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Returning corn straw to soil improves soil carbon sequestration in the Phaeozem regions of Northeast China. This research was to investigate the changes in soil carbon fractions of Phaeozem derived from loess and laterite PM with corn straw incorporation and quantify the influence of the key factors on soil carbon accumulation in order to improve the soil carbon stabilization efficiency. A simulative laboratory incubation experiment was conducted over 12 months using Phaeozem derived from loess and laterite PM and eight corn straw doses. Results showed that the clay mineral of Phaeozem was dominated by a mixed-mineral illite-smectite layer, illite, vermiculite, kaolinite, and smaller amounts of montmorillonite. Clay mineral species of topsoil were identical with its PM. The LOC and HOC of six soils increase with increase in straw incorporation level. The promoting effectiveness of straw incorporation on C accumulation declined when the C inputs reached a certain level. At 15% straw incorporation levels, the LOC and HOC of six soil increased by 1.86–3.01 g kg−1 and 1.33–2.22 g kg−1 than CK, respectively. The increment of LOC and HOC of six soils followed the trend of LHAp > LLAp > RHAp > RLAp > LC > RC. At 15% straw incorporation levels, the RLOC of RC (419%) and LC (296%) was greater than topsoil (103–254%) and the RHOC of RC (90%) and LC (61%) was much greater than topsoil (9–26%). Further analysis suggested that C input, TSOC, and clay content were the most influential variables on carbon sequestration efficiency. They accounted for about 73% of the variations of RLOC and RHOC. The relative contributions of 2:1 clay to RLOC and RHOC were about 10% and 15%, respectively and that of 1:1 clay were about 4.4% and 3.5%, respectively. In conclusion, both the topsoil and PM of Phaeozem have considerable C-stabilizing capacity and the C sequestration efficiency of topsoil and PM derived from loess was greater than those for topsoil and PM derived from laterite.

Converting natural vegetation to other types of land utilization is presently the most common land use change around the world. Conversion of grassland plays an important role in estimating the regional nutrients budget and assessing ecological effects. However, few studies have estimated the impacts of grassland conversion on soil nutrients under different soil pedogenic horizons. This study selected three sites, which were covered by grassland, shelterbelt, and cropland. The study evaluated the effects of grassland conversion and soil pedogenic horizon (to a depth of 100 cm) on the soil organic carbon (SOC), soil total nitrogen (STN), and soil total phosphorus (STP) concentrations and stocks in the Chinese Chernozem region. The results revealed that significant (p &lt, 0.05) differences were seen after grassland conversion for concentrations and stocks of SOC, STN, and STP. The transformation from grassland to shelterbelt and cropland plantations caused soil carbon and soil nitrogen losses but caused soil phosphorus accumulations. Moreover, conversion of grassland made SOC, STN, and STP all drop below the Bk-horizon. Changes in the SOC and STP on an area basis were the greatest after conversion of grassland to cropland, for concentrations of −16% and 26% and for stocks of −15% and 32%, respectively. Land use change and soil pedogenic horizon primarily influenced the distribution patterns of nutrients concentrations and stocks. However, grassland conversion effects on nutrients were mainly at surface horizons. Soil properties, such as calcium carbonate (CaCO3) and soil texture, affected the nutrients from the Bk-horizon to the C-horizon. This study indicates that land use management policies should protect natural grasslands to minimize losses of SOC, STN, and STP.

The soil organic carbon accumulation in soda saline-alkaline soil and the humus composition changes with application of aluminum sulfate and rice straw were investigated by the controlled simulative experiments in laboratory. For evaluating the amelioration effect, organic carbon content and humus composition in soda saline-alkaline soil were investigated with different application amounts of rice straw and aluminum sulfate. Potassium dichromate oxidation titration (exogenous heat) method and Kumada method were used to analyze the contents of organic carbon and humus composition, respectively. The transformation of soil organic matter in the saline-alkali soil during the amelioration has been clarified in this paper. The results demonstrated that the contents of soil organic carbon were significantly increased (13-92%) with different application amounts of rice straw and aluminum sulfate. The contents of free fraction and combined fraction of humus and their compositions (humic acid and fulvic acid) were increased with different application amounts of rice straw. The free fraction of humus was increased more dramatically. Due to aluminum sulfate application, free fraction of humus and humic acid (HA) was transformed to combined fraction partially. Free HA was changed to be P type with rice straw application. With aluminum sulfate application, free form of HA was changed from type P to type Rp. For rice straw application, combined HA only was transferred within the area of type A. Aluminum sulfate addition had no significant effect on the type of combined form of HA. With the same amount of rice straw application, the contents of soil organic carbon were increased by increasing the amount of aluminum sulfate application. Both rice straw and aluminum sulfate applications could reduce the humification degree of free and combined fraction of HA. According to the types of HA, it could be concluded that humus became younger and renewed due to the application of rice straw and aluminum sulfate.

The simulation of Cr(VI) behavior in an unsaturated zone and aquifer, using a 3D experimental set-up were performed to illustrate the distribution, transport and transformation of Cr(VI), and further to reveal the potential harm of Cr(VI) after entering the groundwater. The result indicated that chromium(VI) was transported in the vertical direction, meanwhile, was transported in the horizontal direction under the influence of groundwater flow. The direction and distance away from the pollution source zone had great effect on the chromium(VI) concentration. At the sampling sites near the pollution source zone, there was a sudden increase of chromium(VI) concentration. The concentration of chromium(III) concentration in some random effluent samples was not detected. Chromium had not only transported but also had fraction and specie transformation in the unsaturated zone and aquifer. The relative concentration of residue fraction chromium was decreased with time. The content of Fe-Mn oxide fraction chromium was increased with time. The relative content of exchangeable and carbonate-bound fraction chromium was lower and the content variations were not obvious. Chromium(VI) (91-98%) was first reduced to chromium(III) rapidly. The oxidation reaction occurred later and the relative content of chromium(VI) was increased again. The presence of manganese oxides under favorable soil conditions can promote the reoxidation of Cr(III) to Cr(VI).

Loss of soil and water from sloped farmland is a major cause of regional soil degradation and declining productivity. We conducted a preliminary study on the characteristics of sloped farmland in the black soil region of Northeast China using natural rainfall-runoff plot experiments in the field. In 0-20 cm soil depth, clay content (0.05 mm), 0.02 to 0.05 mm and 0.05 to 0.25 mm microaggregates content, tended to decline. This suggests that soil material and nutrients were gradually transported from the top to the bottom of the slope because of erosion, soil tended toward desertification in texture, and fertility was degraded. The content of available phosphorus and total phosphorus was positively linearly related to clay content, specific surface area, and 0.002 to 0.02 mm microaggregates content. This indicates that soil nutrients migrated down with fine particles. Therefore, soil erosion leads to the migration and loss of soil nutrients

The significant investigation was performed to establish a chemical baseline for snowfall in Northeast of China since there was no such record. The chemical and mineral composition of snowfall samples were evaluated in Jilin Province, Northeast China. The specific purposes of the present study are to characterize the chemical and mineral composition of melted snow-water samples and to identify the sources of atmospheric pollutants, as well as to investigate the spatial variability of melted snow-water chemistry in this region. Snowfall and aerosol samples were collected from Changchun city, Baicheng city, and Yanji city during November 2015 to March 2016. All the filtered (0.45 m) snow-water was analyzed for conductivity, pH, major cations (Na+, K+, NH4 +, Ca2+, Mg2+) and anions (F−, SO4 2−, Cl−, NO3 -, HCO3 -). The pH of these samples ranged from 6.01 to 7.10, with an average value of 6.44. The conductivity ranged between 17.50 μs cm-1 and 86.00 μs cm-1 with an average value of 55.0 μs cm-1. These parameters indicated high chemical concentrations in the snow-water. It was observed that Ca2+ and NH4 + were the major cations which accounted the concentration for 5.05% to 18.71% and 3.47 to15.54%. HCO3 - and SO4 2- were major anions which accounted the concentration for 23.41% to 38.49% and 21.10% to 35.24%, respectively. (SO4 2- + NO3 -)/ (Ca2+ + NH4 +) was 1.38. The organic carbon of particles in the snowfall was higher and the average content was 52.85 g kg-1. The size of the snow-water particles in the three Cities was mainly based on clay complexes ( (>200 μm)> (20-200 μm)> (2-20 μm). The dominant mineral of particles in the snow-water was quartz and feldspar, while clay mineral was composed of montmorillonite, illite, kaolinite and vermiculite. According to the above analyses, the possible sources of the particles in the snowfall should be soil and ground dust and co al-burning.

Soil organic carbon (SOC) associated with clay plus silt sized particles ( Hassink (1997) [Hassink, J., 1997. The capacity of soils to preserve organic C and N by their association with clay and silt particles. Plant and Soil 191, 77–87.]. However, the SOC in clay plus silt fraction of Baijiang soils varied greatly, from ∼40% to 120% of the calculated protective capacity. The SOC contents in the fraction > 20 μm were relatively low and similar amongst all the Black soils. In contrast, SOC in the fraction > 20 μm varied considerably amongst the Baijiang soils. Soils which have the SOC associated with clay plus silt size fraction in amounts approaching or exceeding the protective capacity in general were those which had C accumulation in the > 20 μm size fraction. Since the SOC in Black soils has already decreased to about 50% of the protective capacity, there may be a greater potential for sequestering C in these Black soils than in the Baijiang soils.

Clay mineralogical characteristics of volcanic ash soils in Changbaishan and Sanjiaolongwan, Jilin Province and Wudalianchi, Heilongjiang Province, Northeast China, were investigated. The clay mineral fractions of 8 Changbai-shan pedons, 1 Sanjiaolongwan pedon, and 4 Wudalianchi pedons were characterized by the predominance of 2:1 layer silicates, kaolinite, fine-grained quartz, and opaline silica in the surface (O, OA, A, and AE) horizons. However, the C horizons of some pedons in Changbaishan were characterized by the presence of allophane and ferrihydrite, which are weathering products from Holocene tephra deposits. The Bw and BC horizons exhibited intermediate mineralogical properties between the surface horizons and the C horizon. We assumed that the predominance of 2:1 layer silicates, kaolinite, and fine-grained quartz in the surface horizons of pedons was due to the addition of tropospheric eolian dust transported from arid and semiarid regions in China and Mongolia. Oxygen isotope ratios...

Soil indoors model experiments were carried out to study effects of Al2(SO4)3 on P forms and P adsorption of Soda saline-alkali soils. Available P and P fractions as well as P adsorption of the soils were analyzed. The results showed that available P tended to decrease with the amount of Al2(SO4)3 increasing. When P was not applied, on average, among the inorganic P, the percentage of Ca-P was the greatest, followed by O-P, Al-P and Fe-P. By contrast, both % and contents of O-P forms of 0.4% were the highest. When certain amount of P was applied, total inorganic P, Ca2-P, O-P, and Ca10-P had the trend of downward with the increase of Al2(SO4)3. The results of phosphate adsorption showed that the adsorption isotherms were fitted well with Langmuir equation. According to the Langmuir equation, when c/x/m is plotted against C, from the figure that there are two kinds of straight lines. One is straight line without break point (0%~0.6%), and the other is straight line with a break point (NPA-0%~NPA-0.6%), indicating that the presence of two energy absorption points that have a differing affinity. Taken together, The results suggest that though Al2(SO4)3 can improve physical and chemical properties of soils, they had an effect on available P and P forms as well as P adsorption, and the optimal amount of Al2(SO4)3 was 0.3%~0.4% of the weight of soils.

Determinations by Kumada method showed that with the improvement of black soil fertility, the free and combined humus contents in soil and its different size organo-mineral complexes increased, but the humification degree of free humus decreased, which was more obvious in silt and fine sand size complexes. The organic carbon content in complexes, humus extraction rate, free humus content, and humification degree of free humic acid decreased with the increasing particle size of complexes. All free humic acids in fertile soil were Rp type, while in unfertile soil, they were Rp and B type. With the increasing particle size of complexes, the type of free humic acids changed in the sequence A type (clay)--B type (silt)--Rp type (fine sand). Combined form humic acid mainly belonged to A type, no matter what particle size the complex was. The improvement of soil fertility could make the humification degree of free humus in soil and its complexes decrease, and furthermore, result in type change. In black soil, the type change of free humic acid mainly occurred in silt size complex, and that of combined form humic acid mainly occurred in fine sand size complex.