Scielo RSS <![CDATA[Journal of soil science and plant nutrition]]> vol. 11 num. 2 lang. es <![CDATA[SciELO Logo]]> <![CDATA[<b>EFFECTS OF POST-EMERGENCE HERBICIDES ON IN VITRO GROWTH OF FUSARIUM OXYSPORUM ISOLATED FROM RED CLOVER ROOT ROT</b>]]> In Chile, Fusarium root rot reduces red clover (Trifolium pretense L.) pasture yield and persistence. Fusarium oxysporum (Schlect.) is the most prevalent pathogen in diseased red clover plant roots. Agronomic management of red clover includes applying herbicides such as MCPA, 2,4-DB, flumetsulam, bentazon, and haloxyfop-methyl. In addition to weed control, herbicides can modify disease development, generally as a result of the interaction between direct effects on the pathogen and indirect effects via plant-mediated responses. The objective of this study was to evaluate the influence of these herbicides on in vitro growth of F. oxysporum at four application rates 0, 50, 100, and 200% at the field-recommended active ingredient rate. Herbicides were amended on Petri dishes containing potato dextrose agar (PDA) and buffer MUB (tris-hydroxymethyl-aminomethane). Fusarium oxysporum was cultivated at 22°C for 25 days and colony area was measured every 5 days. The herbicides MCPA and Flumetsulam had no effect on fungal growth. 2,4-DB showing an inverse dose effect on fungal growth varying between 16 and 35% at the end of the experimental period. The contact herbicide Bentazon exhibited the strongest inhibitory effect on F. oxysporum development by the application of the field recommended rate, with a 54% decrease with regard to the control at the end of the experiment. Haloxyfop-methyl showed the highest colony stimulation since 15 days after of the application, increasing 29% the colony area respect to the control at the end of the experiment. These results suggest that applying some herbicides to red clover could affect soil pathogens such as Fusarium oxysporum, increasing or inhibiting its development. <![CDATA[MOLYBDATE TRANSPORT IN THE <b><i>Bradyrhizobium japonicum </i></b>- <b><i>Glycine max </i></b>L. SYMBIOSIS]]> For the molybdoenzymes synthesis as the nitrogenase, the molybdenum, in its most stable form, the molybdate, must be transported inside the cell. In Bradyrhizobium japonicum, the modABC genes code for a high-affinity ABC-type molybdate transporter. This work allowed to study the effect of inoculation of soybean plants with strains affected in the molybdate transport. modA and modB mutants, unable to grow in culture media under molybdate-deficient conditions, were used in our experiments. When soybean plants were inoculated with one of these strains and grown in a molybdate-deficient mineral solution did not affect the nodulation, but the nitrogen-fixing ability of the mod mutants was severely impaired. Addition of molybdate to the nutrient mineral solution used for plant growth fully restaured the wild-type phenotype, and the amount of molybdate required for supression of the mutant phenotype was dependent on sulfate concentration. Molybdate concentration required for the functioning of the mutant strains was greater when the medium was supplemented with high amounts of sulfate. Our results suggest the existence in B. japonicum, at least, three independent molybdate transport systems, a high-affinity transporter encoded by the modABC genes, a low affinity system corresponding to a sulfate transporter, and a third transporter that would be functional in the presence of high sulfate concentrations. <![CDATA[<b>THE INFLUENCE OF ARBUSCULAR MYCORRHIZAL COLONIZATION ON THE GROWTH PARAMETERS OF CAPE GOOSEBERRY <i>(Physalisperuviana </i>L.) PLANTS GROWN IN A SALINE SOIL</b>]]> With the objective of determining whether arbuscular mycorrhizal (AM) colonization would alleviate salt stress on the growth of cape gooseberry plants, a saline soil (ECs of 5.65 dS m-1, available phosphorous of 48.1 mg kg-1) was inoculated with AM fungi (Mycoral®) (+AM) and compared to a non-inoculated saline soil (-AM). The open-field experiment was conducted over the course of 131 days on the Marengo farm of the Universidad Nacional de Colombia (near Bogotá, 4°42' N, 74°12' W, 2543 m a.s.l., 14°C mean temperature, and 800 mm a-1 precipitation) where the plants were irrigated with water (ECs of 1.65 dS m-1) from the salt-contaminated Bogota river. Mycorrhizal dependence, AM colonization, relative field mycorrhizal dependency (RFMD100), dry matter (DM) accumulation and growth parameters (unit leaf rate [ULR], leaf area ratio [LAR] and specific leaf area [SLA]) were determined. The percentage of AM-colonization was 29.7% in +AM plants, but only 12.5% in -AM plants. The RFMD100 index peaked at day 61 (42.5%) and decreased to 7.8% by day 89. Inoculation with AM fungi increased plant dry matter accumulation by 7%, especially stem DM, compared to -AM plants. Generally, growth rates were higher in the +AM plants; ULR increased more in the second half of the experiment in inoculated plants compared to non-inoculated. The mycorrhizal infection enhanced leaf area growth, which resulted in increased LAR and SLA, especially during the initial phases of the experiment. <![CDATA[<b>IDENTIFICATION OF HYDROLOGICAL FACTORS CONTROLLING PHOSPHORUS CONCENTRATION IN DRAINAGE WATER IN SANDY SOILS</b>]]> The relationship between total phosphorus (TP) and molybdate-reactive phosphorus (MRP) concentrations in subsurface drainage waters in the hydrological conditions prevailing during autumn and spring flow events was statistically analysed using multiple linear regression analysis. Data on hydrological conditions in three drainage experimental plots in a loamy sand in south-east Sweden complemented with DRAINMOD-predicted data were used as independent variables. Regression models explained at least 80% of the variation in TP and MRP concentrations in drain outflow, based on adjusted coefficient of determination (R²adj) calculations. DRAINMOD-predicted cumulative infiltration (INFILcum) was identified as the most important hydrological condition controlling TP and MRP concentrations in drain outflow in three autumn events and in two out of three spring events. This suggests that the first infiltrating water found more soluble P forms available for transport, after which TP and MRP concentration in drainage outflows gradually decreased during the flow events. <![CDATA[<b>BIOFERTILIZERS AND COMPOSTING ACCELERATORS OF POLLUTING MACROPHYTES OF A COLOMBIAN LAKE</b>]]> Composting of the macrophytes Eichhornia crassipes (water hyacinth) and Egeria densa (Brazilian elodea) has been proposed as a final disposal, following their mechanical removal in the lake Fúquene (Ubaté, Cundinamarca). Microorganisms, isolated and selected by antagonism, were evaluated as inoculants to accelerate the composting and to stimulate plant growth. In microbial biopreparations of bacteria, actinomycetes and fungi, maximum amylolytic activities were found of 2,422 U L-1, 1,744 U L -1and 1,426 U L-1, respectively; cellulolytic activities of 233.2 U L-1, 668 U L-1 and 701.4 U L-1 and proteolytic activities of 660 U mg-1, 520 U mg-1 and 400 U mg-1. In test of these biopreparations in windrow composting of aquatic macrophytes waste, the best result was obtained with a concentration of 2%. The assay conducted on seedlings of radish (Raphanus sativus L) under greenhouse conditions (P <0.05), using the following treatments: microbial inoculants, compost inoculated to 2%, pure or mixed with soil (1:1), peat 50% and chicken manure at 33% mixed with soil, showed that actinomycetes stimulated plant growth significantly, as did chicken manure and bacteria. Microbial inoculants role for growth, development and nutrients assimilation in radish, was evident, and also for accelerating polluting macrophytes composting process. <![CDATA[<b>PRELIMINARY SURVEY OF SOME SOILS FROM CHILEAN ALTIPLANO NEAR IQUIQUE</b>]]> In the Altiplano of the Iquique Province, Chile, a study was carried out for the purpose of advancing in the knowledge of the soils in the zone, to determine the soil moisture and soil temperature regimes, and to establish its taxonomic classification. In one area, at the base of the slopes of the Irruputuncu volcano, where the occurrence of lahars and the presence of moraine deposits is described, 5 soil profiles were examined morphologically and some of their chemical and physical properties were determined. Moreover, the degree of pedogenic evolution of the volcanic parent materials was assessed. The depth of the solum did not exceed 0.40 m, and the low organic carbon content, combined with the dominance of the sand fraction, determined a low water holding capacity, which hampers the development of vegetation. It was determined that the soil temperature regime is frigid and its moisture regime is ustic. None of the soils showed andic soil properties. Hence, given the limited pedogenic development it was proposed to classify them as Ustorthents (Entisols, USDA, 2010). <![CDATA[<b>EVALUATION OF THE USLE MODEL TO ESTIMATE WATER EROSION IN AN ALFISOL</b>]]> The USLE model was evaluated to estimate water erosion in an Alfisol located in San Pedro, Metropolitan Region of Chile. Values of erosivity (R) obtained by using the Arnoldus approximation (MFI) and equations proposed by the Institute for Nature Conservation (ICONA) in Spain were adapted to the conditions in Chile. For the evaluation of soil loss, data were used for each precipitation event causing erosion during the period 1996-2000, obtained by measurements on experimental plots with treatments of subsoiling, infiltration trenches and natural prairie. They were compared with estimated values of erosion in terms of basic statistics and indices based on variance and regression. In the descriptive and comparative analysis of the selected equations, it was determined that soil losses estimated with USLE using the equation of rainfall erosivity by ICONA provided soil loss values which were well-adjusted to the values recorded in Chile, compared to erosivity calculated by the Arnoldus approximation (MFI) that overestimated the soil loss values. According to the results or estimates in this study it was concluded that the USLE model was capable of detecting the trend of the data, and resulted in estimates consistent with the pattern observed in the field data. <![CDATA[<b>THE EFFECT OF SODIUM HYDROGEN PHOSPHATE/ CITRIC ACID MIXTURES ON PHYTOREMEDIATION BY ALFALFA & METALS AVAILABILITY IN SOIL</b>]]> The effect of sodium hydrogen phosphate/citric acid mixtures on enhancing phytoremediation of heavy metal-contaminated soil by alfalfa (Medicago sativa L.) and the changes of metal availability in soils were investigated. Alfalfa plants grew healthily in heavy metals-contaminated soils (collected from molybdenum mine) for 30 days. The heavy metal content was determined by ICP-OES. In this paper, it was found that: the phytoextraction efficiency of alfalfa plants was enhanced after the sodium hydrogen phosphate/citric acid mixtures were added into soil. As usual, the phosphorus can promote plants to accumulate more biomass (increasing 0.35%-24.62%) even if the availability of metals to extraction were increased by citric acid in the soil. With the treatment of sodium hydrogen phosphate/citric acid mixtures, the bioconcentration factor (BCF) values of alfalfa plants and the acid soluble fractions of heavy metals in soils were increased. The translocation factor (TF) values of all alfalfas in heavy metals were low, but the TF of As, Cr, Hg, Mo tended to increase with sodium hydrogen phosphate/citric acid mixtures. In other words, both the availability and the biological-validity of heavy metals in soils were increased after sodium hydrogen phosphate/citric acid mixtures were added into soils. <![CDATA[<b>EFFECT OF THE STOCKING RATE AND LAND SLOPE ON NITROGEN LOSSES TO WATER ON A GRAZED PASTURE OF SOUTHERN CHILE</b>]]> Most of the studies on nitrogen (N) leaching have been carried out on cut grass, and there is a lack of information on beef grazed grasslands. The objective of this study was to quantify N runoff and leaching losses in beef production systems with two different immediate stocking rates (63 and 191 Holstein Friesian steers ha-1 day-1) and two land slopes (4 and 12%). Runoff and leachate samples were analyzed from 2004 to 2006 for total N, nitrate and ammonium. No significant differences for the total N losses were found between treatments (p > 0.05), which were low ranging from 0.9 to 26.8 kg N ha-1 yr-1. The main pathway for the losses was leaching, which contributed >99% of the total N lost. The main form of N leaching was nitrate-N (>84%). Nitrate-N concentration in runoff samples was high, averaging 14 to 31 mg L-1. We suggest that these low N losses could be related the low N fertiliser inputs in the pasture and to the N adsorption properties of volcanic soils and, so that further research is required on this subject. <![CDATA[<b>EFFECTS OF STERILIZATION AND TEMPERATURE ON THE DECREASE KINETIC OF PHOSPHORUS BIOAVAILABILITY IN TWO DIFFERENT SOIL TYPES</b>]]> The aim of this work was to study the effects temperature and microbial activity on the decrease kinetic of availabile P in two different soil types. Surface soils were sampled from Guilan and Hamadan provinces in north and northwest of Iran with temperate and semiarid climates. The availability of P in soil samples was studied in two (sterile and unsterile) conditions after addition of 400 mg P kg-1 soil as KH2PO4. Treated soil samples incubated in field capacity up to 2880 h at 15 and 28 0C in 3 replicates. Separate batches were taken after 0.16, 0.5, 1, 3, 12, 24, 48, 168, 336, 720, 1440, 2160, and 2880 h for extraction with 0.5 M NaHCO3- Temperate soils had higher clay content, cation exchange capacity (CEC), organic carbon (OC), total nitrogen, biological activity, amorphous and crystalline Fe and Al, but semiarid soils had higher sand content, pH, equivalent carbonate calcium (EEC), available P and K. Soil properties and sterilization had significant effect on P bioavailability after soil treatment with P fertilizers. The temperate soils with high affinity surface sites for P sorption compared to semiarid soils, had a lower available P in each time of extraction. Soil sterilization reduced the rate of P sorption/precipitation processes in initial step. The NaHCO3-extractable P in sterilized soils decreased continuously in first 30 days of soil incubation. After that soil available P did not decrease in sterilized soils significantly. However in unsterile soils after the initial decrease of available P, the bioavailability of P due to soil microbial activity increased. In sterile soils the first order equation, second order equation, Elovich kinetic equation, and power function equation could describe the adsorptive/precipitate process. The second order model and Elovich kinetic equation were selected to express the sorption/precipitation behavior in sterile soils because of the high R² values. The models selected suggest that the sorption mechanism in sterile soils is greatly chemisorption process. However in unsterile soils incubated at 15°C the suitability of the tested equations was considerably low. This study showed that soil biological activity had considerable effects on available P and its decrease kinetic after P addition to soil.