Spatial variability of soil solution nitrates and soil morphology as effected by long term management on a Highland Rim site

A study of the effects of long term management and soil morphology on distribution of soil solution nitrates and chlorides was conducted at the Highland Rim Experiment Station in Robertson County, Tennessee. The site area was a soil fertilization study which had been under continuous corn for 28 years. Two sites were fertilized annually with 336 kg ha-1 nitrogen, 112 kg ha-1 phosphorus, 336 kg ha-1 potassium, and 56 kg ha-1 of a minor element supplement. Two other sites received this same treatment plus 10 tons/acres of manure. Two control sites were sampled in undisturbed native soils on the same landscape. Six pedons were sampled to study spatial variability of the soil taxon. The effect of manuring and long term management on measured soil chemical properties was determined. Fourteen points in each of two plots were randomly sampled to determine distribution and quantity of soil solution nitrates and chlorides. Field morphology included horizon designations, depth, boundary distinctness, texture, color, consistence, and structure. Observations of concretions, fossils,and other soil components were noted. Laboratory data included total carbon analysis, cation exchange capacity, percent base saturation, pH, particle size analysis, KCl total acidity, hydroxylamine-hydrochloride manganese, citrate-bicarbonate-dithionite iron, and Mehlich I extraction of eighteen elements. The soils in pedons 1 and 2 were classified as fine-silty, siliceous, thermic Fragic Paleudults. Pedons 3 and 8 were classified as fine-silty, siliceous, thermic Typic Paleudults. Pedons 4 and 7 were classified as fine-silty, siliceous, thermic Typic Hapludults. Parent material generally was loess over alluvium over residuum. Movement of soil solution nitrates and chlorides was influenced by soil texture, structure, chemical composition, and the presence of pans or discontinuities. Nitrates were concentrated in the horizons above a plow pan at approximately 28 centimeters and above a paleosol at approximately 85 centimeters. The nitrates were moving laterally downslope over the paleosol. Additions of high amounts of nitrogen had no direct correlation with soil solution nitrates. Long term additions of manure and fertilizer amendments influenced the chemical and physical composition of the soil. Total carbon was a good indicator of total nitrogen. A similar relationship was exhibited between Mehlich I extracted manganese and hydroxylamine hydrochloride extracted manganese. Long term management did influence soil morphology. Both management and morphology had an effect on concentration and distribution of nitrates as well as other chemical components in the soil

The Final Fate of Binary Neutron Stars: What Happens After the Merger?

The merger of two neutron stars usually produces a remnant with a mass significantly above the single (nonrotating) neutron star maximum mass. In some cases, the remnant will be stabilized against collapse by rapid, differential rotation. MHD-driven angular momentum transport eventually leads to the collapse of the remnant's core, resulting in a black hole surrounded by a massive accretion torus. Here we present simulations of this process. The plausibility of generating short duration gamma ray bursts through this scenario is discussed.Comment: 3 pages. To appear in the Proceedings of the Eleventh Marcel Grossmann Meeting, Berlin, Germany, 23-29 July 2006, World Scientific, Singapore (2007

Magnetic Braking and Viscous Damping of Differential Rotation in Cylindrical Stars

Differential rotation in stars generates toroidal magnetic fields whenever an initial seed poloidal field is present. The resulting magnetic stresses, along with viscosity, drive the star toward uniform rotation. This magnetic braking has important dynamical consequences in many astrophysical contexts. For example, merging binary neutron stars can form "hypermassive" remnants supported against collapse by differential rotation. The removal of this support by magnetic braking induces radial fluid motion, which can lead to delayed collapse of the remnant to a black hole. We explore the effects of magnetic braking and viscosity on the structure of a differentially rotating, compressible star, generalizing our earlier calculations for incompressible configurations. The star is idealized as a differentially rotating, infinite cylinder supported initially by a polytropic equation of state. The gas is assumed to be infinitely conducting and our calculations are performed in Newtonian gravitation. Though highly idealized, our model allows for the incorporation of magnetic fields, viscosity, compressibility, and shocks with minimal computational resources in a 1+1 dimensional Lagrangian MHD code. Our evolution calculations show that magnetic braking can lead to significant structural changes in a star, including quasistatic contraction of the core and ejection of matter in the outermost regions to form a wind or an ambient disk. These calculations serve as a prelude and a guide to more realistic MHD simulations in full 3+1 general relativity.Comment: 20 pages, 19 figures, 3 tables, AASTeX, accepted by Ap