBC. Soil phosphatase activity was also enhanced by clover during two of the three years of study. Soil elemental properties, including total nitrogen (N), and soil organic matter (SOM) were also enhanced by clover and/or poultry litter, although there was an obvious time lag in the response of soil N to the treatments. Poultry litter application increased soil phosphorus (P) but did not consistently enhance soil biological activity parameters. At times, poultry litter appeared to neutralize or minimize the positive effects of clover on MIP.

Conservation tillage, optimal water and organic nutrient supply enhance soil microbial activities during wheat (Triticum Aestivum L.) cultivation.

The field experiments were conducted on sandy loam soil at New Delhi, during 2007 and 2008 to investigate the effect of conservation tillage, irrigation regimes (sub-optimal, optimal and supra-optimal water regimes), and integrated nutrient management (INM) practices on soil biological parameters in wheat cultivation. The conservation tillage soils has shown significant (p<0.05) increase in soil respiration (81.1%), soil microbial biomass carbon (SMBC) (104%) and soil dehydrogenase (DH) (59.2%) compared to the conventional tillage soil. Optimum water supply (3-irrigations) enhanced soil respiration over sub-optimum and supra-optimum irrigations by 13.32% and 79% respectively. Soil dehydrogenase (DH) activity in optimum water regime has also increased by 23.33% and 8.18% respectively over the other two irrigation regimes. Similarly, SMBC has also increased by 12.14% and 27.17% respectively in soil with optimum water supply compared to that of sub-optimum and supra-optimum water regime fields. The maximum increase in soil microbial activities is found when sole organic source (50% Farm Yard Manure+25% biofertilizer+25% Green Manure) has been used in combination with the conservation tillage and the optimum water supply. Study demonstrated that microbial activity could be regulated by tillage, water and nitrogen management in the soil in a sustainable manner.

Recuperação de solos degradados na exploração mineral de cassiterita: biomassa microbiana e atividade da desidrogenase

A avaliação da qualidade ambiental assume grande importância em programas de recuperação de áreas degradadas, razão pela qual se faz necessário o desenvolvimento de sistemas quantitativos, com base em combinação de indicadores que melhor representem as condições de degradação ou recuperação em curso. O presente trabalho utiliza-se de parâmetros biológicos do solo como a biomassa microbiana e a atividade de desidrogenase, além da análise do material vegetal, para verificar a influência do plantio sucessivo de leguminosas em um solo minerado em processo de recuperação. A atividade microbiana foi determinada a partir da quantificação do carbono e o nitrogênio da biomassa microbiana (BMC e BMN respectivamente), da atividade da desidrogenase e da hidrólise do FDA avaliadas em uma área de piso de lavra após um, dois e três anos de plantio consecutivos de leguminosas e de uma área de deposição de rejeito após um ano de plantio de um mistura de leguminosas: feijão guandu, mucuna preta e crotalária juncea, comparados com o solo sob mata e com áreas sem plantio. O uso dos indicadores biológicos: biomassa microbiana e atividade de desidrogenase, e da análise do material vegetal na avaliação das técnicas e estratégias de recuperação adotadas revelaram que o plantio de leguminosas e sua posterior incorporação vêm promovendo alterações graduais positivas no solo degradado, principalmente em relação à BMC em áreas após o plantio consecutivo de três anos de leguminosas.

Grain Yield, Yield Components, Soil Fertility, and Biological Activity under Organic and Conventional Rice Production Systems

A field experiment was conducted for 2 years on a clayey Vertisol to compare the organic and conventional methods of rice farming. Two main plot treatments were with and without plant protection and four subplot treatments were (1) control (CON); (2) inorganic fertilizers (CF); (3) organics (OF), and (4) inorganics + organics (integrated nutrient management, INM). The organics were green manure, paddy straw, and poultry manure. After 2 years, the main plot effects were not significant in terms of crop productivity though there was a reduction in soil biological parameters. Increase in grain yield was larger with inorganics and INM as compared to the organics because of the higher panicle number. However, organics increased the microbial populations, biomass carbon, nitrogen, enzyme activities, and soil fertility as compared to inorganics. Thus, organics improved the nutrient availability by influencing the soil biological activity although it did not reflect in greater yields.

Short Communication. Effect of saline soil parameters on endomycorrhizal colonisation of dominant halophytes in four Hungarian sites

Soil and root samples were collected from the rhizosphere of dominant halophytes (Artemisia santonicum, Aster tripolium, Festuca pseudovina, Lepidium crassifolium, Plantago maritima and Puccinellia limosa) at four locations with saline soils in Hungary. The correlations- between arbuscular mycorrhiza (AM) fungal colonisation parameters (% colonisation, % arbuscules) and soil physical, chemical and biological parameters were determined Endomycorrhiza colonisation was found to be negatively correlated with the electric conductivity of the soil paste, the salt-specific ion concentrations and the cation exchange capacity, showing the sensitivity of AM fungi at increasing salt concentrations, independently of the types of salt-specific anions. A positive correlation was detected between the mycorrhiza colonisation and the abundance of oligotroph bacteria known to be the less variable and more stable (k-strategist) group. This fact and the negative correlation found with the humus content underlines the importance of nutrient availability and the limitations of the symbiotic interactions in stressed saline or sodic soils.