Abstract:With farming cultivation increasing steadily in intensiveness, obstacles to successive cropping, such as soil-borne pathogens, soil acidification, secondary salinization and unbalanced nutrient supply, occur more frequently, and seriously sabotage sustainability of the intensive agriculture. The threat is even more serious in China due to excessive application of N fertilizers and farmers’ poor knowledge about intensive agriculture. Firstly developed in Japan and the Netherlands in the early 2000’s as an alternative of chemical soil disinfestationand named as biological soil disinfestation (BSD) or reductive soil disinfestation (RSD) in Japan or anaerobic soil disinfestation (ASD) in the Netherlands and the USA, the method is now being widely applied in these countries. RSD refers to the pre-planting soil treatment method, i.e. applying decomposable organic materials at a very high rate to the soils infested with soil-borne pathogens, flooding or irrigating the field to water saturation, and mulching the field with plastic film to limit gas exchange between the soil and the atmosphere and create the soil in a very intensively reductive state for a short period of time (a few days). The method can be conducted in the fallow season between two crops when temperature is higher than 25℃ and the treatment usually lasts 2~4 weeks mainly depending on temperature, amount of the organic material applied, and population of pathogens. The researches have demonstrated that the method controls a broad-spectrum of pests and is an alternative to chemical fumigation with gaseous pesticides, such as methyl bromide, effective to eliminate or reduce the populations of fungal and bacterial pathogens and root-knot nematodes. The mechanisms of RSD for disinfestation include: 1) creating an anaerobic condition that kills aerobic soil-borne pathogens; 2) producing substances harmful and toxic to the pathogens during the treatment period; and 3) altering structure of the soil microbial community and inhibiting the activity ofsoil-borne pathogens. Besides, the RSD method has some effects of increasing soil pH and alleviating soil secondary salinization, and its application is universal and environment-friendly. An introduction is presented in the paper to the development, mechanisms for suppressing soil-borne pathogens and remediation of acidified or secondarily salinized soils, and factors influencing the effectiveness of the RSD method and prospects of the application of the method as well.

Abstract:Soil tends to shrink and form cracks when it gets dried up. Soil cracks are formed under the joint effect of a variety of factors, like soil properties and environment conditions, and very complicate and hard to describe precisely in morphological structure. As they may act as pathways for preferential flow, their presence enhances the risks of water and nutrient loss and pollution of groundwater. Soil properties, such as soil clay content, soil mineral composition, soil organic carbon content and bulk density, etc. are the main factors affecting soil cracking, while wetting and drying alternation, tillage and plant growth are its external affecting factors. So far, the characterizing indices and determination methods available for soil cracks focus mainly on their two-dimensional structural features, and little has been reported about characterizing indices and determination methods for three-dimensional structure of cracks. The methods for measuring preferential flow caused by soil cracks include dye tracer, disc permeameter, breakthrough curve, profile soil water potential measurement and so on. Cracks vary in feature with soil water content, so the effect of soil cracks on preferential flow is complicate, and closely related to soil properties, soil water content and depth of the cracks. The dynamic variation of cracks makes it more difficult to simulate preferential flow caused by soil cracks. It is, therefore, suggested that more efforts should be dedicated in future to conducting in-depth complete researches on crack-forming mechanism; establishing three-dimensional index systems and determination methods for soil cracks and improving the systems and methods; promoting researches on quantification and mathematic simulation of crack-induced preferential flow; and enhancing in situ field study of cracks and preferential flow.

Abstract:Studies on soil aggregate loss in the process of soil erosion have an important significance in exposing mechanism of soil erosion. Rainfall intensity, as an important parameter in characterizing rainfall events, plays a significant role in soil erosion. A large number of studies have shown that there is a certain relationship between rainfall and composition of erosion sediment. However, most studies on soil aggregate loss in the process of soil erosion were conducted in the laboratory, which might affect some of the soil properties, especially the distribution of soil aggregates, when soil samples were collected and moved from the field to the laboratory. In this study, an in-situ field simulated rainfall experiment was conducted on a cropland in the typical black soil region of Heilongjiang Province to investigate characteristics of soil aggregate loss in the process of soil erosion. The experiment was designed to have three rainfall intensities, i.e., 30, 60 and 90 mm h–1 and a set duration, 40 min, for each simulated rainfall event. Variations of characteristic indices of soil aggregate loss, such as mean weight diameter (MWD), geometric mean diameter (GMD), fractal dimension (D), mean weight soil specific area (MWSSA), ≥ 1 mm soil aggregates (PA₁), ≥ 2 mm soil aggregates (PA₂) and ≥ 0.25 mm soil aggregates (PA_0.25), as affected by rainfall intensity, were analyzed. The runoff plots (10 × 1 m, each) of the experiment were deployed in a cropland on a sunny slope, 5° in gradient. The soil of the cropland was typical black soil 38.9% in clay, 55.3% in silt, 5.8% in sand and 28.8 g kg^-1 in organic matter, 1.10 g cm^-3 in bulk density and 6.65 in pH. Results show that rainfall intensity had some significant effects on runoff and soil loss. The ratio of soil loss in the first 20 minutes of a rainfall event to total soil loss increased with increasing rainfall intensity. The sediment resulting from a rainfall event, 30 mm h^-1 in intensity, was dominated with <0.25 mm soil aggregates, which made up 90.0% of the total soil aggregate loss; the sediment from a rainfall event, 60 mm h^-1 in intensity, was mainly composed of <0.25 and 0.5~1 mm soil aggregates, which accounted for 63.7% of the total soil aggregate loss; and the sediment from a rainfall event, 90 mm h^-1 in intensity was mainly of <0.25 and 2~5 mm soil aggregates, which amounted to 31.7% and 31.2% of the total soil aggregate loss, respectively. Rainfall intensity was found to have very significantly positive relationships with PA_0.25, PA₁, PA₂, MWD and GMD, but very significantly negative ones with MWSSA and D. It was also found that indices of PA₁， MWD and GMD are all good indicators characterizing soil aggregate loss in croplands in the typical black soil region of Northeast China.

Abstract:In the Qinghai-Tibet Plateau, a small number of soil samples were collected during surveys of permafrost for the study on building up an index set for predicting thickness of the active layer in the permafrost and for mapping using the digital soil mapping method. By taking into account the relationships between soil and landscape environment, an index set was screened out and established, encompassing, diurnal surface temperature variation, altitude, slope gradient, slope aspect, NDVI and parent rock. With the aid of the method of setting individual samples as representative, a permafrost active layer thickness distribution map of the region was plotted with quite satisfying accuracy and resolution, thus overcoming the difficulty in space extending mapping in the processes of simulating thickness of the active layer of the permafrost with mathematic-physical models and breaking through the limitation of the use of semi-empirical models in mapping being low in resolution. In view of the problem that the sampling sites in the survey were quite limited in number and not so representative of the whole region, the method of modeling based on multi-samplings separately was adopted, instead of the conventional one-time full samples method. Consequently a predictive index set and a map was acquired.

Abstract:Weathering of bedrocks releasing mineral elements into the pedosphere is the starting point of global element recycling. Therefore, the knowledge of the variation of soil minerals in the soil with the soil forming process and its mechanism is the basis for understanding soil weathering and development. Since the end of the Little Ice Age, the glacier at Hailuogou on the east slope of the Gongga Mountains, Sichuan, China has been retreating continuously, leaving bottom moraines exposed to weathering and soil forming. Then the area is invaded successively by Hippophae rhamnoides L, Populous purdomii Rehder, Abies fabri, and Picea brachytyla, forming a 120 year soil development sequence and plant succession sequence. Besides, the area also contains a rich accumulation of climate data and geological structure data. In this study, six sampling sites were set up in this area, representing 0 yr, 30 yr, 40 yr, 52 yr, 80 yr and 120 yr after the retreat of the glacier, for sampling of soil in the humus horizon and parent material horizon. The soil samples were air-dried and ground to pass a chosen sieve for X-ray diffraction (XRD) analysis (organic matter was removed with H2O2 in pretreatment) to determine qualitatively and quantitatively soil minerals therein in a view to analyzing mineral composition of the soil parent material along the soil chronosequence and variation of the soil minerals with soil development. XRD analysis shows that the soil parent material horizon in the area is quite homogenous, and soil minerals are dominated with silicates (about 90%), including quartz (24.5%), plagioclase (28.5%), K-feldspar, augite, hornblende, biotite, chlorite and vermiculite, and some carbonates, like calcite (< 8%) and dolomite (< 2.3%), and phosphate mineral apatite (< 2.1%). However, in some soil samples, some other minerals like pyrite, barites, calcium oxalate, wollastonite and smectite are also detected. The soil in the area is fairly high in content of feldspar, mica and hornblende, which is the feature of entisol. As the pedogenesis proceeds, after 52 years of exposure, calcite in the parent material begins to transform into calcium oxalate. After about 120 years of exposure, biotite or hornblende is very likely to transform into biotite or hornblende, reducing its content in the soil. The soil in the humus horizon is relatively enriched in felsic minerals (quartz, plagioclase and K-feldspar). Correlation analysis shows that the contents of hornblende, apatite, biotite and chlorite decreased significantly with soil development (p <0.05). Surface vegetation biomass and soil pH are two important factors influencing weathering of surface soil. Plant growth and succession not only directly promotes weathering of the minerals in the surface soil, but also speed up, weathering of hornblende, biotite and chlorite along the soil chronosequence by reducing soil pH. And what is more, only when soil pH is dropped down below 5.5, will it accelerate weathering of apatite. In the end, by comparing the Hailuogou Soil Chronosequence with two similar soil chronosequences in the Alps, this paper deduces that mineral composition of the soil forming parent material may affect development of surface vegetation. The high contents of mafic minerals and apatite in the parent material as well as the warm and cool climate are responsible for the flourishing vegetation along the Hailuogou chronosequence. All the findings and data indicate that apparent weathering occurred at the early soil development stage of the Hailuogou Soil Chronosequence.

Abstract:Soil organic carbon (SOC) in farmland ecosystems is essential to agriculture and crucial to ecology and global climate change. Composition and mean residence time (MRT) of SOC are closely related to soil structural stability, sustainable soil nutrient supply, soil biodiversity and mitigation of greenhouse effect. Based on the three-pool first-order kinetics equation and the soil respiration incubation experiment conducted, the major organic carbon components of the paddy soil typical of Chengdu were measured for analogical analysis of SOC composition and for establishment of models for prediction of SOC components by means of quantification of soil properties as well as correlation and regression analyses of various fractions of organic carbon. Results show that the content of active carbon (C_a), slow carbon (C_s) and resistant carbon (C_r), was 0.42, 6.13 and 11.43g kg^-1, respectively, in the surface layer (020cm), and 0.23, 4.09 and 7.50 g kg^-1, in the sub-surface layer (2040cm). Obviously, the contents were higher in the surface layer than that in the sub-surface layer. Although the organic carbon in the sub-surface layer was higher than that in the surface layer in inertness, no significant difference was observed between the organic carbons in the two soil layers in proportion of components. No apparent difference was observed either between paddy soils derived from similar parent materials but sorted into different subgroups in content and proportion of organic carbon components. However, soil texture had some high impacts on content and proportion of organic carbon components in the sub-surface layer. In soil profiles (0100cm), contents of C_a and C_s decreased with increasing depth. However the decrease in content of C_r varied with soil subgroup, in some subgroups it decreased with soil depth, while in some it decreased first and then increased. In paddy soils the constituent proportions of C_a in all soil layers were less than 4% and no obvious change was found with soil depth; the constituent proportion of C_s was lower than that of C_r, and the two fractions of organic carbon varied with soil depth symmetrically, in constituent proportion, that is, C_s decreased with soil depth, while C_r increased significantly with soil depth. Paddy soils and forest soils shared some common characters in distribution of contents and constituent proportions of organic carbon components in soil profile, however, paddy soils, different in subgroup, had something common and something different, as well, in this aspect. Composition of soil organic carbon in paddy soils was subject to the integrated effect of bulk density, texture, particle-size composition,pH, carbon-nitrogen ratio, total nitrogen, total phosphorus, and total potassium, but each fraction of SOC had its own main affecting factors. The analysis results show that the contents of various organic carbon components were in extremely significant negative relationships with bulk density, and in extremely significant positive relationships with total nitrogen and total phosphorus. Clay was favorable to preservation of C_a, and weak alkaline environment was conducive to soil carbon sequestration. Based the relationships of the fractions of organic carbon with various related factors, the significant linear relations (R²= 0.69) observed of C_a with total nitrogen and pH and the significant linear relations of (R²= 0.70)C_r with soil total nitrogen, carbon-nitrogen ratio, pH value as well as the content of fine silt (0.020.002mm), it is feasible to predict contents of various fractions of organic carbon in paddy soil, but the prediction accuracy needs to be improved. However, the findings of this study has some positive reference value to researches and prediction of components of SOC in other regions.

Abstract:Soil temperature and soil moisture regime are two important parameters characterizing soil properties, and two important factors affecting physical, chemical and biological processes of soil formation, and can be used to serve as reference and basis for dividing certain soil suborders, soil groups and soil subgroups in soil taxonomy. Besides, as heat and moisture exchanges occur frequently between the soil and the atmosphere, climate directly affects the soil in hydrothermal condition. Therefore, 60 years (1951-2010) of daily meteorological observation data of 142 meteorological observation stations in Hebei Province, annual cumulative mean aridity index and soil temperature at each station was calculated using the Selianinov’s equation and soil temperature interpolation method. Results of the calculation were subjected to spatial analysis using the geostatistic method and then the GIS spatial analytic technology for laws of the spatio-temporal variation of soil temperature and meteorological aridity and humidity, which can not only be cited to verify the research methods used by the precedent researchers, but also be applied to the soil taxonomy. Results show: (1) during the 60 years the annual mean soil temperature and mean aridity indices displayed a rising trend, with rising rate much higher in the first 30 years than in the second 30 years, which indicates that soil aridity in the province was gradually aggravating; (2) The soils in the province can roughly be divided into two types in terms of soil temperature, i.e. cold soil and warm soil. Compared with the first 30 years, the second 30 years witnessed warm soils expanding 14.26km towards north over an area of 5665 km². Air temperature displayed a similar pattern, moving 18.63km towards north over an area of 6539 km²; And (3) Soil moisture regime varied significantly from region to region, demonstrating an apparent zonality. Surface soil moisture regime in the province can be divided into humid, semi humid and semi-arid. From the perspective of spatial distribution, areas high in aridity are mainly distributed in the southern part of Hebei and the Sangyang basin in Zhangjiakou, while areas low in aridity are mainly in the low-mountains and hills regions along the south piedmont of the Yanshan Mountains, like the southwest of Chengde, the north of Tangshan, a large portion of the central north of Qinhuangdao and a small portion of the north of Hebei, indicating that the climate is obviously more humid in the east and north parts of the province than in the west and south parts, which also indirectly reveals distribution of soil moisture; From the perspective of temporal variation, compared with the first 30 years, the second 30 years had aridity index increased by 0.01 ~0.85 in Bashang plateau, the east part of Hebei and areas south to the Handan-Qinghe-Renxian-Pingxiang line, and decreased by 0.01 ~0.59 in the northeast part of the province, North Hebei Plateau and east part of the central south plain , indicating that air moisture regime varied with time, which in turn affected soil moisture regime in the province. It used to be held that the Plateau in Northwest Hebei province was in the category of semi-arid zone and the remaining part of the province could mostly be sorted into semi humid zone, which is different from the findings of this research. The findings of this study could serve as reference for using quantified diagnostic characteristics in the soil taxonomy to replace the concept of zonality in the traditional soil classification.

Abstract:Vertical distribution of saturated hydraulic conductivity (K_s) has an important influence on soil hydrological processes. However, relatively speaking, few reports are available on this issue in karst areas with special geologic background. To study vertical distribution of soil saturated hydraulic conductivity (K_s) and its influencing factors in a small karst catchment, soil samples were collected from 23 soil profiles at 0～10, 10～20, 20～30, 30～50, 50～70 and 70～100 cm soil layers for measurement of K_s, rock fragment content (RC), bulk density (BD), capillary porosity (CP), non-capillary porosity (NCP) and soil organic carbon (SOC). Besides, environmental factors including slop position (SP), slope gradient (SG), slope aspect (SA), bare rock (BR) and land use type (LU) were investigated at each soil profile site, and all the data obtained were analyzed with the partial correlation analysis and canonical correspondence analysis (CCA) methods. Results show that K_sgenerally decreased with increasing soil depth and the variation could be fitted with a logarithmic function (R²=0.848). The variation of K_s in the soil layers within 20～100 cm was low in amplitude and approximate to each other, which indicates that K_s in the 20~30 cm soil layer could be used to represent K_s in the underlying horizons in building hydrological models. Among the soil properties, RC displayed the highest correlation coefficient (0.484) with K_s. In terms of influences of the environmental factors on vertical distribution of K_s, a decreasing order of SP > SG > SA > LU > BR was found. It is, hence quite obvious that RC is the most important soil property and SP the dominant environmental factor that influences vertical distribution ofK_s. The findings help understand the laws and major influencing factors of rainfall infiltration and also provide some scientific basis for vegetation restoration in small karst catchments and for building of hydrological models, as well.

Abstract:Qingdao is one of the cities in North China, running short of water supply. So it is very important to preserve and save water resources for Qingdao’s sustainable development. In this paper, on the basis of a large number of field experiments and long-term stationary observations conducted in farmlands in the Dagu River Basin in Qingdao, a series of basic information, such as soil moisture, groundwater table depth, soil physicochemical properties, precipitation, irrigation, meteorology and some others were acquired for analysis and computation with the soil water balance equation coupled with the Hydrus-1d software to explore relationship between farmland soil water and groundwater in areas with shallow groundwater table, and further to determine quantity of the soil water resources in this region. Results show that soil moisture regime responds quickly to precipitation and depth of groundwater table; soil water and groundwater supplements each other mutually; and the transformation varies in characteristic with the season. During the corn growing season, soil water and groundwater exchanges frequently, as a result, soil water leaching and drastic fluctuation of groundwater table is likely to occur. During this period, soil water supplements groundwater with 228.0 mm of water and the latter does the former with 287.5mm, while during the wheat growing season, as there is no irrigation done, the relationship of mutual supplementation almost becomes that of one-way supplementation, that is, from groundwater to soil water, quite stable in rate, compared to the corn growing season, soil water supplies groundwater with 70.09 mm and the latter does the former with 266.9 mm. Through calculation, the soil water resource in the study area was worked out to be 4.395 million cubic meters and plays an important role in guaranteeing crops growth. It is essential to formulate a reasonable irrigation scheme so as to make the best use of the soil water resources, and to achieve the goal of water saving agriculture.

Abstract:A chemical method was developed for determination simultaneously of nitrogen and oxygen isotope ratios of nitrate in water samples. This method uses copper-plated cadmium granules to reduce nitrate into nitrite in a weakly alkaline environment and sodium azide to transform nitrite into nitrous oxide in a weakly acid buffer. Then the nitrous oxide is purged from the water sample and trapped cryogenically using an automated system with subsequent release into a gas chromatography column. The isolated nitrous oxide is then analyzed with a continuous flow isotope ratio mass spectrometer for N and O isotope ratios, which is then converted into those of nitrate using an equation. Meanwhile, the experimental conditions of chemical conversion have been optimized by some further experiments. It is found that pH of the solution, reaction time and concentration of nitrate all had some effects on processes of the reducing reaction; When pH of the solution was 8.0, N₂O generation rate reached the highest; When duration of the reaction exceeded 80 min, the reaction was nearly 100% completed; And temperature of the reaction system did not have much obvious effect on completeness of the reaction, but the time of reaching equilibrium. On such a basis, optimal conditions for the reducing reaction are set as: 8.0 for pH, 80min for duration of the reaction and 25℃ for temperature of the reaction system. To prepare a series of standard solutions to form a gradient in nitrogen and oxygen isotopic abundance, two standard sample solutions, USGS34 and USGS32，the same in concentration 20μmol L^-1, were blended in different volume ratios. The standard solutions were used in transformation experiments and eventually a conversion working curve was obtained. Besides, a number of validation experiments were carried out using USGS international standard samples and laboratory standard samples to verify precision and accuracy of the chemical conversion method. The conversion process has only two steps and needs only 4.5μg of NO3--N, while its accuracy in measuring δ¹⁵N and δ¹⁸O reached 0.31‰ and 0.55‰, respectively. The difference between the measured value and the reference value was less than 1σ. So the precision and accuracy of this method are good enough to meet the requirements of the research. Water samples from different sources, including surface water, rainfall and extracted soil solution, were analyzed, using this method. It was found that in rainfall water, δ¹⁵NAir of nitrate was +10.5‰ on average, ranging from +4.5‰ to +18.4‰ and δ¹⁸OSMOW of nitrate was +76.9‰ on average, ranging from +54.8‰ to +84.3‰; in surface water, δ¹⁵NAir of nitrate was +8.9‰, on average, ranging from -1.4‰ to +14.4‰ and δ¹⁸OSMOW of nitrate was +4.8‰ on average, ranging from -2.7‰ to +28.2‰; and in soil solution, δ¹⁵NAir of nitrate was +3.5‰ on average, ranging from -4.3‰ to +8.6‰ and δ¹⁸OSMOW of nitrate was +6.0‰ on average, ranging from -0.1‰ to +13.4‰, which were in good agreement with those in previous researches.

Abstract:Transport and distribution of photosynthetic carbon is an important part of carbon recycling in the “atmosphere-plant-soil” system, but also the main source of soil organic carbon. The development of stable isotope technology enables quantitative research on allocation of photosynthetic carbon. The ¹³C stable isotope labeling technique, featuring zero radioactivity, uniformly marking, safety and reliability, has been widely used in studies on cycling of organic carbon in soil. As an essential nutrient element for plant growth, nitrogen is closely related to the process of photosynthesis of plants. The effect of nitrogen fertilization on the distribution of photosynthetic carbon in plant-soil system may vary with the crop and soil properties. However, so far no much has been reported in this aspect. The ¹³C stable isotope labeling technique was adopted in this study on law of the distribution of photosynthetic carbon in the plant-soil system using paddy red soil as object. The research on effect of N application rate on distribution of photosynthetic carbon has some important scientific significance to understanding in-depth mechanism of soil carbon recycling and formulating management measures to maintain stability and balance of soil organic carbon. A pot experiment, designed to have two nitrogen treatments, N50 and N100, (50 mg kg^-1 and 100 mg kg^-1) and two groups, one labeled 4 times with ¹³C pulse and the other not, was conducted to quantatively study law of the distribution of photosynthetic carbon in the rice-rhizosphere system at different growth stages (tillering, jointing, heading and filling stage). Based on the difference between the two groups in amount of ¹³C, the amount of ¹³C taken up by rice was calculated. It was found that the aboveground biomass of rice in Treatment N100 was significantly higher than that in Treatment N50 treatment (p<0.05) and in the labeled group, it reached 62.05 grams per pot in the former and 47.82 grams per pot in the latter, a 30% difference; The root biomass of rice in Treatment N100 was also higher than that in Treatment N50. In the late rice growing period, root growth was enhanced in Treatment N50, increasing the root-shoot ratio. The δ¹³C‰ in either shoots and roots reached a maximum at the tillering stage. In shoots it reached 927‰ and 1216‰ in Treatments N50 and N100, respectively, and in roots it did 771‰ and 695‰, respectively. The value was the lowest at the heading stage, and did not vary much between the other growth stages, It varied in the range of 621%~671‰ in the shoots and 559‰~676‰ in the roots. δ¹³C‰ in rhizosphere soil increased gradually with rice growth, and was higher in Treatment N100 than in Treatment N50 in all the growth period except for the tillering stage. Throughout the entire growing period, the net ¹³C input into the shoots varied in the range of 2.31~5.55 g kg^-1 and that into the roots in the range of 2.41~2.82 g kg^-1, but the concentration of ¹³C in the rhizosphere soil was only in the range of 0.004~0.014 g kg^-1. After four times of pulse labeling, the total cumulative amount of ¹³C in the rice plants in Treatment N100 reached 265.5 mg, 39% higher than 191.6 mg in Treatment N50, and 46% higher than the amount in the rhizosphere soil. In the early rice growing season, photosynthetic carbon of rice was mainly transported to the underground part (21.7%~52.7%), but the proportion dropped sharply (7.50%~8.90%) at the filling stage. The nitrogen treatments were more or less the same in distribution ratio of cumulative photosynthetic ¹³C in plant and soil, approximately 72% in the shoots and 28% in the underground part (root 7.21%~7.71% and rhizosphere soil 20.3%~21.2%). Appropriate nitrogen fertilization can increase not only crop yield, but also the amount of organic carbon crop transports to the soil. When nitrogen is insufficient, rice enhances its root growth to absorb nutrients. The distribution ratio of photosynthetic carbon input in rice-rhizosphere system varies with the rice growth stage. Nitrogen application promotes growth of the crop, thus increasing accumulation of photosynthetic carbon, but does not have much effect on distribution ratio of the photosynthetic carbon in the rice-soil system throughout the rice growing period.

Abstract:No-tillage ridge-cultivation is a prominent representative of the conservation tillage systems for paddy fields in South China. It is, therefore of some important practical significance to quantify whether the conservation tillage system is able to contribute to improving soil organic carbon (SOC) sequestration and keeping stable and high crop yields as well, in paddy fields. Ridge cultivation changes micro-topography of the surface soil in paddy fields. However, for long, in their studies on organic carbon accumulation in topsoil of cropland under ridge cultivation and under conventional tillage, the difference in micro-topography of the surface soil between the two different cultivation systems has been often neglected, which would inevitably affect accuracy of the comparison. Hence, a long-term field experiment was conducted to investigate effects of no-tillage ridge-cultivation on SOC accumulation in ridge soil and crop yields in paddy fields, taking into full account the effect of ridges on micro-topography of the tested paddy fields. The long-term field experiment, initiated in 1990 and located in the experimental farm of Southwest University in Chongqing city, China (30°26′ N, 106°26′ E), is designed to have four different cultivation treatments in the field experiment, that is, Treatment CP1 (conventional tillage under the rotation of rice and winter fallow), Treatment CP2 (conventional tillage under the rotation of rice and rape), Treatment RN1 (no-tillage ridge-cultivation under the rotation of rice and winter fallow), and Treatment RN2 (no-tillage ridge-cultivation under the rotation of rice and rape). In this study, all the ridges in each plot under ridge cultivation were considered as a whole when calculated and compared SOC accumulation with the topsoil layers in Treatments CP1 and CP2 (the soil layers in the control), and the comparison required that the soil layers in the control and the ridges should have the same soil volume or mass in their respective plots. As the topsoil layers in conventional tillage treatments (CP1 and CP2) and the ridges in ridge-cultivation treatments (RN1 and RN2) had the same soil volume in their respective plots, Treatment RN2 was obviously higher than Treatments CP1, CP2 and RN1 in SOC density (p<0.05), while Treatment RN1 did not differ much from Treatment CP1 in SOC density, but both were obviously higher than Treatment CP2 (p<0.05). When the topsoil layers in conventional tillage treatments (CP1 and CP2) and the ridges in ridge-cultivation treatment (RN1 or RN2) had the same soil mass in their respective plots, SOC storage per unit mass of soil in the ridges and the topsoil layers displayed an order of RN2 > CP1 > RN1 > CP2, and the difference between the treatments was significant (p<0.05). All these indicate that Treatment RN2 is much higher than Treatments CP1, CP2 and RN1 in SOC accumulation efficiency in topsoil. Analysis of labile organic carbon (LOC) in the ridges and the soil layers in the control also indicates that Treatment RN2 was higher in LOC content and LOC/SOC than the others, revealing that Treatment RN2 provides better protection to LOC in SOC against mineralization, which is one of the main reasons why Treatment RN2 is higher in SOC accumulation in the ridges. In terms of their effects on yields of the crops, both Treatments RN1 and RN2 increased significantly rice yield (p<0.05), but Treatment RN2 did have some reverse effect on rape yield (p<0.05), which, however, didn't affect much the total economic output of the field from the two harvests (rice and rape) per year. In conclusion, Treatment RN2 is a kind of conservation tillage system combining environmental and economic benefits for paddy field, and worth extrapolating to the hilly and mountain areas of South China, where cold waterlogged paddy fields are extensively distributed.

Abstract:A pot experiment coupled with short term mineralization incubation were conducted to explore characteristics of residual, mineralization and crop uptake of the ¹⁵N-labeled N fertilizer applied alone and/or together with crop straw in the soils collected from three different treatments of a 19-year fertilizer experiment, i.e. treatment No-F (no fertilization), treatment NPK (long-term NPK fertilization) and treatment MNPK (long-term NPK fertilization plus organic manure). The pot experiment was designed to have two treatments, i.e., treatment +N (100 mg kg^-1 urea-¹⁵N), and treatment +1/2N+1/2S (50 mg kg^-1 urea-¹⁵N + corn stalk equivalent to 50 mg kg^-1N). Fertilizers were added to the pots separately for the first cropping of wheat in 2009. After the first cropping of wheat was harvest, 82.6% ~ 95.1% of the residual fertilizer N in all the three soils under treatment +1/2N+1/2S and NPK soil and MNPK soil under treatment +N were in organic form; and 47.7% of the residual fertilizer N in the No-F soil under treatment +N was in mineral form. After 28 days of incubation for mineralization, the net N mineralization in MNPK soil increased significantly, by 39% ~ 49% over that in NPK soil. In NPK and MNPK soils, 1.23 to 1.90 mg kg^-1 of the residual fertilizer N was mineralized, accounting for 2.78% ~ 5.53% of the total residual fertilizer N in the soils. The net mineralization rate of residual fertilizer N in NPK and MNPK soils was significantly higher than that in No-F soil. Compared to treatment +N, treatment +1/2N+1/2S significantly increased net N mineralization rate in the three soils. However, the two treatments did not affect much the mineralization rate of residual fertilizer N in NPK and MNPK soils. In No-F soil under treatment+N, the residual fertilizer N use efficiency (RNUE) reached 20% in the No-F soilsignificantly higher than that (9%)in NPK and(12%) MNPK soils (p< 0.05). The RNUE in MNPK soil was significantly higher than that in NPK soil regardless of N treatment (i.e., +N, or +1/2N+1/2S). N uptake by the second crop of wheat during the vegetative growing period was found to be significantly and positively related to net soil N mineralization rate during the short incubation period, while no significant correlation was observed between residual fertilizer N mineralization rate and amount of residual fertilizer N absorbed by the second cropping of wheat. To sum up, long-term combined application of organic manure and chemical fertilizer can increase the mineralization rate of residual fertilizer N, and hence improve its bioavailability.

Abstract:Improvement of basic soil productivity (BSP) is crucial to reduction of fertilizer application rate and maintenance of stable and high crop yield, while fertilization is a major factor affecting BSP. The study on effects of long-term fertilization on evolution of BSP is of some important theoretical and practical significance to guiding soil building and guaranteeing national food security. A long-term fertilization experiment coupled with pot experiments was carried out to explore effect of mode of long-term fertilization on yield of double-cropping rice and BSP and to analyze rice yield and fertilizer contribution rate to rice yield in relation to BSP. Results show that long-term chemical fertilizers application (NPK) or long-term chemical fertilizers application combined with rice straw (NPKS) increased rice yield. Compared with CK, NPK increased the grain yield of early rice, late rice and annual yield by 100.7%, 67.0% and 81.9% and NPKS did by 113.8%, 77.7% and 93.7%, respectively. BSP yield of early rice in CK decreased significantly with the experiment going (p＜0.01). BSP yield of late rice decreased significantly with the experiment going on in the first nine years (p＜0.01) and afterwards it remained stable. Long-term application of NPK and NPKS helps improve BSP. In terms of BSP and BSP contribution rate, the three treatments in the experiment followed an order of NPKS ＞ NPK ＞ CK. Compared with CK, NPK and NPKS increased BSP yield of early rice by 38.5% and 68.1%, and that of late rice by 25.8% and 49.0%, respectively. Compared with CK plot, NPK and NPKS plots were 21.4% and 54.9% higher, respectively, in BSP contribution rate to early rice yield and 12.8% and 22.8% higher, respectively, in BSP contribution rate to early rice yield. Whether fertilizers were applied or not, yields of both early and late rice crops increased with increasing BSP, while contribution rate of fertilizers to grain yield decreased significantly with increasing BSP. Soil organic matter, total nitrogen and readily available potassium are the major factors affecting BSP and soil total phosphorus, total potassium, alkalytic nitrogen and available phosphorus are also important factors affecting BSP. Long-term application of NPK with rice straw not only significantly increased rice yield, but also sustained or increased basic soil productivity (BSP). The findings suggest that combined application of chemical fertilizer with rice straw is a recommended fertilization practice for sustainable rice cultivation in South China.

Abstract:Effects of long-term fertilization on yield variation trend, yield stability and sustainability of a double cropping rice system were studied through a 25-year long-term fertilization field experiment in Nanchang, China, of which yield data were analyzed using the linear regression, stability variance and sustainable yield index methods. The field experiment, established in 1984, was designed to have 8 treatments, that is, Treatment CK (a early rice—late rice rotation without fertilizer),Treatment PK (N deficiency), Treatment NP (K deficiency), Treatment NK (P deficiency), Treatment NPK (balanced chemical fertilizer application), Treatment 70F+30M (70% chemical fertilizers plus 30% organic manure), Treatment 50F+50M (50% chemical fertilizers plus 50% organic manure), and Treatment 30F+70M (30% chemical fertilizers plus 70% organic manure), and all the treatments, except CK, were the same in N nutrient supply. Results show that Treatment NPK improved yield, yield stability and sustainability of the double rice cropping system, as compared with Treatments NP, NK and PK. However, Treatments 70F+30M, 50F+50M and 30F+70M further raised the yield by 6.15%, 3.88% and 7.75% and the yield stability by 25.91%, 59.78% and 29.31%, respectively, and Treatment 70F+30M improved the sustainable yield index by 8.57%. Besides in all the treatments as a whole, the higher the initial yield, the lower, the annual variation of the yield, and all showed an increasing trend, except for Treatment NK declining in yield with each passing year. Treatments CK and NK fluctuated the most sharply in yield, reaching 107.95 and 142.30 kg hm^-2 a^-1, respectively, Treatment NPK did the least, reaching 23.74 kg hm^-2a^-1only. However, In OM-involved treatments, the fluctuation in annual yield grew obviously bigger with the rising ratio of F/M. To sum up, Combined application of chemical fertilizers with manure is helpful to obtaining high and stable yields and keeping the double rice cropping system sustainable, with the combination of 30% organic manure and 70% chemical fertilizers being the most optimal.

Abstract:Nitrification is an important biochemical process in the soil, and a cause of soil nitrogen loss. In nature, some plant species can exude from their roots some substances that may inhibit the activity of soil ammonia oxidizing bacteria. This kind of nitrification inhibitory substances is generally referred to as biological nitrification inhibitor (BNI). Sorghum is such a plant species that exudes from its roots methyl hydroxy phenyl propionate (MHPP), which has great inhibitory effect on soil nitrification. To explore underlying mechanism of sorghum roots exuding MHPP, sorghum seedlings were cultivated in hydroponic systems using ammonium and nitrate, separately. Root exudates were collected after a given period of time for analysis of MHPP content with a High Performance Liquid Chromatograph (HPLC) and hydrion content with the micro-titration method. After the collection of root exudates, Sorghum roots were also collected for isolation of plasma membrane of root cells with the two phase method for determination of H+ ATPase activity. Results show that in the hydroponic system with ammonium sorghum roots exuded MHPP at a rate of about 3.52 μmol g^-1 root FW d^-1 and proton at a rate of 16.49 μmol g^-1 d^-1, while in the other, they did almost zero. And in the former, sorghum roots exuded, while in the latter they did almost neither. Moreover, with increasing concentration of ammonium in the hydroponic medium, roots exudation of MHPP and proton increased in rate, too. So, it is obvious that ammonium nitrogen promotes release of MHPP from sorghum roots. However, it was found in further study that although apparently the release of MHPP from sorghum roots was affected by form of nitrogen, the exudation of MHPP was always correlated to that of hydrions in the process, and root cells exuding proton depended on activity of the plasma membrane H^＋ pump. It was also found in the study that MHPP release from sorghum roots was actually regulated by plasma membrane H^＋ ATPase activity. In the absence of nitrogen sources, it is feasible to use fusicoccin or vanadate to affect proton pump activity and hence release of MHPP from sorghum roots. Statistic analysis of all the data acquired in the experiment shows that the release of MHPP and proton was nearly at a ratio of 1:4 and their correlation coefficient r was 0.98. Therefore, it can be held that in the hydroponic system using ammonium nitrogen the secretion of a large volume of MHPP from sorghum roots is to a certain extent induced by enhanced plasma membrane H^＋ ATPase activity resulting from absorption of ammonium ion, which can be deemed as an important physiological mechanism that can be used to prevent ammonium oxidation in rhizosphere and improve nitrogen utilization efficiency.

Abstract:With rapid industrialization and urbanization in progress over the recent decade in China, the issue of Cd contamination of agricultural soils has become more and more serious. According to the surveys and statistics available that show about 7% of the agricultural soils have already exceeded the National Standard for Environmental Quality in Cd contamination and relative to other heavy metals and metalloids, cadmium (Cd) should be deem as an element of the first priority for control. Besides, tobacco is a high Cd accumulator, storing Cd mainly in its leaves, which, if consumed by chronical smokers, would leave Cd accumulated in their bodies. Therefore how to decrease Cd content in tobacco plant, especially in its leaves, has been a hot topic in the fields of tobacco industry and public health. In a three-year field plot experiment, red mud and/or plant straw was amended in addition, or not, to Zn fertilization to explore its long-term effect on Cd in-situ immobilization in the soil and Cd accumulation in tobacco plant, so as to find a best way to reduce cadmium contentin tobacco growing in contaminated soils. The experiment was designed to have five treatments in terms of amendment (red mud, rape straw, corn straw, red mud plus rape straw, and red mud plus corn straw) and two levels of Zn fertilization. The soil in the experiment was artificially contaminated with 1.5 mgkg^-1cadmium added to the soil. Results show that compared with control, the yield of tobacco leaves and the ratio of mid-high grade leavesin amendment treatments were significantly increased by 2.6% ~ 32.3% and 2.9% ~ 20.2%, respectively, which brought about an increase in economicbenefit by 6.6% ~ 31.3%. Among the treatments, the amendment of red mud plus rape straw was found to be the highest in both yield and economic benefit. The amendments stably decreased soil available Cdcontents by 18.6%~47.4% in 2012, and 16.0%~27.0% in 2013. The plants from the treatment were found to follow an order, i.e. bottom leaf > middle leaf and upper leaf > stem in terms of Cd content in plant. The contents of Cd in tobacco were most positively related to soil available Cd content. Therefore, the Cd contentin tobacco leaves in 2011, 2012 and 2013 decreased by 28.3%, 28.1% and 15.2% on average, respectively in all the amendment treatments. The effect was the most apparent in bottom leaves and the least in stem. Rape straw,full of thiols, was higher in Cd immobilization capacity than corn straw. Application of zinc fertilizer in addition to the amendments further significantly lowered Cdcontent in different parts of the tobacco plant at different seasons. In conclusion, the treatment of red mud, rape straw plus zinc fertilizer is the most effective one in this experiment to decrease Cd phytoavailability in soil-tobacco system. Therefore it can be extrapolated as a high cost-efficient measure to decrease Cd content in tobacco plants and increase yield of tobacco leaves in lightly Cd contaminated soils.

Abstract:A field experiment was carried out in Hubei on effects of potassium and humic acid and their interaction on dry biomass, chemical composition, flavoring substances and organic potassium salt index in flue-cured tobacco, Jinshennong # 1. The experiment was designed to have only two factors, potassium and humic acid, two levels each. Result show that amendment of humic acid to fields the same in potassium level or application of potassium fertilizer to fields the same in humic acid level increased dry biomass of the plants at the early flu-curing stage and the total flavoring substances in, improved chemical composition of the cured leaves and raised organic potassium salt index of the flue-cured tobacco leaves; and interaction between potassium fertilizer and humic acid had some significantly positive effects on contents of reducing sugar, total nitrogen and potassium, nitrogen/nicotine ratio and organic potassium salt index, and its effects on dry biomass and the other chemical properties of flue-cured tobacco were far from the significant level. The application of a high rate of potassium plus humic acid was more conducive to improving the quality of flue-cured tobacco leaves and increasing potassium content and organic potassium salt index of the leaves than application of a low rate of potassium fertilizer plus a low rate of humic acid.

Abstract:Eucalyptus is an important tree species for afforestation in tropical or subtropical regions and many countries around the world have used it in afforestation. In South China, millions of hectares of local forests have been converted into Eucalyptus plantations. However, due to soil nutrient limitation in many areas and a high demand of Eucalyptus for nutrients, this kind of change in land use may exhaust soil nutrients and lead to deterioration of the soil in quality. In order to explore impacts of the practice on soil quality, soil samples were collected from 9 pairs of Eucalyptus and Pinus plantations in Guangxi, China, for analysis of soil nutrients, soil microbial biomass and soil enzyme activities and paired-t test. Pearson correlation analysis was done to explore relationships between soil nutrients, soil microbial biomass and enzyme activities. Results show that the replacement significantly decreased soil total carbon, labile carbon pool (I) and (II), recalcitrant carbon pool, total nitrogen and alkalytic nitrogen, but significantly increased soil available phosphorus, which might be a result of fertilization in the Eucalyptus plantations low in phosphorus mobility in the soil. The replacement also significantly decreased soil microbial biomass carbon and nitrogen, and activities of phenol oxidase, peroxidase, protease, urease and acid phosphatase. The significantly lower soil carbon, nitrogen, microbial biomass and enzyme activities suggested that conversion of Pinus plantations to Eucalyptus ones significantly decreased soil quality. Correlation analysis shows that (1) soil total carbon and nitrogen were positively related with soil microbial biomass carbon, microbial biomass nitrogen, cellobiosidase, peroxidase, protease and urease activities, (2) soil carbon/nitrogen ratio was positively related with β-1,4-glucosidase, cellobiosidase and peroxidase activities and (3) soil acid phosphatase activity was negatively related with total and available phosphorus and positively with nitrogen/phosphorus ratio, which suggest that soil carbon, nitrogen, phosphorus and their ratios were the most important factors influencing soil microorganism and enzyme activities. The change in tree species, short felling cycle, poor understory coverage and litter layer, field burning and tillage might be the factors that lead to decrease in soil nutrient, microbial biomass and enzyme activity in the soil, while fertilization might alleviate the effect on soil nutrients. Keeping proper understory coverage and litter layer, reducing soil disturbance and fertilizing properly would help improve soil quality during the replacement processes and follow-on management of the plantations and hence ensure sustainable development of Eucalyptus plantations.

Abstract:Biological soil crusts (BSCs) play an important role in fixation of sand dunes and maintenance of soil biota in arid desert ecosystems. Soil enzyme activities could be used as significant bioindicators of extent of soil restoration and important biological indices in evaluating ecological restoration and health in sandy areas. However, so far little has been reported on relationship between BSCs and soil enzyme activities. To understand how BSCs affect soil enzyme activities, sand dune soil under BSCs in the artificially revegetated areas at the southeastern edge of the Tengger Desert, China was taken as object of this study. Four sample lots different in sand-fixing history (57, 49, 32 and 22 a, respectively) were set for soil sampling, and a tract of mobile sand dunes (0 a) and a tract of natural vegetation land (>100 a) in Hongweiof Shapotou were set as control. Results show that cyanobacteria-lichen and moss crusts could significantly increase activities of soil alkaline phosphatase, protease and cellulase in the artificial revegetation sand fixing areas (p < 0.05). Type of crust significantly affected soil enzyme activities. The effects of moss crusts, typical of the late stage development of BSCs on activities of soil alkaline phosphatase, protease and cellulase were much higher than cyanobacteria-lichen crusts, typical of the early stage development of BSCs（p < 0.05). Sand-fixing history also significantly affected activities of the soil enzymes, displaying a positive linear relationship with activities of the soil enzymes（p < 0.05). BSCs significantly enhanced activities of the soil enzymes in the 0~20 cm soil layer（p < 0.05) and the effects weakened with increasing soil depth. Moreover, activities of the soil enzymes under the crusts varied with the season, following an order of summer > autumn > spring and winter. Therefore, apparently, the presence and succession of BSCs increases activities of the soil enzymes. The findings indicate that BSCs are beneficial to restoration of soil and corresponding ecological systems in the artificially revegetated desert areas at the southeastern edge of the Tengger Desert.

Abstract:Soil organic matter, as a basic substance of soil fertility, is not only a major source of soil nutrients, but also a critical factor controlling soil physic-chemical properties, biological properties and various fertility factors. In China and other countries, soil organic matter in farmland is maintained and raised mostly through incorporation of crop straw. Humification processes of the straw incorporated, and accumulation of organic carbon, composition of soil humus and soil enzyme activities varied sharply between soils different in depth of straw incorporation, and also between soils different in straw incorporation rate. To verify the effects of depth and rate of straw incorporation on these factors. a field experiment was carried out in a tract of farmland of black soil. In the field experiment, corn stalk packed at a rate of 40 g kg^-1 and 80 g kg^-1 soil in nylon bags was buried into three soil layers different in depth (0 ~ 20, 20 ~ 40 and 40 ~ 60 cm) for 4 years of in situ incubation for monitoring variations of corn stalk transformation, organic carbon accumulation, humus composition and soil enzyme activities. Results show that the addition of 40 g kg^-1 soil of the straw increased organic carbon by 31.8%, 96.4% and 171.1%, respectively, at the 0 ~ 20, 20 ~ 40 and 40 ~ 60 cm soil layers,, and the addition of 80 g kg^-1 soil of the straw did by 86.2%, 193.5% and 265.9 %, respectively; demonstrating that depth of the incorporation is conductive to soil organic carbon accumulation, because poor aeration in deep soil layers slows decomposition and transformation of the straw, thus favoring humus accumulation. However, in control (no straw incorporated), organic carbon declined by 29.3% in the 0 ~ 20 cm soil layer, but only by 1.8% in the 20 ~ 40 cm soil layer . The reason is that soil enzyme activity is higher in the shallow soil layer than in the deep soil layer, and hence, soil humus mineralization rate is much higher in the former than in the latter. Higher straw incorporation rate (80 g kg^-1 soil) increased soil organic carbon and soil enzyme activity. As a result humus HA / FA ratio in the soil changed greatly, towards improving humus in quality. Accumulation of humine acid carbon (HS-C) and humic acid carbon (HA-C) varied with soil depth, exhibiting a decreasing order of 20 ~ 40 cm > 0 ~ 20 cm > 40 ~ 60 cm, while accumulation of fulvic acid carbon (FA-C) in the 40 ~ 60 cm soil layer was more prominent. The contents of HA-C and FA-C were in extremely significant positive relationship with catalase activity and in significant positive one with urease and invertase activities. The above-listed findings suggest that incorporation of a high amount of straw may quickly increase soil organic carbon content, and deeper incorporation contributes to accumulation of organic carbon. Straw incorporation also alters soil humus composition and promotes activities of catalase, urease and invertase. For comparison, after the four years of experiment, the control was found to be much lower in soil organic matter content in the surface layer, which indicates that renewal of soil organic matter in farmland is very important to maintenance of soil fertility.

Abstract:To explore influence of soil microbes and their metabolites on crop growth, a platter cultivation experiment was carried out using Rice Spring No.1 to test Streptomyces JD211 for effect of the strain of bacteria on biomass of the seedlings and diversity of soil bacteria. Results show that the effect of the bacterial agent, 10 g kg^-1 in inoculation rate was extremely significant on rice seedlings, which were 52.15%, 44.56% and 65.56% higher than the seedlings in total dry weight, shoot dry weight, and root dry weight, respectively, and 90.10% and 58.51% higher in total nitrogen and total phosphorus, respectively. Compared with the soil in CK, the inoculated soil was 37.49% and 40.62% higher in available nitrogen and phosphorus. T-RFLP analysis of bacterial diversity shows that Streptomyces JD211 promoted the growth of some rare species of bacteria or species weak in ecological potential, thus turning some functional bacteria, which were involved in recycling of soil nutrients, ameliorating soil texture and controlling plant disease, into dominant ones. The changes in soil functional microflora accelerated recycling of soil N, P, etc. and enhance rice absorption of N, P and other mineral nutrients, thereby promoting growth of the rice.

Abstract:Soil quality assessment of the Aler oasis reclamation zone in the upper streams of the Tarim River was performed, taking into account integratedly 14 soil physico-chemical properties including soil water content, bulk density, pH, EC, total salt, organic matter, total N, alkalytic N, available P, available K, catalase, invertase, urease, and alkaline phosphatase, and using the minimum data set defined with the statistics method. And meanwhile comparative analysis was done of the soil quality assessment with the assessment without taking into account soil enzyme activity. Results show that (1) the minimum data set (MDS) suitable for use in the soil quality assessment of the oasis is composed of 4 indices, that is, soil water content, total salt, total N and catalase; (2) most of the cotton fields, newly reclaimed farmlands, orchards and woodlands, distributed in the riparian oasis region, are moderate or over in soil quality (SQI≧0.5 accounting for 78.12%); and (3) weight of total salt in the soil quality assessment without taking into account soil enzyme activity tends to be lower, which would lead to underassessment of the soil quality. This study may provide some references for regional soil resources utilization and decision-making for agricultural industry and ecological restoration.

Abstract:Effects of iron plaque on surface electrochemical properties of rice roots and adsorption and absorption of NH₄⁺ and K⁺, but increased the adsorption of phosphate by the roots were investigated through hydroponic experiments. It was found that the iron plaque formed on rice roots reduced cation exchangeable capacity of the roots and made zeta potential on the roots less negative compared with control, suggesting that the number of negative charges on rice roots became less due to the formation of iron plaque. Iron plaque also inhibited the adsorption of NH₄⁺, K⁺ and phosphate by rice roots. Results of 6-h cultivation experiments showed that iron plaque lowered the uptake rate of NH₄⁺, k⁺ and phosphate by rice by 21.1%, 42.7% and 59.1%, respectively, as compared with control. In conclusion, functioning as physical and chemical barrier or temporary repository, iron plaque inhibit short-term uptake of macronutrient elements, like N, P and K, by rice plants.

Abstract:Based on the long-term fertilization experiment in paddy soil (started in 1981) in the Red Soil Institute of Jiangxi Province, China, effects of fertilization methods (CK: No fertilizer; NPK: chemical fertilizer only; and NPKM: chemical fertilizer plus organic manure) on soil microbial community structure were explored using the phospholipid fatty acid (PLFA) method and BIOLOG technique. Results show that the soil applied with NPK or with NPKM was 0.91% or 3.09%, respectively, higher than the soil of CK in total PLFAs. Principal component analysis (PCA) of PLFAs shows that fertilization promoted changes in soil microbial community structure. It increased the populations of gram-negative bacteria (G^- bacteria), fungi, actinomycetes and protozoa in Treatment NPKM and the population of gram-positive bacteria (G^＋ bacteria) only in Treatment NPK, while the ratio of fungal/bacterial was found to be higher in CK than in Treatments NPK and NPKM. The microbial community structure in CK is very similar to that in Treatment NPK. Comparison between the treatments in Average Well Color Development (AWCD) shows that Treatment NPKM improved carbon utilization capacity of its soil microbial community, and hence overall activity of the soil microorganisms, while Treatment NPK weakened activity of the soil microbes. Shannon-Wiener, Simpson and McIntosh indices show that Treatment NPKM increased soil microbial community diversity, while Treatment NPK did reversely. Correlation analysis of soil PLFAs and soil nutrients shows that soil total PLFAs was extremely significantly related to soil organic matter and total nitrogen (p<0.01), but little to soil readily available nutrients.

Abstract:Soil samples were collected from afforested woodlots different in tree species for in-lab analysis of total salt content, anion and cation compositions, total alkalinity, pH, electrical conductivity, and alkalization degree, of which a systematic study was done. Results show: no CO₃²⁻ was detected in a tract of clearing as control and all the woodlots; afforestation significantly changed the content of soluble salts, like Na⁺, Cl⁻, SO₄²⁻ and HCO₃⁻ and reduced the content of total salt in the soils; in afforested soils, anions SO₄²⁻+ HCO₃⁻replaced SO₄²⁻+ Cl⁻ in dominancy; soil pH and alkalization degree and total alkalinity varied in a similar trend; and among the woodlots, the one of Amorpha fruticosa was the highest in alkalization degree, and followed by Woodlot Tamarix chinensis; Correlation analysis indicates that soil total salt content (y) is in extremely significant positive linear relationship with electrical conductivity (x), so it is feasible to calculate total salt content with soil electrical conductivity in grading the area by salinization degree. The findings of the study may serve as reference in elucidating salinization-alkalization processes of the coastal saline soil and in ameliorating the soil in the Yellow River Delta.