Redwood Reader

22. Measuring Soil Moisture
Global Vineyard: Can technology take on a warming climate?
Science News Week of May 29, 2004; Vol. 165, No. 22 , p. 347 Sid Perkins
http://www.sciencenews.org/articles/20040529/bob9.asp
Scientists assisting grape growers may have stumbled on a good way to discover the amount of ground water in a given area. Using ground radar, they measure the beam back time, which is slower in water. Rather than pinpoint objects, this lets a grower know how much soil moisture there is available. It would seem to mean the depth of the soil moisture zone can be determined in many places, and that deep zones in old growth forests could be measured and compared to second growth areas. This will spell out the need to let trees grow for extended periods in order to restore deep-set rooting and glomalin production, increasing water storage systems in the forest. This relates directly to our discussion because ground water retention is the function of glomalin reserves.
Grape growers are a magnitude of observation ahead of forestry, so we get to see larger systems modeled such as irrigation, spacing, canopy management and nutrition in great detail. According to my viticulture notes from the Humboldt Ag Service notes growers have used potentiometers to measure the soil moisture, using them in pairs set high and low to automate irrigation. Irrigation is triggered when the deep meter is dry and turns back off when the shallow meter starts reading moisture. This gives a pretty good idea of moisture in the root zone and keeps the plants always growing rather than fits and starts.
The advantage of ground radar is that it presumably would allow measuring the entire moisture zone in thickness. We can watch a site develop over time by repeating the scans over extended periods. By comparing growth characteristics of similar forests with known differences in soil moisture we may be able to determine optimum rotations and spacing for restoring water capacity, an idea of a maximum potential, and the amount of precipitation a given area can handle in maximum mode and in impaired mode. This will be useful to flood planners, knowing how much precipitation a region can absorb, and where the danger zones lies, and keep tabs on these conditions as they change over time.
To get this kind of data thousands of observations will be necessary, taken in the framework of the correct questions. Individual land owners will want to know what there potential is and make agronomy choices from there. For example, different sites are being assessed for pH, drainage, water holding capacity and soil depth. All of these are useful parameters in determining glomalins’ role in soil structure. Other variables, such as first and last frost, average temperatures and amount and timing of precipitation may not be important at first glance. It may very well be that the number of fungi associated with Douglas fir is related to all of these parameters with aspect and climate determining which fungi grow in certain areas. These aspects and varieties of type are what create the vast differences in grapes. There is plenty of reason to think tree species are capable of adjusting their chemical production to local conditions. It is also possible that endemic fungi influence grape flavors and so on. We may also find niches for different species in the forest recurring in small patches of landscape.
In forests with long term outlook in mind, we may be able to measure the growth of a subterranean watershed and the health and stability of the site by using the radar on the same site over a period of years. This quantification can prove the need for trees and vegetation in the restoration of devastated landscapes. We need to think long term otherwise the forest will always be short changed when we try to measure its function in terms of human use. As we have noted earlier, man will eventually try to correct the changing climate by using vegetation schemes to regulate atmospheric fertilization by CO2, and to trap other greenhouse gas emissions.
Research shows different areas on the same vineyard may have a yield ten times greater in optimal areas than other areas on the same farm. Intensive management has shown up to a third of the acreage on a productive farm may operate at a loss that can be recovered by intensively managing parameters in each type of ground on the farm. Each of these areas contribute to a grapes flavor, sugar content, aroma, yield and general health of the plants. They can be managed differently to produce a standard crop, or varieties suited to those parameters can be selected for optimal conditions.
Soil conditions can be quite different just yards apart, this could be important in locating future roads. To give farmers a look at what the moisture profile of their cropland is, Susan Hubbard of Livermore National Lab in Berkeley has made a ground radar mounted on a skid to drag through fields, creating a soil moisture picture that can be used row by row and even plant by plant. Measurements before and after cutting should be done. I believe it will show that the soil moisture zone has receded where the ground was not disturbed but the canopy is gone, (and will continue to dwindle as the fungi starve) and is completely absent shortly after the ground is disturbed by roads, decks or skidding.