Northwestern Loess Plateau Research Articles

Crossing latitude introduction delayed flowering and facilitated dry matter accumulation of soybean as a forage crop

Grain soybean [Glycine max (L.) Merr] shows potential as a forage crop following introduction from low to high due to the growth phenotype alteration. However, the application of this approach is impeded by the diverse ecological types of soybeans, their adaptability to the introduction, and the uncertainty surrounding the growth phenotype post-introduction. In this study, 24 grain soybean varieties from low-latitude regions (22-31°N) were introduced to the high-latitude northwestern Loess Plateau (39°N) between 2018 and 2019. The growth phenotypes were observed, and their forage productivity potential was assessed. All varieties displayed delayed flowering following cross-latitude introduction, with the vegetative growth phase of some varieties even exceeding their entire growth duration at their origin. Rapid dry matter accumulation rates were indicative of growth adaptation performance and formed the basis for soybean forage yield. Varieties from the tropical south China region exhibited significant yield advantages, with dry matter yields of 8.97-14.68 t ha-1 and crude protein yields of 1.44-2.51 t ha-1. Varieties HX3 and GX7, originating from this region, demonstrated optimal growth adaptability and productivity in the cross-latitude environment, achieving the highest dry matter yields of 14.68 and 13.86 t ha-1, respectively. As a result, HX3 and GX7 are recommended for local farming systems to provide high-quality forage. The cross-latitude introduction of soybean is proposed as a viable and efficient strategy for forage improvement and application.

Controlling mechanism and water quality assessment of arsenic in China's Yellow River Basin

Arsenic (As) is a well-known toxic and carcinogen element, and As contamination has gained public concerns worldwide. Mechanisms, sources, and potential health risks of high As in the China's Yellow River Basin (CYRB), a water-deficient area and the largest loess deposition area in the world, remain largely unknown. Hydrogen and oxygen isotopes, major ions, and As were analyzed in 409 river water and 164 groundwater samples in dry season to decipher these problems. Samples were alkaline (pH = 8.0 ± 0.4), and As concentrations (5.29 ± 10.5 μg/L) in the CYRB were above the world average, especially in upstream and midstream. About 9.1% and 13.0% of samples in river water and groundwater had As concentrations above the permissible limit of WHO, respectively. Based on self-organizing map (SOM) analysis, about 50.6% of samples with high As were SO4–Cl–Na type while about 46.4% of samples with low As were HCO3–Ca–Mg type. The δD (−62.5 ± 11.3‰) and δ18O (−8.5 ± 2.1‰) values of river water were higher than the groundwater (δD = −69.7 ± 10.2‰, δ18O = −9.9 ± 1.4‰), and most samples with As >10 μg/L were below the local and global meteoric water lines, indicating the evaporation effect on As enrichment, especially for river water. Evaporites dissolution of loess and ion exchange increased water salinity, accelerated desorption of As and enriched As in CYRB. Meanwhile, oil and coal exploitation contributed to the high As in the northwestern Loess Plateau. Health risk assessment indicated that 41.6% and 59.8% of groundwater samples posed high carcinogenic risk for adults and children, respectively. Therefore, corresponding measures must be implemented in these areas. In the future, As geochemistry in wet seasons in the CYRB and the characteristics among different seasons will be explored. These results highlight the impact of dry climate and anthropogenic activity on As enrichment in arid/semi-arid regions.

What drives soil degradation after gravel mulching for 6 years in northwest China?

Gravel mulch is an agricultural water conservation practice that has been widely used in the semi-arid region of northwest China, but its effectiveness is now lessening due to soil degradation caused by long-term gravel mulching. In this study, we report on a 6-year-long gravel mulch experiment conducted in the northwestern Loess Plateau to evaluate the impact of gravel mulch on soil physicochemical properties and microbial communities, with the objective of clarifying the causes of long-term gravel mulching-induced land degradation. After 6 years mulching, we found that gravel mulched soil contained significantly higher concentrations of total carbon and total organic carbon than non-mulched soil (control). Long-term gravel mulching significantly changed the soil microbial diversity and abundance distribution of bacterial and fungal communities. Notably, the relative abundance of Acidobacteria was significantly higher under gravel mulching than the control (no mulching), being significantly greater in the AG treatment (small-sized gravel, 2-5 mm) than all other treatments. Conversely, the relative abundance of Actinobacteria was significantly lower under gravel mulching than the control, being the lowest in the BG treatment (large-sized gravel, 40-60 mm). At the same time, the relative abundance of Bacteroidetes was significantly lower in AG yet higher in BG vis-à-vis the other treatments. Of the various factors examined, on a 6-year scale, the capture of dust by gravel mulch and altered carbon and nitrogen components in soil play major contributing roles in the compositional change of soil microorganisms. These results suggest that modified soil material input from gravel mulching may be the key factor leading to soil degradation. More long-term experimental studies at different sites are now needed to elucidate the mechanisms responsible for soil degradation under gravel mulching.

Legume Integration Augments the Forage Productivity and Quality in Maize-Based System in the Loess Plateau Region

The changing climate, inadequate water supply, insufficient agricultural inputs, decreasing in agricultural arable land areas under forage crops of Northwestern Loess Plateau region, expanding livestock population, increasing demands for meat and milk production, and food and feed security concerns all insist on a necessary requirement in forage quality production. Cereal–legume mixed-cropping is a biological approach to enhancing herbage yield and quality of upgraded animal feed (forage and silage). However, little information exists about the appropriate mixing seeding ratios and its impacts on yield and quality. Therefore, this study was conducted to examine the forage yield and nutritional quality of maize (Zea mays L.) and common bean (Phaseolus vulgaris L.) in mono-and mixed-cropping approaches at the seeding proportions of 100:0, 75:25, 50:50, 45:55, 25:75, and 0:100 in 2019 and 2020 in Northwestern Loess Plateau region. A randomized complete block design with four replicates was used in this experiment. The results indicated that forage quality was significantly affected by the mixture ratios. The land equivalent ratio (LER) of all mixed-cropping treatments greater than 1.0, in which maize–common bean at the 50:50 seeding ratio achieved higher LER (1.46) than that of other treatments, showing that mixed-cropping combination systems are better users of land resources. Laboratory forage quality analysis and Pearson correlation analysis showed that the relative feed value had highly positive correlation with total digestible nutrients and relative forage quality in mixed-cropping treatments. Our results showed that fresh forage yield and dry matter yield were higher in monocropped maize forage than in other intercropped forages, whereas crude protein yield was lower compared with other mixed cropping forages. After 60 days of ensiling, the highest organic acid profile and ammonia-nitrogen were observed in M25:CB75 silage compared with other silages. The highest ensilability of fermentation coefficient was also found in M50:CB50 compared with other intercropped silages. Regarding forage preservation, silage showed higher contents of crude protein, relative feed value and lower crude fiber, water-soluble carbohydrate neutral detergent fiber, and acid detergent fiber contents than forage. This study determined that the ratios of maize–common bean 25:75 and 50:50 were the most desirable mixture ratios among mixed-cropped forage and silage based on chemical composition and quality analysis for livestock feeding.

Detection of vegetation coverage changes in the Yellow River Basin from 2003 to 2020

The Yellow River occupies a pivotal strategic position in the development and economic construction of China. Moreover, grasping the dynamics of change in long-term vegetation cover and predicting future trends in the Yellow River Basin could provide an empirical foundation for improved ecological protection and soil and water conservation initiatives. This study uses statistical methods such as Dimidiate pixel model, linear regression, Moran’s index, and coefficient of variation to conduct a spatio-temporal analysis of the vegetation coverage in the Yellow River Basin. The Hurst exponent is used for further analysis of the trend of change in the vegetation coverage across the study area. The results show that from 2003 to 2020, the fractional vegetation coverage (FVC) in the Yellow River Basin increased at an average rate of 0.19% per year. Furthermore, only 2.22% of the area of the Yellow River Basin shows a relative increase in FVC from 2003 to 2020; most of the increased area is located in the northwestern Loess Plateau. The Global Moran index values from 2003 to 2020 are all greater than 0.8, indicating that the vegetation coverage presents a strong agglomeration. According to the Local Moran index, the vegetation coverage of the Yellow River Basin presents a strong spatial difference. According to the coefficient of variation, 73% of the vegetation coverage in the Yellow River Basin has been highly stable over the past 18 years. In addition, the overall Hurst exponent for the FVC in the Yellow River Basin is less than 0.5, indicating a anti-persistence pattern of change in vegetation.

Study on the Structural Plane Characteristics and Disaster-Induced Mechanism of the Yellow River Jingtai Stone Forest, Northwestern Loess Plateau, China

The Yellow River Jingtai Stone Forest (YJSF) is situated in the northwestern margin of the Chinese Loess Plateau, and it is not only one of the most precious and rare types of natural landforms in the Loess Plateau but also a protected area of valuable geological relics and landscapes in northwest China. Massive rock structural planes are present in the stone forest. However, few studies have been conducted on the rock mass structural planes for the slope’s stability. Based on the detailed field investigation, structural planes and their combination types are classified based on the rock mass. On this basis, combined with physical, mechanical, and hydraulic tests, the disaster-induced mechanism of the rock mass structural planes is classified and discussed. Results show that the structural planes of the YJSF can be divided into three types, namely, the primary structural plane, tectonic structural plane, and secondary plane. They not only combine with each other to cut the rock mass into different shape blocks but also jointly control the stability of the rock mass slope. The physical and mechanical tests and water sensitivity characteristics show that the conglomerates and muddy sandstones which are the main components of the YJSF have strong tensile and shear strengths under natural situations, while their strengths are reduced under immersion infiltration; in particular, the muddy sandstones are more sensitive to water and have a lower strength than that of the conglomerates. Finally, the disaster-induced mechanism of the YJSF is mainly related to the combination of various structural planes, which can be divided into four failure patterns, namely, creeping slide-tension failure, gradual failure, slipping failure, and dumping failure; coupling action of endogenic and exogenic geodynamic processes was responsible for their formation. The studied results will provide critical, theoretical, and technical support for the slope stability analysis, scenic geological heritage protection, and disaster warning in this area.

It All Hinges on China: Environmental Governance in the Twenty-First Century

It All Hinges on China: Environmental Governance in the Twenty-First Century

Influence of conservation tillage on Greenhouse gas fluxes and crop productivity in spring-wheat agroecosystems on the Loess Plateau of China.

The effects of climate change such as dry spells, floods and erosion heavily impact agriculture especially smallholder systems on the Northwestern Loess Plateau of China. Nonetheless agriculture also contributes to global warming through the emission of greenhouse gases such as CO2, CH4 and N2O. Yet this complex conundrum can be alleviated and mitigated through sound soil and water management practices. Despite considerable literature on Conservation Agriculture (CA) as a strategy to improve the resilience and mitigation capacity of agroecosystems, there is still paucity of information on the impacts of CA on crop production and environmental quality on the Plateau. In order to fill this gap this study examined the effects of no-till and straw mulch on crop productivity and greenhouse gas fluxes in agroecosystems on the Plateau where farmers’ common practice of conventional tillage (CT) was tested against three CA practices: conventional tillage with straw mulch (CTS), no-till (NT) and no-till with straw mulch (NTS). The results indicated that all three CA practices (CTS, NT and NTS) markedly increased soil water content (SWC), soil organic carbon (SOC) and soil total nitrogen (STN) but reduced soil temperature (ST). Average grain yields were 854.46 ± 76.51, 699.30 ± 133.52 and 908.18±38.64 kg ha-1 respectively under CTS, NT and NTS indicating an increase by approximately 33%, 9% and 41% respectively compared with CT (644.61 ± 76.98 kg ha−1). There were significant (p < 0.05) reductions of Net CO2 emissions under NT (7.37 ± 0.89 tCO2e ha−1y−1) and NTS (6.65 ± 0.73 tCO2e ha-1y-1) compared with CTS (10.65 ± 0.18 tCO2e ha−1y−1) and CT (11.14 ± 0.58 tCO2e ha−1y−1). All the treatments served as sinks of CH4but NTS had the highest absorption capacity (−0.27 ± 0.024 tCO2e ha−1y−1) and increased absorption significantly (p < 0.05) compared with CT (−0.21 ± 0.017 tCO2e ha−1y−1); however, CA did not reduce emissions of N2O. These had an influence on Global warming potential (GWP) as NT and NTS resulted in significant reduction in net GWP. Grain yield was significantly correlated positively with SOC and STN (p < 0.05); ecosystem respiration was also significantly correlated with SWC and ST while CH4 flux was highly correlated with ST (p < 0.001). Crop yield and GHG responses to CA were controlled by soil hydrothermal and nutrient changes, thus improving these conditions through adoption of sustainable soil moisture improvement practices such as no-till, straw mulch, green manuring, contour ploughing and terracing can improve crop resilience to climate change and reduce GHG emissions in arid and semi-arid regions.

Effects of gravel-sand mulch on the runoff, erosion, and nutrient losses in the Loess Plateau of north-western China under simulated rainfall

Gravel mulching is a characteristic agricultural technique that has been used for hundreds of years in the north-western Loess Plateau of China. However, the effects of the gravel-sand mulch on the processes of the runoff, soil erosion, and nutrient losses are neither fully distinguished nor even known in many parts of the world. This study investigated how different gravel particle sizes in the mulch affected the runoff, erosion as well as the extent of the nutrient losses in the surface runoff. The laboratory experiments were conducted using a rainfall simulator with three gravel mulch treatments: (1) fine gravel mulch (FG); (2) medium gravel mulch (MG); (3) coarse gravel mulch (CG) and a control group, bare soil (BS). The results of these rainfall simulation experiments gave estimates on how the grain size influences the runoff and losses of the soil and its nutrients. Applying the gravel mulch significantly delayed the runoff’s starting time when compared with the bare soil. Both the total runoff and soil loss increased with the grain size of the gravel mulch. Compared with the bare soil, the lowest surface runoff and soil loss was observed from the fine gravel treatment. These results clearly show that gravel mulch plays an important role in the runoff and sediment generation processes, and that it significantly reduces the surface runoff and soil loss. The losses of the total nitrogen (TN), total phosphorus (TP), and total organic carbon (TOC) from the bare soil were much higher than those under the gravel mulching. The fluctuations in these nutrient-loss processes were the most intense in the CG treatment, while the TC content, in initial runoff, was significantly higher in the FG than the other treatments. Our findings suggest gravel mulch is a useful water and soil conservation technique in the loess area of north-western China, and these results can inform one on the theoretical principles for properly utilising gravel-mulched fields.

Historical human activities accelerated climate-driven desertification in China’s Mu Us Desert

China’s Mu Us Desert, located in an energy-rich strategic base of the northwestern Loess Plateau, has acted as a crucial agro-pastoral transition zone for thousands of years. However, the area experienced notable climate and environmental change from 221 BCE to CE 907 (1128 years), which may have profoundly affected its landscape evolution up to modern times. To explore this process and associated driving mechanisms, we conducted a comprehensive study based on a dataset of 882 human archaeological sites (HASs), historical documents, and related environmental data of the Mu Us Desert and its surrounding area (MUDISA). We found that the MUDISA experienced large-scale immigration and an agricultural boom (790 HASs) during the Qin and Han dynasties (221 BCE–CE 220). This coincided with an ecologically favorable environment and may have potentially disturbed the desert’s eco-environmental equilibrium. Coinciding with the deteriorating natural conditions, the MUDISA’s animal husbandry replaced agriculture as the dominant subsistence economy during the era of disunity (CE 220–581, 33 HASs) and during the Sui and Tang dynasties (CE 581–907, 59 HASs). Although natural and political-economic factors together caused a sharp decline in number and scattering for HASs in the desert, people and livestock were widely distributed and maintained a high population level. This situation, coupled with the dry climate and fragile geographical environment, may have significantly accelerated the climate-driven desertification process from CE 220 to CE 907. This study highlights the long-term human–nature relationship and its impact on historical desertification in the Mu Us Desert, and may shed new light on historical environmental change in arid and/or semi-arid areas in northwest China and globally.

Gravel mulching effects on soil physicochemical properties and microbial community composition in the Loess Plateau, northwestern China

Gravel mulch has been used as an agricultural water conservation measure for over three hundred years in China's semiarid regions. In this study, a 3-year gravel mulch experiment on slopes in the northwestern Loess Plateau was conducted to evaluate the impact that different sized gravel mulch and natural rainfall has on surface runoff, soil physicochemical properties and microbial communities. The following three treatments were investigated: small-sized gravel mulch (AG, 2–5 mm particle size), large-sized gravel mulch (BG, 40–60 mm particle size), and no gravel mulch as a control (CK). We found that gravel mulch could effectively control surface rainwater runoff, especially in the AG treatment. AG treated soil was typically oligotrophic compared to BG treated soil with higher soil carbon and nitrogen content.PCR-amplified 16S rRNA genes and internal transcribed spacer (ITS) sequencing showed that soil bacterial and fungal communities in the AG treatment differed from the BG treatment or the CK treatment, and soil bacterial and fungal richness and bacterial diversity changed significantly after mulching. The relative abundance of Acidobacteria, Actinobacteria, Ascomycota and Bacillus significantly increased and the relative abundance of Proteobacteria and Bacteroidetes significantly decreased in the AG treatment compared to the CK treatment. Furthermore, the relative abundance of Bacillus was significantly increased in the AG treatment and was slightly increased (not significant) in the BG treatment compared to the control. Redundancy analysis (RDA) revealed that soil carbon and available nutrients were important driving factors for changes in microbial communities. Overall, the capacity of runoff production suppression and soil bacterial diversity and richness were higher in the AG treatment than the other treatments. Therefore, small-sized gravel mulching is recommended for arid and semiarid areas.

Regulation of mulch conditions on photosynthesis and water utilization of spring wheat in northwest semi-arid area of China.

A field experiment was conducted from 2015 to 2016 in the northwestern Loess Plateau, China, to analyze the relationships among flag-leaf photosynthetic characteristics, water-consumption characteristics, and yield components of spring wheat (Triticum aestivum 'Longchun 35'). There were three treatments: whole-field plastic mulching (PMS), sand mulching (SM), and uncovered (CK). The results showed that soil-water storage levels at 0-300 cm of soil profile before wheat filling under PMS and SM treatments were greater than that in CK by 47.8 and 31.6 mm, respectively, while that under PMS was lower than CK by 15.6 mm at the filling stage. Water consumption under PMS and SM increased in the flagging-heading and flowering-filling stages compared with the CK. Leaf area indices under PMS and SM were increased by 59.0%-73.7% and 40.1%-52.7%, respectively, and leaf SPAD values were increased by 3.5%-28.4% and 2.9%-23.9%, respectively, compared with CK. The net photosynthetic rate of PMS was increased by 23.5%, 33.0% and 17.7% at the flagging, heading, and flowering stages. The corresponding stoma-tal conductance rate was increased by 32.6%, 76.4% and 66.9%, respectively. Net photosynthetic and stomatal conductance rates at the filling stage were decreased by 26.2% and 16.4%, respectively. At the heading, flowering, and filling stages, stomatal limitation values in PMS were decreased by 14.6%, 23.9% and 22.3%, respectively, and by 25.7%, 29.8% and 17.4%, respectively in SM. The instantaneous water-use efficiency of spring wheat in PMS was increased by 57.8% at the flagging stage and decreased by 11.2% at the flowering stage. At the heading and flowering stages, the apparent quantum efficiency was increased by 22.6% and 18.7% in PMS, and by 26.8% and 14.3% in SM, respectively. Plant height and yield component indices in PMS and SM were significantly greater than that in CK, with the enhancement being greater than that in dry years. Grain yield was increased by 36.2% and 8.7% and water-use efficiency increased by 9.4% and 3.4% in PMS and SM, respectively. PMS and SM treatments increased soil water storage before the pre-filling stage of wheat, aggravated water consumption during the flagging-shooting and flowering-filling stages, resulting in greater SPAD values and leaf area indices, which promoted the photosynthetic functions of flag leaves, facilitated sink formation and photosynthetic assimilate transportation, resulting in increased grain yields and water use efficiency of spring wheat. The effects of PMS treatment were more remarkable than those of SM in terms of increasing spring wheat's yield potential in wet years and adaptability in dry years.

Impacts of Chinese Grain for Green program and climate change on vegetation in the Loess Plateau during 1982–2015

Remote sensing based vegetation index provides a practical method for the monitoring of vegetation dynamics at regional and global scales. Here, using a long-term remotely sensed normalized difference vegetation index (NDVI) dataset, we quantified the vegetation changes in the Loess Plateau (LP) over the last three decades (1982–2015), which includes the period before the Chinese“Grain for Green Program”(GGP) was launched (1982–1999), and the period after the GGP (1999–2015). The correlations between the NDVI and four climate related variables, i.e., precipitation, temperature, root-soil moisture (RSM), and a drought proxy-standardized evapotranspiration deficit index (SEDI), were also examined. The results indicated that, (i) the GGP strongly changed the vegetation in the LP. The growing-season mean NDVI (GSM-NDVI) and the annual mean NDVI (AM-NDVI) decreased slightly before the GGP launched in 1999, with slopes of −3.38×10−3 and−8.00×10−4year−1, respectively. However, they showed slight and significant (p<0.05) increases after the GGP, with slopes of 4.75×10−3 and 2.32×10−3year−1, respectively. (ii) Climate change (i.e., warming and drying) resulted in adverse effects on vegetation in the LP during the period before the GGP. However, the observed changes (i.e., wetting and reduced drought) exerted positive effects on the vegetation during the period after the GGP. (iii) Inter-annual variations of spatially averaged NDVI over the LP were primarily determined by RSM rather than any other climate related variables. In the southeastern LP, the inter-annual variation of GSM-NDVI was mainly determined by precipitation and SEDI, while the inter-annual variation of AM-NDVI was mainly caused by SEDI and RSM. Inter-annual variations of both GSM-NDVI and AM-NDVI were mainly determined by SEDI and RSM in the northwestern LP, and by temperature in the southwestern LP.

Copulas-Based Drought Characteristics Analysis and Risk Assessment across the Loess Plateau of China

The Loess Plateau (LP) of China is famous with soil erosion and water shortage problems. Droughts were frequently occurred in this region, which becomes a critical limiting factor to the socioeconomic development, ecology and food production. Therefore, the major motivation of the present study is to investigate the drought characteristics and assess the potential drought risk in this area, which is crucial for drought resistance, water resource management as well as agricultural production. This study analyzes the variations of meteorological drought, characterized by the Standardized Precipitation Evapotranspiration Index (SPEI), and assesses the drought hazards in the LP during 1950–2014. The results show that the northwest of LP is more likely to experience long duration and large severity droughts than the southeast of LP. From the perspective of statistical probability models, the exponential distribution and Gamma distribution can well fit the drought duration and severity, respectively. Compared to Frank and Clayton copula, the Gumbel copula can better model the dependence structure between the drought variables in our study area. Moreover, the estimation of the upper tail dependence coefficient between drought duration and severity also demonstrate that Gumbel copula can provide the best description of the upper tail. The spatial distribution of joint return period under different cases indicates that drought risk in northwestern LP is relatively higher than that in other areas of LP. The results presented in this study can provide some scientific basis for the strategic planning of drought resistance and water resource management in the LP.

Loess caves, a special kind of geo-hazard on loess plateau, northwestern China

The loess caves developed on Chinese loess plateau are not only a typical phenomenon of soil and water loss, but also a special kind of geological hazard. Many loess dilapidations, collapses and medium to small-sized landslides are related to the loess caves. To understand the characteristics and the geo-disasters induced by loess caves, the loess caves developed on Chinese loess plateau were rigorously investigated. Based on a long-term field surveys on about 800 fixed points in Gansu, Ningxia and northern Shaanxi, the classifications and characterization of loess caves in Chinese loess plateau are discussed in detail. Moreover, the regionally developmental regularity hierarchical development regularity of loess cave and its characteristics are studied in this paper, which show that the density of loess caves on the northwestern loess plateau is higher than that in the southeastern loess plateau than that in the southeast in China. And the main control factors affecting the development of loess caves are analyzed. Interestingly, the development of the caves is related to the loess layer, land characteristics, geologic structure (including the joints and the fracture system), micro topography, hydro-geological factors and climatic conditions.

Streamflow responses to climate change and LUCC in a semi-arid watershed of Chinese Loess Plateau

Climate change and Land Use/Cover Change (LUCC) have been identified as two primary factors affecting watershed hydrological regime. This study analyzed the trends of streamflow, precipitation, air temperature and potential evapotranspiration (PET) from 1962 to 2008 in the Jihe watershed in northwestern Loess Plateau of China using the Mann-Kendall test. The streamflow responses to climate change and LUCC were quantified independently by the elasticity method. The results show that the streamflow presented a dramatic decline with a turning point occurred in 1971, while the precipitation and PET did not change significantly. The results also show that the temperature rose markedly especially since 1990s with an approximate increase of 1.74°C over the entire research period (1962–2008). Using land use transition matrix, we found that slope cropland was significantly converted to terrace between 1970s and 1990s and that forest cover increased relatively significantly because of the Grain for Green Project after 2000. The streamflow reduction was predominantly caused by LUCC and its contribution reached up to 90.2%, while the contribution of climate change to streamflow decline was only 9.8%. Although the analytical results between the elasticity method and linear regression model were not satisfactorily consistent, they both indicated that LUCC (human activity) was the major factor causing streamflow decline in the Jihe watershed from 1962 to 2008.

Soil water migration in the unsaturated zone of semiarid region in China from isotope evidence

Abstract. Soil water is an important driving force of the ecosystems, especially in the semiarid hill and gully region of the northwestern Loess Plateau in China. The mechanism of soil water migration in the reconstruction and restoration of Loess Plateau is a key scientific problem that must be solved. Isotopic tracers can provide valuable information associated with complex hydrological problems, difficult to obtain using other methods. In this study, the oxygen and hydrogen isotopes are used as tracers to investigate the migration processes of soil water in the unsaturated zone in an arid region of China's Loess Plateau. Samples of precipitation, soil water, plant xylems and plant roots are collected and analysed. The conservative elements deuterium (D) and oxygen (18O) are used as tracers to identify variable source and mixing processes. The mixing model is used to quantify the contribution of each end member and calculate mixing amounts. The results show that the isotopic composition of precipitation in the Anjiagou River basin is affected by isotopic fractionation due to evaporation. The isotopic compositions of soil waters are plotted between or near the local meteoric water lines, indicating that soil waters are recharged by precipitation. The soil water migration is dominated by piston-type flow in the study area and rarely preferential flow. Water migration exhibited a transformation pathway from precipitation to soil water to plant water. δ18O and δD are enriched in the shallow (&lt; 20 cm depth) soil water in most soil profiles due to evaporation. The isotopic composition of xylem water is close to that of soil water at the depth of 40–60 cm. These values reflect soil water signatures associated with Caragana korshinskii Kom. uptake at the depth of 40–60 cm. Soil water from the surface soil layer (20–40 cm) comprised 6–12 % of plant xylem water, while soil water at the depth of 40–60 cm is the largest component of plant xylem water (ranging from 60 to 66 %), soil water below 60 cm depth comprised 8–14 % of plant xylem water and only 5–8 % is derived directly from precipitation. This study investigates the migration process of soil water, identifies the source of plant water and finally provides a scientific basis for identification of model structures and parameters. It can provide a scientific basis for ecological water demand, ecological restoration, and management of water resources.

A COMPARATIVE ANALYSIS OF CHANGING SEDIMENTATION CONDITIONS DURING THE LAST INTERGLACIAL-GLACIAL MACROCYCLE IN THE LOESS AREAS OF THE SOUTHERN EAST EUROPEAN PLAIN (THE AZOV SEA REGION) AND CENTRAL CHINA (LOESS PLATEAU)

Multi-proxy studies of loess-soil sequences in the eastern Azov Sea region (Beglitsa‑2 section) and the northwestern Loess Plateau of China (Caoxian section) let us to suggest the correlation of the main stratigraphic horizons and to provide the comparison of landscape and climatic changes in these regions during the last interglacial-glacial climatic macrocycle. It was found that the Loess Plateau was characterized by a steady accumulation of loess during both glacial and interglacial epochs, when the so-called “warm” loess was formed. In the NE Sea of Azov region, the main loess accumulation corresponded to cryoarid conditions of the glacial phases, while during the interglacials, loess accumulation became ten times slower. The average sedimentation rate of loess material calculated for Caoxian section was more than 5 times higher than the one calculated for the Beglitsa‑2 section. Late Pleistocene paleosoils in the Beglitsa‑2 section are of the steppe type and correspond to the Salyn (MIS5e), Krutitsa (MIS5c), and Bryansk (MIS3) climate phases. Morphology of the Azov paleosoils is much better expressed than that of the paleosoils at Caoxian, where only the S1SS3 semidesert paleosoil (MIS5e) can be seen directly in the section. Climatic fluctuations in the southern East European Plain within the last interglacial-glacial macrocycle had significantly greater amplitude than that in the north-west of the Loess Plateau. In the latter, cryoarid glacial conditions alternated with warm semiarid interglacial conditions. In the northwestern Loess Plateau, the main climate dynamics was associated with the hydrological regime changes under the influence of the East Asian monsoon activity, which was at its lowest during the glacial stages (drier climatic phases) and increased during the interglacial and interstadials (wetter climatic phases).

Effects of straw incorporation on the soil nutrient contents, enzyme activities, and crop yield in a semiarid region of China

The current cropping system of conventional tillage and stubble removal in the northwestern Loess Plateau of China is known to decrease the water use efficiency and crop yield because of soil infertile and degradation. To determine the effects of straw incorporation on the soil fertility and crop yield, we conducted experiments in semiarid areas of southern Ningxia for 4 years (2007–2010). Four treatments were tested: (i) no straw incorporation (CK); (ii) incorporation of maize straw at a low rate of 4500kgha−1 (L); (iii) incorporation of maize straw at a medium rate of 9000kgha−1 (M); and (iv) incorporation of maize straw at a high rate of 13500kgha−1 (H). After straw incorporation for four years, the results showed that variable straw amounts had different effects on the soil fertility indices, where H treatment had the greatest effect. Compared with CK, the average soil available N, total N, available P, total P, and SOC levels under straw incorporation treatments were 27.5%, 10.8%, 16.6%, 5.2%, and 9.8% higher in 0–40cm soil layers, especially in 0–20cm soil layer. The straw incorporation treatments average increased the soil urease, phosphatase, and invertase activities levels by 19.6%, 39.4%, and 44.3% in 0–60cm soil layers, according to the following order: H>M>L>CK. And higher yields coupled with higher nutrient contents were achieved with H, M and L compared with CK, where these treatments increased the crop yields by 22.5%, 22.8%, and 10.6%, and water use efficiency by 34.6%, 30.7%, and 15.7%, respectively. Our results suggest that straw incorporation (especially in rate of 13500kgha−1) is an effective practice for improving the soil fertility and increased crop yield in semiarid region of China.

Mulching materials improve soil properties and maize growth in the Northwestern Loess Plateau, China

Water deficiency is the main limiting factor for crop growth in rain-fed areas. Mulching can affect the soil microclimate (soil water and temperature) and influence the grain yield of crops. A field experiment was conducted to determine the effect of different mulching materials on soil temperature, soil water, crop growth and yield, and water use efficiency (WUE) in spring maize (Zea mays L.) between 2009 and 2011 in Heyang County, Shaanxi, China. The field experiment used five mulch treatments: polyethylene film (PM), biodegradable polymer film (BM), maize straw (MM), liquid membrane (LM), and an uncovered control (CK). In the early stage of maize growth, the topsoil temperatures (0–10cm) in the PM and BM treatments were significantly (P&lt;0.05) higher than CK, whereas the soil temperature in the MM treatment was significantly (P&lt;0.05) lower than CK. The PM, BM, and MM treatments also significantly increased soil water during the early growth stage. However, soil water (0–200cm) in the PM and BM treatments was lower than in the CK treatment during the middle and later growth stages. There was no significant difference (P&gt;0.05) in soil temperature or soil water in the LM treatment during the entire growing season. Maize yield increased significantly (P&lt;0.05) in both the PM and BM treatments by 26.1% and 27.5% during the experimental period compared to the CK treatment. Water use efficiency also significantly increased in these two treatments by 25.1% and 27.6%. These results show that both PM and BM had significant effects on soil temperature, water conservation and maize yield, but no significant (P&gt;0.05) differences were observed between these two treatments. Biodegradable polymer film is useful in reducing environmental pollution caused by polyethylene film and could potentially replace polyethylene film during agricultural production in the Northwestern Loess Plateau, China.