Increasing soil salinization and scarce freshwater supplies in arid and semi-arid regions means that whenever possible more saline lower quality waters should be used in agriculture, saving fresh water for municipal use. This substitution of lower quality water is especially important when biomass yield is not important, such as with recreational turfgrass. Use of these waters requires careful monitoring of salinity. Assessment of soil salinity has been determined in a number of ways: (i) plant observations, (ii) the electrical conductance of soil solution extracted via soil water extractors (iii) the electrical conductivity (EC) of water obtained by collecting soil samples, adding varying amounts of water to each sample and then extracting, (iv) in situ measurement of electrical resistivity (ER), (v) non-invasive determination of EC with electromagnetic induction (EMI), and most recently (vi) in situ determination of EC with time domain reflectometry (TDR). The techniques of ER, EMI, and TDR measure bulk soil electrical conductance, termed ECa [1].
Compared to other methods, EMI measurements generate both spatially and temporally highly efficient data[2]. However in contrast to the other methods EMI and ER have the disadvantage of requiring calibration to convert the data to soil water or saturation extract EC (ECe).
In the last 20 years, scientists have made advances to better understand the best application procedure for measuring soil salinity, water in soil pores, soil texture and depth etc.[3,4,5,6,7,8]. By identifying the complexities of ECa measurement and how to deal with them, Corwin and Lesch[9] provided guidelines for the use of ECa in agriculture. EM38 is a tool that measures ECa value of approximately 0.75–1.5 m depth of the soil profile, depending on its horizontal and vertical positioning. This device consists of a receiver and a transmitting coil placed at opposite ends of the non-conductive rod at 1 m intervals [10]. The EMI technique produces readings on any conductive surface as ECa, ECa readings can be influenced not only by soil salinity, but also by any property that affects conductivity such as soil water content and clay content. Calibration equations between ECa and ECe should be established taking into account site-specific properties such as soil texture, soil water content, soil salinity etc in an area measured by the EM technique. Three parallel pathways of current flow contribute to the ECa measurement: 1) a liquid phase pathway via dissolved salts contained in the soil water present in medium to large pores, 2) a solid phase pathway via conduction through soil particles that are in continuous, direct contact with one another, and 3) a solid-liquid pathway via hydrated exchangeable cations associated with clay minerals [11].
Remote sensing has made the concept of precision agriculture practical. Precision agriculture utilizes detailed maps of soil or vegetative characteristics for site specific management [12]. Among the soil properties and characteristics of most interest are water content, soil texture and salinity. Precision agriculture has been applied to landscape vegetation as well as agriculture. Carrow[13] et al. used the term precision turfgrass management (PTA) for application of the site specific mapping concepts to turfgrass management of irrigation, salinity and fertilizer application and cultivation, utilizing both soil sampling and various field based sensors. Devitt[14] et al., evaluated the spatial and temporal changes in salinity on turfgrass using insitu sensors. This approach provides more accurate data than that obtained via remote sensing but has limited practicality due to cost of installation and need for many sensors to characterize variability.
To evaluate soil salinity we are interested primarily in the electrical conductance of the soil solution. The ECa measurement includes more than just soil salinity, as it is a measure of the sum of all conductive materials within the volume of measurement and is thus influenced by any soil property that affects bulk soil electrical conductance [13]. Use of a ECa survey to measure salinity within an area has been divided into eight steps: (1) design for the ECa survey, (2) spatially identified ECa data collection (3) soil sampling design based on the spatial variations in the ECa data (4) collection of soil samples at the identified optimal sites for ECa calibration (5) physical and chemical analysis of relevant soil properties, primarily EC of a soil water extract, (6) spatial statistical analysis (7) determination of main soil properties in the study area affecting the ECa measurements (8) GIS application[15]. The U.S. Salinity Laboratory Staff (ARS-USDA, Riverside, California) developed conductivity modeling software (Electrical conductivity Sampling Assessment and Prediction-ESAP)[16,17,18,19,20] to promote efficiency acquisition and construction of ECa data. ESAP, user-friendly software, provides (i) survey maps and directed sample design relying on the maps (ii) calibration of ECa readings to ECe (iii) explication of estimated spatial salinity data. Acquired information is practical for salinity management [20].
The aim of this study is to map the salinity distribution of two fairways at Dove Canyon golf course in Trabuco Canyon, California by means of EM38 sensors in order to determine need for reclamation and then remap the fairways to evaluate the success of attempted soil remediation via leaching. This report represents a use of the EM technique to enable faster diagnosis of salinity in golf courses with minimal detrimental soil disturbance from soil coring, critical to recreational turf.