Understanding soil nitrogen supply: organic matter quality and quantity

The soil organic matter (SOM) contents of organic and conventionally farmed soils were compared. Whilst the quantity of SOM was found to be similar with both systems, the quality of SOM differed in respect of higher amounts of N released by the organic soils under anaerobic incubation. This indicated a greater potential rate of mineralization and suggested that the inherent fertility of the organic soils had been improve

Nonuniversal power-law spectra in turbulent systems

Turbulence is generally associated with universal power-law spectra in scale ranges without significant drive or damping. Although many examples of turbulent systems do not exhibit such an inertial range, power-law spectra may still be observed. As a simple model for such situations, a modified version of the Kuramoto-Sivashinsky equation is studied. By means of semi-analytical and numerical studies, one finds power laws with nonuniversal exponents in the spectral range for which the ratio of nonlinear and linear time scales is (roughly) scale-independent.Comment: 5 pages, 5 figure

Identification of vortexes obstructing the dynamo mechanism in laboratory experiments

The magnetohydrodynamic dynamo effect explains the generation of self-sustained magnetic fields in electrically conducting flows, especially in geo- and astrophysical environments. Yet the details of this mechanism are still unknown, e.g., how and to which extent the geometry, the fluid topology, the forcing mechanism and the turbulence can have a negative effect on this process. We report on numerical simulations carried out in spherical geometry, analyzing the predicted velocity flow with the so-called Singular Value Decomposition, a powerful technique that allows us to precisely identify vortexes in the flow which would be difficult to characterize with conventional spectral methods. We then quantify the contribution of these vortexes to the growth rate of the magnetic energy in the system. We identify an axisymmetric vortex, whose rotational direction changes periodically in time, and whose dynamics are decoupled from those of the large scale background flow, is detrimental for the dynamo effect. A comparison with experiments is carried out, showing that similar dynamics were observed in cylindrical geometry. These previously unexpected eddies, which impede the dynamo effect, offer an explanation for the experimental difficulties in attaining a dynamo in spherical geometry.Comment: 25 pages, 12 figures, submitted to Physics of Fluid

Four suggestions for addressing public concern regarding synthetic biology

The following essay was written by Mr. Alex Hatch, a junior undergraduate student majoring in Biological Engineering at Utah State University. Mr. Hatch submitted a 1000-1200 word essay to the 5th Annual Bioethics Contest sponsored by the Institute of Biological Engineering (IBE). A group of professionals in Biological Engineering assessed and ranked the essays in a blinded process. Five semi-finalists were invited to present their essays at a session at the annual meeting of IBE in Cambridge, MA on March 6, 2010. Five judges scored all the presentations and selected Mr. Hatch's contribution as the overall winner (first place)

The influence of nitrification in determining the supply, distribution and fate of nitrogen in grassland soils

Merged with duplicate record 10026.1/815 on 15.02.2017 by CS (TIS)The microbiology of nitrification has been extensively studied, but the ecology and environmental impact of the process has received less attention. The reason for this has more to do with the difficulties of conducting field experiments to examine the links with other processes which cause losses of nitrogen, than a failure to appreciate its importance in agricultural systems. This project was designed to overcome some of the limitations of existing field techniques to enable simultaneous measurements of nitrification and the major processes of N supply (mineralization) and N loss (denitrification and leaching) to be examined. The study proceeded in three distinct phases: firstly, soils with contrasting N management histories were examined, using laboratory assays for potential activities. Clear differences which resulted from higher N inputs were established, with correspondingly higher nitrifying activities. For example, in a fertilized soil, ammonia-oxidizers produced 48.4 compared with 1.3 nM N02 gˉ¹ soil hˉ¹ in an unfertilized soil. Potential nitrite-oxidizing rates were 93.4 and 62.5 nM gˉ¹ hˉ¹ respectively. Assays of enzyme kinetics, therefore confirmed the higher nitrifying activity in the fertilized soil, but demonstrated a lower affinity of the enzyme for N02- substrate, with K, values of 436 and 310 µM N02 -N, respectively. Nitrifying rates in soils from grass-clover swards were intermediate between the fertilized and unfertilized soils. Secondly, a new field incubation technique was developed and used to obtain actual rates by concurrent measurements of the major N cycling processes. A strong correlation was established between nitrification and denitrification (r² = 0. 98). The measurements were verified by comparison with other independent methods. Net rates of nitrification in the same soil type ranged from 0.55 - 1.17 kg N haˉ¹ dˉ¹ , with the highest rates in the fertilized soil. Over 70% of the mineralized N was nitrified, of which 80% was subsequently lost (i.e. either denitrified or leached). Thirdly, the practical implications of these findings were examined in greater detail using 15N labelling techniques which enabled process rates (net and gross) to be established in a model of the N cycle. When nitrification was inhibited, there were no significant differences between gross or net mineralization rates in the soils from the three swards, which indicated that N-immobilization could be directly influenced by the level of nitrifying activity in these soils. The influence of nitrification in determining the pathways of N loss from grassland soils was quantified in this study. From a detailed investigation of the processes involved in N cycling, it was deduced that nitrification was also one of the major factors in determining the outcome of competition for inorganic N between plant and microbial biomasses.The Institute of Grassland and Environmental Researc

PROCESSOR DEMAND AND PRICE-MARKUP FUNCTIONS FOR CATFISH: A DISAGGREGATED ANALYSIS WITH IMPLICATIONS FOR THE OFF-FLAVOR PROBLEM

Off-flavor in catfish restricts farm marketings 10 to 45% depending on the season. The economic impact on society of this imposed supply restriction depends, in part, on the elasticity of demand for catfish. Econometric estimates based on disaggregated processing plant data indicate an elastic demand at the processor level but an inelastic demand at the farm level. Short-run social welfare gains from the elimination of off-flavor are estimated to equal 12.0% of farm revenues ($10.0 million in 1983). The inelastic demand for catfish at the farm level, however, means that most of the societal gains will accrue to individuals beyond the farm gate. Thus, an economic justification exists for public sector funding of off-flavor research.Demand and Price Analysis,

A TYPICAL FARM SERIES: DEVELOPMENT AND APPLICATION TO A MISSISSIPPI DELTA FARM

Farm Management,

Arctic Fox Migrations in Manitoba

A review is provided of the long-range movements and migratory behaviour of the arctic fox in Manitoba. During the period 1919-75, peaks in population tended to occur at three-year intervals, the number of foxes trapped in any particular year varying between 24 and 8,400. Influxes of foxes into the boreal forest were found to follow decreases in the population of their lemming prey along the west coast of Hudson Bay. One fox was collected in 1974 in the aspen-oak transition zone of southern Manitoba, 840 km from Hudson Bay and almost 1000 km south of the barren-ground tundra, evidently after one of the farthest overland movements of the species ever recorded in North America