Semi-arid Region Of China Research Articles

Targeted control measures for improving the environment in a semiarid region of China

Land degradation results from the interactions among multiple climate and human factors. Solving the problem requires a holistic strategy that deals with all significant factors simultaneously. However, it is difficult to solve such problems because few researchers have studied the simultaneous effects of these interactions, making it difficult to develop a truly holistic strategy. To help land managers find such a strategy, we have proposed and tested a new approach for ecological restoration in which we calculated the simultaneous contributions of multiple factors during vegetation cover change in Yan'an City, Shaanxi Province, China, from 2000 to 2016. After implementing the new approach, the vegetation cover increased by 35.7% during the study period, which is 2.3 times the rate in the rest of Shaanxi Province, where only the national Grain for Green program was implemented. The new approach accounted for 74.0% of the increased vegetation cover in the first year, and comparable values in the second and third years. Our results provide important information to guide sustainable development in China, and our approach can be adapted for use in other nations that are facing similar problems.

A New Method for Mapping Aquatic Vegetation Especially Underwater Vegetation in Lake Ulansuhai Using GF-1 Satellite Data

It is difficult to accurately identify and extract bodies of water and underwater vegetation from satellite images using conventional vegetation indices, as the strong absorption of water weakens the spectral feature of high near-infrared (NIR) reflected by underwater vegetation in shallow lakes. This study used the shallow Lake Ulansuhai in the semi-arid region of China as a research site, and proposes a new concave–convex decision function to detect submerged aquatic vegetation (SAV) and identify bodies of water using Gao Fen 1 (GF-1) multi-spectral satellite images with a resolution of 16 meters acquired in July and August 2015. At the same time, emergent vegetation, “Huangtai algae bloom”, and SAV were classified simultaneously by a decision tree method. Through investigation and verification by field samples, classification accuracy in July and August was 92.17% and 91.79%, respectively, demonstrating that GF-1 data with four-day short revisit period and high spatial resolution can meet the standards of accuracy required by aquatic vegetation extraction. The results indicated that the concave–convex decision function is superior to traditional classification methods in distinguishing water and SAV, thus significantly improving SAV classification accuracy. The concave–convex decision function can be applied to waters with SAV coverage greater than 40% above 0.3 m and SAV coverage 40% above 0.1 m under 1.5 m transparency, which can provide new methods for the accurate extraction of SAV in other regions.

Variations in the Ice Phenology and Water Level of Ayakekumu Lake, Tibetan Plateau, Derived from MODIS and Satellite Altimetry Data

The alpine lakes on the Tibetan Plateau (TP) are highly sensitive to variations in climate changes, and the lake ice phenology and water level are considered to be direct indicators of regional climate variability. In this study, we first used 14 years of moderate resolution imaging spectroradiometer snow cover products to analyse the freeze dates, ablation dates, and ice coverage durations. The lake level changes during 2002–2015 were estimated, derived from satellite altimetry and Hydroweb data. Unexpectedly, the freeze dates of lake ice greatly advanced, and the ablation dates were markedly delayed. The complete freezing duration lengthened by approximately 77 days. As a result of the warm-wet climate in the northern TP, the lake area expanded from 770 to 995 km2 during 2002–2015, and the water levels rose by 4.2 m in total, at a rate of 0.3 m/year. The progressive expansion of Ayakekumu Lake profoundly affected the ice phenology. Larger water volume with larger thermal capacity likely led to the delaying of ablation dates, with the freezing point depression caused by decreasing salinity. Some new narrow and shallow bays located in southern and eastern Ayakekumu Lake were conducive to early freezing of ice. Additionally, the changes in air temperature, precipitation, potential evaporation, and sunshine duration may be related to the prolonged ice cover duration since 2002. In sum, accurate measurements of lake ice and water levels are critical for understanding the water resource balance and hydrologic cycle in arid or semi-arid regions of China.

Tillage and deficit irrigation strategies to improve winter wheat production through regulating root development under simulated rainfall conditions

Knowledge of rooting systems and soil water status across rooting zones is important for stabilizing agricultural productivity in the semi-arid regions of China. In the present study, a mobile rainproof shelter trial was performed to find out the effects of cultivation mode on the temporal and spatial root growth distribution, soil water content, root respiration rate, and grain yield during 2015–2016 and 2016–2017 growing seasons. The two cultivation modes were: (1) the ridge furrow (RF) rainfall harvesting technique; and (2) traditional flat planting (TF). In addition, three simulated rainfall (1: 275, 2: 200, 3: 125 mm) and two deficit irrigation (150, 75 mm) levels were used. Our results showed that different cultivation modes with simulated precipitation levels significantly improved moisture content for wheat growth, improved root growth, and provided favourable conditions for higher wheat production. The RF150 treatment with 200 mm rainfall significantly increased morphology of the wheat rooting system, especially in the top 40 cm soil layer compared with TF cultivation. The RF150 treatment significantly increased root dry weight (47%), root tissue density (6.7%), root fineness (4.8%), root length ratio (20.3%), root mass ratio (27.3%), and grain yield (18.9%) of wheat at 200 mm rainfall than that of TF2150 treatment. Root weight density, root length density, root surface area density, and root diameter were significantly higher under RF150 treatment with 200 mm and 275 mm precipitation in the 40 cm soil layer and reached maximum values at the flowering stage. The root dry weight, root respiration rate, and grain yield were significantly improved under RF2150 treatment, but there were no significant differences when the rainwater increased from 200 to 275 mm under both cultivation modes. Therefore, we suggested that the RF2150 treatment is a suitable water saving strategy to improve temporal and spatial root growth distribution, resulting in higher grain yield in a dry-land farming system.

Effects of different fertilizer strategies on soil water utilization and maize yield in the ridge and furrow rainfall harvesting system in semiarid regions of China

Shortages of water resources and low soil fertility are two key factors that limit crop production in semiarid areas. The ridge and furrow rainfall harvesting (RFRH) system is an effective method for enhancing the efficiency of rainfall water use and fertility. In this study, we conducted a field experiment over five years (2012–2016) to determine the effects of different fertilizer application rates on the soil water consumption properties, water use efficiency, and maize yield under RFRH. We found that the evapotranspiration (ET), maize dry matter (DM), water consumption strength (CD), and soil water use rate (SP) increased with the fertilizer application rate. Compared with the no fertilizer treatment (RCK), ET, DM, CD, and SP increased significantly by 7.2%, 38.3%, 16.4%, and 37.6% under high fertilizer (RH) treatment, respectively, by 6.7%, 35.8%, 18.0%, and 39.1% with medium fertilizer (RM) treatment, and by 5.5%, 31.1%, 16.1%, and 32.6% with low fertilizer (RL) treatment. RM achieved the highest average yield of 11.3 t ha–1 and the lowest coefficient of variation at 12.9%. The yield, DM, and water use efficiency did not differ significantly between RH and RM. Regression analysis showed that the highest yield could be obtained by applying nitrogen at 265.0 kg ha–1 combined with P2O5 at 132.5 kg ha–1. The yield and water use efficiency were significantly higher under RL compared with RH and RM in wet year. However, in both normal and drought years, the grain yield and water use efficiency was significantly higher under RM. These results indicate that the RFRH system can promote crop use of fertilizers by regulating soil moisture. The best fertilization strategy for planting maize with RFRH system was 265.0 kg ha–1 of pure nitrogen combined with 132.5 kg ha–1 of P2O5 in the semiarid area of the Loess Plateau, in China.

Estimating water consumption based on meta-analysis and MODIS data for an oasis region in northwestern China

A severe water shortage in arid and semiarid regions in China has triggered regulations limiting the use of irrigation water in desert-oasis agricultural systems. To determine the actual water demand of agricultural systems and to develop standards for a rational use of water resources, maize evapotranspiration rates was simulated using meta-analysis of published data, determined land-use and soil properties in Zhangye oasis area and then estimated water consumption with MODIS for arid northwestern China for the 2014 growing season. Farmland in Zhangye oasis totaled 2189.88 km2 and accounted for 25.41% of the total oasis area; crop-protecting forestland totaled 8.56 km2 and accounted for 0.10% of the total oasis area, grassland and unutilized land accounted for 1.85%, 71.48% of the total oasis area, respectively. Soil moisture capacity at saturation ranged from 21.0 to 33.0% and at field capacity from 21.0 to 31.5%. Soil bulk density ranged from 1.36 to 1.58 g cm−3. Using meta-analysis, the simulated maize evapotranspiration rate was 655.91± 20.53 mm. During 2014 growing season, minimum, optimum and maximum water consumption used for agricultural yields and oasis stability was 1.14×109 m3, 1.46×109 m3 and 1.75×109 m3, respectively. In future research, increased big picture and high frequency data will allow operational monitoring of water use and requirements and irrigation at a regional scale.

Potential and environmental control of carbon sequestration in major ecosystems across arid and semi-arid regions in China

With the continuous expansion of drylands in the context of global climate change, governments have implemented a series of greening policies such as afforestation, to reduce ecological degradation. However, owing to historical conditions and technical constraints, few attempts have been made to quantitatively assess the differences in carbon sequestration capacity and the associated environmental controls among major ecosystems in the arid and semi-arid areas. Based on six flux towers located in northwestern China measuring the carbon fluxes in a maize (Zea mays L.) cropland, alpine meadow, wetland, swamp meadow, Tamarix, and gobi desert, this work revealed that all ecosystems sequestered CO2 at various magnitudes. The cropland had the highest carbon uptake, followed by the alpine meadow, swamp meadow, wetland and Tamarix, respectively. Distinct seasonal dynamics in carbon sequestration were observed across these ecosystems with the peak values in summertime, whereas the gobi desert exhibited as a weak carbon sink with considerable fluctuations around the year. In this water-limited region, soil water content instead of rainfall, is expected to be the primary environmental control on the land–atmosphere carbon fluxes, and regarded as a key linkage between hydrologic and ecologic processes. Therefore, not only the appropriate vegetation types, but also the water availability controlled by the local climatic constraints and soil characteristics, should be addressed in order to identify management strategies for ecological restoration in the dry areas.

The impacts of land conversion and management measures on the grassland net primary productivity over the Loess Plateau, Northern China

In the 1990s, the Chinese government began implementation of a series of national-scale restoration programs to combat environmental degradation. As one of most important arid and semiarid regions of China, the Loess Plateau has attracted attention related to the effectiveness of these initiatives. The present study analyzed land use and cover change (LUCC) of the grassland in the Loess Plateau and the consequent change in net primary productivity (NPP) based on a consecutive land use data derived from the European Space Agency Climate Change Initiative land cover maps and the CASA (Carnegie-Ames-Stanford Approach) model driven by MODIS-NDVI data. The contributions of climate variation and human activities (including land conversion and management measures) to these changes were also quantitatively differentiated. The results indicated that the area of the Loess Plateau grassland experienced a net increase of 0.43 × 104 km2 over the study period. The total NPP of the Loess Plateau grassland increased by 11,325.13 Gg C·yr−1, of which the human activities and climate variation were responsible for 78.45% and 21.55%, respectively. The land conversion reduced the grassland NPP by 308.60 Gg C·yr−1, whereas management measures increased the NPP by 9197.97 Gg C·yr−1 in the otherwise unmodified grassland. Overall, ecological restoration programs have effectively increased grassland NPP in the Loess Plateau. However, human activities played both positive and negative impacts in this process.

Ridge-furrow mulched with plastic film improves the anti-oxidative defence system and photosynthesis in leaves of winter wheat under deficit irrigation.

In semi-arid areas of China, the ridge-furrow mulched with plastic film (RF) cultivation system is a common water-saving agricultural technique where the shortage of water resources has become a serious problem. Therefore, we aimed to explore whether this cultivation is actually an improvement over the traditional flat planting (TF) method while testing two deficit irrigation (150, 75 mm) levels to grow winter wheat. Furthermore, we examined the responses of the anti-oxidative defence system and photosynthetic capacity of winter wheat flag leaves under three simulated rainfall (275, 200 and 125 mm) conditions. The results showed that the RF system with 150 mm deficit irrigation and 200 mm simulated rainfall condition (RF2150) treatment raised soil water content (%) at the jointing and flowering stages and achieved higher net photosynthesis rates (Pn) in flag leaves. Furthermore, such improvements were due to the reduction of malondialdehyde (MDA) content and oxidative damage during different growth stages of winter wheat. The RF2150 treatment significantly increased the activities of superoxide dismutase (SOD); peroxidise (POD), catalase (CAT) and ascorbate peroxidase (APX) and the content of soluble protein (SP) during different growth stages of winter wheat. Furthermore, RF2150 treatment attained the highest value at the flowering stage, while also exhibiting significant declines in contents of proline, MDA, H2O2 and O2 in flag leaves. The higher free H2O2 and O2 scavenging capacity and better anti-oxidative enzyme activities under the RF2150 treatment were due to the lower level of lipid peroxidation, which effectively protected the photosynthetic machinery. The net photosynthetic rate of flag leaves was positively correlated with SOD, POD, CAT, APX and SP activities, and negatively correlated with proline, MDA, H2O2 and O2 contents. We concluded that the RF2150 treatment was the better water-saving management strategy because it significantly delayed flag leaf senescence and caused the increases in SWC, WUE, Pn, antioxidant enzyme activities and grain yield of winter wheat grown in semi-arid regions of China.

Wheat straw mulching with fertilizer nitrogen: An approach for improving soil water storage and maize crop productivity

Field studies using wheat straw mulching effects on soil water storage and maize development were conducted in China. The studies contained four treatments during three years (2014–2016): CK (no straw and no nitrogen); N (no straw mulching with 172 kg N/ha); HS + N (half straw mulching at the rate of 2500 kg/ha with 172 kg N/ha), and FS + N (full straw mulching at the rate of 5000 kg/ha with 172 kg N/ha). The FS + N treatment significantly increased soil water storage in a drought period during crop growth stages and promoted plant growth along with increased evapotranspiration. The FS + N treatment increased the soil water storage (26.5, 19.9 and 11.1 mm), grain yield (28.7, 6.93 and 2.4%), and water use efficiency (26.6, 6.64 and 2.40%) compared to CK, N and HS + N, respectively. In conclusion, compared to N, HS + N or FS + N increased the biomass (11 and 19%) and water use efficiency (4 and 5%), respectively, and are considered beneficial in Guanzhong, China. Mulching levels were superior to N and compensated the wheat nitrogen requirements. Thus, further studies with minimum fertilizer nitrogen for an environmentally friendly and effective approach are recommended in semiarid regions of China.

Spatio-Temporal Changes in Potential Evaporation and Possible Causes Based on SCRAQ Method: A Case Study in the Wei River Basin, China

Kong, B.; Huang, S.; Ma, L., and Huang, Q., 2018. Spatio-temporal changes in potential evaporation and possible causes based on SCRAQ method: A case study in the Wei River Basin, China. In: Wang, D. and Guido-Aldana, P.A. (eds.), Select Proceedings from the 3rd International Conference on Water Resource and Environment (WRE2017). Journal of Coastal Research, Special Issue No. 84, pp. 94–102. Coconut Creek (Florida), ISSN 0749-0208.It is important for regional agricultural production as well as water resources planning and management to better understand the spatial and temporal variations of potential evaporation (PET) and their possible causes from a perspective of climate change. In this study, the spatial and temporal changes in monthly and annual PET covering 1960~2006 in the Wei River Basin (WRB), a typical arid and semi-arid region in China, were thoroughly examined based on the modified Mann-Kendall trend test method. Additionally, the slope change ratio of accumulative quantity (SCRAQ) method was used to quantify the effects of precipitation, air temperature, percentage of sunshine, and wind speed on PET variations. Results indicated that: (1) the PET in this basin gradually increased from west to east, which had general negative correlations with its corresponding elevation; (2) the WRB was dominated by increasing monthly PET, and obviously decreasing tendencies were observed in summer in the middle basin; (3) the decreasing PET in 1974–1993 in the whole basin was primarily caused by the decreasing percentage of sunshine, whilst the increasing PET in 1994–2006 is mainly induced by the upward air temperature in the WRB.

Effect of ridge-covering mulching materials on hormonal changes, antioxidative enzyme activities and production of maize in semi-arid regions of China

The objectives of this study was to investigate the effect of different ridges covered mulching materials on maize production under different simulated rainfall levels and the relationship with anti-oxidant enzyme activities in leaves and hormonal changes in grains. In the present study, conventional flat cultivation (CK) was compared with several ridge covered mulching materials (PM: plastic film, BM: biodegradable film, SC: soil crust ridges) under 320 mm and 430 mm simulated rainfall levels. The results clearly indicated that the effect of ridge covering mulching materials on antioxidant enzyme activities and hormonal changes of maize were significantly related to precipitation levels. At 430 mm rainfall level, PM significantly promoted indole-3-acetic acid, zeatin + zeatin riboside and abscisic acid contents and decreased ethylene, and gibberellic acid contents in superior, middle and inferior seeds as compared with CK430 treatment. At 430 mm rainfall level, PM significantly increased soil water storage, characteristics of ear, antioxidant enzyme activities in leaves, hormonal changes in seeds and reducing lipid peroxidation which led to increased (43.1%) grain yield of maize than that of CK430 treatment. At 430 mm rainfall level and ridges covered with plastic film significantly increased the activities of peroxidase (33.5%), catalase (76.0%) and superoxide dismutase (43.6%) at grain filling stage, while activity of malondialdehyde (MDA) concentration in leaves significant rise and reached up to maximum (16.7 μmol g−1 FW) value at maturity stage under conventional flat planting. Based on these results, we conclude that the PM treatment with 430 mm simulated rainfall significantly increased the soil water storage, adjusting antioxidant enzyme activities in leaves, debasing lipid peroxidation and balance of hormones in the grains as a result improve maize productivity under semi-arid regions of China.

Interactive effects of planting models with limited irrigation on soil water, temperature, respiration and winter wheat production under simulated rainfall conditions

The development of effective water-saving farming practices have been vitally important for increasing wheat productivity in semi-arid regions of China. Ridge-furrow (RF) rainfall harvesting is a technique for efficient consumption of precipitation that increases water accessibility to crops at critical growth stages. However, this system has not yet been characterized under simulated rainfall conditions with limited irrigation. A two-year field study was carried out from Oct 2015 to May 2017 to investigate the potential role of two planting models: (1) the RF system and (2) traditional flat planting (TF) under three levels of simulated precipitation (1:275 mm, 2: 200 mm, 3:125 mm), with two limited irrigation levels (150 mm or 75 mm). The topsoil (from 5 to 25 cm) temperature and ET were significantly higher under TF planting than in the RF system, which increased both soil moisture between (0–200 cm) and soil respiration rate during different growth stages. The RF system also regulated soil temperature and respiration rate, reduced ET (46%), and prolonged the period of water accessibility which led to exhibited fast and stable seedling establishment. The average grain yield increased by 10.6% and 12.6% for RF1150 and RF175, compared to TF1150 and TF175, and increased by 18.9% and 22.5% for RF2150 and RF275 as compared to TF2150 and TF275, while RF3150 and RF375 treatments significantly increased by 14.3% and 8.9% as compared to TF3150 and TF375, respectively. Average WUE significantly improved by (P < 0.05) in RF1150, RF175, RF2150, RF275, RF3150, and RF375 were 53.3%, 56.4%, 75.8%, 85.1%, 68.2% and 75.3% compared to TF planting, respectively. As precipitation increased from 200 to 275 mm there were no significant increases in moisture contents, soil respiration rate, ET, WUE, and grain yield under both planting models. Therefore, we concluded that the RF2150 treatment is suitable as a water-saving technology to achieve higher wheat production and WUE in semi-arid agro-ecosystems of China.

Performance of common buckwheat (Fagopyrum esculentum M.) in response to row spacing under ridge and furrow cropping systems in a semiarid region of China

ABSTRACTRidge and furrow systems as well as the wide-narrow row spacing are recognized as good management practices in crop production. To obtain some available information concerning the suitable agricultural practices for buckwheat cultivation in arid and semi-arid area, a two-year field study was conducted to investigate the performance of common buckwheat grown under six cropping patterns: conventional flat single/double row planting (NS/ND); furrow single/double row planting (FS/FD); ridge single/double row planting (RS/RD); single row planting with equal row spacing and double row planting with wide-narrow row spacing practice. Plants grown under the FD system exhibited higher water use efficiency (WUE) and rainfall use efficiency (RUE) than plants cultivated with the NS system, increases with 13.7% and 21.9%, respectively, in 2014, while 9.8% and 14.0%, respectively, in 2015. Plants of the FD system also displayed the greatest leaf area index and canopy openness at growth stage of 40, 60, and 80 days after sowing, maximum biomass production (13.96 t ha−1) and grain yield (3486.2 kg ha−1) in 2014, and the least pronounced soil nitrate consumption as compared to plants from other tillage systems. We conclude that FD is the optimum planting pattern for common buckwheat cultivation in semi-arid and arid environments.

Integrating Airborne LiDAR and Optical Data to Estimate Forest Aboveground Biomass in Arid and Semi-Arid Regions of China

Forest Aboveground Biomass (AGB) is a key parameter for assessing forest productivity and global carbon content. In previous studies, AGB has been estimated using various prediction methods and types of remote sensing data. Increasingly, there is a trend towards integrating various data sources such as Light Detection and Ranging (LiDAR) and optical data. In this study, we constructed and compared the accuracies of five models for estimating AGB of forests in the upper Heihe River Basin in Northwest China. The five models were constructed using field and remotely-sensed data (optical and LiDAR) and algorithms including Random Forest (RF), Support Vector Machines (SVM), Back Propagation Neural Networks (BPNN), K-Nearest Neighbor (KNN) and the Generalized Linear Mixed Model (GLMM). Models based on the RF algorithm emerged as being the best among the five algorithms irrespective of the datasets used. The Random Forest AGB model, using only LiDAR data (R2 = 0.899, RMSE = 14.0 t/ha) as the input data, was more effective than the one using optical data (R2 = 0.835, RMSE = 22.724 t/ha). Compared to LiDAR or optical data alone, the AGB model (R2 = 0.913, RMSE = 13.352 t/ha) that used the RF algorithm and integrated LiDAR and optical data was found to be optimal. Incorporation of terrain variables with optical data resulted in only slight improvements in accuracy. The models developed in this study could be useful for using integrated airborne LiDAR and passive optical data to accurately estimate forest biomass.

Limited irrigation and planting densities for enhanced water productivity and economic returns under the ridge-furrow system in semi-arid regions of China

In the semi-arid regions of China, ridge-furrow (RF) planting system is being gradually implemented, in order to improve the soil moisture status and water utilisation efficiency. This study aimed to improve the efficiency of the RF system by investigating the effects of three planting densities (L: 52,500 plants ha−1; M: 75,000 plants ha−1; H: 97,500 plants ha−1) and four kinds of limited irrigation modes (NI: no irrigation; IV: irrigation at the vegetative stage with 11 leaves; IS: irrigation at the silking stage; and IVS: irrigation at the vegetative and silking stages). Maize (Zea mays L.) plants mainly consumed the top surface of (0–60 cm) soil water, whereas the deep layer (120–200 cm) of soil moisture was less affected under the RF system, and the average soil water storage of 0–60, 60–120, and 120–200 cm decreased by 58.7, 39.1, and 7.1 mm, respectively, during the entire growth period. Limited irrigation at the vegetative and silking stages had a positive effect on biomass, leaf area index, and evapotranspiration, but did not significantly increase grain yield, water use efficiency (WUEG), irrigation WUE (IWUEG), and irrigation water productivity (IWPG). The average data obtained over two years showed that medium planting density with limited irrigation at the silking stage (M-IS) treatment significantly increased WUEG, IWUEG, and IWPG by 5.7, 98.5, and 92.6%, respectively, compared with those in the M-IVS treatment. Economic benefit analysis also showed that M-IS treatment resulted in greater net profit (2313.3 USD ha−1). Thus, the M-IS treatment could be a suitable planting model for improving maize grain yield, economic benefit, and water use in the semi-arid regions of China.

Growth performance and weed control effect in response to nitrogen supply for switchgrass after establishment in the semiarid environment

Switchgrass (Panicum virgatum L.) adapts to a wide range of environments. It has been successfully planted in a semiarid region of China’s Loess Plateau as a valuable forage species for restoring vegetation of grassland. However, growth performance of switchgrass needs to be further evaluated after establishment. Relationships between switchgrass growth and outcomes of weed control in terms of nitrogen (N) supply are especially not well understood. Field studies were conducted in 5-year and 8-year switchgrass stands at two semiarid sites. Nitrogen fertilizer (ammonium nitrate) was supplied at rates equivalent to 0 kg N ha−1, 120 kg N ha−1, and 240 kg N ha−1 in switchgrass stands consisted of three upland cultivars (Blackwell, Cave-in-Rock and Pathfinder). A split-plot experimental design was employed with 3 replications. Switchgrass and its associated weed growth were assayed. Switchgrass growth and production were generally improved with N rate increasing, although there were some cultivar and location variations. Cave-in-Rock switchgrass had advantages over other cultivars in plant height, biomass and seed production, as well as weed control effect. The N rate of 120 kg N ha−1 was suggested for seed production of switchgrass. In switchgrass stands, weed density was increased with N rate increasing, whereas biomass was decreased. Weed density was positively related with switchgrass height (P < 0.05), whereas weed biomass were negatively regressed with switchgrass height, tiller density and biomass (P < 0.05). These results demonstrate that N supply is necessary for established switchgrass stands, because there are production and weed control benefits from fertilizing switchgrass with N supply rate of 240 kg N ha−1. Practical implications of this study are that culture practices, such as cultivars selection, N management and integrated weed management strategy will contribute to the productivity of established switchgrass stands in the semiarid Loess Plateau.

Simulation of soil water and heat flow in ridge cultivation with plastic film mulching system on the Chinese Loess Plateau

A widespread measure for improvement of soil water use efficiency (WUE) in the semi-arid region of China is ridge cultivation with plastic film mulching system. However, the modification of soil water and heat flow under this management system is not well understood. The objective of this study was to understand soil water and heat coupling processes by monitoring and modeling of soil water and temperature dynamics in this system that is commonly used on the semi-arid Chinese Loess Plateau. Four treatments were investigated: conventional fertilization (CK, control), recommended fertilization (RF), straw mulching based on RF (SM), and straw mulching in furrows plus plastic film mulching on soil ridges based on RF (FM). Based on the field monitoring results, the process-based model HYDRUS-2D was calibrated to simulate the soil hydrothermal processes for the different treatments, each represented by specific boundary conditions at the soil surface. The model simulations have a good agreement with the field observation, showed that there are significant differences in soil water contents (5%) among the four treatments, with the FM treatment having the highest water storage and the highest WUE. While soil daily mean temperature was very similar, the daily temperature fluctuations were significantly higher under the plastic film mulching compared to the other treatments. The FM treatment performed better during the cold year than a warm year, improved crop production and water resource use through reduced evaporation and elevated transpiration. The modeling approach presented here is an efficient way to clarify the mechanisms of root-zone water and temperature dynamics under mulching and/or tillage that could be adopted for optimizing soil hydrothermal management in this region.

Validation of a Process-Based Agro-Ecosystem Model (Agro-IBIS) for Maize in Xinjiang, Northwest China

Agricultural oasis expansion and intensive management practices have occurred in arid and semiarid regions of China during the last few decades. Accordingly, regional carbon and water budgets have been profoundly impacted by agroecosystems in these regions. Therefore, study on the methods used to accurately estimate energy, water, and carbon exchanges is becoming increasingly important. Process-based models can represent the complex processes between land and atmosphere among agricultural ecosystems. However, before the models can be applied they must be validated under different environmental and climatic conditions. In this study, a process-based agricultural ecosystem model (Agro-IBIS) was validated for maize crops using 3 years of soil and biometric measurements at Wulanwusu agrometeorological site (WAS) located in the Shihezi oasis in Xinjiang, northwest China. The model satisfactorily represented leaf area index (LAI) during the growing season, simulating its peak values within the magnitude of 0–10%. The total biomass carbon was overestimated by 15%, 8%, and 16% in 2004, 2005, and 2006, respectively. The model satisfactorily simulated the soil temperature (0–10 cm) and volumetric water content (VWC) (0–25 cm) of farmland during the growing season. However, it overestimated soil temperature approximately by 4 °C and VWC by 15–30% during the winter, coinciding with the period of no vegetation cover in Xinjiang. Overall, the results indicate that the model could represent crop growth, and seems to be applicable in multiple sites in arid oases agroecosystems of Xinjiang. Future application of the model will impose more comprehensive validation using eddy covariance flux data, and consider including dynamics of crop residue and improving characterization of the final stage of leaf development.

Enlargement of the semi-arid region in China from 1961 to 2010

Due to spatial and temporal heterogeneity in moisture conditions, the responses of arid/humid climate regions (AHCR) to climate change are complex. In this study, we delineated the AHCR of China using information about the balance of the atmospheric water supply and demand collected from 581 meteorological stations over the past 50 years. We also analyzed inter-decadal shifts and linear trends in the AHCR and examined the influence of precipitation and reference evapotranspiration. The results indicate that the semi-arid region expanded significantly over the last five decades, mainly in northwest China, northern China, and the Tibetan Plateau and, by the 2000s, had increased by 33.53% relative to its extent in the 1960s; in contrast, the arid region shrank by 20.75%. The semi-arid region grew mainly because of transfers from the arid region in western China and the sub-humid region in eastern China. The decreased reference evapotranspiration and significantly increased precipitation together contributed to the expansion of the semi-arid region in northwest China and the Tibetan Plateau over the last 50 years. In contrast, the expansion of the semi-arid region in Inner Mongolia and northern China reflects the counteractive influence of decreased reference evapotranspiration and decreased precipitation.