Emergence dynamics of barnyardgrass and jimsonweed from two depths when switching from conventional to reduced and no-till conditions

<p>A cylinder experiment was conducted in northern Greece during 2005 and 2006 to assess emergence dynamics of barnyardgrass (<em>Echinochloa crus-galli</em> (L.) Beauv.) and jimsonweed (<em>Datura stramonium </em>L.) in the case of a switch from conventional to conservation tillage systems (CT). Emergence was surveyed from two burial depths (5 and 10 cm) and with simulation of reduced tillage (<em>i.e.</em> by soil disturbance) and no-till conditions. Barnyardgrass emergence was significantly affected by burial depth, having greater emergence from 5 cm depth (96%) although even 78% of seedlings emerged from 10 cm depth after the two years of study. Emergence of barnyardgrass was stable across years from the different depths and tillage regimes. Jimsonweed<em> </em>seeds showed lower germination than barnyardgrass during the study period, whereas its emergence was significantly affected by soil disturbance having 41% compared to 28% without disturbance. A burial depth x soil disturbance interaction was also determined,<em> </em>which showed higher emergence from 10 cm depth with soil disturbance. Jimsonweed was found to have significantly higher emergence from 10 cm depth with soil disturbance in Year 2. Seasonal emergence timing of barnyardgrass did not vary between the different burial depth and soil disturbance regimes, as it started in April and lasted until end of May in both years. Jimsonweed<em> </em>showed a bimodal pattern, with first emergence starting end of April until mid-May and the second ranging from mid-June to mid-August from 10 cm burial depth and from mid-July to mid-August from 5 cm depth, irrespective of soil disturbance in both cases.</p>

An Experimental and Theoretical Study of Blade–Vortex Interaction Noise

An experimental method to study helicopter blade–vortex interaction (BVI) noise has been developed. Called the blade-controlled disturbance interaction, the method nearly replicates a rotor BVI by having a single-bladed rotor pass through a stationary gust field specially designed to simulate the highly impulsive induced velocity field of a vortex. This approach can be used to evaluate the effectiveness of blade design changes to noise radiation during a BVI event, as well as to study the effect of different interaction geometries on the resulting noise. The first set of experiments in this facility shows that the directionality of BVI noise radiation is very sensitive to the interaction angle. Oblique interactions spread the acoustics energy over wider azimuth angles compared to parallel interactions, as well as move the peak noise location closer to the rotor plane. Linear two-dimensional unsteady aerodynamic theory predicts the overall directionality trends reasonably well. However, the actual pulse shapes do not match and noise levels are underpredicted, particularly for oblique interactions.