Contents

1 Introduction

Central Asia is geopolitically and strategically important because of its geographic position. The Central Asian states Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan are situated in the heart of the Eurasian continent and form a trade link between China, the Middle East, and Europe (Liu 2011). Upon entering into membership in the Shanghai Cooperation Organization, this region has been viewed as a new route of multilateral partnership between the political powers of Russia and China (Wilhelmsen and Flikke 2011). The region is strategically important in the global economy, especially for trading carbon credits (Lal 2007) and exporting natural resources (oil, gas, energy, gold, and minerals). All five countries became independent from the Soviet Union in 1991, and they share a culture and a way of life that incorporate elements from both the East and the West (Olcott 1996). Prior to independence, these countries were socio-economically interdependent within the centrally planned Soviet economy. Agriculture was one of the major economic sectors of the Central Asian countries and accounted for 10 to 45 % of their gross domestic product (GDP), employing 20 to 50 % of the labor force (Qushimov et al. 2007). To date, agriculture remains an important sector in the economy of Central Asia, contributing 5.2 % of the GDP in Kazakhstan, 7.5 % in Turkmenistan, 18.5 % in Uzbekistan, 20.8 % in Kyrgyzstan, and 23.3 % in Tajikistan (Abdullaev 2014; Bobojonov and Aw-Hassan 2014).

Because of the massive extraction of irrigation water for agriculture from the Amudarya and Syrdarya Rivers, the two primary rivers in this region, the ecological conditions around the Aral Sea have deteriorated. Elevated water tables associated with decades of heavy irrigation water use as well as insufficient drainage have led to the secondary salinization of croplands and watercourses (Fig. 1). Major waterlogging problems resulted in a decline in the production of cotton and wheat, which are the primary agricultural crops in the region (Toderich et al. 2002; Hamidov et al. 2007a; Sugimori et al. 2008; Varis 2014). Land salinization now affects over 47.5 % of the irrigated lands of Central Asia (with 33 % of irrigated lands affected in Kazakhstan, 11.5 % in Kyrgyzstan, 16 % in Tajikistan, 95.9 % in Turkmenistan, and 50.1 % in Uzbekistan). Salinization is thus a threat that is leading to declining crop production (van Dijk et al. 1999; Bucknall et al. 2003; Kushiev et al. 2005).

Fig. 1
figure 1

Heavily salinized drainage collector characterized by the milky blue color of the water. The man is measuring the degree of salinization by electro-conductivity (Photo: D. Balla)

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The advancing desertification and soil degradation of the Aral Sea in Kazakhstan’s and Uzbekistan’s territories have further impeded the region’s sustainable land use (Indoitu et al. 2012). The increased dust storms in the Aral Sea area, particularly in the southwestern region of Uzbekistan, represent a challenge impacting human health (Groll et al. 2013). Some authors report that the worsening ecological situation in the Aral Sea zone has led to a prevalence of anemia and restrictive pulmonary dysfunction, as well as a high risk of developing urolithiasis in adults and increased infant mortality (Kaneko et al. 2002; Kunii et al. 2003; Crighton et al. 2011; Groll et al. 2013).

The 1–2 °C increase in the temperature that has occurred in Central Asia since the beginning of the twentieth century has led to impacts on agricultural production and land use practices (Lioubimtseva et al. 2005; Fischer et al. 2002). Climate warming is expected to aggravate the situation, resulting in decreasing snow and glacier reserves in the Tien Shan and Pamir Mountains, which are the only source of water for most of the irrigated croplands in the region (Aleksandrova et al. 2014). Transboundary water management conflicts have resulted in a decline in crop production (Rakhmatullaev et al. 2010a). The ongoing dispute between agriculture and hydropower with regards to water use has implications for the region’s sustainable development (Libert and Lipponen 2012). Varis (2014) noted that Central Asian countries have plenty of water relative to their populations but have a very low economic return on water compared with other parts of the world. For instance, Turkmenistan uses almost three times more water than India to produce one GDP dollar (Varis 2014; World Bank 2013). Some authors suggested that one way to achieve long-term sustainability in terms of agricultural land use in Central Asia was to switch from growing low-return crops on irrigated dry lands to a less water-intensive crop production system (Hamidov et al. 2007b; Bobojonov et al. 2013a; Varis 2014). However, it is important to emphasize that less water-intensive crops may not necessarily cover the cost of the huge and expensive irrigation and drainage system in Central Asia, and alternative crops may be integrated into the crop rotation program of these countries. Nonetheless, prior to achieving this status, the sustainability issues must be better understood.

In addition to the thorough understanding of the drivers for land use changes, including climate change, water conflicts, and resource degradation, policy makers (international and domestic institutions) and land managers need a comprehensive knowledge base regarding the impacts of agricultural land use on environmental, economic, and social dimensions of sustainable development. Research can provide this knowledge base at the highest quality level, as is guaranteed through the international peer-review system. By performing a meta-analysis of existing scientific literature, this knowledge base can be mined, and blind spots can be detected when the data are analyzed against all three dimensions—environmental, economic, and social—of sustainability.

The primary objective of this paper was to analyze the current international literature on agricultural land use in Central Asia and its relevance to sustainable development. We applied the Land Use Functions framework (Perez-Soba et al. 2008) to operationalize the concept of sustainable development in the context of agricultural land use. In particular, we examined the type and relative shares of environmental, economic, and social aspects in agricultural land use that were addressed in the literature. By building upon this review, we aimed to identify existing knowledge gaps and the need for future research on sustainable land use.

2 Methodology

2.1 Study area

Central Asia, which comprises the five former Soviet Union republics of Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan (Fig. 2), covers an area of approximately 4 million km2 and has a total population of 65 million. These countries share their borders with China to the east, Russia to the north, the Caspian Sea to the west, and Iran, Afghanistan, and Pakistan to the south.

Fig. 2
figure 2

Map of the five countries of Central Asia, which are surrounded by China, Russia, Afghanistan, Iran, Pakistan, and Azerbaijan (retrieved from: http://origins.osu.edu/article/69/maps). The total agricultural land in Central Asia is 2.8 million km2. Kazakhstan has the largest territory in the region

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Central Asia is a dryland region, and the climate is continental with hot summers and cold winters (Mueller et al. 2014), particularly in the lowlands of Kazakhstan, Turkmenistan, and Uzbekistan. Kyrgyzstan and Tajikistan are located in the mountainous areas of Tien Shan and Pamir, respectively, with large differences in climatic conditions between the mountains and valleys. Approximately 90 % of Central Asia’s area receives less than 400 mm of rainfall per year: 191 mm in Turkmenistan, 264 mm in Uzbekistan, 344 mm in Kazakhstan, 533 mm in Kyrgyzstan, and up to 691 mm in the mountainous region of Tajikistan (Mueller et al. 2014). The annual potential evapotranspiration in the lowlands exceeds the annual rainfall, and thus, irrigation is required to cultivate agricultural crops.

Agricultural land covers approximately 2.8 million km2 or 70 % of the total land area (Lal 2007). Approximately 2.5 million km2 or 63 % of the total land is in rangelands, whereas approximately 0.3 million km2 or 7 % are croplands. Notably, of the 0.3 million km2, only 0.1 million km2 is under irrigation (Mueller et al. 2014). The irrigated land in Central Asia expanded dramatically during the Soviet Union’s active years, particularly in Uzbekistan, where the irrigated area tripled from 0.14 to 0.42 million km2 between the 1950s and 1990 (Khamraev et al. 2011).

The agricultural sector in Central Asia is undergoing re-organization. According to Suleimenov (2014), the following changes were made: During the time of the Soviet Union, each country specialized in certain agricultural strategies, with Kazakhstan in grain production; Kyrgyzstan in sheep production, alfalfa, and maize; and Tajikistan, Turkmenistan, and Uzbekistan producing as much irrigated cotton and karakul sheep for pelts as possible. During the transition time that followed, the development of the crop production industry began. In Kazakhstan, the cropland area was reduced significantly, and monoculture wheat production followed, with producers recently beginning to include food legumes such as dry peas and chickpeas. Kyrgyzstan specialized in alfalfa seed, potatoes, and maize. During the transition period, the wheat area was doubled. Dry beans under irrigation are now increasing in the current market economy. Tajikistan previously specialized in cotton production. The wheat area has doubled but has a low yield level. Turkmenistan now produces bread wheat at a respectable level, although this level is low for irrigated land. In Uzbekistan, self-sufficiency in bread wheat grain has been a major achievement of agricultural restructuring in recent years. Thus, the area under cotton has been reduced, and alfalfa and other forage crops have been removed from irrigated land. A cotton–alfalfa rotation has been replaced by a cotton–wheat rotation. Livestock and forage production has decreased in most Central Asian countries to a negligible level. However, the demand for food and forage is increasing. Poorly managed rangelands lead to a lack of feed, land degradation, a loss of plant biodiversity, and expanding desertification (Gintzburger et al. 2003). Consequently, researchers are now demanding a change in policies towards the support of rangeland improvement and integrated crop and livestock production (Suleimenov 2014).

With the exception of Kazakhstan, the primary water resources of the Central Asian countries are the melting waters of the Tien Shan and Pamir Mountains, which form the Syrdarya and Amudarya Rivers. Turkmenistan and Uzbekistan are extremely dependent on water resources that come primarily from Kyrgyzstan and Tajikistan. Thus, water distribution is a top political issue and novel methods and knowledge-based developments at a rural scale are necessary to overcome water scarcity and match the rising economic status of the area.

2.2 Land Use Functions: a framework for analyzing sustainable development

Since the Brundlandt Report, sustainable development has become a paradigm for policy making worldwide (WCED 1987). Decision-making that is oriented towards sustainable development requires knowledge and the simultaneous consideration of ecological, economic, and social dimensions. In the case of land use, the Land Use Functions framework helps to make the concept of sustainable development tangible and operational (Helming et al. 2011a). Land Use Functions are defined as “the goods and services provided by different land uses that summarize the most relevant environmental, economic and societal issues of a region” (Perez-Soba et al. 2008). The concept was developed to substantiate the concept of sustainable development with the concept of multifunctional land use and thereby simultaneously consider environmental, economic, and social aspects. This facilitates the assessment and governance of land use to promote sustainable development (Helming et al. 2011a).

The framework is designed such that for each of the three sustainability pillars, three categories are defined that together cover all the important functions of land use. The outcome is nine categories of so-called Land Use Functions: environmental: (1) abiotic, (2) biotic, and (3) ecosystem processes; economic: (4) land-based production, (5) market, and (6) transport/infrastructure; and social: (7) employment, (8) health, and (9) culture. Those nine function categories are generic and must be particularized according to the specific spatio-temporal and sustainability context to which they are applied. For instance, in China, food access and quality were identified as the primary issues related to social Land Use Function 8, namely “health” (König et al. 2014a), and in Europe, this function was related to recreation (Perez-Soba et al. 2008). When determined using adequate indicators and ranked in their relative importance for region-specific sustainable development, the Land Use Functions can be combined to support and evaluate policies (Paracchini et al. 2011). This framework has been applied for sustainability assessments and land use classification in China (Xie et al. 2010; König et al. 2014a), India (Purushothaman et al. 2013), various developing countries (König et al. 2013), and Europe (Helming et al. 2011b; Morris et al. 2011). The framework was also used in a literature review of sustainability issues related to land use in Inner Mongolia, China (König et al. 2014b). This scheme has yet to be applied to the context of Central Asian sustainable agricultural land use, and thus, we used Land Use Functions as the analytical framework for the literature analysis in this study.

2.3 Database search

We included scientific publications that addressed agricultural land use in Central Asia. A systematic database search of peer-reviewed articles was conducted using the electronic Web of Science. We selected only the international journal articles that stayed within the boundaries of internationally acceptable scientific quality management. This approach leaves out the analysis of, e.g., research results published in national publication formats, which might also be of very high information level. However, language barriers and the inaccessibility of “gray” literature created difficulty in the comprehensive analysis of the existing literature on agricultural land use.

All analyses were conducted between July and October 2014. The logic of our analysis was to view agricultural land use as the cause (pressure) and Land Use Functions as effects (impact). We therefore selected search terms that were relevant to agricultural land use and to Central Asian countries. The following thematic search terms were used: agriculture, farm, irrigation, land, land use, and water management. For geographic search keywords, we used Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, Uzbekistan, and Central Asia. The composite terms were placed inside inverted commas, and an asterisk was used at the end of each term capture all possible extensions and variations of a particular word. The documents were considered relevant if they matched at least one of the topical search terms and one of the geographic search terms in their titles, abstracts, or keywords.

The study period covered the 6 years from 2008 to 2013. The selection of this study period was driven by two considerations. First, the severe re-organizations of agricultural land use after independence required some time to settle before sustainability impacts could be analyzed. Second, there was a need to balance the comprehensiveness of the sampling and the workability within a reasonable time period. We selected this study period after first conducting an automated database search with the same search terms for the 1991–2013 time period to cover the entire period since independence. The results showed that almost two thirds (62 %) of the papers were published after 2008. We therefore selected 2008 as the starting year for the analysis. This year also coincides well with the publication date of the Land Use Functions framework by Perez-Soba et al. (2008), which we used for the analysis.

To compare the dynamics of agricultural land use publications in Central Asia with global dynamics, we also performed an automated database search using the same thematic terms for worldwide publications on agricultural land use during the same time period from 2008 to 2013.

After identifying the relevant papers, we reviewed all abstracts; in the case of irrelevance to the research region or agricultural land use, the papers were discarded from the database. Relevance was checked on the basis of Land Use Function categories, and papers were then assigned to one or several of the nine Land Use Function categories. The original definitions of Land Use Functions were specified in accordance with the regional and sustainability context of our research question (Table 1). For instance, the provision of abiotic resources related to land use concentrated primarily on the physical and chemical properties of soil and water resources (Land Use Function 1), whereas the maintenance of ecosystem processes was related to ecological issues, land degradation, and grassland management (Land Use Function 3). The former addressed more technical aspects of research related to the environment, and the latter was more concerned with the broader aspects of environmental improvements. Last but not least, the support and provision of biotic resources were relatively focused on habitats for fauna and flora, as well as other living organisms (Land Use Function 2).

Table 1 Land Use Functions used in this study
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Under the economic dimension of sustainability, the study captured research related to land-based production such as crop yields, value-added chains, and biomass production (Land Use Function 4). The provision of financial services and access to rural banks for agricultural farm management, as well as land competition associated with agriculture, were coded under Land Use Function 5, “market- and land-independent production.” Research on the implementation of large-scale irrigation projects, the management of physical infrastructure, and issues related to transboundary water conveyances in relation to land use practices were included under Land Use Function 6, “transport/infrastructure.”

Finally, the social aspect of sustainability included the provision of job opportunities, income, and livelihood security in rural areas (Land Use Function 7), as well as concern about health-related diseases and malnutrition in the region (Land Use Function 8). The use of these landscapes for cultural heritage and the gender issues involved in accessing agricultural land were the primary concerns of Land Use Function 9.

To reveal the types of scientific methods used, we further analyzed the research methods of each paper. After a detailed review of each paper, we divided them into two categories: direct data analysis (stakeholder-involved analysis, monitoring, and in situ experiments) and indirect data analysis (including geographic information systems (GIS), remote sensing, modeling, and review analysis). Finally, the authors’ institutional affiliations were examined to determine which countries had been active with respect to agricultural land use research in Central Asia during the study period.

3 Results and discussion

The automated database search returned a total of 697 papers. Of these, we found 362 articles (52 %) that were relevant to agricultural land use in Central Asia. The other 335 articles were removed from the database because of their irrelevance to the geographic area or to agricultural land use. For instance, some papers referred to the eastern part of China (Xinjiang), Afghanistan, and Mongolia as Central Asia. Additionally, some papers referred to the thematic search terms we used in the abstract, but the detailed review of the abstract and, in some cases, the whole paper indicated its irrelevance to agricultural land use. Those papers were thus omitted. We noticed an annual increase in the number of selected publications during the study period, indicating that researchers were paying increasing attention to agricultural land use in Central Asia (Fig. 3). The increase in the number of annually published papers on that topic was 67 % in Central Asia over the 6-year period, compared with 48 % worldwide (Fig. 3). The trend in Land Use Function-related papers was higher in Central Asia than in the rest of the world.

Fig. 3
figure 3

Number of articles on Land Use Functions in Central Asia and the world, by year, from 2008 to 2013. Of the 362 papers that were found to be relevant to agricultural land use in Central Asia, almost half were published in the most recent 2 years (2012 and 2013), indicating the overall increase in the attention paid to the region. This increase is larger than that of the world as a whole

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Most of the papers deal with some aspects of the environment associated with agricultural land use, which confirms the critical role of agriculture for environmental degradation in Central Asia, e.g., the drying up of the Aral Sea (Dukhovny and Stulina 2001; Crighton et al. 2011). The distribution of publications across nine Land Use Function categories is given in Fig. 4. Notably, each paper could be allocated to more than one Land Use Function. Of the 362 papers analyzed, the environmental aspects of land use were most often addressed (422 times), followed by the economic aspects of land use (270 times). The social aspects of land use were least often addressed (101 times).

Fig. 4
figure 4

Distribution of Land Use Functions addressed in peer-reviewed publications that focused on Central Asia (LUF 1: provision of abiotic resources, LUF 2: support and provision of biotic resources, LUF 3: maintenance of ecosystem processes, LUF 4: market and land-based production, LUF 5: residential and land-independent production, LUF 6: transport/infrastructure, LUF 7: provision of work, LUF 8: human health and recreation, and LUF 9: culture)

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Among the environmental aspects, the provision of abiotic resources and the maintenance of ecosystem services were most addressed. One hundred sixty-three articles (45 %) addressed the physical and chemical properties of soil and water quality in relation to agronomic activities, including the salinization of irrigated fields, particularly in Kazakhstan, Turkmenistan, and Uzbekistan. The largest number of papers (almost 50 % of the articles) raised concerns regarding ecosystem maintenance and addressed issues related to croplands and grasslands, ecology, and land degradation. The support and provision of biotic resources were least explored within the environmental dimensions of sustainability (23 % of papers). When addressing soil salinity, heavy metal analyses in the soils, and the regulation of water contamination through agricultural runoff, papers also targeted ecosystem services, the improvement of soil and land, and grassland management. We found that 117 papers discussed some aspects of abiotic resources and ecosystem maintenance simultaneously, thereby making use of a broader approach to ecosystem services. In terms of the support and provision of biotic resources with regards to habitats for fauna and flora and other organisms associated with the land capacity, we identified 35 papers that also addressed the economic dimension of agricultural land use, particularly land-based production. Here, the primary issue was the analysis of trade-offs between agronomic performance and biodiversity issues.

Among the economic factors, papers mostly addressed land-based production such as crop yields, value-added chains, and biomass production-related research (47 %), followed by water infrastructure (20 %). In the latter case, the reconstruction and rehabilitation of on-farm and inter-farm irrigation and drainage infrastructures were the primary concerns of most papers. Land-independent production, market mechanisms, financial services, and property rights issues played a minor role in the literature. Of the 362 papers, only 28 articles, corresponding to 7 %, addressed these issues. Dear et al. (2013) argued that in the context of Central Asia, researchers who address the socio-economic aspects of agriculture often do not include any connection to land use, land management, or ecosystem services.

When comparing the distribution of publications on the economic versus social dimensions of sustainable development, social sciences were underrepresented. The World Bank (2006) emphasized that the technical aspects of land management are more locally relevant in Central Asia once the basic “institutional” constraints are resolved. Among the publications that address the social aspects of land use, the highest number (55) addressed the provision of job opportunities for rural inhabitants, income, and livelihood security in relation to agricultural land use. Thirty-two articles presented research on the use of the landscape for cultural heritage and diversity purposes. Although the people in the region are experiencing significant health problems resulting from soil salinization and land degradation (Groll et al. 2013), only 14 articles (4 %) addressed the impacts of land use and degradation on human health. A detailed review of the health-related papers indicated that only three papers discussed some aspects of human health and recreational services in the Aral Sea areas of Central Asia. Of these, Bhaduri and Kloos (2013a) explored whether the water fees that were collected by a water users' association can be used to provide socio-economic benefits to its members. These benefits included the maintenance of health centers and schools and the provision of microcredit (Bhaduri and Kloos 2013a, b). Oberkircher et al. (2011a) explored the importance of the ecological and socio-cultural dimensions of Shurkul Lake, which was formed by transforming a forested landscape to an agricultural landscape. The results indicated that “the lake is part of local ecological knowledge, functions as a prestige object and recreational site, and is rooted in the religious beliefs of the population as a symbol of God’s benevolence” (Oberkircher et al. 2011a, b). Franz et al. (2010) assessed the economic viability of organic cotton produced in Uzbekistan. Their study compared a conventional cotton production system, which contributed to soil degradation, water depletion, and poor human health, with an integrated organic system in Western Uzbekistan. The results revealed that the higher profits achievable under an organic farming system could reduce the pressure on the environment and improve local livelihoods (Franz et al. 2010). Despite these three examples, the scientific evidence base related to the social aspects of land use is very limited, although it is of high societal relevance, particularly regarding the direct effects of salinization and dust storms on human health (Groll et al. 2013). This scientific base is also limited because the interactions between land use and human health are not always explicitly discussed. For instance, Crighton et al. (2011) concluded that human health problems were directly affected by the environmental disaster in the vicinity of the Aral Sea. However, the link with the land use was not explicitly described.

We analyzed the number of papers that covered more than one sustainability dimension to identify the prevalence of the use of an integrated, sustainability-related approach among these publications. One hundred and sixty-seven papers (approximately 46 %) addressed the Land Use Functions of at least two of the three dimensions of sustainable development. However, only 26 papers (approximately 7 %) covered all three dimensions of sustainable development simultaneously, meaning that these papers addressed at least one Land Use Function category from each dimension of sustainable development (environmental, economic, and social).

The distribution of the Land Use Functions across different countries is given in Fig. 5. The country rankings in terms of the number of publications that cover different types and relative shares of Land Use Functions were led by Uzbekistan (first), followed by Kazakhstan (second). At first glance, this result is surprising because the agricultural land area in Kazakhstan is 2.1 million km2, which is eight times larger than the agricultural land area in Uzbekistan (0.26 million km2) (FAO 2012). However, agricultural land use in Kazakhstan is extensive and is associated with low resource input. Another reason for this finding might be the rigorous renouncement of irrigated agriculture in parts of Kazakhstan within the Aral Sea watershed. Thus, conflicts between agriculture and the water management of the Aral Sea have been settled and thus do not require further scientific consideration. However, no research was found addressing the accompanying monitoring of ecological, economic, and social themes.

Fig. 5
figure 5

Distribution of articles for each Land Use Function across the countries of Central Asia. Social issues related to land use are underexplored. This deficiency is particularly severe for the relations between land use and health issues. The implications of land use for biodiversity have been rarely studied. Instead, the focus has been on non-biotic environmental impacts. Of the five countries, Uzbekistan has been addressed most often. The ranking of the bars is as follows: Kazakhstan (KZ), Kyrgyzstan (KG), Tajikistan (TJ), Turkmenistan (TM), and Uzbekistan (UZ). (LUF 1: provision of abiotic resources, LUF 2: support and provision of biotic resources, LUF 3: maintenance of ecosystem processes, LUF 4: market and land-based production, LUF 5: residential and land-independent production, LUF 6: transport/infrastructure, LUF 7: provision of work, LUF 8: human health and recreation, and LUF 9: culture)

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High-intensity, irrigated agriculture is more dominant in Uzbekistan (0.42 million km2) than in Kazakhstan (0.21 million km2) (Kienzler et al. 2012). Highly intensive agriculture is usually associated with a higher research input than low-intensity agriculture. In addition, Uzbekistan benefited from an extensive German research project on land and water resources that involved both local and international scholars. The project was implemented through the Center for Development Research (ZEF) at the University of Bonn from 2000 to 2011, with financial assistance from the German Ministry of Education and Research. In addition, the Central Asian office of the International Water Management Institute (IWMI) in Tashkent has been very active since the beginning of 2000 in promoting research activities in three countries of the Ferghana Valley (namely, Kyrgyzstan, Tajikistan, and Uzbekistan) to implement an integrated water resource management approach. Turkmenistan also has a considerable share of irrigated cropland with 0.18 million km2 (Kienzler et al. 2012), but there are few research papers relevant to this country (Fig. 5). When considering the relative shares of Land Use Functions per country, Fig. 5 clearly shows that papers relevant to Kazakhstan were more frequently concerned with biotic resources and biodiversity compared with other countries. This finding may be explained by the fact that much of Kazakhstan’s economic growth is currently driven by the oil and gas sectors (Petrick et al. 2014), with agriculture being one of the lowest GDP contributors to the national economy of Kazakhstan. Because of this country’s concern with the eradication of the Aral Sea disaster, its focus has shifted towards the restoration of wetlands and fisheries in the vicinity of the lake (World Bank 2010). Consequently, the role of land use in supporting biodiversity received more attention than economic functions.

Given the prominence of empirical papers within the literature on Land Use Functions, it is interesting to investigate the types of scientific methods used in these papers (Fig. 6). The analysis revealed that only 14 % of the papers were based on direct data collection methods, including quantitative sampling and experimental methods (6 %) and qualitative, social science methods (8 %), and that 85 % of the papers used indirect methods. Of these papers, more than half (52 %) employed GIS and remote sensing to analyze land-related issues. Spatiotemporal data on land use and land cover were obtained from various satellites (e.g., MODIS, Landsat, and GRACE) and were processed with GIS and remote sensing. Mathematical modeling was the second most commonly employed method in the portfolio (22 %). Agent-based modeling, farm modeling, household modeling, sector models, scenario modeling, simulations, and sensitivity analysis were also employed. Review studies constituted 11 % of the publications. In comparison, in situ research by means of experiments and collecting quantitative and/or qualitative data was relatively rare. Only 8 % of the papers employed stakeholder-inclusive social science methods, including expert interviews, focus group discussions, and/or participatory approaches. Sampling and experimentation were the least-practiced methods (6 % of publications). These results indicate that of the 362 papers, only 14 % were based on in situ work (quantitative and qualitative analysis), including very little local-scale field work and bottom-up work. This distribution might be associated with a risk of data scarcity for proper ground-truthing in remote sensing and modeling work. Indeed, the risk of misinterpreting indirect and remotely sensed data is high when the in situ database for backing and validation is thin. Additionally, the preference of international authors for using indirect methods might explain the low number of papers that address biodiversity issues and biotic resources or social science issues, which are difficult to analyze with the currently available methods of mathematical modeling or remote sensing.

Fig. 6
figure 6

Articles published on Land Use Functions in Central Asia by type of scientific method used from 2008 to 2013. Of the 362 papers, most (74 %) reported research that was performed with indirect methods of data analysis, namely, remote sensing and modeling. Some ground-truthing work (monitoring and experimentation on the ground) could support the proper validation of the simulated data. Literature describing this type of work is scarce

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When author institutional affiliations were examined, we found that approximately 87 % of all papers were published by international research groups. The data reveal that almost one third of the papers (135) were either individually or jointly authored by researchers affiliated with Germany. As mentioned elsewhere in this paper, this distribution is related to the long-term engagement of a German university in the region. These publications showed that the sustainable management of land and water resources in the Aral Sea area of Uzbekistan was the primary focus of the German research organization ZEF from 2000 to 2011. In particular, the ZEF project in the Aral Sea Basin was aimed at the economic and ecological restructuring of land and water use in the Khorezm region of Uzbekistan by engaging local stakeholders in designing and implementing new innovative solutions (Martius et al. 2012). Only approximately 13 % of the publications were published by Central Asian authors, of which 7 % consisted of IWMI publications.

In the introduction to this paper, we highlighted four key issues in sustainable development that are affected by agricultural land use in Central Asia: (a) soil salinization and land degradation, (b) transboundary water management, (c) climate change, and (d) water use efficiency and the economic return on water use. In the case of soil salinity and land degradation, these factors were mostly addressed under the environmental dimension of sustainable development in relation to abiotic resources and ecosystem maintenance, respectively. These issues were found to be critical for the sustainable development of the Central Asia region because of the worsening situation in the vicinity of the Aral Sea (Dukhovny and Stulina 2001; Crighton et al. 2011). Present transboundary disputes over water management in the region are creating an increasingly challenging situation for the governments of these Central Asian nations that poses a threat to national water security and irrigated agriculture in the region. This literature analysis reflected this challenge: of the 73 papers related to the implementation of large-scale water projects, the management of irrigation infrastructure, and issues related to transboundary water conveyances, 29 articles focused on multinational aspects of water management. For instance, Libert and Lipponen (2012) investigated issues related to transboundary water resources in Central Asia and concluded that “the outdated legal framework for regional cooperation on shared waters requires improvement to help find sustainable long-term solutions for the reasonable and equitable use of shared water resources.” They highlight that reduced flows in transboundary rivers have led to land degradation and negative impact on ecosystems.

The effects of climate change in the region have adversely affected the availability of high-quality water and productive soil for agriculture (Krysanova et al. 2010; Qadir et al. 2013). Additionally, the increased frequency and intensity of droughts and floods might also be directly linked to the climate change in the region (Krysanova et al. 2010). The findings of reviews confirm the role on climate change as an important driver of sustainability impacts on agricultural land use. Climate change issues were at the forefront of many papers (43 papers or 12 %). This review indicated that climate change was primarily discussed in reference to water and soil quality, long-term ecosystem processes such as land degradation and grassland management and the availability of water for agriculture in the transboundary context. There was one publication by Kassam (2009) in which the author discussed the impacts of climate change on local culture, women, and sustainable livelihoods using the example of Tajikistan.

Growing competition between upstream hydropower and downstream irrigated agriculture is representative of the symptoms of water scarcity in Central Asia (Platonov et al. 2008a). Identifying approaches for the application appropriate water-saving techniques in agriculture is the key to sustainable water management in the region. Of the 28 papers that addressed the economic dimension of sustainability and market mechanisms specifically, 11 papers (representing only 3 % of the sample) described some links to the economic return on water use in agriculture. These papers made scientific recommendations for shifting towards economically viable crop production. However, very few papers provided specific evidence of the economic benefits that could be achieved based on numerical data. Therefore, future research should be devoted to this particular shortcoming.

We used the Land Use Functions framework for this research review to investigate sustainability issues related to agricultural land use in Central Asia. The framework was originally designed to assess land use changes in Europe by considering the three sustainability dimensions (environmental, economic, and social) (Perez-Soba et al. 2008). Subsequently, the framework was operationalized in the context of other countries, such as China and India (König et al. 2014a; Purushothaman et al. 2013). In Central Asia, only one study assessed the state of research on sustainable land management in Kyrgyzstan and Tajikistan using the Global Land Project analytical framework (Dear et al. 2013). In that study, Dear et al. (2013) covered the post-independence period from late 1991 to mid-2012 and investigated only the international academic literature published concerning Kyrgyzstan and Tajikistan and gray literature. By covering a different timeline and the complete geographical area of Central Asia and using a different analytical framework and different publication types, the current study furthers the scientific knowledge on sustainable land use.

4 Conclusion

This research revealed key knowledge gaps regarding the contribution of agricultural land use to sustainable development in Central Asia. The analysis focused exclusively on Web of Science-based peer-reviewed international journals covering the 2008–2013 period. All findings and conclusions were therefore restricted to this recent period of time and to internationally accessible publications. It is possible that earlier studies and/or domestic, non-internationally quality-validated publications contain information with the potential to fill some of the knowledge gaps identified here. However, the availability of and access to those studies represent a substantial barrier because of language concerns and non-standardized archiving methods. Given this limitation, the findings indicate that a comprehensive knowledge base is available concerning the impacts of agricultural land use on environmental issues, particularly those related to soil and water issues and to the maintenance of ecosystem processes. Little information was available about the relationships between agricultural land use and biotic resources, such as habitats for fauna and flora and other organisms. With respect to the economic aspects of agricultural land use, the research was focused on the direct economic return of biomass production and on infrastructure issues related to constructing and maintaining irrigation and drainage systems. Given that water scarcity is a key factor affecting agriculture in Central Asia, the economic returns on agricultural water use compared with those of other water uses should be emphasized in the future. The most striking finding was that very few papers addressed the impacts of agricultural land use on the societal dimension of sustainable development. This finding is in contrast to the abundant knowledge of human health concerns related to salinized water and the aspiration of dust-contaminated air. Clearly, the disciplinary research has somehow ignored the causal chain of events relating inappropriate irrigation management and water salinization to land degradation and dust storms through wind erosion. A more systemic, interdisciplinary approach to the analysis of agricultural land use impacts may help to overcome this limitation in the future.

This review revealed the underrepresentation of in situ research by means of collecting quantitative and/or qualitative data. Most papers were based on indirect research methods, such as remote sensing and mathematical modeling. Those methods also build upon a solid database for the ground-truthing of remotely sensed data and for the calibration and validation of model simulation. However, the specific understanding of the complexity of local socio-economic and political situations related to sustainable development requires in-depth case study research. This direction should clearly be prioritized in future research. Finally, the papers mostly focused on arable land use issues in the region, and the inclusion of pasture or rangelands in future studies could further provide a comprehensive overview of land use practices in both the lowlands and uplands of Central Asia.