Loess Plateau In Northwest China Research Articles

Factors Affecting the Spatial and Temporal Variations in Soil Erodibility of China

AbstractSoil erosion occurs extensively across China, leading to severe degradation of the land and ecosystem services. However, the spatial and temporal variations in soil erodibility (k) and the distribution of soil erosion across land use types and slopes remain unclear. We synthesized the results from 325 sites published in 152 literatures to analyze the factors affecting the k, such as land use type, climate, topography, soil, and vegetation restoration age. The results showed that areas with slopes >25° had a larger k factor (k = 0.1047) than did those with slope <6° (k = 0.0637) or 6–25° (k = 0.0832). The k from 2006 to 2011 (k = 0.0725) was higher than that from 1999 to 2005 (k = 0.058) and that from 2012 to 2016 (k = 0.0631). The k value initially increased with vegetation restoration age and then gradually decreased. Land use also had an impact on the k factor, with the k factor of cropland (k = 0.0697) being higher than that of grassland (k = 0.0663) but lower than that of forest (k = 0.0967). Across China, North Shaanxi, Heilongjiang, and South Guizhou, which are located in the Loess Plateau in Northwest China, the Black Soil region of Northeast China, and the Karst areas in Southwest China, respectively, were the three most severely eroded regions due to hydraulic erosion, frost‐thaw erosion, and high‐intensity erosion, respectively. Overall, the most important factors affecting the k were soil characteristics, followed by topography and climate. Among them, soil nitrogen and precipitation were the two most critical factors influencing the k.

Estimating the Spatial Distribution of Soil Properties Using Environmental Variables at a Catchment Scale in the Loess Hilly Area, China.

A comprehensive understanding of the spatial distribution and dynamic changes of soil properties are the basis for sustainable land management. Topography and land use types are key factors affecting soil property variability. This study analyzed the effects of land use types and landscape locations on soil properties, based on data from 111 points of surface soil (0–20 cm) in the Zhujiagou catchment on the Loess Plateau of Northwest China. Soil properties include clay, silt, bulk density (BD), soil organic matter (SOM), total nitrogen (TN) and total phosphorus (TP). Land use types include slope farmland (SFL), terrace farmland (TFL), check-dam farmland (CDL), woodland (WL), shrub land (SL) and grassland (GL). Landscape locations include crest (CT), upper slope (US), middle slope (MS), lower slope (LS) and flat valley (FV). Topographical attributes were divided into primary and secondary (or compound) attributes. Correlation analyses were carried out between soil properties and terrain attribute, and multiple-linear regression models were established to estimate soil properties using land use types and topographic attributes as independents. Results indicated that significant differences in soil properties existed between six land use types, except for bulk density. Higher values of clay, silt, SOM and TN occurred in soils from check-dam farmland, but lower values in soils from shrub land. Significant differences among landscape positions were observed for clay, BD, SOM and TN. Clay, SOM and TN contents on flat valley (FV) positions were higher than those of other positions. Different correlations were found between soil properties and terrain attributes. The regression models explained 13% to 63% of the variability of the measured soil properties, and the model for Clay had the highest R2 value, followed by TN, silt, BD, SOM and TP. Validation results of the regression models showed that the model was precise for soil bulk density, but the variation was large and a high smoothing effect existed for predicted values of other soil properties. For TP, the predicted result was poor. Further observations suggested that land use was the dominant factor affecting soil chemical properties. But for soil physical properties, especially for BD, topography was the dominant factor.

Spatial groundwater quality and potential health risks due to nitrate ingestion through drinking water: A case study in Yan’an City on the Loess Plateau of northwest China

This research was carried out to delineate the spatial distribution of shallow groundwater quality in Yan’an City, an important cultural city on the Chinese Loess Plateau, and to estimate the health risks induced by nitrate exposure in drinking water in this city. For this study, 36 shallow groundwater samples were collected from shallow pumping wells/dug wells. The entropy-weighted water quality index (EWQI) was used to evaluate the overall groundwater quality, and the spatial distribution of the groundwater quality was discussed. The potential health hazards due to nitrate intake through drinking water were also assessed. The results of the study demonstrate that the main hydrochemical facies are governed by natural processes and anthropogenic activities. Over half of the groundwater samples require treatment of different degrees before being consumed. TH, TDS, SO42–, and NO3– are the most prevalent contaminants affecting the groundwater quality in this area. Poor-quality water is prevalent in the region along the main river. Residents in almost half of the study area face noncarcinogenic health risks with children being the more susceptible group to groundwater nitrate contamination. Reducing the concentration of NO3– in drinking water by regulating excessive fertilizer application and issuing regulations supervising the domestic sewage are important to reduce the health risks. Integrated management of groundwater and surface water as well as rainwater is recommended for the groundwater quality management.

Regulatory effects of bundled straw covering on winter wheat yield and soil thermal-moisture utilization in dryland.

Bundled straw covering (BSC), using corn whole straw for partial coverage planting, is a novel dryland cultivation technique. To examine the effects of BSC on the thermal-moisture status and winter wheat yield under typical arid and semiarid conditions in the Loess Plateau of Northwest China, soil temperature, soil water content and consumption, grain yield and water-use efficiency were compared for four treatments, including no-tillage with straw mulch (NTS), whole field plastic mulching with soil covering on the top of the plastic mulch and bunch-seeding (PFM), open field cultivation (CK) and BSC during three growing seasons from 2013 to 2016. The results showed that PFM significantly increased soil temperature of 5-20 cm depth before jointing stage, while the warming effect of BSC and NTS was mainly in the wintering period. The three kinds of coverage methods after jointing stage had significant cooling effects. Both BSC and PFM significantly improved soil water storage effect during the fallow period. BSC significantly elevated soil moisture in the depth of 0 to 200 cm in the whole growing season. The improvement of soil moisture by PFM and NTS mainly occurred before the heading stage, and soil moisture in PFM treatment gradually decreased after heading stage. BSC and PFM significantly increased water consumption in the whole growth period and increased that during the jointing stage to the flowering stage, and promoted the utilization of soil moisture below 120 cm. Compared with CK, BSC, NTS and PFM significantly increased the number of panicles per unit area and biomass at maturity. In those three treatments, grain yield was increased by 19%-52%, 14%-30% and 15%-60%, respectively, and the annual water use efficiency was increased by 19%-61%, 14%-31% and 15%-58%, respectively. BSC had the same potential for increasing yield and water use efficiency as PFM. Based on factors such as winter wheat yield, soil thermal-moisture utilization and annual water consumption, BSC is a high-yield and efficient cultivation method that is conducive to the sustainable development of dryland agriculture in Northwest China.

Adoption of Conservation Tillage on the Semi-Arid Loess Plateau of Northwest China

Conservation tillage is an important approach to prevent water loss and soil erosion and promote soil fertility that has been adopted widely throughout the world. However, despite promotion of the benefits of conservation tillage, obstacles are still encountered in some regions. A survey of 385 farmer households in the semi-arid Loess Plateau of China was conducted to assess the adoption of conservation tillage (ACT). This investigation was located in two counties that have run conservation tillage demonstrations with wheat for at least eight years. A binary logistic regression model was used to quantify the factors determining whether or not farmers adopt conservation tillage. Farmer’s education level, the influence of training, and field demonstrations by agricultural departments had significant positive effects on ACT. Although the adoption rate of conservation tillage in this paper was very high (89%), farmers were reluctant to continue practicing conservation tillage based on their experiences, which is contrary to the expectations of the government. The area available for planting winter wheat and the number of arable plots per household also had significant positive effects on ACT. However, the total cultivated area of land per household had a significant negative impact on ACT. Farmer awareness of conservation tillage technology, the distance from a farmer’s house to the nearest agricultural market, and the size of the active labor force in the family had significant negative impacts on ACT. These results will help in the development of more effective and targeted policies to improve the sustainability of farming systems on the semi-arid Loess Plateau.

Vertical distribution of ammonia-oxidizing microorganisms across a soil profile of the Chinese Loess Plateau and their responses to nitrogen inputs

Ammonia-oxidizing archaea (AOA) and bacteria (AOB) oxidize ammonia into nitrite, the first and rate-limiting step of microbial nitrification, and exert major controls over soil nitrogen transformations. The Loess Plateau in northwest China is characterized with deep soils that are often exposed to the surface and reactive nitrogen (N) inputs due to erosion and human removal of the surface soil. However, few have examined the distribution of AOA and AOB along the profile of Loess Plateau soils and their responses to N inputs. We examined the abundance and diversity of AOA and AOB along the soil profile (0–100cm) and their responses to two levels of N inputs (low at 10, and high at 100μgNg−1 soil) in a 55-d incubation experiment. While AOB were most numerous in the surface soil (0–20cm), AOA were most abundant in the subsoils (20–40 and 40–60cm), suggesting a niche differentiation between AOA and AOB along the soil profile. High N input increased AOB nearly ten-fold in the upper two layers of soils (0–20 and 20–40cm) and sixteen to twenty-five fold in the deeper soil layers (40–60, 60–80 and 80–100cm). However, it only increased AOA by 7% (40–60cm) to 48% (20–40cm). In addition, potential nitrification rate and N2O emissions correlated only with AOB. Finally, high N input significantly increased AOB diversity and led to nitrite accumulation in deep soil layers (60–80 and 80–100cm). Together, our results showed that high N input can significantly alter the diversity and function of ammonia-oxidizing microbes in the deep soil of Loess Plateau, suggesting the need to examine the generality of the observed changes and their potential environmental impacts.

Effects of vegetation restoration on soil physical properties of abandoned farmland on the Loess Plateau, China

To improve the ecological environment in China, the Chinese government implemented a country-wide ecological protection and reforestation project (namely the “Grain for Green Project”) in 1999 to return cultivated land with slopes of 25° or more to perennial vegetation. Vegetation restoration reduces soil erosion mainly by changing the soil physical properties. Different vegetation restoration methods might produce different impacts on soil physical properties. In this study, two vegetation restoration methods (i.e., natural restoration and artificial restoration) were compared on abandoned farmland in the typically hilly and gullied areas of the Loess Plateau of Northwest China. In the natural restoration method, the farmland was abandoned to natural vegetation succession without irrigation, fertilization or other artificial disturbances. In the artificial restoration method, the farmland was planted with black locust (Robinia pseudoacacia L.) and watered and cultivated for the first two years. Three soil physical properties (i.e., soil moisture, bulk density and aggregation) were investigated under the two vegetation restoration methods. The results showed that the soil moisture and soil bulk density were higher under artificial restoration than under natural restoration within the first three years of vegetation restoration. By the fourth year, the soil moisture and soil bulk density were higher under natural restoration than under artificial restoration. For the stability of soil aggregates > 0.25 mm, the soil aggregates in the 0-20 cm soil layer were more stable under artificial restoration than under natural restoration, while the results were the opposite for the 40-60 cm soil layer. Overall, the soil physical properties were continuously improved during the restoration of vegetation on abandoned farmland. In choosing between vegetation restoration methods, natural restoration is preferable to artificial restoration, but artificial intervention is needed during the first three years.

Combination of plastic film mulching and AMF inoculation promotes maize growth, yield and water use efficiency in the semiarid region of Northwest China

Plastic film mulching (PFM) plays a critical role in improving crop production and sustainable development of agroecosystem in semiarid agriculture. Arbuscular mycorrhizal fungi (AMF) can form a mutualistic symbiosis with the vast majority of plant roots and have been shown to contribute to host growth in harsh conditions. Yet, whether the integrated application of PFM and AMF inoculation have an interactive effect on crop growth and production in semiarid regions with poor soil nutrients and water shortage has received rather less attention. Therefore, we performed a two-year field study to investigate the effects of PFM and AMF inoculation on spring maize growth, yield and water use efficiency (WUE). Four treatments, including non-mulching and non-AMF inoculation (CK), plastic film mulching (PFM), arbuscular mycorrhizal fungi inoculation (AMF) and combination of plastic film mulching and arbuscular mycorrhizal fungi inoculation (PAMF), were compared in 2014 and 2015 at Shenmu Country on the semiarid Loess Plateau of Northwest China. Our results indicated that AMF inoculation contributed to increased plant biomass and height, although its effectiveness was lower than PFM alone or combined practice. Compared with the non-mulched control (CK), the mulched treatments significantly increased the average soil water content by 43.2% at the depth of 0–60 cm in 2014 and by 30.3% at the depth of 0–30 cm in 2015. The combination of PFM and AMF inoculation had the greatest soil water content at different soil depths in both years. AMF inoculation significantly improved root mycorrhizal colonization and external hyphal length in both years. Meanwhile, mycorrhizal plants under PFM had significantly greater root tip number and surface area when compared with the control. PAMF treatment had the highest yield and WUE among all treatments. Compared with the CK, PAMF treatment increased the yield and WUE by55.6% and 43.1% in 2014 and by 39.3% and 45.6% in 2015, respectively. Moreover, the mycorrhizal dependency of maize yield was more notable in mycorrhizal plants grown in mulched soils than in bare soils. In conclusion, the combined application of PFM and AMF inoculation is an effective and favorable agricultural practice in nutrition-deficiency soil in semiarid regions of China because of improved root morphological traits and enhanced topsoil water content that increase crop productivity.

Plastic film mulch increased winter wheat grain yield but reduced its protein content in dryland of northwest China

Plastic film mulch has been proved of great potential to enhance crop productivities in drylands, but there is still lacking insight into its underlying changes in crop grain nutritional quality. Therefore, field experiments were conducted to investigate the effects of different soil surface managements on grain yield and its protein content of winter wheat in 2014–2016 at different fertilizer input levels under no mulch and plastic film mulch at seven sites in dryland of the Loess Plateau in northwest China. Compared with no mulch, overall average grain yield was significantly increased by 13.7%, but its protein content was decreased by 7.8% with plastic film mulch. Apart from the dilution effects caused by the much more increase of grain yield, the decreased N remobilization from vegetative parts to grain and the lowered crop N uptake from soil during grain filling stage were found to be the main reasons, when the overall average of N remobilization efficiency, N harvest index and post-anthesis N uptake was respectively decreased by 16.0%, 5.7% and 24.0%. However, the winter wheat grain protein content was observed to increase more quickly with the N rate increase under plastic film mulch, compared to no mulch. This provides opportunity to increase the grain protein content under plastic film mulch to the same level of no mulch by increasing the N fertilizer application rates, and an estimation of optimal N application rates for winter wheat grain yield and its protein content was computed under plastic film mulch in drylands.

How can streamflow and climate-landscape data be used to estimate baseflow mean response time?

Mean response time (MRT) is a metric describing the propagation of catchment hydraulic behavior that reflects both hydro-climatic conditions and catchment characteristics. To provide a comprehensive understanding of catchment response over a longer-time scale for hydraulic processes, the MRT function for baseflow generation was derived using an instantaneous unit hydrograph (IUH) model that describes the subsurface response to effective rainfall inputs. IUH parameters were estimated based on the “match test” between the autocorrelation function (ACFs) derived from the filtered base flow time series and from the IUH parameters, under the GLUE framework. Regionalization of MRT was conducted using estimates and hydroclimate-landscape indices in 22 sub-basins of the Jinghe River Basin (JRB) in the Loess Plateau of northwest China. Results indicate there is strong equifinality in determination of the best parameter sets but the median values of the MRT estimates are relatively stable in the acceptable range of the parameters. MRTs vary markedly over the studied sub-basins, ranging from tens of days to more than a year. Climate, topography and geomorphology were identified as three first-order controls on recharge-baseflow response processes. Human activities involving the cultivation of permanent crops may elongate the baseflow MRT and hence increase the dynamic storage. Cross validation suggests the model can be used to estimate MRTs in ungauged catchments in similar regions of throughout the Loess Plateau. The proposed method provides a systematic approach for MRT estimation and regionalization in terms of hydroclimate and catchment characteristics, which is helpful in the sustainable water resources utilization and ecological protection in the Loess Plateau.

Effects of long-term cultivation practices and nitrogen fertilization rates on carbon stock in a calcareous soil on the Chinese Loess Plateau

Soil organic carbon (SOC) and soil inorganic carbon (SIC) are important C pools in the Loess Plateau of Northwest China, however, variations of SOC and SIC stocks under different cultivation practices and nitrogen (N) fertilization rates are not clear in this area. A long-term field experiment started in June 2003 was conducted to investigate the SOC and SIC stocks in a calcareous soil of the Chinese Loess Plateau under four cultivation practices, i.e., fallow (FA), conventional cultivation (CC), straw mulch (SM), and plastic film-mulched ridge and straw-mulched furrow (RF), in combination with three N fertilization rates, i.e., 0 (N0), 120 (N120), and 240 (N240) kg N/hm2. Results indicate that the crop straw addition treatments (SM and RF) increased the contents of soil microbial biomass C (SMBC) and SOC, and the SOC stock increased by 10.1%–13.3% at the upper 20 cm soil depth in comparison to the 8-year fallow (FA) treatment. Meanwhile, SIC stock significantly increased by 19% at the entire tested soil depth range (0–100 cm) under all crop cultivation practices in comparison to that of soil exposed to the long-term fallow treatment, particularly at the upper 60 cm soil depth. Furthermore, moderate N fertilizer application (120 kg N/hm2) increased SOC stock at the upper 40 cm soil depth, whereas SIC stock decreased as the N fertilization rate increased. We conclude that the combined application of crop organic residues and moderate N fertilization rate could facilitate the sequestrations of SOC and SIC in the calcareous soil.

Spatial patterns and storage composition of woody debris in a natural secondary forest dominated by Pinus tabulaeformis on Loess Plateau, China

Woody debris (WD) is an important part of natural Pinus tabulaeformis mixed stands, and it affects the forest ecosystem stability and development. The WD spatial patterns are especially important structural characteristics that can provide insights into forest dynamics. In this paper, the WD storage, WD spatial patterns and WD associations among the main species were examined in the natural secondary forest on Loess Plateau in northwest China. Data were collected in a 1 ha (100 m × 100 m) permanent plot, and all the trees with a diameter at breast height of more than 3 cm were measured and stem-mapped. Ripley’s K functions from the spatial-point-pattern-analysis method were used to analyze the spatial distribution and associations. The results showed that: (1) The total storage of WD was 10.73 t/ha, fallen wood was the main source of WD, and the majority diameters were greater than 20 cm, and in intermediate levels of decay; (2) The overall spatial pattern was closely related to the spatial scale, which exhibited an aggregated pattern on a small scale, and a random pattern on a large scale. The spatial patterns of coarse woody debris also gradually transitioned from an aggregated pattern in fine scales to a random pattern in broader spatial scales, which matched the overall spatial pattern. The spatial intensity was gradually decreased with the increasing diameters, and increased with the decomposition classes; (3) The WD of Pinus tabulaeformis species was negatively associated with Betula platyphylla and Populus davidiana on a small scale but positively associated with these species on a large scale. The spatial pattern and interspecies relations were the results of long-term interactions between the natural secondary forest community and the surrounding natural environment. These findings would provide a scientific basis for the sustainable management and protection of natural secondary forest ecosystems on Loess Plateau.

Long-term biochar application influences soil microbial community and its potential roles in semiarid farmland

Biochar addition to soil can change soil physicochemical properties, resulting in a shift of the soil microbial community. However, it is uncertain how long-term biochar application affects the soil microbial community and diversity in drylands. To determine the underlying mechanism, a 3.5-year spring maize (Zea mays L.) field experiment with biochar applications was conducted to elucidate the effect of biochar on soil microbial abundance and community composition as well as its potential applications in drylands of the Loess Plateau in Northwest China. Soil samples from a 0–20cm depth for four biochar treatments, including 0 (C0, as the control), 10 (C10), 30 (C30) and 50 (C50) tha−1, were examined using phospholipid fatty acid (PLFA) analysis. It was found that the proportion of arbuscular mycorrhizal fungi (AMF) and the ratio of AMF/saprotrophic fungi (SF) correlated with the biochar levels, for example, the C30 treatment significantly decreased the absolute SF but increased the ratio of AMF/SF. Especially, both the AMF/SF and Fungi/Bacteria ratios were significantly increased in the C50 treatment, suggesting that high amounts of biochar could increase fungal rather than bacterial diversity. In addition, soil organic C (SOC) (P<0.01), KMnO4-oxidizable C (KMnO4-C) (P<0.01), and the C management index (CMI) (P<0.01) were confirmed to play significant roles in shaping the soil microbial community composition. SOC and total N were significantly increased by biochar application, and total P was increased in the C30 treatment. However, compared with the C0 treatment, the C50 treatment significantly decreased KMnO4-C and the CMI, suggesting the proper level of biochar addition to soil should be considered for the improvement of soil organic materials. Accordingly, biochar application at 30tha−1, which was connected with a decreased absolute SF and an increased AMF/SF ratio, could be a choice for improving soil quality and nutrient availability in semiarid farmland.

Effects of Water Saving Practices on Winter Wheat and Summer Maize Yields in South Loess Plateau of Northwest China

A field experiment, laid out in Randomized Complete Block Design (RCBD) with split plot arrangement having four replications, was conducted at the south edge of loess plateau, Shaanxi, China to evaluate the responses of winter wheat and summer maize to different water saving management practices involving four mulching and irrigation treatments, i.e., plastic mulch ridge and straw mulch furrow combined with deficit irrigation (RF+DI), straw mulch combined with deficit irrigation (SM+DI), Deficit Irrigation (DI), and Conventional Flood Irrigation (CFI). Soil temperature and moisture during the crop growth were monitored in two years. RF+DI treatment significantly increased maize yield, and it also had higher wheat yield than SM+DI treatment. SM+DI treatment increased maize yield; however, it did not increase winter wheat yield. Soil water content in RF+DI and SM+DI treatments was significantly higher than those of CFI or DI treatments. Compared with RF+DI treatment, SM+DI treatment had higher soil water content (0-20 cm); however, it had the lowest heat 741 Degree Days of Soil (DDs) among the four treatments. The low soil temperature in SM+DI plots, especially in early spring, delayed winter wheat growth stages and development, thus reduced grain yield compared with RF+DI treatment. The positive effects of ridge-furrow system on both wheat and maize yield could be explained by harmonizing soil moisture and temperature by this treatment.

Impact of soil moisture and winter wheat height from the Loess Plateau in Northwest China on surface spectral albedo

The understanding of surface spectral radiation and reflected radiation characteristics of different surfaces in different climate zones aids in the interpretation of regional surface energy transfers and the development of land surface models. This study analysed surface spectral radiation variations and corresponding surface albedo characteristics at different wavelengths as well as the relationship between 5-cm soil moisture and surface albedo on typical sunny days during the winter wheat growth period. The analysis was conducted using observational Loess Plateau winter wheat data from 2015. The results show that the ratio of atmospheric downward radiation to global radiation on typical sunny days is highest for near-infrared wavelengths, followed by visible wavelengths and ultraviolet wavelengths, with values of 57.3, 38.7 and 4.0%, respectively. The ratio of reflected spectral radiation to global radiation varies based on land surface type. The visible radiation reflected by vegetated surfaces is far less than that reflected by bare ground, with surface albedos of 0.045 and 0.27, respectively. Thus, vegetated surfaces absorb more visible radiation than bare ground. The atmospheric downward spectral radiation to global radiation diurnal variation ratios vary for near-infrared wavelengths versus visible and ultraviolet wavelengths on typical sunny days. The near-infrared wavelengths ratio is higher in the morning and evening and lower at noon. The visible and ultraviolet wavelengths ratios are lower in the morning and evening and higher at noon. Visible and ultraviolet wavelength surface albedo is affected by 5-cm soil moisture, demonstrating a significant negative correlation. Excluding near-infrared wavelengths, correlations between surface albedo and 5-cm soil moisture pass the 99% confidence test at each wavelength. The correlation with 5-cm soil moisture is more significant at shorter wavelengths. However, this study obtained surface spectral radiation characteristics that were affected by land surface vegetation coverage as well as by soil physical properties.

Effect of tillage practices on net carbon flux and economic parameters from farmland on the Loess Plateau in China

It is important to evaluate the effect of tillage practices on carbon flow and economic parameters in order to better understand soil carbon sequestration and mitigation of carbon release into the atmosphere, and to increase income for farmers. A 2-year field experiment was conducted in a winter wheat-summer corn rotation system on dryland farmland on the Loess Plateau in Northwest China with four treatments; zero tillage with straw mulching (zero tillage), rotary tillage with straw incorporation (rotary tillage), chisel plow tillage with straw incorporation (chisel plow), and conventional mouldboard plow tillage without crop straw (conventional tillage). Results showed that zero tillage reduced carbon emissions, mainly through reduction of emissions from tillage practices, and served as a net carbon sink, as did rotary tillage and chisel plow, while conventional tillage served as a net carbon source. Specifically, zero tillage reduced carbon emissions from farm inputs by 168.8 and 75.0 kg C ha−1 yr−1 compared with conventional tillage and rotary tillage (or chisel plow), respectively. The difference in annual rate of carbon sequestration between 2013 and 2015 was 1.21-fold higher with zero tillage than with conventional tillage, suggesting zero tillage released less CO2 and was therefore better able to mitigate against global warming. Chisel plow significantly (P < 0.05) improved net return values by 10.7%–63.2% in the 2013-14 cropping year and by 12.8%–93.7% in the 2014–15 cropping year, respectively when compared to other tillage treatments. Zero tillage was the most effective method for reducing carbon inputs and increasing carbon sequestration, and chisel plow was the best option for provision of economic parameters on dryland farmland in this region. Therefore, the application of conservation (zero, rotary and chisel plow) tillage could be a C-smart and effective economic agricultural practice for winter wheat-summer corn ecosystems under rain fed condition.

Soil and plant components ecological stoichiometry in four steppe communities in the Loess Plateau of China

Grazing exclusion and vegetation restoration practices are the major ecosystem restoration measures that can address ecosystem degradation due to overgrazing and intensive farming in the Loess Plateau in northwest China. We examined plant tissue (root, litter, and living biomass) nutrients of the four most dominant steppe species (Artemisia gmelinii (AR), Thymus mongolicus (TH), Stipa bungeana (ST), and Agropyron cristatum (AG)), and their ecological stoichiometry characteristics. Our results indicated that vegetation types had significant effects on soil nutrients and soil ecological stoichiometry characteristics. TH soils had the highest concentrations of total C, total N and total P, and AR soils had the lowest concentrations of total C and total N. TH species had the greatest effects on improving soil nutrients. The concentrations of total N and total P differed with different plant tissues (P<0.01). Living biomass had higher total N and total P than roots and litter in terms of the exit of nutrient resorption efficiency. However, total C remained in a narrow range for the different tissues. To determine which tissue of the different steppe species was more suitable in terms of plant nutrition limitations, we used N:P ratios in different tissues to estimate the nutrition limitation for the plant growth based on previous studies. Living biomass N:P ratios were significantly correlated with root N:P ratios (P<0.001), reflecting that underlying physiological processes are coordinated among plant tissues. We concluded that TH had the greatest effects on improving soil nutrients after grazing exclusion. Root N:P ratios could also be used to indicate the nutrition limitation for steppe species.

Comparative field tests on uplift behavior of straight-sided and belled shafts in loess under an arid environment

This study elucidates the uplift behaviors of the straight-sided and belled shafts. The field uplift load tests were carried out on 18 straight-sided and 15 belled shafts at the three collapsible loess sites under an arid environment on the Loess Plateau in Northwest China. Both the site conditions and the load tests were documented comprehensively. In general, the uplift load-displacement curves of the straight-sided and belled shafts approximately exhibited an initial linear, a curvilinear transition, and a final linear region, but did not provide a well defined peak or asymptotic value of the load, and therefore their uplift resistances should be interpreted from the load test results using an appropriate criterion. Nine representative uplift resistance interpretation criteria were used to define the "interpreted failure load" for each of the load tests, and all of these interpreted uplift resistances were normalized by the failure threshold, <TEX>$T_{L2}$</TEX>, obtained using the <TEX>$L_1-L_2$</TEX> method. These load test data were compared statistically and graphically. For the straight-sided and belled shafts, the normalized uplift load-displacement curves were respectively established by the plots that related the mean interpreted uplift resistance ratio against the mean displacement at the corresponding interpreted criteria, and the comparisons of the normalized load-displacement curves were made. Specific recommendations for the designs of uplift belled and straight-sided shafts in the loess were given, in terms of both capacity and displacement.

Canopy transpiration of Pinus tabulaeformis plantation forest in the Loess Plateau region of China

Transpiration is a significant hydrological process. Thus, the knowledge on the transpiration of Pinus tabulaeformis obtained from this study should be useful in water balance estimation and ecological vegetation construction and management. The variation in the sap flow of a mature P. tabulaeformis and the environmental conditions in the Anjiagou catchment located in the Loess Plateau of Northwest China during the growing season of 2014 were investigated. Based on the relative extractable water (θe), soil water conditions were classified into water stress (θe 0.425) conditions. Obvious differences were found between the responses of transpiration and its sensitivity to meteorological factors under the two different soil moisture conditions. During the entire growing season, the maximum and minimum daily stand transpiration (Es) rates were 2.18 and 1.39 mm day−1, with a mean Es of 1.83 mm day−1. The total Es from May to September was 277.68 mm. Es was linearly related to solar radiation but logarithmically related to vapor pressure deficit, variable of transpiration, and reference evapotranspiration under both soil moisture conditions. The sensitivity of Es to meteorological factors significantly decreased with increasing water stress conditions. These results not only provide a basis for the detailed analyses of water physiology and the growth of P. tabulaeformis plantations for the later application of a climate driven process model but also offer implications for forest management in the Loess Plateau of China.

Experimental and Stress-Strain Equation Investigation on Compressive Strength of Raw and Modified Soil in Loess Plateau

As a special kind of soil is widely distributed in Loess Plateau of northwest China, it is difficult to use for growing crops and has poor structural property. According to local arid climate, the best utilization of the soil is as earthen construction material and it has been used for thousands of years. To research and improve the mechanical properties, the study investigates the response of soil with cement, lime, sand, and straw as admixtures to compressive loading. The influence on compressive strength and ductility of additives in different proportions is compared and analysed. The experimental data is also used for the formulation of dimensionless and generalized models describing the raw soil and modified soil’s full stress-strain response. The models can be applied to soil and modified soil in Loess Plateau with variable strength and deformation characteristics and therefore may be exploited for earthen construction design and nonlinear structural analyses.