1 Introduction
Agriculture plays a key role in the national economy (Zhang and Diao,
2020). In recent decades, the modernization of agriculture has seen a move away from traditional rain-fed agriculture over large areas to more intensive agriculture over smaller areas, characterized by water-saving technologies and large-scale operations (Qiao,
2017; Chen
et al.,
2019a; Alauddin
et al.,
2020). The Center Pivot Irrigation (CPI) as a typical modern irrigation technique, indicates a circular pattern in crops and centers on the pivot due to irrigation (Splinter,
1976; Chen
et al.,
2019b), which is the most widely used irrigation system globally. It has a range of advantages, including optimizing the design and management of irrigation water, declined labor requirement, and increasing crop yield (Splinter,
1976; Izquiel
et al.,
2015).
The widespread use of these modern irrigation technologies can guarantee the development of modern agriculture and revitalize the rural economies of modern China (Liu and Li,
2017), particularly in the ecologically fragile desert-adjacent areas. Rapid economic and population growth have resulted in increased demand for land of construction and agriculture from the desert land (Hunter
et al.,
2003; Adriansen,
2009; Nassar
et al.,
2014; Zhang and Deng,
2020). Promoting the development of the modernization of agriculture is critical in these relatively backward regions. The Mu Us dune field in Northern China is located on the margin of the East Asian monsoon climate zone and in an agricultural area consisting of a mix between crop agriculture and livestock farming (
Figure 1a), which is highly sensitive to environmental changes driven by nature and anthropogenic factors (Ding
et al.,
2005; Liu
et al.,
2021). In the past 70 years the Chinese government have made remarkable progress in controlling desertification in this area, in particular since 2000, extensive vegetation rehabilitation and widespread dune stabilization occurred in the southeastern Mu Us dune field (Wu and Ci,
2002; Xu
et al.,
2015,
2018; Zhang and Wu,
2020).
Figure 1 Geographical location of the Mu Us dune field, Northern China (a: geomorphology and location of Mu Us dune field; b: the detailed administrative region and location map of the study area, this is the southeastern Mu Us dune field; The example of CPI farmland is derived from the data of 2009; c: an example showed both the real photo and remote-sensing image of Center Pivot Irrigation (CPI) farmland units, including the core well house and the sprinkler wagon.) |
Full size|PPT slide
Seen in satellite remote sensing images of the Mu Us dune field, the green circles of considerable size and number (
Figure 1b) are the distribution of center pivot irrigation (CPI) (
Figure 1c). The driving factors of this significant greening have been attributed to climate change and human interference (Xu
et al.,
2018). Previous studies had just shown that the existence and development of CPI farmlands in the Mu Us dune field were likely related to the distribution of underlying Quaternary sediments (Liu
et al.,
2018), as well as their distances from lakes, rivers, and roads (Qi
et al.,
2019). The CPI as a major way of farming that increased in these years should have caused a considerable impact on local ecological and environmental conditions, though the systematic investigation is lacking. It is still a knowledge gap that how the CPI affect the evolution of desertification. Therefore, a comprehensive study of the development of CPI farmlands over time is very necessary.
In this paper, we focused on the CPI farmland units in the Mu Us dune field representing to some extent modern agriculture. Landsat remote sensing image data from 2009 to 2018 were used to examine the variations and characteristics of these CPI farmland units over the last ten years and the possible influencing factors are discussed. The results of the present study could act as a reference for better understanding the process of regional desertification, which is essential for policy-making on desertification control strategies and land-use management in environmentally sensitive areas.
2 Materials and methods
2.1 Regional setting
The Mu Us dune field (
Figure 1) has an area of ~40,000 km
2, accounting for ~3.6% of the total desert zone in China. The area has a prevailing northwest wind direction for most of the year. The region falls within a typical temperate continental semiarid monsoon climate zone. The climate shows distinct changes from the northwest to the southeast, transitioning from arid and semi-arid to semi-humid climate conditions. Correspondingly, mean annual temperature, annual evaporation, and annual precipitation of the study region are 6.0-8.5℃, 1800-2500 mm, and 250-440 mm, respectively, with 60%-70% of precipitation falling during June-August. The Mu Us dune field receives higher rainfall compared with other dune field areas in Northern China, and surface water and groundwater resources are relatively plentiful. The natural vegetation of the study area mainly consists of
Artemisia ordosica Krasch.,
Tamarix chinensis Lour., and
Hippophae rhamnoides Linn. The study area shows a zonation of vegetation, with desert steppe in the west, typical steppe in the central and southeast parts, and forest steppe in the southeastern marginal area. The northwest part of the study area falls within Erdos City (Otog Banner, Uxin Banner, and Otog Front Banner, etc.) in the Inner Mongolia Autonomous Region in which traditional grazing is the main form of economic activity. Crop agriculture dominates in the southeast, and in particular in Yulin City in the Shaanxi Province (including Yuyang District, Hengshan District, Jingbian County, etc.) (
Figure 1b).
The remote sensing images for 2018 showed that few CPI farmland units were present in the northwest of the study area, which can be attributed to this area being affected by erosion due to a higher altitude and less precipitation (Liu
et al.,
2017). Therefore, the present study focused on the southeastern part of the Mu Us dune field in which traditional agriculture practices dominate.
2.2 Research methods
The original Landsat remote sensing image data used in the study were acquired from the geospatial data cloud (
http://www.gscloud.cn). A total of 20 images from 2009 to 2018 were selected. Most of the images were selected from the growing season since the active cultivation of crops allowed the farmland to be easily identified. All selected images had cloud cover of less than 1% to minimize image errors.
Table 1 shows a summary of the data chosen. In addition, the study used a Digital Elevation Model (DEM) derived from the LocaSpaceViewer software with a resolution of 9.55 m/per pixel.
Table 1 Detailed information for the remote sensing image data |
Serial
number | Data type | Cloud amount
(%) | Date | Serial
number | Data type | Cloud amount
(%) | Date |
| 127/33 | Landsat TM | 0 | 2009/06/30 | 128/34 | Landsat TM | 0.01 | 2009/07/23 |
| Landsat TM | 0.12 | 2010/10/15 | Landsat TM | 0 | 2010/07/10 |
| Landsat TM | 0.07 | 2011/08/07 | Landsat ETM | 0.02 | 2011/08/02 |
| Landsat ETM | 0.26 | 2012/04/27 | Landsat ETM | 0.52 | 2012/10/25 |
| Landsat OLI | 0.01 | 2013/09/13 | Landsat OLI | 0.77 | 2013/08/03 |
| Landsat OLI | 0.03 | 2014/07/30 | Landsat OLI | 0.02 | 2014/10/25 |
| Landsat OLI | 0.01 | 2015/07/01 | Landsat OLI | 0.16 | 2015/07/24 |
| Landsat OLI | 0.35 | 2016/11/24 | Landsat OLI | 0.22 | 2016/11/15 |
| Landsat OLI | 0.73 | 2017/09/08 | Landsat OLI | 0.03 | 2017/07/13 |
| Landsat OLI | 0.02 | 2018/05/22 | Landsat OLI | 0 | 2018/06/23 |
Processing of the Landsat remote-sensing images for 2009 to 2018 included radiometric calibration, atmospheric correction, and data processing integration. These data were then used to determine the distribution of modern agricultural zones in the study area as characterized by the presence of CPI farmlands. More specifically, the yearly total amount of CPI farmland units from 2009 to 2012 was less than 300. The visual interpretation method by ENVI and GIS software was used to identify the CPI farmlands units. Since there has been a large increase in the number of CPI farmlands units from 2012 to 2018, both visual and computerized methods were used within their enumeration. The TM 432 and OLI 543 band combinations were chosen to identify the boundaries of the CPI farmland units. The false color composite images were then used to interpret the units.
3 Results and discussion
3.1 Annual variations in CPI farmland units from 2009 to 2018
The remote-sensing images from 2009 to 2018 were used to extract CPI farmland units. These data were used to create a database to represent the status of CPI farmland agriculture in the Mu Us dune field, mainly in the southeastern region. The results showed yearly increases in the numbers and areas of CPI farmland units (
Figure 2a). While the numbers and total area of CPI farmland in 2009 were only 24 and ~8.11 km
2, their numbers and total area had increased dramatically to 2,149 and ~340.72 km
2, by 2018, respectively. It showed that the CPI farmlands in our study region started from scratch, and then blossom, reflected in the pronounced expansion of numbers and total area (
Figure 2).
Figure 2 The changes in the distribution and size categories of Center Pivot Irrigation (CPI) farmlands from 2009 to 2018 (a: yearly changes in the total area and number; b: yearly variation in the total area and number; c: variation in area according to different size classes; d: satellite image illustrating the different size classes of CPI farmlands in Mengjiawan (38.653°N, 109.605°E). The base map was derived from Google Earth.) |
Full size|PPT slide
The annual variations in the total area and number of CPI farmland units (
Figure 2b) first showed an increasing trend up until 2015, and then declined. This result indicated an increasing oscillation in the development of modern CPI farmlands in the southeastern part of Mu Us dune field. There was a booming in both the total area and number of CPI farmland units from 2009 to 2015. The maximum growth rate during this period occurred in 2014 when the CPI farmland units and area increased by 428 and 80.80 km
2, respectively. However, there were rapid declines in the area and number of CPI farmland units during 2015 to 2016, followed by a further increase in their number from 2016 to 2017 during they increased by 293, although their total area continued to rapidly drop. This contradiction could be attributed to a rise in the number of CPI farmlands with a small area, particularly in the 0-0.2 km
2 and 0.2-0.4 km
2 ranges (Figures 2c and 2d). As shown in
Figure 2c, over the past ten years, CPI farmland units with areas in the range of 0-0.2 km
2 and 0.2-0.4 km
2 have become dominant, with few units with an area larger than 0.8 km
2. During the initial years of the study period, the proportion of CPI farmland units with an area 0.2-0.4 km
2 was very high (71%), followed by those with an area of 0.4-0.6 km
2 (29%). The proportions of the CPI farmland units with these sizes gradually dropped with the progression of the study period (
Figure 2c). While local people and the local government initially attempted to promote the use of CPI farmland units with larger areas exceeding 0.6 km
2 or 0.8 km
2, the results of the present study showed that these larger units were not in expected expansion. It was increasingly realized that small-scale CPI farmland units (0-0.2 km
2) were more applicable to the region, with the proportion of this size range progressively increasing during the study period (Figures 2c and 2d). In general, the meso- and micro-scale CPI farmland units, mainly with areas of 0-0.2 km
2 and 0.2-0.4 km
2, became increasingly popular.
The total area and number, their variation, and the variation in the proportions of CPI farmland units of different sizes showed that the development processes could possibly be divided into three stages: (1) the period of rapid development during 2009-2015, including the maximum value during 2014-2015; (2) the turning point period during 2015-2016; (3) a possible stable development period after 2016. In addition, it was assumed that the development of modern agriculture, characterized by the use of CPI farmland, will enter a period of stability in the future.
3.2 Spatial variation in CPI farmland units from 2009 to 2018
The study identified the spatial variation in the CPI farmland units using density analysis to explore the development of modern agriculture. The results of the interannual variability (
Figure 3) in the CPI farmland units during the early period showed that CPI farmlands began to appear in the western part of Erdos City in the Inner Mongolia Autonomous Region and in Yulin City in Shaanxi Province (Figures 3a-3c), with relatively limited areas and numbers. There were extensive increases in the numbers and area of CPI farmland units during 2011 to 2012, particularly in the Otog Front Banner, western Erdos City. The most noticeable change during 2012 to 2015 (
Figure 3d-3f) was the centralization of CPI farmland units with scalable development, distinguished from their scattered and sporadic previous distribution. The Yulin City showed prominent increases in the use of CPI farmland units during this time span. In general, western Erdos City constituted the centroid of CPI farmland development in the study area over the study period. As shown in
Figure 3e, there were remarkable increases in the number and area of CPI farmland units during 2014 to 2015, coinciding exactly with the variations in total area and total number mentioned in Section 3.1. However, the growth rates in the number and area of CPI farmland units during 2015 to 2016 showed clear declines, as reflected in the degree of scatter and density. The declines in the CPI farmland units in the Erdos region were larger than those during the other years. There was a general recovery in the area and numbers of CPI farmland units from 2016 to 2018, mainly in Otog Front Banner and Uxin Banner, Western Erdos region, whereas there were only minor increases in Yulin City, Shaanxi Province.
Figure 3 Spatial and temporal distribution of the Center Pivot Irrigation (CPI) farmland units in the Mu Us dune field |
Full size|PPT slide
Regardless of the development period, CPI farmlands remained dominant in the Western Erdos region in the southeastern Mu Us dune field, primarily with the centralized type. In contrast, the development of CPI farmlands remained limited in the Yulin region. However, the results of a field campaign and image interpretation showed that the CPI farmlands in the Yulin region were marked by the emergence of the form of combinations, exactly as shown in
Figure 2d. Therefore, the degree of mechanization was relatively higher than that in the Erdos region, Inner Mongolia.
3.3 Possible natural factors influencing the variation in CPI farmlands
The development of the CPI farmlands from 2009 to 2018 in the southeastern Mu Us dune field were shown in the section above. To understand these changes involved, we now consider some possible natural influence factors below.
3.3.1 Analysis of topographic and climate factors
As shown in the remote sensing images of the study area for 2018 (
Figure 4), Zone I affiliated to Erdos City was the main area in which the CPI farmlands were distributed, followed by Zone II mainly affiliated to Yulin City. An analysis of the DEM (
Figure 4a) and topography relief data (
Figure 4b) showed that all 2149 CPI farmland units were distributed in relatively flat areas. The elevation of Zone I with dense green dots mainly ranged from 1291 m to 1385 m, whereas that of Zone II with sporadic green dots mainly ranged from 1185 m to 1290 m. The topography in the southeastern region was hillier and was not suitable for the widespread construction of CPI farmland units. Since irrigated agriculture in this region depends on groundwater resources, it was recognized that precipitation was not the factor restricting the development of CPI farmland units, with groundwater resources able to satisfy farmland irrigation in study area. However, since the growth of crops requires sufficient effective accumulated temperature, the mean annual temperature of the study region may be a significant constraint. As shown in
Figure 4b, the 7.6℃ isoline was associated with the minimum temperature limit line.
Figure 4 (a) Digital elevation model (DEM) database map (http://www.gscloud.cn/) and distribution of the Center Pivot Irrigation (CPI) in the southeastern Mu Us dune field. (b) Topographic relief base map and distribution of the CPI farmlands superimposed with climate information, including mean annual precipitation and the temperature isoline inferred from Liu et al. (2017). Zone I and Zone II represent the most concentrated areas of CPI farmlands. (c) Map of groundwater resources (www.geomapapp.org) and distribution of the CPI farmlands and the spatial scale is 1:12,000,000. RM refers to Runoff Modulus and WRM refers to Resource Module of Natural Recharge. (d) Synthesis of the distribution of peat-containing and palaeosol-containing sites (Liu et al., 2018) and the distribution of the CPI farmlands |
Full size|PPT slide
On the whole, topography was the primary factor influencing the distribution of CPI farmland units. This is because the establishment of CPI farmland requires large expanses of relatively flat land, which can mostly be found in the western part of Erdos City, particularly Otog Front Banner. Temperature was also an important factor, with areas of sufficiently high temperature required to facilitate the growth of crops.
3.3.2 Analysis of hydrological factors
Since large CPI sprinkler systems consist of a central pivot containing a groundwater well, the study assumed that groundwater is required for the development of regional modern agriculture. The distribution of CPI farmland units was overlayed onto a map of groundwater resources in the study area (
Figure 4c). The results showed that access to groundwater was not the main factor restricting the expansion of CPI farmland. Although a large-scale groundwater map has a limited precision, it is suggested that groundwater is relatively plentiful in the study area, and is therefore not a factor limiting the distribution of CPI farmlands.
3.3.3 Analysis of geological substrate
The results of extensive field campaigns together with research on the Quaternary sediments in the area showed that the CPI farmland units had been constructed on peat/sandy peat-based or palaeosol-based stratum areas (Liu
et al.,
2018). These results appear to indicate that certain substrates are preferred for the construction of CPI farmland units. In general, peat sediment is a good soil medium for plant growth (Sjoers,
1980) since peat layers are able to absorb water of up to 20 times their own dry weight, thereby acting as an impermeable boundary. Palaeosols have similar properties to peat and are also preferred for placement of cultivated land in the Mu Us dune field (Liu
et al.,
2018). Therefore, areas of peat substrate soil appear to be optimal for the placement of agricultural fertilization and irrigation.
The available data showing the distribution of peat and palaeosol sediments were superimposed over the newly acquired remote sensed images of CPI farmlands for 2018 to explore their relationship. The overlay chart indicated that the exposed surface soil rich in organic matter was correlated with the distribution of CPI farmlands, although it was not the decisive factor. It is recommended that un-reclaimed peatland or palaeosol-based lands be identified for future development of CPI farmland units.
Topography, temperature, and geological substratum were preliminarily identified as the major natural factors driving the development of the CPI farmlands. Additionally, there may be other factors influencing the distribution of CPI farmland units that were not investigated in the present study, such as road layout (Amadi,
1988; Kalliola and Kai,
2001), population distribution (Shi
et al.,
2018), traditional customs (Ellis and Wang,
1997), climate change (Xu
et al.,
1999), water balance (Qassim
et al.,
2008) and crop rotation system (Chen
et al.,
2019b). Future research should consider these additional factors.
3.4 Implication for regional land use planning based on the development of CPI farmlands
Agricultural development in China remains in a transitional stage (Dcr et al., 2021). A certain spatial disparity in the level of agricultural mechanization in China remains. Consequently, government policies have encouraged the adoption of modern agricultural practices in the Mu Us dune field, such as the CPI farmland units. The question should therefore be asked whether the continued expansion of the CPI farmlands in the high-profile Mu Us dune field is sustainable. Our study indicates that the main natural factors influencing the distribution and development of CPI farmlands, whereas from the perspective of different stakeholders including the government, the field master/enterprise and the local farmer, anthropogenic factors may be vital.
Government perspective. Policy-driven, large ecological restoration projects implemented in recent decades can exert a positive impact on vegetation restoration (Xu
et al.,
2018). In the Mu Us dune field, government policy plays a large role in regional agricultural development. In particular, in recent years there has been a focus on the construction of high-quality farmland to lay a solid foundation for the modernization of agriculture and to ensure grain security. Agricultural schemes issued by local government (
Figure 5, Published) in the study area included the
Policies on Supporting the Development of Modern Agriculture (
Trial) in 2018 in the city of Yulin, Shaanxi Province and
The Enforcement Advice about Further Enhancement of Construction of High Standard Farmland in order to improve national capacity to ensure food security in 2020 in the city of Erdos, Inner Mongolia Autonomous Region (
Figure 5, Public Document). These schemes have in particular recommended the development of CPI-dominated water-saving irrigation projects through the awarding of large financial incentives (
Figure 5, Bonus) for the construction of high-standard modern agriculture farmlands, thereby providing essential technical (
Figure 5, Technical Support) and financial support (
Figure 5, Initial Investment) for new large-scale intensive agriculture (area exceeding 7 acres).
Figure 5 A relational graph illustrating different stakeholders in the Mu Us dune field and a flow chart of possible advantages and disadvantages of the development of CPI farmlands in the Mu Us dune field |
Full size|PPT slide
Field master/Enterprise perspective. It is clear that substantial investment from field master/enterprise has been made to promote modernization of regional agriculture (
Figure 5, Investment). The study found that the development of most of the modernized farmland, mainly represented by vast areas of CPI farmlands, was supported by government policies (
Figure 5, Public Document). This result considered with the variations in the areas of CPI farmland units of different sizes (
Figure 2c) indicates that decision-makers including the local government and actual investor had identified the optimal size and scale of the CPI farmlands through years of trial and error, with these aspects stabilizing after 2014. In addition, these policies had some negative outcomes, such as the conversion of some sandy area to wasteland.
Local farmer perspective. Supported by favorable policies, measures, and funds, the local farmer as the actual practitioner, made these big and rapid changes in the development of CPI farmlands from decades in the study area, meanwhile they obtained real profits from the technical improvement of modern intensive agriculture.
Advantages. Clearly policies by national and local government in China have served as a guideline for scaling up effective investments in agriculture and in rural areas as part of efforts to eradicate poverty. The CPI technology has facilitated greater agricultural productivity, thereby increased food production and realized food security. Previous studies have shown that the adoption of the CPI systems increase crop yield and improve water-use efficiency (O'Shaughnessy
et al.,
2016; Darko
et al.,
2017).
Disadvantages and further adverse effects. The Mu Us dune field has become popular in recent years for research into the prevention and management of desertification and both the government and people have made great effort to control desertification. Nevertheless, the question remains whether the policy regulating modernization of regional agriculture is beneficial from an ecological perspective. It is suggested that the current trend in agricultural modernization in the Mu Us dune field area is unsustainable and will inevitably lead to the destruction of native arenicolous vegetation. Generally, the development of new CPI farmlands required reclaiming sandy land, which lead to the loss of natural vegetation and increase the risk of soil erosion and reactivation of fixed dunes. From November to April, the developed CPI farmland units lie dormant. These large expanses of bare ground experience aggravated wind erosion, leading to land degradation. A previous study identified that serious environmental problems, such as intensified soil erosion, were triggered by the large-scale land consolidation and development in the Mu Us dune field (Shi
et al.,
2019).
Field observations in the Mu Us dune field show a lack of soil and water conservation measures, such as straw covering and stubble mulch farming. From the angle of irrigation, reasonable irrigation management based on the water balance was needed (Qassim
et al.,
2008). The optimal pattern of irrigation application could prevent water stress, control salinification, and resulted in high irrigation efficiency (Izquiel
et al.,
2015; Domínguez
et al.,
2022). The Mu Us dune field contains the main area of the Three-North Shelter Forest Program and is also a source area of the sand and dust affecting the cities of Beijing and Tianjin in China. Therefore, the unplanned development of CPI farmlands in Mu Us dune field can possibly have a detrimental effect on the acquirement of government ecological and environmental targets. In addition, the results of field surveys (
Figure 5) indicated that local farmers utilizing CPI farmlands considered the operating costs to be prohibitive. Therefore, these respondents were not willing to accept the costs associated with the expansion of CPI farmlands.
Proposal. Based on the background in understanding of interactions between regional ecological recovery, desertification combating work, and economic development, although the construction of CPI farmlands in Mu Us dune field was partially policy driven, for the policy-makers, both natural and socioeconomic factors must should be considered. In terms of the development process, the scale of CPI farmland units was adjusted effectively and stabilized at the economical and practical meso- and micro-scale after 2016.
Figure 5 shows a summary of the different stakeholders and their relationships as well as advantages and disadvantages of the development of CPI farmlands. In conclusion, our study indicates that the disadvantages of the CPI farmlands generally outweigh their advantages. Nevertheless, modern agricultural development remains a priority within the sandy land areas, because these areas with unconsolidated sediments could meet the need of relatively flat terrain after the land consolidation, generally (Chen
et al.,
2019b). Although Chen
et al. (
2019b) considered that it was not sustainable to vigorously popularize CPI farmland at improving the agricultural production conditions in the Farming-Pastoral Ecotone of Northern China, the Mu Us dune field has its particularity. As a natural resource widely distributed in the southeastern Mu Us dune field, the ancient peat has a high water-retention capacity and high organic matter content, which could improve the agriculture production efficiency (Liu
et al.,
2018).
Given the ecological significance and risk of further desertification, it is suggested that further modernization of regional agriculture should be more forward-looking and well-planned, which should take many natural and anthropogenic factors into consideration, such as terrain, climate patterns, geological substrate, and other feasible national and regional development strategies. Besides, further study is still needed to uncover the optimal quantity, scale and spatial distribution of CPI farmland.
4 Summary and conclusions
Based on the remote sensing image data, and the field investigation, we present an analysis of variations in Center Pivot Irrigation farmland units and the influencing factors over the last ten years in southeastern part of Mu Us dune field. The current study obtained the following conclusions:
(i) From 2009 to 2018, the number and total area of CPI farmlands showed dramatically rising trends. After years of trial and error, the meso- and micro- scale farmland stabilized at 0-0.2 km2 and 0.2-0.4 km2, respectively; (ii) Topography, temperature, and geological substratum were found to be the major natural factors influencing the distribution and development of the CPI farmlands. In addition, government policies played a decisive role; (iii) Within the context of varying stakeholders’ priorities, potential risk of soil erosion, and damage to natural vegetation, our study suggests the urgent need for strict control of further development in CPI farmlands in the Mu Us dune field. This requires rigorous planning and long-term effective land-use policies. The results of the present study can assist local government in achieving a better balance between economic demands and ecological protection.
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Figure 1 Geographical location of the Mu Us dune field, Northern China (a: geomorphology and location of Mu Us dune field; b: the detailed administrative region and location map of the study area, this is the southeastern Mu Us dune field; The example of CPI farmland is derived from the data of 2009; c: an example showed both the real photo and remote-sensing image of Center Pivot Irrigation (CPI) farmland units, including the core well house and the sprinkler wagon.)
Table 1 Detailed information for the remote sensing image data
