Scielo RSS <![CDATA[Journal of soil science and plant nutrition]]> vol. 15 num. 4 lang. es <![CDATA[SciELO Logo]]> <![CDATA[<b>Response of microbial activity and biomass to soil salinity when supplied with glucose and cellulose</b>]]> Two incubation experiments were carried out to determine the impact of salinity on microbial activity and biomass when organic carbon is supplied as different proportions of glucose and cellulose or when glucose and cellulose were added every 2 weeks in different order. The first experiment was conducted with a non-saline soil and two saline soils (ECe 11 and 43 dS m-1) amended with 5 g C kg-1 as different percentages of glucose and cellulose: glucose: 100% and 0-20% and cellulose: 0-100%. In the second experiment a non-saline loamy sand soil was used which was salinized to ECe 12.5 and 37.4 dS m-1. The C form was maintained or changed over time by addition of 1.5 g C kg-1 every two weeks as glucose or cellulose. In Experiment 1, mixing glucose with cellulose increased cumulative respiration compared to cellulose alone. Cumulative respiration increased with increasing proportion of glucose in the combined treatments with glucose >2.5%.With 100% glucose, cumulative respiration was significantly lower than in the non-saline soil only in EC43. But with 100% cellulose and all combined treatments, cumulative respiration was significantly lower than in the non-saline soil in EC11 and EC43. Cumulative respiration did not differ between EC11 and EC43 with 100% cellulose but decreased significantly in the mixed treatments except with 10% glucose. In Experiment 2, cumulative respiration in the first period (0-14) was always higher with glucose than with cellulose; it decreased with increasing EC. The impact of salinity was smaller when C was added repeatedly compared to a single addition. Cumulative respiration increased when glucose was added after cellulose addition. In conclusion, mixing small amounts of glucose with cellulose could make microbes more sensitive to salinity compared to 100% cellulose. Further, maintaining high C availability with repeated C addition reduces the negative impact of salinity on soil microbes. <![CDATA[<b>Enzymes in the rhizosphere of plants growing in the vicinity of the Polish Arctowski Antarctic Station</b>]]> In maritime Antarctica soil enzymes have been little researched, mainly in the rhizosphere of the only two vascular plants that grow there: Colobanthus quitensis and Deschampsia antarctica. This study evaluated the activities of hydrolytic enzymes β-glucosidase, phosphatase and urease in the rhizospheric soils of C. quitensis and D. antarctica from three different sites in the Polish Arctowski Station in Antarctica. The sensitivity to temperature changes of the enzymes was also evaluated using two incubation temperatures (37 and 12 °C). The highest activities related to the C and P cycles, β-glucosidase and acid phosphatase, respectively, were detected in the rhizospheric soils at the site with the greatest variety of plant cover. Urease activity, related to the N cycle, was high in two of the three sites, and the lowest activity was detected at the site where only D. antarctica was found. The activity of the enzymes decreased when the temperature of incubation was reduced, but the magnitude of the decrease depended on the enzyme. β-glucosidase was the most sensitive to temperature change, whereas urease was least affected. Therefore, temperature changes in rhizospheric soils could lead to changes in substrate degradation rates and consequently in the availability of nutrients (C, N and P) for C. quitensis and D. antartica in maritime Antarctica. <![CDATA[<b>Biofortification of cowpea beans with iron</b>: <b>iron´s influence on mineral content and yield</b>]]> Iron (Fe) deficiency is the most prevalent nutrient deficiency worldwide. Agronomic biofortification is an agricultural strategy for improving the micronutrient concentrations in staple food plants. At present, fertilization is a major vehicle for changing plant mineral contents and food quality. A greenhouse study was conducted to assess the effects of iron chelate and ferrous sulfate applications on the biofortification of Fe and its impacts on the mineral content and yield of cowpea beans. Four application rates of both forms were tested (0, 25, 50, and 100 µM L-1) for 40 d. The amount and type of Fe application affected the mineral seed content, yield and yield components. Applying of Fe in the form of ferrous sulfate at 25 µM L-1 was found to be the optimal rate for biofortifying the cowpea bean plant, because it favored the seed yield and increased the bioavailable Fe content in the seeds over that of the control. The best iron chelate rate was 100 µM·L-1. Thus, it was considered feasible to implement an Fe fertilization program to improve the nutritional quality of cowpea bean crops by increasing the Fe concentrates in the seeds. <![CDATA[<b>Assessment of microbial biomass and enzyme activities in soil under temperate fruit crops in north western himalayan region</b>]]> Microbial communities are important for the functioning of the ecosystem, both in relation to direct interactions with the plants and with regard to nutrient and organic matter recycling. A study in field condition was undertaken in Kashmir valley to reveal the effect of various temperate fruit crops viz. apricot, peach, plum and cherry along with a control (no-plantation) on microbial biomass carbon (MBC), nitrogen (MBN), phosphorus (MBP) and dehydrogenase, phosphomonoesterase (acid and alkaline) and urease activities in soil at two different depths (0-20 and 21-40 cm). All the fruit crops showed a sharp decline in microbial biomass and enzyme activities with the increase in soil depth. Each of the four fruit crops showed significant (p<0.05) impact on MBC over the control and the maximum MBC was recorded in plum (1000 mg kg-1) and the lowest value was observed in control (457 mg kg-1), at the surface layer. Since there is a relationship between MBC and MBN, the similar trend was also observed in MBN as in case of MBC. For MBP, fruit crops showed any significant effect neither on surface soil, nor on subsurface soil layer over control. At the surface layer, unlike microbial biomass the highest dehydrogenase activity was observed in peach (318 mg TPF g soil-1 h-1) and the lowest value (166 mg TPF g soil-1 h-1) was attained at control plot. Maximum alkaline phosphomonoesterase activity was observed in peach (381 mg PNP g soil-1 h-1), although for acid phosphomonoesterase the highest value recorded in apricot (306 mg PNP g soil-1 hr-1), at surface soil. A significant positive correlation (p <0.01) was observed amongst MBC, MBN and MBP. Both the phosphomonoesterase activities were significantly (p <0.05) correlated with MBP in soil. It can be concluded that the influence of the studied fruit crops on the soil was not uniform, in terms of the measured parameters. <![CDATA[<b>Interaction of arbuscular mycorrhizal inoculants and chicken manure in avocado rootstock production</b>]]> The nursery stage of avocado plant production provides the best opportunity for introducing mycorrhizal inoculants. Three single-species inocula (Acaulospora laevis, Cetraspora pellucida and Pacispora scintillans), an inoculum using a consortium of these three species, an inoculum from a native orchard mycorrhizal community and an uninoculated field soil control were compared experimentally using a factorial experimental design in combination with 8, 17, or 25 g of chicken manure per kg soil. The height, stem diameter, number of leaves, pathogen damage level, and herbivory in "criollo" avocado rootstocks were recorded every two weeks. The leaf area, biomass and mycorrhizal colonization of the roots were measured 7 months after sowing. Overall, responses to mycorrhizal inoculation were minor and increasing fertilization negatively affected most variables. The best inocula were the Cetraspora pellucida and native orchard mycorrhizal community inocula. The negative effects of high chicken manure fertilization on plant growth and health have important implications for nursery management because chicken manure is a preferred fertilizer. <![CDATA[<b>Impact of mechanically pre-treated anaerobic digestates on soil properties</b>]]> The production of biogas by anaerobic digestion results in the production of digestates, which are intended to be used as organic fertilizer in agriculture. However, these anaerobic digestates (AD) - besides having benefits for the nutrient status of soils - are assumed to have adverse consequences for soil properties. It is thus the objective of this study to determine the effects of 30 m³ ha-1 of AD´s on pH, electrical conductivity (EC), and the wetting behavior determined by the Repellency Index (RI) and the contact angle (CA) of a loamy Cambic Luvisol and a sandy Podzol. The AD´s, derived from mechanically pre-treated (grinding/chopping) input substrates (IS) from maize (Zea mays L.) and sugar beet (Beta vulgaris L.) in variable shares (100 %, 80 % / 20 %), were mixed with homogenized (sieved to ≤ 2 mm) soils by stirring. Blending of the AD increased the EC significantly and induced more alkaline conditions; the extent of this change was highly dependent on soil texture. The use of AD derived from ground IS resulted in more hydrophobic conditions compared to AD from chopped IS. This leads in the current study to the conclusion that the mechanical pre-treatment of the IS for anaerobic digestion and also the soil texture are decisive factors controlling both the physicochemical and the hydraulic effects of digestates to the soils. <![CDATA[<b>Stabilization of nickel in a contaminated calcareous soil amended with low-cost amendments</b>]]> A laboratory study was planned to delineate the benefits of some low-cost soil amendments on Nickel (Ni) stabilization in a Ni-spiked soil. Six different kinds of amendments were evaluated by desorption kinetic test and sequential extraction procedure to determine their ability to reduce mobility of Ni in a Ni-spiked soil. The Ni-spiked soil was separately incubated with coal fly ash (CFA), rice husk biochars prepared at 300 °C (B300) and 600 °C (B600), municipal solid waste compost (MSWC), zero valent iron (Fe0) and zero valent manganese (Mn0) at 2 and 5% (W/W) for 45 and 90 days at 25 °C. The kinetic data obtained from 0.01 M EDTA was used to simulate desorption equations. The Sequential extraction method was also used as a suitable method for identification of chemical forms of Ni and its mobility. According to the results, application of amendments reduced exchangeable and carbonate forms of Nirate with respect to control treatment. Changes in chemical forms of Ni and their conversion into less soluble forms in treated soils was observed with incubation time. Application of Mn0, Fe0, CFA, and B300 to soil samples significantly decreased Ni desorption rate compared to the control treatment. The lowest Ni release was achieved by Mn0-treatment at 5%. Biphasic pattern of Ni desorption kinetic was fitted well by the model of two first-order reactions. From the practical point of view, Fe0, Mn0, CFA, and B300 treatments are effective in Ni stabilization, while using Mn0 and Fe0 at 5% can be recommended for immobilization of Ni from calcareous polluted soil. <![CDATA[<b>Influence of the rhizosphere in a biopurification system on the dissipation of a pesticide mixture</b>]]> In a biopurification system such as a biobed, the rhizosphere of the grass layer may be a significant factor for promoting pesticide dissipation in the biomixture. The rhizosphere effect of a Lolium perenne, Festuca arundinacea and Trifolium repens mixture on the dissipation of a pesticide combination that was composed of atrazine, chlorpyrifos and isoproturon was studied. The assay was performed using glass pots divided into two separate compartments (root surface and root-free), each filled with an organic biomixture (oat husk, top soil and peat) and contaminated with the pesticide mixture at 5 mg kg-1.Non-planted and non-contaminated pots were also used as controls. The results indicated that there were high atrazine, chlorpyrifos and isoproturon dissipation in the planted pots compared with the unplanted pots. An inverse correlation was found throughout the assay between phenoloxidase activity and residual pesticide (0.684 to 0.952). Indeed, fungal biomass was positively correlated with phenoloxidase activity on day 1 (r =0.825) and day 30 (r =0.855). Besides, exudation of oxalic and malic acid in contaminated pots was higher than in the control without pesticides, associated with oxidation of the pesticide mixture in the biomixture of a bioded system. Therefore, the grass layer enhances pesticide removal in biobeds. <![CDATA[<b>Nitrogen and potassium application by fertigation at different watermelon planting densities</b>]]> The effects on the production of ,Top Gun, watermelons were evaluated at N and K (N+K2O) doses via fertigation of 79.8+106.7, 106.4+142.2, 133.0+177.7, and 159.6+213.2 kg ha-1 and at plant spacings of 0.5, 1.0, 1.5, and 2.0 m. The experiment had a split-plot randomised block design with three replicates. N+K2O doses and plant spacings were randomised in the plots and subplots, respectively. We evaluated foliar N and K contents, average mass of commercial fruits (MF), total (FT) and commercial (FC) number of fruits, and total (PT) and commercial (PC) productivity of weight classes 6-8, 8-10, 10-12, and >12 kg per area and plant. The N+K2O doses only influenced the foliar K content. The other variables were not influenced by the interaction of factors or by the N+K2O doses. Plant spacing influenced fruit number and production. Reducing plant spacing from 2.0 to 0.5 m decreased MF, FT, FC, PT, and PC of the classes per plant but increased FT, FC, PT, and PC of the 6-8 and 8-10 kg classes per area. <![CDATA[Determination of the fluorescence spectrum of <i>Botrytis cinerea</i> Pers: Fr. isolated from highbush blueberry (<i>Vaccinium corymbosum</i> L.)]]> The prompt diagnosis of an attack by phytopathogens associated with the deterioration of the quality and condition of highbush blueberry is of great interest, particularly when dealing with Botrytis cinerea in pre- and postharvest stages. Real-time technologies that complement traditional diagnostic methods during the processing, storage and transport of fruit are advisable. The aim of this study was to determine the fluorescence spectrum of the B. cinerea mycelium in culture medium as well as its temporal variation. Two evaluations were conducted daily for 18 days using a fluorimeter with a 100 mW, 405 nm laser light, which excited the mycelium of each of five isolates of B. cinerea in two fixed positions. The fluorescence emission of the malt agar culture medium and the emission obtained from the fungus Trichothecium roseum were quantified for comparative reference. It was found that B. cinerea fluoresces mainly in the red-infrared area of the spectrum and T. roseum does so with greater intensity in the green-red segment. The energy of the fluorescence spectrum did not vary significantly according to the development of the B. cinerea mycelium in artificial culture medium. <![CDATA[<b>Foliar application of micronutrients on essential oils of borago, thyme and marigold</b>]]> To study the effect of micronutrients foliar applications in medicinal plants contain of Borago, Calendula and Thyme on yield and essence production, the investigations were performed in complete randomized block design with 3 replications at 2011 and 2012 in Shahrekord, Iran. Results showed that Fe2+, Cu2+, Zn2+ and Mn2+ applications on flavonoids, phenols, carotenoids, essence percentage, fresh/dry flower matter, number of flowers, and root/shoot dry/fresh matter in Borago officinalis and Calendula officinalis L.; carvacrol and thymol percentage, essence percentage, number of stem, height, and root/shoot dry/fresh matter in Thymus vulgaris L.,the combinations of 400ppm of Fe, Cu,Zn and Mn (Fe3Cu3Zn3Mn3) produced the greatest amounts in most of measured characters. The most of phenols, carotenoids and flavonoids in Calendula and Borago; thymol and carvacrol in Thyme; weight of dry flower and number of flower per plant in two seasons were produced by Fe3Cu3Zn3Mn3treatment. <![CDATA[<b>Comparative study of methodologies to determine the antioxidant capacity of Al-toxified blueberry amended with calcium sulfate</b>]]> Blueberry (Vaccinium corymbosum L.) is well adapted to acidic soils where aluminum (Al3+) can be linked to oxidative stress and antioxidant capacity (AC). Calcium sulfate (CaSO4) is used to alleviate Al3+ because it does not alter soil acidity. However, the role of Ca addition in AC, based on a single electron transfer reaction (SET), remains unknown.The aim was to evaluate the AC using SET methodologies, i.e., 2,2-diphenyl-2-picrylhydrazyl (DPPH), 2,2´-Azinobis-bis (3 ethylbenzothiazoline-6-sulphonic acid) (ABTS) and ferric reducing-antioxidant power (FRAP). Blueberry cultivars Elliot and Jersey were grown and exposed to the following treatments for 15 days: Control (nutrient solution alone, pH 4.5); control+Al (Al); control+Al+Ca (Al+Ca) and control+Ca (Ca). The Ca and Al concentrations, total phenol (TP) content and radical scavenging activity (RSA) were evaluated at 7 and 15 days. The Al+Ca and Ca treatments increased the Ca concentration in the leaves (22%) and roots (40%) of both cultivars compared with the control. The Ca in the tissues varied with cultivar and time. After 15 days, increases in TP, DPPH, ABTS and FRAP were detected. The cultivars showed positive relationships between the TP and AC in the leaves and roots. Thus, CaSO4 is an important tool to improve the AC in Al-stressed fruit crops grown in acid soils. <![CDATA[<b>Effects of decreasing levels of n amendments on organic “granny smith” apple trees</b>]]> The effect of decreasing levels of organic N-fertilization on fruit production, mineral composition and fruit quality was evaluated in organically cultivated “Granny Smith” apples trees. Treatments included the application of decreasing levels of N fertilization (100 kg N ha-1, 75 kg N ha-1, 50 kg N ha-1 and 0 kg N ha-1 ) applied as fossilized red guano (50% of the total amount of N) and blood meal (50% of the total amount of N) to twelve years old Granny Smith apple trees. Yield was not affected by the treatments (yield ranged from 0.28 to 0.4 kg cm-2 SCSA). Fruit mineral concentration and ratios were not affected by treatments. Fruits showed low Ca concentrations (2.8 to 3.3 mg Ca 100 g-1 FW), high levels of K (118.6 to 130.1 mg K 100 g-1 FW) and high values for K+Mg/Ca (> 12) and K/Ca (> 30) ratios. Mineral concentration on leaves was not affected by treatments (normal concentrations for macro and microelements). Bitter pit was only detected after 60 days of storage (100 kg N ha-1 tree, 1.1 in a scale 1-4). Besides orchard nitrogen management, fruit mineral ratios and Ca foliar applications should be considered for managing fruit production and quality in organic apples. <![CDATA[<b>Wild type and <i>vte<sub>4</sub></i> mutant <i>Arabidopsis thaliana</i> responses to different water frequencies</b>: <b>genetic engineering towards stress tolerance</b>]]> Growth and development of plants are severely affected once exposed to soil water deficit. In addition, plants experience different levels of water stress in which their adaptation and response will be different. In this paper, we sought to investigate the growth, development and water relations of both wild-type (Col-0) and vte4 mutant Arabidopsis thaliana under different water frequencies. These water treatments, including control condition, 4 days of water withholding and 8 days of water withholding were imposed on the plants. Each water treatment was replicated three times in a complete randomized design with factorial arrangement. Wild type and mutant A.thaliana plants were subjected to the abiotic stress (water stress) for up to 24 days. The results indicated that under water stress, the performance of wild type plants were stronger than vte4mutants. Under control condition, specific leaf area, rosette dry weight and rosette dry weight at bolting of wild type A.thaliana scored the highest values of 47.66 mm²/mg, 13.67 mg and 201.5 mg, respectively in comparison with vte4mutant. However, both wild type and vte4mutant plants were negatively affected as the water treatments continued. The root mass fraction showed an increase in vte4 mutant and wild type A.thaliana as they scored 0.136g/g and 0.17 g/g, respectively. Under the same treatment, water potential indicated a reduction for both plan types where vte4and wild type plants obtained the values of -1.4 and -1.3 MPa, respectively after 24 days of stress initiation. As a result, our findings suggested that different water treatments significantly differed in growth characters in which the absence of γ-tocopherol methyltransferase (γ -TMT) gene in vte4had an impact on the plant’s response towards the water deficit. <![CDATA[<b>Crucial variations in growth and ion homeostasis of <i>Glycine gracilis</i> seedlings under two types of salt stresses</b>]]> Based on Glycine gracilis growth and ion homeostasis testing, neutral salt (NS)and alkaline salt (AS) stress were characterized and the responses of G. gracilis were investigated.The injurious effects of AS on G. gracilis were obviously stronger than those of NS.The effects of both stresses on the Na+ content and Na+/K+ ratio were similar at low concentrations, but as the stress increased, the effects of a greater Na+ content and Na+/K+ratio increased slowly under NS conditions, but sharply under AS. The roots of G. gracilis accumulated NO3−and H2PO4−, while the stems and leaves accumulated C2O4(2−) and H2PO4−to maintain thein tracellular ion balance. The dominant intracellular anions in the stipes were NO3- and C2O4(2-) under control conditions, and NO3- and H2PO4- under salt stress. With the increasing AS, the Cl−, NO3− and H2PO4− concentrations decreased, and G.gracilis might have increased SO4(2−) and C2O4(2−)levels to compensate for the shortage of inorganic anions. Under NS, the NO3− and C2O4(2−) concentrations decreased, and G. gracilis might have increased Cl−, H2PO4− and SO4(2−)levels to compensate for the shortage of inorganic anions. G. gracilis seedling showed a special nutritional metabolism and some growth adaptability under salt stress. <![CDATA[<b>Chemical speciation and suitability of soil extractants for assessing Cu availability to maize (<i>Zea mays</i> L.) in acidic soils</b>]]> Twenty surface (0-15 cm) samples of acidic soils were analysed for different chemical fractions of soil Cu namely; water soluble (WS), exchangeable (EX), lead displaceable (Pb-disp.), acid soluble (AS), Mn oxide occluded (MnOX), organically bound (OB), amorphous Fe oxide occluded (AFeOX), crystalline Fe oxide occluded (CFeOX), residual (RES) and also for soil extractable Cu using DTPA (pH 7.3), DTPA (pH 5.3), AB-DTPA (pH 7.6), Mehlich 3 (pH 2.0), Modified Olsen, 0.005 MCaCl2, 1 M MgCl2 extractants and ion exchange resins to understand the significance of different chemical fractions of Cu and suitability of soil extractant for predicting Cu availability to maize plants. Chemical fractions of Cu in acidic soils could be arranged in the following order: RES > MnOX > AFeOX > OB > CFeOX > AS > EX > Pb-disp. > WS. Chemical fractions of Cu in acidic soils and Cu extracted by the examined soil extractants were correlated with general soil properties. Water soluble (WS) and organically bound (OB) fractions of soil Cu showed significant and positive correlation with Cu uptake by maize. Among different examined soil extractants, DTPA (pH=5.3) and Mehlich 3 (pH = 2.0) showed significant and positive correlation with the dry matter yield, Cu concentration and uptake by maize plants in acidic soils. <![CDATA[<b>The effect of inoculation with mycorrhiza</b>: <b>AM on growth, phenolics, tannins, phenolic composition and antioxidant activity in <i>Valeriana jatamansi</i> Jones</b>]]> The mycorrhizal inoculation often reported to increase plant growth and secondary metabolites production, however, little is known on the effect of arbuscular mycorrhizal fungi (AMF) on different growth parameters in Valeriana jatamansi, an important Himalayan medicinal herb. To evaluate mycorrhiza leffect, V. jatamansi collected from natural population were planted and growth parameters, phytochemicals, antioxidant and phenylalanine ammonia lyase (PAL) activities were determined. Significantly (p<0.05) higher above ground fresh weight (AGFW), above ground dry weight (AGDW), below ground fresh weight (BGFW), below ground dry weight (BGDW) were recorded in plants after the 2nd year. The total phenolics were maximum in aerial [18.03±0.05 (1st year) and 10.88±0.52mg GAE/g (2nd year)] and root portions [(14.30±0.04 (1st year) and 7.92±0.27 (2nd year)] of the treated plants as compared to corresponding portions of control plants in both the years. Similarly, the tannin content was higher in treated plants as compared to untreated controls. Variation in different phenolic compounds was also recorded and significantly higher contents of gallic acid, chlorogenic acid, Catechin, and Hydroxy benzoic acid during 1st year was observed. Antioxidant activity of aerial and root portion measured by three in vitro assays, showed significant variation (p<0.05) among plants of both the years. Significantly (p<0.05) higher PAL activity was recorded in treated over control plants in 2nd year. The results demonstrated that inoculation with AMF enhances both phenolics and tannins as well as stimulates antioxidant activity suggesting a positive influence of AMF inoculation on yield and for the production of nutraceuticals. <![CDATA[<b>Exogenous silicon nutrition ameliorates salt-induced stress by improving growth and efficiency of PSII in <i>Oryza sativa</i> L. cultivars</b>]]> Nutrient management of plants is the most practical and easiest way of combating salt stress. The effect of silicon (Si) nutrition on salt stress symptoms was investigated in hydroponically grown rice seedlings. Seeds from Khazar (salt sensitive) and Zayandehrood (salt tolerant) cultivars of rice were exposed to 0 and 100 mM NaCl in the absence and presence of silicon (3 mM) using sodium silicate. Plant growth parameters, sodium (Na+) and potassium (K+) concentrations, Si accumulation, chlorophyll content and efficiency of PSII (Fv/Fm) were determined in 25 days old seedlings exposed to salinity for 96 h. The results showed that salt stress generally inhibited seedling growth and reduced photosynthesis efficiency. However, the addition of Si significantly decreased shoot Na+ concentration, but increased Si uptake. Additionally, in salinized plants, the addition of Si increased Fv/Fm in Khazar cultivar. It could be concluded that Na+ concentration, Si accumulation and Fv/ Fm ratio play key role in salinity stress tolerance. Application of Si, however, alleviated to some extent detrimental effects of salinity stress by improving growth and physiological performance of both cultivars under saline conditions. <![CDATA[<b>Effects of land use change on P bioavailability determined by chemical fractionation and <sup>31</sup>P-NMR spectroscopy in a <i>Nothofagus</i> forest and adjacent grassland</b>]]> The aim of this study was to compare P bioavailability in a Nothofagus rainforest Andisol (FS) and an adjacent clear-cut grassland soil (GS) in southern Chile to evaluate the effects of land use change on P chemical forms determined by chemical fractionation and 31P-NMR spectroscopy. Total phosphorus (P), Olsen P, microbial P, different soil P fractions (determined using a modified Hedley procedure), 31P-NMR spectroscopy results, acid phosphatase (P-ase) activity, pH and organic C were analyzed and compared. Forest samples were collected from the mineral soil at a depth of 2-20 cm and were compared with those collected from grassland soil at the same depth. Total P ranged from 2028 mg kg-1 (FS) to 2157 mg kg-1 (GL)and total organic P ranged from 829 mg kg-1 (FS) to 1176 mg kg-1 (GL). On the contrary, Olsen P, microbial P, labile P and P-ase activity were higher in the evergreen forest soil than in the grassland, with the predominance of the moderately labile (NaOH-Po) fraction, which ranged from 668 to 720 mg kg-1 in both soils. Phosphorus was mainly present in monoester-P form in the NMR extract in both soils (67 % on average). Other 31P-NMR signals were identified as C2-myo-inositol phosphate and scyllo-inositol hexakisphosphate. The results suggest that land use change from forest to grassland will reduce P bioavailability and P-ase activity. <![CDATA[<b>The effects of neem extract and azadirachtin on soil microorganisms</b>]]> Both neem extract and azadirachtin are widely used in agriculture as organic pesticides because they are nontoxic to humans, animals, and the environment. However, their effects on soil microorganisms and plant growth-promoting rhizobacteria (PGPR), which directly affect soil quality, remain largely unexplored. In this study, the effects of neem extract and azadirachtin on the activity of soil microbes and rhizosphere microorganisms was evaluated. We found that 0.1 and 0.4 gmL-1 of the extract and 1.25 and 2.5 µgmL-1 of azadirachtin inhibited the activity of soil microorganisms in vitro. Treating soil with azadirachtin for two months reduced the number of microorganisms present, while two months of treatment with neem extract increased the number of microorganisms in both the soil and the rhizosphere. The phytopathogenic bacterium Pectobacterium carotovorum was more resistant to azadirachtin than Rhizobium sp. Moreover, treatment of mung beans with neem extract or azadirachtin reduced the number of root nodules and Trichoderma asperellum in the rhizosphere, when compared to the control.