Factors affecting symbiotic nitrogen fixation in organic farming systems

Nitrogen (N) fixation by white clover (Trifolium repens L.) was measured in the ley phases of three experimental organic ley-arable rotations at two sites, between 1997 and 2000, using the 15N dilution technique. Soil nitrate-N, ammonium-N, and total soluble N were measured at one of the sites between 1999 and 2001. Variation of soil N was assessed in different ages of ley, year, month, rotation, site and microsite type (grass or clover). Data for soil pH, organic matter, P, K, and Mg, was also compared, as was weather data for the period. Variation of N fixation, grass and clover dry matter, proportion of nitrogen derived from the atmosphere, grass and clover N concentrations, grass and clover non symbiotic N-yield, and N transfer from clover to grass were compared in different ages of ley, years, months, rotations and sites. Flowering rates and presence of clover tap-roots were also examined. Above ground N fixation varied between 26 and 75 kg ha'1 over the course of the growing season. Estimated total N fixation ranged from 70-214 kg ha'1. N fixation was closely related to yield of clover. There were clear relationships between soil nitrate and the behaviour of the grass and clover components of the leys. Nitrate-N was slightly higher under clover patches than under grass patches in mid-late summer.White clover and perennial ryegrass were grown in circular chambers, divided radially, and their invasion into microsites with different vegetation, different management and different N treatments was observed. Ryegrass was not capable of rapidly colonising microsites by vegetative spread alone. Clover was more likely to successfully invade microsites containing grass with no added N than microsites with added N, or bare soil microsites

Nitrogen fixation and soil nitrogen in organic ley arable rotations

This report was presented at the UK Organic Research 2002 Conference. Nitrogen (N) fixation in a white clover/ryegrass mixture was measured in 1,2,3 and 4-year-old organically managed leys during 2000. N fixation varied between 73.7 in 1-year-old leys and 33.5 kg ha-1 in 4-year-old leys. Soil nitrate-N, grass N yield and N content of grass and clover were all lowest in 2-year-old leys and highest in 3-year-old leys. The proportion of clover nitrogen derived from the atmosphere (pNdfa) was significantly lower in 3-year-old leys

Design of Control System with Feedback Loop for a Pulsatile Pump

This paper describes the design and implementation of a closed-loop proportional, integral, differential (PID) control system for a custom in-house pulsatile pump apparatus for the University of Arkansas Biomedical Department. The control system is designed to control a MOONS’ PL34HD0L8500 hybrid stepper motor using a dual H-bridge motor driver network with four pulse-width modulated (PWM) inputs to drive a pulsatile pump apparatus at motor stepping frequencies up to 2kHz. The speed of the motor is controlled from a pressure profile transmitted from an external source over RS-232 communication that specifies the motor speed, number of datapoints, and an array of pressure data. Data will be measured from the pump using pressure, flow, and temperature sensors that will output analog data and be read to the control board using analog-to-digital converters (ADCs). A PID controller will be used to match the speed of the motor to the control data by calculating the error between the sensor outputs and the desired profile. The circuit board is separated into two sections for the control board and motor circuit to isolate the 68V and motor circuity from the rest of the control board circuitry. The control system circuitry was tested, and while the control board systems were found to be functional, the motor circuit was found inefficient due to the high L/R time constant of the motor, resulting in greatly reduced speed and torque. A new chopper driver design was proposed to solve this issue and simulations conducted through MATLAB Simulink to prove the feasibility of the design

Aboriginal health and institutional reform within Australian federalism

This paper examines relationships between institutional reform within Australian federalism and Aboriginal health, both historically and in prospect. It begins with a brief historical analysis of government involvement in the general health arena within Australian federalism. It then provides a more extended historical account of government involvement in Aboriginal health and the emergence in the last 25 years of a group of important non-government players, the Aboriginal community-controlled health services. A more normative prescriptive analysis then follows, which identifies lessons from past experiences and enunciates principles for future action. These lessons and principles relate in particular to ideas about complexity and the need for greater role clarification and coordination in institutional arrangements for Aboriginal health. We argue for a view which in large part accepts this complexity and sees a need to draw organisations and their efforts into the Aboriginal health arena, rather than drive them out. We also, however, caution against drawing in all relevant organisations in related fields such as housing, education and infrastructure provision in the name of 'intersectoral collaboration'. A third argument suggests, perhaps counter intuitively, that measuring the success of institutional reform in Aboriginal health should to some extent be disarticulated from changes in substantive Aboriginal health status. A brief penultimate section of the paper looks at current general developments in the health arena. The conclusion of the paper identifies the key challenge and current opportunity for institutional reform within Australian federalism relating to Aboriginal health. This relates to the linking of responsibility sharing within Australian federalism and Aboriginal self-determination

Recombination in Glomus intraradices, a supposed ancient asexual arbuscular mycorrhizal fungus

Background: Arbuscular mycorrhizal fungi (AMF) are important symbionts of most plant species, promoting plant diversity and productivity. This symbiosis is thought to have contributed to the early colonisation of land by plants. Morphological stasis over 400 million years and the lack of an observed sexual stage in any member of the phylum Glomeromycota led to the controversial suggestion of AMF being ancients asexuals. Evidence for recombination in AMF is contradictory. Results: We addressed the question of recombination in the AMF Glomus intraradices by sequencing 11 polymorphic nuclear loci in 40 morphologically identical isolates from one field. Phylogenetic relationships among genotypes showed a reticulate network pattern providing a rationale to test for recombination. Five statistical tests predicted multiple recombinant regions in the genome of a core set of isolates. In contrast, five clonal lineages had fixed a large number of differences. Conclusion: Our data show that AMF from one field have undergone recombination but that clonal lineages coexist. This finding has important consequences for understanding AMF evolution, co-evolution of AMF and plants and highlights the potential for commercially introduced AMF inoculum recombining with existing local populations. Finally, our results reconcile seemingly contradictory studies on whether AMF are clonal or form recombining populations