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Search Results: 1 - 10 of 144920 matches for " F. Azam "
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Nodulation in Cereals as a Means to Decreasing Their Dependence on Nitrogenous Fertilizers An Achievable Target or a Dogma
F. Azam
Pakistan Journal of Biological Sciences , 2002,
Abstract: Nitrogen is the most common nutrient element, limiting crop production. Introduction and use of chemical N fertilizers has therefore led to a significant increase in crop yields. A major proportion of the nitrogenous fertilizers used in agriculture is applied to staple cereals like rice, wheat and maize. However, because of inherent economical and environmental implications of fertilizer N use, efforts have consistently been made to induce/enhance biological nitrogen fixation in cereals. Induction of nodulation has therefore been the main target of researchers over the past few years. This paper presents an evaluation of the achievements and prospects of nodulation in cereals (with particular reference to wheat and rice) as a means to decrease their dependence on fertilizer N.
Legume-bacterium (Rhizobium) Association-Symbiosis, A Marriage of Convenience, Necessary Evil or Bacterium Taken Hostage by the Legume
F. Azam
Pakistan Journal of Biological Sciences , 2001,
Abstract: Nitrogen (N) is the key nutrient element, limiting crop production under most situations. A major reason for insufficient N supplies being its presence in soil in organic forms which must be mineralized before being used by the plants. However, leguminous plants are equipped with the facility to acquire a major portion of N directly from atmospheric N2 through bacterial fixation (reduction). The bacteria (Rhizobium spp) reside inside the special structures on plant roots i.e., nodules and reduce atmospheric N at the expense of C supplied by the plant. This paper presents an analysis of the nature of association between the legume and bacterium.
Studies on Organic Matter Dynamics and Nitrogen Availability Using 14C and 15N
F. Azam
Journal of Agronomy , 2002,
Abstract: Studies conducted under controlled laboratory conditions using 14C showed a reduction in the rate of decomposition of plant residues with increased chemical complexity of the material; glucose being the most rapidly decomposed and least transformed into humic compounds. Lignin carbon was the most recalcitrant, but up to 50% was transformed into stable humus fractions. Rate and extent of immobilization and remineralization of N decreased with increased complexity of the plant residues/components; maximum being observed for glucose and minimum for lignins. Immobilization and remineralization turnover of N was used to determine dynamics of microbial biomass as well as to test assumptions used for its quantification with chloroform fumigation method. Chloroform fumigation was found to cause a substantial increase in the extractability and mineralization of non-biomass N. Quality of plant residues had a significant bearing on mineralization of N and its interaction with native soil N. Residues with narrow C/N ratio and high content of labile C had a positive effect on release of N from soil organic matter and its availability to crop plants. A substantial and real added nitrogen interaction was observed following application of fertilizer N (more for NH4 than NO3) and leguminous plant residues. In plant experiments, the interaction was exhibited by a substantial increase in root biomass especially under salinity stress. Higher amounts of N were released from leguminous plant residues in the presence of NH4 than NO3. Residues from cereal crops like rice and wheat had a negative effect on the plant availability of N from soil organic matter rather than from applied fertilizer. Studies under field conditions compared leguminous and non-leguminous crops for biomass accumulation and grain yield. When used as a green manuring crop, maize had an effect similar to recommended dose of fertilizer. Green manuring of cereal crop residues like wheat, avena and barley also had a positive effect on yield of wheat.
Added Nitrogen Interaction in the Soil-Plant System-A Review
F. Azam
Journal of Agronomy , 2002,
Abstract: Application of fertilizer N to soil or to the soil-plant system often leads to enhanced mineralization and plant availability of N. By using 15N isotope methodology, it has been found that the extra N comes from soil organic matter as a result of interaction of the added N. This phenomenon is termed "priming" action or added nitrogen interaction (ANI) and may be apparent or real and positive or negative. Apparent ANI is supposedly caused by pool substitution, while real ANI results from changes in the processes that move N into or out of a given pool. Although ANI is generally positive, negative ANIs may arise from processes like net immobilization, denitrification and NO3- leaching. Occurrence of ANI has implications to the determination of fertilizer use efficiency as well as to the fate of fertilizer and soil N. Hence, an understanding of the occurrence of ANI and the mechanisms involved is necessary to devise strategies for improved fertilizer management practices.
Food Security in the New Millennium-I: The Role of Agricultural Biodiversity
S. Farooq,F. Azam
Pakistan Journal of Biological Sciences , 2002,
Abstract: This paper describes the concept of agricultural biodiversity and its importance in present and future food security. Some facts and figures are being presented in order to apprise the reader about the state of agricultural biodiversity in this country and elsewhere. The term agricultural biodiversity has been elaborated at length with special reference to the type of biodiversity available in Pakistan. The importance of biodiversity has been discussed in relation to its role in value addition to commercial crops in the form of resistance against pests and diseases. Its contribution, to human foodstuff, removal of genetic vulnerability and food security has also been discussed in detail. How agro-biodiversity has been utilized in crop production programmes and how rapidly it is being eroded, has also been described. Emphasis has been made on the conservation (both in situ and ex situ) of sites rich in agro-biodiversity along with its characterization and utilization in order to enhance its present status and to create new biodiversity to meet the future demand of crop improvement especially for tolerance to abiotic stresses.
Molecular Markers in Plant Breeding-lll: Practical Applications and Difficulties Encountered
S. Farooq,F. Azam
Pakistan Journal of Biological Sciences , 2002,
Abstract: Some of the empirical results obtained through the use of RFLP, AFLP, SSR and RAPD markers in the areas of DNA fingerprinting, measurement of genetic distance and heterosis, marker-assisted selections and abiotic stress tolerance are being described. Various difficulties that a user can encounter during the ontogeny of marker`s application have also been discussed. Marker mediated varietal fingerprinting and germplasm characterization appeared most common and most pervasive application with AFLP and SSR markers. Being cost effective, easy to handle and devoid of any radioisotope requirement, SSR markers are considered as the most suitable and reliable system for DNA fingerprinting. Capturing heterosis appeared most difficult with very little success due to lack of a facile marker system that could unconditionally identify the heterotic groups, population and progenies. Marker-assisted selections for qualitative traits appeared most successful after DNA fingerprinting while for quantitative characters, major disease resistance genes and genes controlling QTL for abiotic stress tolerance, the success is limited. It is anticipated that application of markers will remain restricted in these areas till the allele-specific markers are available and the cost of marker analysis is reduced significantly.
Molecular Markers in Plant Breeding-I: Concepts and Characterization
S. Farooq,F. Azam
Pakistan Journal of Biological Sciences , 2002,
Abstract: Plant breeding is a combination of principles and methods of changing the genetic constitution of a plant to make it more suitable for human needs. Conventional plant breeding has evolved with the passage of time from simple seed saving of the best harvest to the selection of seeds according to the laws of Mendel. With the advent of morphological and biochemical markers, the selection process has hastened and the scope of conventional plant breeding increased many folds during the recent years. However, the process that actually revolutionized the plant breeding in the 20th century was the realization that there exist a widespread polymorphism in natural populations, the degree of which can be assessed by sequencing or making restriction maps: an application of new tools of molecular biology. The first and the foremost molecular markers system i.e., restriction fragment length polymorphism (RFLP) was developed in early 1980. These are co-dominant markers and are available in unlimited number. Another breakthrough was the emergence of polymerase chain reaction (PCR) in 1990. With this technology, a new generation of DNA markers such as randomly amplified polymorphic DNA (RAPDs), sequence characterized amplified regions (SCARs), sequence tagged sites (STS), single polymorphic amplification test (SPLAT), variable number of tendom repeats (VNTRs), amplified fragment length polymorphism (AFLP), DNA amplification fingerprinting (DFA), single strand conformational polymorphism (SSCP), single nucleotide polymorphism (SNPs), micro-satellites or short tandem repeats (STRs), cDNA, DNA micro arrays and rDNA-ITS were introduced into the modern plant breeding systems. The concept of DNA based markers has increased our ability many folds, to follow minute regions of chromosome through opportunities such as map based cloning and Marker-assisted Plant (MAP) Breeding. In MAP breeding, the new ideas and concepts have been introduced which need to be understood thoroughly, before applying these ideas in practical breeding programmes particular in country like Pakistan where application of molecular biological approaches are still in its infancy. In order to achieve this objective, efforts were made to write a series of review articles in which concept of MAP breeding is being described thoroughly yet in a simple way so that student and researchers can build their understanding of plant molecular breeding and application of DNA based markers for the genetic dissection of qualitative and quantitative traits. In the present paper, concepts of MAP breeding and the type and cha
Nitrification Inhibition in Soil and Ecosystem Functioning An Overview
F. Azam,S. Farooq
Pakistan Journal of Biological Sciences , 2003,
Abstract: Form (NH4 or NO3) and availability of N has significant implications to the functioning and sustainability of agroecosystems. Most of the fertilizer nitrogen (N) applied to agricultural soils is in the form of NH4 or NH4-forming fertilizers. This form of N is rapidly oxidized to NO3 by nitrifying microorganisms leading to significant losses of N through NO3-leaching and denitrification. Both denitrification and NO3-leaching have environmental implications and economic concerns. Strategies have therefore been sought to regulate the process of nitrification leading to its complete or partial inhibition. Indeed, climax ecosystems are developed in such a way that the process of nitrification is already fairly inhibited. This paper presents an overview on: I) the process of nitrification, ii) microorganisms involved, iii) the implications of nitrification and nitrification inhibition to ecosystem functioning and finally iv) the methods to inhibit nitrification.
Response of Wheat (Triticum aestivum L.) to Application of Nitrogenous Fertilizer and Sewage Sludge
F. Azam,A. Lodhi
Pakistan Journal of Biological Sciences , 2001,
Abstract: Interactive effect of inorganic fertilizer and sewage sludge on nitrogen nutrition and growth of wheat was studied. Nitrogen was applied as 15N-labelled (NH4)2SO4 at 0, 50 , 150, and 300 mg pot 1 in all possible combinations with 0, 16, 24, 32, and 64 g pot 1sewage sludge (SS). Fertilizer N had no significant effect on the dry weight of roots. The above-ground plant components responded positively to the application of both fertilizer N and SS. The positive effect increased with the rate of application. In absence of SS, grain yield increased from 4.8 g pot 1 in the control to 10.6 g pot 1 at the highest level of fertilizer N. Likewise, the increase in grain yield due to different treatments ranged between 97 and 233% as compared to 23.3 and 82.5% recorded for straw component. The trends in N content of different plant components were fairly similar to those observed for dry matter yield and a significant correlation was observed between two parameters. Combination of both treatments at highest rate resulted in 127% increase in the total N yield of the plants. The contribution of N fertilizer to the total N content of the whole plant and its components remained fairly low and ranged between 11 and 45% in different treatments. The percent fertilizer N uptake (%FNU) varied from 22.6% at the highest level of application in the absence of sludge to 79.4% at the lowest level of application and in the presence of highest amount of SS. Fertilizer N uptake increased with the amount of SS; the extent of increase being more at the lower level of fertilizer N. Application of SS significantly improved the amount of unlabeled N determined in plants, with maximum effect being observed at the highest level of application. A part of this increase was due to N uptake from SS itself, while a substantial amount could be derived from the soil organic matter
Food Security in the New Millennium-II. The Role of Agriculture Biotechnology
S. Farooq,F. Azam
Pakistan Journal of Biological Sciences , 2002,
Abstract: Plant breeding in its primitive form is being practiced since the transition of human being from hunter/gatherers to settled agriculturist, approximately 10,000 thousand years ago. Without knowing genetics and its principal, it was used genetics to modify crops and their products. The selection of plants with best characteristics as source of next year seeds quickly resulted into domestication of crops that were distinct from their wild relative. Genetic modification (GM) has emerged against this historic background of breeding and selection and is thus, the extension of existing techniques and not something, which is unprecedented. In present paper, efforts have been made to review situation (s) that are responsible for the origin of genetically modified (transgenic) approaches to be used for crop improvement. The outcome of these approaches and the credibility of the resultant products along with their impact and significance on crop productivity in particular have also been reviewed. Impact of GM technology on the poor farmers in the developing countries with special reference to their needs and resources has been discussed in detail. The current status of genetically modified crops in the developed countries and also in the developing countries willing to adopt this technology albeit slowly has also been described along with their fears and concerns in order to provide the readers the choice to select this technology or otherwise according to their own needs and resources. The paper also provides information on the genetically modified products that can have significant impact in improving nutritional status of food generally consumed by millions of people living in the hart land of poverty that is South Asia and Sub-Saharan Africa.
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