Desertification research in arid and semi-arid regions has always been actively pursued. In China, the problem of desertification in Xinjiang has also received extensive attention. Due to its unique geography, many scholars have conducted corresponding research on the desertification status of Xinjiang. In this paper, we comprehensively reviewed desertification in Xinjiang, and compared the underlying mechanisms of desertification and the status of desertification conditions after the implementation of ecological control projects. On a larger scale, desertification in Xinjiang can be divided into soil salinization inside oases and sandy desertification on the edges of oases. Human activities are considered the main cause of desertification, but natural factors also contribute to varying degrees. Research on the mechanisms of desertification has effectively curbed the development of desertification, but unreasonable use of land resources accelerates the risk of desertification. For desertification control, there are several key points. First, desertification monitoring and the early warning of desertification expansion should be strengthened. Second, monitoring and reversing soil salinization also play an important role in the interruption of desertification process. It is very effective to control soil salinization through biological and chemical methods. Third, the management of water resources is also essential, because unreasonable utilization of water resources is one of the main reasons for the expansion of desertification in Xinjiang. Due to the unreasonable utilization of water resources, the lower reaches of the Tarim River are cut off, which leads to a series of vicious cycles, such as the deterioration of ecological environment on both sides of the river and the worsening of desertification. However, in recent years, various desertification control projects implemented in Xinjiang according to the conditions of different regions have achieved remarkable results. For future studies, research on the stability of desert-oasis transition zone is also significantly essential, because such investigations can help to assess the risk of degradation and control desertification on a relatively large scale.

The ecological quality of inland areas is an important aspect of the United Nations Sustainable Development Goals (UN SDGs). The ecological environment of Northwest China is vulnerable to changes in climate and land use/land cover, and the changes in ecological quality in this arid region over the last two decades are not well understood. This makes it more difficult to advance the UN SDGs and develop appropriate measures at the regional level. In this study, we used the Moderate Resolution Imaging Spectroradiometer (MODIS) products to generate remote sensing ecological index (RSEI) on the Google Earth Engine (GEE) platform to examine the relationship between ecological quality and environment in Xinjiang during the last two decades (from 2000 to 2020). We analyzed a 21-year time series of the trends and spatial characteristics of ecological quality. We further assessed the importance of different environmental factors affecting ecological quality through the random forest algorithm using data from statistical yearbooks and land use products. Our results show that the RSEI constructed using the GEE platform can accurately reflect the ecological quality information in Xinjiang because the contribution of the first principal component was higher than 90.00%. The ecological quality in Xinjiang has increased significantly over the last two decades, with the northern part of this region having a better ecological quality than the southern part. The areas with slightly improved ecological quality accounted for 31.26% of the total land area of Xinjiang, whereas only 3.55% of the land area was classified as having a slightly worsen (3.16%) or worsen (0.39%) ecological quality. The vast majority of the deterioration in ecological quality mainly occurred in the barren areas Temperature, precipitation, closed shrublands, grasslands and savannas were the top five environmental factors affecting the changes in RSEI. Environmental factors were allocated different weights for different RSEI categories. In general, the recovery of ecological quality in Xinjiang has been controlled by climate and land use/land cover during the last two decades and policy-driven ecological restoration is therefore crucial. Rapid monitoring of inland ecological quality using the GEE platform is projected to aid in the advancement of the comprehensive assessment of the UN SDGs.

Drought occurs in almost all climate zones and is characterized by prolonged water deficiency due to unbalanced demand and supply of water, persistent insufficient precipitation, lack of moisture, and high evapotranspiration. Drought caused by insufficient precipitation is a temporary and recurring meteorological event. Precipitation in semi-arid regions is different from that in other regions, ranging from 50 to 750 mm. In general, the semi-arid regions in the west and north of Iran received more precipitation than those in the east and south. The Terrestrial Climate (TerraClimate) data, including monthly precipitation, minimum temperature, maximum temperature, potential evapotranspiration, and the Palmer Drought Severity Index (PDSI) developed by the University of Idaho, were used in this study. The PDSI data was directly obtained from the Google Earth Engine platform. The Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI) on two different scales were calculated in time series and also both SPI and SPEI were shown in spatial distribution maps. The result showed that normal conditions were a common occurrence in the semi-arid regions of Iran over the majority of years from 2000 to 2020, according to a spatiotemporal study of the SPI at 3-month and 12-month time scales as well as the SPEI at 3-month and 12-month time scales. Moreover, the PDSI detected extreme dry years during 2000-2003 and in 2007, 2014, and 2018. In many semi-arid regions of Iran, the SPI at 3-month time scale is higher than the SPEI at 3-month time scale in 2000, 2008, 2014, 2015, and 2018. In general, this study concluded that the semi-arid regions underwent normal weather conditions from 2000 to 2020. In a way, moderate, severe, and extreme dry occurred with a lesser percentage, gradually decreasing. According to the PDSI, during 2000-2003 and 2007-2014, extreme dry struck practically all hot semi-arid regions of Iran. Several parts of the cold semi-arid regions, on the other hand, only experienced moderate to severe dry from 2000 to 2003, except for the eastern areas and wetter regions. The significance of this study is the determination of the spatiotemporal distribution of meteorological drought in semi-arid regions of Iran using strongly validated data from TerraClimate.

Agriculture faces risks due to increasing stress from climate change, particularly in semi-arid regions. Lack of understanding of crop water requirement (CWR) and irrigation water requirement (IWR) in a changing climate may result in crop failure and socioeconomic problems that can become detrimental to agriculture-based economies in emerging nations worldwide. Previous research in CWR and IWR has largely focused on large river basins and scenarios from the Coupled Model Intercomparison Project Phase 3 (CMIP3) and Coupled Model Intercomparison Project Phase 5 (CMIP5) to account for the impacts of climate change on crops. Smaller basins, however, are more susceptible to regional climate change, with more significant impacts on crops. This study estimates CWRs and IWRs for five crops (sugarcane, wheat, cotton, sorghum, and soybean) in the Pravara River Basin (area of 6537 km²) of India using outputs from the most recent Coupled Model Intercomparison Project Phase 6 (CMIP6) General Circulation Models (GCMs) under Shared Socio-economic Pathway (SSP)245 and SSP585 scenarios. An increase in mean annual rainfall is projected under both scenarios in the 2050s and 2080s using ten selected CMIP6 GCMs. CWRs for all crops may decline in almost all of the CMIP6 GCMs in the 2050s and 2080s (with the exceptions of ACCESS-CM-2 and ACCESS-ESM-1.5) under SSP245 and SSP585 scenarios. The availability of increasing soil moisture in the root zone due to increasing rainfall and a decrease in the projected maximum temperature may be responsible for this decline in CWR. Similarly, except for soybean and cotton, the projected IWRs for all other three crops under SSP245 and SSP585 scenarios show a decrease or a small increase in the 2050s and 2080s in most CMIP6 GCMs. These findings are important for agricultural researchers and water resource managers to implement long-term crop planning techniques and to reduce the negative impacts of climate change and associated rainfall variability to avert crop failure and agricultural losses.

Information on rare earth elements (REEs) in soils and plants of the Qinghai-Tibet Plateau is very limited. Therefore, in this study, we performed field sampling to explore the geochemical signatures and human health risk of REEs in soils and plants of the northeastern Qinghai-Tibet Plateau, China. A total of 127 soil samples and 127 plant samples were collected from the northeastern Qinghai-Tibet Plateau to acquire the geochemical signatures and related human health risks of REEs. The mean total concentrations of REEs in soils and plants of the study area reached 178.55 and 10.06 mg/kg, respectively. The light REEs in soils and plants accounted for 76% and 77% of the total REEs, respectively. REEs showed significantly homogenous distribution in soils but inhomogeneous distribution in plants of the study area. Characteristic parameters indicated that light REEs were enriched and fractionated significantly, while heavy REEs were moderately fractionated in soils and plants. REEs in soils and plants showed significantly negative Europium anomaly. Cerium showed slightly positive anomaly in plants and slight anomaly in soils. The normalized distribution patterns of REEs were generally similar in the analyzed soils and the corresponding plants of the study area. The average bio-concentration factor of REEs ranged from 0.0478 (Scandium) to 0.0604 (Europium), confirming a small accumulation of REEs by plants. Health risks caused by REEs in soils and plants were negligible, while risks for adults were lower than those for children. This study provides important information on REEs in soils and plants of the northeastern Qinghai-Tibet Plateau.

Water scarcity is the most significant barrier to agricultural development in arid and semi-arid regions. Deficit irrigation is an effective solution for managing agricultural water in these regions. The use of additives such as vermicompost (VC) to improve soil characteristics and increase yield is a popular practice. Despite this, there is still a lack of understanding of the interaction between irrigation water and VC on various crops. This study aimed to investigate the interaction effect of irrigation water and VC on greenhouse cucumber yield, yield components, quality, and irrigation water use efficiency (IWUE). The trials were done in a split-plot design in three replicates in a semi-arid region of southeastern Iran in 2018 and 2019. Three levels of VC in the experiments, i.e., 10 (V₁), 15 (V₂), and 20 t/hm² (V₃), and three levels of irrigation water, i.e., 50% (I₁), 75% (I₂), and 100% (I₃) of crop water requirement were used. The results showed that the amount of irrigation water, VC, and their interaction significantly affected cucumber yield, yield components, quality, and IWUE in both years. Reducing the amount of irrigation water and VC application rates reduced the weight, diameter, length, and cucumber yield. The maximum yield (175 t/hm²) was recorded in full irrigation using 20 t/hm² of VC, while the minimum yield (98 t/hm²) was found in I₁V₁ treatment. The maximum and minimum values of IWUE were recorded for I₁V₃ and I₃V₁ treatments as 36.07 and 19.93 kg/(m³?hm²), respectively. Moreover, reducing irrigation amount decreased chlorophyll a and b, but increased vitamin C. However, the maximum carbohydrate and protein contents were obtained in mild water-stressed conditions (I₂). Although adding VC positively influenced the value of quality traits, no significant difference was observed between V₂ and V₃ treatments. Based on the results, adding VC under full irrigation conditions leads to enhanced yield and IWUE. However, in the case of applying deficit irrigation, adding VC up to a certain level (15 t/hm²) increases yield and IWUE, after which the yield begins to decline. Because of the salinity of VC, using a suitable amount of it is a key point to maximize IWUE and yield when applying a deficit irrigation regime.

Droplet shear stress is considered as an important indicator that reflects soil erosion in sprinkler irrigation more accurately than kinetic energy, and the effect of droplet impact angle on the shear stress cannot be ignored. In this study, radial distribution of droplet impact angles, velocities, and shear stresses were investigated using a two-dimensional video disdrometer with three types of low-pressure sprinkler (Nelson D3000, R3000, and Komet KPT) under two operating pressures (103 and 138 kPa) and three nozzle diameters (3.97, 5.95, and 7.94 mm). Furthermore, the relationships among these characteristical parameters of droplet were analyzed, and their influencing factors were comprehensively evaluated. For various types of sprinkler, operating pressures, and nozzle diameters, the smaller impact angles and larger velocities of droplets were found to occur closer to the sprinkler, resulting in relatively low droplet shear stresses. The increase in distance from the sprinkler caused the droplet impact angle to decrease and velocity to increase, which contributed to a significant increase in the shear stress that reached the peak value at the end of the jet. Therefore, the end of the jet was the most prone to soil erosion in the radial direction, and the soil erosion in sprinkler irrigation could not only be attributed to the droplet kinetic energy, but also needed to be combined with the analysis of its shear stress. Through comparing the radial distributions of average droplet shear stresses among the three types of sprinklers, D3000 exhibited the largest value (26.94-3313.51 N/m²), followed by R3000 (33.34-2650.80 N/m²), and KPT (16.15-2485.69 N/m²). From the perspective of minimizing the risk of soil erosion, KPT sprinkler was more suitable for low-pressure sprinkler irrigation than D3000 and R3000 sprinklers. In addition to selecting the appropriate sprinkler type to reduce the droplet shear stress, a suitable sprinkler spacing could also provide acceptable results, because the distance from the sprinkler exhibited a highly significant (P<0.01) effect on the shear stress. This study results provide a new reference for the design of low-pressure sprinkler irrigation system.

Afghanistan is located in the Eurasian loess belt, however, there is little information on the soils in the area. Loess has covered the Herat Plain in western Herat City, Afghanistan. Despite the diversity of landform and parent material, there is no information on the soil and landform evolution in this area. The objectives of this study were to identify the soils along a transect of different landforms in the Herat Plain and determine the role of geomorphic processes on the soil and landform evolution. Five pedons from an alluvial fan, the depression between alluvial fan and piedmont plain, saline and non-saline piedmont plains, and the flood plain of the Hariroud River, were sampled. Then, the physical-chemical properties, mineralogy, and micromorphology of the samples were determined. Results showed that the soil parent material in the piedmont plain is loess, whereas, in the flood plain it is a combination of loess and river alluvial sediments. Calcification, lessivage, salinization, and gleization are the most important pedogenic processes. The calcification and lessivage appear to be the result of a wetter climate during the late Quaternary, whereas the present topography causes the gleization and salinization. Clay coatings on carbonate nodules and iron nodules are abundant pedofeatures in the Btk (argillic-calcic) horizon. Iron oxides nodules are common in the soils of the flood plain. The formation of palygorskite in both alluvial- and loess-derived soils implies the onset of aridity and the trend of increase in environmental aridity in the region. It seems that after the formation of a well developed paleosol on the alluvial fan in a more humid climate in the past, the piedmont plain has been covered by loess deposits, and the calcification, gleization, and salinization cause the formation of weakly developed surficial soils. This study highlights the role of the late Quaternary climatic changes on the evolution of landforms and soils in western Afghanistan.