On Wednesday, April 26th, 2017, at 3:15 PM, class worked at the south side community gardens near Eau Claire South Middle School collecting point soil data. The fenced garden is just to the south-east of the intersection of Hester St and Mitchell Ave. TDR (Time Domain Reflectrometry), Ph, and temperature were collected and then recorded at each point. Measurements were taken on independent instruments, then recorded on the survey grade dual frequency Topcon GPS unit when the sub-meter accuracy point was taken at the location of sample collection.
This process mimicked data collection for soil monitoring on a farm, a useful practice because of the crop health diagnostic utility of the soil information taken. While remote sensing can tell you what crops are doing well and which are doing poor, soil monitoring can diagnose the factors causing the health condition. The types of soil data that were collected in this survey and their uses in crop diagnostic are below. This is not a comprehensive list of useful measurements, rather what the class took for practice in this assignment.
Time Domain Reflectrometry: This is a measurement technique of moisture content. The strong relationship between the permittivity of a substance and its water content is exploited to get a reading. Using two probes, a permittivity measurement is taken, then a moisture content is calculated by the device based on the measurement. Moisture is a necessity for good crop health.
Temperature: Different crops require different minimum temperatures. Tomatoes, cucumbers and snap peas thrive in soils at least 16 degrees Celsius, however Watermelon, peppers, squash, okra, cantaloupe and sweet potatoes thrive at soil temperatures around 20 degrees Celsius.
pH: This is the measurement of acidity or basicity, or respectively the concentration of hydrogen ions or hydronium ions. The acidity or basicity of the soil can affect crop yield. Figure 1 shows the relationship between pH and yield of several crops.
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| Figure 1 |
Methods:
After splitting into groups, each group collected information on the soil at the same marked points that the first group designated with flags. Each group member took turns with each instrument, collecting each type of data, while an assisting group member recorded the measurements in a field notebook. A Spectrum Technologies Fieldscout TDR 200 was used to take multiple TDR readings at each individual flagged point (Figure 2). These were then averaged to find a more accurate value which was recorded with the point data. Probe measurements were also taken with a thermometer in the same manner (Figure 3). pH measurements were taken with a probe and and a mixture of soil and distilled water in a sample container. After the the tree measurements were taken, they were recorded into a new point's attributed fields on the GPS unit. The unit was the placed as vertical as possible and the point location recorded with a tap on the appropriate button. The GPS unit took 30 coordinate measurements to average and get accurate coordinates. GPS use is depicted in Figure 4.
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| Figure 2 |
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| Figure 3 |
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| Figure 4 |
Sources:
http://soilquality.org/indicators/soil_ph.html
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