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External Inputs (external + input)
Selected AbstractsSoil quality and fertilizer use rates among smallholder farmers in western KenyaAGRICULTURAL ECONOMICS, Issue 5 2009Paswel P. Marenya Fertilizer demand; Fertilizer policy; Soil carbon; Soil organic matter; Switching regression Abstract Studies of fertilizer use in sub-Saharan Africa have been dominated by analyses of economic and market factors having to do with infrastructure, institutions, and incentives that prevent or foster increased fertilizer demand, largely ignoring how soil fertility status conditions farmer demand for fertilizer. We apply a switching regression model to data from 260 farm households in western Kenya in order to allow for the possibility of discontinuities in fertilizer demand based on a soil carbon content (SCC) threshold. We find that the usual factors reflecting liquidity and quasi-fixed inputs are important on high-SCC plots but not on those with poorer soils. External inputs become less effective on soils with low SCC, hence the discernible shift in behaviors across soil quality regimes. For many farmers, improved fertilizer market conditions alone may be insufficient to stimulate increased fertilizer use without complementary improvements in the biophysical conditions that affect conditional factor demand. [source] Refilling, ageing and water quality management of Brucher ReservoirLAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 1 2002Wilfried Scharf Abstract Refilling of the formerly oligo-mesotrophic, softwater Brucher Reservoir commenced in April 1993 and took 11 months to completely fill. A severe ,trophic upsurge' in the sense of nutrient enrichment (phosphorus, dissolved organic material) as a result of the decomposition of the inundated vegetation occurred. However, algal crop and phosphorus utilization efficiency, expressed as chlorophyll concentrations per unit of total phosphorus, remained very low. In the absence of any fish stock, a single species, Daphnia galeata, monopolized the resources. Sustained by the detritus food chain, daphnids exerted a severe,,top-down' control upon phytoplankton, thereby preventing any net algal growth. In 1994, artificial mixing prevented the occurrence of anoxic water conditions and internal nutrient enrichment of the lake. Although the decay of the inundated vegetation was still of importance, phosphorus concentrations in the water column approached equilibrium with the external input while dissolved organic material concentrations clearly declined. That year, the reservoir became stocked with minnows, sun bleak (Leucaspius delineatus) and trout. As food limitation, as a result of reduced heterotrophic production, became more severe in the face of an increasing predation pressure, the daphnid population density declined, resulting in a decreasing but still adequate community filtering rate providing pronounced ,clear-water phases' of up to 10 m that were features of the period 1995,1997. Although D. galeata defended its key position in the food web, its life-history traits (e.g. body size) changed. Submerged macrophytes, which since 1995 gradually colonized suitable areas of the reservoir, provided a favourable refuge for minnows from trout predation that resulted in reduced predation pressure upon pelagic daphnids. However, in 1998, ungrazeable algae became prominent, adversely affecting transparency. That year, the significant inverse relationship between chlorophyll : total phosphorus ratios and daphnids became uncoupled during the summer (July,August) by indigestible chlorococcalean algae. Nevertheless, the fishery management that was implemented was successful in sustaining not only the lowest yield of algae at the given nutrient concentration but also the most favourable species composition with respect to water quality. [source] Role of catchment area in the transport of nutrients to lakes in the Wielkopolska National Park in PolandLAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 1 2002Halina Szyper Abstract The external loading of 14 lakes in the Wielkopolska National Park was calculated, including nitrogen and phosphorus loads from point, diffuse and dispersed sources, precipitation and recreation. The basic source of nitrogen and phosphorus for most lakes in the Park is the export of diffuse pollution from the catchment area. Only four lakes are contaminated by sewage, which accounts for 0.1,61.2% of total nutrient loading. Annual unit area loads of phosphorus and nitrogen estimated for each lake were 2,51 times higher than Vollenweider's critical loading levels. Estimated mass loading and annual unit area loads of nutrients for each lake were compared with lake water quality, expressed as the trophic state index. Analysis of the physico-geographical structure of the catchment area and natural resistance of lakes to external input of nutrients allowed us to assess the role of the catchment in the deterioration of water quality and to indicate the protective measures required. [source] Late prehistoric soil fertility, irrigation management, and agricultural production in northwest coastal PeruGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 1 2004Lee Nordt The Pampa de Chaparrí (Pampa) in hyperarid northwest coastal Peru is an ideal area to study late prehispanic agricultural technology and production because irrigation canals and furrowed fields have been preserved since abandonment approximately 500 years ago. We collected 55 samples for soil characterization, fertility, and micromorphic analyses and compared these results to a noncultivated control soil previously sampled in an adjacent valley. Natural soil fertility levels for maize, cotton, and bean production were generally high during late prehispanic cultivation in the Pampa. Maintaining adequate nitrogren levels for production, however, would have required external inputs from livestock manure, guano, or leguminous plants. The management of low soil salinity levels was possible because of rapidly permeable soils and irrigation waters low in salt. Based on available water capacity and climate conditions, the Blaney-Criddle Equation yields evapotranspiration rates indicating that irrigation frequency was necessary in a range of every 10,16 days during the growing season. © 2004 Wiley Periodicals, Inc. [source] Quantitative framework for reliable safety analysisAICHE JOURNAL, Issue 1 2002Haitao Huang The effectiveness of any methodology used to identify hazards in chemical processes affects both safety and economics. To achieve maximum safety at minimum cost, a conservative, but realistic, analysis must be carried out. An approach to hazard identification is proposed based on a detailed process model which includes nonlinear dynamics and uncertainty. A new modeling framework, the region-transition model (RTM), is developed, which enables the simulation of regions of the operating space through an extension of the hybrid state transition system formalism. The RTM is illustrated on a nonlinear batch reactor with parameter uncertainty. A safety-verification algorithm identifies regions of the input space (initial conditions and external inputs) which guarantee safe operation. The algorithm is successfully applied to three examples: a tank with overflow and underflow, a batch reactor with an exothermic reaction, and a CSTR with feed preheating. [source] AGGLOMERATION EXTERNALITIES, PRODUCTIVITY, AND TECHNICAL INEFFICIENCY,JOURNAL OF REGIONAL SCIENCE, Issue 4 2006Ragnar Tveteras ABSTRACT Agglomeration externalities can have positive effects on both the production possibility frontier and technical inefficiency of firms. Increased levels of localized knowledge spillovers and substitution of internal inputs with external inputs may lead to fewer errors in decision-making and execution of production tasks, thus causing firms to become technically more efficient relative to the production frontier. When we estimate a stochastic frontier production model on a large panel of salmon aquaculture farms, we find econometric support for positive agglomeration externalities on both the production frontier and technical inefficiency. [source] Nitrogen fertilisation in coriander (Coriandrum sativum L.): a review and meta-analysisJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 6 2009Alessandra Carrubba Abstract Nitrogen (N) fertilisation is one of the most important external inputs in assessing coriander seed yield and plant growth. Recent concerns related to the misuse of N fertilisers in agricultural environments, however, stress the opportunity for a fine-tuning of N management in order to optimise the use of this element, avoiding losses and reducing environmental hazards. In this study, some results from the literature concerning N fertilisation in coriander are reviewed and, by means of statistical analysis, an attempt is made to derive from them some general suggestions about practices of N fertilisation. In most cases examined, N fertilisation allowed a 10,70% increase in seed yields in comparison with each respective untreated control. The efficiency of use of this element, however, has proven to be greatly dependent on the overall fertility conditions of the growing site. The greatest yield advantages were actually found in more favourable environments, whereas in low-yielding environments plants reached their maximum yield with a comparatively reduced N supply. In low-yielding environments a careful risk/benefit assessment of this practice is therefore advisable. No definite conclusion could be drawn at this stage about essential oil yield and composition in relation to N fertilisation. Copyright © 2009 Society of Chemical Industry [source] | |||||||||||||