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Date: Fri, 13 Dec 96 16:11:58 +200 From: Bruce Metelerkamp <BRUCE@mailgate.icfrnet.unp.ac.za> To: METELE@gis1.icfrnet.unp.ac.za Subject: Re: microprobes -Reply -Forwarded (Forwarded mail received from: rdbriggs@mailbox.syr.edu) SOWACS I was interested to see your observations regarding the Theta Probe and the variability attributed to the surface layer of dry soil. I have remained relatively aloof during these discussions not for lack of interest, but for lack of time. With 111 students in Introductory SOils (4 lab sections) all I can manage this semester is to teach (that, just barely managed). I purchased a Theta Probe to use for measurement of soil moisture in the greenhouse where we are growing willow in a silt loam soil to which we have added a variety of biosolid ammendments (sludge cake, lime stabalized sludge, poultry manure compost, etc.). We are using ion exchange resins to capture nitrate and ammonium, and ultimately to measure N mineralization. Although we are attempting to keep the soil near field capacity, we felt that it was necessary to measure the moisture content. Our primary concern is with temperature because we are building a model of N mineralization from these various ammendments from a related growth chamber incubation experiment. Finally, we have a field trial to evaluate those organic ammendments applied to a willow bioenergy plantation (also includes inorganic fertilizer treatments). There we are measuring soil temperature continuously, and soil moisture periodically, with the Theta Probe. Our approach is to measure moisture in the rooting zone, then at the base of the rooting zone with the Theta Probe. In order to provide access, we plan to use a soil auger to remove a plug of soil, then insert the Theta probe into the soil. We have made a device that serves as a template for the three prongs, just smaller than the prong diameter. Before we did this, the simple act of pushing the probe into the soil in the field cause one of the probes to break. I want to thank you for sharing his observations - they will prevent some noise from creeping into our measurements. We have no results yet, as we are just getting underway. I would also appreciate a copy of your internal report mentioned in your posting (Little and Metelerkamp. ICFR Bulletin 10/96) Regarding your second posting, this is an extremely important issue. The greatest difficulty, in my estimation, is that the root systems for pines become so complex relative to spatial extension, that the impact of surface weeds may be impossible to quantify and eventually may become irrelevent. In the first year(s) of seedling establishment, I would hypothesize that the surface weeds are important, but become much less important as the pine roots explore greater volumes of soil, extending both laterally and deeper. We in the Forest Soils division of S-7 are constantly reminded that these are trees and much of the action occurs below the top 50 cm. When (at what point in development) this occurs as seedlings grow is quite interesting and your proposed work appears to be a good idea. We are attempting to get funding to do a similar thing in a willow bioenergy plantation, focused on root dynamics and soil water within the planted rows and between the planted rows over the depth of the solum (surface to fragipan). We will not hear about the outcome of that proposal for a couple of months. >Where should one measure the top soil water content in order to >assess the competition for water? > >My idea was to place a sensor almost beneath each tree, and then >another in the middle of the row (as far from the tree as >possible), in the weeds. The extent of the hydraulic gradient >away from the tree position would indicate which was using water >more rapidly. The absolute dryness across different weed types >would indicate which type was a greater water hog. Question - would the sensors be placed in the approximate mid-point depth of root extension for the first year? If so, what about the second year? Would it be feasible to install two sensors at each depth- sensor 1 at the midpoint of predicted first year root depth, sensor two at the deeper depth representing the midpoint of cumulative root extension at year two. That would provide a vertical gradient in year one (roots to no roots) as well as a lateral gradient. > >I am planning to use the CS615 sensors which integrate over >300mm. So I could integrate the top 150mm if I place them at 45 >degrees angle. >With a limited number of sensors, we have decided to concentrate >on the topsoil, but the woody weeds could well have their >influence below this level. The pines are slow growers only >closing canopy after several years, and not much is known about >their weed interactions in our conditions. One other possibility regarding sensors. Have you heard of Gabel Corp. They manufacture sensors that integrate over several depths. I just had a quote from them to construct a system that would monitor 24 plots, two depths in the solum, with moisture probes in the center of planted rows and between double rows for approximately $12,000. Our idea is similar to yours, but we added a vertical dimension. > >Placement of these long sensors presents a problem in that they >must be buried under disturbed soil prior to planting (and cannot >simply be pushed in after planting). I have no idea for a solution to the above. I have not figured out how to do this without soil disturbance. Regards Russell D. Briggs Associate Professor of Forest Soils 350 Illick Hall SUNY ESF One Forestry Drive Syracuse, NY 13210 (315)470-6989 EMAIL RDBRIGGS@MAILBOX.SYR.EDU