Economic control of fertilizer in highly productive pastoral systems. I. A theoretical framework for the fertilization problem

A hypothetical model, based on plant physiology and termed ‘Mitscherlich-Liebig’, is proposed as a general solution to the problem of estimating an optimum fertilizer rate from results in a field trial; in combining the ideas of Liebig and Mitscherlich the model involves the following proposals:

1. Diminishing returns in a smooth exponential relation between input and output culminating in a yield-plateau.
2. The difference between this plateau and the ideal asymptotic maximum is the result of an unavoidable osmotic depression caused by salts in the root zone.
3. Liebigian nonsubstitution of one essential elemental nutrient by another.
4. Quantitative equivalence in output from essential inputs when each is expressed in terms of a physiologically standardized amount defined as a Baule unit.
5. Pooling response data according to a relative yield theory and the Baule unit concept, rather than grouping data according to a soil type theory and the concept of a response curve unique for the element concerned.

In addition to certain other biometrical implications, these concepts provide an explicit method for estimating the composition of a balanced fertilizer mixture, whereby a profit maximising calculation may be applied through the ratio: cost of applied fertilizer/price of harvested yield. This approach to the problem permits a formulation of fertilizer advice theoretically sound in plant physiology as well as economics.     

Economic control of fertiliser in highly productive pastoral systems. V. Extending advice through the Mitscherlich-Liebig model

A general solution is proposed to the problem of extending economic fertilizer advice over a highly productive pastoral area. The scheme implies a subdivision of the area through objective information obtained from widely dispersed, long-term, 3 level field trials; within sub-areas advice appropriate to a particular farm, or part thereof, is specified by incorporating more or less subjective estimates concerning level of output from the current input of fertilizer and carry-over of fertility in the field from one year to the next. The mathematical model used to facilitate an economic evaluation has been termed ML because it combines two cardinal principles: Mitscherlich's Law of Diminishing Returns and Liebig's Law of the Minimum, and is thus in accord with both economic and physiological theory. The model has been used to assess the effectiveness of chemical soil testing as a means of estimating carryover of fertility and to study the sensitivity of economic advice to error in the vital ratio: cost of input/selling price of output. The concept of a common response curve for essential elements has been developed as a basis for calculating the composition of a complete physiologically balanced fertilizer.The articles I–IV appeared inFertilizer Research 4:4 (1984)     

Economic control of fertilizer in highly productive pastoral systems. IV. An appropriate model for a stable upgraded state

Data from a stable upgraded grass-clover system were used to show that an exponential model, based on the ideas of Liebig and Mitscherlich, may be simplified to permit a prediction of yields over years through three constant parameters for the fertilizer effect and one varying parameter for the climatic effect; this result is in accord with the Mitscherlich relative yield theory. When the model was applied to an economic analysis of the data, the result emphasized the importance of the concept of an average year in calculating fertilizer recommendations; also, it became apparent that completely unfertilized plots should be excluded from field trials intended as a base for such economic advice.     

Economic control of fertilizer in highly productive pastoral systems. III. A hypothetical model to quantify upgrading from a primitive into a highly productive state

A model suitable for quantifying the upgrading of primitive pasture by phosphatic fertilizer is described; the model, based on the Mitscherlich-Spillman equation, provides a criterion for judging when upgrading is complete. Such information is essential to permit a successful experimental attack on the problem of providing fertilizer-advice for highly productive systems where the nutritional requirements both of pasture plants and grazing animals have to be satisfied. The advice must therefore have a sound basis in physiology as well as in economics; but, the generally accepted modern approach cannot be integrated into a logically consistent and practically possible solution to this complex problem. Consequently, the present proposals involve a number of innovations to replace inadequate concepts in the current approach; the most important of these are as follows.

1. Replacement of the economic theory of isoquantal substitution by production function analysis of long term average response by pasture to a complete (physiologically balanced) mixture of fertilizers.
2. Use of a hypothetical model justified by biological theory rather than an empirical model justified by a least squares-best fit criterion.
3. Replacement of multilevel factorial field experiments by simple 3-level trials representatively dispersed over the whole of the commercially productive area and carried on for a decade.
4. Exclusion of grazing animals from the main phase of a simple trial, but with their heterotrophic cycling of nutrients effectively simulated by a modified experimental technique.
5. Systematic use of foliar chemical analysis, which in one way or another is essential to supplement each of the first 4 innovations.

     

Revision of the conceptual model of combustion mechanism in a liquid-propellant rocket on the basis of the results of highly informative experiments. II. Updating of the model

On the basis of the accumulated experimental data, it is established that gas recirculation in the combustion chamber of a liquid-propellant rocket is due not to a single factor (ejection by a fuel injection) but two factors; the second factor is the nonequilibrium (over the chamber cross section) distribution of the sources and outflows of gases from the combustion process. The second factor, acting on recirculation, acts again on combustion with a certain delay, etc. Taking other characteristics into account, the combustion process in this case should be examined in the context of the theory of self-organization of nonequilibrium systems. A corresponding conceptual model is constructed that is consistent at a qualitative level with the expermental data on various forms of parametric instability of combustion in a liquid-propellant rocket.     

Frozen-in birefringence and anisotropic shrinkage in optical moldings: II. Comparison of simulations with experiments on light-guide plates

The thermally-, flow-induced and total birefringence components and anisotropic shrinkages in LGP moldings were simulated by using a combination of a CV/FEM/FDM technique nonlinear viscoelastic and photoviscoelastic constitutive equations and orientation functions, as described in Part I of this study. The simulated results were compared with measurements on LGP moldings of a polystyrene (PS) and two optical grade polycarbonates (PCs) OQ1030 and OQ3820 having low and high molecular weights. The thermally-induced birefringence was simulated by a combination of constrained and free cooling during molding. In LGP moldings of PS, the simulated thermally-induced birefringence indicated a minor variation with location in the mold plane, a parabolic shape in the core region and an increase towards the wall. Compared to the flow-induced birefringence, the thermal birefringence provided a minor contribution to the total transverse birefringence Δn₁₂. In LGP moldings of PCs, the simulated thermally-induced birefringence showed a significant variation with location in the mold plane, nearly constant value in the core region and high value in the wall region. In LGP moldings of both PCs, the contributions of the thermally- and flow-induced birefringence to the total transverse birefringence Δn₁₂ were significant. The effect of processing conditions on the development of the normal birefringence in LGP moldings of PCs was ranked from most to least: the packing pressure, mold temperature, melt temperature, injection speed and packing time. However, in LGP moldings of PS the packing time effect was significant due to a longer gate freezing time. Simulated and measured normal birefringence along the flow direction was in fair agreement, but simulations were unable to describe the observed birefringence maximum arising near the gate. The averaged luminance of LGP moldings exhibited some correlation with the averaged normal birefringence. LGP moldings of PC OQ1030 indicated a pronounced maximum in the simulated transverse flow birefringence in the core but a low value near the wall. In contrast, the LGP molding of PC OQ3820 showed a high simulated birefringence near the wall and a low value of maximum in the core. The simulated and measured total transverse birefringence in LGP moldings was in fair agreement. LGP molding of both PCs showed similar tendency in shrinkage variation with processing conditions. However, the thickness shrinkage was higher in LGP moldings of PC OQ3820. The effect of processing conditions on the development of shrinkage in LGP moldings of both PCs was ranked from most to least: the packing pressure, melt temperature, mold temperature, injection speed and packing time. In LGP moldings of PS, the thickness shrinkage slightly increased with increasing melt temperature and significantly increased with reducing packing time. A good agreement between the simulated and measured anisotropic shrinkages in LGP moldings at various processing conditions was observed.     

Application of volumetric electrodes to the recuperation of metals in industrial effluents—II. Design of an axial field flow through porous electrodes

The potential drop occurring in the bed of the flow-through porous electrode (fpe) changes the local metal-solution potential difference (lpd). Thus it may destroy the considered electrochemical reaction specificity or limit the electrolytic cell efficiency.So, it's necessary to compute the fpe geometry (bed height, particles diameter) which satisfies the lpd for a chosen pair flow-yield.This study, realized in the case of a fixed bed built with very conductive particles, proposes a generalized equations system which permits the fpe design. It's possible to do the same for an undistinguished electrochemical reaction by introducing a characteristic number of this system. From these equations a design diagram is established.A discussion about the axial field electrode limits as performing reactor follows.     

Analysis of resin injection molding in molds with preplaced fiber mats. II: Numerical simulation and experiments of mold filling

This work presents the results of numerical simulation and experimental visualization of the mold filling process in resin injection molding with preplaced fiber mats. The mold filling experiments were conducted with various mat stacks consisting of continuous random glass fiber mats and bidirectional stitched glass fiber mats. The use of two different mat types in the mat stack created porosity and permeability variations. The effect of these permeability variations was studied by taking flow pressure measurements and observing the progress of the flow front of a non-reactive fluid filling a clear acrylic mold that contained the reinforcement mat stack. Numerical simulation corresponding to each experiment was also carried out. The numerical results were compared to the experimental measurements.     

Kinetics of structuring in the sol-gel systems based on tetraethoxysilane with organic additives: II. Gels

This paper reports on the results of investigations into the rheological properties of gels that are prepared by aging sols based on water-alcohol solutions of tetraethoxysilane (TEOS) modified by a number of metal salts and organic polyhydroxyl compounds, such as glycerol, poly(ethylene glycol) (PEG-300), and hyperbranched aliphatic complex polyol polyethers (HBP-49, HBP-64). It is demonstrated that the strength of the gels formed can be controlled using these additives.     

Early-stage sintering in a powder compact of polyhedral particles II. Experimental analysis with a highly sinterable Al2O3

A model of early-stage sintering for polyhedral particles is examined with a highly sinterable Al₂O₃ powder. Combining of the initial and intermediate stages based on the model concerned describes quantitatively its sintering data such as power dependence of time and reduction in a specific surface area. Valid estimations of a model and/or mechanisms of sintering necessitate the accurate measurement of both shrinkage versus sintering time and specific surface area versus shrinkage.     

Stability of moving surfaces in fluid systems with heat and mass transport II. Combined effects of transport and density difference between Phases

Stability of interfaces moving as a result of phase transformation or mass transfer is considered. Effects of transport and of the density difference between phases known to significantly influence stability during solidification and combustion respectively are here studied theoretically in fluid systems. The analysis indicates that instability is possible during vaporization of liquids under vacuum and perhaps during growth of cavitation bubbles. But except when interfacial tension is very low, instability is unlikely during mass transfer in liquid-liquid systems because the density difference between phases is small. A density difference can also produce cellular convection at an unstable interface during solidification.     

A new type of organic electrosynthesis reactor with a two-phase gas-electrolyte stream flowing through a mercury cathode,II. Limiting currents and mass-transfer studies in organotin electrosynthesis

A new electrochemical reactor involving a mercury cathode and a two-phase (gas-liquid) flow has been studied with a view to continuously manufacturing hexaphenyl and hexabutyldistannane b'y reduction of triorganotin chloride R₃SnCl. In each case the interpretation of the determining step of the process is discussed after a study of the electrochemical kinetics. In the reactor an efficient renewal of the cathodic surface is obtained by passing the electrolysis solution together with nitrogen gas through the mercury pool. Results of mass transfer rate studies with the cell working either as a plug-flow reactor or as a continuously stirred reactor are compared for different gas and electrolyte flows. The experiments show that gas and electrolyte flows through a mercury pool offer attractive possibilities of application for large-scale preparative electrolysis, by solving simultaneously the problems of mass transport and electrode surface renewal.     

Catalyst based on BaZrO3 with different elements incorporated in the structure: II. BaZr(1−x)RhxO3 systems for the production of syngas by partial oxidation of methane

New catalytic systems, synthesised by a variant of the citrate route, are proposed for the partial oxidation of methane. They consist of solid solutions – barium, zirconium, rhodium and oxygen – with a perovskite structure of formula BaZr_(1−x)Rh_xO₃. Detailed analysis of the XRD diffractograms and the TGA cycles show that Rh is randomly distributed as Rh^IV among the B sites of the perovskite, together with Zr. The activities of the catalysts have been tested for the catalytic partial oxidation of methane at short contact times to evaluate the potential of materials giving promising results in terms of syngas yield at low Rh loading.