730 research outputs found
Arctic Investigations by the Fisheries Research Board of Canada, 1956-57
... In 1956 fisheries studies were concentrated in the Mackenzie Delta region between Herschel Island and Tuktoyaktuk, where fishes are relatively varied and abundant. ... In addition to substantial beluga and ringed seal collections which were made for the mammal investigations, about 11,000 fish were sampled in all. ... a preliminary survey of fish stocks in Pelly and Garry lakes of the Back River system was undertaken .... The lakes, which are shallow (20-30 feet), were found to support sufficient stocks of whitefishes and lake trout to permit organized subsistence fishing should this be necessary. ... In 1957 one party carried out fisheries studies up the Mackenzie River from Aklavik to Fort Norman, and another surveyed fish stocks at Coppermine, N.W.T. An intensive study was made of the char run in Rowley River on Rowley Island, Foxe Basin by the M .V. Calanus and in northern Hudson Bay by whaleboat and by peterhead from Coral Harbour. Forty-five walrus were tagged in the latter area, and 20 were examined in detail. In Foxe Basin 60 walrus and 220 seals were sampled. The reproductive cycle, ages at maturity, and life expectancy have to a large extent been clarified by work on aging from growth layers in the cementum of molar teeth and in tusk development. ... In 1956 and 1957, a continued increase in the fishery for pilot whales in Newfoundland (1956 catch, about 10,000) led to emphasis on population studies. Investigations were begun as well on minke whales or lesser rorquals, with a small fishery at Dildo, Newfoundland as the source of material. ... During a 12-month period beginning in September 1955, collecting of plankton, benthos and hydrographic samples was carried out in northern Foxe Basin from the M.V. Calanus, based at Igloolik. Biological samples included net plankton, microplankton, bottom fauna and intertidal collections. Hydrographic sections were run across Fury and Hecla Strait, and between Jens Munk and Koch, Koch and Rowley, Koch and Baffin, Baffin and Bray, and Bray and Rowley Islands. Additional stations were occupied and water temperature, salinity, oxygen and phosphate values were determined. It thus has been possible to follow through a complete yearly cycle of hydrography and productivity in Foxe Basin. ..
An Inexpensive Method of Determining Plant Moisture Stress Using Freezing Point Depression
The measurement of freezing point depression
as a method of determining osmotic potentials
in solutions has been used for some time. Recently,
this same principle has been applied to
the determination of moisture stress in plant
leaves. The advent of efficient solid state Peltier
cooling units has made possible the construction
of portable field freezing-point meters of relatively
low cost and acceptable accuracy (1)
Irrigation Decisions Simplified with Electronics and Soil Water Sensors
Two simple, inexpensive systems use electrical resistance measurements
to provide useful, immediate information to assist decisions
made on irrigation water application. in one system a microprocessor-based
circuit coupled to a programmable calculator provides
an on-site estimate of the time until the next irrigation will be required,
based on field data and an operator-supplied parameter. The
second system simply signals the arrival of the wetting front at any
location in the soil by giving a visual indication, such as raising a
mechanical flag. The microprocessor-based circuit measures and
stores the resistance of four gypsum blocks once a day. The program
in the portable calculator accesses this information and uses it to
extrapolate the soil drying rate to predict the number of days until
the next irrigation. By restricting the microprocessor circuit to data
acquisition only and putting all number-handling routines into the
calculator program, the cost and complexity of the microprocessor
circuit is minimized, whereas maximizing the programming flexibility.
This makes it feasible to install a number of these devices at
different locations, all serviced by the same portable calculator.
The water infiltration circuit intermittently scans eight sets of
stainless steel electrodes to locate the soil wetting front during irrigation.
When the resistance across the electrodes decreases, sig-
'sling the arrival of the front, the circuit trips a spring-loaded Bag.
This provides a visible sign that the wetting front has reached that
point in the soil. The equipment worked well. When irrigation was
required in six or fewer days, the microprocessor/calculator system
made correct predictions 85% of the time. An example of how easily
any irrigation scheduling method may be converted to the microprocessor/calculator
system is presented
A Photoelectric Seed Counter
Small scale yield studies, germination tests, controlled
plantings, and packaging often require the counting of
large numbers of seeds. The system described in this
paper uses a photosensitive detector and a vacuum pickup
to count individual seeds and gives a direct digital readout.
The count rate is limited only by how quickly the
seeds can be fed through the counting tube without clogging
it or having them touch each other. This greatly
speeds seed counting, eliminates operator error, and reduces
operator fatigue.
With the addition of a relatively simple predetermining
circuit, a fixed number of seeds may be counted
and a control function can be exercised. This capability
is immediately applicable to packaging or repetitious
batching of seeds. Zero error for any given number of
seeds is attainable if the seeds are fed through the count
tube carefully because of the completely digital nature
of the circuit
Electronic Single Station Irrigation Timer/Controller
Automation is being used increasingly to improve farm water application efficiency and to reduce labor requirements. For many years, farmers have wanted and needed time-controlled devices and structures to change their irrigation sets automatically, particularly when it is inconvenient for them to make the change, such as at night. Such equipment has not been available commercially
Water sensor feedback control system for surface irrigation
A water sensor feedback control system was developed to control semiautomatic irrigation of basins and
borders. When water reaches a sensor at a downfield irrigation cutoff point, a signal to terminate irrigation is sent via
wire or infrared (IR) telemetry to a station controller or receiver at the upper end of the field. The sensor uses a
monostable interface to strengthen the signal for wire transmission, and prevents continuous IR transmission during the
time the sensor is immersed or remains wet. The water sensor controller, powered by a 12-V battery, uses a silicon
controlled rectifier (SCR) triggered by the feedback signal to discharge a capacitor through an electric solenoid. The
energized solenoid actuates a gate release or valve to terminate irrigation of one field segment and begin irrigation of
another. The water sensor system was tested in a level basin irrigation system.
A sensor costs approximately U.S. 65 to 80. Both can be
portable to minimize the number of units required
Plant Water Potential Gradients Measured in the Field by Freezing Point
A portable freezing point meter was used in the field to
measure the water potential gradients in sunflower (Helianthus
annuus), beans (Phaseolus vulgaris), corn (Zea mays),
wheat (Tritium aestivum), pumpkin (Cucurbita pepo), potato
(Solanam tuberosum), alfalfa (Medicago sativa), and sugarbeets
(Beta vulgaris). The measurements were made between
daybreak and sunrise, and again during the middle of the
afternoon on days when the potential evapotranspiration
varied between 6.5 and 8.0 mm of water.
The gradients varied from a maximum of 0.2 bar per cm
in a wheat, down to an undetectable value for pumpkin. Although
most of the soil in the root zone was kept at potentials
above –1 bar, the bulk of the root tissue had water
potentials of –5 to –10 bars. Differences in water potential
between shaded and unshaded leaves, and between leaf tissue
and guttation fluid suggested a similar drop of several bars
between xylem elements and the surrounding leaf tissue in
some plant species. The implications of such drops are discussed
with respect to plant water transport equations and
pressure cell potential measurements
A radio-controlled trencher for accurate installation of shallow ditches and pipelines
An inexpensive, radio-controlled, rotary trencher was
developed for installing partially-buried surface pipes on
an accurate grade. The method was developed for use with
the Cablegation automated surface irrigation system and
other gated pipe systems. The trencher is mounted on a
farm tractor and offset to cut the trench behind the rear
tractor wheel. The grade is remotely controlled by an
operator sighting through an ordinary surveying instrument
and adjusting the cutting depth via a radio control. Tests
have shown that the trench grade can be controlled to an
accuracy of ±10 mm (0.03 ft). The trencher and control
system costs about $1500, not including the surveying
instrument
Accumulation of Mercury Vapor in Soils Laboratories
The rate of accumulation of mercury vapor in a closed room
was determined as a function of surface area of the exposed
mercury, ambient temperature, and air flow. The rate of mercury
vapor accumulation was much higher than suspected by
many soil scientists. For example, in a 3- by 3- by 2-m constant
temperature room, 250 cm² of mercury surface produced toxic
levels of mercury vapor within 13 minutes. Water or oil covering
the surface of the mercury was a highly effective means of
suppressing vaporization. The standard decontamination treatment
with sulfur proved effective, but only after complete
amalgamation occurred
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