proudly sponsored by
|
archiving of SOWACS proudly sponsored by |
|
Richard, (concerning "feel and appearance") I have a confession. I love gadgets. I love clever gadgets. I even collect gadgets that don't work or are not useful because they might be useful in the future. I have worked as a researcher, and have followed tangents that have little practical value using gadgets. I enjoyed myself using those gadgets. On the other hand, I have faced the "rock hard pragmatism" of an irrigating farmer who was attempting to find a better way to measure the effectiveness of his efforts. Unfortunately, the research world tends to gain so much speed, that they leave the orbit of their "home planet". The research product needs to be (widely) usable, and effective, and affordable. In my humble opinion, the shovel is the most under valued irrigation scheduling device; that being said, read on. I am working on a field demonstration conducted by the Idaho Department of Water Resources. We are using Neutron Probe for moisture measurements. In Oregon, Washington, and Idaho, most of the professional irrigation scheduling is partially or totally accomplished by "feel and appearance". I have been encouraging the "craft" of "feel and appearance" with farmers and "ag vendors", but with the aid of a known standard; for the IDWR "Scientific Irrigation Scheduling" project, that known standard is a calibrated reading from a Neutron Probe site, and of course there are others. My personal opinion is that anyone who goes to the trouble of planting a crop and irrigating it, should gage his effort with "feel and appearance", if nothing else; and most irrigators do that, because of their nature. We have installed N-Probe access tube in fields being scheduled by "feel and appearance" practitioners. There are mixed comparative results; and as of this date, we cannot define the nature of that difference in irrigation frequency and volume recommendation. I will be tracking those variability issues this fall (i.e., "the uncertainty principle", scrutiny now would ruin the experiment). Bear in mind that our project is being run by "Engineers" with an "Ag" bias, not by "Agronomist" with and "Engineering" bias. For example: I prefer the Neutron Probe, because it delivers an instant volumetric readout; since we are calculating volumes and dates of irrigation application, the soil moisture delivered in a volumetric format is convenient. Yes, we have to calibrate access tube sites, but once done in the spring, there is a very strong confidence factor in all of the succeeding season readings. (We have quite a wide range of soil textures in this mountain valley - desert setting.) We have made a compromise in selecting the Neutron Probe (limited number of sites that ate stationary). Other than soil sampling, there probably is not a more accurate, and repeatable moisture measuring device. I have been encouraging using the established N-Probe sites as a standard, and extrapolating that standard to the adjacent portions of that field and the perhaps the one across the fence. The ENGINEERs (a group of which I claim only nominal membership) will usually set limits for high and low moisture values in the profile, and "lock" those limits into his mind or software; this kind of "left brain" thinking can be a curse and blessing; for example: germinating small seeds, and perhaps potato seed pieces and establishing a root system in unusual weather is an art form, not a "rock hard" science. On the other hand, because of increasing pressures in agriculture narrower limits on moisture in irrigated fields will be necessary. We have the Irish "late blight fungus" infesting potato fields; one management technique is to keep the same width on the "moisture management envelope" but to move it to a dryer beginning and ending point. This is a difficult undertaking, and it requires frequent, and accurate volumetric soil data (converted to pivot ground speed, or set system application timing). We have other economic and environmental pressures dealing with fertilizer leaching, canopy humidity, water supply, salts, run-off, crop yield and quality, soil structure maintenance, and leaching to a "sole source aquifer". The agronomy types tend to be "right brain" fellows that have a less structured agenda; staying between the original limits may not important, depending on the timing and field conditions. His agenda is a multifactored complex one. Using a Tensiometers makes perfect sense to an agronomist because he "feels the pain" of the plant. (Oh boy! Am I going to get burned on that one!) Your comments about the subjective nature of "feel and appearance" is correct and absolutely true; on the other had I seek the advice of an agronomist. I am not aware of a secrete cult of agronomy practitioners, the entrance requirement of which is the ability to "divine" the moisture content of a random soil texture with a specific bulk density to plus or minus 2% (who knows, perhaps there is a organization called "Men in Brown"). I routinely estimate moisture within 5% compared to a known standard on a wide variety of soils. (Do I miss one in a while? - Yes. Oddly enough, I have the most difficulty with very fine sands, not heavy textured soils. ) One of the Winter Workshop topics proposed (by myself) is a "feel and appearance" demonstration. The purpose of the demonstration, conducted for consultants and farmers, is to "calibrate" fingers and eyes to a known standard. Rather like an excursion into "dirt level" virtual reality. If I may, ... perhaps I could suggest a new category for your "hardware" paper. Call it "Tactile Enhancements" for the "Feel and Appearance Method" of soil moisture estimation. Sub-titled: "Improvements in the oldest, most practical, most widely used, least expensive, intuitive, grass level method of gagging the effectiveness of irrigation." The main focus of this discussion would be the use of gadgetry to perfect the sensory ability of the biotic element (the irrigator) in the soil moisture data acquisition process. To keep the discussion simple, avoid the extended discussion of "what to do with the information" after it is acquired. Robin Wells, P.E. 3219 E. 3600 N. Kimberly, Idaho 83341 1-208-733-7352 "robwel@magiclink.com" owner-sowacs@aqua.ccwr.ac.za wrote: > NOTE: To get off this list, send email to majordomo@aqua.ccwr.ac.za > with the body of the message containing the line: > unsubscribe sowacs > > Hello SoWaCS members, > > Things have been rather calm on SoWaCS...time to start discussing moisture > widgets again, agreed? > > I have been asked to write a short paper on soil moisture sensor technology > for the Irrigation Journal. The main focus of the article is on the newer > sensors on the market. However, I thought I'd cover the main sensor > categories and also pose some generic questions/comments. > > The categories I'm thinking of are: > > - neutron attenuation > - tensiometery > - heat dissipation > - capacitance (TDR, FDR, Phase transmission) > > Am I leaving any category out? > > > Gypsum blocks? (Electrical resistance). > > Also, does anyone know of the pros/cons of the "soil feel" method some > irrigation consultants use? I understand some people make a good living > doing this, yet I find it quasi-quantitative and subjective [he said > naively]. Comments? > > I'd be happy to quote certain individuals that contribute to this > conversation within my Irrigation Journal article. > > Sincerely, > > Richard Mead > Trickle-L & MIF owner > www.mif.org