内蒙古黄河流域水土保持工程水文频率设计模型研究

内蒙古黄河流域水土保持工程水文设计模型把水土保持工程设计中水文计算复杂繁琐的过程变的十分简捷。通过研究绘制水土保持工程所需不同频率24h降雨等值线图,将直接应用于水土保持工程设计中,使工程设计水文计算简便、准确、缩短设计时间,提高设计水平和效率。     

Quantifying Tillage and Vetiver Grass(Vetiveria nigritana Stapf)Strips Spacing Effects on Runoff,Soil Loss and Maize Yield in Southern Guinea Savanna of Nigeria

Soil erosion induced by inappropriate tillage remains a serious problem on many agricultural fields in the humid tropics. Studies were conducted between 2004 and 2006, on an Alfisol in Ogbomoso in the Southern Guinea Savanna of Nigeria to evaluate the effectiveness of Vetiver Grass(Vetiveria nigritana)Strips(VGS)under different tillage systems.The experiment was split-plot laid out in a randomized complete block design with two replications on 6% slope with 18 runoff plots. Main plot treatments were tillage systems; Manual Clearing (MC), Ploughing (P) and Ploughing plus Harrowing (PH). Subplot treatments were VGS spaced at intervals of 5 m (eight strips) and 10 m (four strips) with the control (no-vetiver). Runoffs and soil losses were collected after each major storm. Chemical analyses of eroded sediments and runoff were determined. Data were analyzed using ANOVA at p<0.05. The results showed that tillage had no significant reduction in runoffs and soil losses, but they were reduced with MC compared with P and PH. Mean total runoff on 5 and 10 m VGS plots were significantly (p<0.05) lower than that of the control by 74.4% and 45.0%, respectively. Corresponding soils loss on 5 and 10 m VGS plots were 27.1% and 53.5%, respectively. Mean NO3-N levels in runoff water were lower under PH plots than those under MC plots by 79.0% and 66.5%, respectively in 2004 and 2006 growing seasons. VGS spaced at 5 m significantly (p<0.05) reduced NO3-N loss than the control by 108.8% in 2004. Nutrients loads of eroded sediments were consistently higher for the control (no-vetiver) plots and least for 5 m VGS plot. Carbon, nitrogen and phosphorus contents of eroded sediments were 90%-92.4%, 83%-83.6% and 97%-97.8%, respectively, and were lower on 5 m than other treatments. Maize grain yield was significantly (p<0.05) affected by both tillage and VGS spacing only in 2005 growing season. P plot produced higher grain yield than MC and PH by 79.9% and 99.1%, respectively. Also, grain yield on VGS plot was significantly (p<0.05) higher on 5 and 10 m VGS plots than the control by 82.2% and 85.4%, respectively. The significant beneficial effect of PH in producing higher yields was dwarfed by the potential danger of soil erosion in the absence of a soil erosion control measure. The results showed that a balance needed to be struck between mechanical clearance and protective measure against soil erosion.     

Relationships between soil spectral and chemical properties along a climatic gradient in the Judean desert

Regions of rainfall gradients at desert margins are areas where eco-geomorphic changes and degradation in response to global warming and grazing are most intensive. Assessment and understanding of the consequences of global warming and human disturbance of these vulnerable ecosystems requires detailed information regarding the spatial variation of soil and vegetation properties and their dependence on rainfall. Such detailed information is still of limited availability. This study aimed to rectify this shortcoming by analyzing data on the chemical and spectral properties of soil samples collected along the Judean Desert climatic gradient. Six clusters of typical chemical soil properties were identified. Dependencies of clusters’ chemical properties (total iron, organic and inorganic carbon) on annual rainfall amounts were found to be significant. Two spectral Landsat TM band ratios introduced to assess soil conditions showed significant correlations with these chemical properties. These ratios were found to be higher correlated than individual chemical properties with average rainfall suggesting that spectral data may represent a broader range of chemical, physical, and biological site properties. Examining the three-way relationships between soil chemical properties, their spectral reflectance characteristics and rainfall, facilitates a better understanding of the generalized trends along the climatic gradient and more specifically of modes of transition from semi-arid to arid zones.     

Contents of soil organic carbon and nitrogen in water-stable aggregates in abandoned agricultural lands in an arid ecosystem of Northwest China

Soil organic matter content in water-stable aggregates(WSA) in the arid ecosystems(abandoned agricultural lands especially) of China is poorly understood. In this study, we examined the WSA sizes and stability, and soil organic carbon(OC) and nitrogen(N) contents in agricultural lands with abandonment ages of 0, 3, 12, 20, 30 and 40 years, respectively, in the Minqin Oasis of Northwest China. The total soil OC and N contents at depths of 0–20, 20–40 and 40–60 cm in abandoned agricultural lands were compared to those in cultivated land(the control). Agricultural land abandonment significantly(P0.05) influenced the distribution of MWD(mean weight diameter), and OC and N contents. There were significant increases in MWD and the proportion of macroaggregates(sizes 0.25 mm) as the age of agricultural land abandonment increased. The effect of abandonment ages of agricultural lands on MWD was determined by the changes of OC and N accumulation in WSA sizes 2 mm. The total OC and N contents presented a stratification phenomenon across soil depths in this arid ecosystem. That is, both of them decreased significantly at depths of 0–20 and 40–60 cm while increased at the depth of 20–40 cm. The WSA sizes 0.053 mm had the highest soil OC and N contents(accounting for 51.41%–55.59% and 42.61%–48.94% of their total, respectively). Soil OC and N contents in microaggregates(sizes 0.053–0.25 mm) were the dominant factors that influenced the variations of total OC and N contents in abandoned agricultural lands. The results of this study suggested that agricultural land abandonment may result in the recovery of WSA stability and the shifting of soil organic matter from the silt+clay(0.053 mm) and microaggregate fractions to the macroaggregate fractions. However, agricultural land abandonment did not increase total soil OC and N contents in the short-term.     

Design Problems of Internal Bracing and Composite Soil Nailing Wall in Foundation Pits under Binary Geological Conditions

Combined with the design practice in foundation excavation engineering,the problems for combined supporting from inner supports and composite soil nailing wall under binary geological conditions,including soil layers and rock stratum with weak intercalation in range of excavation depth,are analyzed.These problems mainly include the following: calculation model of earthen pressure,the local bearing capacity of foundations below steel pipe piles,stiffness coordination at the junction of rigid and flexible supports,internal bracing stability influencd by restrained condition of upright post,etc.Problems of concern for design of similar foundation pit supports are pointed out,and measures for solving these problems are proposed.All these can provide references for similar projects.     

Einfluss eisenhaltiger Klärschlämme auf Kenngrößen der P‐Verfügbarkeit in Ackerböden

Influence of iron content in sewage sludges on parameters of phosphate availability in arable soils The use of iron salts for the P elimination in sewage plants is widely used. But it is not clear whether the P availability in arable soils is negatively influenced by iron compounds or not. The aim of the investigations was, therefore, to study the influence of two sewage sludges with a high and a low Fe content respectively on P sorption and phosphate concentration (P_i) in the soil solution after application of CaHPO₄ or sewage sludge to 5 loamy and 4 sandy soils (pot experiments and 1 silty loam (field experiment)). Soils were analyzed 1, 6, and 13 months after P application. Sludge Gö contained 12 kg P and 65 kg Fe (t DM)^—1 (P : Fe = 1 : 5.4) and sludge Sh 25 kg P and 39 kg Fe (t DM)^—1 (P : Fe = 1 : 1.5). The basic P application was 60 kg P ha^—1 (= 30 mg P (kg soil)^—1 in the pot experiment, as sludge or as CaHPO₄). P uptake by maize was determined in a separate pot experiment with a loamy soil and the same P application rate. The P sorption capacity remained similar in all soils after application of sludge Sh (P : Fe = 1:1.5) compared with soils without sludge, however, after application of sludge Gö the P sorption increased by 16% (0—59%). After application of sludge Sh the mean P_i concentration increased in loamy soils by 34% and in sandy soils by 15%. On the other hand the P_i concentration decreased after applying sludge Gö by 13% and 36% as compared to the controls of the respective soils. In the field experiment the P_i concentration of plots with a high P level (50 mg lactate soluble P (kg soil)^—1) was also significantly decreased after application of 10 t sludge Gö (126 kg P ha^—1) in comparison with triple phosphate. One month after the application of increasing amounts of sludge Gö (5, 10, 15 t DM ha^—1) both the concentration of oxalate‐soluble Fe in the soil and the P sorption were increased. The elevated relationship between these two parameters was highly significant (r² = 0.6 — 0.97). Plant uptake of P was less after application of sludge Gö than after application of sludge Sh and much less than P uptake from CaHPO₄. Sewage sludges with a P : Fe ratio of 1 : 5 should not be recommended for agricultural use, as the P availability is significantly reduced. Iron salts should not be used for conditioning of sludges.     

Microclimate and CO2 fluxes on continuous fine days in the Xihu desert wetland,China

The Xihu desert wetland is located in an extremely arid area in Dunhuang,Gansu province of Northwest China.The area is home to an unusual geographic and ecological environment that is considered unique,both in China and the world.Microclimate is not only related to topography,but is also affected by the physical properties of underlying ground surfaces.Microclimate and CO2 flux have different characteristics under different underlying surface conditions.However,until now,few studies have investigated the microclimate characteristics and CO2 flux in this area.The eddy covariance technique(ECT) is a widely used and effective method for studying such factors in different ecosystems.Basing on data from continuous fine days obtained in the Dunhuang Xihu desert wetland between September 2012 and September 2013,this paper discussed and compared the characteristics of daily microclimate variations and CO2 fluxes between the two periods.Results from both years showed that there was a level of turbulent mixing and updraft in the area,and that the turbulent momentum flux was controlled by wind shear under good weather conditions.The horizontal wind velocity,friction wind velocity and vertical wind velocity were commendably consistent with each other.Air temperature in the surface layer followed an initial decreasing trend,followed by an increasing then decreasing trend under similar net radiation conditions.With changes in air temperature,the soil temperature in the surface layer follows a more obvious sinusoidal fluctuation than that in the subsoil.Components of ground surface radiation during the two study periods showed typical diurnal variations.The maximum diurnal absorption of CO2 occurred at around 11:00(Beijing time) in the Xihu desert wetland,and the concentrations of CO2 in both periods gradually decreased with time.This area was therefore considered to act as a carbon sink during the two observation periods.     

甘肃省主要耕作土壤对施入钾的吸收能力研究

研究了甘肃省主要耕作上壤对施入钾吸收的数量和比例。结果表明,经过一次干湿交替后,在施钾0～1600mg／kg范围内,随着施钾数量的增加,土壤中速效钾含量、施入钾被土壤吸收量呈直线上升,吸钾率也逐渐增加。随着干湿交替次数的增加,吸钾量及吸钾率随之增加。对施入钾的吸收率与土壤速效钾含量成负相关。     

Secondary Metabolites from Marine-Derived Bacillus: A Comprehensive Review of Origins,Structures, and Bioactivities

The marine is a highly complex ecosystem including various microorganisms. Bacillus species is a predominant microbialflora widely distributed in marine ecosystems. This review aims to provide a systematic summary of the newly reported metabolites produced by marine-derived Bacillus species over recent years covering the literature from 2014 to 2021. It describes the structural diversity and biological activities of the reported compounds. Herein, a total of 87 newly reported metabolites are included in this article, among which 49 compounds originated from marine sediments, indicating that marine sediments are majority sources of productive strains of Bacillus species Therefore, marine-derived Bacillus species are a potentially promising source for the discovery of new metabolites.