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Yield prediction has been determined to be vital in sustainable forest management. Recently, research trends have shifted from stand-level to individual-level yield prediction. In this study, we examined the effectiveness of yield prediction models based on a distance-independent approach for Japanese cedar (Cryptomeria japonica (L.f.) D.Don) trees in western Japan. We further examined the accuracy of the models with reference to existing data collected over the long-term. First, we constructed distance-independent height, diameter growth, and survival models. Then, we simulated for approximately 50 years individual tree height, diameter at breast height (DBH), and volume growth using the test data. We then compared the predicted and observed values and calculated root-mean-square error (RMSE) and bias to evaluate the model accuracy. The models were noted to perform well when predicting mean height, DBH, and volume for Japanese cedar trees; in fact, they adequately predicted the diameter distribution. Our results suggest that distance-independent models could adequately predict long-term mean values and diameter distribution. However, RMSE and bias indicated that error propagation occurred over longer time spans. Thus, it is effective to conduct actual measurements at some point in the forest development phase and use the measurements as initial values for short- or mediumterm predictions. Key words: yield prediction, distance-independent competition index, simulation, generalized linear mixed model, Japanese cedar. La prevision du rendement a ete determinee comme etant essentielle pour l'amenagement forestier durable. Recemment, les tendances de la recherche sont passees d'une prevision de rendement de niveau de base a un niveau individuel. Dans la presente etude, nous avons examine l'efficacite des modeles de prevision du rendement en nous fondant sur une approche independante de la distance pour les cedres du Japon (Cryptomeria japonica (L.f.) D.Don) dans l'ouest du Japon. Nous avons de plus examine la precision des modeles en reference aux donnees existantes collectees a long terme. D'abord, nous avons construit des modeles de survie et de croissance du diametre et de la taille independante de la distance. Puis, nous avons fait une simulation pour la croissance de la taille, du diametre a hauteur d'homme (DHH) et du volume d'un arbre individuel d'environ 50 ans en utilisant les donnees des tests. Nous avons alors compare les valeurs prevues et observees et nous avons calcule l'ecart type (ET) et le biais pour evaluer la precision du modele. Les modeles ont obtenu une bonne note lorsqu'ils prevoient la taille moyenne, la DHH et le volume pour les cedres du Japon; en fait, ils ont prevu adequatement la distribution des diametres. Nos resultats suggerent que les modeles independants de la distance pourraient prevoir adequatement a long terme la distribution des diametres et des valeurs moyennes. Toutefois, l'ET et le biais ont indique qu'une propagation des erreurs s'est produite sur des periodes de temps plus longues. Ainsi, il est efficace de faire des mesures reelles a un certain point dans la phase de developpement de la foret et d'utiliser les mesures comme valeurs initiales pour les previsions a court ou a moyen terme. [Traduit par la Redaction] Mots-cles : prevision du rendement, indice de concurrence independant de la distance, simulation, modele mixte lineaire generalise, cedre du Japon., 1. Introduction Yield prediction is crucial to sustainable forest management and planning, and various methods have been validated in countries targeting many species (e.g., Monserud and Sterba 1996; Fox et [...]

Aquaponics have related food and nutrition security benefit that are important for this country (South Africa). The aim of this study was to apply aquaponics decision-making tool to provide potential aquaponics production data and information for South Africa. This study was designed as 2X3X3 factorial study giving 18 interactions. Because aquaponics are the production of fish and crops concurrently, yield production had two levels-fish and crop, fish stocking density had three levels-low, optimum and higher and aquaponics scale of production had 3 levels-hobby, subsistence and commercial scale. The summary of data of aquaponics variables from the literature was used as optimum level, lower and higher levels were based on experimental design. Yield production (kg) of both fish and plants increased significantly (p Key words: Fish stocking density, Yield production, Fish feed, Planting area, INTRODUCTION Poverty and inequalities have risen with the advent of Covid-19 across the world, particularly in South Africa. Aquaponics is the innovative production of fish and crops concurrently in one [...]

The impact of future climate change on sugar beet yields is assessed over western Europe using future (2021-2050) climate scenario data from a General Circulation Model (GCM) and the Broom's Barn simulation model of rain-fed crop growth and yield. GCM output for the 1961-1990 period is first compared with observed climate data and shown to be reliable for regions west of 24[degrees]E. Comparisons east of this meridian were less reliable with this GCM (HadCM2) and so were omitted from simulations of crop yield. Climate change is expected to bring yield increases of around 1 t/ha of sugar in northern Europe with decreases of a similar magnitude in northern France, Belgium and west/central Poland, for the period 2021-2050. Averaged for the study area (weighted by current regional production), yields show no overall change due to changed climate. However, this figure masks significant increases in yield potential (due to accelerated growth in warmer springs) and in losses due to drought stress. Drought losses are predicted to approximately double in areas with an existing problem and to become a serious new problem in NE France and Belgium. Overall west and central Europe simulated average drought losses rise from 7% (1961-1990) to 18% (2021-2050). The annual variability of yield (as measured by the coefficient of variation) will increase by half, from 10% to 15% compared to 1961-1990, again with potentially serious consequences for the sugar industry. The importance of crop breeding for drought tolerance is further emphasised. These changes are independent of the 9% yield increase which we estimate, on the basis of work by Demmers-Derks et al. (1998), is the likely direct effect of the increase in atmospheric C[O.sub.2] concentration by 2021-2050.

Important characteristics of spatial agricultural production functions are derived by introducing a non-negative curvilinear spatial demand function for production input intensities. Given the usual neoclassical rationale assumptions of spatial demand [...]

Agricultural output productivity measurement has traditionally relied on marketed outputs and inputs. Productivity changes can be measured more accurately by integrating nonmarketed commodity conditions. Such a productivity index approach considers the possibility of pollution reductions as agricultural gains. Output distance functions can help measure nonmarketed output changes, although they do not address consumer shadow prices.

Environmentally interactive technologies beyond those affecting private goods require integration of public goods, quasi-public goods and conditionally productive goods in productivity analysis. Shadow prices for goods exposed to externalities can be measured, but will be unable to include productivity of other vital nonmarket goods. Adjustment of total factor productivity to total resource productivity will account for market failure differences under such externalities.

US farms have been established as major areas of productivity growth, posting growth rates three times higher than that of other nonfarm industries through updated studies in 1985. However, productivity declines also affected agriculture in the 1970s, as they posted negative growth rates. This decline has been attributed particularly to stricter environmental regulation, particularly those restricting agricultural pesticides. Such productivity effects can be measured in terms of a proposed total resource productivity model based on an integration of welfare maximization and producer orientation.

Byline: George E. Battese (1), Sumiter S. Broca (2) Keywords: Stochastic frontiers; production functions; technical efficiency Abstract: This paper considers translog and Cobb-Douglas stochastic frontiers in which the technical inefficiency effects are defined by three different models. The models involved are the time-varying inefficiency model, proposed by Battese and Coelli (1992), the inefficiency effects model for panel data, proposed by Battese and Coelli (1995), and the non-neutral frontier model, proposed by Huang and Liu (1994). Technical change is also accounted for in the frontier models. Predicted technical efficiencies of the wheat farmers and estimates of the elasticities of wheat production with respect to the different inputs and the returns-to-scale parameter are compared under the different model specifications. Author Affiliation: (1) Department of Econometrics, University of New England, Armidale, NSW, 2351, Australia (2) National Council of Applied Economic Research, 11 IP Estate, New Delhi, 110002, India Article History: Registration Date: 29/09/2004

The impact of agricultural reform policies on the consumption, production and trade of the former Soviet Union was analyzed in a model of world agricultural trade. The reform policies would include the establishment of a price-driven market economy and acceptance of world prices as the basis of producer and consumer prices. The model forecasted that liberalization of agricultural trade would result in lesser grain imports, an increase of oilseed and soybeal meal imports and insignificant changes in meat imports.

The major aim of this short paper is to provide an original systematic statement of the index number problem involved in obtaining internationally comparable agricultural production aggregates. Alternative output repricing and implicit exchange rates methods are expounded. The standard method of comparison based on wheat-relatives, as used in the work of Hayami and associates, is critically reviewed, and a case is made for the use of alternative procedures.