Effect of soil moisture on the release of alachlor from alginate-based controlled-release formulations

The release of alachlor from controlled-release formulations (CRFs) based on alginate-montmorillonite matrices into aqueous polyethylene glycol (PEG) solutions of different concentrations and into a soil at different moisture contents was studied. In distilled water and in PEG-containing solutions displaying -0.1 MPa potential and up, the beads imbibe water and swell. The ensuing increase in weight is about 5%, and the increase in the bead's diameter is about 10%. At water potentials of -0.5 MPa and lower, loss of weight and shrinkage of the beads were observed. The changes in weight and diameter of the alginate-clay beads incubated in a Hamra loamy sand soil at 26.5% moisture content (w/w; -0.18 MPa) were similar to those observed in PEG solutions of >-0.5 MPa moisture potential. The weight and diameter losses observed in the drier soils (12.0 and 7.1% water content; -0.49 and -1.11 MPa) were similar to those in the more concentrated PEG solutions. A decrease in the rate of release of the active ingredient from the beads into soil was observed as the water potential decreased (drier soils). The release of the active ingredient from the investigated CRFs displayed a linear relationship to the square root of time, suggesting a diffusion-controlled-release rate. Data extracted from this relationship enabled the formulation of a mathematical model that correlates rate of release to water content.     

Gas chromatographic determination of alachlor in microencapsulated formulations: mini-collaborative study

An isothermal gas chromatographic method for measuring alachlor in Micro-Tech (microencapsulated) formulations was tested by 5 collaborators. The samples were prepared in acetone, and alachlor was determined using a gas chromatographic column of 10% SP-2250 on 100-120 mesh Supelcoport. Di-n-pentylphthalate was used as the internal standard. Collaborators made single determinations on 5 samples distributed as blind duplicates. The mini-collaborative study generated 47 data points. The coefficient of variation (CVo-pooled) was 1.35%, and CVx-pooled was 0.73%. The method was simple to use and did not reveal any interferences in samples tested. The method has been adopted official first action as an AOAC-CIPAC method.     

Ethylcellulose formulations for controlled release of the herbicide alachlor in a sandy soil

The development of controlled-release formulations of alachlor to diminish its leaching in sandy soils, avoiding groundwater contamination and maintaining its efficacy, was studied. For this purpose, ethylcellulose (EC) microencapsulated formulations (MEFs) of alachlor were prepared under different conditions and applied to soil columns to study their mobility. The results show that in all cases the release into water of alachlor from MEFs was retarded when compared with commercial formulation. Total leaching losses in soil columns were reduced to 59% from 98%. The mobility of alachlor from EC microspheres into soil columns has been greatly diminished in comparison with its current commercial formulation (CF), above all with increasing EC/herbicide ratios. Distribution of alachlor applied as MEFs at different depths in the soil was higher in the soil surface (66.3-81.3% of herbicide applied at the first 12 cm). In contrast, the residues from CF along the complete soil column were only 20.4%. From the results of bioassays, MEFs showed a higher efficacy than CF at 30 days after the treatment. The use of ME formulations could provide an advantage in minimizing the risk of groundwater contamination by alachlor and reducing the application rates, as a result of maintaining the desired concentration of the herbicide in the top soil layer, obtaining longer periods of weed control.     

Environmentally friendly formulations of alachlor and atrazine: preparation, characterization, and reduced leaching

Atrazine and alachlor formulations were designed by encapsulating the herbicide molecules into phosphatidylcholine (PC) vesicles, which subsequently were adsorbed on montmorillonite. PC and montmorillonite are classified as substances of minimal toxicological risk by the U.S. EPA. PC enhanced alachlor and atrazine solubilities by 15- and 18-fold, respectively. A 6 mM PC:5 g/L clay ratio was found as optimal for PC adsorption on the clay. Active ingredient contents of the PC-clay formulations ranged up to 8.6% for atrazine and 39.5% for alachlor. Infrared spectroscopy showed hydrophobic interactions of herbicide molecules with the alkyl chains of PC, in addition to hydrophilic interactions with the PC headgroup. Release experiments in a sandy soil showed a slower rate from the PC-clay formulations than the commercial ones. Soil column experiments under moderate irrigation and bioactivity experiments indicate that a reduction in the recommended dose of alachlor and atrazine can be accomplished by using PC-clay formulations.     

Volatilization of ketones from water

The overall mass-transfer coefficients for the volatilization from water of acetone, 2-butanone, 2-pentanone, 3-pentanone, 4-methyl-2-pentanone, 2-heptanone, and 2-octanone were measured simultaneously with the oxygen-absorption coefficient in a laboratory stirred water bath. The liquid-film and gas-film coefficients of the two-film model were determined for the ketones from the overall coefficients, and both film resistances were important for volatilization of the ketones. The liquid-film coefficients for the ketones varied with the 0.719 power of the molecular-diffusion coefficient, in agreement with the literature. The liquid-film coefficients showed a variable dependence on molecular weight, with the dependence ranging from the ?0.263 power for acetone to the ?0.378 power for 2-octanone. This is in contrast with the literature where a constant ?0.500 power dependence on the molecular weight is assumed. The gas-film coefficients for the ketones showed no dependence on molecular weight, in contrast with the literature where a ?0.500 power is assumed.     

Volatilization of organic chemicals from water

Liquid-phase transfer coefficients of ten selected organic pollutants were measured simultaneously with the O₂ reaeration coefficient in a 2L reactor. The contents of the reactor were stirred in the laboratory by a 0.15 m diameter propeller attached to a constant speed motor. The ratio of the mass transfer coefficient of the chemical to that of O₂ is found to vary between 0.43 and 0.60 for eight of the chemicals tested. This result is in good agreement with the literature concerning high volatility chemicals. The value of this ratio for the other two chemicals was found to be 0.10 for nitrobenzene and 0.01 for phenol, confirming the predominance of gas phase resistances in the transport process for these two compounds.     

Nitrogen Volatilization from Arizona Irrigation Waters

A laboratory study was initiated to investigate the effects of temperature (25, 30, 35, and 40 °C) and water quality on the loss of fertilizer nitrogen (N) through volatilization out of irrigation waters collected from 10 different Arizona sources. A 300‐mL volume of each water source was placed in 450‐mL beakers open to the atmosphere in a constant‐temperature water bath with 10 mg of analytical‐grade ammonium sulfate [(NH₄)₂SO₄] dissolved into each sample. Small aliquots were drawn at specific time intervals over a 24‐h period and then analyzed for ammonium (NH₄ ⁺)‐N and nitrate (NO₃ ^?)‐N concentrations. Results showed potential losses from volatilization to be highly temperature dependent. Total losses (after 24 h) ranged from 30–48% at 25 °C to more than 90% at 40 °C. Volatilization loss of fertilizer N from irrigation waters was found to be significant and should be considered when making decisions regarding fertilizer N applications for crop production in Arizona particularly when using ammonia‐based fertilizers.     

Volatilization of sulfur from unamended and sulfate-treated soils

Volatilization of sulfur from unamended and sulfate-treated soils was studied by sensitive gas chromatographic techniques using a flame photometric detector fitted with a sulfur filter. The soils employed were surface samples of 25 Iowa soils selected to obtain a wide range in properties. No release of volatile sulfur compounds was detected when 11 of these soils were incubated under aerobic or waterlogged conditions before or after treatment with sulfate (400 μg sulfate S/g soil). Fourteen soils released volatile sulfur compounds when incubated under waterlogged conditions before and after addition of sulfate, but only 4 of these soils released volatile sulfur compounds when incubated under aerobic conditions. Where volatilization of sulfur was observed, the volatile sulfur detected was identified as dimethyl sulfide or as dimethyl sulfide associated with smaller amounts of carbonyl sulfide, carbon disulfide, methyl mercaptan, and (or) dimethyl disulfide. No trace of hydrogen sulfide was detected. Where release of volatile sulfur was observed, the amount of sulfur volatilized at 30°C in 60 days under aerobic or waterlogged conditions was very small and did not account for more than 0–05% of the sulfur in the unamended or sulfate-treated soils studied. It is concluded that gaseous loss of sulfur from unamended or sulfate-treated soils is insignificant under conditions likely to be encountered in the field.     

NH3 Volatilization from Urea-NBPT in Eucalyptus

High losses of nitrogen (N) by volatilization of ammonia from urea applied in Eucalyptus are expected due to the influence of plant residues on the soil surface. The study evaluated the N losses by volatilization of ammonia from urea coated with Thiophosphate N-(n-butil) triamide (NBPT) applied in soil with eucalyptus residues in surface under moisture treatments: fertilization in dry soil without irrigation; fertilization in dry soil with posterior irrigation depth (3 mm); fertilization in moist soil without irrigation and fertilization in moist soil with irrigation depth (3 mm). NBPT is a potential inhibitor of urease. Urea with NBPT shows lower losses by volatilization of ammonia when it is applied in dry soil; however in soil conditions of high moisture the losses as well as inhibitor effect of the NBPT are lower. The inhibitor effect of NBPT is reduced over time when it is subjected to moisture conditions.     

鸡粪施入农田土壤的氨挥发研究

在北京海淀区东北旺乡利用风洞法氨挥发测定系统,研究了不同施肥方式、施肥量和添加剂对鸡粪在农田施用过程中氨挥发的影响。结果表明,施肥方式显著影响鸡粪氨挥发,试验期间在田间裸地24000kg·hm^-2施肥量下,表施的累积氨挥发氮损失为19．8％,而表施后立即深翻5-9cm,氨挥发损失为3．3％;不同施肥量下,24000kg·hm^-2之比12000kg·hm^-2和8000kg·hm^-2的氨挥发损失分别减少2．1％和4．9％,但统计差异不显著;锯末对鸡粪氨挥发没有起到抑制作用,未添加锯末处理的氨挥发损失为19．5％,而添加锯末处理的氨挥发损失为21．1％;过磷酸钙对鸡粪氨挥发抑制效果显著,未添加过磷酸钙处理的氨挥发损失为31．8％,而添加过磷酸钙处理的氨挥发损失为21．9％,比未添加降低了31．1％。     

Laboratory Evaluation on Ammonia Volatilization from Coated Urea Fertilizers

Coated urea fertilizers are assumed to enhance crop yield and reducing the environmental pollution. Nevertheless, many of the coated urea fertilizers are expensive, thus not readily available for most farmers. In addition, many of these fertilizers release N not in tandem with the plant’s need, thus retard growth. Therefore, a laboratory study was conducted to evaluate effects of coated urea fertilizers on N losses via volatilization. Measurement of ammonia volatilization was carried out using the closed-dynamic air flow system. The study for ammonia volatilization was conducted using different rates of fertilizer (50, 100, and 200 kg N ha^?1) with different types of fertilizer (Urea, Sulfur-coated urea; SCU and Gypsum sulfur coated urea using rotating drum; GSCUD) in 37 days of incubation. The results indicate that SCU represents the best fertilizer which decreases the amount of ammonia volatilization at each rate of fertilizer. Besides, the rate of 50 kg N ha^?1 has the lowest percentage of ammonia volatilization. Moreover, the result proved the effectiveness of coating urea fertilizer may reduce the ammonia loss to the environment and new product which GSCUD can be comparable to the commercial product.     

大量沼液施灌稻田的氨挥发特征

基千沼液灌溉田间试验,采用通气法研究化肥和沼液施灌稻田的氨挥发特征及其差异性.结果表明,尿素施用处理的氨挥发速率峰值出现在每次施氦后当天或第2天,而各沼液施灌处理则在施氮后当天.氨挥发速率和累计量均随着施氮量的增加而提高.沼液灌溉田间氨挥发速率随时间的动态变化主要取决于田面水中铵氮浓度的变化.每次沼液施灌后的前7天是稻田氨挥发的关键时期.水稻分蘖初期氨挥发明显高于其他时期的.等氮量沼液施灌处理的平均氨挥发速率为(1.48±2.08)kg/(hm2·d),累计量为(51.00±4.46)kg/hm2,全生育期氮素损失率(14.90±1.65)%,分别是尿素施用处理的5.1,3.0,6.4倍.因此,若以等氮量的沼液代替尿素不仅存在稻田供氮不足的风险,而且增加了氨挥发对生态环境产生不良影响的可能,这需要在沼液广泛应用于水稻生产的过程中特别关注.     

田间土壤氨挥发的原位测定——风洞法

详细介绍了农田土壤氨挥发风洞法测定系统的原理、构造和特点,并通过回收率试验和田间试验进行了验证。所选用的德国风洞主要包括采样箱、采样系统和控制系统3部分,系统内部的气压、温度、湿度、风速等微气象条件接近自然环境条件,测量结果有较好的代表性。回收实验结果表明,回收率为90%,说明风洞的密闭性和浓度分布的均匀程度较好,适合于土壤氨挥发的多处理、多重复的田间原位测定,尤其适用于多因子对比实验。风洞法测定不受天气的影响,对实验区面积要求不高,重复性及可靠性较好,不仅可以测定农田土壤的氨挥发,还可以测定有机肥贮存和施用以及各种肥料形态的氨挥发状况。     

Volatilization of demethylmercury and elemental mercury from river Elbe floodplain soils

It has been shown that an untreated mercury-polluted floodplain soil (containing 10 μg/g per dry weight (d.w.) total Hg and 12 ng/g (d.w.) monomethylmercury compounds (MMM)) of the river Elbe in Northern Germany contains both dimethylmercury (DMM) and elemental mercury (Hg°). This is the first time ever that DMM has been detected in unmodified soils. A novel purge- and-trap-technique involving a sequential thermodesorption-separation of the two species after trapping on a carbon molecular sieve (CMS) has been developed that allows the determination of the two species DMM and Hg° from aqueous solutions or soil samples by GC-CVAFS. The compounds' identities as Hg-species were confirmed by GC-ICP/MS. A DMM-concentration of 740 pg/g (d.w.) was determined in the soil; the Hg°-concentration was found to be at least four times larger, but could not yet be quantified. Since no precautions against losses via evapoartion were taken during sampling and storage, the original concentrations were probably much higher. Both DMM and Hg° are easily purged with N₂ from soils as well as from soil suspensions, indicating that the two species may readily evaporate from those soils under natural conditions. The amount of DMM determined in the soil suspension was significantly lower (80 pg/g (d.w.)) compared to that in the original soil sample, suggesting that DMM might not be stable under these conditions. Also, it was shown that in natural samples, MMM can be converted into DMM in the presence of sulfide, at S^2?-levels as low as 100 μg/g.     

Assessing Tillage Systems for Reducing Ammonia Volatilization from Spring-Applied Slurry Manure

The effect of tillage management on NH₃-N volatilization and its influence on succeeding corn (Zea mays L.) silage production were studied at the University of Massachusetts Agricultural Experiment Station (South Deerfield, MA) during 2010–2012 growing seasons. Tillage treatments consisted of disking before and after manure application, solid-tine aeration before and after manure application, and no-till management. The greatest NH₃-N loss (61 percent) occurred within the first 8 h after slurry manure application regardless of tillage management. The greatest NH₃-N emission occurred with surface application (no-till), which ranged between 5.2 and 10.3 kg NH₃-N ha^?1 (9–20 percent of NH₃-N applied) over the 3 years of the study. Immediate incorporation of manure into soil through disking reduced NH₃-N loss by 66 to 75 percent. Ammonia loss abatement with aeration before or after manure application ranged from 13 to 41 percent compared with surface manure application. Tillage management did not influence corn silage yield or quality.     

黑土氮肥氨挥发损失特征研究

采用密闭室法测定土壤氨挥发通量.进而计算施入土壤中氮肥的氨挥发损失量,研究了东北黑土区不同作物镲施氮量和施肥深度下氮肥的氨挥发.结果表明,施用尿素促进了农田氨挥发损失,并随施肥量的增加而增加,当表施氮量30 g/m2时,氨挥发损失率达21.68%,在相同施氮量的条件下,随施肥深度的增加而减少,当施肥深度为9cm,施氮量30 g/m2时,氨挥发损失率仅达2.49%.氨挥发损失氮量与施氮量(＞ 0)呈抛物线性关系.推荐东北黑土区种植大豆优化施肥深度在3 cm以下;而玉米基肥优化施肥在6 cm以下,追肥施肥深度在3 cm以下.     

Volatilization of Ammonia Derived from Fertilizer and Its Reabsorption by Coffee Plants

Abstract

Volatilization of ammonia derived from nitrogen (N) fertilizers and its possible reabsorption by crops depend on specific soil, climate, and atmospheric conditions, as well as the method of fertilizer application and plant architecture. In an experiment carried out in Piracicaba, State of São Paulo, Brazil, the volatilization of ammonia derived from urea, ammonium sulfate, and natural soil were quantified using static semi‐open N‐ammonia (NH₃) collectors. Fertilizers were top‐dressed under the plant canopy on top of dead leaf mulch. In another experiment, the reabsorption of the volatilized ammonia by plants was quantified using ¹⁵N‐labeled urea. Results showed, as expected, that volatilization derived from urea was seven times more intense in relation to ammonium sulfate, whose volatilization was very low, and slightly more than the natural volatilization from soil at pH 5.3. The loss of ammonia from the ammonium sulfate was very low, little more than twice of that of the natural soil. Through isotopic labeling, it was verified that 43% of the volatilized N‐NH₃ was reabsorbed by coffee plants, which gives evidence that volatilization losses are greatly reversed through this process.     

Multi-Year Measurements of Field-Scale Metolachlor Volatilization

Volatilization is a critical pathway for herbicide loss from agricultural fields, and subsequently deposited downwind from the edge of the field. To better understand the volatilization process, field-scale turbulent volatilization fluxes of metolachlor (2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide) were quantified for 13 consecutive years using a combination of herbicide concentration profiles and eddy diffusivities derived from turbulent fluxes of heat and water vapor. Site location, type of herbicides, and agricultural management practices remained unchanged during this study in order to evaluate the effect of soil moisture on metolachlor volatilization. Twenty gravimetric surface soil moisture samples (0–5 cm) were collected immediately after herbicide application and then at 0430 hours each morning to determine the impact of surface moisture on herbicide volatilization. Five days after application, cumulative herbicide volatilization ranged from 5 to 63% of that applied for metolachlor. Metolachlor volatilization remained an important loss process more than 5 days after application when the soil surface was moist. Conversely, if the soil surface was dry, negligible volatilization occurred beyond 5 days. Furthermore, the total amount of metolachlor volatilized into the atmosphere increased exponentially with surface soil water content during application (r ²?=?0.78). Metolachlor volatility was found to be governed largely by surface soil moisture.     

Volatilization losses of surface-applied urea nitrogen from Vertisols in the Indian semi-arid tropics

The N loss from Vertisols was estimated by measuring the loss of ¹⁵N-labelled urea N under conditions that promote NH₃ volatilization. Urea granules were placed on the top of 150-mm deep soil columns (Vertisols) collected from three sites with a range in pH, electrical conductivity, and cation exchange capacity. There were two contrasting moisture treatments, one near field capacity (wet) and another with intermittent wetting of the soil surface before allowing the columns to dry (moist-dry). The results indicated that losses were influenced markedly by pH and moisture treatment, being 29.5, 33.5, and 33% from the wet soils and 37, 42, and 40.5% from the moistdry soils with pH values of 7.7, 8.2, and 9.3, respectively. These observations clearly indicate that broadcasting of urea on the surface of Vertisols may cause substantial N losses.