970 resultados para Agronomy and Crop Science


Relevância:

100.00% 100.00%

Publicador:

Resumo:

Application of nitrogen (N) fertilizers in agricultural soils increases the risk of N loss to the atmosphere in the form of ammonia (NH3), nitrous oxide (N2O) and nitric oxide (NO)and the water bodies as nitrate (NO3-). The implementation of agricultural management practices can affect these losses. In Mediterranean irrigation systems, the greatest losses of NO3-through leaching occur within the irrigation and the intercropperiod. One way to abate these losses during the intercrop period is the use of cover crops that absorb part of the residual N from the root zone (Gabriel and Quemada, 2011). Moreover, during the following crop, these species could be applied as amendments to the soil, providing both C and N to the soil. This effect of cover and catch crops on decreasing the pool of N potentially lost has focused primarily on NO3-leaching. The aim of this work was to evaluate the effect of cover crops on N2O emission during the in tercrop period in a maize system and its subsequent incorporation into the soil in the following maize crop.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Long-term conservation tillage can modify vertical distribution of nutrients in soil profiles and alter nutrient availability and yields of crops.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

All crop models, whether site-specific or global-gridded and regardless of crop, simulate daily crop transpiration and soil evaporation during the crop life cycle, resulting in seasonal crop water use. Modelers use several methods for predicting daily potential evapotranspiration (ET), including FAO-56, Penman-Monteith, Priestley-Taylor, Hargreaves, full energy balance, and transpiration water efficiency. They use extinction equations to partition energy to soil evaporation or transpiration, depending on leaf area index. Most models simulate soil water balance and soil-root water supply for transpiration, and limit transpiration if water uptake is insufficient, and thereafter reduce dry matter production. Comparisons among multiple crop and global gridded models in the Agricultural Model Intercomparison and Improvement Project (AgMIP) show surprisingly large differences in simulated ET and crop water use for the same climatic conditions. Model intercomparisons alone are not enough to know which approaches are correct. There is an urgent need to test these models against field-observed data on ET and crop water use. It is important to test various ET modules/equations in a model platform where other aspects such as soil water balance and rooting are held constant, to avoid compensation caused by other parts of models. The CSM-CROPGRO model in DSSAT already has ET equations for Priestley-Taylor, Penman-FAO-24, Penman-Monteith-FAO-56, and an hourly energy balance approach. In this work, we added transpiration-efficiency modules to DSSAT and AgMaize models and tested the various ET equations against available data on ET, soil water balance, and season-long crop water use of soybean, fababean, maize, and other crops where runoff and deep percolation were known or zero. The different ET modules created considerable differences in predicted ET, growth, and yield.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

v. 15 (ser. 3, v. 6) (1896)

Relevância:

100.00% 100.00%

Publicador:

Resumo:

The intent of the study was to understand the changes that have occurred over the last 25 years in library programs as far as enrollment and diversity of students, number and ethnicity of the faculty, program income and expenses, cost of attendance, and scholarship and fellowship aid, in an effort to better understand library programs granting the MLIS degree. The study also endeavored to identify institutional factors associated with the retention and productivity rates of White students and students of color in schools of library and information science. During the period studied, the proportional representation of White students decreased. For students of color, proportional representation was stable during the same time period. Results revealed a medium effect size of time with productivity rates for both groups declining over time. Retention rate differed significantly by time, with a small effect size with retention rate that initially increased over time, but is now decreasing. The final analyses were meta-regressions to determine if retention and productivity rates can be predicted by cost of attendance, scholarship and fellow aid, and program size. Results indicated that for students of color, program size in 2000 was significantly predictive of retention, cost of attendance was predictive in 2002, and scholarship and fellowship aid was predictive of retention in 2004. No variables were significantly predictive for retention of White students. The last analysis was to determine if productivity rate can be predicted by cost of attendance, scholarship and fellow aid, and program size. Results indicate that for White students in 2002, the cost of attendance was predictive of productivity rating. In 2003, scholarship and fellowship aid was predictive of productivity rate and in 2004, scholarship and fellowship aid was predictive of productivity rating. For students of color, results indicate that only scholarship and fellowship aid in 2005 was predictive of productivity rate. No other variables in any of the years studied showed any significant prediction of productivity rating for students of color.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

This article examines the U.S model of library and information science (LIS) education in light of the changes brought about by information and communication technology. The accepted model of professional preparation in the United States has emphasized graduate education on a Master’s level from LIS programs accredited by the American Library Association (ALA). The authors trace the historical development of this approach and provide an overview of the ALA accreditation process. Furthermore, they examine the strategies of LIS programs in adjusting to the changing information environment, present the debate about the iSchool movement, and discuss the evolution of the core curriculum. In addition, the article explores the relationship between LIS education and the field of practice and presents a practitioner’s perspective on educating library professionals. The authors conclude that the model of advanced professional preparation for librarianship is still relevant in the digital environment, but it requires greater flexibility and close cooperation with the field of practice.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

The purpose of this study is multifaceted: 1) to describe eScience research in acomprehensive way; 2) to help library and information specialists understand the realm of eScience research and the information needs of the community and demonstrate the importance of LIS professionals within the eScience domain; 3) and to explore the current state of curricular content of ALA accredited MLS/MLIS programs to understand the extent to which they prepare new professionals within eScience librarianship. The literature review focuses heavily on eScientists and other data-driven researchers’ information service needs in addition to demonstrating how and why librarians and information specialists can and should fulfill these service gaps and information needs within eScience research. By looking at the current curriculum of American Library Association (ALA) accredited MLS/MLIS programs, we can identify potential gaps in knowledge and where to improve in order to prepare and train new MLS/MLIS graduates to fulfill the needs of eScientists. This investigation is meant to be informative and can be used as a tool for LIS programs to assess their curriculums in comparison to the needs of eScience and other data-driven and networked research. Finally, this investigation will provide awareness and insight into the services needed to support a thriving eScience and data-driven research community to the LIS profession.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

The thousands of books and articles on Charles de Gaulle's policy toward European integration, whether written by historians, social scientists, or commentators, universally accord primary explanatory importance to the General's distinctive geopolitical ideology. In explaining his motivations, only secondary significance, if any at all, is attached to commercial considerations. This paper seeks to reverse this historiographical consensus by examining the four major decisions toward European integration during de Gaulle's presidency: the decisions to remain in the Common Market in 1958, to propose the Foucher Plan in the early 1960s, to veto British accession to the EC, and to provoke the "empty chair" crisis in 1965-1966, resulting in the "Luxembourg Compromise." In each case, the overwhelming bulk of the primary evidence-speeches, memoirs, or government documents-suggests that de Gaulle's primary motivation was economic, not geopolitical or ideological. Like his predecessors and successors, de Gaulle sought to promote French industry and agriculture by establishing protected markets for their export products. This empirical finding has three broader implications: (1) For those interesred in the European Union, it suggests that regional integration has been driven primarily by economic, not geopolitical considerations--even in the "least likely" case. (2) For those interested in the role of ideas in foreign policy, it suggests that strong interest groups in a democracy limit the impact of a leader's geopolitical ideology--even where the executive has very broad institutional autonomy. De Gaulle was a democratic statesman first and an ideological visionary second. (3) For those who employ qualitative case-study methods, it suggests that even a broad, representative sample of secondary sources does not create a firm basis for causal inference. For political scientists, as for historians, there is in many cases no reliable alternative to primary-source research.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

The thousands of books and articles on Charles de Gaulle's policy toward European integration, whether written by historians, political scientists, or commentators, universally accord primary explanatory importance to the General's distinctive geopolitical ideology. In explaining his motivations, only secondary significance, if any at all, is attached to commercial considerations. This paper seeks to reverse this historiographical consensus by the four major decisions toward European integration taken under de Gaulle's Presidency: the decisions to remain in the Common Market in 1958, to propose the Fouchet Plan in the early 1960s, to veto British accession to the EC, and to provoke the "empty chair" crisis in 1965-1966, resulting in Luxembourg Compromise. In each case, the overwhelming bulk of the primary evidence speeches, memoirs, or government documents suggests that de Gaulle's primary motivation was economic, not geopolitical or ideological. Like his predecessors and successors, de Gaulle sought to promote French industry and agriculture by establishing protected markets for their export products. This empirical finding has three broader implications: (1) For those interested in the European Union, it suggests that regional integration has been driven primarily by economic, not geopolitical considerations even in the least likely case. (2) For those interested in the role of ideas in foreign policy, it suggests that strong interest groups in a democracy limit the impact of a leaders geopolitical ideology even where the executive has very broad institutional autonomy. De Gaulle was a democratic statesman first and an ideological visionary second. (3) For those who employ qualitative case-study methods, it suggests that even a broad, representative sample of secondary sources does not create a firm basis for causal inference. For political scientists, as for historians, there is in many cases no reliable alternative to primary source research.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Mode of access: Internet.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Editors: 1890-95, E. J. James; 1896-1900, R. P. Falkner; Jan. 1901-Mar. 1902, H. R. Seager; May 1902-Sept. 1914, E. R. Johnson; Nov. 1914-July 1929, C. L/ King; Sept. 1929- T. Sellin.