Spatial variability of soil total nitrogen and soil total phosphorus under different land uses in a small watershed on the Loess Plateau, China

The spatial variability of soil total nitrogen (STN) and soil total phosphorus (STP) levels, which may be greatly affected by land use, plays an important role in both agriculture and the environment, especially with regard to soil fertility, soil quality, and water-body eutrophication. Little research has been done that addresses the spatial patterns of STN and STP under different land use types at a watershed scale. We collected 689 soil surface (0-20 cm) samples, using a grid sampling design, from the Liudaogou watershed (6.89 km(2)) on the Loess Plateau of North China. Using classical statistical and geostatistical methods, we characterized and compared the spatial heterogeneities of STN and STP under different land use types (farmland, grassland, and shrubland).Concentrations of STN and STP were normally distributed with the exception of STP in grassland, and decreased in the order: farmland > grassland > shrubland. Stepwise multiple regression analysis indicated a strong relationship between STN and soil organic carbon (which was mainly controlled by plant growth and microbial activity), while STP was associated with the content of finer soil particles (which absorb P more readily and whose distribution is related to slope aspect and altitude). Both STN and STP showed moderate variability under different land use types. Nugget ratios for STN showed a moderate spatial dependence and decreased in the order: farmland > grassland > shrubland, whereas STP increased in that order and showed strong, moderate, and weak spatial dependence, respectively. The type of optimal theoretical isotropy models differed for STN and STP as well as for the land use type. We concluded that spatial patterns of STN and STP would change significantly with land use changes currently being implemented to achieve sustainable agriculture development and environmental restoration. Taking land use type into account when considering the spatial variation of STN and STP would increase the accuracy in modeling and prediction of soil nutrient status and nutrient movement at the watershed scale. (C) 2009 Elsevier B.V. All rights reserved

Origin of Smectite in Salinized Soil of Junggar Basin in Xinjiang of China

In this paper, salinized soils with different degrees of salinity are sampled in Junggar Basin of Xinjiang of China. The X-ray diffraction, transmission electron microscopy, and inductively coupled plasma mass spectrometry are employed to investigate the morphology and distribution characteristics of smectite in salinized soil profiles. In the salinized soil profiles of this region, crystals of smectite are poor where lattice fringes are not parallel. In all soil layers, the content of smectite in the soil increases with the decrease in content of illite, which has demonstrated significant negative correlation (r = 0.79, n = 50, p < 0.01) between illite and smectite. This phenomenon has demonstrated that illite may be transformed into smectite in salinized soils of studied regions. In general, the transformation process of illite to smectite is affected by climate condition. The δ18O values of secondary carbonate in the 0⁻10 cm soil layers is higher than that in deep soil layers, which indicates that δ18O concentrates in surface soil and reflects temperature rise during soil layer formation. The δ13C values of secondary carbonate and soil organic matter in 0⁻10 cm soil layers are higher than that in deep soil layers. It indicates that C4 plants were the main plants, which reflects that the climate was relatively dry during the formation of the surface soil. Thus, the climate during the surface soil formation is arid, which is not conducive for leaching K+ from illite of the 0⁻10 cm soil to form smectite. As a result, the content of the smectite becomes lowest in the soil surface. In the relative humid condition of deep soil layers, the K+ of the illite of the soil would be relative easily leached and more smectite may be formed. Furthermore, the presence of salt in the salinized soil would promote the formation of smectite in Junggar Basin of Xinjiang. A lot of Ca2+, Na+ and Mg2+ in the soil solution of salinized soils would enter into the illite and occupy K+ positions. The studied result shows that the amount of smectite would increase with the increase of salt below 10 cm of the soil layer, where the amount of smectite would be significantly correlated with soil electrical conductivity (r = 0.64, n = 39, p < 0.01). In the Junggar Basin in Xinjiang, therefore, the salinized soil below 10 cm would have the necessary water conditions and chemical components for illite transformation to smectite

Cadmium removal potential by rice straw-derived magnetic biochar

eISSN: 1618-9558Cadmium removal from wastewater is a difficult problem, so our aim was to develop a novel biochar and method of biochar preparation for the high-efficiency removal of cadmium. First, common biochars created using different pyrolysis conditions were tested to determine the best absorbance using the iodine absorption test. Magnetic biochar was prepared using a one-step synthesis by treating rice straw with Fe2+/Fe3+ and pyrolizing using the working conditions that exhibited the best absorbance. Second, the prepared biochars were used as adsorbents for Cd(II) removal from a solution. The magnetic biochar showed high efficiency for the removal of Cd(II): up to 91 %. This rate is much greater than that of the original biocharVytauto Didžiojo universitetasŽemės ūkio akademij

Crystal structures of the 2:2 complex of 1,1′-(1,2-phenylene)bis(3-m-tolylurea) and tetrabutylammonium chloride or bromide

The title compounds, tetrabutylammonium chloride–1,1′-(1,2-phenylene)bis(3-m-tolylurea) (1/1), C16H36N+·Cl−·C22H22N4O2 or [(n-Bu4N+·Cl−)(C22H22N4O2)] (I) and tetrabutylammonium bromide–1,1′-(1,2-phenylene)bis(3-m-tolylurea) (1/1), C16H36N+·Br−·C22H22N4O2 or [(n-Bu4N+·Br−)(C22H22N4O2)] (II), both comprise a tetrabutylammonium cation, a halide anion and an ortho-phenylene bis-urea molecule. Each halide ion shows four N—H...X (X = Cl or Br) interactions with two urea receptor sites of different bis-urea moieties. A crystallographic inversion centre leads to the formation of a 2:2 arrangement of two halide anions and two bis-urea molecules. In the crystals, the dihedral angle between the two urea groups of the bis-urea molecule in (I) [defined by the four N atoms, 165.4 (2)°] is slightly smaller than that in (II) [167.4 (2)°], which is probably due to the smaller ionic radius of chloride compared to bromide

Crystal structure of a host–guest complex of the tris-urea receptor, 3-(4-nitrophenyl)-1,1-bis{2-[3-(4-nitrophenyl)ureido]ethyl}urea, that encapsulates hydrogen-bonded chains of dihydrogen phosphate anions with separate tetra-n-butylammonium counter-ions

The title compound, C25H25N9O9·C16H36N+·H2PO4− (I) or (C25H25N9O9)·(n-Bu4N+)·(H2PO4−) (systematic name: 3-(4-nitrophenyl)-1,1-bis{2-[3-(4-nitrophenyl)ureido]ethyl}urea tetrabutylammonium dihydrogen phosphate), comprises a tris-urea receptor (R), a dihydrogen phosphate anion and a tetra-n-butylammonium cation. It crystallizes with two independent formula units in the asymmetric unit. The conformations of the two tris-urea receptors are stabilized by N—H...O and C—H...O intramolecular hydrogen bonds. Each dihydrogen phosphate anion has two O—H...O intermolecular hydrogen-bonding interactions with the other dihydrogen phosphate anion. Inversion-related di-anion units are linked by further O—H...O hydrogen bonds, forming a chain propagating along the a-axis direction. Each dihydrogen phosphate anion makes a total of four N—H...O(H2PO4−) hydrogen bonds with two ureido subunits from two different tris-urea receptors, hence each tris-urea receptor provides the two ureido subunits for the encapsulation of the H2PO4− hydrogen-bonded chain. There are numerous intermolecular C—H...O hydrogen bonds present involving both receptor molecules and the tetra-n-butylammonium cations, so forming a supramolecular three-dimensional structure. One of the butyl groups and one of the nitro groups are disordered over two positions of equal occupancy

Effect of different vegetation cover on the vertical distribution of soil organic and inorganic carbon in the Zhifanggou Watershed on the loess plateau

Understanding the carbon cycle of the terrestrial ecosystem and estimating the potential of carbon sequestration in soils requires adequate information on the relationship between soil organic carbon (SOC) and inorganic carbon (SIC). The vertical distribution and transformation of SOC and SIC under different types of vegetation and slope aspects in the Zhifanggou Watershed on the Loess Plateau were investigated. The distribution of SOC with soil depth in the 0-200cm soil can be described by the exponential model. The theoretical initial accumulation of organic carbon at the litter/soil contact increased with the decrease in the C/N ratio of the litter from the vegetation and followed the order shrub>forest>grass. Compared to the shady slope, the low theoretical initial accumulation of organic carbon at the litter/soil contact resulted from the relatively small quantity of SOC formation by the decomposition of litter on the sunny slope. The variation tendency of SIC in the 0-50cm is opposite to that of SOC. The transfer of the soil carbonate slowed down with the decrease in the soil water content (SWC), which was reflected by the significant negative correlation between SIC content and SWC (r=-0.400, p3 can be formed by precipitating with more Ca released from the decomposed shrub litter and (2) the dissolution and precipitation of the pedogenic carbonate is comparatively slow due to the relatively low SWC under shrub cover