scholarly journals Effects of renewal time, taproot cutting, ploughing practice, false seedbed and companion crop on docks (Rumex spp.) when renewing grassland

2019 ◽  
Vol 103 ◽  
pp. 54-62 ◽  
Author(s):  
Björn Ringselle ◽  
Therese W. Berge ◽  
Daniel Stout ◽  
Tor Arvid Breland ◽  
Paul E. Hatcher ◽  
...  
Keyword(s):  
Renewal Time ◽  
Companion Crop

Introduction to the Northwest Ontario Lake Size Series (NOLSS)

1992 ◽  
Vol 49 (12) ◽  
pp. 2434-2444 ◽  
Author(s):  
E. J. Fee ◽  
R. E. Hecky
Keyword(s):  
Turbulent Energy ◽  
Morphological Similarity ◽  
Experimental Lakes Area ◽  
Mixing Depth ◽  
Biological Communities ◽  
Renewal Time ◽  
Northwest Ontario ◽  
Per Se ◽  
Lake Size ◽  
Size Series

The rationale, design, and limitations of the Northwest Ontario Lake Size Series (NOLSS) research program are described. The primary purpose of NOLSS is to discover how lake size per se influences limnological and fisheries phenomena, so that conclusions drawn from studies of particular lakes can be rigorously scaled and applied to lakes of other sizes. NOLSS consists of six lakes located in a remote wilderness region of Northwest Ontario. These lakes were chosen for their geological, hydrological, and morphological similarity (Canadian Shield geology; water renewal time> 5 yr; fully stratified in summer), but they form an exponential gradient in surface area (from 89 to 34 700 ha.) Associated with this gradient of lake size are gradients of physical properties (turbulent energy, mixing depth, thermal behaviour) to which biological communities must adapt. NOLSS fills the conspicuous gap in size that separates two well-studied groups of lakes in Northwest Ontario: the Experimental Lakes Area (ELA), where whole-lake manipulation experiments are performed, and the Laurentian Great Lakes (Nipigon, Superior), where these experiments find some of their most important applications.

Comparison of Conventional and Alternative Nursery Weed Management Strategies

1995 ◽  
Vol 9 (4) ◽  
pp. 761-767 ◽  
Author(s):  
James B. Calkins ◽  
Bert T. Swanson
Keyword(s):  
Weed Management ◽  
Cover Crop ◽  
Production Systems ◽  
Management Strategies ◽  
Life Cycles ◽  
Weed Suppression ◽  
Winter Rye ◽  
Field Management ◽  
Companion Crop ◽  
Herbicide Management

Soil cultivation (3 to 5 times/yr) and herbicide management (oxadiazon, 3.92 kg ai/ha), agricultural standards for reducing weed competition, were compared to three alternative nursery field management systems regarding weed suppression: ‘Norcen’ bird's-foot trefoil companion crop, ‘Wheeler’ winter rye cover crop/mulch, and grass sod (80% ‘Eton’ perennial ryegrass and 20% ‘Ruby’ red fescue). Field management treatment had a significant effect on observed weed populations. Weed densities were also subject to yearly variations caused by climate and endogenous weed life cycles. Herbicide management (oxadiazon) consistently provided the best control of undesired vegetation (0.3 weeds/m2) followed by the grass sod (0.7 weeds/m2), Wheeler rye cover crop/mulch (1.7 weeds/m2), Norcen bird's-foot trefoil companion crop (8.6 weeds/m2), and cultivated (55.7 weeds/m2) treatments, respectively. Although the grass sod treatment provided excellent control of undesired vegetation, as an alternative to cultivation and herbicide use, it proved to be excessively competitive with the nursery crop. The bird's-foot trefoil treatment quickly became infested with broadleaf weeds the eradication of which proved difficult. The Wheeler winter rye cover crop/mulch field management system provided acceptable weed control combined with other beneficial effects on the plant/soil environment. Results support the effectiveness of Wheeler winter rye and perhaps other allelopathic cover crop/mulch systems in controlling undesired vegetation in horticultural field production systems.

INFLUENCE DE LA FERTILISATION AZOTEE ET DE L’ECARTEMENT ENTRE LES RANGS DE CEREALES-ABRI RECOLTEES COMME FOURRAGE SUR L’ETABLISSEMENT DE LA LUZERNE

1983 ◽  
Vol 63 (2) ◽  
pp. 443-452 ◽  
Author(s):  
GILLES DEPUIS
Keyword(s):  
Fertilizer Application ◽  
Forage Yield ◽  
Yield Reduction ◽  
Average Weight ◽  
Row Spacing ◽  
Pure Stand ◽  
Seeding Rate ◽  
Companion Crop ◽  
Number Of Stems ◽  
Forage Yields

The effect of companion crop management on the establishment of alfalfa was evaluated. The studied variables included species of cereals, row spacing and seeding rate of companion crop, stage of maturity of the companion crop at harvest, and an additional nitrogen fertilizer application. The cereals were harvested as forage. In the year after the seeding year, the first yield of alfalfa was determined. In seven trials, forage yields of a pure stand of alfalfa were 3350 kg/ha in the first cut of the seeding year. These yields averaged 60% of forage yields obtained from the combination of alfalfa and companion crop. However, cereals substantially reduced the total digestible nutrients, crude protein and calcium contents of the forage as compared to the pure alfalfa. The additional 38 kg/ha of nitrogen at tillering provided an extra yield of 600 kg/ha. Row spacing had little or no effect on forage yield. Even though wider spacings has considerably reduced seeding rates increased spacing from 18 to 54 cm did not affect barley yield while wheat was reduced by 400 kg/ha and oat increased by 300 kg/ha. Also, the average number of stems per meter of row increased by 89% with an average weight gain of 23% for each stem at the 54-cm spacing. At the first cut in the year following establishment, yields of alfalfa established with a companion crop were equal to or lower than those in pure stand. Yield reductions varied from 0 to 13% with barley and wheat but approached 30% when oats were seeded in 18-cm rows. However, the yield reduction was only 14% in the 54-cm row spacing of oats.Key words: Medicago sativa L., nitrogen fertilization, companion crop

scholarly journals Renewal time and transport of unventilated Central Intermediate Water of the Weddell Sea derived from biogeochemical properties

2002 ◽  
Vol 60 (5) ◽  
pp. 677-697 ◽  
Author(s):  
Mario Hoppema ◽  
Hein J. W. de Baar ◽  
Eberhard Fahrbach ◽  
Richard G. J. Bellerby
Keyword(s):  
Weddell Sea ◽  
Intermediate Water ◽  
Renewal Time

Establishment of Legumes as Influenced by the Rate of Sowing the Oat Companion Crop 1

1954 ◽  
Vol 46 (10) ◽  
pp. 449-451 ◽  
Author(s):  
Dale Smith ◽  
H. J. Lowe ◽  
A. M. Strommen ◽  
G. N. Brooks
Keyword(s):  
Companion Crop

The Effects of Small-Scale Turbulence on Air–Sea Heat Flux

2011 ◽  
Vol 41 (1) ◽  
pp. 205-220 ◽  
Author(s):  
Fabrice Veron ◽  
W. Kendall Melville ◽  
Luc Lenain
Keyword(s):  
Field Experiments ◽  
Renewal Theory ◽  
Small Scale ◽  
Surface Renewal ◽  
Near Surface ◽  
Turbulence Measurements ◽  
Renewal Time ◽  
Surface Turbulence ◽  
The Mean ◽  
Renewal Events

Abstract The air–sea exchange of heat is mainly controlled by the molecular diffusive layer adjacent to the surface. With an order of magnitude difference between the kinematic viscosity and thermal diffusivity of water, the thermal sublayer is embedded within its momentum analog: the viscous sublayer. Therefore, the surface heat exchange rates are greatly influenced by the surface kinematics and dynamics; in particular, small-scale phenomena, such as near-surface turbulence, have the greatest potential to affect the surface fluxes. Surface renewal theory was developed to parameterize the details of the turbulent transfer through the molecular sublayers. The theory assumes that turbulent eddies continuously replace surface water parcels with bulk fluid, which is not in equilibrium with the atmosphere and therefore is able to transfer heat. The so-called controlled-flux technique gives direct measurements of the mean surface lifetime of such surface renewal events. In this paper, the authors present results from field experiments, along with a review of surface renewal theory, and show that previous estimates of air–sea scalar fluxes using the controlled-flux technique may be erroneous if the probability density function (PDF) of surface renewal time scales is different from the routinely assumed exponential distribution. The authors show good agreement between measured and estimated heat fluxes using a surface renewal PDF that follows a χ distribution. Finally, over the range of forcing conditions in these field experiments, a clear relationship between direct surface turbulence measurements and the mean surface renewal time scale is established. The relationship is not dependent on the turbulence generation mechanism. The authors suggest that direct surface turbulence measurements may lead to improved estimates of scalar air–sea fluxes.

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