Semi-humid Regions Research Articles

Drought Characteristics and Its Response to the Global Climate Variability in the Yangtze River Basin, China

The frequent occurrence of drought events in humid and semi-humid regions is closely related to the global climate variability (GCV). In this study, the Standard Precipitation Evapotranspiration Index (SPEI) was taken as an index to investigate the drought in the Yangtze River Basin (YRB), a typical humid and semi-humid region in China. Furthermore, nine GCV indices, such as North Atlantic Oscillation (NAO) were taken to characterize the GCV. Correlation analysis and a joint probability distribution model were used to explore the relationship between the drought events and the GCV. The results demonstrated that there were six significant spatiotemporal modes revealed by SPEI3 (i.e., seasonal drought), which were consistent with the distribution of the main sub basins in the YRB, indicating a heterogeneity of drought regime. However, the SPEI12 (i.e., annual drought) can only reveal five modes. Precipitation Indices and El Niño/Southern Oscillation (ENSO) Indices were more closely related to the drought events. A causal relationship existed between ENSO precipitation index (ESPI), NAO, East Central Tropical Pacific Sea Surface Temperature (Nino3.4) and Northern Oscillation Index (NOI) and drought in the YRB, respectively. Drought events were most sensitive to the low NAO and high NOI events. This study shows a great significance for the understanding of spatiotemporal characteristics of meteorological drought and will provide a reference for the further formulation of water resources policy and the prevention of drought disasters.

Characterization of Humic Acids in Mountainous Meadow Soils and Burozems of the Crimea Using 13C-NMR

A comparative analysis of organic matter in the mountainous soils under the main plant communities of the Crimea was performed. The humus state of burozems and mountainous meadow soils under natural meadow vegetation and planted forests was studied using traditional methods and 13C-NMR spectroscopy for the determination of the contents of total organic carbon, carbon of humic acids and optical density of humic acid solutions. The highest humus content in the A horizon was found in the dark burozem under the beech–hornbeam forest on the Chatyr-Dag Plateau. The meadow soils of the Ai-Petri Plateau were significantly inferior in terms of humus content than the dark burozem and meadow soils of other Crimean plateaus due to the intensive anthropogenic impact on these lands until the 1970s. The lowest humus content was found in the meadow soils of the forested Ai-Petri areas because of the strong degradation of the grass cover after planting trees. The investigation of humic acids using the 13C-NMR method showed that humic acids of Crimean mountainous soils were characterized by the elevated hydrogen content, which well agreed with the content of alkyl fragments. The structural molecular composition of humic acids was dominated by aliphatic components, aromatic components being weakly expressed. At the same time, the aromaticity was somewhat higher in the cases when the soil was formed in the meadow ecosystem; it was lower in the upper soil horizons of the forest ecosystems. The degree of aromaticity of humic acids is intermediate between that of podzolic and chernozem soils, which is typical for soils of semihumid regions. The substitution of herbaceous vegetation in the course of natural overgrowing or afforestation of areas with meadow soils has led to an increase in their acidity, but it had no noticeable effect on the elemental and structural composition of humic acids.

Tree-ring response of Larix chinensis on regional climate and sea-surface temperature variations in alpine timberline in the Qinling Mountains

Tree-ring width chronologies of Larix chinensis were developed from the northern and southern slopes of the Qinling Mountains in Shaanxi Province, and climatic factors affecting the tree-ring widths of L. chinensis were examined. Correlation analysis showed that similar correlations between tree-ring width chronologies and climatic factors demonstrated that radial growth responded to climate change on both slopes. The radial growth of L. chinensis was mainly limited by temperature, especially the growing season. In contrast, both chronologies were negatively correlated with precipitation in May of the previous year and April of the current year. Spatial climate-correlation analyses with gridded land-surface climate data revealed that our tree-ring width chronologies contained a strong regional temperature signal over much of north-central and eastern China. Spatial correlation with sea-surface temperature fields highlights the influence of the Pacific Ocean, Indian Ocean, and North Atlantic Ocean. Wavelet coherence analysis indicated the existence of some decadal and interannual cycles in the two tree-ring width chronologies. This may suggest the influences of El Nino-Southern Oscillation and solar activity on tree growth in the Qinling Mountains. These findings will help us understand the growth response of L. chinensis to climate change in the Qinling region, and they provide critical information for future climate reconstructions based on this species in semi-humid regions.

Accumulation of nitrate and dissolved organic nitrogen at depth in a red soil Critical Zone

Nitrate accumulation has been reported in the top 1 m and subsurface soil (>1 m) across arid to semi-humid regions, but not in humid regions. Nitrate inventories through the whole regolith, referred to collectively as soil and saprolite, in humid regions have received little attention to date, likely due to previously assumed low nitrification rates and large nitrogen (N) losses by severe surface runoff and erosion. In order to understand if and how reactive N exists in the below ground (soil and saprolite) in humid environment, the amount of NO3−-N, NH4+-N and dissolved organic N (DON) present in the regolith to a depth of 9 m in a typical red soil Critical Zone was investigated under different land uses (upland, woodland and paddy field). The Red Soil Critical Zone Observatory is located in the subtropical Jiangxi Province, China, with a mean annual precipitation of 1795 mm and mean annual potential evapotranspiration of 1229 mm. The examined regoliths were acidic, highly weathered, and mainly clay loam to clay in texture. Results showed that on average 92% (827 ± 97 kg N ha−1) of NO3−-N and 82% (521 ± 153 kg N ha−1) of DON were stored at depth (from a depth of 1 m to the bedrock surface) in the upland regolith, while 92% (283 kg N ha−1) of NO3−-N and 78% (820 kg N ha−1) of DON were stored at depth in the woodland regolith. Nitrate N significantly accumulated with depth in the upland regolith from the 1- to 4-m depth interval (p < 0.01), while the inventory (632 ± 75 kg N ha−1) in the top 3-m zone accounted for on average 71% of the total. Dissolved organic N significantly accumulated with depth in the upland regolith from the 0- to 3-m depth interval (p < 0.01), while the inventory (408 ± 75 kg N ha−1) in the top 3-m zone accounted for on average 64% of the total. There was no significant accumulation for NH4+-N throughout the upland regolith (p = 0.35). No substantial accumulation of dissolved N was measured at depth in paddy field regoliths with different cultivation ages. The finding that large reservoirs of reactive N can exist in deep regolith rather than in the routinely investigated solum of subtropical regions shows a missing part of the terrestrial N budget and raises concerns about potential groundwater nitrate pollution.

Larix olgensis growth–climate response between lower and upper elevation limits: an intensive study along the eastern slope of the Changbai Mountains, northeastern China

Larix olgensis is a dominant tree species in the forest ecosystems of the Changbai Mountains of northeast China. To assess the growth response of this species to global climate change, we developed three tree-ring width and biomass chronologies across a range of elevations in the subalpine forests on the eastern slope of the Changbai Mountains. We used dendroclimatic analyses to study key factors limiting radial growth in L. olgensis and its variation with elevation. The statistical characteristics of chronologies suggested that elevation is a determinant of tree growth patterns in the study area. Response function analysis of chronologies with climate factors indicated that climate–growth relationships changed with increasing elevation: tree growth at high elevation was strongly limited by June temperatures of the previous year, and as elevation decreases, the importance of temperature decreased; tree radial growth at mid-elevation was mainly controlled by precipitation towards the end of the growing season of the current year. Biomass chronologies reflected a stronger climatic signal than tree-ring width chronologies. Spatial correlation with gridded climate data revealed that our chronologies contained a strong regional temperature signal for northeast China. Trees growing below timberline appeared to be more sensitive to climate, thus optimal sites for examining growth trends as a function of climate variation are considered to be just below timberline. Our study objective was to provide information for more accurate prediction of the growth response of L. olgensis to future climate change on the eastern slope of the Changbai Mountains, and to provide information for future climate reconstructions using this tree species in humid and semi humid regions.

Plastic film mulch promotes high alfalfa production with phosphorus-saving and low risk of soil nitrogen loss

Plastic film mulch and phosphorus (P) fertilization usually increase alfalfa (Medicago sativa L.) forage yield in semi-arid regions by improving soil moisture and P availability. However, this does not always occur. The present study explored the P level for highest forage yield under film mulch and the mechanism underlying yield decrease at high P levels. A six-year study was conducted with randomized blocks of split-plot design with and without plastic film mulch as main plots: M0, no film mulch with flat planting; and M1, film mulching with ridge-furrow field regimes. Four P rates were applied in sub-plots: P0, P1, P2 and P3 with 0, 9.73, 19.3 and 28.9 kg P ha–1, respectively. Film mulch greatly increased forage yield, resulting in 14% higher yield in M1P0 than in M0P3. Forage yield under mulching decreased for 19.3 and 28.9 kg P ha−1. The P rate for maximum yield was 16.1 kg P ha−1. Soil total nitrogen (N) and inorganic-N decreased at 19.3 and 28.9 kg P ha−1 with mulching compared with 9.73 kg P ha−1, and the latter was about 90% lower than that of alfalfa lands in semi-humid region. Soil microbial biomass carbon (C) and C/N ratio in microbial biomass in mulched P2 and P3 subplots were significantly lower than for P1. With mulching, soil organic C mineralization was significantly less for P3 than for P1 and P2. Shoot N/P ratio decreased with increasing P with mulching. Thus shoot N uptake for P2 and P3 mulched plots was associated with low soil N availability. It is concluded that the highest forage yield was obtained with mulching, P-saving and low risk of N loss on the semiarid Loess Plateau.

Impacts of climate change on annual diameter increment of natural Calabrian pine (Pinus brutia Ten.) forests in Kahramanmaras

The effects of global warming on climate change have been recognized in global scale and it is expected that these effects will become even more obvious in near future. The climate change, especially in arid, semi-arid, and semi-humid regions, may result in detrimental effects on forests and water resources. Turkey is among the most affected countries from climate change due to located in Mediterranean region. With the global climate change, dams and ponds also influence on tree growth. This study was carried out in Menzelet watershed dam located in Kahramanmaras, Turkey. Menzelet dam was established during 1980-1989 and water deposition started in 1990. The climate of research area is semi-arid and characterized by extreme summer drought. The purpose of this study was to investigate the local climate effects on diameter increments resulted by Menzelet Dam Lake on the naturally distributed Calabrian pine (Pinus brutia Ten.) forests. Therefore, sampling areas were chosen from two different places namely as dam site and control site. Sample plots in dam site and control site were selected from the same stand structure and have the same properties such as site index, altitude, age distribution classes and aspect. Increment cores were taken from 20 Pinus brutia trees using increment borer at breast height (1.30 m) in each sample plots and two increment cores were taken from each tree. WinDENDRO software package was used on the measurement and determination of annual diameter increment. Annual diameter increment of trees in dam site and control site were compared with independent t test using SPSS 20.0 statistical program. The relationships between annual diameter increment and climatic factors such as temperature and precipitation were evaluated using Pearson correlation analysis. According to results, there is a statistically significant difference between average annual diameter increment in dam site and control site and dam influenced forest areas positively with respect to annual diameter increment. The values of the mean annual diameter increment of the trees in dam site are greatly higher than trees in control site. According to correlation analysis, temperature increase negatively affects annual diameter increment in control site. Important increase or decrease of annual total rainfall cause more significant changes in annual diameter increment in control site compare to dam site.

Geospatial comparison of three models to predict soil properties in semi-humid region of West Bengal, India

Investigation of soil properties are important for sustainable soil nutrient management. This paper presented spatial variability of soil properties at large scale based on GIS based geostatistical model. A total 27 soil samples were collected and physio-chemical analysis in laboratory using standard methods. Three geostatistical models i.e. Inverse distance weighted, radial basis functions and ordinary kriging were used to predict spatial variability of soil properties. The ordinary krigging method has provided is the lowest RMSE, indicated the higher accuracy to predict the soil properties compared to RBF and IDW methods.

Multiple hydrological models comparison and an improved Bayesian model averaging approach for ensemble prediction over semi-humid regions

In semi-humid regions, accurate prediction of flood processes is challenging. The goal of this study is to gain more insights into the runoff generation mechanism in semi-humid regions using multiple-model comparison method and explore the Bayesian model averaging (BMA) approach to improve flood prediction. This study compares seven runoff generation models for three semi-humid catchments in northern China. Flood events were classified into three categories, low-flow, medium-flow, and high-flow, according to flood peak flow in order to quantify the performance of each model and identify the dominant runoff generation mechanism for semi-humid catchments. Based on the performances of seven runoff generation models, three BMA schemes were used to integrate these models to compare the advantages of different combination methods. For the purpose of improving the performance of BMA over semi-humid regions, a physically based BMA approach, Green-Ampt-BMA approach (G-BMA), was proposed. In the G-BMA approach, an infiltration-excess flow module was added with the surface runoff calculated using the Green-Ampt equation. Considering the heterogeneity of precipitation and underlying surface characteristics, a distribution curve of infiltration capacity was introduced to simulate runoff processes. The results show that models with saturation-excess mechanism perform well for semi-humid catchments. The saturation-excess and infiltration-excess runoff exist simultaneously in a flood process over different catchments with different ratios of infiltration-excess to saturation-excess runoff. We found that the BMA approach effectively takes advantage of each model to provide more accurate forecasts. The physically based G-BMA approach performs better than the BMA approach for semi-humid regions with high ratio of infiltration-excess surface flow, especially in reducing flood peak error and forecast uncertainty.

Spatiotemporal Variation Characteristics of Vegetative PUE in China from 2000 to 2015

Vegetative precipitation-use efficiency (PUE) is a key indicator for evaluating the dynamic response of vegetation productivity to the spatiotemporal variation in precipitation. It is also an important indicator for reflecting the relationship between the water and carbon cycles in a vegetation ecosystem. This paper uses data from MODIS Net Primary Production (NPP) and China’s spatial interpolation data for precipitation from 2000 to 2015 to calculate the annual value, multiyear mean value, interannual standard deviation, and interannual linear trend of Chinese terrestrial vegetative PUE over the past 16 years. Based on seven major administrative regions, eleven vegetation types, and four climate zones, we analyzed the spatiotemporal variation characteristics of China’s vegetative PUE. The research results are shown as follows: (1) China’s vegetative PUE shows obvious spatial variation characteristics, and it is relatively stable interannually, with an overall slight increasing trend, especially in Northwest and Southwest China. The vegetative PUE is higher, and its stability is declined in Xinjiang, western Gansu, and the southern Tibetan valley. The vegetative PUE is lower, and its stability is increased in northeastern Tibet and southwestern Qinghai. An increasing trend in vegetative PUE is obvious at the edge of the Tarim Basin, in western Gansu, the southern Tibetan valley, and northwestern Yunnan. (2) There is a significant difference in the PUEs among different vegetation types. The average PUE of Broadleaf Forest is the highest, and the average PUE of Alpine Vegetation is the lowest. The stability of the PUE of Mixed Coniferous and Broadleaf Forest is declined, and the stability of the PUE of Alpine Vegetation is increased. The increasing speed of the PUE of Grass-forb Community is the fastest, and the decreasing speed of the PUE of Swamp is the fastest. (3) There is a significant difference in the PUEs among different vegetation types in the same climate zone, the difference in vegetative PUE in arid and semiarid regions is mainly affected by precipitation, and the difference in vegetative PUE in humid and semihumid regions is mainly affected by soil factors. The PUEs of the same vegetation type are significantly different among climate zones. The average PUE of Cultural Vegetation has the largest difference, the stability of the PUE of Steppe has the largest difference, and the increasing speed of the PUE of Swamp has the largest difference.

Nitrogen mineralization indicators under semi-arid and semi-humid conditions: influence on wheat yield and nitrogen uptake

ABSTRACTThe objectives were i) to assess indicators for potential nitrogen (N) mineralization and ii) to analyze their relationships for predicting winter wheat (Triticum aestivum L.) growth parameters (yield and N uptake, Nup) in Mollisols of the semi-arid and semi-humid region of the Argentine Pampas. Thirty-six farmer fields were sampled at 0–20 cm. Several N mineralization indicators, wheat grain yield and Nup at physiological maturity stage were assessed. A principal component (PC) analysis was performed using correlated factors to grain yield and Nup. The cluster analysis showed two main groups: high fertility and low fertility soils. In high fertility soils, combining PCs in multiple regression models enhanced the wheat yield and Nup prediction significantly with a high R2 (adj R2 = 0.71–0.83). The main factors that explained the wheat parameters were associated with water availability and N mineralization indicator, but they differ according to soil fertility.Abbreviations: N: nitrogen; SOM: soil organic matter; POM: particulate organic matter; SOC: soil organic carbon; SON: soil organic nitrogen; POM-C: particulate organic carbon; POM-N: particulate organic nitrogen; Nan: anaerobic nitrogen; Nhyd: hydrolyzable N; NO3-N: cold nitrate; N205: N determined by spectrometer at 205 nm; N260: N determined by spectrometer at 260 nm; Pe: extractable P; Nup: wheat N uptake; NO3-N: inorganic N in the form of nitrate; FR: fallow rainfalls (March-Seeding rainfall); FLR: flowering rainfalls (October-December rainfall); GFR: grain filling rainfall (November rainfall); CCR: crop growing season rainfall (June-December rainfall); PCA: principal component analysis; PC: principal component; MR: multiple regression

Sap flow of black locust in response to short-term drought in southern Loess Plateau of China

Soil water shortage is a major factor influencing the ecology and hydrology of vegetation in China’s semihumid Loess Plateau. However, few studies have experimentally assessed how expected changes in precipitation will affect sap flow in semihumid forest ecosystems. In this study, we measured the sap flow of black locust (Robinia pseudoacacia Linn.) under ambient and drought (induced by throughfall exclusion) conditions in 2015 and 2016, and investigated the relationship between stand transpiration and environmental factors in the semihumid China’s Loess Plateau. Throughfall exclusion significantly decreased sap flux density and stand transpiration by 39% and 28%, respectively, in 2016, which may have been due to the cumulative droughts effect from both 2015 and 2016. Throughfall exclusion caused a significant reduction in soil moisture, leaf area index (LAI), and stem diameter. Stand transpiration was positively correlated with LAI (P < 0.01), but precipitation and soil moisture did not correlate with stand transpiration at a daily timescale, suggesting that LAI can be used as a proxy for stand transpiration. Our results highlight that precipitation must be considered when planting black locust in semihumid regions. These findings provide basic information about the management of water resources and vegetation restoration in the semihumid China’s Loess Plateau and possibly other water-limited regions around the world.

Comparison between the TOPMODEL and the Xin’anjiang model and their application to rainfall runoff simulation in semi-humid regions

To study the application of the TOPMODEL and the Xin’anjiang model to rainfall runoff simulation in semi-humid regions, the Holtan excess infiltration runoff module was added to the TOPMODEL structure. The basin of the Heihe Jinpen Reservoir in Shaanxi Province, China, was selected as the study area. Rainfall and runoff data and digital elevation models were collected. The watershed topographic parameters and 21 floods that occurred from 2005 to 2013 were obtained to simulate rainfall runoff. Results show that the improved TOPMODEL and the Xin’anjiang model can effectively stimulate rainfall runoff. The average values of their Nash coefficient are 0.84 and 0.83, respectively, upon calibration, and 0.78 and 0.80, respectively, upon validation. The Xin’anjiang model performs slightly better than the improved TOPMODEL. The results of large flood peaks are better than those of ordinary floods. Both results can be used to simulate the rainfall runoff of a watershed.

Improvement of Short-Term Climate Prediction with Indirect Soil Variables Assimilation in China

AbstractShort-term climate prediction based on a regional climate dynamical model heavily depends on atmospheric forcing and initial soil moisture state. In this study, the Weather Research and Forecasting (WRF) Model with different nudging schemes is used for approximate 2-yr simulations for investigating the importance of soil variables in seasonal temperature and precipitation simulations. The results show that the improvement of seasonal climate simulation (precipitation and air temperature) is more evident in the experiment of assimilating both soil and atmospheric variables than that in the experiments of assimilating atmospheric variables only. Further investigation of the impact of indirectly assimilating soil moisture on precipitation prediction with an indirect soil nudging (ISN) scheme shows that the precipitation reproducibility in summer is better than that in winter, and the effect of ISN is particularly prominent in the region where seasonal precipitation exceeds 200 mm. Moreover, statistical results also illustrate that initial soil moisture plays a crucial role in seasonal precipitation forecasts because of its slowly evolving nature, and its effect is more distinct in semiarid and semihumid regions than in arid and humid regions. The effects of indirectly assimilating soil moisture on precipitation can last two and three months in semiarid and semihumid areas, respectively.

How shallow and how many points of measurements are sufficient to estimate the deep profile mean soil water content of a hillslope in the Loess Plateau?

Soil water content (SWC) measurements for deep soil profiles involve large and expensive expenditures of time and labor. However, understanding of soil water dynamics for deep soil profiles is very important for soil and water resource management and hydrological modeling. This study was aimed at (1) testing whether the mean SWC for the deep profile of a hillslope could be well estimated using the SWC measurements only made at a limited number of time stable locations (TSLs), which were identified from the SWC measurements of the shallow profile (i.e., within 0–100cm) and (2) subsequently determining the optimal depth of the shallow profile and the optimal number of TSLs using the relative bias to the mean (RBM) SWC and the corrected Akaike information criterion (AICc). SWC in the 0–300cm profile was measured at 40 locations along a 243m long transect on a hillslope where is located in the semiarid region of the Chinese Loess Plateau with a mean annual precipitation (MAP) of 437mm. A total of 46 SWC measurements made over three growing seasons at each location were divided into the calibration and validation periods. The same method was repeated on the other two hillslopes in the semiarid and semi-humid regions with the MAP of 505 and 580mm, respectively, for further assessing the effect of soil moisture conditions on the optimal number of TSLs and the optimal depth of the shallow profile. Results indicated that there were significantly correlations between the spatial patterns of SWC in the shallow soil profiles (0–10, 0–20, …, 0–100cm) and that in the 0–300cm deep soil profile (p<0.01), and the mean SWC in the deep profile on the hillslope could be well estimated using the SWC measurements only at several TSLs identified from the SWC measurements in the shallow soil profile (within 0–100cm depth). Moreover, the optimal number of TSLs and the optimal depth of the shallow profile varied with soil moisture conditions. In the semiarid region, the optimal depth of the shallow profile was 0–40cm and the optimal number of TSLs varied from 2 to 3; in the semi-humid region, the optimal depth of the shallow profile was 0–30cm and the optimal number of TSLs was 3. The RBM values between the predicted and measured mean SWCs in the 0–300cm deep profile during the calibration and validation periods were in the range of 1.6 to 4.0% on three hillslopes, which are regarded as the acceptable prediction accuracy in the hydrology community. The proposed approach could greatly reduce the expenditures of time and cost in monitoring the mean SWC for the deep profile at various spatial scales and could be applied well to the regions with similar hydrological and climatic conditions.

Correlation Analysis of the Urban Heat Island Effect and Its Impact Factors in China

Urban heat islands (UHIs), which are urban areas with higher surface or air temperatures than surrounding rural areas, can further enhance the heat stress already exacerbated by global warming. This poses great challenges to human health and sustainable development. China has been burdened with heavy air pollution in recent years, and the effect of haze pollution on UHIs is still far less well understood. This study investigated the spatial variations of daytime, nighttime, and seasonal surface UHI effects in China during 2003-2013, based on MODIS land surface temperature data, and analyzed the correlations between the UHI effect and its impact factors from both biophysical and biochemical perspectives. Our results show that MODIS-derived annual nighttime UHI effect (3.4 K±0.2 K, mean±1 s.e.) is higher than the annual mean daytime UHI effect (2.1 K±0.3 K). The daytime UHI effect is strongest in summer and weakest in winter but contrasts with the seasonal variation characteristics of nighttime UHI effect. During daytime, UHI effects in humid and semi-humid regions are much more obvious than those in semi-arid/arid regions; during nighttime, the UHI effect in semi-humid and semi-arid/arid regions is much stronger than that in humid regions. A Daytime Urban Cool Island effect exists in semi-arid/arid regions during spring, autumn, and winter seasons. Population, vegetation activity, and irrigation are three factors controlling annual mean daytime UHI effect. The nighttime UHI is significantly influenced by latitude, albedo, precipitation, and aerosol concentrations. We provide evidence for a long-held hypothesis that the biogeochemical effect of urban aerosols is an important contributor to the UHI effect. The important role played by rural background environment in calculating the UHI effect is further discussed in terms of surface aerodynamic roughness and the contrast in albedo between urban and rural areas. Mitigation of haze pollution has a co-benefit of reducing the UHI effect and heat stress for urban dwellers. It is also conducive to reducing negative impacts of regional and global climate change.

Dynamics of Land Cover Change from 2001 to 2013 in China

In order to explore spatial-temporal land cover dynamics in China, we use MODIS data from 2001 to 2013 to statistic the percent of land coverage change and analyze the spatial pattern of land cover change in each natural regions. The results show that: (1) From 2001 to 2013, forest, arable land and water are increasing, and annual growth rates are 1.81%, 0.66% and 0.36% respectively. Shrubs, grassland and unused land are decreasing, and the average annual reduction rates are 2.61%, 0.51% and 0.63%. (2)In A (humid, semi-humid region in Northeast), B (warm temperate humid, semi-humid region in North China) and E (temperate steppe in Inner Mongolia) regions, the major land cover change is from grassland to arable land; in C (subtropical humid region in South and central China) and D (Tropica humid l region in South China) regions, the major land cover change is from grassland to forest; in the F (temperate and warm temperate desert region in Northwest) and G (Tibetan Plateau) regions, the major land cover change is from unused land to grassland. (3) In the Northeast China, arable land area increased; in the Tibetan plateau and northwest arid region, the utilization of unused land area increased; in central and south China, forest increased.

Effects of lateral depth and irrigation level on nitrate and Escherichia coli leaching in the North China Plain for subsurface drip irrigation applying sewage effluent

Subsurface drip irrigation is a sound method to apply sewage effluent, but there is a risk of nitrate and pathogen leaching. Field experiments were conducted during the maize growing seasons of 2014 and 2015 in the North China Plain to investigate the effects of lateral depth, irrigation level, and water quality on the deep percolation and the nitrate (NO3–N) and Escherichia coli (E. coli) leaching under semi-humid conditions. The experiments were designed with three lateral depths of 0 cm (D1), 15 cm (D2), and 30 cm (D3) beneath the soil surface along with three irrigation levels of 70% (I1), 100% (I2), and 130% (I3) of crop evapotranspiration requirements. Secondary sewage effluent and groundwater were used as irrigation water. The results indicated that the intensive rainfall caused most of the deep percolation and NO3–N leaching during the maize growing seasons. A high irrigation level usually produced more deep percolation and NO3–N leaching, but no significant difference was found among the treatments. In general, the cumulative NO3–N leaching beyond the root zone increased as lateral depth increased. In addition, the lateral depth obviously influenced the distribution of E. coli in soil, and subsurface drip irrigation usually induced E. coli contamination deeper in the soil. With relatively high nitrate and E. coli concentration, sewage effluent irrigation significantly increased the risk of NO3–N leaching beyond the root zone in the 2014 season, but imposed an insignificant influence on the presence of E. coli in soil. Furthermore, no E. coli was detected in the leachate following an irrigation event with sewage effluent or a rainfall event during the both maize growing seasons. A dripline depth of 15 cm with deficit irrigation can be conductive to reducing NO3 leaching as well as avoiding sewage effluent contact contamination during the maize growing season in the semi-humid region of the North China Plain.

Reprint of “An integrated dual strategy to control Fusarium graminearum sensu stricto by the biocontrol agent Streptomyces sp. RC 87B under field conditions”

Fusarium head blight (FHB) caused by species within the Fusarium graminearum complex is a devastating disease that causes extensive yield and quality losses to wheat in humid and semi-humid regions of the world. The disease can cause not only yield losses but also grain contamination with mycotoxins such as deoxynivalenol (DON). Several epidemics have occurred in Argentina, the last in 2012, with yield losses up to 70%. Control of the disease is partially achieved by chemical treatments, crop rotation, breeding for resistance and tillage practices. Biocontrol can be used as part of an integrated pest management. The objetives of this study were: 1- to evaluate the biological control effect of Streptomyces sp. RC 87B on FHB disease incidence, severity and DON accumulation and 2- to evaluate if Streptomyces sp. RC 87B reduces F. graminearum inoculum when applied to wheat stubble. Streptomyces sp. RC 87B was applied at wheat anthesis to determine effects on FHB disease parameters and over wheat stubble left after harvest to evaluate effects on the survival of F. graminearum. FHB incidence and severity were visually estimated and DON content was assessed by HPLC after harvest. On stubble, F. graminearum prevalence was monitored by using TaqMan PCR for 180days. A significant disease severity and DON reduction were observed with the biocontrol treatments during the field trials (29–39% and 69–85%, respectively), but no reduction on disease incidence was achieved. On wheat stubble, Streptomyces sp. 87B reduced F. graminearum inoculum after 45days (82%) and after 90days no inoculum was detected in the first of two trials. In a second trial, a significant reduction (46%) in F. graminearum inoculum was observed after 90days. The biocontrol strain Streptomyces sp. 87B showed high potential for contributing to the reduction of FHB on wheat at different times in the F. graminearum life cycle.

Assessing efficiency and economic viability of rainwater harvesting systems for meeting non-potable water demands in four climatic zones of China

Rainwater harvesting is now increasingly used to manage urban flood and alleviate water scarcity crisis. In this study, a computational tool based on water balance equation is developed to assess stormwater capture and water saving efficiency and economic viability of rainwater harvesting systems (RHS) in eight cities across four climatic zones of China. It requires daily rainfall, contributing area, runoff losses, first flush volume, storage capacity, daily water demand and economic parameters as inputs. Three non-potable water demand scenarios (i.e., toilet flushing, lawn irrigation, and combination of them) are considered. The water demand for lawn irrigation is estimated using the Cropwat 8.0 and Climwat 2.0. Results indicate that higher water saving efficiency and water supply time reliability can be achieved for RHS with larger storage capacities, for lower water demand scenarios and located in more humid regions, while higher stormwater capture efficiency is associated with larger storage capacity, higher water demand scenarios and less rainfall. For instance, a 40m3 RHS in Shanghai (humid climate) for lawn irrigation can capture 17% of stormwater, while its water saving efficiency and time reliability can reach 96% and 98%, respectively. The water saving efficiency and time reliability of a 20m3 RHS in Xining (semi-arid climate) for toilet flushing are 19% and 16%, respectively, but it can capture 63% of stormwater. With the current values of economic parameters, economic viability of RHS can be achieved in humid and semi-humid regions for reasonably designed RHS; however, it is not financially viable to install RHS in arid regions as the benefit-cost ratio is much smaller than 1.0.