Estimating annual soil carbon loss in agricultural peatland soils using a nitrogen budget approach.

Around the world, peatland degradation and soil subsidence is occurring where these soils have been converted to agriculture. Since initial drainage in the mid-1800s, continuous farming of such soils in the California Sacramento-San Joaquin Delta (the Delta) has led to subsidence of up to 8 meters in places, primarily due to soil organic matter (SOM) oxidation and physical compaction. Rice (Oryza sativa) production has been proposed as an alternative cropping system to limit SOM oxidation. Preliminary research on these soils revealed high N uptake by rice in N fertilizer omission plots, which we hypothesized was the result of SOM oxidation releasing N. Testing this hypothesis, we developed a novel N budgeting approach to assess annual soil C and N loss based on plant N uptake and fallow season N mineralization. Through field experiments examining N dynamics during growing season and winter fallow periods, a complete annual N budget was developed. Soil C loss was calculated from SOM-N mineralization using the soil C:N ratio. Surface water and crop residue were negligible in the total N uptake budget (3 - 4 % combined). Shallow groundwater contributed 24 - 33 %, likely representing subsurface SOM-N mineralization. Assuming 6 and 25 kg N ha-1 from atmospheric deposition and biological N2 fixation, respectively, our results suggest 77 - 81 % of plant N uptake (129 - 149 kg N ha-1) was supplied by SOM mineralization. Considering a range of N uptake efficiency from 50 - 70 %, estimated net C loss ranged from 1149 - 2473 kg C ha-1. These findings suggest that rice systems, as currently managed, reduce the rate of C loss from organic delta soils relative to other agricultural practices

Rising Off the Plateau in Learning Arabic

Experiencing plateaus in second language learning is a common experience, especially for language student studying Arabic or one of the other languages considered more difficult. Some of the causes for the plateau experience in Arabic are its complex grammar, its vast amount of vocabulary, and the different roles of Modern Standard Arabic and the spoken dialects of Arabic. Rising off the Plateau in Studying Arabic is a thesis project, which analyzes this second language learner’s attempt to make significant progress in studying Modern Standard Arabic. The project was based on a self-directed, semi-intensive Arabic language program, which prioritized the reading skill because of this learner’s visual learning style. The importance of analyzing one’s own second language acquisition process was emphasized throughout the project. The ACTFL Proficiency Guidelines (American Council on the Teaching of Foreign Languages) were used as an evaluation tool to guide self-assessment of progress being made. This thesis project was the final requirement for a M.A.T. (Masters of Arts in Teaching) degree from the School of International Training. The required classes of this program provided the knowledge, hope, and inspiration that enabled this project to be envisaged, planned, and completed. The Second Language Acquisition course played the most significant role in that process

Knockdown of vitellogenin by RNAi increases survivorship but exhibits similar physiological responses to ovariectomy in grasshoppers

Reduced reproduction has been shown to increase lifespan in many animals, yet the mechanisms behind this trade-off are mostly unknown. A previous study has shown that in the lubber grasshopper, Romalea microptera, ovariectomized (OVX) individuals have a 30% increase in lifespan relative to controls (Sham). In a separate study, an increase in fat body mass and a halting of ovarian growth were seen upon reduction of vitellogenin transcript via RNAi (VgRNAi). These data suggest that VgRNAi increases lifespan through the trade-off between reproduction and longevity and animals with combined ovariectomy and VgRNAi, might show additive physiological responses. In this study, we used two injection control groups for the VgRNAi treatment, namely buffer injection or injection with RNAi against a 90kDa hexamerin storage protein (Hex90RNAi). We have combined these manipulations to test lifespans upon: OVX & VgRNAi, OVX & Hex90RNAi, OVX & Buffer, Sham & VgRNAi, Sham & Hex90RNAi, and Sham & Buffer. Ovariectomy and VgRNAi exhibited similar reductions in feeding (~40%) and extensions in lifespan (13-21%) but showed differences in vitellogenin protein levels. This study also observed the effects of reduced reproduction on hexamerin storage proteins. We observed that upon ovariectomy and VgRNAi, hexamerins were increased, emphasizing the importance of protein in insect life extension. When methods to reduce reproduction were combined (OVX VgRNAi), no additive physiological responses were observed, suggesting ovariectomy and VgRNAi each extend lifespan by overlapping or convergent pathways

Kinetic vs. Thermal-Field-Theory Approach to Cosmological Perturbations

A closed set of equations for the evolution of linear perturbations of homogeneous, isotropic cosmological models can be obtained in various ways. The simplest approach is to assume a macroscopic equation of state, e.g.\ that of a perfect fluid. For a more refined description of the early universe, a microscopic treatment is required. The purpose of this paper is to compare the approach based on classical kinetic theory to the more recent thermal-field-theory approach. It is shown that in the high-temperature limit the latter describes cosmological perturbations supported by collisionless, massless matter, wherein it is equivalent to the kinetic theory approach. The dependence of the perturbations in a system of a collisionless gas and a perfect fluid on the initial data is discussed in some detail. All singular and regular solutions are found analytically.Comment: 31 pages, 10 figures (uu encoded ps-file appended), REVTEX 3.0, DESY 94-040 / TUW-93-2

The Innermost Stable Circular Orbit of Binary Black Holes

We introduce a new method to construct solutions to the constraint equations of general relativity describing binary black holes in quasicircular orbit. Black hole pairs with arbitrary momenta can be constructed with a simple method recently suggested by Brandt and Bruegmann, and quasicircular orbits can then be found by locating a minimum in the binding energy along sequences of constant horizon area. This approach produces binary black holes in a "three-sheeted" manifold structure, as opposed to the "two-sheeted" structure in the conformal-imaging approach adopted earlier by Cook. We focus on locating the innermost stable circular orbit and compare with earlier calculations. Our results confirm those of Cook and imply that the underlying manifold structure has a very small effect on the location of the innermost stable circular orbit.Comment: 8 pages, 3 figures, RevTex, submitted to PR

Introduction of a Fallow Year to Continuous Rice Systems Enhances Crop Soil Nitrogen Uptake

Rice grown in California constitutes 20% of total U.S. rice production and is typically grown in a continuous rice monoculture system. In recent years, growers have been forced to fallow their lands often due to winter droughts leading to water restrictions or spring rains leading to prevented planting. Increased soil aeration due to fallowing creates knowledge gaps in soil nitrogen (N) availability. A two-year field study was conducted to evaluate differences in crop N uptake between rice cultivation following a fallow season, fallow rice (FR) and continuous rice (CR) systems. Crop uptake of soil N (N uptakesoil) and fertiliser N (N uptakefertilizer) were quantified using 15N-enriched ammonium sulfate applied in microplots as a preplant (150 kg N ha−1) or topdress (30 kg N ha−1) application. In both seasons when N was applied as a preplant fertiliser, the FR treatment had a higher grain yield than did the CR treatment, with yield differences of 2.3 Mg ha−1 in 2021 (p < 0.05) and 1.7 Mg ha−1 in 2022 (p < 0.05). Examining the sources of crop N uptake for preplant applied N, on average, N uptakesoil in the FR treatment was 16.7 kg N ha−1 higher than the CR treatment at maturity (p < 0.05). In contrast, N uptakefertilizer was similar between treatments. Additionally, comparable soil and crop fertiliser N recoveries in CR and FR preplant N suggested that the pathways and magnitudes of fertiliser N losses were similar in both systems. These results indicate that N uptakesoil was primarily responsible for lower N uptake in CR. Similar results were found when N was applied as a topdress, where FR had increased N uptakesoil in both years. We further investigated the reason for lower rates of N uptakesoil in CR. Soil phenols, which have been documented to accumulate in continuously flooded rice systems and stabilise soil N, were quantified in the field study. Complementing the rigorous field study, a regional survey study that incorporated nine paired fields was conducted to quantify regional phenol levels. In both the field and the regional survey studies, soil phenols were higher in CR than in FR fields. Together, higher phenol levels and lower N uptakesoil in CR provide mechanistic evidence that the introduction of a season-long fallow to continuous rice systems enhances soil N availability by reducing organic substrate recalcitrance. Future work should identify the duration needed for soil phenol accumulation to impair soil N cycling under continuous rice cultivation, as well as any roles of soil microbial populations in these soil N cycling patterns

Biomass and elemental concentrations of 22 rice cultivars grown under alternate wetting and drying conditions at three field sites in Bangladesh

As the global population grows, demand on food production will also rise. For rice, one limiting factor effecting production could be availability of fresh water, hence adoption of techniques that decrease water usage while maintaining or increasing crop yield are needed. Alternative wetting and drying (AWD) is one of these techniques. AWD is a method by which the level of water within a rice field cycles between being flooded and nonflooded during the growth period of the rice crop. The degree to which AWD affects cultivars differently has not been adequately addressed to date. In this study, 22 rice cultivars, mostly landraces of the aus subpopulation, plus some popular improved indica cultivars from Bangladesh, were tested for their response to AWD across three different field sites in Bangladesh. Grain and shoot elemental concentrations were determined at harvest. Overall, AWD slightly increased grain mass and harvest index compared to plants grown under continually flooded (CF) conditions. Plants grown under AWD had decreased concentrations of nitrogen in their straw compared to plants grown under CF. The concentration of elements in the grain were also affected when plants were grown under AWD compared to CF: Nickel, copper, cadmium and iron increased, but sodium, potassium, calcium, cobalt, phosphorus, molybdenum and arsenic decreased in the grains of plants grown under AWD. However, there was some variation in these patterns across different sites. Analysis of variance revealed no significant cultivar × treatment interaction, or site × cultivar × treatment interaction, for any of the plant mass traits. Of the elements analyzed, only grain cadmium concentrations were significantly affected by treatment × cultivar interactions. These data suggest that there is no genetic adaptation amongst the cultivars screened for response to AWD, except for grain cadmium concentration and imply that breeding specifically for AWD is not needed