Soil Moisture 'Shake-n-Bake' Tests:
Date/Time A B C D Notes
--------- ----- ----- ----- ----- -----
96/06/15, wet 33.06 30.23 33.50 30.70 Several dry days since last rain
~18:30Z dry 28.72 26.33 28.98 26.73 (~5). Before that there were
Sta-1 diff 4.34 3.90 4.52 3.97 heavy rains, and in general it's
(%h2o/Dry) 15.11% 14.81% 15.60% 14.85% been a very wet year here, up
until now.
2 samples taken and mixed: 1
between rows, 1 closer to corn.
Campbell Reading, PAM1 18:30Z ~= 31% See Note on Soil Moisture/temp.
96/06/17, wet 42.77 52.23 49.75 46.90 Lots of rain last night...a
~16:30Z dry 30.77 37.25 35.31 33.55 really gooey mess.
Sta-3 diff 12.00 14.98 14.44 13.35
96/06/19, wet 34.35 30.29 32.96 35.89 No rain for 2 days
~17:30Z dry 28.63 25.18 27.44 29.96
Sta-2 diff 5.72 5.11 5.52 5.93
96/06/23, wet 25.86 26.03 30.97 31.07 Rain storm last night in the
~17:30Z dry 21.54 21.65 25.75 25.92 area. ground somewhat moist
Sta-2 diff 4.32 4.38 5.22 5.15 but not a lot
96/06/25, wet 31.60 27.25 31.18 28.15 No rain since last storm.
~17:00Z dry 26.76 23.04 26.41 23.83 conditions may be about the
Sta-1 diff 4.84 4.21 4.77 4.32 same as 6/15 except the corn
is taller.
96/07/02 wet 31.51 30.18 30.90 ----- no rain for days. 8cm sample
? dry 29.34 28.04 28.77 ----- taken.
Sta-1 diff 2.17 2.14 2.13 -----
96/07/02 wet 30.59 30.77 30.20 ----- refer to above
? dry 26.93 27.09 26.59 -----
Sta-2 diff 3.66 3.68 3.61 -----
96/07/02 wet 30.86 31.05 29.59 ----- refer to above
? dry 26.74 26.79 25.53 -----
Sta-3 diff 4.12 4.26 4.06 -----
96/07/07 wet 34.10 33.51 36.80 ----- dry conditions
15:45Z dry 32.48 31.83 34.96 -----
Sta 1 diff 1.62 1.68 1.84 -----
96/07/07 wet 27.59 29.37 29.60 ----- dry conditions
17:00Z dry 24.96 26.45 26.68 -----
Sta 2 diff 2.63 2.92 2.92 -----
96/07/07 wet 38.58 32.38 34.28 ----- dry conditions
17:30Z dry 35.05 29.47 31.19 -----
Sta 3 diff 3.53 2.91 3.09 -----
96/07/12 wet 35.76 33.17 30.55 31.52
18:00Z dry 34.08 31.73 29.20 30.13
Sta 1 diff 1.68 1.44 1.35 1.39
96/07/12 wet 25.64 28.08 29.27 34.60
17:30Z dry 23.75 26.05 27.12 32.01
Sta 2 diff 1.89 2.03 2.15 2.59
96/07/12 wet 37.00 33.63 34.77 33.61
17:00Z dry 35.06 31.91 32.95 31.86
Sta 3 diff 1.94 1.72 1.82 1.75
96/07/15 wet 28.64 26.93 27.15 24.71 special sample just after rain
~18:00Z dry 25.15 23.61 23.79 21.68
Sta 1 diff 3.49 3.32 3.36 3.03
96/07/15 wet 25.98 22.35 30.92 27.90
~18:00Z dry 22.12 18.91 26.32 23.58
Sta 2 diff 3.86 3.44 4.60 4.32
96/07/15 wet 29.01 27.79 27.33 27.94
~18:00Z dry 24.88 23.80 23.40 23.90
Sta 3 diff 4.13 3.99 3.93 4.04
96/07/17 wet 26.04 26.15 25.69 28.48
17:00Z dry 22.71 22.84 22.44 24.87
Sta 1 diff 3.33 3.31 3.25 3.61
96/07/17 wet 24.02 27.38 30.03 28.47
17:00Z dry 20.78 23.67 26.12 24.58
Sta 2 diff 3.24 3.71 3.91 3.89
96/07/17 wet 29.25 31.47 30.79 30.29 This looked the driest.
17:00Z dry 25.78 27.73 27.16 26.71 Also, it was the smallest
Sta 3 diff 3.47 3.74 3.63 3.58 volume (though supposedly same)
96/07/22 wet 25.06 26.41 27.89 28.73
17:00Z dry 20.31 21.38 22.55 23.28
Sta 1 diff 4.75 5.03 5.34 5.45
96/07/23 wet 27.83 24.61 24.30 32.29
17:00Z dry 23.20 20.36 20.15 26.64
Sta 2 diff 4.63 4.25 4.15 5.65
96/07/23 wet 30.67 27.84 27.06 29.93
17:00Z dry 24.52 22.03 21.61 24.01
Sta 3 diff 6.15 5.81 5.45 5.92
96/07/27 wet 22.97 30.09 26.38 27.25 This looked the wettest.
17:00Z dry 18.88 24.62 21.72 22.46
Sta 1 diff 4.09 5.47 4.66 4.79
96/07/27 wet 31.58 30.84 26.80 34.90
17:00Z dry 27.19 26.42 23.05 29.95
Sta 2 diff 4.39 4.42 3.75 4.95
96/07/27 wet 35.00 30.29 27.51 32.23
17:00Z dry 29.90 25.91 23.53 27.54
Sta 3 diff 5.10 4.38 3.98 4.69
96/08/01 wet 19.17 22.01 21.58 21.90
16:00Z dry 16.32 18.75 18.43 18.70
Sta 1 diff 2.85 3.26 3.15 3.20
96/08/01 wet 24.95 24.23 28.41 26.89
16:00Z dry 22.13 21.49 25.11 23.78
Sta 2 diff 2.82 2.74 3.30 3.11
96/08/01 wet 20.63 24.73 22.49 26.25
16:00Z dry 17.42 20.82 18.98 22.07
Sta 3 diff 3.21 3.91 3.51 4.18
96/08/06 wet 20.74 22.66 20.92 26.23
16:00Z dry 18.08 19.77 18.25 22.87
Sta 1 diff 2.66 2.89 2.67 3.36
96/08/06 wet 21.97 26.01 19.69 22.56
16:00Z dry 20.08 23.70 17.93 20.58
Sta 2 diff 1.89 2.31 1.76 1.98
96/08/06 wet 23.54 22.56 21.04 27.82
16:00Z dry 20.53 19.64 18.33 24.22
Sta 3 diff 3.01 2.92 2.71 3.60
96/08/12 wet 32.96 36.46 45.86 33.38
17:00Z dry 29.31 32.34 40.82 29.74
Sta 1 diff 3.65 4.12 5.04 3.64
96/08/12 wet 37.36 32.77 30.52 31.46
17:00Z dry 33.41 29.53 27.42 28.19
Sta 2 diff 3.95 3.24 3.10 3.27
96/08/12 wet 30.58 33.36 27.57 33.99
17:00Z dry 27.31 29.71 24.52 30.40
Sta 3 diff 3.27 3.65 3.05 3.59
96/08/20 wet 42.93 48.67 45.03 41.35
17:30Z dry 33.84 38.23 35.41 32.50
Sta 1 diff 9.09 10.44 9.62 8.85
96/08/20 wet 35.03 24.42 32.45 33.66
16:30 dry 28.42 19.58 26.31 27.17
Sta 2 diff 6.61 4.84 6.14 6.49
96/08/20 wet 41.20 41.58 43.67 46.04
17:00 dry 32.48 32.83 34.56 36.28
Sta 3 diff 8.72 8.75 9.11 9.76
Campbell Soil Moisture Probes all appear to have a significant temperature dependence that causes about a 3-5% diurnal change when the soil temperature varies about 10-20 degrees. I don't know the specifics of the sensor enough to say whether this is a real problem or not (need to R.T.F.M.!), but that does appear to be the case. .... YES, the Campbell manual does include a reference and a description of a temperature correction equation. That has not been put into the Campbell software program, or in EVE yet.
The soil temperature plots show that station 1 is noticeably warmer than stations 2 and 3. When I installed this particular sensor, I recall that the wire near the sensor was very close to the surface. I visited the site around 1400 CST and found that a short length of cable near the sensor was actually on the surface. I tried to push the sensor a little deeper and reburied the cable.
Station 1 Visit Buried about 4" more of the Tsoil cable to see if there was any heat conduction from that to the sensor that was causing greater variations during the day. However, the corn rows are oriented E-W and it is possible to observe leaf shading that 'comes and goes' as the sun transits. (see station photos)
Soil samples were taken at all sites today. The digging depth was 8 cm. Measurements will be added to log entry # 35 after baking.
visit time: 15:30 - 16:00 GMT A soil sample and measurement of the crop height was done at station 1 around 15:45 GMT. Refer to logbook entry #35 for soil and #39 for height. The crop height along the fetch angle is at 1.7m so we will need to move the sonic.
visit time: 16:45 - 17:15 GMT Soil and crop height measurement were made. Refer to logbook entries 35 and 39.
visit time: 17:15 - 17:45 GMT Soil and crop height measurement were made. Refer to logbook entries 35 and 39.
Went around and took soil samples today since we got some rain yesterday. Refer to logbook entry #35 for numbers.
Refer to logbook entries 35 and 39 for more information. Site 1 corn is in about "V6" stage, still without tassels or ears. Site 2 corn had tasseled about a week ago, now tassels are shedding pollen. 4 days ago, we saw small ears, now many plants have corn ears in "R1" (silking). Site 3 beans to the north are about "V5" (not "branching" yet) and to the south are just getting to "V3".
My first CRUDE attempt to get soil density yielded 2.5g/cm3. I am simply weighing the samples which Steve took on 7/15, assuming that he cut out a perfect 5cm x 5cm x 5cm cube. Obviously, this should be done with dry soil to get the dry soil density, but I wanted to use the oven to process the samples we took today. Thus, I dried only the sample from PAM1 for only about 4 hours. This measurement was further complicated since I used a plastic plate which melted (slightly) in the oven. This one (partially dried) sample weighed 308g - nearly the same as the samples from the other 2 stations which have simply been sitting exposed in the trailer. 308g/125cm3 = 2.46 g/cm3. I'll get some metal pans and try drying these (and today's) samples more tomorrow after the "dry" weighing of today's samples.
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Graphics file: CSI615 and gravmoist soil moisture 
There now is a function "fun.add.gravmoist", (in $ASTER/apps/sfun/FLATLAND96) which overplots gravimetric soil moisture values on a plot made by fun.qsoil.plot, assuming a constant soil density for all 3 sites (currently set to 2 g/cm3 to make the data work out - I should have a better guess tomorrow after soil samples dry out). A call to this function is loaded into the dplot menu. I chose not to have this function called by fun.qsoil.plot itself, because fun.add.gravmoist is not general-purpose for all projects (yet). Please see comments at the beginning of this function on how it grabs the gravimetric values - it is pretty clumsy. The comparison is quite variable, with a hint of a gain error, i.e. values of soil moisture from the CSI are too high when q ~ 15% and too low when q ~ 30%. It also is not obvious that PAM3 is any worse than the other two stations. I've inserted the plot into this comment, so others can see what I've seen.
- 309: SOIL, Site all, Fri 19-Jul-1996 22:29:38 GMT, soil densities measured
I've finally weighed the dried soil samples from the 7/15 collection. I get for the dry weights (in g): PAM1: 308.40 2.5 g/cm3 PAM2: 274.71 2.2 g/cm3 PAM3: 270.41 2.2 g/cm3 Assuming that Steve S. dug out perfect 5cm x 5cm x 5cm cubes, these yield the densities also listed above. I'm processing the 7/17 samples now - expect more later.
- 317: SOIL, Site all, Sat 20-Jul-1996 20:02:43 GMT, new soil densities
Well, I've just weighed the 7/17 samples which I dug out and get: PAM1 167.57g 1.34 g/cm3 PAM2 243.97g 1.95 g/cm3 PAM3 152.39g 1.22 g/cm3 I think the PAM3 sample ended up small, though I don't know why, so it should be discarded. These numbers are obviously quite different than those from the 7/15 samples which Steve S. dug out - perhaps he extracted more than 125 cm3. I am tempted to say that there was some other problem with the PAM1 sample, and that a density of about 2 g/cm3 is okay. We may want to get/make a core sampler to more accurately extract a fixed volume.
- 331: SOIL, Site all, Tue 23-Jul-1996 19:32:11 GMT, soil samples and crop heights taken
Soil samples were taken and crop heights measured at sites 2 and 3 - a day late by Steve S.'s schedule because I was busy yesterday. See entries #35 and #39 as usual for the results. The south bean plot at station 3 is beginning to grow in, and the ears are developing nicely at station 2. According to Tom's rule of 3.0m < sonic-crop < 3.5m, it is now time to raise the #3 sonic. We've put it on our list for tomorrow.
- 356: SOIL, Site all, Fri 26-Jul-1996 14:34:44 GMT, more soil densities
From the last samples (7/22 & 7/23), the total (dry) sample weights are: PAM1: 189.55 g => 1.52 g/cm3 PAM2: 177.24 g => 1.42 g/cm3 PAM3: 169.07 g => 1.35 g/cm3 The volumes I cut out did not look quite cubic. I would guess that they could have been either 5 x 5 x 4 cm = 100 cm3 or 6 x 6 x 5 = 180 cm3 (rather than 5 x 5 x 5 = 125 cm3 used above). Thus, the above values probably are only good to +/- 30%. We still need to get a soil corer to sample accurate volumes. (Matt thinks the volumes were 5 x 5 x 3.5 = 87.5 => 1.9 - 2.2 g/cm3)
- 388: SOIL, Site all, Tue 30-Jul-1996 15:41:47 GMT, latest soil densities
The dry weights of the total samples taken 7/27/96 are: PAM1: 172.5g => 1.38g/cm3 PAM2: 192.3g => 1.54g/cm3 PAM3: 177.9g => 1.42g/cm3 Matt and I feel more confident that these were true 125cm3 samples, so I suggest that we go with 1.4 g/cm3 as the density.
- 403: SOIL, Site all, Sat 03-Aug-1996 17:38:53 GMT, Soil Moisture
Soil moisture samples taken for all three PAM site on Thursday 1 Aug 96. The results are in the soil moisture logbook entry
- 404: SOIL, Site all, Sat 03-Aug-1996 17:43:33 GMT, Soil bulk density
Samples were taken Friday, 2 Aug 96 for soil bulk density. The blocks will be baked, weighed. waxed and dunked. Dry wt Volume Density g cm3 g.cm-3 PAM 1 77.93 50 1.54 PAM 2 114.89 70 1.64 PAM 3 141.23 95 1.49- 477: SOIL, Site all, Thu 22-Aug-1996 18:26:10 GMT, Campbell and soil rad sensor s/n and stations
These serial numbers noted at teardown. Station # CR10 and soil/rad unit # 1 3 2 1 3 2 Note, the soil moisture probe at station 3 had the rods spread by perhaps 25%. This was visually observed during sensor removal.
- 492: SOIL, Site all, Fri 11-Oct-1996 17:11:32 GMT, Soil Moisture Post Calibrations
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Graphics file: Soil Moisture Time Series, Pre and Post Cal 
Graphics file: Time Plot of CS615 Errors 
The calibration equation for the CS615 soil probes is shown as follows: V(%volume) = ((t-tsdry) / (15625 * tair - 10752)) * 1966.826 * 100% t is the CS615 output in milliseconds tsdry is the CS615 output in an oven dried soil sample tair is the CS615 output in air LAB RESULTS =========== Dry Dry Dry Probe Air Site1 Site2 Site3 ----- --- ----- ----- ----- Spare 1.037 1.159 1.145 1.134 1.129 1.149 1.138 1.152 1.142 SN1 (site1) dead dead dead dead SN3 (site2) 1.022 1.147 1.148 1.119 1.12 1.138 1.134 SN2 (site3) 1.063 1.198 1.183 1.164 when spread 1.18 1.132 1.154 when narrower 1.211 Least Squares Fit ================= Fit of the gravimetric soil measurements to the raw time output of the CS615 probes. With this fit, the equation for V(%volume) is solved to find values for tair and tsdry. Using the slope and intercept values from the L.S. fit, the following equations are solved. tair = 1/15625 * (1966.826/slope + 10752) tsdry = -1 * intercept * (15625 * tair - 10752) / 1966.826 Assumptions: density of soil is 1.5 g/cm^3 Temperature errors of CS615 are ignored Solutions are presented only for the probes matched with their soil sample. Probe tair tsoil slope intercept ----- ---- ----- ----- --------- SN1 (site1) 0.985813 1.3208245 .4228520 -0.5585132 SN3 (site2) 1.0985959 1.1410048 0.2984762 -0.3405628 SN2 (site3) 0.9238607 1.696495 0.53398142 -0.9058971 Conclusions =========== The lab results from inserting the probes in oven dried soil samples do not agree with the least squares fit. Since the gravimetric readings are as close to a reference standard as possible, the data from the least squares fit would seem to be more plausible. However, this means there is an unexplained discrepancy between the field and lab data. Two plots are included with this log entry. The first plots shows the time series of the original and L.S. fit corrected soil moistures. The second plot shows the CS615-gravimetric error versus time. There seems to be some correlation between time and the moisture error. As the errors tend closer to 0 towards the end of the project, this suggests some settling time for the probes to become integrated with the soil. In the case of station 3, a large crack in the soil was observed during the project. This may have been the cause of the larger errors at this site. Another plot showing error versus moisture was generated, but is not included here. There did not appear to be a correlation between the moisture and the error reading.