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Afforestation is a prospective strategy to improve soil fertility of salt-affected, irrigated croplands in Central Asia. The effect of macro- and mesofauna and microflora on the decomposition of tree leaves, collected ca. 2 weeks before natural fall, was monitored during 367 days. The three-year-old tree plantations consisted of Elaeagnus angustifolia L., Ulmus pumila L., and Populus euphratica Oliv. The leaf decay rate was determined in 25 × 25 cm sized polyester litterbags with mesh sizes of 10,000 μm (coarse), 250 μm (medium), and 20 μm (fine). Decomposition in the coarse litterbags, allowing access by the entire decomposer community, was highest in P. euphratica at 61% weight loss after 367 days. In the same period, the weight loss in E. angustifolia was 51% and in U. pumila 52%. Combined correlation and multiple regression analyses revealed that decomposability was determined by mesh size, initial C/N ratio, crude fiber-to-N (CF/N) ratio, leaf area, and specific leaf area. A high correlation existed between traits impacting decomposition by the entire decomposer population and the digestibility of leaves by animals as measured in the laboratory (the in vitro digestibility). Initial leaf N (34 g N kg−1 DM) content was highest in E. angustifolia, followed by 23 g N kg−1 DM in U. pumila and 22 g N kg−1 DM in P. euphratica. The C/N ratio followed the order of P. euphratica (21.8) > U. pumila (19.4) > E. angustifolia (13.1). The CF/N ratio followed the order P. euphratica (5.2) > E. angustifolia (3.9) > U. pumila (2.9). Despite a lower decay rate and a higher N content remaining in leaves after 367 days in comparison to both other species, E. angustifolia had the highest potential for soil bio-amelioration. This was due to its foliage production (6 t ha−1 on average), which was about 2.5 times higher than that of the other species, giving a total leaf N loss of about 97 kg N ha−1 in coarse mesh bags. The N loss from U. pumila and P. euphratica leaves amounted to 33 and 23 kg N ha−1, respectively. The potential of leaf decomposition for supplementing soil N in the region depends on the decay rate, the initial leaf N content, the annual leaf biomass production, and differences between N contents over the course of the decomposition period. These can be additional criteria for selecting tree species suitable for afforestation of the degraded, irrigated croplands in Central Asia.

This study examined the early growth and water use of tree plantations established on a marginalized irrigated cropland in northwest Uzbekistan, where salinization of agricultural soils is widespread due to shallow saline groundwater tables. During the first two growing seasons in 2003–2004, the tree stands consisting of Elaeagnus angustifolia L., Populus euphratica Oliv., and Ulmus pumila L. were irrigated with 80 mm year −1 , and, in 2005, were left to rely on the shallow (0.9–2.0 m deep) groundwater with a salinity of 1–5 dS m −1 . Soil salinity increased but remained within the range of moderate-to-strong (4–14 dS m −1 ) during the three years. In the course of the growing season, plantations transpired 0.1–7 mm day −1 in 2003 and 1–13 mm day −1 in 2004–2005, as determined with the Penman–Monteith model. In the absence of irrigation, the annual stand transpiration averaged 1250, 1030, and 670 mm for E. angustifolia , P. euphratica and U. pumila , respectively. In 2005, the leaf area index of E. angustifolia ranged from 5 to 10, surpassing that of the other two species more than two-fold. Differences in canopy conductance and transpiration were significant among the tree species and the decoupling coefficient at no time exceeded 0.3, indicating strong physiological control of transpiration. The vigorous juvenile growth and high transpiration under deficit irrigation and after irrigation was terminated, suggested that afforestation with well-adapted tree species is a viable land use option for degraded cropland. The plantation responses to increasing soil salinity must be monitored to determine potential leaching demands in the long run.

Extensive degradation of irrigated croplands, due to increasing soil salinity and depletion of soil nutrient stocks, is a major problem in Central Asia (CA), one of the largest irrigated areas in the world. To assess the potential for improving the productive capacity of degraded lands by afforestation, we examined N(2) fixation of Elaeagnus angustifolia L. in mixed plantations with non-fixing Populus euphratica Oliv. and Ulmus pumila L. Fixation of N(2) was quantified by the (15)N natural abundance technique based on both foliar and whole-plant sampling during five consecutive growing seasons. Despite elevated root-zone soil salinity (6-10 dS m(-1)) and deficiency in plant-available P (4-15 mg kg(-1)), N(2) fixation (%Ndfa) increased from an initial value of 20% to almost 100% over 5 years. Within each growing season, %Ndfa steadily increased and peaked in the fall. Annual N(2) fixation, determined using foliar delta(15)N, initially averaged 0.02 Mg ha(-1), peaked at 0.5 Mg ha(-1) during the next 2 years and thereafter stabilized at 0.3 Mg ha(-1). Estimates based on whole-plant delta(15)N were

Degraded land within the irrigated areas of the Aral Sea Basin is characterized by high soil salinity, shallow saline groundwater (GW), low irrigation water availability and thus is often unsuitable for crop cultivation. Afforestation is one option for mitigating such degraded land but to be successful it requires the selection of appropriate tree species and irrigation techniques for tree establishment. In a two factorial split–plot experiment the survival, dry matter production, root growth, and biomass partitioning of Elaeagnus angustifolia L., Ulmus pumila L., and Populus euphratica Oliv. were compared under three irrigation regimes for two consecutive years. During the third year, the response of the plantations to the cessation of irrigation was evaluated. A “deficit” and “full” water treatment, respectively amounting to 80 and 160 mm year−1 was applied via drip irrigation. Traditional furrow irrigation supplied at the deficit rate, served as the control. Mixed linear model analysis showed significantly enhanced growth of P. euphratica under drip irrigation exceeding 7–14 times that under the control. Drip irrigation was not advantageous for the other species which effectively used the shallow (0.9–2.0 m deep) GW with a salinity ranging between 1.2 and 4.8 dS m−1. After cessation of irrigation, all species at the deficit-irrigated plots retained or increased their growth rates. In contrast, formerly full-irrigated P. euphratica slowed down by about 50%, indicating that deficit watering created better pre-conditions for coping with the termination of irrigation. E. angustifolia produced about 30 t ha−1 year−1 of above-ground biomass more than twice that of the other species, thus showing in the short-run its high potential on marginal land. U. pumila showed stable, albeit moderate growth rates and could be mixed with the short-living, fast-growing E. angustifolia plantations to optimize the yields. Low initial survival (57%) of P. euphratica was compensated for by its strong regeneration and drastically increasing growth rates. Initially high root-zone salinity exceeding 30 dS m−1, stabilized over time within the medium range even in the absence of irrigation. The application of costly drip irrigation for plantation establishment appears unnecessary in the Aral Sea region Khorezm where a shallow, slightly-to-moderately saline GW table prevails throughout the growing season.

Despite compelling evidence supporting the contribution of Tree Intercropping Systems (TIS) to farmers' livelihoods, little research has addressed farmers' knowledge of TIS in the ecologically deteriorated zones of Uzbekistan, Central Asia. Similarly, farmers' understanding of the motivation for practicing TIS is poorly known. A survey conducted with 133 households during 2003–2005 showed that the surveyed farmers managed 17 different tree-crop simultaneous systems with 97% of all sites including fruit species. The annual components were commercially the more important and were given the highest priority—with cereals (47%), vegetables (27%), fodder (19%) and cash crops (7%). Irrespective of tree species and plantation age, the most frequently observed tree density was 200–500 trees ha−1, although subject to large variations. The dominance of younger trees

The establishment of forests on small-scale marginal lands in the Amu Darya Lowlands in Uzbekistan is an alternative use of land abandoned from cropping. Over four consecutive years biomass data were collected from Elaeagnus angustifolia, Ulmus pumila, and Populus euphratica plantings and complemented with data of mature trees (15–20 years) growing naturally on marginal land. These formed the basis for elaborating 20-year growth functions for these species. The potential for capital investment in the small-scale forests was assessed by considering annual fuelwood, fodder and fruit production, plus the stumpage value after 20 years. The benefit to cost ratio (BCR) and Net Present Value (NPV) were compared at 10%, 16% and 24% discount rates. At a 16% discount rate (base case), the NPV for E. angustifolia was greatest (13,924 US$ ha−1)1, followed by P. euphratica(4,096 US$ ha−1), and U. pumila (1,717 US$ ha1) showing a BCR of 7.8, 2.2 and 1.8, respectively. These suggest that afforestation is a prom...

Groundwater (GW) management is an essential element in irrigated agriculture. This paper analyzes the temporal dynamics of GW table and salinity in Khorezm, a region of Uzbekistan which is situated on the lower Amu Darya River in the Aral Sea Basin and suffering from severe soil salinization. We furthermore identify the critical areas for potential soil salinization by examining GW table and salinity measured during 1990–2000 in 1,972 wells, covering the entire region. Additionally, case studies were performed to assess the contribution of the GW to the soil salinization on a field scale. Over the entire area, GW was only moderately saline averaging 1.75 ± 0.99 g l−1 However, GW levels were generally very shallow averaging 148 ± 57 cm below the ground surface and thus likely to prompt secondary soil salinization. Three case studies where GW table, soil and GW salinity were closely monitored at the field scale, suggested that the elevated GW levels forced soil salinization by annually adding 3.5–14 t ha−1 of salts depending on the position and salinity of the GW table. Maps interpolated from the regional dataset revealed that GW was significantly shallower and more saline in the western and southern parts of Khorezm despite the presence of a drainage network which is rather uniformly distributed throughout the region. The results of the current study will assist the development of an improved drainage management in Khorezm.

This paper evaluates the potential of nine multipurpose tree species for afforestation of degraded land in the Khorezm region, Central Asia, particularly their suitability for biodrainage i.e., lowering the elevated groundwater table through the transpirative capacity of plantations. For this purpose water use (WU), water use effi- ciency (WUE) and tree physiological factors influencing transpiration were assessed during two consecutive years. Mean daily leaf transpiration differed significantly among the species and ran- ged during the seasons from 4.5-5.2 mmol m -2 s -1 for Prunus armeniaca L. to 4.5-10 mmol -2 s -1 for Elaeagnus angustifolia L. WU differences were triggered by species physiological features such as capability of water uptake by roots. Transpiration rates and the length of fine roots correlated highly (r = 0.7). Correlations of leaf transpiration rates with leaf area were weaker (r = 0.6). No correla- tions were found between salt content in plants and water uptake under conditions of slight-to- moderate rootzone soil salinity. Values of WUE per root and shoot DM were similar averaging, respectively, 0.2 and 0.3 g DM g -1 water for two- year-old trees, and decreased with age. In addition to WU characteristics, also salinity tolerance, growth rate and the ability to produce fodder and fuelwood must be considered during species selection. Regarding these features, the N-fixing E. angustifolia ranked the highest, combining high WU, fast growth and production of nutritious feed. Examined Populus spp. and Ulmus pumila L. ranked lower but still represented potential candidates for biodrainage purposes. Typical fruit species in the region such as P. armeniaca and Morus alba, showed low biodrainage potential.

Land degradation is a serious hindrance to agricultural development in Uzbekistan, a country striving to rebuild its agricultural sector for self-sustained production. The potential of multipurpose trees for upgrading degraded land is enormous. However, knowledge is lacking about the establishment and growth characteristics of different species, the energy content of firewood and the nutritive value of fodder. This study presents such data for 10 selected local multipurpose species grown on gleyic solonchak soil. Elaeagnus angustifolia L. and Tamarix androssowii showed superior biomass growth, respectively producing up to 11.0 and 10.4 t ha−1 of utilizable aboveground dry matter (DM). E. angustifolia showed high potential for rapid establishment evidenced by root elongation of over 100 m tree−1 at the age of 3 years. T. androssowii, Prunus armeniaca L. and Populus nigra var. pyramidalis Spach exhibited the greatest fuelwood characteristics, showing calorific values in the range of 14.4 – 16.2 MJ DM kg−1. E. angustifolia and Morus alba L. demonstrated superior fodder potential given by the crude protein content of 216 and 117 g DM kg−1. Recommendations on species selection are proposed based on various species characteristics. In assessing the potential of trees for afforestation of degraded land a reliable economic analysis of these aspects must be taken into account. When considering all characteristics concurrently, a mixture of species instead of monocrop cultivation seems to provide the best solution for improving degraded land.

The establishment of woody fallow systems is an option for the improvement of degraded agricultural landscape within the ecologically deteriorated Aral Sea area in northwest Uzbekistan. Growth and development of ten tree species, differing in tolerance to drought and salinity, were studied over 24 months. To determine species suitability for afforestation, conventional diameter and height measurements were compared to Relative Growth Rate (RGR) and its underlying components, Net Assimilation Rate (NAR), Specific Leaf Area (SLA) and Leaf Weight Ratio (LWR), as well as the Crop Growth Rate (CGR) as a function of NAR and Leaf Area Index (LAI). RGRs varied between 0.46 and 2.16 mg g � 1 day � 1 and showed highly significant differences among species, but also between years, which reduces the parameter’s suitability for species selection. The same is true for NAR and SLA. CGR values ranged from 0.01 to 0.71 g m � 2 day � 1 , increased with age of the trees, and showed significant species differences. CGR correlated better with NAR (r = 0.89) and SLA (r = 0.86) than RGR. Overall CGR correlated highly with the RGRs in height and diameter (in 80% and 71% of all cases, respectively). Thus, CGR appears to be a suitable indicator complementing RGR, NAR and SLA estimates to decide on species suitability for afforestation. The intensive measurements for RGR should be done later, rather than earlier in the tree life cycle. At an early age, CGR and diameter measurements are more meaningful. A combination of estimates, not a single factor, best assesses the long-term sustainable growth under natural conditions and allows early selection of species suitable for afforestation of degraded patches in the agricultural landscape. Ranking of all parameters concurrently showed the high potential of Elaeagnus angustifolia and Populus euphratica, which matched previous rankings based on total biomass production and financial added value. # 2005 Elsevier B.V. All rights reserved.

Land provides a host of ecosystem services, of which the provisioning services are often considered paramount. As the demand for agricultural products multiplies, other ecosystem services are being degraded or lost entirely. Finding a sustainable trade-off between food production and one or more of other ecosystem services, given the variety of stakeholders, is a matter of optimizing land use in a dynamic and complex socio-ecological system. Land degradation reduces our options to meet both food demands and environmental needs. In order to illustrate this trade-off dilemma, four representative services, carbon sinks, water storage, biodiversity, and space for urbanization, are discussed here based on a review of contemporary literature that cuts across the domain of ecosystem services that are provided by land. Agricultural research will have to expand its focus from the field to the landscape level and in the process examine the cost of production that internalizes environmental costs. In some situations, the public cost of agriculture in marginal environments outweighs the private gains, even with the best technologies in place. Land use and city planners will increasingly have to address the cost of occupying productive agricultural land or the conversion of natural habitats. Landscape designs and urban planning should aim for the preservation of agricultural land and the integrated management of land resources by closing water and nutrient cycles, and by restoring biodiversity.

The sustainability of irrigated croplands in Central Asia is threatened by degradation of their productive function. To quantify the extent of the cropland degradation, this paper combines object-based change detection and spectral mixture analysis for vegetation cover decline mapping in irrigated agro-ecosystems in Uzbekistan based on multitemporal Landsat TM images from 1998 to 2009. The results of the change detection reveal that the cadastral field parcels, characterized by vegetation cover decrease, occupied 18% (52,938 ha) of the cropland area. Spatial distribution of fields with decreased vegetation cover was mainly associated with abandoned cropland and land with inherently low-fertility soils located on the outreaches of the irrigation system and bordering natural sandy deserts. The comparison with the land degradation map based on trend analyses of 250 m MODIS NDVI time series 2000–2010 yielded an overall agreement of 93%. The proposed approach is a useful supplement to the commonly applied trend analysis for detecting land degradation in cases when plot-specific data are needed but satellite time series of high spatial resolution are not available. The derived parcel-specific, spatial information supports better informed decisions on cropland rehabilitation measures.

Sustainability of irrigated agriculture-based economies, such as in Central Asia, is threatened by cropland degradation. The field-based identification of the degraded agricultural areas can aid in developing appropriate land rehabilitation and monitoring programs. This paper combined the object-based change detection and spectral mixture analysis to develop an approach for identifying parcels of irrigated degraded cropland in Northern Uzbekistan, Central Asia. A linear spectral unmixing, followed by the object-based change vector analysis, was applied to the multiple Landsat TM images, acquired in 1987 and 2009. Considering a spectral dimensionality of Landsat TM, a multiple 4-endmember model (green vegetation, water, dark soil, and bright soil) was set up for the analysis. The spectral unmixing results were valid, as indicated by the overall root mean square errors of

Advancing land degradation in the irrigated areas of Central Asia hinders sustainable development of this predominantly agricultural region. To support decisions on mitigating cropland degradation, this study combines linear trend analysis and spatial logistic regression modeling to expose a land degradation trend in the Khorezm region, Uzbekistan, and to analyze the causes. Time series of the 250-m MODIS NDVI, summed over the growing seasons of 2000–2010, were used to derive areas with an apparent negative vegetation trend; this was interpreted as an indicator of land degradation. About one third (161,000 ha) of the region’s area experienced negative trends of different magnitude. The vegetation decline was particularly evident on the low-fertility lands bordering on the natural sandy desert, suggesting that these areas should be prioritized in mitigation planning. The results of logistic modeling indicate that the spatial pattern of the observed trend is mainly associated with the level of the groundwater table (odds = 330 %), land-use intensity (odds = 103 %), low soil quality (odds = 49 %), slope (odds = 29 %), and salinity of the groundwater (odds = 26 %). Areas, threatened by land degradation, were mapped by fitting the estimated model parameters to available data. The elaborated approach, combining remote-sensing and GIS, can form the basis for developing a common tool for monitoring land degradation trends in irrigated croplands of Central Asia.

This study analyzed the financial attractiveness of Clean Development Mechanism Afforestation and Reforestation (CDM A/R) in irrigated agricultural settings. The Net Present Value (NPV) and Internal Rate of Return (IRR) of CDM A/R were estimated by analyzing the case of Khorezm region in Uzbekistan, where a mixed-species tree plantation was established on marginal cropland. The dual purposes of carbon sequestration and production of fruits, leaves as fodder, and fuelwood were studied over a seven-year rotation period. We compared the opportunity costs of land in marginal agricultural areas between this short-rotation plantation forestry and the annual cultivation of the major crops in the region, i.e., cotton, winter wheat, rice, and maize. The analyses were performed considering different levels of irrigation water availability, from 0 to 30,000 m 3 /ha, to reflect the reality of a high variability of water supply in the region. The NPV of CDM A/R ranged between 724 and 5794 USD/ha over seven years, depending on the tree species. Among the latter, Elaeagnus angustifolia L. had the highest profits due to the annually recurring cash flows generated from fruit production. Temporary Certified Emission Reductions (tCER) ranged within 399–702 USD/ha after the assumed 7-year crediting period and would not suffice to cover initial investments and management costs of tree plantations. IRR peaked at 65% with E. angustifolia under the conventional afforestation and measured − 10% and 61% when considering only the tCER and the CDM A/R, respectively. In contrast, other species had higher IRRs in case of the CDM A/R. The total profits from tree plantations exceeded those of both cotton and winter wheat, even with the assumption that there was an optimal irrigation supply for these crops. Rice production was overall the most profitable land use option but required water input of 26,500 m 3 /ha/year, which is not consistently available for marginal croplands. We argue that the current global average price of 4.76 USD/tCER is insufficient to initiate forestry-based CDM projects but, in the absence of other incentives, can still motivate forestation of degraded croplands for land rehabilitation and the provisioning of non-timber products. Given the low irrigation needs of trees, 3–30% of the crop water demand, a conversion of degraded cropland to forested areas could save up to 15,300 m 3 /ha/year at the current tCER price. Combining the monetary value of water and carbon would enlarge the scope for CDM A/R in irrigated drylands, thus enhancing the investments in marginal land rehabilitation and strengthening the resilience of rural populations to the repercussions of climate change.