Abstract:Determining reasonable nitrogen (N) fertilizer rate is the key point for getting higher target yield, maintaining soil N fertility and reducing environmental pollution. Since N fertilizer invention and application a century ago, although it had been carried out more than hundred of years’ researches, people didn’t find the satisfied methods that could determine the reasonable N application rate on the field scale. Based on the previous concept and method of theoretical N rate (TNR) and on the conditions of considering other sources of nitrogen inputs, this paper further deduce the calculation of TNR according to the N requirement per hundred kilograms (kg) of grain. The results showed that, after determining the N requirement per hundred kg of grain (N₁₀₀), the TNR (N_fert, N kg hm^-2) is the only function of target yield (Y, kg hm^-2) as: N_fert ≈ Y/100×N₁₀₀. After integrating the results from all kinds of literatures, the N requirement per hundred kilograms of wheat, maize and rice was 2.8, 2.3 and 2.4 kg, respectively, under current production conditions and yield levels. Comparing the TNR with economic optimum N rate (EONR) from a large number of field experiments’ results on the literatures, in most case, the two rates are very close in other regions of China except for the northeast China. The TNR of wheat, maize and rice in the northeast region is much higher than the regional N recommended rate (RNRR). The main reason is that the soil N mineralization is greater than immobilization during growth period, which means the crops utilizing part of soil mineralized N and soil organic N is depleted. Combining with the TNR, this paper also analyzed the scientific basis, recommendation results and applicability of other N recommendation methods established in recent years in China in details. The paper recognized that to adjust the excessive and deficient N application rates to the reasonable scope is the urgent task nowadays and in the future, and the TNR could meet this actual demand by maintaining high and stable target yield, soil N balance and low environmental risk. It is very convenient for extension technicians and farmers to determine the reasonable N application rate according to the target yield of their own field.

Abstract:Continuous accumulation of nitrous oxide (N₂O) in the atmosphere leads to global warming and ozone depletion. Forest ecosystems act as source and sink of atmospheric N₂O, posing a great uncertainty in budgeting of atmospheric N₂O. Exogenous nitrogen inputs into terrestrial ecosystems are an alternative explanation for this uncertainty. Therefore, exploring mechanisms involved in responses of N₂O emission from forest soils to increased atmospheric nitrogen deposition is of some important theoretical and practical significance. However, due to complexity of soil nitrogen cycling and high spatial heterogeneity of forest ecosystems, progress of the research on soil N₂O flux response to N addition has been quite slow. N₂O emission in forest soils is mediated by microbial communities, and nitrification, denitrification, nitrifier denitrification and chemical denitrification are the four main processes of soil N₂O production. Presently, which one of nitrification and denitrificatiopn is the leading contributor to soil N₂O emission under nitrogen enrichment is still controversial; and how N₂O emission responds to increased N deposition and what mechanism is involved in soil microbes driving the porcess are not well known. In this paper, a review is presented of the progresses of the study on identification of sources of N₂O in forest soils using the stable isotope labelling technique, laws of the responses of total N transformation in and N₂O emission from forest soils to nitrogen addition, as well as effects of increased N depostion on activity and composition of soil microbial community. Also, the paper points out weak links in the present studies and possible research priorities in the future. Generally, soil N₂O flux is influenced by many environmental factors including soil temperature, soil moisture, pH, Eh, and N availability. Increased nitrogen deposition may increase, decrease or have little effect on forest soil N₂O emission, depending on forest types, initial nitrogen content in soils, and dose and duration of nitrogen application. Overall, the response of N₂O emission from forest soils to increased atmospheric N deposition exibits a nonlinear pattern, including no significant response at the early stage, linear increase at the medium stage, and exponential increase at the late stage. The three-stage pattern depends on degree of "N saturation" of the forest ecosystems. Besides, significant relationships were observed between soil NO₃- content and abundance of denitrobacterial genes, between soil NH4+ content and abundance of nitrobacterial genes, and between soil N₂O flux and abundance of denitrobacterial genes. Nitrogen application leads to change in status of soil available N from N deficiency to N sufficiency, and hence changes in abundance and composition of nitrobacteria and dennitrobacteria, thus affectng soil N₂O emission. Moreover, as the monitoring of N₂O emission from forest soils and the researches on transformation of soil TN and dynanucs of N₂O producing bacterium communities are often carried out independently, making it hard to elaborate on the coupling relationship between soil microbial functional groups and soil N₂O emission. It is, therefore, suggested that future researches should focus on the following three aspects 1) to lay out and conduct some multi-dosage multi-form N fertilizer application experiments to work out equations for response of soil N₂O to N addition and threshold of N deposition that may cause significant change in N2O flux response curve; 2) to define relationships between soil N transformatioon and soil N₂O emission and explore relative contributions of soil nitrification and denitrification to soil N₂O generation by means of the ¹⁵ N-¹⁸ O labeling technique in combination of molecular biology, of which the findings may explain the difference between the forests in North China and in South China in source of soil N₂O; and 3) to quantify the coupling relationships of soil N₂O flux with major soil microbial functional groups, such as nitrifiers, denitrifiers, and ammonia-oxidizing bacteria, and use molecular biological and matagenomic methods and techniques to determine effects of N addition on abundance and composition of N₂O producing bacterial community. By so doing, it is expected that the mechanism of the non-linear response of N₂O emission to increased N depostion in forest soils could be fully understood.

Abstract:Investigations were done of micromorphological features of the soils derived from loess, with a view to revealing diagnostic significance of these features and providing reliable micromorphological basis so as to define positions of these soils in the Chinese Soil Taxonomy. A soil profile at Chafangcun, Shaanxi Province, China was selected as object of the study. Soil samples were collected from the profile for analysis of relevant soil physical and chemical properties (including chroma, magnetic susceptibility, particle-size composition, total iron and free iron content, etc.) in laboratory. The soil was prepared into thin slices, which were put under a Leica -DMRX petrographic microscope for observation of soil micromorphology and the images were processes with the Nis-Elments BR 3.2 image analysis software for extraction of micromorphologic unit images and quantitative measurement of relevant parameters. Results show that the Chafangcun soil profile has an A-AB-Bt-BC-C profile structure, with a large volume of secondary illuvial clay accumulated in Bt Horizon (110～230 cm in depth), reaching to 15% ~ 30% in content and making the illuvial clay/residual clay ratio (K_i/r) varying between 4 and 9. The illuvial clay minerals exist mainly in the form of irregular lumps, and then in the form of clay cutan, mostly < 0.15mm in thickness. Compared with Bt Horizon, the upper eluvial horizon is apparently lower in secondary clay mineral (< 5%), dominated with residual clay mostly in the form of concentrate; and the lower parent material layer is much lower in secondary clay (generally > 3%), mostly in the form of very thin clay cutan, sparsely present on edges of the pores. In the upper eluvial horizon coarse particles (> 10 μm) are generally in the form of subangular - subround lumps, 30.0 μm in average particle size, moderate in content (10.4%), and unevenly distributed in the horizon,. In the parent material layer, coarse particles are in the form of apparent sub-angular – angular lumps, 32.0 μm in average particle size, 24.6% in content and very evenly distributed in the horizon. But in Bt Horizon (110～230cm in depth), they are in the form of round - subround lumps, 25.4μm or the smallest in average particle size, 4.6% or the lowest in content in the profile and sparsely distributed patches in the horizon. The differences are obvious in mean particle size and content of clay particles between Bt horizon, the upper leached layer and the lower parent material layer. Pores in A horizon are very complex in shape with jigsaw like boundary, varied in pore size, and very unevenly distributed, appearing on the whole like an equiaxe. In the parent material layer, pores are small in size and limited in range of verification and evenly distributed, appearing on the whole like an equiaxe. But, pores in Bt horizon are small in number but big in size of single pores, appearing in the form of elongated fractures, with an average aspect ratio between 10 to 30. The pores have smooth edges coated with clay cutan. The above-described micromorphological features indicate that the soil profile at Chafangcun is characterized by vigorous leaching with plenty of water, and large volumes of secondary clay was formed in soil forming process, releasing a certain amount of free irons. Both of them keep migrating into Bt horizon and accumulating therein. These micromorphological features can be used as micromorphological index of the diagnostic horizon, “Argic horizon”, which reliably demonstrates that the Bt horizon (110～23 cm in depth) of the Chafangcun soil profile is a typical “Argic horizon”. Hence, by taking into account of other soil forming factors, the soil can be sorted as Hapli-Udic Argosol.

Abstract:Based on nitrogen (N) balance in soil system, a new N fertilization recommendation method, i.e. “N return index (NRI)” method, was introduced. The NRI concept was brought forth by the Nutrient Return Doctrines, and means how much N must be returned to soil in order to maintain soil N balance when one kilogram N is taken off by crop harvesting. On the assumption that other than N fertilization, the N inflow via atmosphere deposition, irrigation and seeding (N biofixation and N in straw incorporation exclusive) and the N outflow via erosion, runoff, leaching, volatilization, and nitrification-denitrification, are constant, an equation for calculation of NRI (NRI=1−⊿E/F_N) was deduced, where ⊿E stands for increase in N output from soil to environment induced by N application; F_N for N input with fertilizer applied, and ⊿E/F_N is net N loss. With the target yield (Y_t) of the fields most farmers are familiar with set as the only variable to distinguish fields different in soil fertility, an equation for NRI-based recommendation of N fertilization was worked out, i.e. RNR= RNRI×N₁₀₀×Y_t/100”, where RNR stands for recycled N rate, RNRI for the regional NRI, which is a relatively stable constant in a specific farming area, N₁₀₀ for N uptake by one hundred kilogram grains, which is in a significant linear relationship with crop yield. By taking into account the actual production practices, the equation was finally amended as "RNR=RNRI×N₁₀₀×Y_t/100−W_N", where W_N stands for N input via biofixation and straw incorporation. To verify effectiveness of NRI, two regions in Lixiahe Plain and Taihu Lake Basin in Jiangsu Province were selected as for the study. Based on the soil N budgeting data of the study areas during the rice growing season, RNRI was worked out to be 1.52, based on traits of rice cultivars, N₁₀₀ was 8.67×10 ^-5Y_t+1.161 (r=0.828 0**) and based on N biofization and straw incorporation, WN was N 52.3 kg hm ^-2, then the equation of “RNR=1.32×10 ^-6Y_t² 1.76×10 ^-2Y_t−52.3” for recommendation of N fertilization for rice in the study areas was figured out. Based on the data of the fertilization experiment on 45 cultivars of japonica rice in recent years, comparison was performed between N fertilization recommendations using different methods, the fertilizer effective function (FEF), NRI and theoretical N rate (TNR) in effectiveness. Results show that the optimal economic N application rate (OENR) recommended by FEF, the N-recycling N application rate (RNR) by NRI and the theoretic N application rate (TNR) by TNR was N 246.8±42.5 kg hm ^-2, 216.9±27.3 kg hm ^-2 and 176.9±22.3 kg hm ^-2 respectively. Compared with OENR, RNR was 2.4% less in rice grain yield and 500 yuan hm ^-2 in economic benefits, but saved N 29.9 kg hm ^-2 and 10.3 kg hm ^-2, respectively, from N application and soil-N net loss and moreover kept soil-N in a rough balance. The new method can be used to make recommendation for N fertilization with target yield being the only variable and without the need to go through field experiment, however, further study is still required to see whether RNRI will remain relatively stable for long, and whether long-term use of the method would lead to soil-N surplus or not.

Abstract:The existence of rock fragments is one important features of purple soil. However, the variation in rock fragments on purple soil-mantled hillslope is poorly understood. In order to understand the spatial distribution pattern of rock fragments in purple soil, a typical catena which contained both a relatively steep slope and a relatively gentle one was selected. Ten pedons from pits dug on hillslope from crest to foot were selected and the content and size of rock fragments of soil layers varied in depth at different position of hillslope were investigated. Results show that: (1) the rock fragment content of purple soil varied in 0.4%~50%. The content of rock fragments were divided into five grades of <5% (low), 5%～10% (medium-low), 10%～20% (medium), 20%～40% (medium-high) and >40% (high). The content of rock fragments concentrated in low, medium-low, medium and medium-high grade. The small rock fragments with diameter of 5~20 mm and medium rock fragments with diameter of 20~76 mm were the main components. (2) With increasing depth of soil layer, the distance between soil layer and parent material horizon become shortening and the influence of parent material horizon on soil’s properties would increase. The contents of medium rock fragments and big rock fragments (76~250 mm) increased and the content of small rock fragments didn’t change significantly. Thus the total content of rock fragments increased as soil layer deepened. The equivalent diameter of rock fragments depended on rock fragment content ratio (content of rock fragments with different diameter divided by total rock fragment content). The relationship between equivalent diameter of rock fragments and content ratio of big rock fragments was positive very significantly, while the relationship between equivalent diameter of rock fragments and content ratio of small rock fragments was negative significantly, and there was no significant relationship between equivalent diameter of rock fragments and content ratio of medium rock fragments. With increasing depth of soil layer, the content ratio of big rock fragments increased and the content ratio of small rock fragment decreased, thus the equivalent diameter of rock fragment enlarged as soil layer deepened. (3) On the relatively steep slope, the rock fragments, especially the bigger rock fragments, rolled or crept down under the action of gravity because of the steeper slope, thus the content and equivalent diameter of rock fragments increased from crest to foot. On the relatively gentle slope, the efficiency of gravity pulling down rock fragments was induced while sorting impact of erosion was strengthened because of the gentler slope: fine earth was moved down and coarse materials was stayed in situ under the action of runoff scouring and raindrop splash. The content and equivalent diameter decreased from crest to foot. We can concluded that vertical distribution of rock fragments within soil column was determined by pedogenic process and the depth of soil layer significantly influence rock fragment content, rock fragment size and content ratio of rock fragments with different diameter, while slope-scale variation of rock fragments depended on dominant hillslope transport process, i.e. water erosion processes or gravity erosion process.

Abstract:Infiltration is a process of water penetration through the soil surface. During rainfall events, the amount of infiltration determines the quantity of water available for plant uptake, and abundant water helps increase crop yield. In the arid and semi-arid regions, water availability is one of the greatest factors affecting vegetation restoration and ecological environments, especially in the Chinese Loess Plateau area. Proper tillage practices can significantly alleviate certain soil-related constraints to crop production, such as compaction, crusting, low infiltration, poor drainage, and unfavourable soil moisture and temperature regimes. Traditional tillage practices used in the Loess Plateau, include contour tillage and artificial digging, can increase soil roughness and decrease runoff and soil erosion. However, the soil in the Loess Plateau has been reported to be poor in structure, susceptible to erosion and liable to form soil crusts during rainfall events. Soil crusts can reduce the amount of infiltration and hence soil moisture availability. The objective of this laboratory study is to explore characteristics of the formation of different types of soil crusts on slopelands different in soil micro-topography and effects of structural crusts and depositional crusts on soil water infiltration from the rainfall-infiltration perspective. For that end, an indoor experiment was designed to have simulated slopelands adjustable to 5°, 10°, 15° and 20° in slope gradient, three different tillage treatments (contour tillage, artificial digging and straight slope as control) and artificial rainfall events. Two rainfall events were simulated in the experiment. After the first rainfall event, structural crusts and the depositional crusts were formed on the slopeland 0° in gradient after 30 min of 80 mm h-1 rainfall, and then the slope lands were adjusted to 5°, 10°, 15° and 20° in gradient, step by step and each subjected to 30 min of 80 mm h-1 rainfall, to investigate rain water infiltration rates in the slopelands as affected by tillage pattern and slope gradient. Results show that soil crusts retarded water infiltration into the soil; consequently, runoff formed earlier on slopes with crusts than on slopes without crusts, and cumulative rain water infiltration was much lower on the former than on the latter. Infiltration rate decreased with increasing slope gradient regardless of the effect of soil crusts. Regression analysis of model simulation indicates that the Jiang Dingsheng model was optimal to describe variation of soil infiltration rate in this study. What type of soil crusts would be formed was significantly affected by tillage treatments. The structural crusts tended to form on ridges, which were directly impacted by rain drops while the depositional crusts formed in furrows between ridges as sediments in runoff deposited. Meanwhile, the structural crusts were lower in bulk density, but higher in porosity and in shear strength than the depositional crusts. The effects of the two types of soil crusts on soil water infiltration rate were different. Depositional crusts reduced accumulative water infiltration by 37.13%, while structural crusts did by 19.79% compared with the accumulative water infiltration on uncrusted slopes. It is quite obvious that the effect of depositional crusts reducing soil water infiltration is much higher than that of structural crusts.

Abstract:Diffuse reflectance spectroscopy within the visible and near-infrared (Vis-NIR) range is a promising way for acquisition of soil properties and digital soil mapping. The diffuse reflectance spectroscopy technique is rapid, nondestructive, environment-friendly and more efficient than the conventional analysis method. However, due to the diversity and spatial heterogeneity of soil, the prediction model based on the technique will have to face the issue of universality. Total nitrogen (TN) in soil is not only a significant index of soil fertility but also an important factor deciding crop yield. It is, therefore, essential to timely acquire the information of TN in soil. This paper introduces a method, i.e. locally weighted regression (LWR), as supplement to the use of the Vis-NIR spectrum technique in predicting TN in soil at a regional scale, and evaluates accuracy of the prediction using Vis-NIR plus LWR. To that end a total of four hundred and fifty soil samples were collected from Zhejiang, Jilin, Yunnan, Hainan and Gansu, air dried and ground to pass a 2 mm sieve. Their Vis-NIR diffuse reflectance spectra were collected using a FieldSpec Pro FR Spectrometer. The reflectance spectra in the wavelength range from 400 to 2 450 nm were denoised by Savitzky-Golay and first derivatived. Three fourths of the samples were selected for calibration dataset using the Kennard-Stone algorithm and the remaining one fourth were used as validation dataset. The core of the LWR method is to select samples from the calibration dataset most spectrally similar to those in the validation dataset. The algorithm of LWR goes in three steps: to decompose and compress the spectral matrix through Principal Component Analysis and pick out local modeling subsets from the modeling dataset similar to the validation dataset by Euclidean distance. Based on the spectral distance of each sample in the local modeling subset to the validation sample, weight of the sample in the regression model is defined, by means of tri-cube weight function. The number of principle components and the number of similar samples were the crucial parameters in the LWR model, and in this study, the two parameters were optimized to be 5 and 40, respectively. The determination coefficient (R_P 2), the root mean square error (RMSE_p ) and ratio of standard error of performance to standard deviation (RPD) was 0.63, 0.36 g kg-1 and 1.63, respectively, in the PLSR model. However, the support vector machine (SVM) model and artificial neural network (ANN) model was higher than the PLSR model in prediction accuracy (R_P 2=0.75~0.80, RMSE_p =0.27~0.30 g kg^-1, RPD=1.98~2.22). Thanks to the advantages of LWR in algorithm, the LWR model reduced the interference of samples lower in similarity in local modeling, and hence increased the accuracy of TN prediction (R_P 2=0.83, RMSE_p =0.25 g kg^-1, RPD=2.41). The findings demonstrate that correlation coefficient between soil TN and the spectral reflectance after first-order differential transformation peaks at 820, 1 400, 1 430, 1 630, 1 800, 1 930, 2 100, 2 200 and 2 300 nm, which overlap the important bands for spectral modeling of soil organic matter. Due to the spatial heterogeneity of the study areas and soil samples, the two crucial parameters, i.e. number of similar samples and number of principle components, of the LWR model vary with the modeling datasets, so they should be optimized when LWR is used to predict TN. The LWR TN prediction model diminishes the probability of underestimating TN content as the PLSR model would, and makes the prediction closer to 1:1 line. Besides, the LWR model performs better than the non-linear ANN and SVM models in TN prediction, and does not have any black-box problem. Therefore, it can be concluded that LWR is a reliable method for prediction of soil TN content when a large spectral database is available. With the consummation of various large-scaled soil spectral libraries, LWR can be used to tap more useful information out of these soil database and bring them into full play.

Abstract:Through soil column leaching experiments, migration of antimony in red and brown calcareous soil, typical to South China was studied. Samples were collected from the columns at the end of the experiment for analysis of proportions of varieus fractions of Sb(V) different in binding form using the sequential extraction method, based on which impacts of redox potential on migration of antimony, and of pH on migration of antimony in iron-coated quartz sands. The experimental results show that the migration of antimony in the brown calcareous soil had a higher peak value (C/C₀ = 0.88) on its penetration curve than that in the red soil (C/C₀= 0.26), and the effluence of antimony was observed earlier in the former than in the latter. In the red soil, "hangover" of the penetration curve was quite apparent. Things went just reversely with the second leaching effluence. The peak value of the penetration curve increased significantly with C/C₀ reaching up to 0.58 in the red soil, but decreased significantly in the brown calcareous soil as compared with the first leaching and C/C₀ reduced to 0.70, which indicates that the first leaching was imcomplete in the red soil and fairly thorough in the brown calcareous soil. The sequential extraction experiment reveals in the acid red soil antimony exists mainly in the form fairly strong in binding energy and stable chemically, so it takes a longer time for antimony to get through the soil column and the process of penetration is not so clear. In the brown calcareous soil, antimony exists quite similarly to its presence in the red soil in form and distribution pattern, but the proportion of weakly bonded forms of antimony (non-specifically adsorbed and specifically adsorbed forms) is higher than that in the red soil, which indicates that its adsorption is somewhat reversible, and may also explain why Sb in the brown calcareous soil needs less time to penetrate with a higher penetration peak. Soil pH has some effect on migration of antimony in iron-coated quartz sands. When pH was 4, antimony penetrated iron-coasted quartz sands displaying a nice symmetric penetration curve, without much hangover. With rising pH, symmetry of the curve was disturbed and the phenomenon of hangover became obvious. Based on the experiments it could be concluded that the antimony in the red soil is quite lower in mobility than that in the brown calcareous soil as is shown in the first leaching experiment, and the mobility improves in the red soil when leaching lasts long enough as is indicated in the second leaching experiment. Through the soil column extraction experiment, it is found that the antimony in the soils exists mainly in iron and aluminum oxides-complexed form, and a limited proportion in non-specifically adsorbed, specifically adsorbed or residue form, while the antimony content in brown calcareous soil consists more of weakly bonded forms, and that soil pH has some obvious effect on migration of antimony in iron-coated quartz sands and with rising pH, antimony weakens in mobility in the quartz sands.

Abstract:The ex-situ incubation method coupled with the atomic force microscopy in contacting imaging and phase imaging modes was used to explore how the surface of biotite, a phyllosilicate K-bearing mineral, is eroded or dissolved and its microstructure is altered by citric acid (CA) in simulation of what happens in rhizosphere environment. CA, a kind of low molecular weight organic acid is one of the most important components of root exudate and, therefore, ubiquitous in rhizosphere environment. Results show that in weakly acidic aqueous solution, 4.0 in pH, 24 hours of incubation left some tiny etch pits, about 0.1~0.9 nm in depth, on the surface of biotite (001), making the surface rough. After 96 h of incubation, pits became more apparent, averaging 0.957 nm in depth, and more in number, but only covering 4.8% of the surface. After 140 h, an unstable coating precipitated on the surface, hindering the process of dissolution. However, in citric acid solution (CA) 4.0 in pH, after 24 h of incubation, large numbers of etch pits appeared on the surface of biotite (001) and dissolution of the surface layer became apparent. After 48 hr, the surface terrace dissolution rate of the biotite increased significantly, with dissolved area reaching 48.7% of the surface. And 140 hr later, circular spallings were observed on the (001) surface, leading to breakage of the layer (1~2 nm in thickness) into fragments and promoting further rise in dissolution rate. In CA solution containing Na⁺, rising Na concentration increased dissolution rate of the surface and was a secondary coating was formed, too. Meanwhile, K -Na ion exchange on the solid-fluid interface was enhanced and spalling in the (001) surface structure, about 2~10 nm in depth became more and more apparent. With the incubation going on (140 hr), biotite expanded in depth (~20 nm), causing cracks in the perimeters (0.1~1.9 nm in depth) and eventually zonal hydration of the surface microstructure, and formation of hydrous mica (illite) on the surface of the biotite.

Abstract:Soil oxidation with reactivated sodium persulfate (SPS) is a new kind of in situ soil remediation technology. In order to assess scientifically the environmental risks of the chemicals to oxidized soil, two types of soils obviously different in organic matter(OM) content were oxidized with ferrous ion activated SPS and then used to explore the effects of oxidation on sorption behaviors of three volatile organic contaminants (VOCs) in the two soils. Results show that the oxidation had great effects on soil organic matter (e.g., humic acids and humins). It removed 71.9% of the organic matter in Soil No. 1, which was relatively high in soil organic matter and 49.9% in Soil No. 2, which was relatively low in soil organic matter. The sorption of the three compounds in Soil No. 1 was dominated by the mechanism of partition. Soil oxidation did not alter the dominance, but slightly increased its sorption capacity. The sorption of the three compounds in Soil No. 2 was somewhat nonlinear, implying the existence of some other sorption mechanisms. However, the sorption isotherms became more linear after oxidation. The normalized logarithm of partition coefficient of organic carbon content (lg K_foc ) was used to evaluate OM sorption capacity of the soils as affected by oxidation. Lg K_foc of the three compounds in the two oxidated soil samples were substantially higher than those in the original soil samples. The analysis indicates that activated SPS oxidized quite a portion of polar components (such as carboxyl and hydroxyl etc.) of OM so that the polarity of the OM was reduced, thus in turn enhancing its sorption of non-polar compounds.

Abstract:To explore characteristics of δ ¹³C value of soil organic carbon (SOC δ ¹³C) under naturally restoring degenerative forest in the karst region of Maolan, the technique of stable carbon isotopes coupled with the concept of space substituting time was adopted. Results show that as a whole, SOCδ ¹³C in the 0~20 cm soil layer(-25.72‰~-19.91‰) increased along with the restoration in process, turning gradually towards positive, but SOCδ ¹³C in soil layers >20 cm (-23.76‰~-18.13‰)in depth turned towards positive at early stages and then backwards at later stages; SOC δ ¹³C turned towards positive increased with soil depth at all stages except at the grass-shrub and shrub-arbor stages; SOC in the upper soil layer at the grass-stage and in the lower soil layer at the arbor and climax stages was dominated with C₄; SOC δ ¹³C were jointly affected by zonality and karst environment; δ ¹³C in litters of dominant species (-31.79‰~-16.76‰)turned towards negative along with the restoring process, indicating that the habitat was improving, and besides, it was significantly and positively related to SOCδ ¹³C in the 0~20 cm soil layer（R²>0.96，p<0.01）, but negatively to that in the soil layers >20 cm in depth, indicating that the carbon in the upper layer was new; the turn-over rate of SOC increased with the restoring process, but decreased with soil depth; soil biochemical reaction occurred mainly on the surface of the soil; SOC δ¹³C exhibited significant negative relationships with contents of mineralizable carbon and readily oxidizable carbon (R²>-0.50, p<0.05), and certain negative relationship with microbial biomass carbon(R²=-0.389), indicating that SOC δ¹³C can, to a certain extent, be used as indicator of SOC activity; natural restoration of karst forest vegetation was a complicated and variable integration of multi ways, among which C4 plants played a role of important significance in process of natural restoration. The stable carbon isotope technique coupled with the concept of “space substituting time” can be used to rehearse the history of vegetation succession in karst regions.

Abstract:A field experiment was conducted to study effects of slow-release compound fertilizer on yield and quality of eggplant relative to timing of harvest. The study is of some great theoretical and practical significance to application of slow-release compound fertilizer in production of solanaceous vegetable. Harvests of eggplants throughout the entire harvesting period were recorded and samples of eggplants were collected 3 times during the harvesting period for determination of nutritional quality (vitamin C, amino acid and soluble sugar), hygienic quality (nitrate) and health quality (flavonoids, rutin and solanine) of the eggplant. Results show that slow-release compound fertilizer (Treatments SRF) increased the yield of eggplant by 3.5%～29.1% and 3.7%～24.8% compared to chemical fertilizer (Treatment CF) and common compound fertilizer (Treatment CCF). In terms of yield level, the treatments were in the sequence of SRF1 ＞SRF4 ＞ SRF2 ＞ SRF3 ＞ CCF ＞ CF. Besides, the treatments also significantly increased the content of vitamin C, amino acid and soluble sugar in the fruits harvested at the late full fruiting stage and Treatment SRF3 significantly lowered the content of nitrate in the fruits harvest at the mid and late full fruiting stage compared to Treatment CF and Treatment CCF. As to health quality, Treatments SRF significantly increased the content of rutin by 10.0%～24.0% and 10.0%～50.0% in the fruits harvest at the mid and late fully fruiting stages, and lowered the content of solanine by 33.9%～47.7%, 36.8%～49.0% and 18.7%～35.4% in the fruits harvested at all the full fruiting stage. The effects of Treatments SRF1 and SRF2 were the highest. Among the three SRF treatments, Treatment SRF1 was the best in terms of yield and quality of eggplants, and followed by Treatment SRF2, while in terms of yield/efficiency of the crop, Treatment SRF2 was No. 1.

Abstract:Innovative management practices are required to increase soil fertility and to reduce nitrous oxide (N₂O) emission from agricultural soils. Spatial heterogeneity of N₂O flux is attributed to various soil properties associated with different management practices. N₂O flux is the result of integration of N₂O production, consumption, and transport processes within soil profiles. N₂O production, consumption, and transport processes varied markedly with depth near the soil surface. Variations of N₂O concentration were monitored at 7 cm, 15 cm, 30 cm, and 50 cm in depth along a soil profile (each monitoring point covering a range of 5 cm of soil layer) using an in-situ gas collection system under the rice-wheat annual rotation cropping system. The experiment was designed to have 2 levels of N application and 3 levels of straw incorporation, i.e. N0 (N 0 kg hm^-2 crop^-1) and N1 (N 250 kg hm^-2 crop^-1), and S0 (straw 0 t hm^-2 crop^-1), S1(straw 3 t hm^-2 rice crop^-1), and S2 (straw6 t hm^-2 rice crop^-1), forming four treatments, i.e. N0S0, N1S0, N1S1 and N1S2, and each treatment had 3 replicates. The observations, once a week over the two cycles of rice and wheat rotations from June 2010 to May, 2012 found that N₂O concentrations in soil profiles demonstrated a significant feature of spatio-temporal distribution for all the treatments. N₂O concentration peaked during the early growth stages of both wheat and rice, and then fluctuated slightly during the rest of the growth season; N fertilization significantly boosted the peak, while incorporation of rice straw, particularly in Treatment N1S2, lowered the peak. However, neither N fertilization nor straw incorporation affected seasonal dynamics of N₂O concentrations in various soil layers of a profile. During the wheat seasons, distinct N₂O concentration distributions were observed in the soil layers at 30 cm and 50 cm in depth. During the first wheat season, N₂O concentration in soil profile displayed a decreasing order of 30 cm ≥ 50 cm ≥ 15 cm ≥ 7 cm and during the second wheat season, 50 cm ≥ 30 cm ≥ 15 cm ≥ 7 cm; But during the rice seasons, N2O focused in the surface soil layers, at 7 cm and 15 cm, and followed an order of 15 cm ≥ 7 cm ≥ 30 cm ≥ 50 cm in both rice seasons. Soil N₂O concentrations in the three N fertilized treatments, N1S0, N1S1 and N1S2, were significantly higher than that in CK (N0S0). Particularly in Treatment N1S0, it was 2 to 3 times that in CK in all the corresponding soil layers during the two rice-wheat cycles (p<0.05). To the contrary, straw incorporation at a high rate significantly reduced N₂O concentrations in the near surface soil layers (p<0.05), but increased to some extent in the lower soil layers in the rice season. The findings indicate that N₂O concentrations vary markedly with depth in the soil layer between 0 and 50 cm under the annual rice and wheat rotation and that straw incorporation at a high rate markedly reduces N₂O concentration near in the surface soil layer. The underlying mechanism of straw incorporation reducing N₂O concentration in the surface soil layer requires further research.

Abstract:Freshwater scarcity is a serious long-term hindrance to the agricultural production in arid and semi-arid regions. While the supply of brackish water is quite plenty, therefore the use of brackish water or saline water for irrigation has received considerable attention in those regions. A field experiment was carried out to study the effect of drip irrigation with saline or brackish water in cotton (Gossypium hirsutum L.) fields on fate of nitrogen in the soil relative to salinity of the water, irrigation rate, and N application rate. ¹⁵N-labeled urea was applied in the experiment field or plots to trace N movement in the soil. The experiment was designed to have three treatments (S_0.35, S_4.61, and S_8.04) in salinity of irrigation water (0.35, 4.61, and 8.14 dS m^-1, respectively), two levels in irrigation rate (405 mm and 540 mm), and two levels in N application rate (240 and 360 kg hm^-2, 360 kg hm^-2 is a common rate used by local farmers). The experiment shows that both cotton yield and N uptake were significantly lower in Treatment S_8.04 than those in Treatment S_0.35 and S_4.61, and there was no significant difference in either cotton yield or N uptake between Treatment S_0.35 and Treatment S_4.61. Salinity of the water affected mainly the number of cotton bolls and hence yields of the crop. Cotton yield and N uptake increased with irrigation rate and N application rate. Results of ¹⁵N tracing show that the plant 15N recovery rate ranged from 34.20% to 62.51%, and followed a curve that rose first and then declined with rising salinity of the water. Plant ¹⁵N recovery rate in Treatment S_4.61 was 30.70% higher than that in Treatment S_0.35 and 41.77% higher than that in Treatment S_8.04. Higher irrigation rate or N application rate significantly increased plant ¹⁵N recovery rate, however, higher salinity of the irrigation water decreased that. Treatment S_8.04 and Treatment S_8.04was 4.03% and 23.88% higher, respectively, than Treatment S_0.35 in soil ¹⁵N residue rate. Increase in N application rate from 240 kg hm^-2 to 360 kg hm^-2increased soil ¹⁵N residue rate by 9.51%. Total ¹⁵N recovery rate was significant higher in Treatment S_4.61than in Treatment S_0.35and Treatment S_8.04 ¹⁵N leaching rate in the treatments ranged from 0.35%~3.59%, depending on treatment and was significantly affected by salinity of the irrigation water. When N application rate was low (240 kg hm^-2), ¹⁵N leaching rate did not differ much between Treatment S0.35 and Treatment S_8.04, but the rate in Treatment S_8.04 was 187% higher than that in Treatment S_0.35 and 84% higher than that in Treatment S_4.61. When N application rate was high (360 kg hm^-2), ¹⁵N leaching rate increased significantly with salinity of the irrigation water, irrigation rate, and N application rate increased. The above-listed findings suggest that the use of brackish water in drip irrigation, if salinity of the water, irrigation rate and N application rate are all controlled to a proper level, would not affect growth, yield and N recovery of the cotton crop. But if the water is too high in salinity it would inhibit cotton growth and lower cotton yield and nitrogen use efficiency as well. In this experiment, 60.22% to 86.70% of the N fertilizer applied was recovered by the crop, 0.35% to 3.59% lost through leaching and the remaining 12%~38% through ammonia volatilization, nitrification and denitrification. Therefore, a suitable “water-salt-fertilizer” management helps improve nitrogen fertilizer utilization efficiency and reduce N loss.

Abstract:The processes of modernized infrastructure construction and urbanization in China are promoting rapid development of the economy of the country. By 2013, the national highway and high speed railway traffic mileage had reached 104 400 km and 13 000 km, ranking first in the world. However, any one of the national major engineering construction projects is done at the expense of soil ecology, disturbing the circulation of material and biomass in the pedosphere, aggravating soil erosion and geological planation process. It is, therefore, essential and imperative to remedy the soil ecology after the construction is completed. A review is presented here of the researches and development in this aspect in the past 15 years, elaborating emphatically characteristics of the soil destruction caused by the national major engineering construction, like highways, high-speed railways traffic network construction, urbanization; discussing innovative technologies for soil ecology remediation of roadside slopes, city high steep rock slopes, etc. by taking into account a large number of soil ecology remediation engineering practices as examples; and providing a technical support system for ecology remediation of erosive soils in infrastructure construction in South China. After the construction of highways and high-speed railways, large tracts of soil ecology alongside the highways or railways were disturbed or damaged. About 70% of the soils existed in the form of slope, complete in soil structure and profile feature. Subjected to long term exposure, those bare slopes tend to generate large volumes of runoffs of water and sediment. The road or railway construction projects are often laid out linearly, stretching over a wide range of bio-climate zones with zonal climate interlaced with stereo climate. So in restoring vegetation on the slopes, shrubs, leguminous plants and plants of local varieties should be used as mainstay. Such vegetation integrating trees, shrubs, grass and vine, which mutually supplement each other in plant shape, forming a harmonious landscape. Urban steep rock slopes often result from explosions in engineering and lack such basic conditions as soil, water, nutrient, for plants to survive. Revegetation on such slopes is costly and technically does not have much choice. The technique of V type groove coupled mulching with nets fixed with bolts on the slopes and spraying suspension of grass seeds can be used to restore soil ecological landscape. This is a quite mature inventive technique for restoration of soil ecology on steep rock slopes in China.

Abstract:For further revealing the influence of inoculating arbuscular mycorrhizal (AM) fungi on the microbial community structure of soybean rhizosphere, this in field experiment were carried out taking soybean as the study object. Two AM fungi strains, Glomus mosseae (GM) and Glomus intraradices (GI), were inoculated with soybean in field, setting fertilization treatment (F) and no AM inoculation

Abstract:Potassium (K) is an essential nutrient element for plant growth. However, in most soils, K is low in both concentration and availability. Chemical K supplemented through fertilization is rapidly adsorbed by soil minerals or transformed by soil microbial organisms, resulting in low K use efficiency, as low as 20%~35%. Studies have found that Azotobacter sp., which can fix nitrogen from the atmosphere to supplement plants with nitrogen nutrient, also has the ability to mobilize soil K for plant use. The finding has aroused much attention the world over. However, little information is available to illustrate the mechanisms of Azotobacter mobilizing K in the soil. Five strains of Azotobacter sp., which were isolated from a gray brown purple soil in Chongqing, South China and coded as N01, N02, N03, N04 and N05, separately, were cultured a liquid medium in an experiment to study their K mobilization capacities. The medium contained 1L of H₂O, 10 g of mannitol, 0.176 g of NaH₂PO₄, 0.2 g of MgSO₄•7H₂O, 0.2 g of NaCl, 0.2 g of CaSO₄•7H₂O and 5.0 g of CaCO₃. Compared to the non- Azotobacter control, all the five Azotobacter treatments were found to be 40 times higher in concentration of hydrogen ions in the liquid media, as a consequence, pH dropped significantly after 7 days of incubation. The Azotobacterstrains all exude organic acids, including formic acid, acetic acid, oxalic acid, succinic acid, citric acid, malic acid and lactic acid, but vary in capacity and excretion of acids. Oxalic acid and malic acid was the most common ones all the five strains could exude. K concentrations in the liquid media were significantly higher than in the control, whilst the contents of soil mineral structure K were significantly lower in the Azotobacter treatments than in the non- Azotobacter treatment. Taking into account the soil being the sole K source, it is quite obvious that Azotobacter could promote dissolution of mineral K in the soil. Correlation analysis shows that content of soil mineral structure K is negatively related to the total organic acids Azotobacter exude (r= -0.845*,n = 6), but positively related to pH of the liquid medium (r = 0.702*, n = 6), which indicates that both the organic acids Azotobacters exude and hydrogen ions could dissolve soil K. Oxalic acid is the major organic acid Azotobacters exude in high volume and the most competent in complexing calcium, magnesium, iron and aluminum, and moreover, it is positively correlated with total organic acid (r= 0.990**, n = 6), which suggests that oxalic acid exuded by Azotobacter might contribute directly to the mobilization of soil K. Meanwhile, soil mineral K was significantly reduced in all the Azotobacter treatments, to a varying extent, which depended on which strain of Azotobacter was used in this study, because the strains of Azotobacters vary sharply in exudation, in terms of amount and type of organic acids they exude. The findings demonstrate that inoculation of Azotobactersor intercropping with legumes is a good alternative to improve plant K nutrition, besides, Azotobactersand legumes can also help supplement the soil with nitrogen by fixing it from the atmosphere,. Therefore, more efforts should be devoted to researches on the capability of Azotobacters of mobilzing soil K, and their associated nitrogen and K benefits to their host plants and neighbouring plants.

Abstract:Conservation tillage, a new kind of cultivation technique or agricultural practice includes no-till, reduced tillage and straw mulching. The aim of conservation tillage is to protect the environment, improve soil quality and save farming cost. Straw degradation plays a very important role in implementation of conservation tillage. Therefore, it is of great significance to study diversity of cellulose degrading bacteria in the soils different in conservation tillage practice. Currently, scholars at home and abroad have been doing a lot to study cellulose degrading bacteria, focusing mainly on screening and isolating of cellulose degrading bacteria and cloning of cellulose degrading gene. But little has been reported on diversity of cellulose degrading genecbhⅠ. It is, therefore, necessary to do something in depth on diversity of cellulose degrading gene cbhⅠ in soils under different conservation tillage practices. Hence, effects of four conservation tillage practices, i.e. C_ntW_tS (tillage with mulching), C_ntW_ntS (no-tillage with mulching), C_ntW_t (tillage without mulching) and C_ntW_nt (no-tillage without mulching) were explored on diversity of cellulose-degrading bacteria in typical fluvo-aquic soil in the Huang-Huai-Hai Plain. Cellulose degradation bacteria in soils of different treatments were counted using the traditional plate colony counting method, and diversity of cellulose-degrading gene cbhⅠ was analyzed using the PCR-RFLP techinique (Polymerase Chain Reaction-Restriction Fragment Length Polymorphism). Results show that Treatment C_ntW_ntS was 148% higher than Treatment C_ntW_nt in population of cellulose-degrading bacteria, and Treatment C_ntW_tS was 130% higher than Treatment C_ntW_t, too. And the four treatments were all quite rich in cbhⅠ genotyping, amounting to 44 OTUs in total. Treatnent C_ntW_ntS was found to have 35 OTUs, Treatment C_ntW_tS 34 OTUs, Treatment C_ntW_nt 30 OTUs and Treatment C_ntW_t 30 OTUs, indicating that straw mulching could increase the number of cellulose-degrading bacteria that can decompose the straw, releasing nutrients into the soil. Analysis of diversity index shows that Shannon-Wiener index varied in the range between 3.09 and 3.36, and that straw mulching and no-tillage improved the diversity of cellulose degradation bacteria. Phylogenetic analysis shows that the cellulose-degrading bacteria in the libraries mainly belong mainly to Basidiomycota and Ascomycota. And Basidiomycota is the dominant phylum. Tillage and no-tillage have some influence on Basidiomycota, but almost none on Ascomycota. Meanwhile, a large number of uncultured cellulose-degrading bacteria were found living in the soils. Therefore, it can be concluded that conservation tillage, like no-tillage and straw mulching, can significantly increase the number of cellulose-degrading bacteria and enrich its cbhⅠ gene diversity.

Abstract:As rice is one of the most important crops in the world, paddy ecosystems has attracted worldwide attention because of their importance in food supply and their eco–functions as wetland. In paddy fields, frequent alternation of wetting and drying required in rice production leads to drastic fluctuation of soil redox potential, thus affecting various microbe-driven aerobic and anaerobic biogeochemical element recycling processes in the soil, including nitrification, respiration and denitrification etc. Since the 1980s, excessive application of chemical fertilizers in various paddy field system management practices in China has brought about a series of environmental consequences, and most of the relevant research efforts in the country have been focused on emission of N₂O, nitrification and denitrification, nevertheless, little is known about the underling microbiological mechanism. Nitrification is an aerobic microbe catalyzed aerobic process, consisting of two steps, i.e. ammonia oxidation and nitrite oxidation. Ammonia oxidation, the rate-limiting step, is mainly catalyzed by ammonia-oxidizing bacteria (AOB) and recently discovered ammonia-oxidizing archaea (AOA). It is generally held that soil moisture ranging between 50% and 70% of water holding capacity (WHC) is the most suitable moisture condition for nitrification, and soils, too dry or too wet, are unfavorable to nitrification. Compared with upland soil, paddy soil is subjected to frequent alternation of drying and wetting, which leads to drastic fluctuation of soil redox potential, thus affecting microbe-driven biogeochemical element recycling processes and metabolic activity and functional succession of soil microbes. Being the major factors affecting soil redox potential, moisture and oxygen therefore become the key factors in the study on nitrogen recycling in paddy soil. To investigate responses of nitrification and nitrifying microbes to change in soil moisture and their underlying microbiological mechanisms, soil sample was collected from a paddy field of alkaline paddy soil, typical of Binhai County, Jiangsu Province, and soil microcosm experiments were set up with 4 moisture gradients including 30%WHC (Treatment 1), 60%WHC(Treatment 2), 90%WHC (Treatment 3), and 2 cm of overlaying water (Treatment 4). Results show that soil Eh was significantly lowered in Treatment 4, and did not differ much between the other three treatments. It varied from 330 to 500 mV, in all the treatments, indicating that on the whole the soils in all the treatments remained in oxidation state that satisfied nitrification basically even under flooded conditions. During the 60-day incubation period, 10 mg kg^-1 NH₄⁺-N was added into soil once every 7 days. Apparent decrease in concentration of NH₄ -N was observed in all the moisture treatments over time, accompanying rapid accumulation of NO₃^--N, which was the most obvious and rapid in Treatment 2 (60%WHC) and then in Treatment 3 (90%WHC). Even though accumulation of NO₃^--N was slow in Treatment 1 and Treatment 4, active nitrification was also observed with the incubation going on. Compared with Treatments 1, 2 and 3, Treatment 4 was much higher in abundance of ammonia oxidizing bacteria (AOB). The dominant AOB bands in DGGE profiles were more distinct and brighter in Treatment 4 than in the others, and the number of AOB bands in the DGGE profiles increased significantly in the late incubation period, that is, from 30 days to 60 days, while AOA (ammonia oxidizing archaea) did not differ much either in abundance or in community structure between the 4 treatments. In addition, AOA dropped sharply in abundance in all the treatments after 15 days of incubation, which may be attributed to the inhibitive effect of continuous nitrogen addition on AOA. All the above described findings indicate that different ammonia oxidizing microbes have different requirements for water and oxygen, and the AOB in this type of soil, being very sensitive to changes in soil moisture condition, are responsible for the nitrification in the tested soil, especially, in waterlogging conditions.

Abstract:Soil erosion is an important driving factor of soil organic carbon (SOC) dynamics and plays an extremely important role in the long-standing problem of "missing of carbon sink". Transport and deposition of soil particles on the earth’s surface triggered by soil erosion cause variation of soil microbes in distribution with the position of soil erosion. which in turn affects carbon sequestration and mineralization on the soil. Therefore, it is necessary to figure out how soil erosion affects soil microorganisms and then acts on soil organic carbon. The knowledge will help understand correctly the role of soil erosion in global carbon recycling A field simulated rainfall experiment was conducted on a runoff plot (2m × 5m) in a red soil hilly region of South China, to study dynamic changes in SOC and number of microbes in the surface soil of the plot within a short time period (10 days) as affected by rainfall and the resultant soil erosion with the aid of quantitative Polymerase Chain Reaction (qPCR) technology. On such a basis, relationship between soil microbes and SOC was analyzed, so as to provide some fundamental theoretical basis for the exploration of the role of soil microbes in SOC dynamics as affected by soil erosion. The plot was evenly divided into five sections along the slope, namely, A, B, C, D, and E (each 1 m long). Prior to rainfall simulation, soil samples were collected separately from the soil layers (0～10 cm depth) of Sections A (Up slope, US), C (Middle slope, MS), and E (Lower slope, LS) for analysis of basic soil properties. Boreholes left by the samples were immediately filled up with soil from nearby and carefully leveled so as to minimize any possible impact of the sampling on effect of the later rainfall simulation. Soil samples were collected again in the same manner as soon as the simulated rainfall stopped. The second batch of samples were collected 35 h after the rainfall stopped, and then the third, forth ..... batches were at 24 h intervals within the 10 days after the simulated rainfall. The soil samples were all analyzed for basic soil properties and number of soil microbes immediately as they were collected. Results show that after the rainfall, SOC content in the surface soil layer increased in Sections US and MS, but decreased in Section in LS, as a result of rainfall erosion, however, the changes were not significant. Meanwhile, the rainfall and its resultant erosion significantly changed the distribution pattern of soil microbes. The number of soil bacteria in the surface soil layer dropped significantly down to 58.76% (US) , 55.22% (MS) and 55.82% (LS) of that, respectively, before the rainfall, and the number of fungi increased to 105.51% in Section US, and fell to 2.29% in Section MS, and 12.20% in Section LS. After the rain, SOC content number of bacteria and number of fungi all significantly increased and peaked within a short time period, and then decreased, however, the peaks of the three appeared differently in time, which may be attributed to the difference between bacteria and fungi in multiplication rate and magnitude. In addition, correlation analysis shows that rainfall erosion disturbed greatly the relationships of SOC with soil bacteria and fungi, as a result, the post-rainfall relationships of SOC with soil bacteria and fungi in different sections varied from what was found in other studies and no positive correlation was found between them, except for the umber of bacteria in Section LS and the number of fungi in Sections MS and LS and the whole runoff plot, which were found positively related to SOC. In a word, soil erosion does not only directly affect SOC distribution on the earth's surface, but also alter the abundance and activity of soil microbes and hence further influence SOC decomposition and mineralization. Therefore, more attention should be paid to the role of soil microbe in global carbon recycling as affected by soil erosion. However, this experiment was quite limited in simulation of soil erosion. More efforts should be devoted in future to studies on dynamics of soil microbes and SOC in soils under different extents of soil erosion with foci on specific role of soil microorganisms in SOC dynamics and related microscopic mechanism.

Abstract:In plotting a 1:50 000 soil map of China, color matching of soil types is required to manifest characteristics of the distribution of soil types or soil categories, higher in soil classification level than soil type, and to demonstrate, as well, differences between soil categories, low in soil classification level, like soil genera. As in soil classification, China has a huge number of low-grade soil taxons, and a 1:50 000 national soil map of China consists of at least 20 000 rolls of sectional soil maps, the use of the conventional manual coloring method in soil mapping is not only very low in efficiency, but also finds it hard to keep all these rolls of soil maps consistent in color. To solve this technical problem, a soil type color matching model (SCO-Model) was developed, based on the designing concept of human-computer interaction and the inter-roll similar color matching method, The SCO-Model consists of three major components: i) a multi-level management color table, ii) QC table for user to define color matching unit Q of soil types and 3 similar color systems or color groups for each Q, iii) five Sub-models, including a statistical analysis model for soil types, a threshold determination model for unit Q, a color selection model for unit Q, a calculating color-code model, and a browsing map model. Results show that the SCO-Model can not only manifest the characteristics of the overall distribution of soils in a region, and the differences between soil types, but also realize rapid intellectural color matching of soil types in large scale soil mapping.

Abstract:Sampling site maps not only show intuitively distribution of the sampling sites where soil samples have been collected, but also provide reference for researchers to determine where supplementary soil samples should be taken. Traditionally, in soil mapping, codes were used to label each sampling point in the map for identification. However, as affected by their spatial geographic locations, it is impossible to label the sampling sites in sequence, thus making it very hard to locate a required sampling site in the map, especially when it has too many sampling sites located densely or is too large in format. To realize orderly labeling of sampling points, a “Soil Sampling Point Labeling Model for thematic soil maps (SAMPLA)" was developed, consisting of three sub-models, i.e. map reading vision zone division model, soil sampling site attribution map reading vision zone determination model and, sampling point sequential labeling model. With the aid of ArcGIS 10.0 and Human Machine Interaction（HMI）design, SAMPLA was translated into a computer program with the C# programming language, and tested with soil sampling points in the 1:50 000 national standard map sheets and county-level maps. Results show that the model is applicable to maps different in type and scale, helps realize standardized mass mapping, and improves map reading efficiency. But labeling was slightly affected by the map reading vision zone division program. However, besides in soil sciences, SAMPLA can also be used in other scientific fields, such as environmental science, water science, and geological science, for making sampling point distribution maps.

Abstract:Potential in electric double layer is a principal parameter of significant importance in researches on particle-particle interactions and availability of nutrient elements in soil. In this study, a new method was designed to determine surface potential and Stern potential. This method can used to describe Stern potential by taking into account polarization of the strong surface electric field and to obtain surface potential of soil particles by taking into account the effect of coupling of ion steric hindrance and polarization. Tests of the method reveal that only point charge H+ (no steric hindrance and polarization) can be used as signal transmission to characterize charged particle surface. The surface potential determined is 5 times as high as Stern potential. In the light of distribution of the potential, the potential declines linearly in the Stern layer, and follows the Boltzmann pattern in distribution in the diffuse layer, and the descent is much faster in the Stern layer than in the diffuse layer.

Abstract:Vegetation reconstruction is the most direct biological measure and the most effective one as well to control soil and water losses from dump slopes of an opencast coal mine. The knowledge of spatial distribution variability of soil organic carbon (SOC) and total nitrogen (TN) contents in the dump slope as affected by revegetation pattern is essential to selection of proper vegetation patterns that fit the dump slope. The study area was set in the Heidaigou opencast coal mine in Inner Mongolia Autonomous Region, where the dump slopes had been under management for 15 years, using 4 revegetation patterns (natural recovery land, grassland, shrub land, woodland). A total of 270 soil profiles (0~100 cm) were collected as samples for analysis of variability of SOC storage as affected by revegetation pattern. Results show as follows: (1) Revegetation patterns significantly affected SOC and TN contents and their distribution in the soil profile (p<0.05). In terms of SOC and TN contents in the 0~10 cm and 10~20 cm soil layers, the four revegetation patterns displayed an order of grassland > shrub land > woodland > natural recovery land, while in terms of SOC and TN contents in the soil layers below 20 cm, a similar trend could be found, but the differences between the four narrowed with increasing soil depth. (2) In terms of SOC density and storage, an order of undisturbed land > managed watershed> managed dump > new dump was found. After 15 years of revegetation, the dump slopes demonstrated a tremendous carbon sequestration capacity. The SOC storage in the 1 m soil layers of the woodland and grassland was 5.38 t hm^-2 and 11.85 t hm^-2, respectively, higher than that in the new dump, but only reached 1/2 and 3/5 of that in the undisturbed land. (3) The carbon sequestration rate of the woodland and grassland was 35.87 g m^-2 a^-1 and 79.01 g m^-2 a^-1, respectively. The latter was 2.2 times of the former. From the perspective of soil organic carbon sequestration and soil erosion control, grassland is the priority revegetation pattern recommended for management of dump slopes of opencast coal mines and followed by shrub land.

Abstract:To boost food production in coastal regions, a study was carried out to analyze relationships between soil properties and wheat production. For that end, soil samples were collected in the soil layer (0~20cm) of salinized wheat fields for determination of soil physicochemical properties, and wheat yield and biomass of the sampling sites were monitored. Results show that yield and biomass of wheat was significantly and negatively related to soil salt content (p<0.01), and the relationsip fitted a cubic equation well. If 4 500 kg hm^-2 was set as the minimum target yield, salt content in the soil should be lowered below 3.1 g kg^-1. Soil salt content was significantly and negatively related to organic matter content in the soil, while yield and biomass of the wheat crop was significantly and positively related to that (p<0.01), which suggests that increasing soil organic matter content can reduce soil salt content and boost wheat production. To evaluate of effect of soil organic matter suppressing soil salinity, ratio of soil salt content in the sub-surface soil layer (>10~20 cm) to that in the surface layer (0~10 cm) was used as salinity suppressing efficiency (E ). The relationship between E and organic matter content in the surface soil fitted a quadratic functional equation well. The effect of organic matter on suppressing soil salinity became obvious, when soil organic matter content in the surface soil was increased up to or higher than 19.1 g kg^-1, which can, therefore, be set as a target value for soil fertility building of saline soil. Besides, increasing soil readily available K content can significantly boost wheat production, too, in saline soil. In a word, the findings of this study are of great significance to soil building and grain production in the studied and similar regions.