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Benchmarking productive efficiency of selected wheat areas in Pakistan and India using data envelopment analysis,

IRRIGATION AND DRAINAGE, Issue 4 2006
Naeem M. Malana
MEG (/DEA); analyse comparative; productivité de l'irrigation; productivité; blé; Pakistan; Inde Abstract Food demand is bound to increase significantly in future as a result of a growing world population. As a large proportion of the available land and water resources have been developed, there is limited scope for further increase in the use of these resources. Thus future increases in food production will originate from improvements in performance of existing agriculture rather than development of new resources. It is anticipated that wheat demand in the South Asia will rise significantly in future. In order to increase production and overcome diminishing water availability for irrigation, performance of wheat farms must increase. This paper describes the process of benchmarking the productive efficiency of wheat in selected areas of Pakistan and India. Data envelopment analysis (DEA) is used to evaluate and rank productivity performance of wheat growing areas in both countries based on three inputs: irrigation (m3,ha,1), seed (kg,ha,1) and fertiliser use (kg,ha,1). The results of analysis show that DEA is an effective tool for analysing and benchmarking productive efficiency of agricultural units. Ranking of productive efficiency based on three inputs is also shown to differ significantly from that based on a single resource (irrigation). Copyright © 2006 John Wiley & Sons, Ltd. La demande de nourriture est appelée à augmenter de façon significative du fait de la croissance de la population mondiale. Une forte proportion des ressources en terre et en eau ayant déjà été utilisée, leur potentiel d'accroissement est faible. La production supplémentaire de nourriture devra donc venir de l'amélioration des performances de l'agriculture plutôt que du développement de nouvelles ressources. Il est prévu que la demande de blé en Asie du Sud-Est augmente significativement dans le future. Afin d'augmenter la production et de surmonter la raréfaction de l'eau pour l'irrigation, la performance de la culture du blé doit progresser. Cet article décrit le processus d'analyse comparative appliquée à la productivité de certaines zones à blé du Pakistan et de l'Inde. La Méthode d'Enveloppe Graphique (MEG) est utilisée pour évaluer et classer les productivités des zones à blé de ces deux pays sur la base de trois intrants: l'irrigation (m3/ha), les semences (kg/ha) et les engrais (kg/ha). Les résultats de l'analyse montrent que la MEG est un outil efficace pour l'analyse comparative des productivités d'exploitations agricoles. Le classement des productivités à partir de trois intrants est également différent de celui obtenu à partir d'une seule ressource (l'irrigation). Copyright © 2006 John Wiley & Sons, Ltd. [source]

Shape, shear and flexion: an analytic flexion formalism for realistic mass profiles,

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2009
P. D. Lasky
ABSTRACT Flexion is a non-linear gravitational lensing effect that arises from gradients in the convergence and shear across an image. We derive a formalism that describes non-linear gravitational lensing by a circularly symmetric lens in the thin-lens approximation. This provides us with relatively simple expressions for first- and second-flexion in terms of only the surface density and projected mass distribution of the lens. We give details of exact lens models, in particular providing flexion calculations for a Sérsic-law profile, which has become increasingly popular over recent years. We further provide a single resource for the analytic forms of convergence, shear, first- and second-flexion for the following mass distributions: a point mass, singular isothermal sphere (SIS); Navarro,Frenk,White (NFW) profile; Sérsic-law profile. We quantitatively compare these mass distributions and show that the convergence and first-flexion are better indicators of the Sérsic shape parameter, while for the concentration of NFW profiles the shear and second-flexion terms are preferred. [source]

A MICRO-LEVEL ,CONSUMER APPROACH' TO SPECIES POPULATION DYNAMICS

NATURAL RESOURCE MODELING, Issue 1 2007
THOMAS CHRISTIAANS
ABSTRACT. In this paper we develop a micro ecosystem model whose basic entities are representative organisms which behave as if maximizing their net offspring under constraints. Net offspring is increasing in prey biomass intake, declining in the loss of own biomass to predators and Allee's law applies. The organism's constraint reflects its perception of how scarce its own biomass and the biomass of its prey is. In the short-run periods prices (scarcity indicators) coordinate and determine all biomass transactions and net offspring which directly translates into population growth functions. We are able to explicitly determine these growth functions for a simple food web when specific parametric net offspring functions are chosen in the micro-level ecosystem model. For the case of a single species our model is shown to yield the well-known Verhulst-Pearl logistic growth function. With two species in predator-prey relationship, we derive differential equations whose dynamics are completely characterized and turn out to be similar to the predator-prey model with Michaelis-Menten type functional response. With two species competing for a single resource we find that coexistence is a knife-edge feature confirming Tschirhart's [2002] result in a different but related model. [source]

A competitive coexistence principle?

OIKOS, Issue 10 2009
Cathy Neill
Competitive exclusion , n species cannot coexist on fewer than n limiting resources in a constant and isolated environment , has been a central ecological principle for the past century. Since empirical studies cannot universally demonstrate exclusion, this principle has mainly relied on mathematical proofs. Here we investigate the predictions of a new approach to derive functional responses in consumer/resource systems. Models usually describe the temporal dynamics of consumer/resource systems at a macroscopic level , i.e. at the population level. Each model may be pictured as one time-dependent macroscopic trajectory. Each macroscopic trajectory is, however, the product of many individual fates and from combinatorial considerations can be realized in many different ways at the microscopic , or individual , level. Recently it has been shown that, in systems with large enough numbers of consumer individuals and resource items, one macroscopic trajectory can be realized in many more ways than any other at the individual , or microscopic , level. Therefore, if the temporal dynamics of an ecosystem are assumed to be the outcome of only statistical mechanics , that is, chance , a single trajectory is near-certain and can be described by deterministic equations. We argue that these equations can serve as a null to model consumer-resource dynamics, and show that any number of species can coexist on a single resource in a constant, isolated environment. Competition may result in relative rarity, which may entail exclusion in finite samples of discrete individuals, but exclusion is not systematic. Beyond the coexistence/exclusion outcome, our model also predicts that the relative abundance of any two species depends simply on the ratio of their competitive abilities as computed from , and only from , their intrinsic kinetic and stoichiometric parameters. [source]