Published online 26 May 2006
Published in Vadose Zone J 5:801-804 (2006)
DOI: 10.2136/vzj2005.0137
© 2006 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
NOTES
An Automated Rotating Lysimeter System for Greenhouse Evapotranspiration Studies
Naftali Lazarovitcha,*,
Alon Ben-Galb and
Uri Shania
a Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel
b Agricultural Research Organization, Gilat Research Center, Israel
* Corresponding author (lazarovi{at}agri.huji.ac.il)
Received 23 November 2005.
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ABSTRACT
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Lysimeters are important tools in soil–plant–atmosphere research because they allow direct measurements of evapotranspiration and facilitate studies of water, nutrient, and solute balances. Heterogeneity in the atmospheric conditions in greenhouses causes spatial variations in evapotranspiration. Accurate design and management of water balance research in greenhouses is difficult due to restraints of replication and placement needed to statistically minimize the influence of heterogeneity. Precision and control are necessary to maintain precise boundary conditions, a prerequisite for accurate investigations of selected variables. We present a rotating structure that significantly enhances uniformity in environmental conditions between individual free-standing lysimeters placed on the structure. The system contains automatic irrigation (water and fertilizer) delivery and drainage collection devices. The system was tested in evaporation and plant growth experiments. A dual carousel setup was used to measure evaporation from containers placed on the soil surface of the lysimeters, as well as yield of lettuce (Lactuca sativa L.) plants growing in the lysimeters. Half of each carousel was covered with netting to reduce solar radiation by 50%. One carousel rotated throughout the experiment while the other one remained stationary. Variability in measured data was reduced as a result of rotation. The CV of measured evaporation from the rotating system (3.3%) was significantly lower than that of the stationary system (16.2%). Similarly, the CV of relative lettuce yields of the rotating system was 11.9% as compared with 20.9% for the stationary system. The proposed apparatus is very attractive as a research and teaching tool for studying plant physiological processes, flow and transport in soils, and plant response to management or environmental variables.
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INTRODUCTION
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LYSIMETERS are important tools in soil–plant–atmosphere research because they can directly measure evapotranspiration and facilitate water, fertilizer, and solute balance studies (Van Bavel, 1961; Hillel et al., 1969). Reliable measurements of drainage quantity and content, generally very difficult under field conditions, are much easier to make using lysimeters. For instance, water percolating through the root zone may be collected and analyzed when using percolation lysimeters, while changes in water content can be determined by weighing lysimeters. The main differences between lysimeters and the field are that the lysimeters have (i) a limited root zone volume and (ii) side and bottom boundary conditions determined by the container. While both problems can be resolved by assuring sufficient lysimeter size, much deeper and thus more expensive and bulky lysimeters are needed to solve the problem of undesirable saturation conditions at the lower boundary (Van Bavel, 1961; Klocke et al., 1993). The latter problem can be minimized using a drainage extension made of a highly conductive porous medium, in which saturation is limited to the very bottom part of the extension (Ben Gal and Shani 2002a), while moisture in the root zone of the lysimeters can be maintained at levels similar to those found in the field.
The quality and quantity of leachate draining from lysimeters can be measured using one of several methods. One technique is to allow accumulation of drainage water in a reservoir and to occasionally collect and measure the liquid quantity and its concentration (Roy et al., 2000; Jabro et al., 2001; Ben-Gal and Shani, 2002b). Automation of this method requires pumping of the drainage solution from each lysimeter through piping and a manifold with valves that may be vulnerable to contaminants. An alternative method of measuring drainage water is to use tipping buckets (Gee et al., 2002; Preedy et al., 2001). While tipping buckets can produce very high-resolution data, they are limited due to the need for a leveled surface, moving parts that can become jammed, and calibration problems resulting from solute sedimentation, while they also do not easily facilitate automatic quality monitoring of the leachate.
The distribution of solar radiation and temperature in greenhouses influences transpiration, photosynthesis, and respiration, together with such factors as air movement and relative humidity. The radiation level is generally highly dependent on greenhouse design, the radiative capacity of covering material, and weather conditions. Wang and Boulard (2000) found up to 50% difference in solar radiation measured within a greenhouse. Nonuniformity of incident radiation within a greenhouse, due to temporal and spatial variability, will lead to uneven production potential. Tourdonnet et al. (2001) found varied degrees of variability in the fresh weight of harvested lettuce along a transversal gradient in a greenhouse, with differences reaching 33%. Spatial variability in climate inside a greenhouse results from its high surface/volume ratio. This phenomenon increases with association to gable ends, vent openings, and frames (Wang and Boulard, 2000). Spatial surface effects and variable environmental conditions are particularly troublesome in the small-volume greenhouses often used in research and as such can be problematic in conducting accurate evapotranspiration studies.
The objective of this note is to describe a system of rotating automated lysimeters for evapotranspiration research in greenhouses. Design criteria included provisions for having uniform growing conditions for a large number of plants and obtaining accurate water and solute balance measurements.
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MATERIALS AND METHODS
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Carousel Design
Forty-eight independent free-standing lysimeters were placed on a pair of slowly rotating (one revolution per hour) carousels. The dual carousel system is illustrated in Fig. 1
. A schematic of a single lysimeter and the system's automation center, which was located between the two carousels, is depicted in Fig. 2
. A photograph of a single carousel during an experiment with corn (Zea mays L.) is found in Fig. 3
. Each lysimeter consists of a plastic container (Fig. 2A) (60-cm height, 30-cm radius) filled with Arava sandy loam soil (soil properties can be found in Shani et al., 1987). A layer of highly conductive porous media (rockwool) is located below the soil, while a drainage tube (Fig. 2B) (60 cm long, 2.5-cm radius) filled with rockwool extends downward from the lysimeter bottom. Care was taken during installation to ensure continuous contact between and within the media layers (Ben-Gal and Shani, 2002a). The diameter and length of the drainage tube needed to provide the desired soil water conditions are functions of the hydraulic properties of the rock wool and the soil (Ben-Gal and Shani, 2002a). Each lysimeter was continuously weighed by a single point load cell (Fig. 2C) (Model 1250, Tedea-Huntleigh, Inc., Chatsworth, CA).
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Fig. 1. A schematic representation of the carousel construction: barcode reader (A) , infrared ray (B), and rotary electrical interface (C).
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Fig. 2. View of a single lysimeter and the system's automation center: plastic container (A), highly conductive drainage extension (B), load cell (C), preparation container (D), suspended load cell (E), storage tanks (F),manifold of valves (G), water valve (H), irrigation valve (I), intermediate spillway (J), low pressure emitters (K), rinse valve (L), drainage container (M), drainage tube (N), spring loaded handle (O), piston (P), container (Q), electrical conductivity sensor (R) load cell (S), and piston (T).
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Fig. 3. An automated rotating carousel being used for water balance research with a corn crop. The photograph shows individual lysimeters, their drainage pipes, and leachate collection containers.
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Lysimeter placement was identified using a barcode reader (Fig. 1A) (BCL 80, Leuze Electronic, Westland, MI). The barcode reader was triggered with an infrared ray (Fig. 1-B) (XsunX, Aliso Viejo, CA). The controller (SLC 5/03, Allen-Bradley, Milwaukee, WI) recognizes each lysimeter unit, automatically prepares and delivers irrigation water, and collects and analyzes leachate. Hence, irrigations were reliably applied to the correct lysimeters. Monitoring and automation required communication and power cables that reached each lysimeter. To prevent the tearing of cables due to the rotation of the lysimeters, the center of the carousel was equipped with a rotary electrical interface (Fig. 1C) (Poly-Scientific, Blacksburg, VA). Irrigation solutions were prepared using a container (Fig. 2D) hanging from a suspended s-type load cell (Fig. 2E) (XLS2-HSS, Load Cell Central, Monroeton, PA). Concentrated solutions located in four storage tanks (Fig. 2F) with volumes of 0.5 m3 each flowed gravitationally downward to container D via a manifold of valves (Fig. 2G). Low pressure, 13-mm (1/2 inch), two-way electric valves (ACL, Caponago, Italy) were utilized for flow control throughout the project. Water for final irrigation solution dilution was supplied through an additional valve (Fig. 2H) to the weighing container D such that the irrigation solution can be prepared by sequentially measuring preferred weights of each concentrated solution and the dilution water. Valves (Fig. 2I) at the bottom of the weighing container allowed flow to one or the other carousel by gravitationally delivering the irrigation solution to an intermediate spillway (Fig. 2J) attached to each of the lysimeters. Water flowed from the spillway to the soil by way of two non-pressure-compensated drip emitters (Fig. 2K) (1.6 L h–1, Netafim, Israel). Fresh water rinses the weighing container D after each irrigation event, and an additional valve (Fig. 2L) is used to dispose of the rinse water. Upon completing delivery of irrigation water to one lysimeter, the system prepares a solution for the next irrigation. Application of preset desired water quality and quantity to each lysimeter can be facilitated through the use of multiple tanks of concentrated solutions.
Leachate draining from the lysimeters is collected in a container (Fig. 2M) located under the drainage tube (Fig. 2B). A flexible rubber pipe (6-mm radius) (Fig. 2N) connected to a hole in the bottom of this container is connected to a spring-loaded handle (Fig. 2O) and held above the level of the collected leachate. When the lysimeter is in position, a pneumatic cylinder (Fig. 2P) (Peninsular Cylinder Co., Roseville, MI) that acts like a piston lowers the tube and empties drainage water into a subsequent container (Fig. 2Q) that contains an electrical conductivity sensor (Fig. 2R) (LTH Electronics Ltd., Bedfordshire, England) and is weighed by a platform bench scale (Fig. 2S) (Model CWP, Load Cell Central, Monroeton, PA). After measuring and recording drainage water quantity and its electrical conductivity, leachate is disposed via a second exit tube and piston system (Fig. 2T).
Experiments
Uniformity experiments were conducted in a greenhouse situated at the Arava Research Station in the Southern Arava Valley in Israel (29°53' N, 35°3' E). To increase the spatial variability in the greenhouse, the southern half of each carousel was covered with netting to reduce solar radiation by 50%. One carousel was continuously rotated while the second remained stationary. In the first experiment, water evaporated during 4 d from open containers situated on the soil surface of each lysimeter was measured. A second experiment investigated the effect of carousel rotation on yield of lettuce plants. Four lettuce plants were planted in each lysimeter and grown for 40 d. Each lysimeter was irrigated daily using a single pre-prepared nutrient solution. A water balance calculation was used to determine daily evapotranspiration (ET) from each lysimeter following ET = I – D, where I is irrigation and D is drainage. Irrigation quantity was set to return 120% of the maximum ET of all lysimeters calculated each day. Yield was measured as total aboveground fresh biomass per lysimeter. Data were analyzed using the JMP 5.0 software (SAS Institute Inc., Cary, NC). Group differences for evaporation and yield were assessed with ANOVA, with shading and rotation as factors. Significance levels were set at 0.05.
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RESULTS AND DISCUSSION
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Four-day evaporation losses from free water under shade in the stationary carousel were significantly (
= 0.05) lower than from nonshaded containers (Table 1). Average evaporation from all lysimeters in the stationary carousel (0.34 kg) was not significantly different from that in the rotating lysimeters (0.355 kg) but had a higher standard deviation (0.055 kg compared with 0.012 kg) and coefficient of variation (16.2% compared with 3.3%). Furthermore, the coefficients of variation for evaporation from both the shaded stationary lysimeters (10.35%) and the nonshaded stationary lysimeters (5.55%) were both greater than that of the rotating system, probably due to nonhomogenous climatic conditions within the shaded and nonshaded zones themselves. While average yield of lettuce plants grown in the systems was somewhat greater, but not significantly, for the rotating lysimeters (Table 2), the coefficient of variation of the lettuce plants grown in the rotating lysimeters (11.9%) was indeed significantly smaller ( = 0.05) than for the nonrotating lysimeters (20.9%). Higher variability within the lettuce experiment compared with the evaporation experiment should be expected when variability among the plants is added. The significant difference in relative variability between the carousels is evidence of the success of rotation in eliminating effects due to location.
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Table 1. Evaporation of free-water from containers on the soil surface of lysimeters in half-shaded rotating and stationary carousel systems after 4 d.
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Because of heterogeneity in the atmospheric conditions in greenhouses, evapotranspiration will vary spatially. Accurate management of multiple lysimeters utilizing automation for irrigation supply and drainage collection becomes particularly difficult under the constraints of random blocks, in which considerable replication is needed to minimize the influence of heterogeneity. We have demonstrated that a rotating structure carrying free-standing lysimeters with automatic irrigation (water and fertilizer) delivery and automatic drainage collection successfully eliminates unwanted variability due to location. The lysimeter carousel system should be an attractive research and teaching tool for studying plant physiological processes, flow and transport through soil, and plant response to management or environmental variables. The specific dimensions of the lysimeter systems described here were designed to facilitate water and salt balance studies on annual vegetable crops. The system can be easily adapted for a wide range of applications in vadose zone research. The rotating design of the lysimeter system allows simple and reliable automation of water delivery and leachate collection and disposal. This is manifested by the use of mechanical (rather than electrical) devices that incorporate a relatively large flow pathway and provide reliable, low maintenance operation of the system. The proposed setup sustains high-resolution exploration of a wide range of phenomena, including studies of multiple stress-causing factors. The automated rotating lysimeter system was successfully used in a number of crop water requirement, nutrient response, and salinity and boron toxicity studies (Ben-Gal and Shani, 2002b; Shenker et al., 2003; Shani et al., 2005).
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REFERENCES
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- Ben-Gal, A., and U. Shani. 2002a. A highly conductive drainage extension to control the lower boundary condition of lysimeters. Plant Soil 239:9–17.[CrossRef]
- Ben-Gal, A., and U. Shani. 2002b. Yield, transpiration and growth of tomatoes under combined excess boron and salinity stress. Plant Soil 247:211–221.[CrossRef]
- Gee, G.W., A.L. Ward, T.G. Caldwell, and J.C. Ritter. 2002. A vadose zone water fluxmeter with divergence control. Water Resour. Res. 38(8):1141. doi:10.1029/2001WR000816.[CrossRef]
- Hillel, D., S. Gairon, V. Falkenflug, and E. Rawitz. 1969. New design of a low-cost hydraulic lysimeter system for field measurement of evapotranspiration. Isr J. Agric. Res. 19(2):57–63.
- Jabro, J.D., W.L. Stout, S.L. Fales, and R.H. Fox. 2001. SOIL–SOILN simulations of water drainage and nitrate nitrogen transport from soil core lysimeters. J. Environ. Qual. 30:584–589.[Abstract/Free Full Text]
- Klocke, N.L., R.W. Todd, G.W. Hergert, W.G. Watts, and A.M. Parkhurst. 1993. Design, installation, and performance of percolation lysimeters for water quality sampling. Trans. ASAE 36:429–435.
- Preedy, N., K. McTiernana, R. Matthewsa, L. Heathwaiteb, and P. Haygartha. 2001. Rapid incidental phosphorus transfers from grassland. J. Environ. Qual. 30:2105–2112.[Abstract/Free Full Text]
- Roy, J.W., G.W. Parkin, and C. Wagner-Riddle. 2000. Water flow in unsaturated soil below turfgrass: Observations and LEACHM (within EXPRES) predictions. Soil Sci. Soc. Am. J. 64:86–93.[Abstract/Free Full Text]
- Shani, U., A. Ben-Gal, and L.M. Dudley. 2005. Environmental implications of adopting a dominant factor approach to salinity management. J. Environ. Qual. 34:1455–1460.[Abstract/Free Full Text]
- Shani, U., R.J. Hanks, E. Bresler, and A.S. Oliveira. 1987. Field method for estimating hydraulic conductivity and matric potential-water content relations. Soil Sci. Soc. Am. J. 51:298–302.[Abstract/Free Full Text]
- Shenkar, M., A. Ben-Gal, and U. Shani. 2003. Sweet corn response to combined nitrogen and salinity environmental stresses. Plant Soil 256:139–147.[CrossRef]
- Tourdonnet, S., J.M. Meynard, F. Lafolie, J. Roger-estrade, J. Lagier, and M. Sebillotte. 2001. Non-uniformity of environmental conditions in greenhouse lettuce production increases the risk of N pollution and lower product quality. Agronomie 21:297–309.[CrossRef]
- Van Bavel, C.H.M. 1961. Lysimetric measurements of evapotranspiration rates in the eastern United States. Soil Sci. Soc. Am. Proc. 25:138–141.
- Wang, S., and T. Boulard. 2000. Measurement and prediction of solar radiation distribution in full-scale greenhouse tunnels. Agronomie 20:41–50.[CrossRef]
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ABSTRACT
INTRODUCTION
