1. A Rapid and Precise Method to Measure Infiltration in situ Charles Schmid 1, Roch Gaussoin 1, George Meyer 2, Robert C. Shearman 1, and Gary DeBerg 2. (1)Dept. of Agronomy & Horticulture (2) Biological Systems Engineering Abstract Assessing field infiltration on research plots with a high number of experimental units can be imprecise and time consuming. The objective of this study was to develop a method that rapidly and precisely measures infiltration relative to other commonly used methods. The method is based on the resistance difference between an electrical current traveling through air vs. water. The leading and tailing edge of the water column signals the computer via stainless steel rods tipped with conductive foam. The foam is necessary to alleviate bubble formation on the sensing rod because of the DC current passing through the sensor and disassociation of the water molecule. The method used a single-ring infiltrometer in concert with computerized data collection. Up to16 infiltrations can be collected simultaneously. This method was compared to both single and double-ring infiltrometers on creeping bentgrass (Agrostis palustris L.) maintained at 0.325 cm and 1.30 cm. The data were subjected to correlation analysis. The method was highly correlated with conventional methods. A significant time saving and increased or equal precision to conventional methods was also realized. Fig. 1. Computer automated infiltrometer setup (a) infiltration ring and current probes (b) motherboard (c) data logger (d) ground (e) shadow box and laptop computer Fig. 2. Turf-Tec infiltrometer (a) digital timer (b) water level gauge Fig. 3. Single-ring infiltrometer (a) with water level gauge Fig. 4. Infiltrometer setup (a) acrylic platform (b) stainless steel probes with conductive foam tips (c) output cables Fig. 5. Motherboard (a) input cables from infiltrations ring (b) resistors and capacitors (c) output cables to data logger Fig. 6. LabJack U3 data logger (a) input cables from motherboard (b) ground input (c) power for motherboard (d) USB computer connection Fig. 7. Shadow box with laptop computer (a) LabView computer program Materials and Methods Research was conducted in July 2007 on three different soil types planted to creeping bentgrass (Agrostis palustris L.) at the University of Nebraska-Lincoln John Seaton Anderson Turfgrass Research Facility near Mead, NE (41º11’ N, 96º28’ W). Two out of the three creeping bentgrass sites were putting greens mowed at 0.325 cm one a California constructed root zone and the other a USGA constructed root zone. The third site was a native soil (Tomek silty clay loam) root zone mowed at 1.30 cm. Two methods of measuring infiltration rate were compared to a prototype computer automated infiltrometer (CAI) to determine precision and efficiency of the prototype method and conventional procedures. Methods evaluated were the Turf-Tec infiltrometer (Model IN2-W, Turf-Tec International, Tallahassee, FL., 32303) (Fig. 2). Turf-Tec is a double-ring infiltrometer with the outside ring measuring 10.79 cm and inside measuring 6.03 cm. Infiltrations rates taken with the Turf-Tec infiltrometer follow methods described in Turf-Tec instruction manual. The second method examined was a thin-walled single-ring infiltrometer (Fig. 3) with a ring size of 15.6 cm. Infiltration rates obtained with the single-ring infiltrometer are based on methods described by Bouwer (1986). These methods were compared to the CAI (Fig. 1). The concept for the CAI was also based on the method described by Bouwer (1986). Computer software (LabVIEW 8.2.1, National Instruments, Austin, TX., 78759) (Fig. 8) analyzes currents sent from the stainless steel probes (Fig.4) through the motherboard (Fig. 5) into the data logger (Model U3, LabJack Corp., Lakewood, CO., 80227) (Fig. 6) and ultimately into the computer. The three methods were compared at each site and measurements were replicated five times. Experimental design was a randomized incomplete block and the treatment design was a split-block with site as main plots and method as sub-plots. Data were subjected to analysis of variance and treatment means were separated using Fishers protected least significant difference multiple comparison technique (Dowdy, 2004). The precision of the three methods was compared by calculating summary statistics for each method. The efficiency of the methods was compared using the relative time of setup and completion for 16 infiltration measurements. SourcedfProb > F Site2** Method2** Interaction4* Results and Discussion CAI and single-ring infiltrometer were not significantly different in infiltration rates between the USGA and California root zones while both sand based root zones were significantly different from the native soil root zone (Fig. 8). The Turf-Tec infiltrometer was significantly different among sites (Fig. 8). The CAI and single-ring infiltrometer had similar standard error (Table 2). The Turf-Tec infiltrometer had a higher standard error compared to the other methods. This leads us to believe that the CAI and single-ring infiltrometer are more precise then the Turf-Tec infiltrometer. The relative efficiency of the single-ring and Turf-Tec infiltrometers were similar while both methods were substantially slower than the CAI (Table 2). Four infiltrations is the maximum number that can be run simultaneously with the single-ring and the Turf-Tec infiltrometers. The CAI is a relatively fast method for measuring infiltration (Table 2) primarily due to simultaneous measurement of up to 16 infiltrations. References Anonymous. 2006. Turf-Tec infiltrometer instruction manual. http://www.turf-tec.com/Instructions/IN2- W%20Instructions.pdf. Turf-Tec International. Tallahassee, FL. Bouwer, Herman. 1986. Intake Rate: Cylinder Infiltrometer. In Methods of Soil Analysis, Part I: Physical and Mineralogical Methods, Arnold Klute Editor. pp. 834-838. American Society of Agronomy, Inc. Madison, WI. Dowdy, S., S. Wearden, D. Chilko. 2004. Statistics for Research. pp. 283-285. John Wiley & Sons, Inc. Hoboken, NJ MethodRangeMeanStd Error Efficiency Increase Single-ring8.01 - 94.5457.98.111 X Turf-Tec13.86 - 133.7275.1710.711 X Computer8.01 - 92.6657.158.353 X Conclusions The CAI and single-ring methods result in more precise measurement of infiltration rate then the Turf- Tec method. CAI is also a 33% faster method of taking infiltration rates compared to the single-ring and Turf-Tec infiltrometers. Of the methods evaluated, the CAI was the most efficient and precise method tested for measuring infiltration rate in situ. 656 Infiltration (cm / hr) Table 1. Analysis of variance table for infiltrometer study, Mead,NE 2007. Table 2. Range, mean, standard error and relative increase in efficiency for measurement of data from three infiltration methods tested at three sites. a b c d e a b a a b c a b c a b c d Fig. 8. Mean infiltration rates of three different infiltration methods on a California, USGA and a native soil root zone. Within a root zone columns with different upper case letters and within a method different lower case letters are significantly different based on Fishers protected LSD at P=0.05. Site X method was a significant (P=0.05) source of variability (Table 1). Infiltration rate differences within each site showed similar trends. Within each site, the CAI and the single-ring infiltrometer had significantly lower infiltration rates then the Turf-Tec infiltrometer while the CAI and single-ring infiltrometer were not different from each other. (Fig.8). The significantly lower intake rates of these two methods may also suggest that the Turf-Tec infiltrometer results in data with elevated infiltration rates. **, * indicate significant source of variability at P= 0.01 and 0.05 respectively A b B a A a B a A c B b a