37 research outputs found
Crop and Soil Productivity Response to Corn Residue Removal: A Literature Review
Society is facing three related issues: over-reliance on imported fuel, increasing levels of greenhouse gases in the atmosphere, and producing sufficient food for a growing world population. The U.S. Department of Energy and private enterprise are developing technology necessary to use high-cellulose feedstock, such as crop residues, for ethanol production. Corn (Zea mays L.) residue can provide about 1.7 times more C than barley (Hordeum vulgare L.), oat (Avena sativa L.), sorghum [Sorghum bicolor (L.) Moench], soybean [Glycine max L.) Merr.], sunflower (Helianthus annuus L.), and wheat (Triticum aestivum L.) residues based on production levels. Removal of crop residue from the field must be balanced against impacting the environment (soil erosion), maintaining soil organic matter levels, and pre- serving or enhancing productivity. Our objective is to summarize published works for potential impacts of wide-scale, corn stover collection on corn production capacity in Corn Belt soils. We address the issue crop yield (sustainability) and related soil processes directly. However, scarcity of data requires us to deal with the issue of greenhouse gases indirectly and by inference. All ramifications of new management practices and crop uses must be explored and evaluated fully before industry is established. Our conclusion is that within limits, corn stover can be harvested for ethanol production to provide a renewable, domestic source of energy that reduces greenhouse gases. Recommendation for removal rates will vary based on regional yield, climatic conditions, and cultural practices. Agronomists are challenged to develop a procedure (tool) for recommending maximum permissible removal rates that ensure sustained soil productivity
Tillage and wheel traffic affect soil compaction
This archival publication may not reflect current scientific knowledge or recommendations.
Current information available from Minnesota Extension Service
Electrovacuum Static Counterrotating Relativistic Dust Disks
A detailed study is presented of the counterrotating model (CRM) for generic
electrovacuum static axially symmetric relativistic thin disks without radial
pressure. We find a general constraint over the counterrotating tangential
velocities needed to cast the surface energy-momentum tensor of the disk as the
superposition of two counterrotating charged dust fluids. We also find explicit
expressions for the energy densities, charge densities and velocities of the
counterrotating fluids. We then show that this constraint can be satisfied if
we take the two counterrotating streams as circulating along electro-geodesics.
However, we show that, in general, it is not possible to take the two
counterrotating fluids as circulating along electro-geodesics nor take the two
counterrotating tangential velocities as equal and opposite. Four simple
families of models of counterrotating charged disks based on Chazy-Curzon-like,
Zipoy-Voorhees-like, Bonnor-Sackfield-like and Kerr-like electrovacuum
solutions are considered where we obtain some disks with a CRM well behaved.
The models are constructed using the well-known ``displace, cut and reflect''
method extended to solutions of vacuum Einstein-Maxwell equations.Comment: 19 pages, 16 figures, revtex
An infinite family of magnetized Morgan-Morgan relativistic thin disks
Applying the Horsk\'y-Mitskievitch conjecture to the empty space solutions of
Morgan and Morgan due to the gravitational field of a finite disk, we have
obtained the corresponding solutions of the Einstein-Maxwell equations. The
resulting expressions are simply written in terms of oblate spheroidal
coordinates and the solutions represent fields due to magnetized static thin
disk of finite extension. Now, although the solutions are not asymptotically
flat, the masses of the disks are finite and the energy-momentum tensor agrees
with the energy conditions. Furthermore, the magnetic field and the circular
velocity show an acceptable physical behavior.Comment: Submitted to IJTP. This paper is a revised and extended version of a
paper that was presented at arXiv:1006.203