## 1 Introduction  
According to the 2021 Food and Agriculture Organization (FAO) report, the total global area of salt-affected soils, including saline and socio soils, is 833 million hectares [1]. These areas extend over Africa, Asia, Australasia, and America. The distribution of saline and socio soils based on the FAO/UNESCO Soil Map of the World covers 397 million hectares and 434 million hectares, respectively. Most salt-affected land lies in arid and semi-arid environments. Soil salinization is a significant threat to many countries' agricultural production systems and food security. At the global level, salinity affects almost 1 billion hectares of land worldwide, equivalent to 7% of the Earth's continental extent [2; 3]. [PERSON] and [PERSON] [4] reported that the estimated soil salinity affected area was 20% of the total cultivated lands and 33% of the irrigated agricultural lands globally. Salinized areas increase at an annual rate of 10% for various reasons, including low precipitation, high evaporation, saline water for irrigation, and poor drainage. [PERSON] et al. [5] reported that more than 50% of global arable land would be affected by soil salinity by 2050. In Thailand, the soil salinity distribution in the Northeast region is related to geopedologic settings and has been affected by deep-seated rock salt [6; 7; 8; 9; 10; 11], i.e., Maha Sarakham formation. [PERSON] et al. [12] reported that the salts' movement relates to groundwater flow and is leached away in the rainy season. Salt-bearing rocks occur at about 80 m depth, affecting the groundwater. Salt is interspersed on the lowland ground surface during the rainy season. Salt spreading at the surface of paddy fields has been related to a densipan occurrence at around 50-70 cm depth. This impervious layer has been locally broken, letting the saline groundwater reach the surface. The Department of Mineral Resources (DMR) reported that Thailand's saline-affected areas in 2015 were primarily situated in the northeast region and covered 48.64 million sq. km [13]. In Nakhon Ratchasima province, most soil resource problems related to agriculture include soil degradation (due to land use misuse or land use inappropriate for soil properties), soil erosion, defective soil, saline soils, sandy soils, and shallow soil. The Land Development Department (LDD) reported the distribution of saline soil and its severity in Nakhon Ratchasima province, shown in Table 1[14]. In this study, we introduce an electromagnetic induction (EMI) method, which has been applied and suggested by many researchers [15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30], to measure the apparent soil electrical conductivity for predicting and mapping soil salinity with a suitable interpolation method. The EMI method measures the electrical conductivity (EC) of undisturbed soil in the field. The reading responds to salt content, moisture, and clay levels. When calibrated and interpreted with soil test results, an electromagnetic (EM) sensor can provide helpful information on salt and water movement [31]. An EM device has two wire coils at each end of the cable. One coil transmits a low-frequency radio signal to the ground, while the second coil (the receiver) acquires the secondary (return) signal from the ground (Figure 1). Highly electromagnetically conductive ground (such as saline, clay, or wet ground) produces a stronger secondary signal than less conductive ground. By measuring the difference in strength between the original signal and the secondary signal, the EM device can measure the ground's conductivity [32].