1,857 research outputs found
Some personality and cognitive correlates of career maturity.
The principal objective of this study was to determine the personality and cognitive correlates of career maturity. The sample comprised 1476 first-year students from different faculties at a South-African university. The Career Development Questionnaire was used to determine the career maturity levels of the respondents. Based on the scores in respect of the Career Development Questionnaire the respondents were divided into a career mature, a career immature and a middle group. These groups were then compared in respect of various personality and cognitive constructs. Statistically significant differences were found in respect of most of the personality constructs but not in terms of the cognitive constructs. The implications of the findings are discussed
Yield Response and N-fertilizer recovery of rainfed wheat growing in the Mediterranean region
Yield response and isotopic N-fertilizer recovery of rainfed wheat were assessed as influenced by fertilizer rate and timing. A popular bread wheat cultivar, Seri 82, was planted in a 4-year experiment from 1994/1995 to 1997/1998. Urea fertilizer was applied at rates of 0-240 N ha-1 in two split applications. Fertilizer-N recovery and residual N remaining in the soil after wheat harvest were measured using 15N-labelled fertilizers. The highest wheat grain yield ranged from 4.9 to 6.9 t ha-1 with 240 kg N ha-1 fertilizer. The 4-year results showed that wheat benefited least from the fertilizer applied near planting. N-fertilizer recovery was higher from fertilizer applied during tillering compared with application at emergence. The results suggest that applying one-third or less of the total N at planting and applying the remained at tillering can minimize leaching risks. Another befit of this strategy would be an overall increase in N-fertilizer recovery. Residual fertilizer-N left in soil after wheat harvest was proportional to N application rates and mainly confined t the upper 40 cm depth. 15N recovery by wheat at maturity was 50-60%, indicating that 40-50% of fertilizer-N remained in the soil or was lost. Over 95% of total fertilizer application to wheat could be accounted for in the wheat crop or soil after harvest at the 240 kg N ha-1 rate. The results, therefore, suggest that leaching losses of fertilizer-N below 90 cm were not likely during the growing season for rainfed what grown on these heavy-textured soils (Palexerollic Chromoxeret) of the Mediterranean region
Appropriateness of Management Zones for Characterizing Spatial Variability of Soil Properties and Irrigated Corn Yields across Years
Recent precision-agriculture research has focused on use of management zones (MZ) as a method for variable application of inputs like N. The objectives of this study were to determine (i) if landscape attributes could be aggregated into MZthat characterize spatial varia- tion in soil chemical properties and corn yields and (ii) if temporal variability affects expression of yield spatial variability. This work was conducted on an irrigated cornfield near Gibbon, NE. Five landscape attributes, including a soil brightness image (red, green, and blue bands), elevation, and apparent electrical conductivity, were acquired for the field.Ageoreferenced soil-sampling scheme was used to determine soil chemical properties (soil pH, electrical conductivity, P, and organic matter). Georeferenced yield monitor data were collected for five (1997–2001) seasons. The five landscape attributes were aggregated into four MZ using principal-component analysis of landscape attributes and unsupervised classification of principal-component scores. All of the soil chemical properties differed among the four MZ. While yields were observed to differ by up to 25% between the highest- and lowest-yielding MZ in three of five seasons, receiving average precipitation, less-pronounced (≤5%) differences were noted among the same MZ in the driest and wettest seasons. This illustrates the significant role temporal variability plays in altering yield spatial variability, even under irrigation. Use of MZ for variable application tem, of inputs like N would only have been appropriate for this field in three out of the five seasons, seriously restricting the use of this approach under variable environmental conditions
Appropriateness of Management Zones for Characterizing Spatial Variability of Soil Properties and Irrigated Corn Yields across Years
Recent precision-agriculture research has focused on use of management zones (MZ) as a method for variable application of inputs like N. The objectives of this study were to determine (i) if landscape attributes could be aggregated into MZthat characterize spatial varia- tion in soil chemical properties and corn yields and (ii) if temporal variability affects expression of yield spatial variability. This work was conducted on an irrigated cornfield near Gibbon, NE. Five landscape attributes, including a soil brightness image (red, green, and blue bands), elevation, and apparent electrical conductivity, were acquired for the field.Ageoreferenced soil-sampling scheme was used to determine soil chemical properties (soil pH, electrical conductivity, P, and organic matter). Georeferenced yield monitor data were collected for five (1997–2001) seasons. The five landscape attributes were aggregated into four MZ using principal-component analysis of landscape attributes and unsupervised classification of principal-component scores. All of the soil chemical properties differed among the four MZ. While yields were observed to differ by up to 25% between the highest- and lowest-yielding MZ in three of five seasons, receiving average precipitation, less-pronounced (≤5%) differences were noted among the same MZ in the driest and wettest seasons. This illustrates the significant role temporal variability plays in altering yield spatial variability, even under irrigation. Use of MZ for variable application tem, of inputs like N would only have been appropriate for this field in three out of the five seasons, seriously restricting the use of this approach under variable environmental conditions
Corn Stalk Nitrate Concentration Profile
The end-of-season nitrate test provides a method of assessing the N available to the corn (Zea mays L.) crop during the latter part of the season. This study was conducted to determine how stalk nitrate test results and interpretations are affected by sample composition. Stalks were collected from three filed sites and separated into phytomers (node plus internode above), which were subdivided into three or five segments after length was measured. Nitrate-N concentration of phytomers decreased linearly from the soil to the ear. Within a phytomer, segments also decreased acropetally (from base to apex). Node tissue NO3-N concentration did not differ from that of the internode segment immediately above the node. Weighted means were used to compute NO3-N concentration of stalk samples collected 5 cm higher (from 20 to 40 cm above the soil) or lower (from 10 to 30 cm above the soil). Although the three samples (10-30, 15-35, and 20-40 cm) differed in NO3-N concentration, the difference was only about 15% compared with the 25% difference in sampling position (± 5 cm of 20-cm sample length). The phytomer nearest the soil had 35 to 40% greater NO3-N concentrations than the section of stalk 15 to 35 cm above the soil. Critical values delineating yield-limiting adequate, and excessive N availability should be modified if stalk sections other than the standard 15 to 35 cm section are used. However, the qualitative nature of the stalk nitrate test and the range of NO3-N concentrations observed with reasonable corn cultural practices (1000x) make this test quite robust and precise definition of sample composition and critical values less necessary
EC03-702 Precision Agriculture: Applications of Remote Sensing in Site-Specific Management
Precision farming is an emerging agricultural technology that involves managing each crop input on a site-specific basis to reduce waste, increase profits, and maintain the quality of the environment. Remote sensing is a technology that can be used to obtain various spatial layers of information about soil and crop conditions. It allows detection and/or characterization of an object, series of objects, or landscape without having the sensor in physical contact
Maize Production Impacts on Groundwater Quality
The cumulative effects of management pratices on nitrate-nitrogen (NO3-N) leaching and groundwater quality are frequently difficult to document because of the time required for expression and the diversity of interacting process involved. This work reports results of a N and water management program initiated by the Central Platte Natural Resource District (CPNRD) in Nebraska. Cultural pratices recommended by the CPNRD and reported by producers for the 1988 growing season, representing approximately 3900 fields and fertilizer N application rates. Groundwater NO3-N concentrations were positively correlated with ressidual N in the surface 0.9 m of soil prior to the growing season, reflecting the effects of past N and water management practices. Yield goals in 1988 averaged 9% higher than the average 10.0 Mg ha-1 in excess of the average N recommendation. By comparison, in a 1980 to 1984 study from an area within the CPNRD, yield goals averaged 28% greater than actual yields. Overly optimistic yield goals in 1988 accounted for 42% of the average excess N application rate 48 kg ha-1 (based on University of Nebraska recommendations). A large portion of average excess N application is attributed to producers in 14% of the area who applied \u3e 100 kg N ha-1 more than the recommened rates. Fertilizer N applied showed little relationship to fertilizer N recommended. Better education and more stringent measures may be required to address the select group of producers who fail to follow CPNRD recommendations
Spatio-temporal development of vegetation die-off in a submerging coastal marsh
In several places around the world, coastal marsh vegetation is converting to open water through the formation of pools. This is concerning, as vegetation die-off is expected to reduce the marshes\u27 capacity to adapt to sea level rise by vegetation-induced sediment accretion. Quantitative analyses of the spatial and temporal development of marsh vegetation die-off are scarce, although these are needed to understand the bio-geomorphic feedback effects of vegetation die-off on flow, erosion, and sedimentation. In this study, we quantified the spatial and temporal development of marsh vegetation die-off with aerial images from 1938 to 2010 in a submerging coastal marsh along the Blackwater River (Maryland, U.S.A). Our results indicate that die-off begins with conversion of marsh vegetation into bare open water pools that are relatively far (\u3e 75 m) from tidal channels. As vegetation die-off continues, pools expand, and new pools emerge at shorter and shorter distances from channels. Consequently larger pools are found at larger distances from the channels. Our results suggest that the size of the pools and possibly the connection of pools with the tidal channel system have important bio-geomorphic implications and aggravate marsh deterioration. Moreover, we found that the temporal development of vegetation die-off in moderately degraded marshes is similar as the spatial die-off development along a present-day gradient, which indicates that the contemporary die-off gradient might be considered a chronosequence that offers a unique opportunity to study vegetation die-off processes
The Staudinger Ligation
While the Staudinger reaction has first been described a hundred years ago in 1919, the ligation reaction became one of the most important and efficient bioconjugation techniques in the 1990s and this century. It holds the crucial characteristics for bioorthogonal chemistry: biocompatibility, selectivity, and a rapid and high-yielding turnover for a wide variety of applications. In the past years, it has been used especially in chemical biology for peptide/protein synthesis, posttranslational modifications, and DNA labeling. Furthermore, it can be used for cell-surface engineering, development of microarrays, and drug delivery systems. However, it is also possible to use the reaction in synthetic chemistry for general formation of amide bonds. In this review, the three major types, traceless and nontraceless Staudinger Ligation as well as the Staudinger phosphite reaction, are described in detail. We will further illustrate each reaction mechanism and describe characteristic substrates, intermediates, and products. In addition, not only its advantages but also stereochemical aspects, scope, and limitations, in particular side reactions, are discussed. Finally, the method is compared to other bioorthogonal labeling methods
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