Degradation of Metribuzin in Two Soil Types of Lebanon

The degradation of metribuzin [4-amino-6-tert-butyl-3-methylthio-1,2,4-triazin-5(4H)-one] as influenced by soil type, temperature, humidity, organic fertilizers, soil sterilization, and ultra-violet radiation was studied in two soil types of Lebanon under laboratory conditions. The two soil types were sandy loam and clay. Deamination of metribuzin in the sandy loam soil to its deaminometribuzin (DA) derivative was basically a result of biological activity. In the clay soil the first metabolite diketometribuzin (DK) was a result of oxidative desulfuration, while diketo-deaminometribuzin (DADK) was the product of reductive deamination. The two soils represented major differences in the pesticide transformation processes. Photodecomposition on the soil surface and in aqueous media was also an important process in the degradation of metribuzin. Furthermore, the increase in soil organic matter enhanced degradation.     

Sorption of 3,4-dichloroaniline on four contrasting Greek agricultural soils and the effect of liming

Sorption of 3,4-dichloroaniline (3,4-DCA) on four typical Greek agricultural soils, with distinct texture, organic matter content and cation exchange capacities, was compared by using sorption isotherms and the parameters calculated from the fitted Freundlich equations. The sorption process of 3,4-DCA to the soil was completed within 48–72 h. The 3,4-DCA sorption on all soils was well described by the Freundlich equation and all sorption isotherms were of the L-type. The sandy clay loam soil with the highest organic matter content and a slightly acidic pH was the most sorptive, whereas the two other soil types, a high organic matter and neutral pH clay and a low organic matter and acidic loam, had an intermediate sorption capacity. A typical calcareous soil with low organic matter had the lowest sorption capacity which was only slightly higher than that of river sand. The 3,4-DCA sorption correlated best to soil organic matter content and not to clay content or cation exchange capacity, indicating the primary role of organic matter. The distribution coefficient (K _d) decreased with increasing initial 3,4-DCA concentration and the reduction was most pronounced with the highly sorptive sandy clay loam soil, suggesting that the available sorption sites of the soils are not unlimited. Liming of the two acidic soils (the sandy clay loam and the loam) raised their pH (from 6.2 and 5.3, respectively) to 7.8 and reduced their sorption capacity by about 50 %, indicating that soil pH may be the second in importance factor (after organic matter) determining 3,4-DCA sorption.     

Sorption of 3,4-dichloroaniline on four contrasting Greek agricultural soils and the effect of liming

Sorption of 3,4-dichloroaniline (3,4-DCA) on four typical Greek agricultural soils, with distinct texture, organic matter content and cation exchange capacities, was compared by using sorption isotherms and the parameters calculated from the fitted Freundlich equations. The sorption process of 3,4-DCA to the soil was completed within 48-72 h. The 3,4-DCA sorption on all soils was well described by the Freundlich equation and all sorption isotherms were of the L-type. The sandy clay loam soil with the highest organic matter content and a slightly acidic pH was the most sorptive, whereas the two other soil types, a high organic matter and neutral pH clay and a low organic matter and acidic loam, had an intermediate sorption capacity. A typical calcareous soil with low organic matter had the lowest sorption capacity which was only slightly higher than that of river sand. The 3,4-DCA sorption correlated best to soil organic matter content and not to clay content or cation exchange capacity, indicating the primary role of organic matter. The distribution coefficient (K(d)) decreased with increasing initial 3,4-DCA concentration and the reduction was most pronounced with the highly sorptive sandy clay loam soil, suggesting that the available sorption sites of the soils are not unlimited. Liming of the two acidic soils (the sandy clay loam and the loam) raised their pH (from 6.2 and 5.3, respectively) to 7.8 and reduced their sorption capacity by about 50 %, indicating that soil pH may be the second in importance factor (after organic matter) determining 3,4-DCA sorption.     

Impact of redox conditions on metolachlor and metribuzin degradation in Mississippi flood plain soils

The effect of soil redox conditions on the degradation of metolachlor and metribuzin in two Mississippi soils (Forrestdale silty clay loam and Loring silt loam) were examined in the laboratory. Herbicides were added to soil in microcosms and incubated either under oxidized (aerobic) or reduced (anaerobic) conditions. Metolachlor and metribuzin degradation under aerobic condition in the Forrestdale soil proceeded at rates of 8.83 ngd(-1) and 25 ngd(-1), respectively. Anaerobic degradation rates for the two herbicides in the Forestdale soil were 8.44 ngd(-1) and 32.5 ngd(-1), respectively. Degradation rates for the Loring soil under aerobic condition were 24.8 ngd(-1) and 12.0 ngd(-1) for metolachlor and metribuzin, respectively. Metolachlor and metribuzin degradation rates under anaerobic conditions in the Loring soil were 20.9 ngd(-1) and 5.35 ngd(-1). Metribuzin degraded faster (12.0 ngd(-1)) in the Loring soil under aerobic conditions as compared to anaerobic conditions (5.35 ngd(-1)).     

Effect of soil amendments on sorption and mobility of metribuzin in soils

Metribuzin (4-amino-6-tert-butyl-4,5-dihydro-3-methylthio-1,2,4-triazin-5-one), is weakly sorbed to soil therefore, leaches easily to lower soil profiles. Soil amendments play a significant role in the management of leaching losses of pesticides. Therefore, present study reports the effect of organic manure and fly ash amendments on metribuzin downward mobility in sandy loam soil columns. Application of animal manure [T-1(OM) and T-2(OM)] and fly ash [T-1(FA) and T-2(FA)] at 2.5% and 5.0% levels increased the metribuzin retention in the soil. Freundlich constant [K(f)(1/n)] values of metribuzin for treatments T-1(OM) and T-2(OM) were 0.70 and 1.11, respectively, which were significantly higher than the value (0.27) in natural soil (T-0). The respective values for treatments T-1(FA) and T-2(FA) were 1.80 and 4.61. Downward mobility of metribuzin was studied in packed soil columns [300 mm (l)x59 mm (i.d.)]. Both the amendments significantly reduced the downward mobility of metribuzin and affected breakthrough time and maximum concentration of metribuzin in the leachate. Leaching losses of metribuzin were decreased from 97% in natural soil (T-0) column to 64% [T-1(OM)] and 42% [T-2(OM)] for animal manure-amended columns and 26% [T-1(FA)] to 100% [T-2(FA)] for fly ash-amended columns, as metribuzin did not leach out of 5% fly ash-amended column. Study indicates that both animal manure and fly ash were quite effective in reducing the downward mobility of metribuzin in packed soil columns of a sandy loam soil.     

Impact of redox conditions on metolachlor and metribuzin degradation in mississippi flood plain soils

Abstract

The effect of soil redox conditions on the degradation of metolachlor and metribuzin in two Mississippi soils (Forrestdale silty clay loam and Loring silt loam) were examined in the laboratory. Herbicides were added to soil in microcosms and incubated either under oxidized (aerobic) or reduced (anaerobic) conditions. Metolachlor and metribuzin degradation under aerobic condition in the Forrestdale soil proceeded at rates of 8.83 ngd^‐1 and 25 ngd^‐1, respectively. Anaerobic degradation rates for the two herbicides in the Forestdale soil were 8.44 ngd^‐1 and 32.5 ngd^‐1, respectively. Degradation rates for the Loring soil under aerobic condition were 24.8 ngd^‐1 and 12.0 ngd^‐1 for metolachlor and metribuzin, respectively. Metolachlor and metribuzin degradation rates under anaerobic conditions in the Loring soil were 20.9 ngd^‐1 and 5.35 ngd^‐1. Metribuzin degraded faster (12.0 ngd^‐1) in the Loring soil under aerobic conditions as compared to anaerobic conditions (5.35 ngd^‐1).     

Dissipation of racemic mecoprop and dichlorprop and their pure R-enantiomers in three calcareous soils with and without peat addition

Two racemic herbicides, mecoprop (R,S-MCPP) and dichlorprop (R,S-DCPP), as well as their enantiopure R-forms, were incubated in three calcareous soils at 15 degrees C and 80% of their field capacity to try to elucidate their behaviour in soil and compare the dissipation rates when racemic and enantiopure compounds are used. Quantitation of pesticides is made by HPLC and the R/S ratio by GC-MS. The inactive S-enantiomer from the racemic forms persists longer than the R-forms in silt and sandy loam soils, but for shorter time in the clay loam soil. The pure R-enantiomers, both for MCPP and DCPP, after incubation in soil, are partially converted into their S-forms. In all cases, the dissipation of racemic and pure enatiomeric forms is lower in the clay loam soil than in the silt and sandy loam soils. The R-forms' peristence, in the three soils, is approximately two times lower when they are incubated alone than when they are incubated as racemic compounds. When peat is added, the persistence of these herbicides in the silt and sandy loam soils increases, while in the clay loam soil it decreases. Besides, in the clay loam soil, the enantiomeric ratio (ER) changes from its S-preferential degradation to a preferential degradation of its R-form, so an increase in the persistence of the inactive S-form occurs.     

Aflatoxin decomposition in various soils

The persistence of aflatoxin in the soil environment could potentially result in a number of adverse environmental consequences. To determine the persistence of aflatoxin in soil, 14C-labeled aflatoxin B1, was added to silt loam, sandy loam, and silty clay loam soils and the subsequent release of 14CO2 was determined. After 120 days of incubation, 8.1% of the original aflatoxin added to the silt loam soil was released as CO2. Aflatoxin decomposition in the sandy loam soil proceeded more quickly than the other two soils for the first 20 days of incubation. After this time, the decomposition rate declined and by the end of the study, 4.9% of the aflatoxin was released as CO2. Aflatoxin decomposition proceeded most slowly in the silty clay loam soil. Only 1.4% of aflatoxin added to the soil was released as CO2 after 120 days incubation. To determine whether aflatoxin was bound to the silty clay loam soil, aflatoxin B1 was added to this soil and incubated for 20 days. The soil was periodically extracted and the aflatoxin species present were determined using thin layer chromatographic (TLC) procedures. After one day of incubation, the degradation products, aflatoxins B2 and G2, were observed. It was also found that much of the aflatoxin extracted from the soil was not mobile with the TLC solvent system used. This indicated that a conjugate may have formed and thus may be responsible for the lack of aflatoxin decomposition.     

Paraquat adsorption, degradation, and remobilization in tropical soils of Thailand

Paraquat adsorption, degradation, and remobilization were investigated in representative tropical soils of Yom River Basin, Thailand. Adsorption of paraquat in eight soil samples using batch equilibration techniques indicated that adsorption depended on soil characteristics, including exchangeable basic cations and iron content. Multiple regression analysis indicated significant contribution of exchangeable calcium percentage (ECP), total iron content (TFe) and exchangeable sodium percentage (ESP) to paraquat sorption (Q). ESP and TFe were significant at all adsorption stages, whereas ESP was significant only at the initial stage of paraquat adsorption. Adsorption studies using two soils representing clay and sandy loam textures showed that paraquat adsorption followed the Freundlich model, exhibiting a nonlinear sorption curve. Paraquat adsorption was higher in the clay soil compared to the sandy loam soil with Kf values of 787 and 18, respectively. Desorption was low with 0.04 to 0.17% and 0.80 to 5.83% desorbed in clay and sandy loam soil, respectively, indicating some hysteresis effect. Time-dependent paraquat adsorption fitted to the Elovich kinetic model indicated that diffusion was a rate-limiting process. Paraquat mobility and degradation studies conducted using both field and laboratory soil column experiments with clay soil showed low mobility of paraquat with accumulation only in the surface 0-5 cm layer under field conditions and in the 0-1 cm layer in a laboratory soil column experiment. Degradation of paraquat in soil was faster under field conditions than at ambient laboratory conditions. The degradation rate followed a first-order kinetic model with the DT50 at 36-46 days and DT90 around 119-152 days.     

Leaching of trifluralin,metolachlor, and metribuzin in a clay loam soil of Louisiana

Trifluralin[2,6-dinitro-N,N-dipropyl-4-(trifluormethyl)benzenamine], metolachlor[2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], and metribuzin[4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)one] were applied in field plots located on a Commerce clay loam soil near Baton Rouge, Louisiana at the rate of 1683 g/ha, 2759 g/ha and 609 g/ha, respectively. The half-lives of trifluralin, metolachlor, and metribuzin in the top 0-15 cm soil depth were found to be 54.7 days, 35.8 days and 29.8 days, respectively. The proportion of trifluralin, metolachlor, and metribuzin in the top 0-15 cm soil depth was 94.7%, 86.6%, and 75.4%, respectively of that found in the top 0-60 cm soil depth 30 days after application. Trifluralin concentrations were within a range of 0.026 ng/mL to 0.058 ng/mL in 1 m deep well water, and between 0.007 ng/mL and 0.039 ng/mL in 2 m deep well water over a 62 day period after application. Metolachlor concentrations in the 1 m and 2 m wells ranged from 3.62 ng/mL to 82.32 ng/mL and 8.44 ng/mL to 15.53 ng/mL, respectively. Whereas metribuzin concentrations in the 1 m and 2 m wells ranged from 0.70 ng/mL to 27.75 ng/mL and 1.71 ng/mL to 3.83 ng/mL, respectively. Accordingly, trifluralin was found to be strongly adsorbed on the soil and showed negligible leaching. Although metolachlor and metribuzin were also both readily adsorbed on the soil, their leaching potential was high. As a result, in the clay loam soil studied, metribuzin concentration in groundwater with shallow aquifers is likely to exceed the 10 mg/L US Environmental Protection Agency (EPA) advisory level for drinking water early in the application season, whereas trifluralin and metolachlor concentrations are expected to remain substantially lower than their respective 2 ng/mL and 175 ng/mL EPA advisory levels.     

Effect of nitrogen amendment on respiration and respiratory quotient (RQ) in three hydrocarbon contaminated soils of different type

Three soil types (sandy gravel, silty clay and sandy loam) from sites historically contaminated with total petroleum hydrocarbon (TPH) were amended with NH(4)NO(3) at concentrations ranging from 16 to 2133 mg/kg soil(dry weight). Microbial activity was measured as O(2) consumption and CO(2) production in order to assess nitrogen limitation. Although activity was stimulated in all three soils under NH(4)NO(3) amendment (after 72 h), the level of nitrogen required was soil specific. For the sandy gravel and silty clay soils, O(2) consumption and CO(2) production both showed enhanced microbial activity when amended with 16 mg/kg soil(dry weight) NH(4)NO(3), whereas, these two parameters gave differing results for the sandy loam soil. Specifically, CO(2) production and O(2) consumption were stimulated with 66 mg/kg and 133 mg/kg soil(dry weight) of NH(4)NO(3) respectively. In addition, respiratory quotient kinetic analysis suggested different decomposition processes occurring in this soil under different NH(4)NO(3) amendment concentrations.     

Sorptive interactions and binding of δ‐endotoxin protein from bacillus thuringiensis subsp. kurstaki inforest soils

Abstract

The adsorption, desorption and binding of the insecticidal protein from Bacillus thuringiensis subsp. kurstaki (Btk toxin) onto autoclaved sandy and clay loam forest soils were studied at 23°C in a buffer medium (pH 10.2) using the precipitated protein mixture (active + inactive) obtained from a commercial Btk formulation. The active protein in the buffer solution was quantified by ELISA technique. Maximum adsorption of the toxin onto the sandy (301 μg/g) and clay (474 μg/g) loam soils was found to occur after 3 and 4 hours of agitation, respectively. Adsorption of the toxin was higher in the clay loam soil than in sandy loam. Adsorption parameters were calculated using the Freundlich and linear isotherm equations. The K_F and 1/n values for the soils were 1.12 and 1.48 (sandy), and 20.42 and 0.874 (clay), respectively, indicating stronger affinity of the toxin for the clay compared to the sandy loam soil. The linear model showed deviations at higher concentrations, nevertheless using the best fit, K_D and K_OC values were computed for the two soils. For sandy loam, the K_D and K_OC values were 9.38 and 391, respectively; the corresponding values for clay loam were 13.19 and 425, confirming the higher sorption affinity of the toxin for clay loam. The adsorption data did not fit the Langmuir equation because of heterogeneity of the soil surface. Desorption studies showed that more than half of the adsorbed toxic protein remained firmly attached to sandy (162.6 μg/g or 54.5%) and clay (314.0 μg/g or 67.4%) loam soils after six 0.5‐h washes (total 3.0 h wash time). Although the toxin appears to be a non‐leacher, its lateral mobility, soil persistence and biological consequences, including bioavailability of the bound residues, are poorly understood and require further investigation.     

Persistence of metsulfuron‐methyl in two soils

Abstract

The persistence of metsulfuron‐methyl in sandy loam and clay soil incubated at different temperatures and moistures contents was investigated under laboratory conditions using longbean (Vigna sesquipedalis L.) as bioassay species. A significant degradation of metsulfuron‐methyl was observed in non‐autoclaved soil rather than the autoclaved soil sample. At higher temperature, the degradation rate in non‐autoclaved soil improved with increasing soil moisture content. In non‐autoclaved sandy loam and clay soil, the half‐life was reduced from 9.0 to 5.7 and from 11.2 to 4.6 days, respectively when moisture level of sandy loam increased from 20 to 80% field capacity at 35°C. In the autoclaved soil, herbicide residue seems to have been broken down by non‐biological process. The rate of dissipation was slightly increased after the second application of the herbicide to non‐autoclaved soils but not in autoclaved soil, indicating the importance of microorganisms in the breakdown process.     

Paraquat Adsorption,Degradation, and Remobilization in Tropical Soils of Thailand

Paraquat adsorption, degradation, and remobilization were investigated in representative tropical soils of Yom River Basin, Thailand. Adsorption of paraquat in eight soil samples using batch equilibration techniques indicated that adsorption depended on soil characteristics, including exchangeable basic cations and iron content. Multiple regression analysis indicated significant contribution of exchangeable calcium percentage (ECP), total iron content (TFe) and exchangeable sodium percentage (ESP) to paraquat sorption (Q). ESP and TFe were significant at all adsorption stages, whereas ESP was significant only at the initial stage of paraquat adsorption. Adsorption studies using two soils representing clay and sandy loam textures showed that paraquat adsorption followed the Freundlich model, exhibiting a nonlinear sorption curve. Paraquat adsorption was higher in the clay soil compared to the sandy loam soil with K _f values of 787 and 18, respectively. Desorption was low with 0.04 to 0.17% and 0.80 to 5.83% desorbed in clay and sandy loam soil, respectively, indicating some hysteresis effect. Time-dependent paraquat adsorption fitted to the Elovich kinetic model indicated that diffusion was a rate-limiting process. Paraquat mobility and degradation studies conducted using both field and laboratory soil column experiments with clay soil showed low mobility of paraquat with accumulation only in the surface 0–5 cm layer under field conditions and in the 0–1 cm layer in a laboratory soil column experiment. Degradation of paraquat in soil was faster under field conditions than at ambient laboratory conditions. The degradation rate followed a first-order kinetic model with the DT₅₀ at 36–46 days and DT₉₀ around 119–152 days.     

Aflatoxin decomposition in various soils

Abstract

The persistence of aflatoxin in the soil environment could potentially result in a number of adverse environmental consequences. To determine the persistence of aflatoxin in soil, ¹⁴C‐labeled aflatoxin B₁, was added to silt loam, sandy loam, and silty clay loam soils and the subsequent release of ¹⁴CO₂ was determined. After 120 days of incubation, 8.1% of the original aflatoxin added to the silt loam soil was released as CO₂ ? Aflatoxin decomposition in the sandy loam soil proceeded more quickly than the other two soils for the first 20 days of incubation. After this time, the decomposition rate declined and by the end of the study, 4.9% of the aflatoxin was released as CO_2. Aflatoxin decomposition proceeded most slowly in the silty clay loam soil. Only 1.4% of aflatoxin added to the soil was released as CO₂ after 120 days incubation. To determine whether aflatoxin was bound to the silty clay loam soil, aflatoxin B₁ was added to this soil and incubated for 20 days. The soil was periodically extracted and the aflatoxin species present were determined using thin layer chromatographic (TLC) procedures. After one day of incubation, the degradation products, aflatoxins B₂ and G₂, were observed. It was also found that much of the aflatoxin extracted from the soil was not mobile with the TLC solvent system used. This indicated that a conjugate may have formed and thus may be responsible for the lack of aflatoxin decomposition.     

Effect of moisture and compost on fate of azoxystrobin in soils

The effect of compost-amendment and moisture status on the persistence of azoxystrobin [methyl (E)-2-{2-(6-(2-cyanophenoxy) pyrimidin-4-yloxy) phenyl}-3-methoxyacrylate], a strobilurin fungicide, in two rice-growing soils was studied. Azoxystrobin is more sorbed in the silt loam (K _f – 4.66) soil than the sandy loam (K _f – 2.98) soil. Compost-amendment at 5 % levels further enhanced the azoxystrobin sorption and the respective K _f values in silt loam and sandy loam soils were 8.48 and 7.6. Azoxystrobin was more persistent in the sandy loam soil than the silt loam soil. The half–life values of azoxystrobin in nonflooded and flooded silt loam soil were 54.7 and 46.3 days, respectively. The corresponding half–life values in the sandy loam soils were 64 and 62.7 days, respectively. Compost application enhanced persistence of azoxystrobin in the silt loam soil under both moisture regimes and half-life values in non–flooded and flooded soils were 115.7 and 52.8 days, respectively. However, compost enhanced azoxystrobin degradation in the sandy loam soil and half-life values were 59 (nonflooded) and 54.7 days (flooded). The study indicates that compost amendment enhanced azoxystrobin sorption in the soils. Azoxystrobin is more persistent in non-flooded soils than the flooded soils. Compost applications to soils had mixed effect on the azoxystrobin degradation.     

Influence of ageing of residues on the availability of herbicides for leaching

Losses by leaching of chlorotoluron, isoproturon and triasulfuron from small intact columns of a structured clay loam and an unstructured sandy loam soil were measured in five separate field experiments. In general, losses of all three herbicides were greater from the clay loam than from the sandy loam soil and the order between herbicides was always triasulfuron > isoproturon > chlorotoluron. Differences between experiments were also consistent for every soil/herbicide combination. There was no relationship between total loss and either total rainfall or cumulative leachate volume. When weighting factors were applied to the rainfall data to make early rainfall more important than later rainfall, there were significant positive relationships between cumulative weighted rainfall and total losses. Also, there were significant negative correlations between total losses and the delay to accumulation of 25 mm rainfall (equivalent to one pore volume of available water) in the different experiments. In laboratory incubations, there was a more rapid decline in aqueous (0.01 M calcium chloride) extractable residues than in total solvent extractable residues indicating increasing sorption with residence time. However, the rate of change in water extractable residues could not completely explain the decrease in leachability with ageing of residues in the field. Short-term sorption studies with aggregates of the two soils indicated slower sorption by those of the clay loam than by those of the sandy loam suggesting that diffusion into and out of aggregates may affect availability for leaching in the more structured soil. Small scale leaching studies with aggregates of the soils also demonstrated reductions in availability for leaching as residence time in soil was increased, which could not be explained by degradation. These results therefore indicate that time-dependent sorption processes are important in controlling pesticide movement in soils, although the data do not give a mechanistic explanation of the changes in leaching with ageing of residues.     

Adsorption,desorption, and mobility of two insecticides in Malaysian agricultural soil

Laboratory studies utilizing radioisotopic techniques were conducted to determine the adsorption, desorption, and mobility of endosulfan (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodioxanthiepin3-oxide) and methamidophos (O,S-dimethyl phosphorothioate) in sandy loam and clay soils of the Cameron Highlands and the Muda rice-growing area, respectively. High Freundlich adsorption distribution coefficients [Kads(f)] for endosulfan (6.74 and 18.75) and low values for methamidophos (0.40 and 0.98) were obtained in the sandy loam and clay soils, respectively. The observed Koc values for endosulfan were 350.85 (sandy loam) and 1143.19 (clay) while Koc values of 20.92 (sandy loam) and 59.63 (clay) were obtained for methamidophos. Log Kow of 0.40 and 1.25 were calculated for endosulfan as well as -1.96 and -1.21 for methamidophos in the sandy loam and clay soils, respectively. Desorption was common to both pesticides but the desorption capacity of methamidophos from each soil type far exceeded that of endosulfan. Soil thin layer chromatography (TLC) and column studies showed that while methamidophos was very mobile in both soils, endosulfan displayed zero mobility in clay soil.     

Influence of cadmium on carbon and nitrogen mineralization in sewage sludge amended soils

The effect of cadmium on C and N mineralization in sewage sludge amended and unamended sandy loam, loam and clay loam soils was studied during 2 months incubation at 30+/-1 degrees C. The sludge amendment caused 15-39% increase in microbial respiration, with the maximum C mineralization in sandy loam and the minimum in loam soil. The addition of 10 microg Cd g(-1) soil had no remarkable effect on C and N mineralization and microbial biomass; whereas significant decreases in the above parameters were observed at 25 and 50 microg Cd g(-1) soil, irrespective of the sludge addition. Less NO3(-)-N accumulated at higher Cd concentration. Cd recovery was high in sandy loam and low in clay loam soil. DTPA extractable Cd exhibited a significant negative correlation with microbial biomass (r=-0.58* to -0.86*; p < 0.05).     

Dynamic chemical characteristics of soil solution after pig manure application: A column study

When manures from intensive livestock operations are applied to agricultural or vegetable fields at a high rate, large amounts of salts and metals will be introduced into soils. Using a column leaching experiment, this study assessed the leaching potential of the downward movement of Cu and Zn as well as some salt ions after an intensive farm pig manure at rates of 0%, 5% and 10% (w/w) were applied to the top 20 cm of two different textured soils (G soil -sandy loam soil; H soil-silty clay loam soil), and investigated the growth of amaranth and Cu and Zn transfer from soil to amaranth (Amaranthus tricolor). Soil solutions were obtained at 20, 40 and 60 cm depth of the packed column and analyzed for pH, electrical conductivity (EC), dissolved organic matter (DOC) and Cu and Zn concentrations. The results indicated that application of pig manure containing Cu and Zn to sandy loam soil might cause higher leaching and uptake risk than silty clay loam soil, especially at high application rates. And manure amendment at 5% and 10% significantly decreased the biomass of amaranth, in which the salt impact rather than Cu and Zn toxicity from manures played more important role in amaranth growth. Thus the farmer should avoid application the high rate of pig manure containing metal and salt to soil at a time, especially in sandy soil.