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Agr. Nat. Resour. 55 (2021) 229–236 AGRICULTURE AND NATURAL RESOURCES Journal homepage: http://anres.kasetsart.org Research article Spatial distribution characteristics and types of salt-affected soils spots developed on alluvial fan complex over old marine sediment, Thailand Napaporn Phankamolsila,†,*, Kiattisak Sonsria,†, Irb Kheoruenromneb,†, Robert J. Gilkesc,†, Yutthana Phankamolsild,† a Department of Soil Science, Faculty of Agriculture at Kamphaeng Saen, Kasetsart University, Kamphaeng Saen Campus, Nakhon Pathom 73140, Thailand b Department of Soil Science, Faculty of Agriculture, Kasetsart University, Bangkok 10900, Thailand c School of Earth and Environment, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia d Environmental Engineering and Disaster Management Program, Mahidol University, Kanchanaburi Campus, Kanchanaburi 71150, Thailand Article Info Abstract Article history: Salt-affected soils are universally known as one of the most important problematic soils causing Received 29 July 2020 a negative impact on agricultural lands worldwide. Thus, the aims of the current were: 1) to elucidate Revised 7 January 2021 Accepted 5 February 2021 the spatial distribution of salt-affected soils, 2) to investigate the spatial factors impacting the Available online 19 April 2021 distribution of salt-affected soils and 3) to classify the types of salt-affected soils. The study sites were located in Kamphaeng Saen district, Nakhon Pathom province, Thailand where the soils have Keywords: developed under old marine sediment. Orthographic mapping was used to identify the locations Old marine sediment, of salt-affected soils; subsequently, 38 locations were selected. At these sites, soil samples were Orthographic map, Spatial analysis, collected using a hand auger at four depths (0−20 cm, 30−50 cm, 60−80 cm, 80−120 cm) for Types of salt-affected soils analysis of their chemical properties. The ArcGIS software was used to analyze the spatial factors influencing the distribution of salts comprising the irrigation canal system, road construction, elevation and surface slope of the study area. The results indicated that the majority of salt-affected soils appeared where there was a salt crust, bare surface and halophytic plants were present, which all acted as environmental indicators. Generally, these soils were spatially distributed in the north of Kamphaeng Saen district, Nakhon Pathom province; the irrigation canal system, road construction and elevation may be regarded as the spatial factors leading to the occurrence of the salt-affected soils. Furthermore, these salt-affected soils were deep, moderately developed with possessing the ranges of ECe, SAR and ESP values from 0.20–74.70 dS/m, 2.30–85.09 and 2.74–113.23%, respectively. Thus, our finding indicated that the types of these salt-affected soils could be classified into two groups: 1) saline-sodic soils appearing at 34 study locations and 2) saline soils appearing at 4 study locations. † Equal contribution. * Corresponding author. E-mail address: [email protected] (N. Phankamolsil) online 2452-316X print 2468-1458/Copyright © 2021. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/), production and hosting by Kasetsart University of Research and Development Institute on behalf of Kasetsart University. https://doi.org/10.34044/j.anres.2021.55.2.10 230 N. Phankamolsil et al. / Agr. Nat. Resour. 55 (2021) 229–236 Introduction Materials and Methods Salt-affected soils are the principal and imperative problem affecting Site description and soil sampling extensive agricultural and environmental areas in both developed and developing countries (Farifteh, 2007). These soils incorporate An orthographic map with a scale of 1:4,000 generated and considerable concentrations of soluble salts that impose restrictions published by the Land Development Department in 2005–2008 was on plant growth, crop cultivation and food quality (Feng et al., 2003; used as a base map to identify the locations of salt-affected soils that Chhabra, 2004; Fan et al., 2016). In principle, salt-affected soils can be commonly presented as bare areas on that map. After exploration classified into three groups comprising saline, saline-sodic and sodic of salt-affected soils based on the orthographic map, 38 locations soils. According to Brady and Weil (2008), saline soils have electrical in Kamphaeng Saen district, Nakhon Pathom province, Thailand conductivity (ECe) of a saturation extract greater than or equal to were chosen as possessing salt-affected soils and subsequently soil 4 dS/m. Their sodium adsorption ratio (SAR) is less than 13. Saline-sodic samples were collected for the current study (Fig. 1). All the study soils have an ECe value of a saturation extract and SAR greater than or sites had a tropical savanna climate with a mean annual temperature equal to 4 dS/m and 13, respectively. Sodic soils have an ECe of the of 27−30°C. In general, the rainy season is between mid-August saturation extract less than 4 dS/m and their SAR levels are greater than and mid-October with average annual precipitation of 903 mm/y or equal to 13. The formative areas of salt-affected soils are common (Thai Meteorological Department, 2015). The soils investigated in this in arid or semi-arid zones where the amount of rainfall is inadequate research had been formed on an alluvial fan. The parent materials were to leach and remove the salts and potential evaporation is higher derived from the alluvium complex mixed with marine sediments. than atmospheric precipitation (Fullen and Catt, 2004; Luedeling et The disturbed soil samples at each location were collected using al., 2005). However, in Thailand, the majority of salt-affected soils a hand auger at four depths (0−20 cm, 30−50 cm, 60−80 cm and occur in three main locations consisting of the Northeast Plateau 80−120 cm) to investigate the chemical properties. Undisturbed soil basin, the Central Plain and the Coastal area with the total area cores were collected at depths of 0−20 cm and 30−50 cm to determine being approximately 2.302 million ha. Furthermore, each location is the soil bulk density (BD) and soil saturated hydraulic conductivity controlled by different environmental conditions (Takai et al., 1987; (Ksat). Disturbed soil samples collected using the hand auger were Arunin, 1992; Arunin and Pongwichian, 2015). air-dried, gently disaggregated and passed through a 2 mm stainless Observation of salt-affected soils on the Central Plain of steel sieve to eliminate gravel, plant debris and plant litter before Thailand revealed that six provinces (Nakhon Pathom, Suphan Buri, analysis. Kanchanaburi, Sing Buri, Ang Thong and Chai Nat) have areas with salt-affected soils (Arunin, 1998). Generally, salt-affected soils in these provinces have developed from marine sediment (Hattori and Takaya, 1989). Therefore, the influence of marine activity in former times seems to be directly consistent with the formation of salt-affected soils in these areas. In particular, areas of Kamphaeng Saen district, Nakhon Pathom province, where the farmers produce many economic crops, are faced with substantial problems due to salt-affected soils (Fakon, 2012). Thus, these soils have a negative impact on the growth and yield of plants as well as the accumulation of salt that reduces the productivity of the soils. Salt-affected soils need intensive management for both the soil and plants to overcome the negative impacts of the salts and to prevent the problem worsening. Knowledge of management strategies for salt-affected soils is essential to address the causes and mechanisms of the pedogenic Fig. 1 Sampling locations for salt-affected soils in Kamphaeng Saen district, processes. Hence, the objectives of this study were: 1) to determine Nakhon Pathom province, Thailand the spatial distribution of salt-affected soils, 2) to investigate the spatial factors impacting the distribution of salt-affected soils; and 3) to classify the type of salt-affected soils. This research was Soil preparation and analysis conducted in Kamphaeng Saen district, Nakhon Pathom province where the soil has been designated as originating from old marine The physicochemical properties of the whole soil samples sediments. were investigated according to standard procedures. The BD was determined using a cold method (Blake and Hartge, 1986). The Ksat was determined using the variable head method (Klute and Dirksen, 1986). The electrical conductivity (ECe) of a saturation extract at 25°C was measured using an electrical conductivity meter N. Phankamolsil et al. / Agr. Nat. Resour. 55 (2021) 229–236 231 (U.S. Salinity Laboratory Staff, 1954). The saturation extractions of the analysis revealed that the largest distribution of salt-affected of Ca2+, Mg2+ and Na+ cations were determined using an atomic soils was in close proximity to irrigation canals and the level of absorption spectrophotometer (National Soil Survey Center, 1996) salt-affected soil distribution decreased further from canals, especially and subsequently, the sodium adsorption ratio (SAR) was calculated where the distance was greater than 3 km. The elevation in the study by dividing the molar concentration of Na+ in the saturation extract area was in the range 6–16 m. However, the salt-affected soils were by the square root of the molar concentration of Ca2+ plus Mg2+ generally distributed in areas having an elevation range of 8–10 m divided by two and recorded in centimoles per kilogram (U.S. Salinity (Fig. 4B). The surface slope factor analysis showed that most of Laboratory Staff, 1954). The exchangeable sodium percentage the study area had a surface slope in the range 0–2%. There was no (ESP) was calculated using the exchangeable sodium divided by relationship identified between the surface slope and the distribution the exchange capacity determined using the NH4OAC method of salt-affected soils (Fig. 4C). Nevertheless, salt-affected soil is (CEC-7) and further multiplied by 100 (U.S. Salinity Laboratory Staff, expected to occur on the side slope from the lower position to the 1954).