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We currently have two monitoring systems to record the influence of
field windbreaks on microclimate in crop fields.
Full-Season Weather Data:
Figure 1. (above-left). A weather station of the type
used to monitor microclimate at 25 heights distance from a windbreak. Li-Cor
Inc..
One system incorporates weather stations set up to record a wide range of microclimate parameters for long-term periods, often over several growing seasons. These weather stations monitor solar radiation, rainfall, wind direction, wind speed, temperature and humidity on an hourly basis for a full growing season. Each site usually comprises two weather stations; one is located at 25 tree heights leeward distance from the windbreak (considered to be un-sheltered) and the other is located at 3 tree heights leeward distance form the windbreak (considered to be near the maximum sheltered point). The 25H station provides us with a full season dataset of non-sheltered microclimate data useful to model the influence of climate on such aspects as crop production and soil erosion. The 3H station provides us with a full season measure of the sheltering effects of the windbreak at one location. Pairs of stations have been set up at windbreak sites in Iowa, Nebraska, and Indiana and soon will be set up in Minnesota and Wisconsin.
Figure 2. (above-left). A preliminary sample of the
data from the 25H and 3H stations showing differences in wind speed reduction
due to original approaching wind speed and angle. C. Mize.
Short-Term Microclimate Profiles:
Figure 3. (above-left). A line of equipment monitoring
microclimate on the leeward side of a windbreak. On top of each post is
a cup anemometer and each white radiation shield contains a temperature/humidity
sensor. G. Horvath.
The second equipment ‘array’ is a short term, high sampling intensity, mobile system designed to monitor many sites across a sheltered field at one time. This ‘array’ is setup in a sheltered field for a period of two to three weeks and monitors and records microclimate data over time periods as short as 10 second and as long as 15 minutes. The equipment monitor wind direction (2 sensors), wind speed (16 sensors), temperature (10 sensors), humidity (10 sensors) and static air pressure (16 sensors). The array is setup along line perpendicular to the tree line to cover both the leeward and windward sides of a windbreak out to a distance of approximately 16 heights. 16H distance on the therefore acts as a ‘reference’ for the remaining sensors. Direction sensors are set at 16H on either side of the tree line. Eight wind speed and pressure sensors on each side, while the temperature and humidity sensors are concentrated on the predominantly leeward side. Over the monitoring period this array will provide a sample of the wind profiles across the sheltered field for winds approaching from almost all directions. Corresponding profiles can be developed for temperature, humidity and pressure. Through the growing season this array is moved from site to site to obtain as broad a range of microclimate and windbreak profiles as possible.
Figure 4. (above-left). Daily cycle of temperature
differences between an unsheltered location and 3 sheltered locations leeward
of a windbreak. G. Horvath.
Combined Datasets:
Figure 5. (above-left) Crop response to shelter modeled
across a sheltered field based on microclimate data collected from both
sensor arrays described above. M. Egeh.
One of the sensor stations from the short-term array corresponds with
the 3H station of the full season system. The two datasets will be combined;
the short-term data used to create profiles such as wind speed reduction
while the 25H – 3H relationships will ‘anchor’ these curves so that season
length predictions can be made for any location across the sheltered field.
This corn field dataset can then be used to model crop production across
the field for the full season.
Windbreak Parameters:
Figure 6. (above-left). A profile of a four-row hybrid
poplar windbreak detailing height, row spacing, primary branch arrangement
and foliar surface area. G. Horvath.
The shelterbelt itself is also measured and described in significant
detail including such characteristics as species, row number, row spacing,
in-row spacing and arrangement, height, diameters, general health, surface
area distribution and optical porosity. Some of these parameters will eventually
be used to predict the nature of the wind flow profiles being measured.