Construction and Performance of Large Soil Core Lysimeters

This may cause an unrealistic soil moisture regime and may effect crop growth. A method was developed to obtain large undisturbed soil cores To more closely represent an uninterrupted soil coland instrument those cores to collect vadose zone leachate data under agricultural field conditions. Twenty undisturbed soil core lysimeters umn at the point of leachate collection, a vacuum extracwere constructed at an irrigated-field site in southeastern North Dation device has been installed in a number of studies. kota. Construction of the undisturbed lysimeters consisted of utilizing Tension plates (Cole, 1958) and ceramic suction cups a steel cutting bit to collect large (0.61-m diam. by 1.68-m deep) soil (Wagner, 1962) have been employed to extract leachate cores in sections of polyvinyl chloride (PVC) pipe, installing a leachate samples. A vacuum trough extractor utilizing ceramic collection system, installing time domain reflectometry (TDR) soil cylinders described by Montgomery et al. (1987) and moisture probes, and then finally placing them below grade so normal first introduced by Duke and Haise (1973) extracted farming practices could continue. The described method of core collecleachate samples without a convergence of flow often tion is an improvement over other methods in that the cutting bit is seen with ceramic cups. More recently, Strock and Casreusable, the resulting core is larger and deeper than other methods, sel (2001) and Bejat et al. (2000) used a grid lysimeter no heavy static weights are required, and it is not necessary to expose a free-standing soil column. Leachate quality and quantity data is plate under constant tension to collect leachate from reported for 1990 through 1995 and compared favorably with larger, specific areas at the bottom of a soil block, which is reconstructed profile lysimeters on the same site. Overall, the lysimeimpractical in a field setting. Brye et al. (1999) used ters functioned as intended for the first 6 yr of operation; however, soil matric potential sensors to maintain equilibrium two developed leaks and rodents damaged another. Possible sidewall between lysimeter suction and soil matric potential. flow was observed and may be avoidable in future designs. Our objectives were to: (i) develop a method to repeatedly collect undisturbed, coarse-textured soil cores large enough to accommodate the rooting area of sevT use of lysimeters is a proven method for meaeral corn plants while reducing compaction, minimizing suring movement of water and chemicals through cost, and increasing safety; and (ii) instrument the cores the soil profile. A number of methods for obtaining with tension leachate collection and soil moisture meaundisturbed soil monoliths for lysimeters have been surement systems and evaluate the functionality of the used. One method involves excavating around a column lysimeters to quantify leachate losses in a farm field enof soil and encasing it in a steel or plywood box (Bowvironment. man et al., 1994; Brown et al., 1974; Strock and Cassel, 2001). This method works well in heavy soils where a MATERIALS AND METHODS freestanding soil column can be maintained but not in coarse-textured soils where an exposed soil column canSite Description not support itself. Similarly, other researchers have Figure 1 shows the lysimeter locations and soil type within pressed steel cylinders over an exposed soil column the 65-ha field. Eight lysimeters are located along each of two (Brown et al., 1985; Meshkat et al., 1999). The majority access trails through the irrigated portion of the field and four of these methods yield cores that are too small in either lysimeters are located in the southeast dryland corner. The area or depth to fully encompass the root zone of several site is dominated by Hecla loamy fine sand soil (sandy, mixed, frigid Oxyaquic Hapludoll) on the south half and Wyndmere actively growing corn (Zea mays L.) plants. Another fine sandy loam soil (coarse-loamy, mixed, superactive, frigid method involves using a static load to force steel cylinAeric Calciaquoll), and Stirum fine sandy loam soil (Coarseders or tanks into the soil (Tackett et al., 1965; Moyer loamy, mixed, superactive, frigid Typic Natraquolls) on the et al., 1996; Schneider et al., 1996). This method requires north half. Soil texture, bulk density, and soil water characterheavy duty crane equipment and very heavy steel istic data are presented in Table 1. Samples for bulk density weights or water tanks that could pose a safety hazard. and moisture release data were taken directly adjacent to the A leachate collection system must also be installed location of each lysimeter. Topography of the site is gently in the lysimeters after the soil core is obtained. The rolling 0 to 3% slopes with the lowest elevation in the northsimplest method for collecting leachate is to simply atwest corner (395.6 m above sea level) and highest in the southtach a drainpipe to a hole in the bottom of the lysimeter. east portion of the field (398 m above sea level). Lysimeters were placed in groups of four in each quadrant Although simple, this gravity drainage can only occur of the field to provide four replications in four irrigation schedwhen the soil above the drain exceeds field capacity. uling method treatments that were part of a larger project investigating best management practices for irrigation and Nathan E. Derby, Dep. of Soil Science, North Dakota State Univ., fertilizer use (Steele et al., 2000). The site was not irrigated Fargo, ND 58105-5638; Raymond E. Knighton, USDA-CSREESprior to 1989 and was planted to corn in 1989 to 1995. The NRE, Washington, DC 20250-2210; and Bruce R. Montgomery, Agronexact centers of each lysimeter were located by triangulation omy and Plant Protection Section, MN Dep. of Ag., St. Paul, MN 55107. Received 2 Apr. 2001. *Corresponding author (nathan.derby@ Abbreviations: EXT, extractor system only; PVC, polyvinyl chloride; ndsu.nodak.edu). REC, reconstructed lysimeter drainage; TDR, time domain reflectometry; TOT, total of extractor plus gravity drainage. Published in Soil Sci. Soc. Am. J. 66:1446–1453 (2002).