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991.
Purpose
Developing routine methods that accurately predict soil nitrogen (N) mineralization is essential for fertilization recommendation; thus, chemical soil testing has received worldwide attention. However, the optimal chemical soil test for predicting soil N mineralization is region specific. This study aimed to determine suitable chemical soil tests for predicting N mineralization in paddy soils of the Dongting Lake region, China.Materials and methods
Composite surface samples (0–20 cm) of soils (n?=?30) with diverse inherent properties were collected from representative paddy fields across the region. The benchmark indices for soil N mineralization were the net mineralization rate of soil N in a 112-day anaerobic incubation under waterlogged conditions (NMRN112) and N mineralization potential (N o ) estimated using a modified double exponential model. Laboratory-based measurements of soil labile organic N (SLON) were conducted using chemical fractionation methods including 0.01 M NaHCO3 extraction, hot 2 M KCl hydrolysis, phosphate-borate (PB) buffer hydrolysis, acidic KMnO4 oxidation, and alkaline KMnO4 oxidation. These were compared with the benchmark indices to assess their suitability for use as indicators for N mineralization.Results and discussion
Acidic KMnO4-oxidative organic N (acidic KMnO4-N) and PB buffer-hydrolysable organic N (PBHYDR-N) correlated strongly with NMRN112 and N o (r?=?0.825–0.884, P?<?0.001, n?=?30). Grouping of soils based on soil texture generally provided no improvement in the relationships of chemical soil tests with NMRN112 and N o . Multiple stepwise regression analysis indicated that combining acidic KMnO4-N and PBHYDR-N yielded the best prediction of soil N mineralization, explaining 86.1 and 85.5 % of the variation in NMRN112 and N o , respectively, of the 30 tested paddy soils.Conclusions
The results of acidic KMnO4-N and PBHYDR-N as indicators for soil N mineralization were promising, and the operations of acidic KMnO4 oxidation and PB buffer hydrolysis procedures are simple and cost-effective. Therefore, a combination of acidic KMnO4-N and PBHYDR-N shows promise in predicting N mineralization in paddy soils of the Dongting Lake region. However, further calibration through field studies is required and the chemical characteristics of acidic KMnO4-N and PBHYDR-N needs to be further clarified.992.
Scott D. Foster Arūnas P. Verbyla Wayne S. Pitchford 《Journal of Agricultural, Biological & Environmental Statistics》2007,12(2):300-314
The identification of quantitative trait loci (QTL) can be viewed as a subset selection problem. In a simulation study the
least absolute selection and shrinkage operator (LASSO) is shown to be a useful and powerful tool for QTL identification.
LASSO effects are embedded into a mixed model allowing simultaneous modeling of genetic and experimental effects. This provides
the flexibility to model the experiment in conjunction with the power of LASSO QTL identification. Estimation is performed
using an approximation to the restricted likelihood and modified Gaussian elimination. The extended mixed model is used to
analyze a cattle gene mapping dataset. 相似文献
993.
Carmen G. Méndez-García Mayra Y. Luna-Porres Maria E. Montero-Cabrera Marusia Renteria-Villalobos Bernardo Pérez-Cázares Rafael García-Tenorio 《Journal of Soils and Sediments》2016,16(7):1970-1985
Purpose
The El Granero reservoir is the last reservoir of the Rio Conchos before it joins the Rio Grande at the Mexico–USA border. This reservoir, together with the San Marcos reservoir, is located in the arid region of Chihuahua, Mexico. High, naturally occurring radioactivity levels, as well as high arsenic (As) concentrations, have been found in both reservoirs. The main goal of this research was to establish the spatial and temporal distribution of trace and radioactive elements in surface sediments and cores collected from these reservoirs.Materials and methods
Sediment cores were dated using 210Pb and 137Cs measurements and applying the constant rate of supply (CRS) model. Major, trace, and radioactive elements were determined in surface samples and three sediment cores. Radioactive elements were determined by both alpha and gamma spectrometry. Major and trace elements were determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using the EPA 3051a method. Enrichment factors (EF), contamination factors (CF), and pollution load indexes (PLI) were calculated in order to identify the human impact in both reservoirs, whereas the chemical index weathering (CIW) was used to assess differences in the degree of weathering.Results and discussion
High uranium (U) enrichment (EFs?=?24.9–54.7) was observed in core layers at the San Marcos reservoir, while in surface sediments, this enrichment was lower. The high variability of lead (Pb) and As in sediment cores from the Granero reservoir was attributed to human influence. Arsenic and Pb enrichment differences between entry and exit sediment cores were explained by the filtering capabilities of the elongated shape, the topography, and the presence of plants on the reservoir’s bed. The highest PLI was found at the entrance core of the Granero reservoir.Conclusions
The natural element concentration levels of As, Pb, and U were established at the Granero reservoir. High EFs for As and Pb suggest an anthropogenic origin of these pollutants at specific time intervals. High U concentrations in the San Marcos area are explained as naturally occurring. The concentrations of As in most of the studied sediments could pose a risk to human health by As ingestion, since they are above the probable effect level (PEL).994.
Purpose
The potential heat load and stormwater reduction of the anthropogenic, lightweight soil systems, such as green roofs, are valuable to heat island effect mitigation and to urban water management. Benefits of extensive green roofs, as widely used vegetated roof system with very thin soil layer, could be threatened by temporal changes of the soil structure.Materials and methods
Green roof raised beds filled with two different anthropogenic soils (artificially constructed stripped topsoil with admixed crushed bricks and a commercial mixture of a technogenic substrate) were built to investigate the benefits of such systems in a temperate climate. These two soils were chosen with the intent to compare their thermal and water regime. One soil is expected to be favorable for hydrological functioning, whereas the other one for the thermal performance. Temperature and water balance measurements complemented with meteorological observations and knowledge of physical properties of the soil substrates provide the basis for detailed analysis of a thermal and hydrological regime in green roof raised beds. Moreover, the state of pedogenesis was studied on undisturbed soil samples by means of X-ray computed tomography.Results and discussion
The water balance of green roof raised beds was calculated for a whole vegetation season and individual rainfall events. Runoff from raised beds was 38 and 63 % of received rainfall. On the basis of a detailed analysis of individual rainfall events, rainfall-runoff dependency was found for both raised beds. The difference between measured actual evapotranspiration and calculated potential evapotranspiration was discussed on the period with contrasting conditions in terms of moisture stress. Thermal characteristics of soil substrates result in a highly contrasting diurnal variation of soil temperatures. Analysis of X-ray computed tomography-derived macroporosity profiles reveals significant temporal changes in the soil comprised of the stripped topsoil with admixed crushed bricks.Conclusions
Both green roof systems were able to reduce heat load of roof construction when comparing with the concrete roof construction. Similarly, received rainfall was significantly reduced. The extent of rainfall reduction mainly depends on soil, vegetation status, and experienced weather patterns. Methods used for non-invasive imaging proved to be beneficial for studying of soil structure changes.995.
Maria Durban Christine A. Hackett James W. McNicol Adrian C. Newton William T. B. Thomas Iain D. Currie 《Journal of Agricultural, Biological & Environmental Statistics》2003,8(1):48-66
This article examines the practical use of semiparametric models in the analysis of field trials—that is, models with parameterized treatment effects and additive terms derived by a data-driven approach using a locally weighted running line smoother (loess). We discuss graphical methods to identify spatial structure in the data and model selection procedures to choose the degree of smoothing. Once the spatial part of the model has been chosen, hypotheses about the treatment effects may be tested. Semiparametric models are used to analyze two barley field trials exhibiting spatial trends. The first has a single experimental treatment and a row-column design. The second has a split-plot design, and we use a semiparametric model which accounts for the randomization at the different strata of this design. We compare the semiparametric analyses with classical analyses of variance and with alternative spatial models. We find that semiparametric models give a good insight into spatial variation in the field and can improve the precision of parameter estimates. 相似文献
996.
Paola Bortot Carlo Gaetan 《Journal of Agricultural, Biological & Environmental Statistics》2016,21(3):531-547
Two features are often observed in analyses of both daily and hourly rainfall series. One is the tendency for the strength of temporal dependence to decrease when looking at the series above increasing thresholds. The other is the empirical evidence for rainfall extremes to approach independence at high enough levels. To account for these features, Bortot and Gaetan (Scand J Stat 41:606–621, 2014) focus on rainfall exceedances above a fixed high threshold and model their dynamics through a hierarchical approach that allows for changes in the temporal dependence properties when moving further into the right tail. It is found that this modelling procedure performs generally well in analyses of daily rainfalls, but has some inherent theoretical limitations that affect its goodness of fit in the context of hourly data. In order to overcome this drawback, we develop here a modification of the Bortot and Gaetan model derived from a copula-type technique. Application of both model versions to rainfall series recorded in Camborne, England, shows that they provide similar results when studying daily data, but in the analysis of hourly data the modified version is superior. 相似文献
997.
Carbon dioxide emissions after application of tillage systems for a dark red latosol in southern Brazil 总被引：3，自引：0，他引：3
Soil tillage may influence CO2 emissions in agricultural systems. Agricultural soils are managed in several ways in Brazil, ranging from no tillage to intensive land preparation. The objective of this study was to determine the effect of common soil tillage treatments (disk harrow, reversible disk plow, rotary tiller and chisel plow tillage systems) on the intermediate CO2 emissions of a dark red latosol, located in southern Brazil. Different tillage systems produced significant differences in the CO2 emissions, and the results indicate that the chisel plow produced the highest soil carbon loss during the 15 days period after tillage treatments were performed. Emissions to the atmosphere increased as much as 74 g CO2 m−2, at the end of a 2-week period, in the plot where the chisel plow treatment was applied, in comparison to the non-disturbed plot. The results indicate that the total increase on the intermediate term soil CO2 emissions due to tillage treatments in southern Brazil is comparable to that reported for the more humid and cooler regions. 相似文献
998.
Mario A. Pagnotta Alfredo Impiglia Oronzo A. Tanzarella Miloudi M. Nachit Enrico Porceddu 《Genetic Resources and Crop Evolution》2005,51(8):863-869
The durum wheat landrace Haurani (Triticum durum Desf.) is grown under contrasting climatic regions of Syria from Deir Ezzor, in the North-East (230 m altitude, 150 mm mean annual rainfall), to Qunaytra, in the South-West (1060 m altitude, 825 mm mean annual rainfall). In order to assess the genetic variation between and within Haurani populations, samples from eight provinces of Syria (Daraa, Damascus, Qunaytra, Deir Ezzor, Hassakeh, Aleppo, Homs and Hama) were analysed by RFLPs and seed storage proteins of glutenin subunits as markers. The analyses showed the presence of genetic polymorphisms in all populations with the highest values in those from Homs and Hassakeh. Moreover, the results point out differences in genetic distances between populations; some populations were further apart, such as Damascus and Aleppo, whereas others were closer to each other, for instance Homs and Hama. Cluster analysis identified two distinct groups of populations, characterized by geographical proximity, with similar rainfall and altitude. It is suggested that the similarity of landraces at locations close to each other might be the result of more frequent seed exchanges between farmers or of gene flow due to 5% estimated outcross rate of Haurani. 相似文献
999.
Determination of some heavy metals and selenium in Sicilian and Calabrian citrus essential oils using derivative stripping chronopotentiometry 总被引：1，自引：0，他引：1
La Pera L Lo Curto R Di Bella G Dugo G 《Journal of agricultural and food chemistry》2005,53(13):5084-5088
This paper aims to bring some novelty about the concentration of some heavy metals and selenium in biological citrus essential oils (CEO) produced in Sicily and Calabria in different crop years. Derivative stripping chronopotentiometry has been used as an accurate, sensitive, and rapid technique for the determination of Cd, Cu, Mn, Ni, Pb, Zn, and Se in hydrochloric acid extracts of CEO; in the optimized electrochemical conditions, detection limits of <1 microg kg(-1) were obtained for all of the studied metals. In particular, the concentrations of metals were determined in biological bergamot essential oils produced in Calabria in 1999 and 2000 and in biological CEO produced in Sicily in 2003 and 2004. The obtained results provided evidence that Mn was the most abundant metal in all of the studied CEO followed by Zn, Ni, Cu, Pb, and Se; Cd concentrations were always lower than the limit of detection (0.6 microg kg(-1)). 相似文献
1000.
Ranalli A Gomes T Delcuratolo D Contento S Lucera L 《Journal of agricultural and food chemistry》2003,51(9):2597-2602
Three major virgin olive oil varieties (Dritta, Leccino, and Coratina) extracted by a modern centrifugation system aided with a new plant enzyme preparation (having prevalently pectolytic activity) were characterized. These oils showed a clearly enhanced quality standard, owing to higher levels of some important minor components (phenolics, volatiles, tocopherols, carotenes, and chlorophylls) and to frequently lower concentrations of oxidized triglycerides and diglycerides. The oils were therefore characterized by lower susceptibility to oxidation and longer shelf life, and their flavor, aroma, and color features appeared to be significantly improved. The saponifiable fraction was practically not affected as the enzymatic effects involved only the membranes of the oil droplets, where the nonglyceridic compounds are essentially located. 相似文献