Geostatistical monitoring of soil salinity for precision management using proximally sensed electromagnetic induction (EMI) method

Abstract

Accurate and real-time information on soil salinity is required to understand the evolution of soil salinization, to develop appropriate management strategies, and to implement practices to improve the soil productivity and land development. This is particularly the case for the coastal agroecosystem in which the farmlands were developed from marine alluvial sediments and naturally saline. Our primary objectives were to calibrate soil salinity with proximal sensing electromagnetic induction (i.e., EM38) measurements obtained at different heights above ground, to delineate the spatial pattern of soil salinity and its temporal dynamics, and to determine potential management zones of soil salinity. Intensive EMI survey with EM38 positioned at five heights above ground was made in a coastal salt-affected farmland, and soil samples at 0–1.0 m layer were collected for calibration. This work was repeatedly conducted on January 9, 2012, September 3, 2012, March 31, 2013, and October 16, 2013. EMI measurements were calibrated to root zone soil salinity using multiple linear regression (MLR) and restricted maximum likelihood, and spatial pattern of soil salinity on different dates was generated, and management zones were determined based upon the spatial–temporal variability of soil salinity. Results indicated that EMI measurements obtained at 0, 20, 40, and 60 cm heights above ground were optimal to develop a MLR model identifying the relationship between root zone ECe and ancillary variables. The generated spatial distribution of soil salinity showed that the predominant soil types were moderately saline and very saline soils during the four survey periods. The spatial pattern of soil ECe was closely related to the layout of field drainage ditches, and significant spatial trend was well fitted by a parabolic curve in various periods. A general increasing trend of soil ECe occurred, and a drastic increase in soil salinity was observed from January 9, 2012, to March 31, 2013, and soil ECe across the field exhibited temporal dynamic during the survey periods. Two clearly defined management zones were determined based upon the spatial variability and temporal stability of ECe. Site-specific management and periodical soil salinity monitoring and assessment were recommended in this experimental site. It could be concluded that repeated proximal sensing EMI surveys could be effectively used to characterize the spatial pattern of soil salinity, to monitor the spatial–temporal changes in soil salinity, and to distinguish site-specific zones for precision management of soil salinity.