Graciela Palma

Effect of liquid cow manure on andisol properties and atrazine adsorption.

Application of animal manure amendments to agricultural soils is a common practice to improve soil fertility through the addition of essential plant nutrients. This practice may increase the potential for atrazine (2-chloro-4-ethylamino-6-isopropylamino-1, 3, 5-triazine) leaching due to competition for adsorption sites between the pesticide and dissolved organic carbon (DOC) added through manure. We evaluated the influence of liquid cow manure (LCM) application on soil properties, atrazine adsorption, and the physicochemical controlling mechanisms in an Andisol. The LCM was applied at rates equivalent to 0, 100,000, 200,000, and 300,000 L ha(-1), resulting in treatments S-0, S-100, S-200, and S-300, respectively. The LCM application increased DOC and pH of the soils immediately on addition, but pH returned to S-0 values 30 d after application. The LCM application did not modify atrazine adsorption with the two lowest application rates (S-100 and S-200), but atrazine adsorption was decreased in S-300 (K(f) = 0.96) compared with the control (S-0) (K(f) = 1.19), possibly due to the competitive adsorption of DOC with the pesticide. The Fourier-transformed infrared analysis showed that LCM increased aliphaticity and presence of N-containing groups and polysaccharide-like groups in amended soils; however, these properties did not modify the atrazine interaction in the studied amended soils. Interestingly the addition of DOC to soil at the high application rate (S-300) reduced atrazine adsorption in this rich OM Andisol despite the LCM not raising the concentration of stable organic matter. The application of high rates of liquid manure containing DOC incurs an increased risk of pesticide leaching.

Effect of dairy manure rate and the stabilization time of amended soils on atrazine degradation

The application rate of liquid cow manure (LCM) in the field and the stabilization time of amended soils before application of pre-plant herbicides are factors that determine their efficiency. This study includes evaluation of residual atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) in soil and amended soils with equivalent rate of 100,000; 200,000; and 300,000 L ha(-1) of LCM and the effect of pre-incubation time of amended soils on atrazine degradation. The study was carried out under controlled conditions using an Andisol with previous historical application of atrazine. The respiratory activity and fluorescein diacetate (FDA) studies indicated that the time necessary for stabilization of amended soils is over 20-30 d. During the measurement of respiratory and FDA activity, no significant differences were observed when atrazine was applied. The half-life of atrazine ranged from 5 to 8d and the relative distribution of degradation products seem to be affected by the application of LCM. The pre-incubation time of amended soil and LCM dose would not affect atrazine degradation rate, when the soil has a history of herbicide application. However, repeated applications of LCM in a long period of time could change the soil pH and increase the content of dissolved organic carbon (DOC) which could further contribute to a faster degradation of atrazine. Both effects would reduce the effectiveness of atrazine in weed control.

Effect of cow slurry amendment on atrazine dissipation and bacterial community structure in an agricultural Andisol.

Atrazine is a commonly used herbicide for maize production in Chile, but it has recently been shown to be ineffective in soils that receive applications of cow slurries generated from the dairy industry. This effect may be caused either by the sorption of the pesticide to organic matter or more rapid degradation in slurry-amended soils. The objectives of this study were to evaluate the effects of cow slurry on atrazine dissipation, the formation of atrazine metabolites and the modification of bacterial community in Andisol. The cow slurry was applied at doses of 100,000-300,000 Lha(-1). After 4 weeks, atrazine was applied to the slurry-amended soils at concentrations of 1-3 mg kg(-1). The amounts of atrazine and its metabolites were determined by high performance liquid chromatography (HPLC). The soil microbial community was monitored by measurement of CO(2) evolution and changes in bacterial community using PCR-DGGE of 16S rRNA genes. The results show that cow slurry applications had no effect on atrazine dissipation, which had a half-life of 15-19 days. The atrazine metabolites were detected after 20 days and were significantly higher in soils amended with the slurry at both 20 and 40 days after application of the herbicide. Respiration rates were elevated after 10 days in all soils with atrazine addition. Both the atrazine and slurry amendments altered the bacterial community structures, indicated by the appearance of specific bands in the DGGE gels after 10 days. Cloning and sequencing of the 16S rRNA genes from the DGGE gels showed that the bands represented various genera of beta-proteobacteria that appeared in response to atrazine. According to our results, further field studies are required to explain the lower effectiveness of atrazine in weed control. These studies may include the effect of dissolved organic carbon on the atrazine mobility.

Removal of the insecticide diazinon from liquid media by free and immobilized Streptomyces sp. isolated from agricultural soil.

From an agricultural soil that had received continuous applications of organophosphorus pesticides, 30 actinobacteria strains were isolated. Two strains, identified as Streptomyces sp. AC1‐6 and Streptomyces sp. ISP4, were selected because of their tolerance to diazinon and based on the relationship between diazinon removal and microbial growth. In liquid medium with diazinon at concentrations of 25 and 50 mg L−1, both strains were able to remove approximately 40–50% and 70–90% of the initial diazinon after 24 and 96 h of incubation, respectively. This diazinon removal was accompanied by microbial growth of the strains, an initial pH decrease, and glucose consumption in the liquid medium. Evaluation of the diazinon removal achieved by the free actinobacteria and Streptomyces sp. AC1‐6 immobilized on alginate beads revealed that the immobilized cells exhibited a 60% higher diazinon removal compared with the free cells. The reusability of the encapsulated biomass was confirmed, and a diazinon removal rate of more than 50% was obtained after the second batch. This work constitutes one of the few reports that describe Streptomyces strains as diazinon degraders. Given the high diazinon removal found, the streptomycetes exhibit suitable potential as diazinon‐degrading actinobacteria for elimination of diazinon from liquid residues.

Atrazine efficiency in an Andisol as affected by clays and nanoclays in ethylcellulose controlled release formulations.

Atrazine, a herbicide used for the control of broadleaf weeds of different crops, was incorporated in ethylcellulose controlled release formulations (CRFs) by using the solvent evaporation technique. Allophanic clays and nanoclays were incorporated as matrix modifying agents. The formulations were characterized by scanning electron microscopy (SEM) and infrared spectroscopy (FTIR), and their behavior was determined in aqueous phase. Dissipation studies and soil columns experiments with CRFs were also carried out, and compared with commercial formulations (CFs). In addition, a short-term bioassay was performed to evaluate the effect of CRFs and CFs on the emergence and growth of field mustard (Brassica campestris L.) under greenhouse conditions. The matrix modifiers (clays and nanoclays) showed little influence on the particle morphology and atrazine encapsulation efficiency. Furthermore, these matrix modifiers had a slight effect on the atrazine release into water, its dissipation and its behavior in soil compared with the formulation without them. All CRFs increased the atrazine herbicidal activity and reduced their loss by leaching in soil. Although some similarities were found in the efficiency to reduce the seedling emergence between CRFs and CFs, a greater death of seedlings was observed in the CRFs, especially when nanoclays were added into the formulation. These facts denote an advantage of CRFs over CFs due to prolonged bio-efficiency, and longer applications intervals will be produced, minimizing the harmful impact on the environment.

Production of microbial protein from forest products.

Abstract Evaluation of single cell proteins produced by Chrysonilia sitophila (TFB-27441 strain) with tannin, phlobaphene, bark and lignocellulosic material from Pinus radiata D. Don was made. The amino acids content and its quality were measured by their ratios of individual amino acids to total essential amino acids (A/E ratio) and total essential amino acids to total amino acids (E/T ratio). The values obtained were similar to those of egg and casein proteins. The same trends in the chemical scores were observed. The results of this study indicate that amino acids profiles obtained using bark components as substrates underwent some modification, but in general the obtained proteins could be considered as of excellent quality.

EFFECTS OF POST-EMERGENCE HERBICIDES ON IN VITRO GROWTH OF FUSARIUM OXYSPORUM ISOLATED FROM RED CLOVER ROOT ROT

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 (trishydroxymethyl-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.

Effect of pH on sorption kinetic process of acidic herbicides in a volcanic soil

Kinetic studies of pesticides in soil are of great importance to know the processes and parameters that govern their fate in the environment. The aim of this study was to evaluate the influence of pH on the kinetic sorption process of four acidic herbicides, clopyralid, fluroxypyr, picloram and triclopyr on an Andisol, characterized by high organic matter content and acidic pH. The pseudo-second-order model appeared to fit the data better than other models (R2 > 0.999). All herbicides were adsorbed rapidly during the first stage, but their adsorption was affected by pH and their chemical nature. The initial rate of reactions strongly decreased by increasing pH. The initial adsorption rates (h) and the sorption capacity of the herbicides showed the following order: fluroxypyr > triclopyr > picloram > clopyralid. At pH 4.0 the maximum amounts of fluroxypyr, triclopyr, picloram, and clopyralid adsorbed were respectively 75.2, 69.7, 40.5 and 11.7 %. The application of Elovich and Weber-Morris models suggests that mass transfer through the boundary layer and to a lesser degree intra-particle diffusion, control sorption kinetics, which appeared to be influenced by pH and chemical nature of the herbicides. The results obtained in this work suggest that soil pH and acidic character of herbicides could strongly affect the bioavailability of these herbicides on soil and their potential leaching.

THE MARKOVNIKOV-ANTIMARKOVNIKOV ADDITION OF M-THIOCRESOL AND P-NITROTHLOPHENOL TO INDENE

Abstract The addition of m-thiocresol and p-nitrothiophenol to indene has been studied under a variety of acidic conditions. The reaction of indene and m-thiocresol gave both Markovnikov and anti-Markovnikov adducts, in 58% and 42% yields, respectively. Surprisingly, in the reaction of p-nitrothiophenol and indene only the anti-Markovnikov adduct was formed. No adduct was obtained when this last reaction was run in the absence of an acid catalyst, whereas the anti-Markovnikov adduct was the only product formed in the case of m-thiocresol.

Advances in Chile for the Treatment of Pesticide Residues: Biobeds Technology

The widespread use of pesticides for agricultural and for nonagricultural purposes worldwide has resulted in the presence of pesticide residues in various environmental matrices. The occurrence of pesticide residues in surface waters, groundwater, and large volumes of soil is mainly due to the inadequate management of these compounds. In this context, a biobed system was developed in Sweden in response to the need for a simple and effective way to minimize environmental contamination from pesticide manipulation, particularly when filling the spraying equipment, a typical point source of contamination. Biobeds are based on the adsorption and degradation potential of organic biomixtures composed of top soil, peat, and straw that fills a deep hole in the ground and a grass layer that covers the surface. Recently, the use of biobeds has expanded to other countries in Europe and Latin America. In Chile, four biobeds similar to the European ones have been installed, making this country a pioneer in this type of decontamination system. This chapter gives a general overview of biobeds technology and the advances in research at laboratory scale related to the treatment of pesticide residues in a biobed system in Chile.