Effects of fallow replacement green manuring with annual legumes on soil nitrogen availability

Non-Peer ReviewedLegume green manures are used in crop rotations to enhance soil nitrogen availability and to provide ground cover for soil conservation. The annual legumes Black Lentil, Chickling Vetch, Tangier Flatpea, and a Feedpea were grown with tall stubble snow trapping in rotation with spring wheat to determine their suitability for fallow replacement in wheat production systems in the Brown soil zone. The field experiment, conducted at Swift Current Research Station from 1984 to 1991, was designed to assess the different legume types and green manure management practices (inoculation, incorporation, and desiccation). The RCB included fallow-wheat and continuous wheat as controls. Only continuous wheat received nitrogen (N) fertilizer. Soil N availability was measured by analyzing five soil segments down to 120 cm depth for exchangeable ammonium and nitrate up to four times each year. The topsoil was also analyzed by an incubation/leaching technique to determine the potential N mineralization after three cycles of the rotation in 1990. Soil nitrate showed large treatment related variation. Nitrate values for legume green manuring were consistently higher after incorporation than after desiccation. In all treatments, topsoil nitrate was high in spring and lowest in July. In fall and spring following fallow and green manuring nitrate was high for the fallow-wheat and the legume-wheat rotations and low for continuous wheat. The initial potential rate of nitrogen mineralization reveals a lower nitrogen supplying power of the topsoil for fallow wheat than for legume/wheat and for fertilized continuous wheat

Long-term use of urea vs. anhydrous ammonia for N-fertilization of a Dark Brown loam: III. Soil microbial populations and activities

Non-Peer ReviewedThe influence of fertilizers on soil quality, including soil microbial well-being, has been frequently questioned by proponents of organic farming and Low Input Sustainable Agriculture (LISA). A 10-yr experiment, conducted on a Dark Brown loam at Scott, in which the influence of urea and and anhydrous ammonia at rates up to 180 kg N ha-1 on yields of cereals and oilseeds was examined, provided the basis for this study. In the tenth year we took soil samples at 2 depths (0 to 7.5-, 7.5 to 15-cm) at 3 times (3 days before, 6 days, and 26 days after fertilizer application) . We assessed the impact of these treatments on populations of filamentous fungi, yeasts, bacteria, actinomycetes, nitrifiers, and denitrifiers. The fertilizer effects were most pronounced 6 days after N application but were also apparent just prior to N application, confirming a residual treatment effect. Generally, the effects were greater in the second depth where the fertilizer was placed. There were no obvious effects on yeasts or denitrifiers. Generally bacterial and fungal populations were directly related to N rates and were increased more by anhydrous ammonia than by urea. In contrast, actinomycete populations were inversely related to rate of N and the population was lower for anhydrous ammonia than for urea. Nitrifiers responded positively to N rate near the depth of N placement with the response peaking at the 90 kg ha-1 rate. The pHCaCl2 of the check soil, which was already low (5.2) was further decreased to 4.2 by 180 kg N ha-1, the decrease being greater for the anhydrous ammonia source. We believe positive responses in microbial populations are due to the nutritive value of N and negative responses related to soil acidification

Extraction of arbitrarily shaped objects using stochastic multiple birth-and-death dynamics and active contours

We extend the marked point process models that have been used for object extraction from images to arbitrarily shaped objects, without greatly increasing the computational complexity of sampling and estimation. The approach can be viewed as an extension of the active contour methodology to an a priori unknown number of objects. Sampling and estimation are based on a stochastic birth-and-death process defined in a space of multiple, arbitrarily shaped objects, where the objects are defined by the image data and prior information. The performance of the approach is demonstrated via experimental results on synthetic and real data

First Sagittarius A* Event Horizon Telescope results. I. The shadow of the supermassive black hole in the center of the Milky Way

Galaxie

First Sagittarius A* event horizon telescope results. II. EHT and multiwavelength observations, data processing, and calibration

Instrumentatio

Nonlinear multigrid optimization for Bayesian diffusion tomography

Optical diffusion tomography attempts to reconstruct an object cross section from measurements of scattered and attenuated light. While Bayesian approaches are well suited to this difficult nonlinear inverse problem, the resulting optimization problem is very computationally expensive. In this paper, we propose a nonlinear multigrid technique for computing the maximum a posteriori (MAP) reconstruction in the optical diffusion tomography problem. The multigrid approach improves reconstruction quality by avoiding local minimum. In addition, it dramatically reduces computation. Each iteration of the algorithm alternates a Born approximation step with a single cycle of a nonlinear multigrid algorithm