Direct Steam Distillation Research Articles

Kajian Pengolahan Nilam (Patchouli) Menggunakan Metode Penyulingan Uap di Kecamatan Poleang Utara Kabupaten Bombana

This study examines the processing of patchouli oil using the steam distillation method in North Poleang District, Bombana Regency. Data collection methods: (a) observation; (b) interviews); (c) questionnaires; and (d) documentation. The method in this study is to describe the processing of patchouli oil using the steam distillation method. The results showed the processing of patchouli oil using the steam distillation method in North Poleang District, Bombana Regency. Distilleries are used with water and steam distillation systems. Distil water and steam through a kettle filled with water to the limit of the filter and patchouli leaves on the filter. Then the water is heated and produces steam passing through the material and flowing through a stainless pipe. (a) Patchouli oil is obtained from the leaves, stalks, stems and patchouli plants. Harvesting can be done 6 - 8 months after planting in plants that grow well. Nilan harvest is usually done by pruning as high as 10 - 20 cm from the ground. Production of the first leaves and twigs is still low (about 50 - 75% of normal production). Done every 4 - 6 months depending on the rainfall and soil fertility; (b) drying is usually carried out by drying, the crop (pattern leaves and stalks) are dried in the sun for 5 hours followed by wind-drying for 2 - 3 days until the moisture content reaches 12 - 15%; and (c) direct steam distillation, in which the material is in a still boiler and water vapour is drained from the boiler at the bottom of the distillate. The duration of direct steam distillation ranges from 4-6 hours.

Predicting nitrogen mineralization potential and availability of biochar-based agro-municipal solid waste co-compost using alkaline hydrolysis

Valorization of agro-municipal solid wastes into value-added nutrient-enriched slow-release organic amendments (OAs) for ameliorating soil fertility constraint has been proposed as an environmentally friendly and sustainable approach to managing challenges associated with disposal of organic wastes. However, for soils receiving OAs of complex composition, such as biochar-manure-compost (BMC), the predictive knowledge needed to synchronize amount and timing of nitrogen (N) release with plant demand, thereby minimizing environmental pollution, is still lacking. This study validated results from an alkaline hydrolysis method for estimating N mineralization potential with: (i) the standard long-term N mineralization procedure and (ii) actual N uptake from soils amended with BMCs of varied C/N ratios. The alkaline hydrolysis procedure involves direct steam-distillation of BMC-soil mixtures, requiring only 40-min for estimating N mineralization potential, whereas the standard N mineralization procedure followed 26-week laboratory incubation. For both procedures, cumulative N mineralized or hydrolyzed was fitted to the first-order exponential equation to determine the potentially mineralizable N (No) and an analogous “potentially hydrolyzable N (Nmax)” for the BMCs. Nitrogen uptake by maize was evaluated in a six-week pot experiment. The results showed that Nmax and No values differed among the BMCs, indicating differences in chemical composition, and potential mineralizabilities of the BMCs. Increasing biochar content of the BMCs decreased kinetic parameters of N mineralization compared to compost alone. Estimated Nmax values significantly correlated with No (p = 0.023) and N uptake (p = 0.005), suggesting that alkaline hydrolyzable ON can replace the long-term procedure for estimating No in BMC-amended soils, reducing experimental cost and time.

Soil Carbon and Nitrogen Forms and Their Relationship with Nitrogen Availability Affected by Cover Crop Species and Nitrogen Fertilizer Doses

Cover crops and N fertilization strongly impact the forms of soil organic C and N and their availability, which change the responses of plants to N fertilization and soil organic C accumulation. Our study objectives were to evaluate the effects of cover crops and N doses on soil total and soluble C and N contents, N fractions, and potentially available N in a long-term no-till experiment. The experiment was conducted in a randomized block design with split plots and four replicates. The main treatments were cover crops species, jack bean, lablab bean, millet, velvet bean, and fallow cultivated prior to maize. Secondary treatments included two doses of mineral N (0 and 120 kg ha−1). Soil samples were collected at depths of 0–5, 5–10, 10–20, and 20–40 cm, which were analyzed for total and water-soluble C and N contents, N fractions (acid hydrolysis method), and potentially available N (hot KCl solution and direct steam distillation methods). Cover crop velvet bean resulted in the highest soil organic carbon levels, and cover crop millet plus fertilization resulted in the highest levels of soil total N. The amino sugar was the largest N fraction, which decreased by 8% with N fertilization. The soluble C and N content strongly correlated with total and available N content. The changes in soil N were influenced by cover crop species and fertilization and the interactions of both, so the combination of fertilization regime and cover crops must be chosen with care. Additionally, legumes are a good source of plant and soil N in systems with low input of N via fertilizer; however, the combination of N fertilizer with legumes can reduce soil N reserves, leading to its long-term depletion.

Optimisation of distillation process parameters for extraction of Tay Giang citronella essential oil by direct steam distillation method

In Vietnam, there were several research on essential oil extraction from citronella leaves by direct steam distillation. However, most studies focused on the effects of temperature, pressure, and distillation time on essential oil yield, mainly aiming to reduce distillation time with little attention to the chemical composition of the citronella oil obtained. Meanwhile, citronella essential oil contains no fewer than 20 constituents with the 3 most important constituents being citronellal, geraniol, and citronellol. The Vietnamese National Standard 11426:2016 (equal to ISO 3848:2016) regulates the chemical content of Java citronella essential oil for export as citronellal 31-40%, geraniol 20-25%, and citronellol 8.5-14%. The current Java citronella oil often has a citronellol content below 20%, thus failing to meet the standard in ISO 3848:2016. The aims of this research were to optimise the distillation process parameters, including temperature, pressure, and distillation time for extraction of citronella essential oil from Tay Giang citronella by direct steam distillation method in order to maximise yield and maintain geraniol content above 20%. The research results have determined the following optimal technical parameters for the extraction of Tay Giang citronella essential oil: temparature 116±1oC, pressure 1.2±0.05 atm, and distillation time 126±1 min to obtain an essential oil yield of 0.94% with a geraniol content of 20.17%. These results can be used to identify the technology for industrial-scale production of Tay Giang citronella essential oil for export purposes.

Design, Development and Experimentation of Distillation Unit for Essential Oil

Essential oil is extracted from distillation unit. Steam distillation is most process is used for extraction of essential oil. The unit capacity is available for distillation process is very small and these are mostly used for laboratory purpose such as modular distillation apparatus or clevenger apparatus. For large scale production the distillation unit can be used as a product. The product can be beneficial. A new large size capacity of portable distillation unit is presented which can extract oil up to 500 kg. A selection of plant species from geraniaceae family which is geranium subjected to direct steam distillation. The experimentation will work two season plants which are summer and winter. The combination of cost effectiveness and flexibility with high yield of better quality of essential oil after varieties of options in new agricultural production system and startup.

Evaluation of potentially available nitrogen by biological and chemical methods in soil cultivated with maize in succession to cover crops

Estimating mineralization rates is one of the best ways to predict N availability over time. However, different methods can lead to distinct predictions, especially when different production systems are used. The aim of this study was to compare biological and chemical methods commonly used to estimate the potentially available N in a soil cultivated with maize in succession to cover crops and N fertilization. The experimental area has been cultivated with cover crops (jack bean, velvet bean, millet and spontaneous vegetation) and N fertilization (0, 60, 120 and 180 kg N ha−1) since the year 2000 in a split-plot design with cover crops as the main treatments and N rates as secondary treatments. The biological evaluation of N mineralization was performed by means of an aerobic incubation of soil samples, while the chemical methods were either by the use of saline ((Ca(H2PO4)2, CaCl2, KCl) and Illinois soil test and direct steam distillation (DSD). Soil C and N contents were not affected by the cover crops, even after sixteen years of cultivation. The utilization of N by maize plants was affected by cover crops, especially for jack bean, while N fertilization led to a maximum absorption point, estimated in 158 kg N ha−1. The methods for evaluating the potentially available N behaved differently among treatments. The DSD method has significantly correlated with maize N uptake and yield, which demonstrates that it was the most promising method to estimate the potentially available N, although it is not yet calibrated for all agricultural systems.

Alkaline Hydrolyzable Organic Nitrogen as an Index of Nitrogen Mineralization in Soils: Relationship with Activities of Arylamidase and Amidohydrolases

ABSTRACT This study investigated the relationship between a recently proposed alkaline hydrolysis method for estimating the chemical index of nitrogen (N) mineralization potential of soils and the activities of arylamidase and four amidohydrolases involved in hydrolysis of organic N (ON) in soils. Nitrogen mineralization was studied in 13 soils from uncultivated fields in Iowa, USA, by direct steam distillation of 1 g field-most soil treated with 1 M KOH or 1 M NaOH. The distillate was collected in boric acids, which was changed every 5 min for a total of 40 min. The NH4 +-N in the distillate was determined by titration with 0.005 M H2SO4. The cumulative amounts of N hydrolyzed were fitted to the first-order exponential equation to determine the “potentially hydrolyzable N (Nmax )” for the soils. The activities of arylamidase, L-asparaginase, L-glutaminase, amidase, and L-aspartase were assayed at their optimal pH values. Results showed that estimated Nmax values were strongly correlated with the activities of arylamidase and amidohydrolases. The activities of arylamidase and the amidohydrolases were significantly correlated, indicating that the activities of the two groups of enzymes are coupled in mineralization of ON in soils. Based on the specificity of enzyme reactions and the strong relationship between estimated Nmax values and the activities of arylamidase and amidohydrolases, we concluded that similar amide-N bonds were susceptible to enzymatic and alkaline hydrolysis, and that alkaline hydrolyzable ON can be used as an index of N mineralization in soils.

DIVERSIFIKASI RESIDU PRODUK OLAHAN HOME INDUSTRY SIRUP JERUK KALAMANSI DI KABUPATEN BENGKULU TENGAH

Community Service Activities for Residual Diversification of Processed Products Home Industry Syrup Kalamansi in Bengkulu Tengah has been completed. This activity aims to reduce the residual volume of unused Kalamansi syrup yields, the production of high value essential oils and various essential and economically valuable essential oil-based citrus oil products. In this activity we have conducted training on the way of extraction of essential oil from citrus peel residue and crude fiber (dregs) leftover of Kalamansi syrup using direct steam distillation method, followed by training of various essential oil based health products in form of aromatherapy roll oil, and Antiseptic liquid soap. From the results of the activities that have been done, the essential oil from the residue of K alamansi syrup made of clear liquid smelling orange K alamansi. It has also been produced several products made from active essential oil of orange Kalamansi such as wind oil roll on, liquid bath soap, lotion and liquid washing soap. The four products have a typical citrus scent K alamansi, but need to be refined formula to produce a quality product and selling value. Keywords : Citrus Kalamansi, Steam Distillation, essential oils, wind aromatheraphy oil.

Esential oils extraction: a 24-hour steam distillation systematic methodology

Steam distillation is known to be the most prevalent method of essential oil extraction. Despite many studies on extraction methods, there is no report about the impact of distillation process duration on the yield and oil quality. A new 24-h steam distillation process for extraction of plant essential oils is presented. For improving the total yield, prolonged and continued isolation was used. A selection of plant species from Lamiaceae and Apiaceae families was subjected to direct steam distillation and essential oils were collected at different times (1, 2, 3, 6, 12 and 24 h). The analysis included either annual or perennial species monitored in terms of different harvesting time. From these studies, it is conclusively that there is no rule about appropriate extraction time, and different plants need different periods for the essential oils to achieve the desired quality or quantity of extract. Thus, extraction duration is directly dependent on what the study is conducted for.

Techno-economic analysis of extraction-based separation systems for acetone, butanol, and ethanol recovery and purification

BackgroundDual extraction, high-temperature extraction, mixture extraction, and oleyl alcohol extraction have been proposed in the literature for acetone, butanol, and ethanol (ABE) production. However, energy and economic evaluation under similar assumptions of extraction-based separation systems are necessary. Hence, the new process proposed in this work, direct steam distillation (DSD), for regeneration of high-boiling extractants was compared with several extraction-based separation systems.MethodsThe evaluation was performed under similar assumptions through simulation in Aspen Plus V7.3® software. Two end distillation systems (number of non-ideal stages between 70 and 80) were studied. Heat integration and vacuum operation of some units were proposed reducing the energy requirements.ResultsEnergy requirement of hybrid processes, substrate concentration of 200 g/l, was between 6.4 and 8.3 MJ-fuel/kg-ABE. The minimum energy requirements of extraction-based separation systems, feeding a water concentration in the substrate equivalent to extractant selectivity, and ideal assumptions were between 2.6 and 3.5 MJ-fuel/kg-ABE, respectively. The efficiencies of recovery systems for baseline case and ideal evaluation were 0.53–0.57 and 0.81–0.84, respectively.ConclusionsThe main advantages of DSD were the operation of the regeneration column at atmospheric pressure, the utilization of low-pressure steam, and the low energy requirements of preheating. The in situ recovery processes, DSD, and mixture extraction with conventional regeneration were the approaches with the lowest energy requirements and total annualized costs.

Disponibilidade de nitrogênio para o arroz irrigado por inundação, pelo método de destilação a vapor direta

Resumo: O objetivo deste trabalho foi avaliar a capacidade do método de destilação a vapor direta (DVD) em extrair a fração de nitrogênio do solo hidrolisável em meio alcalino, e em predizer a disponibilidade de N em solos aptos ao cultivo de arroz irrigado por inundação. Vinte e cinco amostras foram coletadas da camada de 0-20 cm do solo, com diferenças de textura e teor de matéria orgânica. A mineralização de N por incubação anaeróbica foi realizada em laboratório, e os teores foliares e o acúmulo de N pelas plantas de arroz irrigado foram obtidos em casa de vegetação, pela simulação de condições de alagamento em vasos. Estas variáveis correlacionaram-se ao N extraído pelo método DVD. Os teores de N do solo obtidos com o método, bem como o N disponibilizado após 28 dias de incubação anaeróbica e o N acumulado pelas plantas após 45 dias de cultivo, apresentaram valores elevados. A avaliação de uma fração mais lábil do N, pelo método DVD, melhora a estimativa da disponibilidade de N, em comparação a métodos que avaliam apenas o teor de matéria orgânica, indício de que o método DVD tem potencial para avaliar a disponibilidade de N em solos sob cultivo de arroz irrigado por inundação.

Influence of management systems on the nitrogen mineralization and fertilization of sugarcane

In Colombia, nitrogen fertilizer recommendations for sugarcane are based on data obtained with the WalkLey & Black method, but they do not always result in the best yield. In this sense, the present study aimed to compare the results of the determination of fast mineralizable nitrogen (amino sugars), performed with the Illinois Soil Nitrogen test (ISNT) and Direct Steam Distillation method (DSD) for nitrogen recommendations for crops. A complete randomized block design was used with six treatments, adding nitrogen through urea and compost to Pachic haplustoll soils in Valle del Cauca with organic and conventional production systems that were evaluated from 2011 to 2014. The results showed that higher nitrogen mineralization was estimated using ISNT and DSD methodologies than with the Walkley-Black method, and that its content was different depending on the management system. The best methodology that quantified mineralizable N was Direct Steam Distillation (DSD); however for conventional systems sugarcane was Illinois Soil Nitrogen Test (ISNT), showing differences for the variables associated with the production and yield between the tested systems.

Estimation of Mineralizable Nitrogen from 15N-Labelled Crop Residues using Alkaline-Hydrolyzable Nitrogen Methods

Crop residues play a significant role in soil N cycling. The type of residue, C/N ratio, tillage, and soil moisture influence potentially mineralizable soil-N. This study was established to estimate the N mineralization potential of various crop residues using Direct Steam Distillation (DSD) and the Illinois Soil Nitrogen Test (ISNT). Corn (Zea mays L.), soybean (Glycine max L.), wheat (Triticum aestivum L.), rice (Oryza sativa L.), and grain sorghum (Sorghum bicolor L.) residues were grown in a greenhouse and labeled with 15N using 10 atom% 15N labeled-urea. To assess the N mineralization potential of various crop residues, 0.2 g of residue was subjected to both the DSD and ISNT. Hydrolyzed-N was captured and analyzed for atom% 15N to compare fertilizer atom% 15N to that of the original residue. Total N was quantified to establish recovery percentage. For percentage of N recovery there was a significant residue by method interaction (p < 0.0001) indicating that the two methods recovered varying amounts of N based on the type of residue. Atom% 15N recovered from the soybean residue as alkaline hydrolyzable-N (AH-N) was significantly lower than what was quantified in the plant tissue using TN. Conversely, atom% 15N recovered from the rice residue as AH-N was significantly greater than that which was quantified in the original plant tissue using TN. Comparison of atom% 15N in the residue and recovered AH-N suggested that certain crop species partition fertilizer N differently. Specific estimation of N mineralization potential of crop residues could aid producers in determining fertilizer N needs and encourage the development and implementation of soil-based N tests.

MODIFIKASI SISTEM DESTILASI MINYAK ATSIRI DAUN SIRIH (PIPER BETLE LINN) DENGAN PENERAPAN VOLUME AIR REBUSAN KONSTAN

Most of the cultivation of essential oils, done with the process of distillation such as water distillation systems, direct steam distillation and steam boiler distillation. And was developed on a small/medium scale industry throughout the archipelago. In the process of water distillation, the flow rate and level of oil transport are determined by the ratio of raw materials volume versus distillations water volume. Later on, affected by the steam temperature as well. Both were influenced by the vapor pressure inside the boiling tank, which will determine the level of vapor saturation of oil to be transported. Modifiying the distillations process with applying a control tank to avoid decreasing of distillations watter during the process, with increasing the steam pressure, has successfully improove the oil transports until its optimum rates. By ratio of 4:1 with increasing steam pressure up to 0.3 kgf/cm2, has affecedt to incresing the steam temperature and the rate of oil transport, there for iproofing the yield from 0.44% to 0.71% by total of 80 l water condensate.

Quantifying soil nitrogen mineralization to improve fertilizer nitrogen management of sugarcane

Intensive use of synthetic nitrogen (N) fertilizers for sugarcane (Saccharum spp.) production presents environmental challenges for water and air quality as well as impacts profitability for producers. Central to these concerns is a widespread reliance on yield-based recommendations that invoke generic models of crop N response but lack any means to account for variations in soil N-supplying power, a critical determinant of fertilizer N need for cereal, fiber, and tuber crops. The work reported herein was designed to ascertain the impact of soil N mineralization on sugarcane response to N fertilization and was carried out in conjunction with eight N-response trials conducted between 2006 and 2010 at field sites in the largest sugarcane-cultivated area in Brazil. Soil samples were utilized in categorizing the sites as highly responsive, moderately responsive, or nonresponsive to fertilizer N, based on two chemical indices of soil N availability, the Illinois Soil Nitrogen Test (ISNT) and direct steam distillation (DSD), and assessments of (1) net mineralization during aerobic incubation for 12 weeks and (2) incubation-induced changes in soil N fractions obtained by acid (total hydrolyzable N, hydrolyzable NH4 +-N, amino sugar N, and amino acid N) or alkaline (ISNT-N) hydrolysis. Sugarcane varied widely in response to N fertilization, indicating that yield-based recommendations would often under- or overestimate N requirement and thus adversely impact sustainability of sugarcane-based ethanol production. In studies to evaluate feasibility of soil N testing to improve fertilizer N recommendations, mineral N production upon aerobic incubation was accompanied by significant decreases in hydrolyzable NH4 +-N and ISNT-N, indicating that both fractions were liberating mineralizable forms of soil N. Test values by the ISNT and DSD were highly correlated, and both showed promise for differentiating soil responsiveness to fertilizer N.

Field Validation of N-STaR for Rice Produced on Silt Loam Soils in Arkansas

To facilitate the incorporation and understanding of the Nitrogen Soil Test for Rice (N-STaR), field validation studies were implemented to evaluate the ability of N-STaR to predict the field-specific N rates required to maximize rice yield on silt loam soils in Arkansas. Before flooding, soil samples to a 45-cm depth were taken and analyzed by N-STaR, a direct steam distillation procedure. These field trials compared N rates from three calibration curves, developed to predict 90, 95, and 100% relative grain yield (RGY), with the standard recommendation for rice (Oryza sativa L.) grown on silt loam soils (168 kg N ha−1). Nitrogen fertilizer rates predicted from the three calibration curves ranged from 22 to 252 kg N ha−1. Rice grain yields fertilized with N rates from the N-STaR 90% RGY curve were equal to or greater than the standard recommendation for nine of the 14 sites. Grain yields for rice receiving the N-STaR 95% RGY N rates were equal to or greater than the standard recommendation for 13 of the 14 sites. Similarly, rice yields obtained from the N-STaR 100% RGY curve were equal to or greater than the standard N rate at all of the study sites. Despite visual differences in rice height and color, there were little to no differences in rice yield. These results indicate the importance of field-scale demonstration trials of the N-STaR technology to educate producers, consultants, and extension personnel before full release of this soil-based N test for rice grown on silt loam soils.

Factors Influencing the Recovery of Glucosamine Nitrogen from Soils Commonly Cropped to Rice

The Illinois soil N test (ISNT) is intended to predict the amount of mineralizable N in a soil by estimating the amount of amino sugar N present. The objective of this study was to compare the ISNT with a direct steam distillation (DSD) method for recovering 15N‐labeled glucosamine added to soil collected from the 0‐ to 15‐, 15‐ to 30‐, 30‐ to 45‐, and 45‐ to 60‐cm depth increments. Four clay and four silt loam soils where chosen from rice (Oryza sativa L.) production regions in the mid‐South United States. When the ISNT and DSD were compared across all soils and for all depths, the N liberated with the DSD was, on average, 19.2 mg N kg−1 soil greater than the N liberated with the ISNT. The ISNT recovered 89.2 to 97.9% and the DSD method 88.5 to 99.1% of the 15N‐glucosamine added to the four soil depth increments for all eight soils. There was a significant interaction between soil depth and method; the ISNT recovered a greater amount of added glucosamine‐N from the 0‐ to 15‐cm depth than the DSD. Overall, the ISNT and the DSD methods recovered similar amounts of added glucosamine N from each soil depth below 15 cm but alkaline hydrolyzable N (AH‐N) and total N (TN) appear to influence the recovery of glucosamine when using the DSD. The results of this study indicate that the ISNT and DSD methods can recover similar amounts of glucosamine N in soils with different textures; however, the glucosamine N recovery by DSD is highly influenced by the presence of AH‐N, as indicated by a significant negative relationship.

Predicting Nitrogen Fertilizer Needs for Rice in Arkansas Using Alkaline Hydrolyzable-Nitrogen

The immediate profitability and long-term sustainability of domestic crop production have been threatened by increasing N fertilizer costs. Currently, there is no soil test which can accurately predict the N fertilizer needs of direct-seeded, delayed-flood rice (Oryza sativa L.) produced on silt loam soils in Arkansas. Fertilizer N recommendations could be improved substantially with a calibrated soil N test, while also lowering potential environmental impacts. Twenty-five N response trials were conducted between 2004 and 2008 to correlate alkaline-hydrolyzable N (AH-N), as quantified by the Illinois Soil N Test (ISNT) and direct steam distillation (DSD), with rice response parameters such as total N (TN) uptake, check plot grain yield, and percentage of relative grain yield (RGY) and calibrate AH-N to predict the fertilizer N rate required to achieve 95% RGY. Relationships with the selected parameters were evaluated for both methods over a series of soil depth increments that included 0 to 15, 15 to 30, 30 to 45, 45 to 60, 0 to 30, 0 to 45, and 0 to 60 cm using linear regression models. Alkaline hydrolyzable-N was significantly and positively correlated with all rice response parameters except check plot grain yield and percentage of RGY using AH-N at the 45- to 60-cm depth. Coefficients of determination were greatest for percentage of RGY at the 0- to 30- and 0- to 45-cm depth for the ISNT (r2 = 0.57) and DSD (r2 = 0.73), respectively. Calibration of the fertilizer N rate to achieve 95% RGY resulted in similar trends as the correlation of rice response parameters, but with higher r2 values. Alkaline hydrolyzable-N explained 68 and 89% of the RGY variability in calibration for the ISNT using the 0- to 30-cm depth and the DSD using the 0- to 45-cm depth, respectively. These successful calibrations can be attributed to the N dynamics that exist in direct-seeded, delayed-flood rice production systems and identification of the proper sampling depth.

Changes in Alkaline Hydrolyzable Nitrogen Distribution with Soil Depth: Fertilizer Correlation and Calibration Implications

Alkaline hydrolyzable N (AHN) quantified by the Illinois Soil N Test (ISNT) or direct steam distillation (DSD) may index potentially mineralizable N in the soil. Limited success has been achieved utilizing the ISNT to predict corn (Zea mays L.) yield response when soils are sampled to a depth of 30 cm, and a strong correlation of ISNT to total N (TN) has raised concerns about the sensitivity of the method in determining potentially mineralizable N. A study was implemented to determine the effects of site and soil depth on AHN. Soil samples were collected from 0 to 60 cm in 15‐cm depth increments and analyzed for AHN (by ISNT and DSD) and TN. Analyses of variance for AHN and TN each showed a significant site × soil depth interaction. Alkaline hydrolyzable N ranged from 22 to 280 mg N kg−1 soil and the highest values were not always in the top 15 cm of the soil. Total N ranged from 191 to 1542 mg N kg−1 soil and the highest values were always in the top 15 cm. Soil TN from the 15‐ to 60‐cm depths was generally uniform among 15‐cm increments within each soil, but AHN was not. Alkaline hydrolyzable N accounted for 11 to 38% of soil TN and was variable across sites and depths. Variation in AHN and the fraction of TN quantified as AHN with site and soil depth indicates the importance of proper sampling depth (i.e., to the rooting depth of a given crop) for correlation and calibration of crop response using either the ISNT or DSD. Significant changes in AHN with depth could influence crop‐available N and thus the reliability of a soil test to predict crop response to N fertilization.

The Effects of Drying and Extraction Methods on Essential Oil Content and Composition of Eucalyptus spathulata

The fresh leaves of Eucalyptus spathulata, cultivated in Kashan (central region of Iran), were collected in the middle of spring and dried by five different drying methods (sundrying, shade-drying, oven-drying at 30°C, 40°C and 50°C). The essential oils of every treatment were obtained by hydro-distillation. In addition, the essential oil of shade-dried sample was obtained by two other distillation methods (water and steam distillation and direct steam distillation). The oils were analyzed by capillary GC and GC-MS. Statistical analysis showed significant difference between oil yield (w/w) of the shade-dried sample (2.68 %) compared to sun-dried (2.57 %), ovendried at 30°C (2.42 %), oven-dried at 40°C (2.34 %) and oven-dried at 50°C (2.25 %). The oil yield of the shade-dried sample by hydro-distillation (2.68 %), was higher than those of the water and steam distillation (2.28 %) and steam distillation (1.14 %). Twenty-three components were identified in the oils of E. spathulata obtained by different drying methods, including 1,8-cineole (54.3 - 58.7 %) and α-pinene (25.4 - 33.6 %) as main components. Twenty-five compounds were characterized in the oils of E. spathulata obtained by different distillation methods, including 1,8-cineole (55.8 - 58.2 %) and α-pinene (24.4 - 32.2 %) as major compounds. The results showed for obtaining the highest amount of oil yield and 1,8-cineole content from leaves of E. spathulata, the best drying and distillation methods were shade-drying and hydro-distillation, respectively.