Abstract:As the second most abundant element in the Earth crust after oxygen, the transfer and transformation of silicon (Si) are one of the most important processes of soil formation and evolution. Biological processes are known to play significant roles in soil formation and mineral weathering. Especially, plants can take up dissolved silicon (DSi) and deposit it to produce silicified structure as phytolith, a kind of biogenic silicon (BSi). In this paper, a chronosequence including seven basalt-derived soil profiles in northern Hainan Island was studied. The extraction of BSi was conducted following a wet extraction procedure, in which heavy liquid of ZnBr₂ (2.35 g cm_-3) was used to separate phytoliths from other heavy mineral fractions. Results showed that contents of BSi in the soils varied widely from 2.9 to 54.0 g kg^-1. The highest concentration of BSi occurred in the surface horizon of profile HE09, a young soil on basalt, while the lowest was found in the B2 layer of HE11, an older soil in the sequence. In general, the contents of BSi, OC and TN are high in the surface horizon of soil profiles and decrease rapidly with depth. This phenomenon is prominent in topsoil, especially from surface to 40 cm. The finding implies that the accumulation of BSi in topsoil is mainly due to BSi release from organic matter during its decomposition. During soil development, these soils became progressively more weathered, with base cations depleting, clay fraction increasing and pH decreasing. Furthermore, a linear correlation between BSi and TSi was found for all soil samples, indicating that BSi determines to a certain extent the whole Si cycles during soil development. In the initial stage of soil development, DSi from weathering of primary minerals may contribute to the conservation of BSi, while with time, continuous high rainfall and depletion of cations leads to leaching or recycling of BSi faster than plants can bring it to the surface. As a result, the contents of BSi may maintain a relatively stable state with the function of biogenic pump in the soil-plant system. In conclusion, BSi is playing a very important role in tropical soil formation and evolution, especially in the biogeochemical cycles of Si.

Abstract:Soil formation is the basis for determinantion of soil permissible erosion rate. In this study, soil formation rates (SR) of the purple soils (Regosols) different in parent material, vegetation and thickness in hilly areas of Sichuan, China were calculated using the Barth model that is based on the material recycling theory, and measured at the stationary experiment sites in the field. Results show that estimated-SRs were generally, smaller than measured-SRs, and varied significantly with parent material, but not with vegetation or soil depth. Moreover, they were closely related to runoff volume. Measured-SRs varied substantially between the treatments, owing to different characteristics of soil parent materials and different temperature and soil moisture at the interface between soil and parent materials. In terms of measured-SR the three types of soils showed an order of J₂s> J₃p> J₃s, and the three vegetations did an order of crop> trees> grass. The general trend of soil formation rate in relation to soil depth was that the thinner the soil layer was; the higher the rate was. Based on the measured-SR, the SR was determined to be 800 t km^-2 a^-1 for J₃s purple soils, and 1 200 t km^-2 a^-1 for J₂s purple soils and for J₃p purple soils in the study region.

Abstract:Based on a simulated rainfall experiment in the field, effect of grass coverage on slope erosion was studied, and comparison between runoff erosion power, expressed by runoff depth and peak discharge modulus, and rainfall erosion force by sediment yield was conducted to analyze the role of the vegetation regulating erosion dynamics on the slope. Results show that the vegetation cover affected runoff and sediment generation significantly. Runoff and sediment yield reduced rapidly with the vegetation coverage increasing from 0% to 60%, however, when coverage exceeded a critical value, 80%, the effect was not so significant and leveled off. The critical vegetation coverage ranging from 60% to 80% is determined in this study. Both runoff erosion power and rainfall erosion force were positively related with sediment yield, and the former was more significant than the latter, suggesting that runoff erosion power may be used to better simulate erosion dynamics. The presentation of the effect of vegetation coverage on erosion by the ratio of runoff erosion power/erosion volume reflects existence of critical vegetation coverage, which can be used as a new index to evaluate regulatory effects of vegetation cover on soil erosion dynamics.

Abstract:An experiment was carried out in the Yimeng Mountains, a typical earth-rocky mountainous region, in Shandong Province, China. Derived from gneiss and sandstone, the soil therein is loosen in texture and susceptible to soil erosion. Owing to lack of historical data on soil erosion and sediment transferring, it is hard to predict any mediumlong term (50 a) mean soil erosion rate. The method of using ¹³⁷Cs as soil tracer makes it feasible to study soil redistribution on a catchment scale. Moreover, it is reliable and time- and labor- saving. In this experiment this technique was used to study soil erosion and deposition rates in the area. A total of 72 samples were collected and tested for contents of ¹³⁷Cs. Based on the findings, the background value of ¹³⁷Cs of the catchment for the first time defined as 1740 Bq m^{-2 137}Cs. Soil erosion and deposition were calculated by following the soil erosion model constructed by Yang Hao. Results show that the mean soil redistribution rate of uncultivated soil is 2 5305 t km^-2 a^-1 and the cultivated land is 6 952.5 t km^-2 a^-1 on the slope. And the soil erosion and deposition rates are influenced by human cultivated activities and the complex variability of concave and convexity on slopes. The soil in the region is severely eroded, causing decline in water retention capacity of the soil, triggering frequent floods and droughts, and eventually affecting sustainable development of the agriculture and living standard of the people in the region.

Abstract:Characteristics of vertical one-dimensional infiltration of soil water in three soils under different negative hydraulic heads were analyzed through a laboratory simulation experiment. Based on the Brook-Corey model, coupled with the Darcy law and the Richard equation, theoretical relationships were developed to describe cumulative infiltration, infiltration rate, wetting front and infiltration time of vertical one-dimensional infiltration of soil water under a boundary condition of negative hydraulic head. With the help of the data obtained in the infiltration experiment, relationships between these variables were analyzed, and fitness of the Philip infiltration equation under negative hydraulic head was verified. Results show that these theories can be used to better describe the characteristics of vertical one-dimensional infiltration of soil water under negative hydraulic head.

Abstract:Spatial distribution characteristics of total salt content (TS), ion components, exchangeable sodium percentage (ESP) and pH in the mudflat of North Jiangsu Province were investigated using conventional statistics and canonical correspondence analysis. Results show 1) the soil is slight to moderate in alkalization, e.g. moderate in topsoil (0~40 cm) and slight in subsoil (40~120 cm); 2) Na⁺ and Cl^-, K⁺ and Mg²⁺ are well correlated in all soil layers; 3)Cl^-, SO₄^2- and Na⁺ are the main factors controlling spatial distribution of soil total salt throughout the profile, which though varies slightly from layer to layer, Na⁺ remains to be one of the main factors; 4) the spatial distribution of ESP in the whole profile is restricted by CO₃^2-and HCO₃^-, with the former affecting ESP mainly in the soil layers of 0~10 cm and 20~40 cm and the latter in the soil layer of 10~20 cm. However, in the soil layer of 40~100 cm Na⁺ is still the dominant one; 5) In the whole profile pH is more evenly distributed and slightly affected by salt ions.

Abstract:Salt contents in soils different in cultivation age in Qitai County of Xinjiang were investigated for analysis of rules of the variation of soil salt content, types of soil salinity profiles and their affecting factors, using the cluster analysis method and some other related methods. Results show that along with the transformation of wasteland into farmland (at least 5 years in cultivation history), characteristics of soil salt content distribution in the soil profiles varied and fell into four types, i.e. surface accumulation profiles (SAP), even distribution profiles (EDP), oscillation profiles (OP) and bottom accumulation profiles (BAP). Uncultivated land high in salt content is typical of salinized soil, with an apparent phenomenon of surface salt accumulation; and the salt in the surface layer (0~20 cm) accounted for 34.31% of the tatol in the soil profile. Farmlands, 5 or 10 years old, are mostly of the type of BAP. With the farming operation going on and on, soil salt content in various salt-containing layers varied in activity degree showing an order of active layer (AL), sub-active layer (SAL) and relatively stable layer (RSL), and the relationship between soil salt content and soil organic matter content gradually turned from extremely positive one into extremely negative one, while the correlation between soil salt content and soil pH went the other way round. Under farming activities, soil salinization developed reversely. The average salt content in farmlands 10 years old was only 20.90% as much as in wasteland. The desalination rate was reducing with the farming operation going on from 0.156% a^-1 in the first three years of farming down to 0.004% a^-1 in the years beyond 5.

Abstract:Investigations on residues of organochlorine pesticides (OCPs) in soils in Huizhou, China were conducted. A total of 42 soil samples were collected from sites representative of the region for analysis of contents of OCPs. And with the aid of multi-variate geostatistics and GIS, residue and spatial distribution of 17 types of OCPs were analyzed. Results show that the 17 OCPs were detected, various in content in all the soil samples. HCHs and DDTs residues were detected, but below the criteria of the national standards for soil environment quality. Residue content of β-HCH was the highest among HCHs, which implied some recent input of HCH to soils, while for DDT, no sign of new input was found. Compared with other regions in the country, Huizhou city was lower in soil HCH and DDT content. Principal component analysis demonstrated that the abovesaid 17 OCPs in the soil may have 5 major contributors, corresponding respectively to industrial use of HCH, natural factors, use of lindane, use of heptamul and use of Drinox. By means of ordinary Kriging interpolation, spatial distribution of OCPs was studied with results indicating that the 17 OCPs variaed greatly in spatial distribution between types.

Abstract:A Study on chemical properties of lowmolecularweight organic reducing substances was carried out by multi-disciplinary means, involving electroanalytical chemistry, biochemistry and organic chemistry. Its principal results were presented as follows:Low-molecular-weight organic reducing substances were substances, consisting of -COOH and -C^=O_-NH2 functional groups, phenol compounds, and volatile organic acids, with isoelectric points varying between 3.5～9.5, peak potentials mostly distributed in range of 0.00～0.70 V depending on components different in reducing strength, negatively charged organic reducing substances accounting for 70%～80% of the total, and apparent molecular weight being less than 500～1 000. They demonstrate obvious voltammetric behaviors in electrode process.

Abstract:Nutrient adsorption characteristics of soil are important issues in the study of soil chemistry and plant nutrition. An experiment was carried out on NH₄⁺, PO₄^3- and K⁺ adsorption in 9 soils. Results show that Langmuir, Freundlish and Temkin isothermal adsorption equations described the sorptions quite well, but they were not perfect. A concept of “shape factor d ” of genecology was introduced to create a new adsorption model based on the Langmuir equation. Theoretical analysis indicates that the new adsorption model reflected comprehensively dynamic characteristics of the three isothermal adsorption equations. Simulation results show that the soils which the three isothermal adsorption equations didn’t fit well, were well described by the new model. The new model was higher in simulation precision （R²） and lower in standard deviation than the three isothermal adsorption equations. Its shape factor “d ” varied between 0.608 0~2.929 0, demonstrating effect of physical-chemical properties of the soils on shapes of NH₄⁺, PO₄^3- and K⁺isothermal adsorption curves. The linear correlation coefficient between the new model and Langmuir equation inq_m values of NH₄⁺ and PO₄^3- and K⁺ was 0.851 5^**, 0.825 8^** and 0.912 8^** (n=9) respectively. According to the new adsorption model, soil physicalchemical analysis show significantly positive linear correlation between q_m values of PO₄^3- or K⁺ calculated by the new model and soil organic matter content, between q_m values of NH₄⁺ or K⁺ and CEC, and between q_m value of NH₄⁺ and soil available nitrogen as well, but significantly negative correlation between q_mvalue of PO₄^3- and available phosphorus in the soil. The new adsorption model, concise in mathematical form, provides a new approach to using a uniform model for quantification of NH₄⁺, PO₄^3- and K⁺ adsorption characteristics in soil.

Abstract:Effect of fertilization and straw application on soil acidification has been one of the foci in research of agricultural management and soil acidification. Based on a longterm fertilization experiment in paddy soil in the Taihu Lake region, China, effect of the longterm (26 years) fertilization on acidification of its topsoil (0～15 cm) was studied under a rice/wheat rotation system. The experiment was designed to have six treatments, i.e. (1) no fertilizer (control, C0), (2) pig manure alone (M0), (3) urea alone (CN), (4) urea combined with pig manure (MN), (5) urea combined with rice straw (CRN), and (6) urea combined with pig manure and rice straw (MRN). After 26 years, significant effects, different between treatments, were observed on soil pH and acidification buffering capacity. Treatment M0 was lower than Treatment C0 in pH but higher in acidification buffering capacity. Treatment CN and Treatment CRN was lower than Treatment C0 by 0.45 and 0.66 in pH, and by 1.52 and 0.95 mmol kg^-1 in acidification buffering capacity, respectively In terms of soil acidification rate, ranging from H⁺ 0.61 to 1.74 kmol hm^-2 a^-1 among the treatments, Treatment CN was higher than Treatments C0 and M0, but lower than Treatments MN, CRN and MRN, and Treatment MRN was the highest Correlation analysis revealed that soil pH were significantly related to input rate of exogenous nitrogen, soil total nitrogen level and available nitrogen level, which indicates that soil acidification is mainly related to nitrogen in the chemical fertilizer, manure and rice straw. However, the effects of urea differed from that of manure and rice straw on soil acidification. The former decreased both soil pH and soil acidification buffering capacity, while the latter maintained or slightly increased the capacity. Obviously long-term application of urea significantly stimulates soil acidification, and combined application of urea with rice straw does even more.

Abstract:A static adsorption and desorption experiment in couple with a simulated flooding experiment was carried out to study effect of combined application of polyacrylamide (PAM) and enhancers (lime, gypsum, natural zeolite and humus) on retention characteristics and translocation and release of soil P to water body in purple soil. Results of the adsorption/desorption experiment show that application of PAM coupled with any of the four enhancers enhanced soil P fixation capacity, with average P desorption volume and rate being lower than in CK. Of the four combinations, Treatment P_0.2+L (PAM+lime) was the highest in P adsorption capacity, which was followed by Treatment P_0.2+H (PAM+humus). In addition, Elovich and Two constant models could be used successfully to describe the sorption processes of all treatments except for PAM+gypsum (P_0.2+G) and P_0.2+H, which fitted the paraboloid diffusion equation Results of the flooding batch experiment show that monoapplication of PAM, regardless of rate (0.1%PAM(P_0.1), 0.2%PAM(P_0.2) and 04%PAM(P_0.4)), reduced the strength of BAP release, and when combined with enhancers, PAM effectively inhibited release of BAP and reduced strength of the release, except for Treatment P_0.2+H. The effect of Treatment P_0.2+L was the best, keeping the mean BAP concentration and release strength at the lowest (0.267 mg L^-1 and 1.852 mg m^-2 d^-1 respectively) in the overlaying water body. After alternation of wetting and drying, the effect of PAM mono-application, regardless of rate, decreased significantly, showing no much difference from CK. However combined application with chemical enhancer, except for Treatment P_0.2+H, improved the effect of PAM inhibiting BAP release to water body.

Abstract:An experiment using monolith lysimeter was conducted to compare dry deep-placement of urea (DPU) in plowed paddy field before permanent flood with wet broadcast of urea (WBU) on puddled paddy field in effect on fertilizer N loss and rice N uptake at the Jiangsu-Changshu National Agroecological Experiment Station (31°33′ N, 123°38′ E). The experiment was designed to have three treatments, i.e. deep-placement, broadcast and CK (no urea applied), and ammonia volatilization, N leaching and rice N uptake were measured during the rice growing season. Results show that NH₃ volatilization flux from DPU was significantly lower than from WBU, being 40.1 and 68.8 kg hm^-2, or 13.4% and 22.9%, respectively, of the fertilizer N used in the lysimeter in 2007, and 19.2 and 26.2 kg hm^-2, or 7.7% and 10.4%, respectively, for DPU and WBU in field trial in 2004. Leaching of total N (TN) in DPU was markedly higher than in WBU, being 14.3 and 4.6 kg hm^-2, or 4.8% and 1.5% of the fertilizerN applied, respectively. Nitrogen was leached away mainly in the form of NO₃^--N in the ricegrowing season, accounted for 73.7%~97.3% of the total N leaching. But NH₄⁺-Nleaching did not show much difference between DPU and WBU. Compared with WBU, DPU reduced net N loss by 19.0 kg hm^-2 and increased rice N uptake by 15.2 kg hm^-2 and plant apparent recovery of fertilizer-N by 5%, i.e. 34% in WBU and 39% in DPU. DPU raised crop yield slightly over WBU, but did not affect much soil N content. The results indicate that the DPU method is superior to the common practice of broadcasting urea into flooded paddy field and is worth extrapolating.

Abstract:Nitrogen is the key nutrient for crop growth, and proper N applications not only improve soil productivity but also reduce N losses. Knowledge of soil N supply is the basis for making optimum N fertilization recommendation. Field experiments were conducted to explore effects of different N strategies, including N application rates and topdressing, on nitrogen use efficiency (NUE) and spatial-temporal distribution of NO₃^--N. Results show that NUE obviously decreased with increasing N rate. Soil NO₃^--N content was highest at the beginning of winter, and then decreased, but it increased with nitrogen application rate and more significant in the deep soil layer (40~60 cm) than in the middle soil layer (20~40 cm). After crops were harvested, N deficit was found in zero N treatment appeared N deficit, while N surplus was in all fertilization treatments, and increased with N application rate. This study recommends that it is not advisable to apply a large quantity of N fertilizer all at once as basal dressing. Splitting N application favors N absorption by wheat and reduces soil nitrate accumulation in the deep soil layer.

Abstract:Nitrogen (N) and potassium (K) fertilizers are often applied together with phosphorus (P) fertilizer in farming, which may possibly affect chemical behavior of P in the soil. Effects of NH₄Cl and KCl on movement and transformation of P from monocalcium phosphate (MCP) in fertilizer microsites in red soil were studied through an incubation experiment using soil columns.The coapplication of NH₄Cl or KCl with MCP did not affect much the distance of P movement but did P transformation from MCP in fertilizer microsites. Compared with the application of MCP alone, the addition of N or K significantly decreased soil pH in fertilizer microsites. Determination on D7 and D28 revealed that the addition of NH₄Cl did no have any significant effect on concentration of water-extractable P in the soil close to fertilizer placement, while the addition of KCl decreased the concentration significantly on D7, but increased it on D28. The concentrations of acid-extractable P and available P were significantly increased by the addition of NH₄Cl or KCl on both D7 and D28. The findings indicated that the movement of P from MCP into the red soil was significantly enhanced by the addition of NH₄Cl or KCl.

Abstract:Relationship between total phosphorus (TP) and available phosphorus (P) in a red soil under a long-term fertilization experiment beginning from 1988, was discussed through statistical analysis of its historical data. At the same time, sequential Olsen-P extraction was carried out to examine sustained P supply capacity in the red soil. Results show that the content of available soil P was a direct indicator of P fertility in the red soil and increased with the accumulation of TP; the supply levels of TP and available P in the red soil were determined by the amount of P surplus. According to the findings, the P content in the soil is adequate to meet the P need of at least 3~4 crops, if P fertilization decreases or ceases now. Consequently a new fertilization system should be worked out by taking into account both the agricultural effects and environment safety of soil P, to further rationalize the use of P resources.

Abstract:Dynamics of potassium in root-zone and non-root-zone red paddy soils under rapeseed-rice rotation was studied through a rhizobox equipment. Results showed that soil water soluble K and exchangeable K in root-zone soils were reduced first at the early stage of rapeseed growth. Along with plant growing and K uptake, soil water soluble K in the inner (0~20 mm), middle (20~40 mm) and outer (40~60 mm) parts of the non-root-zone were moving towards to the root zone. Soil exchangeable K were transformed into water soluble K, thus decreasing gradually. In the early stage of rice growth, water-logging promoted diffusion of soil water soluble K from non-root-zone to root zone and transformation of exchangeable K into water soluble K. Along with growth of rice plant and K uptake, soil exchangeable K in each part decreased significantly. In the late stage of rice growth, plant K uptake reduced in intensity. Soil water soluble K in the root zone dropped to a certain extent and then stopped declining, while soil water soluble K in the non-root-zone kept on diffusing towards the root-zone. During the whole rotation cycle, the treatment (with cropping) and CK (without cropping) were not much different in nonexchangeable K in the root-zone and non-root-zone. It revealed that the plant first absorbed K in the root zone, of which the K reserve was replenished with K gradually diffused from the non-root-zone. The closer to the root zone, the greater the contribution to K uptake by plant. Within one rotation cycle, soil exchangeable K and water soluble K are the main forms of potassium available to the plant, and little nonexchangeable K could be absorbed.

Abstract:An experiment was conducted using a resistant cultivar of wheat (Triticum aestivum L. Nannong 99-18) and a susceptible cultivar wheat ( Sumai No. 3) to investigate effects of silicon (Si) on activities of defenserelated enzymes (chitinase, β-1,3-glucanase, phenylalanine ammonialyase (PAL) and polyphenoloxidase (PPO) ) and microregional distribution of silicon in leaves infected by powdery mildew (Blumeriae graminis f. sp. Tritici). When wheat plants were not inoculated with powdery mildew, application of Si did not have much effect on activities of β-1, 3-glucanase, PAL and PPO in both wheat cultivars or on activities of chitinase in the susceptible wheat cultivar, however, Si application was found to increase the activity of chitinase in the resistant wheat cultivar. Moreover, the activities of chitinase, β-1,3-glucanase，PAL and PPO increased significantly in both wheat cultivars after infection of powdery mildew. Except for the activities of PAL and PPO in the resistant wheat cultivar, all enzyme activities were significantly higher in Si-treated plants than in non-Si-treated plants after wheat plants were infected by powdery mildew. In addition, regardless of inoculation and Si addition, Si was mainly concentrated in trichomes and vascular bundle tissues. However, the relative content of Si markedly increased in leaf tissues, and Si rapidly accumulated at infected sites when plants were infected by powdery mildew, especially in plants treated with Si. These findings suggest that Si enhances wheat resistance to powdery mildew not only by promoting expression and activities of defense-related enzymes, but also by building up physical barriers against pathogens through Si accumulation in plants infected by powdery mildew.

Abstract:Effects of pH（pH 3.0, 5.0 and 8.0）on mechanism of selenite uptake by rice roots were studied using excised roots of rice seedlings. Results indicate that in solutions of pH 3.0 and pH 8.0, 0.10 m moll^-1 DNP, 1.0 m molL^-1NaF and low temperature (4°C) could only inhibit selenite uptake to a small extent, and selenite uptake varied with selenite concentration, showing a linear curve. However, pH 5.0 inhibited uptake of most selenites, showing a saturation curve. Further study revealed that both HgCl₂ and AgNO₃inhibited uptake of most selenites at pH 3.0, while anion channel inhibitors did that of a few at pH 8.0. Apparently, selenites infiltrated into roots actively at pH 5.0 and was absorbed passively by the roots at pH 3.0 and pH 8.0. Furthermore, selenites were absorbed into the roots through aquaporins at pH 3.0 but absorbed into the roots via other routes than anion channels at pH 8.0.

Abstract:Mudflat soils different in salt concentration were collected from Dafeng, Jiangsu Province, China. The soils were tested for culturability of bacteria, using different culture schemes and the technology of DGGE (denaturing gradient gel electrophoresis). Results show that natural sea water was necessary as a media supplement in culturing bacteria in all soils. For cAMP did not show much improvement in bacterial culturability. Concentration of the medium was a key factor affecting the culturability. Prolonged incubation up to 25 days increased the number of colony-forming units on the plate. Liquid media were better than solid ones in terms of culturing maximal number of bacteria. By the most probable number method, it was noted that tubes with limpid solution and some mucous precipitation, which used to be overlooked as “negative”, should be taken as “positive”. Microscopic and sequence examination revealed that the mucous precipitation consisted mainly of small short rodshaped bacteria (0.6×1.2~2.6 μm), highly similar to Bacillus sp. An optimal culture scheme for the mudflat soils is proposed to have liquid culture medium consisting of 1/10 nutrient broth and 100% natural sea water, and 25-day incubation. Further study should be conducted to optimize carbon compounds in the media.

Abstract:A pot experiment designed to have 5 treatments, i.e. Treatment CK (litter of Atractylodes lancea (thunb) DC only); Treatment MB (endophytic fungus Phomopsis sp. And sterilized A.lancea litters); Treatment WB (Phomopsis sp. and A.lancea litters); Treatment WBF, (Phomopsis sp., A.lancea litters and fermentation broth); and Treatment WMF (A.lancea litters and sterilized fermentation broth), was carried out. After the treatment, decomposition rates of cellulose and lignose of the litters and activities of their degrading enzymes in the soils were determined regularly, and meanwhile, variation of endophytic fungus B3 in the soil was tracked by means of nested PCR, to study effect of the addition of endophytic fungus to soil on decomposition of A.lancea litters and activities of soil degrading enzymes. Results indicate that even when detached from their host, the endophytic fungus still remained physiologically active, got adapted to non-host conditions and survived for more than 30 days. During this period of time, the fungus significantly accelerated decomposition of cellulose and lignin. Measurements of the samples taken on D10, D30 and D60 showed that the activity of cellulase was significantly higher in Treatments WBF and MB than in other treatments, and the activity of ligninase was significantly higher in Treatments MB and WB than in other treatments.

Abstract:‘Fertile island’ characteristics of soil nutrient in Haloxylon ammodendron lands in North Xinjiang were studied by means of typical case survey and geostatistics. Results show that the roots of big and small Haloxylon ammodendron plants were relatively stronger in ‘fertile island’ effect, while wilted Haloxylon ammodendron was weak in the effect. In terms of soil nutrient contents in the rhizosphere of Haloxylon ammodendron a decreasing order of big Haloxylon ammodendron > medium Haloxylon ammodendron > small Haloxylon ammodendron. Soil nutrient enrichment rate in the rhizosphere of the plant varied sharply with growth stage, but at the canopy brim, it did not. Stem diameter, plant height and canopy size was positively correlated with enrichment of alkalytic nitrogen (p<0.01), and negatively correlated with enrichment of available K in the rhizosphere (p<0.01). However, enrichment of available P there was positively correlated with stem diameter (p<0.01). The mean effective range of nutrient enrichment of Haloxylon ammodendron was smaller than the average diameter of their canopies. Analysis by means of Kringing interpolation revealed that the soil nutrients in the rhizosphere of the plants were much higher than in other areas, demonstrating the characteristics of ‘fertile island’.

Abstract:To explore expression of nutrients productivity of the soil per se, a 13-year stationary fertilization experiment on soil nutrient depletion was carried out in fluvo-aquic soil under a winter wheat (Triticum aestivum L.)–maize (Zea mays L.) double cropping system in Xiongxian County of Hebei Province. The experiment was designed to have eight treatments, namely control (no fertilizer applied), complete fertiliztion, and complete fertilization except N, P, K, Mn, Zn, or B alternately, and “sustaining yield” was used as the index of soil nutrient productivity. Results show that the sustaining yield of soil N, P, K, Zn, Mn, and B was 2 553, 3 918, 5 668, 6 571, 6 871, and 7 353 kg hm^-2 for wheat, and 2 280, 4 576, 6 875, 8 788, 9 465, and 9 188 kg hm^-2 for maize, respectively. The lower sustaining yields of soil N, P, and K showed high possibility of yield promotion through lifting their respective nutrient barrier. Regarding the selfbalancing and recylcing ability, the six soil elements followed an order of N < P < K < Zn < Mn < B in the wheat cropping season, and N < P < K < Zn < B < Mn in the maize cropping season. The sustainable yield indexes (SYI) of the eight treatments show that the complete fertilization treatment was the highest in soil nutrient productivity, whereas the rest were much lower because of imbalance of nutrient supply with Treatments N₀ and P in particular.

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