Enzyme activities and microbial community structure in semiarid agricultural soils

This study investigated the effect of management on -glucosidase, -glucosaminidase, alkaline phosphatase, and arylsulfatase activities and the microbial community structure in semiarid soils from West Texas, USA. Surface samples (0–5 cm) were taken from a fine sandy loam, sandy clay loam, and loam that were under continuous cotton ( Gossypium hirsutum L.) or in cotton rotated with peanut ( Arachis hypogaea L.), sorghum ( Sorghum bicolor L.), rye ( Secale cereale) or wheat ( Triticum aestivum L.), and had different water management (irrigated or dryland), and tillage (conservation or conventional). The enzyme activities were higher in the loam and sandy clay loam than in the fine sandy loam. Soil pH was not affected by management, but the soil organic C and total N contents were generally affected by the different crop rotations and tillage practices studied. The trends of the enzyme activities as affected by management depended on the soil, but in general crop rotations and conservation tillage increased the enzyme activities in comparison to continuous cotton and conventional tillage. The soil enzyme activities were significantly correlated with the soil organic C ( r -values up to 0.90, P< 0.001), and were correlated among each other ( r -values up to 0.90, P <0.001). There were differences in the fatty acid methyl ester profiles between the fine sandy loam and the sandy clay loam and loam, and they reflected the differences in the enzyme activities found among the soils. For example, a 15:0 ranged from 1.61±0.25% in cotton-peanut/irrigated/no-till in the fine sandy loam to 3.86±0.48% in cotton-sorghum/dryland/conservation tillage in the sandy clay loam. There were no differences due to management within the same soil.Trade names and company names are included for the benefit of the reader and do not infer any endorsement or preferential treatment of the product by USDA-ARS     

Influence of organic fertilizer application on pendimethalin volatilization and persistence in soil

Laboratory studies were undertaken to evaluate the influence of fertilizers on pendimethalin volatilization and persistence in soil. Various organic fertilizers such as liquid humic substances and urea were used at doses of 100 L/ha or 170 kg of N/ha, respectively. Herbicide residues were determined in air, soil solution, and soil samples by GC-ECD; the recovery of pendimethalin from spiked fertilized or control samples was found to be 81-103%. Liquid humic fertilizers increased pendimethalin dissipation during the first part of the assay, although 4 months after application, herbicide levels were similar to those observed in unfertilized soil. Fertilization of soil with urea decreased, in general, pendimethalin volatilization but increased herbicide levels in soil solution and persistence in soil, with a pendimethalin half-life approximately 70% higher than that found in unfertilized soil.     

Changes in broccoli (Brassica oleracea L. Var. italica) health-promoting compounds with inflorescence development

Changes in phenolic compounds, total glucosinolates, and vitamin C were monitored during the productive period along five inflorescence development stages of three broccoli commercial cultivars (Marathon, Monterrey, and Vencedor). In an attempt to identify differences due to agronomic factors, broccoli cultivars were grown under different sulfur fertilization with poor (15 kg/ha) and rich (150 kg/ha) rates. Phenolic compounds and vitamin C concentrations showed, in all broccoli cultivars, a rising trend from the first stage until the over-maturity stage, both for rich and poor sulfur fertilization. Significant differences were detected in the first two stages between rich and poor sulfur fertilization in total glucosinolates for all broccoli cultivars, where the highest concentration was always observed in the second development stage (used as minimally processed product) during poor fertilization. With regard to the last three stages, the glucosinolate concentration in the poor sulfur fertilization started to slope down until the over-maturity stage. Where rich sulfur fertilization is concerned, the highest level was reached during the third stage (used as minimally processed product also), and after that, glucosinolate concentration decreased until the fifth stage.     

Organophosphorus pesticide residues in Mexican commercial pasteurized milk

A study was conducted to measure residues of 13 organophosphorus (OP) pesticides, widely used as dairy cattle ectoparasiticides or in crops used for animal feed, in homogenized and pasteurized Mexican milk samples. Four different milk brands with high distribution were collected biweekly during a 12 month period (n = 96) in supermarkets. OP pesticide residues were measured by gas chromatography with a flame photometric detector. Approximately 39.6% of the samples contained detectable levels of OP pesticide residues. Eight samples contained residues exceeding established maximum residue limits (MRL), and the OP pesticides present in these samples were dichlorvos (five samples), phorate, chlorpyrifos, and chlorfenvinphos (one sample, respectively). Average residues of 13 OP pesticides measured were below established MRLs ranging between 0.0051 and 0.0203 ppm.     

Volatile compounds in Spanish, French, and American oak woods after natural seasoning and toasting

The volatile composition (volatile phenols, phenolic aldehydes, furanic compounds, lactones, phenyl ketones, and other related compounds) of Spanish oak heartwood of Quercus robur, Quercus petraea,Quercus pyrenaica, and Quercus faginea was studied by gas chromatography/mass spectrometry, in relation to the processing in barrels cooperage and in relation to the French oak of Quercus robur (Limousin) and Quercus petraea (Allier) and American oak of Quercus alba (Missouri), which are habitually used in cooperage. The volatile composition of seasoned oak woods varied according to individual trees, species, and origins, and the differences were more significant in Spanish species with respect to American species than with respect to French species. The toasting process influenced the volatile composition of wood. It led to high increases in the concentration of volatile phenols, furanic aldehydes, phenyl ketones, and other related structures, but the effect on w-lactones levels depended on species and origin. The volatile composition in Spanish oak species evolved during toasting like in French and American oak, but quantitative differences were found, especially important in American species with respect to European species.     

Participatory landrace selection for on-farm conservation: An example from the Central Valleys of Oaxaca, Mexico

On-farm conservation is recognized as a key component of a comprehensive strategy to conserve crop genetic resources. A fundamental problem faced by any on-farm conservation project is the identification of crop populations on which efforts should be focused. This paper describes a method to identify a subset of landraces for further conservation efforts from a larger collection representing the diversity found in the Central Valleys of Oaxaca, Mexico. Mexico is a center of origin and diversity for maize (Zea mays L.). The 17 landraces selected from an initial collection of 152 satisfy two criteria. First, they represent the diversity present in the larger collection. Second, they appear to serve the interests of farmers in the region. Data for applying the method were elicited through participatory as well as conventional techniques. They incorporate the complementary perspectives of both men and women members of farm households, and of plant breeders and social scientists.     

Rapid quantitative assessment of the adulteration of virgin olive oils with hazelnut oils using Raman spectroscopy and chemometrics

The authentication of extra virgin olive oil and its adulteration with lower-priced oils are serious problems in the olive oil industry. In addition to the obvious effect on producer profits, adulteration can also cause severe health and safety problems. A number of techniques, including chromatographic and spectroscopic methods, have recently been employed to assess the purity of olive oils. In this study Raman spectroscopy together with multivariate and evolutionary computational-based methods have been employed to assess the ability of Raman spectroscopy to discriminate between chemically very closely related oils. Additionally, the levels of hazelnut oils used to adulterate extra virgin olive oil were successfully quantified using partial least squares and genetic programming.     

Persistence of simazine and terbuthylazine in a semiarid soil after organic amendment with urban sewage sludge

The persistence of two herbicides, simazine and terbuthylazine, and appearance of their principal dealkylated chloro-s-triazine metabolites have been studied in agricultural soil after the addition of urban sewage sludge as organic amendment. Both herbicides and metabolites were monitored during long-term laboratory incubation (140 days) and analyzed by gas chromatography with a nitrogen-phosphorus detector (GC-NPD). Residues were confirmed by gas chromatography with a mass selective detector (GC-MSD). A sonication microextraction method was used to extract the compounds. The organic amendments used were urban sewage sludge and the humic fraction of this sludge, to increase the organic matter content of the soil from 1% to 2%. For both compounds, simazine and terbuthylazine, the degradation began earlier in the amended soils. Simazine showed a higher dissipation rate than terbuthylazine, the percentage of the former at the end of the experiment being lower than 2% in all cases, while for terbuthylazine the corresponding percentage ranged from 5% to 46%. Organic amendment, mainly its humic fraction, caused a certain stabilization of terbuthylazine in the soil, but did not greatly influence the residual amount of simazine at the end of the experiment. The periodic aeration of the soil caused a greater degradation in the case of terbuthylazine. Only mono-deethylsimazine and deethylterbuthylazine were isolated from the soil during the time the experiment lasted, while the di-deethylated metabolite of simazine was not found.     

A new methodology based on GC-MS to detect honey adulteration with commercial syrups

Honey adulterations can be carried out by addition of inexpensive sugar syrups, such as high fructose corn syrup (HFCS) and inverted syrup (IS). Carbohydrate composition of 20 honey samples (16 nectar and 4 honeydew honeys) and 6 syrups has been studied by GC and GC-MS in order to detect differences between both sample groups. The presence of difructose anhydrides (DFAs) in these syrups is described for the first time in this paper; their proportions were dependent on the syrup type considered. As these compounds were not detected in any of the 20 honey samples analyzed, their presence in honey is proposed as a marker of adulteration. Detection of honey adulteration with HFCS and IS requires a previous enrichment step to remove major sugars (monosaccharides) and to preconcentrate DFAs. A new methodology based on yeast (Saccharomyces cerevisiae) treatment has been developed to allow the detection of DFAs in adulterated honeys in concentrations as low as 5% (w/w).