Metal-induced sulfate adsorption by soils

Sulfate is present in soils as salts of various metals, and the different metals associated with sulfate may significantly affect its reactions on colloidal surfaces and consequently its mobility in soils. Four analytical methods, based on different principles, were evaluated for determination of sulfate in the presence of different counter-ions (metals) and in soil extracts obtained with 0.1 M LiCl, 0.15% CaCl[subscript]2, or 500 mg P L[superscript]-1 as Ca(H[subscript]2PO[subscript]4)[subscript]2. The recovery of sulfate associated with various mono-, di-, and tri-valent metals was quantitative by the methylene blue (MB) method. But, tri-valent metals, such as Al, In, La, and Sc, decreased the recovery of sulfate by the ion chromatographic (IC), turbidimetric (TD), and indirect Ba atomic absorption spectrophotometric (SP) methods. Among the four methods, the MB and IC methods were the most accurate and precise. Studies on the effect of the sulfate counter-ions (metals) on sulfate adsorption by four acid soils (two from Iowa, one from Chile, and one from Costa Rica) at various equilibrium solution pH (3.5-7.0) and two background electrolyte concentrations (1 and 10 mM NaCl) showed that sulfate adsorption was affected by point zero of charge (PZC) and was the greatest at the lowest pH values (ca. 3.5) and decreased with increasing the equilibrium solution pH and background electrolyte. Sulfate adsorption envelopes and isotherms for different sulfate forms were greatly affected by the type and charge of the sulfate counter-ion and, in general, followed the order: In[subscript]2(SO[subscript]4)[subscript]3 \u3e Al[subscript]2(SO[subscript]4)[subscript]3 \u3e CaSO[subscript]4 \u3e MgSO[subscript]4 \u3e Cs[subscript]2SO[subscript]4 \u3e K[subscript]2SO[subscript]4 \u3e (NH[subscript]4)[subscript]2SO[subscript]4. For the same valence of the sulfate counter-ion, sulfate adsorption increased with increasing ionic radius of the sulfate counter-ion. When its counter-ion was maintained at a constant concentration (12.0 mmol[subscript] c L[superscript]-1), sulfate adsorption was greater than when sulfate and its counter-ion were added at equivalent concentrations. Based on solubility diagrams and distribution coefficients (K[subscript] d) vs sulfate surface density ([sigma]) at maximum adsorption (X[subscript] m) relationships, precipitation reactions of metal sulfates were ruled out. The effects of the type and valence of the sulfate counter-ion on sulfate/metal adsorption ratios at various pH values and on the slopes of the linear relationships between sulfate and its counter-ion adsorbed were greater in soils with greater concentrations of hydrous Al and Fe oxides. The K[subscript] d values and the adsorption parameters of the one-surface and two-surface Langmuir equations for sulfate adsorption were greatly affected by the type, valence, and concentration of the sulfate counter-ion. Application of the three transformations of the Langmuir, a modified Langmuir, and the BET equations to the calculation of the sulfate adsorption parameters were compared

Fumigant emission reductions with TIF warrant regulatory changes

With methyl bromide's phase-out, most growers have turned to alternative fumigants, particularly 1,3-dichloropropene (1,3-D) and chloropicrin. These alternatives are tightly regulated because they are classified as toxic air contaminants and volatile organic compounds; the latter combine with other substances to produce ground-level ozone (smog). Two ambient air monitoring studies were conducted to evaluate the potential of totally impermeable film (TIF) to reduce emissions from shank applications of chloropicrin and 1,3-D. In 2009, a study demonstrated that TIF reduced chloropicrin and 1,3-D peak emissions by 45% and 38%, respectively, but TIF did not reduce total emissions when it was cut after 6 days. In 2011, increasing the tarp period from 5 to 10 days decreased chloropicrin and 1,3-D peak emissions by 88% and 78%, and their total emissions by 64% and 43%, respectively. Concurrent dynamic flux chamber results corroborated the ambient air monitoring data. These studies provide regulatory agencies with mitigation measures that should allow continued fumigant use at efficacious application rates

TIF film, substrates and nonfumigant soil disinfestation maintain fruit yields

A 5-year project to facilitate the adoption of strawberry production systems that do not use methyl bromide initially focused on fumigant alternatives and resulted in increased use of barrier films that reduce fumigant emissions. The focus shifted in year 3 to evaluating and demonstrating nonfumigant alternatives: soilless production, biofumigation, anaerobic soil disinfestation (ASD) and disinfestation with steam. In the 2010–2011 strawberry production season, fruit yields on substrates were comparable to fruit yields using conventional methods. Anaerobic soil disinfestation and steam disinfestation also resulted in fruit yields that were comparable to those produced using conventionally fumigated soils. Additional work is in progress to evaluate their efficacy in larger-scale production systems in different strawberry production districts in California

Metal-induced sulfate adsorption by soils

Sulfate is present in soils as salts of various metals, and the different metals associated with sulfate may significantly affect its reactions on colloidal surfaces and consequently its mobility in soils. Four analytical methods, based on different principles, were evaluated for determination of sulfate in the presence of different counter-ions (metals) and in soil extracts obtained with 0.1 M LiCl, 0.15% CaCl[subscript]2, or 500 mg P L[superscript]-1 as Ca(H[subscript]2PO[subscript]4)[subscript]2. The recovery of sulfate associated with various mono-, di-, and tri-valent metals was quantitative by the methylene blue (MB) method. But, tri-valent metals, such as Al, In, La, and Sc, decreased the recovery of sulfate by the ion chromatographic (IC), turbidimetric (TD), and indirect Ba atomic absorption spectrophotometric (SP) methods. Among the four methods, the MB and IC methods were the most accurate and precise. Studies on the effect of the sulfate counter-ions (metals) on sulfate adsorption by four acid soils (two from Iowa, one from Chile, and one from Costa Rica) at various equilibrium solution pH (3.5-7.0) and two background electrolyte concentrations (1 and 10 mM NaCl) showed that sulfate adsorption was affected by point zero of charge (PZC) and was the greatest at the lowest pH values (ca. 3.5) and decreased with increasing the equilibrium solution pH and background electrolyte. Sulfate adsorption envelopes and isotherms for different sulfate forms were greatly affected by the type and charge of the sulfate counter-ion and, in general, followed the order: In[subscript]2(SO[subscript]4)[subscript]3 > Al[subscript]2(SO[subscript]4)[subscript]3 > CaSO[subscript]4 > MgSO[subscript]4 > Cs[subscript]2SO[subscript]4 > K[subscript]2SO[subscript]4 > (NH[subscript]4)[subscript]2SO[subscript]4. For the same valence of the sulfate counter-ion, sulfate adsorption increased with increasing ionic radius of the sulfate counter-ion. When its counter-ion was maintained at a constant concentration (12.0 mmol[subscript] c L[superscript]-1), sulfate adsorption was greater than when sulfate and its counter-ion were added at equivalent concentrations. Based on solubility diagrams and distribution coefficients (K[subscript] d) vs sulfate surface density ([sigma]) at maximum adsorption (X[subscript] m) relationships, precipitation reactions of metal sulfates were ruled out. The effects of the type and valence of the sulfate counter-ion on sulfate/metal adsorption ratios at various pH values and on the slopes of the linear relationships between sulfate and its counter-ion adsorbed were greater in soils with greater concentrations of hydrous Al and Fe oxides. The K[subscript] d values and the adsorption parameters of the "one-surface" and "two-surface" Langmuir equations for sulfate adsorption were greatly affected by the type, valence, and concentration of the sulfate counter-ion. Application of the three transformations of the Langmuir, a modified Langmuir, and the BET equations to the calculation of the sulfate adsorption parameters were compared.</p

Totally impermeable film retains fumigants, allowing lower application rates in strawberry

The California strawberry industry is highly dependent on soil fumigation to control soil pests and maintain high productivity. Plastic films are used to hold fumigants in the soil at the doses needed to control pests and to prevent the loss of fumigant. Totally impermeable film (TIF) was compared to standard film (STD) for the retention of soil fumigants. 1,3-dichloropropene plus chloropicrin concentrations under TIF were 46% to 54% higher than under standard film, and higher fumigant concentrations under TIF were correlated with higher strawberry fruit yields and better weed control. The results suggest that to achieve fruit yield and weed control similar to methyl bromide and chloropicrin, 33% less 1,3-dichloropropene plus chloropicrin is needed under TIF than standard films

Totally impermeable film retains fumigants, allowing lower application rates in strawberry

The California strawberry industry is highly dependent on soil fumigation to control soil pests and maintain high productivity. Plastic films are used to hold fumigants in the soil at the doses needed to control pests and to prevent the loss of fumigant. Totally impermeable film (TIF) was compared to standard film (STD) for the retention of soil fumigants. 1,3-dichloropropene plus chloropicrin concentrations under TIF were 46% to 54% higher than under standard film, and higher fumigant concentrations under TIF were correlated with higher strawberry fruit yields and better weed control. The results suggest that to achieve fruit yield and weed control similar to methyl bromide and chloropicrin, 33% less 1,3-dichloropropene plus chloropicrin is needed under TIF than standard films

Totally impermeable film retains fumigants, allowing lower application rates in strawberry

The California strawberry industry is highly dependent on soil fumigation to control soil pests and maintain high productivity. Plastic films are used to hold fumigants in the soil at the doses needed to control pests and to prevent the loss of fumigant. Totally impermeable film (TIF) was compared to standard film (STD) for the retention of soil fumigants. 1,3-dichloropropene plus chloropicrin concentrations under TIF were 46% to 54% higher than under standard film, and higher fumigant concentrations under TIF were correlated with higher strawberry fruit yields and better weed control. The results suggest that to achieve fruit yield and weed control similar to methyl bromide and chloropicrin, 33% less 1,3-dichloropropene plus chloropicrin is needed under TIF than standard films

Zinc Fertilization Plus Liming to Reduce Cadmium Uptake by Romaine Lettuce on Cd-Mineralized Lockwood Soil

Lockwood shaly loam (Pachic Argixerolls) and similar Cd mineralized soils derived from marine shale in California contain higher Cd levels and higher Cd:Zn ratios than uncontaminated US soils, and produce leafy vegetables with considerably higher Cd than is normal for US lettuce. Previous work by Burau et al. suggested that, in contrast with geogenic Zn+Cd enriched soils, liming the Cd-mineralized soils did not effectively reduce crop Cd concentration. Our previous studies found for high Cd:Zn soils, liming may not reduce crop Cd but liming plus Zn fertilizer can strongly reduce crop Cd. Greenhouse pot trials were undertaken with addition of 0-500 mg Zn kg-1 to Lockwood soil (5.3 mg Cd and 54 mg Zn kg-1). All pots were made calcareous with reagent CaCO3 (harvest pHW 7.8), or adjusted to a range of pH without Zn fertilizer. The zero Zn calcareous treatment produced lettuce with 13.2 mg Cd kg-1 DW and only 10.5 mg Zn kg 1 DW; adding 100 mg Zn kg-1 soil produced lettuce containing 2.53 mg Cd kg-1 and 35 mg Zn kg-1; adding 250 mg Zn kg-1, 6.3 mg Cd kg-1 lettuce; and 500 mg Zn kg-1, 3.9 mg Cd kg-1 lettuce. For the 0 Zn treatment, acidification or liming increased lettuce Cd. The key finding is that if Zn is added to raise Cd:Zn ratio, liming these soils can be highly effective in reducing lettuce Cd, much like found for other Cd+Zn enriched soils

Soil Microbial Community Structure and Target Organisms under Different Fumigation Treatments

Producers of several high-value crops in California rely heavily on soil fumigants to control key diseases, nematodes, and weeds. Fumigants with broad biocidal activity can affect both target and nontarget soil microorganisms. The ability of nontarget soil microorganisms to recover after fumigation treatment is critical because they play an important role in sustaining the health of agricultural and natural soil systems. Fumigation trial was conducted in Parlier, CA, and the study focuses on the effects of different rates of Telone C35 and also methyl bromide fumigation with polyethylene (PE) and totally impermeable film (TIF) tarps on target and nontarget soil microorganisms using field samples. Results indicated that the populations of target organisms, such as Fusarium oxysporum and Pythium spp., were reduced at all rates of fumigants. Phospholipid fatty acid (PLFA) analysis indicated that all major nontarget soil microbial groups such as Gram positive bacteria, Gram negative bacteria, fungi, and arbuscular mycorrhizal fungi (AMF) were affected by methyl bromide (MeBr) fumigation treatment. In general, the effects of Telone C35 (299 L/ha) under PE tarp had the least impact on microbial community structure and better effect on controlling target microorganisms and, therefore, indicated the better option among fumigation treatments