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Pedotransfer Functions for Estimating the Field Capacity and Permanent Wilting Point in the Critical Zone of the Loess Plateau, China

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Pedotransfer Functions for Estimating the Field Capacity and Permanent Wilting Point in the Critical Zone of the Loess Plateau, China Journal of Soils and Sediments https://doi.org/10.1007/s11368-018-2036-x SOILS, SEC 2 • GLOBAL CHANGE, ENVIRON RISK ASSESS, SUSTAINABLE LAND USE • RESEARCH ARTICLE Pedotransfer functions for estimating the field capacity and permanent wilting point in the critical zone of the Loess Plateau, China Jiangbo Qiao1 & Yuanjun Zhu2 & Xiaoxu Jia3 & Laiming Huang3 & Ming’an Shao2,3 Received: 26 February 2018 /Accepted: 18 May 2018 # Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract Purpose Field capacity (FC) and permanent wilting point (PWP) are important physical properties for evaluating the available soil water storage, as well as being used as input variables for related agro-hydrological models. Direct measurements of FC and PWP are time consuming and expensive, and thus, it is necessary to develop related pedotransfer functions (PTFs). In this study, stepwise multiple linear regression (SMLR) and artificial neural network (ANN) methods were used to develop FC and PWP PTFs for the deep layer of the Loess Plateau based on the bulk density (BD),sand, silt, clay, and soil organic carbon (SOC) contents. Materials and methods Soil core drilling was used to obtain undisturbed soil cores from three typical sites on the Loess Plateau, which ranged from the top of the soil profile to the bedrock (0–200 m). The FC and PWP were measured using the centrifugation method at suctions of − 33 and − 1500 kPa, respectively. Results and discussion The results showed that FC and PWP exhibited moderate variation where the coefficients of variation were 11 and 23%, respectively. FC had significant correlations with sand, silt, clay, and SOC (P < 0.01), while there were also significant correlations between all of the variables and PWP. In addition, sand was an important input variable for predicting FC, and clay and BD for predicting PWP. The performance of the SMLR and ANN approaches was similar. Conclusions In this study, we developed new PTFs for FC and PWP as the first set of PTFs based on data obtained from deep profiles in the Loess Plateau. These PTFs are important for evaluating the soil water conditions in the deep profile in this region. Keywords Earth’scriticalzone . Field capacity . Pedotransfer function . Permanent wilting point 1 Introduction thereby making it the key area for sustaining ecosystem func- tioning and human survival (Lin 2010). The field capacity The Earth’s critical zone (CZ) is located vertically from the top (FC) and permanent wilting point (PWP) are important input of the plant canopy to the weathered bedrock and it is related variables in a wide range of agro-hydrological models, as well to soil development, water flow, and geochemical cycles, as being important soil physical properties for evaluating the soil water conditions in the CZ. Therefore, it is important to obtain accurate estimates of FC and PWP in the CZ. However, Responsible editor: Saskia D. Keesstra obtaining direct measurements of FC and PWP is tedious, time consuming, and expensive. Pedotransfer functions * Yuanjun Zhu [email protected] (PTFs) can be used for estimating them by using the basic soil properties as inputs and producing complex variables as out- puts (Bouma 1989). 1 College of Resources and Environment, Northwest A&F University, Yangling 712100, China Bouma (1989) introduced PTFs to model the basic soil properties as inputs and obtain hydraulic parameters as 2 State Key Laboratory of Soil Erosion and Dryland Agriculture on the Loess Plateau, Northwest A&F University, Yangling 712100, China outputs. Subsequently, PTFs have become increasingly im- portant in soil science research and many PTFs with dif- 3 Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, ferent data requirements have been proposed. Reviews of Chinese Academy of Sciences, Beijing 100101, China the state of the art in this research field were provided by J Soils Sediments Wösten et al. (2001), Shein and Arkhangel’skaya (2006), 2000). The region is surrounded by mountains, where the and Vereecken et al. (2010). loessial landforms include Yuan (a large flat surface with little Many previous studies have developed PTFs for estimating erosion), ridges, hills, and gullies. FC and PWP in different regions and soil types (Aina and Periaswamy 1985; Saxton and Rawls 2006; Balland et al. 2008). Thus, Berg et al. (1997) developed PTFs for FC and 2.2 Soil sampling PWP for Ferralsols and related soils. Cemek et al. (2004) developed regression models for estimating FC and PWP in Three typical sampling sites (Yangling, Changwu, and An’sai) the Erzincan plain in the Eastern Anatolia region of Turkey. (Fig. 1b) were selected from south to north on the Loess Givi et al. (2004) predicted the soil moisture contents to de- Plateau, and soil samples were collected from the soil surface termine FC and PWP in the Zagros mountain region of Iran. to the bedrock using drilling equipment (assembled by Xi’an Jap (2008) proposed a reliable method for estimating the soil Qinyan Drilling Co. Ltd). At each sampling site, metal cylin- moisture to predict FC and PWP based on the soil texture and ders (diameter: 5 cm, length: 5 cm) were used to collect un- bulk density (BD) using data from the Data and Information disturbed soil samples from the middle of the soil column at 1- System of the International Geosphere Biosphere Programme m intervals (0.5, 1.5, 2.5, 3.5 m,…) in order to obtain mea- soil data set. Nguyen et al. (2015) evaluated PTFs for estimat- surements of FC, PWP, and BD. Similarly, disturbed soil sam- ing FC and PWP for soils in the tropical Mekong Delta in ples were collected to determine the soil particle composition Vietnam. In addition, Ghanbarian et al. (2015) developed sam- and soil organic matter contents. It should be noted that the ple dimension-dependent PTFs for predicting soil water reten- undisturbed soil samples were not replicated due to the possi- tion curves. However, it should be noted that the PTFs devel- ble cost incurred and challenges obtaining the samples. In oped previously for estimating FC and PWP were mainly addition, some soil cores were damaged during drilling. designed for the upper soil layers (< 1 m) and few studies have Therefore, the numbers of undisturbed soil samples were 30, developed PTFs for the deep layers in the CZ. 100, and 76 for Yangling, Changwu, and An’sai, respectively, The Loess Plateau in China (~ 620,000 km2) is covered and the corresponding soil drilling depths were 104.5, 204.5, largely by loess-paleosol layers ranging from 50 to 200 m in and 161.6 m. thickness, and two-thirds of this area comprises arid and semi- arid regions. Thus, reliable FC and PWP data are necessary in order to study the hydraulic processes that occur in the CZ. 2.3 Laboratory analysis However, the great depth of the soil on the Loess Plateau makes it difficult to obtain direct measurements of FC and The FC and PWP were measured using the centrifugation PWP in deep soil profiles. Therefore, new PTFs are required method (Hitachi CR21G centrifuge; 20 °C) at the suctions of for estimating FC and PWP in deep profiles on the Loess − 33 (1700 rpm; 42 min) and − 1500 kPa (12,000 rpml; Plateau in China. 95 min), respectively (Lu et al. 2004), and BD was determined Thus, the objectives of the present study were (1) to devel- based on the volume-mass relationship for each oven-dried op new PTFs for estimating the FC and PWP in the CZ on the core sample (105 °C, 48 h) (Wang et al. 2008). The disturbed Loess Plateau, China, and (2) to compare the performance of soil samples were air-dried and passed through a 2.0- and the developed PTFs with the existing PTFs. 0.25-mm mesh, respectively. Soil samples less than 2 mm were used to measure the soil particle composition by laser diffraction (Mastersizer 2000, Malvern Instruments, Malvern, 2 Materials and methods UK) (Liu et al. 2005). Soil samples less than 0.25 mm were used to determine the soil organic carbon (SOC) contents by 2.1 Study area description dichromate oxidation (Nelson and Sommers 1982). The study was carried out on the Loess Plateau of China (33° 43′–41° 16′ N, 100° 54′–114° 33′ E), which is located in the 2.4 PTF development continental monsoon climate region and is about 6.5% of the area of China (Fig. 1a). The annual evaporation on the Loess In this study, the 206 soil samples were divided randomly into Plateau is 1400–2000 mm, and the annual temperature ranges two groups: group A (137) for deriving the PTFs (including from 3.6 °C in the northwest to 14.3 °C in the southeast (Shi calibration data sets for FC and PWP) and group B (69) for and Shao 2000). The annual solar radiation ranges from 5.0 × validating the PTFs. And new PTFs were developed by using 109 to 6.7 × 109 Jm−2. The annual precipitation ranges step-wise multiple linear regression (SMLR) and artificial from150 mm in the northwest to 800 mm in the southeast, neural network (ANN) approaches, respectively. where 55–78% falls from June to September (Shi and Shao J Soils Sediments Fig. 1 Location of the Loess Plateau region in China (a)and the sampling sites (b) 2.4.1 Step-wise multiple linear regression where Y is the dependent variable (FC and PWP), α0 is the intercept, α1,…, α5 are regression coefficients, and X1–X5 are Multiple linear regression (MLR) is a traditional method for the independent variables (BD, sand, silt, clay, and SOC). In developing PTFs, which is widely applicable in soil science addition, a stepwise regression method was employed in the for developing the PTFs of soil parameters (Liao et al.
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