• Volume 58,Issue 1,2021 Table of Contents
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    • >Insights and Perspectives
    • The Principles and Indicators of Rational N Fertilization

      2021, 58(1):1-13. DOI: 10.11766/trxb202006220322

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      Abstract:The main objectives of nitrogen (N) fertilization to cropland are to obtain high target yield, accepted product quality and economic benefits, and maintain or improve soil fertility. In recent years, overemphasizing the environmental effects of N fertilization by unreasonable "reducing N" are becoming fashion while paying less attention to the production target and soil fertility, which might lead to reduce crop yield or product quality, or soil fertility. Here, we define the principles of rational N fertilization, i.e. in a given climate-soil-crop system with given relatively stable agronomic managements (such as crop rotation, tillage, cultivar and irrigation etc.), N rate should be in an rational range which could achieve high target yield, accepted product quality and economic benefits, maintain or improve soil fertility, and control N losses (thus environmental effects) in an acceptable level. We discussed the methods for determining the rational N rate and the indicators for evaluating N management. We emphasize that the essential of reducing current farmers' conventional unreasonable high N rates is to minimize N losses via improving N fertilization techniques rather than simply cutting the N application rate. We also emphasize that the rational N fertilization should implement the "4R" nutrient stewardship or techniques together with the recycling of manure and straw to cropland, and balancing other nutrients include phosphorus, potassium, middle and micronutrients, and integrating to other agronomic managements. We suggest to do long-term field experiments in different climate-soil zones to study crop yield, product quality, economic benefits, ammonia volatilization, nitrate leaching, nitrous oxide emission and soil fertility simultaneously, and to explore the relationship among fertilizer N, soil N and crop N in these climate-soil -crop systems, and further to evaluate the production target, environmental effects and soil fertility comprehensively. By using the indicators of N input, N output, N surplus, N use efficiency, N losses and change of soil organic carbon (SOC). We need form rational specific fertilization techniques by machinery to minimize N losses, thus to maximize crop N uptake according to the regional climate-soil crop systems and production conditions.

    • >Reviews and Comments
    • Soil Protozoa: Research Methods and Roles in the Biocontrol of Soil-Borne Diseases

      2021, 58(1):14-22. DOI: 10.11766/trxb202002010039

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      Abstract:Protozoa are a type of protists that act as consumers in the soil food web preying on other microorganisms such as bacteria and fungi, even nematodes. Soil protozoa are known to have an important impact on soil microbial communities and elements cycling. Recent studies reveal that soil protozoa might act, together with some soil microorganisms, such as bacteria, fungi, etc. forming a biological network barrier and playing an important role in defending plant roots from invasion of soil borne pathogens. Relative to the researches on beneficial bacteria and fungi, much less have been done on effects and mechanisms of soil protozoa controlling soil-borne diseases, either abroad or at home. Therefore, this paper calls for more scholars to pay attention to and to study soil protozoa and their functions in the ecosystem, and to explore their important values in soil health and sustainable agriculture. To achieve this goal, this paper first introduces soil protozoa and their ecological functions, and especially reports on their roles in controlling soil-borne plant diseases. In the next section, this paper summarizes potential mechanisms of soil protozoa preventing and controlling soilborne diseases. 1) Soil protozoa can not only prey direct on pathogens but also secrete secondary metabolites that will inhibit growth of pathogen, thus lowering pathogen density and disease incidence; 2) Their predation of soil microorganisms could induce the preys to generate more antagonistic compounds, which could help guard them from predation and indirectly inhibit growth of pathogens; and 3) Their predation can alter the structure and function of indigenous microbial communities. For instance, the highly selective predation behavior of protozoa could form a highly competitive microbial community, thus leading to a higher inhibiting effect on invading pathogens. The traditional method of studying soil protozoa depends mainly on isolation, culture and morphological observation. With development of the modern molecular technology, the research method has changed dramatically. In order to better study protozoa in the soil food chain from multiple angles, the third section of this paper summarizes the main methods used in studying biomass, diversity, community structure, and ecological functions of soil protozoa, including culturological/morphological methods, identification with biochemical methods, modern molecular technology, and screening and counting of protozoa with flow cytometry. Although protozoa play an important role in preventing and controlling soil-borne diseases, they have just made their debut on the stage of scientific research, waiting for more in-depth researches, as compared to other soil microorganisms. Then, the last section of this paper lists some future research topics related to soil biology researchers. 1) Explore diversity and structure of the soil protozoan community and their relationships with occurrence of soil-borne diseases; 2) establish technologies for identification, isolation, and culture of crop health related protozoa; 3) investigate effects of soil protozoa and other soil organisms on crop health; and 4) strengthen the research and development of technologies for collection and exploitation of protozoan resources.

    • Mechanisms Underlying the Regulation of Soil Nitrous Oxide Emissions by Arbuscular Mycorrhizal Fungi

      2021, 58(1):23-30. DOI: 10.11766/trxb201907010336

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      Abstract:Nitrogen, the major limiting factor of primary production in terrestrial ecosystem, contributes greatly to crop production since the invention of Haber-Bosch process. However, a substantial of nitrogen is lost to the surrounding environment, leading to low nitrogen use efficiency, nitrogen deposition, nitrate runoff and N2O emission. The microbial groups of nitrogen fixers, nitrifier and denitrifier carry out nitrogen fixation, nitrification and denitrification, respectively. Another group of symbiotic fungi, Arbuscular mycorrhizal fungi (AMF), is also found to be important for nitrogen cycling. Recent studies reported that AMF could significantly affect soil nitrification, denitrification and N2O emission. This review summarized the advance in the mechanisms by which AMF reduce N2O emission:(I) AMF inhibit nitrifier activities and reduce N2O production; (II) AMF exude labile carbon compounds to alleviate the competence between N2OR and other Nr reductase, which promotes N2O reduction to a greater extent; (III) AMF take up soil nitrogen and deliver them to host-plant and thus decrease nitrogen availability, lowering N2O production. Finally, we envisaged future studies in strengthening the role of indigenous AMF in reducing N2O emission. This review provides scientific evidence for future application of AMF in regulating N2O emission and N cycling.

    • Research Progress on Soil Silicon in Different Ecosystems in China

      2021, 58(1):31-41. DOI: 10.11766/trxb202005310409

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      Abstract:Silicon is a basic component of soil and rock. It can promote plant growth, enhance plant resistance, participate in biogeochemical cycle, regulate global carbon cycle and mitigate global warming trend. Based on the comprehensive introduction of fractions, availability, and biological cycling characteristics of soil silicon, this paper analyzes the contents of silicon and phytoliths in the soils of different ecosystems in China, and expounds the differences and influencing factors of available silicon and phytolith contents in the soils of different ecosystems in China. The research progress on the relationship between available silicon in paddy soils and rice growth, the relationship between available silicon in forest soils and the formation of phytoliths and in the forests are mainly discussed in this paper. The mechanisms of phytolith formation and its important role in global soil carbon sink are also pointed out. Some issues which are to be further studied proposed in the last section provide a good reference for the development of study on soil available silicon and phytoliths in China in the future.

    • >Research Articles
    • Modeling for Soil Organic Matter Content Based on Hyperspectral Feature Indices

      2021, 58(1):42-54.

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      Abstract:[Objective] The analysis of soil properties using routine chemical analysis method is rather costly and time-consuming, and so hard to meet the requirement for handling large volumes of soil samples fast and efficiently to monitor soil properties. Continuous soil spectral curves obtained with the aid of the hyperspectral technology encompass abundant spectral information, and reflect comprehensively various soil attribute information. Therefore, modeling can be done to predict some soil properties efficiently and accurately based on the hyperspectral technology. This paper was oriented to build a model for predicting soil organic matter (SOM) content based on hyperspectral feature indices with an expectation to provide a new method for rapid and effective determination of SOM content. [Method] In this study, a total of 178 soil samples were collected from the surface soil layers (0~20 cm) of farmlands of paddy soil and fluvo-aquic soil in the central plain of Jiangsu province for analysis of SOM content. Hyperspectral curves of the soil samples were obtained with the aid of the ASD FieldSpec 3 spectrometer. Firstly, the original spectra were processed with the algorithms of reciprocal log transformation (Log(1/R)) and continuum-remova l (CR) for analysis of hyperspectral characteristics of the soil samples different in SOM content and in soil type. Secondly, based on the data of the original, Log (1/R) and CR spectra, spectral feature indices, including deviation of arch (DOA), difference index (DI), ratio index (RI), and normalized difference index (NDI), were calculated, and relationships of SOM content with the four indices were analyzed. Finally, linear regression models for SOM content were established based on the selected spectral feature indices. Accuracies of the models were evaluated and compared. [Result] Results show:(1) SOM content was significantly and negatively related to original spectra, but significantly and positively to reciprocal log spectra. The relationship was the most significant at the waveband of 400~900 nm, with the absolute correlation coefficient value reached above 0.6. After the spectral curves being CR transformed, their differences in characteristic became extraordinarily significant different, and significant absorption valleys appeared near 420 nm, 480 nm, 660 nm, and 900 nm; (2) The DOAs of the original, Log (1/R) and CR spectra showed extra-significant relationships with SOM content (P<0.01) at wavelength of 600 nm, with correlation coefficient being -0.66, 0.61 and-0.33, respectively; and (3) Based on the combinations of DOA with DI, RI, and NDI of the three different spectra, the model established for predicting SOM content performed quite effectively, with relative percent deviation ranging from 1.78 to 1.94, R2 from 0.56 to 0.64, and RMSE from 4.98 g·kg-1to 5.50 g·kg-1. And the validation sets had R2 ranging from 0.67 and 0.73, and RMSE from 3.21 g·kg-1 to 3.51 g·kg-1.[Conclusion] The spectral feature indices, including DOA, DI, RI, and NDI, can be used effectively for modeling for SOM content, and the model may explain about 67%~73% of the SOM variability. The model established with RI and DOA of the Log (1/R) spectrum is an optimal one.

    • Attribution of Typical Aridisols and Halosols of Xinjiang Uygur Autonomous Region in Soil Taxonomy

      2021, 58(1):55-68. DOI: 10.11766/trxb201910290572

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      Abstract:[Objective] To have the soils in Xinjiang (short for the Xinjiang Uygur Autonomous Region of China) reasonably, clearly and scientifically classified will lay down a good foundation for development, utilization, mapping and management of the soil resources in the arid regions of China. In the process of the research, contradictions are found in the Chinese Soil Taxonomy (3rd ed.). The definition of the Aridic epipedon in the CST states that "from the soil surface, there is no salt or sodic vesicular layer or a mixture layer of soil and salt underlying it", however, this definition does not specify depth of the specific underlay. In addition, according to this definition, the surface or the underlying soil layer without "saltilizing" is excluded. At the same time, the Sali-Orthic Aridosols is defined as " Salic horizon, Hypersalic horizon or Salipan with upper boundary within 100 cm of the mineral soil surface", which is obviously contradictory to the previous one, thus leading to classifying some of the soils containing Salic horizon into Aridisols. Moreover, under Calci-Orthic Aridosols, no Subgroup is set specifically for salt accumulation. Hence, even though some soil profiles do have Aridic epipedon, Calcic horizon and Salic horizon, their characteristics of salt accumulation are not reflected in their names as a type of soil. Therefore, it is necessary to study these contradictions for solution.[Method] In this paper, 17 typical Aridisols and Halosols soil profiles of Xinjiang were selected as objects for the study. Based on analyses of their morphological properties and physicochemical properties, the 17 soil profiles were sorted in attribution in CST. And as to the above contradictions, the following suggestions were put forth. The definition relevant to Aridic epipedon should be modified to:Down from the soil surface, no salt vesicular layer or sodic vesicular layer or underlying soil and salt mixture layer (not in compliance with the salt horizon condition). The definition of Sali-Orthic Aridosols should be modified to:Other Orthic Aridosols that contain a Salic horizon, a Hypersalic horizon or a Salipan with its upper boundary varying in the range of 30 cm to 100 cm in depth. And in addition, a Subgroup named Salic Calci-Orthic Aridosols should be augmented. Then classification of the 17 soil profiles was performed according to the proposed revisions, and Profiles No.1~No.11 were used as references between WRB, ST and CST.[Result] Classification in light of CST shows that of the 17 soil profiles, 15 profiles are of Aridisols and 2 profiles of Halosols. However, nine of the soil profiles (No.1, 4, 5, 9, 12, 14, 15, 16 and 17) are found to have a Salic horizon within 30 cm in depth, and hence they do not comply with the proposed definition of Aridic epipedon in CST, and should be shifted from Aridisols to Halosols in classification. Profile No.2 has an Aridic epipedon and a Calcic horizon, and a Salic horizon, too, down below 30cm in depth, but was named as Salic Calci-Orthic Aridosols. References between WRB, ST and CST show that Profiles No.1~No.11 are all in the order of Aridisols in light of ST and 10 in the order of Solonchaks and one in the order of Solonetz in light of WRB.[Conclusion] The contradictions in CST has expanded the area of Aridisols and reduced that of Halosols, which is not conducive to the amelioration and exploitation of Halosols. In this paper, the suggestions are put forward for revision of certain definitions to settle the contradictions in CST, such definitions of Aridic epipedon and Sali-Orthic Aridosols, and for augmentation of a Subgroup. "Salic Calci-Orthic Aridosols". According to the proposed revisions, among the 17 soil profiles, the number of Aridisols reduced from 15 to 6, and the number of Halosols increased from 2 to 11, and one soil profile was renamed as "Salic Calci-Orthic Aridosols", a newly augmented suborder as proposed. In this paper, only the typical Aridisols and Halosols in Xinjiang are taken as examples for the preliminary study. The next step is to expand the study area to have Aridisols and Halosols in other arid areas covered, for comparative analysis so as further perfect the Chinese Soil Taxonomy.

    • Effects of Sampling Site Spacing and Soil Classification on Analysis of Soil Bacterial Diversity in Farmland on A County Scale

      2021, 58(1):69-81. DOI: 10.11766/trxb201907170324

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      Abstract:[Objective] Sampling site spacing and soil classification granularity are two important indices for measuring representativeness of soil samples and accuracy of a survey. The objectives of this study were to characterize variability of soil bacterial diversity on different scales and explore effects of soil sampling site spacing and soil classification granularity on analysis of soil bacterial diversity.[Method] Considering differences in soil classification granularity and spatial scale (village, town and county), this study had 8 sample farmland areas set up in a region under the rice-wheat rotation system in Changshu City, Jiangsu Province, and four adjoining sampling sites (6 m by 10 m) in each sample area. Surface soil samples were collected from five sampling points, arranged in a plum blossom pattern, in each of the sampling site and then blended into one mixture sample, thus making up a total of 32 soil samples for analysis of soil bacterial diversity by means of the High-throughput sequencing analysis technique and eventually effects of spacing of sampling sites and classification granularity on variability of the diversity. Spacing of the sampling sites was designed to have four scales, i.e. <50 m, <10 km, 10-20 km and >20 km, and soil classification granularity, four levels, i.e. species, family, subgroup, and great group, which were formed into various spacing-classification combinations. Then comparisons were made between the combinations in coefficient of variation (CV) of α diversity index and bacterial community dissimilarity (β diversity).[Result] Results show that CV of the α diversity index of soil bacteria decreased with declining soil classification granularity and with declining sampling site spacing, as well, while bacterial community dissimilarity tended to decline slightly with lowering soil classification granularity, but to increase significantly with increasing sampling site spacing from a field scale to a town scale, but not so significantly when the spacing went from a town scale to a county scale. CVs of the α diversity index of soil bacteria and bacterial community dissimilarity were lower in the group of two factor combinations than in the one factor group. The decline of the CV of α diversity and bacterial community dissimilarity with declining soil classification granularity on the town scale(10-20 km)was more obvious than that on the village scale (<10 km). Dummy correlation analysis shows that bacterial community dissimilarity was more closely related to sampling site spacing (Pearson correlation coefficient:0.585, R2=0.34; Spearman correlation coefficient:0.503, P<0.01)than to soil classification granularity(Pearson correlation coefficient:0.340, R2=0.11; Spearman correlation coefficient:0.318, P<0.01). Variation of soil physico-chemical properties and farmland management measures with elevating spatial scale was an important factor affecting effect of special spacing of sampling sites on soil bacterial community structure, which indicates that sampling area and sampling site spacing should be the prime factors in the surveys of soil microbial community structure in farmland, and soil classification granularity was another one to be taken into account in surveys of areas above a town scale. The lower the soil classification granularity, the more representative the sampling points.[Conclusion] All the findings in this study may serve as scientific reference for future studies on soil microbial diversity in farmland on a county scale and arrangement of sampling points for the study.

    • Accumulation and Sources of Heavy Metals in Agricultural Soil in A City Typical of the Yangtze River Delta, China

      2021, 58(1):82-91.

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      Abstract:[Objective] Zhangjiagang City, located at the Yangtze River Delta, China, has experienced rapid economic development since the unfolding of the reform and opening up policy, and consequently the economic development has brought about a series of environmental problems that have aroused concerns among the society in recent years. For the purpose of scientifically managing soil resources and providing to decision-making support in the effort to control the heavy metal pollution problems from the source and to remedy contaminated farmland soils, this study was carried out to explore how heavy metals accumulate and to identify sources of the heavy metal pollutions in this city.[Method] Totally, a total of 188 sampling sites were set up for collection of samples of surface and subsurface soils in the study area, in the light of soil types, land uses, sampling homogeneity, and surrounding contamination conditions. Totals of the six elements, i.e. Cd, Hg, As, Pb. Cr, and Cu, soil pH, and soil organic matter in the samples were measured. Sources and driving factors of the heavy metal pollution in the soil were analyzed and identified with the aid of principal component analysis (PCA) and GeoDetector.[Results] Results show that:(1) In terms of accumulation degree, the six heavy metals follow a descending order:Hg > Cd > Cu > As > Pb > Cr; (2) With reference to the "Soil Environmental Quality Risk Control Standard for Soil Contamination of Agricultural Land (GB 15618-2018)", about 2.13%, 1.06% and 0.53%, respectively, of the farmland soils polluted with Cu, Cd and Hg had the elements exceed the criteria, while almost none of the farmland soils polluted with As, Pb, and Cr do. Pollution assessment with the Geo-accumulation index method shows that among the six heavy metal pollutants, Cd and Hg were the two major ones and detected in 12.83% and 21.28% of the sampling sites, respectively; (3) Performance of the GeoDetector shows that among all the nine factors (pH, soil organic matter, soil type, fertilization application rate, pesticide application rate, population density, GDP, distance from road, and industrial output) discussed in this study, fertilization and pesticide application rates as well as industrial output were the main factors contributing to spatial variation of the six pollutants, while population density, GDP and distance from road were the ones explaining spatial variation of Pb; and (4) As and Cr came mainly from agricultural and industrial activities, Cd and Hg came from soil parent materials in addition to agricultural and industrial activities, Cu in the surface soil came from agriculture, livestock breeding, and industrial activities, while Pb came mainly from agricultural, transportation and industrial activities.[Conclusion] In summary, the six heavy metals in the study area vary in accumulation characteristics. Agricultural and industrial activities are the major causes leading heavy metals pollution of the soil. Nevertheless, further researches should be carried out to figure out influences of social and transportation activities on accumulation of some certain heavy metals, such as Pb.

    • Rainfall Erosion Process on Earth Road as Affected by Thickness of the Surface Regolith Layer in Loess Region

      2021, 58(1):92-105. DOI: 10.11766/trxb201908280282

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      Abstract:[Objective] Having long been used for transportation and traffic, earth roads have a regolith layer formed on their surface, which aggravates erosion of the roads. Up to now, very little knowledge is available about how erosion proceeds on the earth roads with a surface regolith layer and how the regolith layer affects erosion of the earth roads.[Method] An indoor artificially simulated rainfall experiment was used to investigate characteristics of the runoff and sediment production on roads with a surface regolith layer varying in thickness (thin layer=1.0 cm, and thick layer=4.0 cm). In the experiment a movable hydraulic slope-changeable steel trough, 2m in length, 0.5m in width and 0.55m in height, was used and packed with loess soil to simulate a earth road with a surface regolith layer. The trough was packed first with a layer of loess soil as road, 1.68 g·cm-3 in bulk density, and then with a layer of regolith, 1.20 g·cm-3 in bulk density. The experiment was designed to have 3 levels of slope, 4°, 8° and 16° and 4 levels of intensity, 1.0, 1.5, 2.0 and 2.5 mm·min-1. Before each test, a white nylon thread was placed between the road and the regolith layer at the bottom end of the trough, and used to determine sources of the erosive materials by the degree of its exposure. And then the erosion process of the regolith covered road was divided into two stages:1) mere regolith erosion and 2) regolith and road soil mixed erosion.[Result] Results show:(1) The mean runoff rate of regolith on the road with a thin layer of regolith was 1.01-1.52 times at the first stage and 1.26-2.44 times at the second stage that on the road with a thick layer of regolith. When the artificial rainfall was set at 2.5 mm·min-1 in intensity, the average runoff yield per rainfall event was 43.44 L from the road regardless of slope degree, and 37.36%-82.05% higher than that when the rainfall was 1.0-2.0 mm·min-1 in intensity; (2) During the second stage erosion, the average sediment concentration was 227.30 g·L-1 on the road 16° in slope, and about 2.14 times and 1.37 times that on the road 4° in slope and 8° in slope, respectively. Under rainfalls low in intensity (1.0 and 1.5 mm·min-1), sediment yield per rainfall event was high on the road with a thick regolith layer, being about 1.39-2.14 times that on the road with a thin regolith layer; whereas under rainfalls high in intensity (2.0, 2.5 mm·min-1), it was high on the road with a thin regolith layer, being about 1.14-1.67 times that on the road with a thick regolith layer. And under rainfalls 1.0 mm·min-1 in intensity, the average sediment yield per rainfall event on roads regardless of slope degree was 2.08 kg, which equaled to 23.57%-68.59% of that under rainfalls 1.5-2.5 mm·min-1 in intensity; (3) During the second stage erosion and the entire course of a rainfall event, sediment concentration in the runoff was more closely related to runoff rate on the road with a thin regolith layer than on the one with a thick regolith layer.[Conclusion] All the findings in this study may serve as a scientific basis for prevention and control of erosion on regolith-covered earth road erosion in the Loess areas.

    • Mechanism of Effects of Soil Organic Matter on Splash Erosion Disintegrating Aggregates

      2021, 58(1):106-114. DOI: 10.11766/trxb201907270327

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      Abstract:[Objective] Soil organic matter is an important component of soil aggregate. Though much study has already been done on its role and mechanism in the forming of soil aggregate, little is available in the literature about its effects on splash erosion disintegrating soil aggregates and on contributions to the mechanical impact and slaking effect of raindrops disintegrating soil aggregates, too. So more studies need to be done in this aspect. The purpose of this study is to explore effects of organic matter content on breakdown of soil aggregates in splash erosion.[Method] An indoor splash erosion experiment was conducted in the State Key Laboratory of Dryland Farming and Soil Erosion on the Loess Plateau, Institute of Soil and Water Conservation, Chinese, Academy of Sciences and Ministry of Water Resources, China. Soil samples different in soil organic matter content were collected from Fuxian of Shanxi Province for test in the experiment, which was designed to have home-made needle nozzles to simulate rainfalls of 95% alcohol solution and ultra-pure water, separately to distinguish effect of mechanical impact from slaking effect of raindrops on soil aggregates. The nozzle setting was designed to have four levels of height, i.e. 0.5 m, 1 m, 1.5 m and 2 m for controlling strength of the impact of raindrops.[Result] Results show that of the five soil samples different in soil organic matter content, soil aggregate stability exhibited an order of MWDSW > MWDWS > MWDFW, indicating that the higher the content of soil organic matter, the higher the stability of the soil aggregates and the higher the breakdown resistance of the soil. A significant relationship was observed between the content of organic matter and the stability index of soil aggregates. In soils high in organic matter content, the fraction of large aggregates (>0.25 mm) after the rainfall was approaching to that in proportion before the rainfall with the organic matter content increasing. The amount of large aggregates was significantly higher in the soil subjected with rainfall of alcohol than in the soil done with ultra-pure water. Splash erosion rate in all the five soils increased with rising height of the nozzles or kinetic energy of raindrops, regardless of type of raindrops and their relationship could be described with a power function. With rising kinetic energy of the rainfall, contribution rate of the slaking effect and mechanical impact decreased and increased, respectively. Under raindrops the same in kinetic energy, contribution of the slaking effect decreases with increasing organic matter content.[Conclusion] Increase in organic matter content enhances stability of the soil aggregates and reduces contribution of the slaking effect in the process of splash erosion. All the findings in this study can serve as a scientific basis for evaluation of stability of soil aggregates and exploration of factors disintegrating soil aggregates during the process of splash erosion.

    • A Comparative Study on Relationship between Rill Morphology and Sediment Yield on Slopes of Two Types of Engineering Mounds

      2021, 58(1):115-127. DOI: 10.11766/trxb201909100333

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      Abstract:[Objective] Production and construction activities, like digging, excavating, dumping and piling-up of earth, form a large number of engineering mounds, which are ordinarily complex in underlying and surface structure and poor in erosion resistance. The mounds are mainly in the form of flat tops and slopes, whereon, rill erosion is easily occurring on slope surface with scouring flow running down from the top of the mound. In the process of rill erosion, rill morphology is closely related to hydrodynamic characteristics, and the relationship tends to be affected by soil texture. So it is essential to explore the relationships of slope rill morphology with hydrodynamic parameters, sediment yield and soil texture of the engineering mound.[Method] To that end, a field scouring-erosion experiment was carried out on an engineering mound of red soil and another of lou soil. Changes in rill morphology parameters, including rill width, rill depth and width-depth ratio, were monitored on slopes 32° in gradient, with scouring water flowing down at 8, 12, 16 and 20 L·min-1(designated as Treatment I, II, III and IV), separately.[Result] Results show:(1) In the first 24 min, rill width and rill depth on the slope of the two kinds of engineering mounds developed rapidly. With increasing volume of the scouring water (8-20 L·min-1), both exhibited a rising trend; compared with Treatment I, Treatment II, III and IV was 0.8%, 19.3% and 27.2% higher in mean rill width, and 24.5%, 126.2% and 95.1% higher in mean rill depth, respectively, on the mound of red soil, and 3.7%, 62.4% and 108.2% higher and 18.2%, 87.9% and 95.5% higher, respectively, on the mound of lou soil. The relationships of rill width and depth with duration of scouring was statistically significant on the mound of red soil (R2>0.858, P<0.01), and of lou soil (R2>0.689, P<0.01), too; (2) Rill width-depth ratios on the two types of mounds both fluctuated during the initial period (0-24min) and then levelled off during the late period (24~45min); compared with Treatment I, Treatment III was the lowest in mean width/depth ratio on either mound, being 115% lower on the mound of red soil and 20% lower on the mound of lou soil; (3) The relationships of runoff shear force and power of rill flow on slope surface with width and depth of rill could be described with a power function (R2>0.602, P<0.01); runoff shear force was a parameter more suitable for describing development of rill depth on the mound of red soil, and runoff power was for describing development of rill width on the mound of lou soil; and (4) Extremely significant linear function relationships were observed of cumulative sediment yield of the slope with rill width and rill depth (R2>0.897, P<0.01); rill width contributed 84.9% and rill depth did 15.1% to the cumulative sediment yield on the mound of red slope, and 22.5% and 77.5%, respectively, on the mound of lou soil.[Conclusion] This study may provide a theoretical reference for research on rill erosion mechanism on engineering mounds different in texture.

    • Hydraulic Properties and Saturated Hydraulic Conductivity Pedo-Transfer Function of Rocky Purple Soil

      2021, 58(1):128-139. DOI: 10.11766/trxb202003250399

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      Abstract:[Objective] The knowledge about soil hydraulic characteristics plays an important role in optimal soil water management and conservation practices, and hence is essential to evaluation of soil water storage capacity and prediction of water and solute fluxes in soil, which may affect crop yield, fate of agrochemicals, and eventually groundwater quality. Rock fragments are the main factor in rocky purple soils affecting hydraulic properties, such as saturated hydraulic conductivity and water characteristic curve.[Method] Two soils derived from different parent materials, i.e. purple shale and purple mudstone, separately, were studied in this paper. The soils were divided into groups, separately, different in rock fragment size (0.25~2, 2~5 and 5~10 mm) and in rock fragment content (0, 30%, 50%, 70% and 100%) for test. Soil particle size composition was measured with the pipette method. Microscopic morphologies of the purple shale, the purple mudstone, and the groups of soils were observed with a ZEISS EVO 18 scanning electron microscope. Water characteristic curves and saturated hydraulic conductivities of the soils were measured with the pressure film method and constant head method, respectively. Two transfer functions (PTF1 and PTF2) were established to predict saturated hydraulic conductivity with the aid of the BP neural network. PTF1 consisted of four input variables (rock fragment content, rock fragment size, initial soil bulk density, and texture), while PTF2 did of two more input variables (air entry value and S index (absolute value of the slope at the inflection point of water characteristic curve)) in addition to the four in PTF1.[Result] Results show that saturated hydraulic conductivity was significantly related to rock fragments content, S index, and air entry value. Saturated hydraulic conductivity and S index of the soil improved with increasing rock fragments content, while air entry value did reversely. Moreover, with increasing rock fragment size from 0.25~2 to 5~10 mm, saturated hydraulic conductivity increased by 2.3 times on average. Rock fragment size had little effects on air entry value and S index. The maximum error between predicted and measured values was 0.2225 and 0.1058, and the average error, 0.0756 and 0.0422, respectively for PTF1 and PTF2. The regression coefficients of PTF1 and PTF2 was 0.9416 and 0.9873, respectively. The geometric mean, geometric standard deviation, root mean square error, and AIC index of PTF2 and PTF1 was 1.27 and 1.17, 5.57 and 1.70, 0.16 and 0.060, 2.94, and 53.2808, respectively, and the correlation value of PTF2 was lower than that of PTF1. indicating that PTF2 performed better than of PTF1 in predicting saturated hydraulic conductivity.[Conclusion] In summary, the presence of rock fragments significantly affects the hydraulic properties of the purple soil, thus improving water conductivity and decreasing water holding capacity of the saturated purple soil. The transfer function PTF2 based on the neural network performs well in predicting saturated hydraulic conductivity of rock-containing soils.

    • Response of Cover Crop Roots to Soil Compaction in a Vertisol(Shajiang Black Soil)

      2021, 58(1):140-150. DOI: 10.11766/trxb201909250409

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      Abstract:[Objective] As farming mechanization is developing rapidly in agriculture, more and more large-sized farming machines are running in farmlands, bringing high pressure onto the soils and making them higher in soil bulk density, and consequently lower in water and air permeability, which eventually lead to lower crop yields. Rotation with cover crops that have taproots going deep into the soil is believed to be an effective measure to improve soil structure and alleviate soil compaction. However, cover crops vary in adaptability to soil compaction with climate and soil properties. The objectives of this study were to investigate responses of cover crops different in species (modes) to soil compaction, and to verify which one is the best to adapt to soil compaction relative to region.[Method] A field experiment, laid out in a field of Vertisol in the Longkang Farm of Anhui, was designed to have two treatments different in soil compactness (not compacted vs compacted) and four cover crop treatments (Fallow, Alfalfa, Oil Rape, Radish + Hairy Vetch mixture). Soil bulk density, penetration resistance, shrinkage behaviors, and cover crop root systems were measured and analyzed for characterizing response of the root systems of the cover crops to soil compaction.[Result] Results show that in the compacted treatment, soil bulk density in the 0~30 cm topsoil layer (P<0.05) and soil penetration resistance in the 0~27.5 cm and 37.5~45 cm soil layers was significantly higher (P<0.05), and soil shrinkage behavior in the 0~20 cm soil layer was altered, relative to those in the non-compacted treatment. Besides, in the compacted treatment, Alfalfa, Oil Rape and Radish+Hairy Vetch was lower in root dry weight density in the 0~50 cm soil layer, but higher in root specific surface area; Radish+Hairy Vetch was higher in average root dry weight density, root volume density and root length density in the 50~70 cm soil layer than Alfalfa and Oil Rape, indicating that Radish+Hairy Vetch was higher than Alfalfa and Oil Rape in root penetration capability. In the compacted treatment, in terms of coverage and shoot biomass, the cover crops exhibited an order of Radish+Hairy Vetch > Oil Rape > Alfalfa. Compared with the cover crops in the non-compacted treatment, Alfalfa, Oil Rape and Radish+Hairy Vetch in the compacted treatment was 62.5%, 67.6% and 15.8%, respectively, higher in shoot biomass and 61.4%, 57.7% and 47.8%, respectively lower in root biomass.[Conclusion] In conclusion, the root systems of Alfalfa, Oil Rape and Radish+Hairy Vetch respond differently to soil compaction. Radish + Hairy Vetch is the most adaptable to soil compaction.

    • Effects of Different Microhabitat Types on Rock Dissolution in Maolan Karst Forest, Southwest China

      2021, 58(1):151-161. DOI: 10.11766/trxb201911040354

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      Abstract:[Objective] Karst mountain areas are generally thin in surface soil layer and fragile in ecological environment. Dissolution of carbonate rocks is the main way of soil formation in karst mountain areas. It is of great significance to study dissolution of carbonate rocks for protection of the soil environment and sustainable utilization of the soil resources in the areas.[Method] Different types of microhabitats, such as stone cavern, stone crevice, stone gully, stone groove, earthy surface, and stone surface, were selected as research objects for the study in the Maolan Karst forest, Guizhou. The method of sheet dissolution test was used to determine carbonate rock dissolution rates in these microhabitats. Spatio-temporal variation of the dissolution rate and shape of the rocks therein was observed, and relationships of dissolution rate with type of the microhabitat, soil physicochemical properties and microorganisms therein were analyzed. In the end, relationship of carbonate rock and soil formation was discussed.[Result] Results show that with the dissolution lasting from 0.5 to 2 years, the highest sheet dissolution rate of the rock appeared in stone grooves, followed by earthy surface and stone surface. And slight dissolution was observed in stone gullies, but no significant sign in stone caverns and stone crevices. In general, the rocks buried in the soil were higher than the outcropped ones in the habitat in dissolution rate. Correlation and random forest analyses show that type of a habitat was the primary factor affecting rock dissolution, and the soil moisture content and pH were factors promoting and inhibiting rock dissolution, respectively. As the dissolution process going on and on, the morphology of dissolution became more and more apparent in the microhabitats with dissolution rate changing significantly.[Conclusion] All the findings demonstrate that type of a microhabitat has a significant impact on rock dissolution in karst mountain areas.

    • Effects of Amendment of Glucose on Fertilizer Nitrogen Transformation and Acidification in Ultisol Cropland

      2021, 58(1):162-168. DOI: 10.11766/trxb201907190315

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      Abstract:[Objective] Soil acidification intensifies extensively in cropland due to anthropogenic activities, thus restraining sustainable development of agriculture on the soil and affecting environmental safety. Long-term excessive application of ammonium nitrogen fertilizer results in strong nitrification, and intensive leaching of nitrate accompanied with base cations, which are the main mechanisms of soil acidification in cropland. However, so far little has been reported in the literature on effective methods to exert source control over soil acidification triggered by nitrogen fertilizer application. It has been reported that amendment of readily utilizable carbon sources, such as glucose and sucrose, can promote microbial assimilation of soil inorganic nitrogen and reduce N mineralization and nitrification in forest soils. Based on the relationship of nitrogen transformation and proton flux, this type of organic-carbon-promoted microbial assimilation of inorganic nitrogen could also retard N-fertilization-induced soil acidification. Does the amendment of this type of readily utilizable carbon sources also have the effect of controlling or retarding nitrogen transformation and soil acidification in cropland? This question deserves further investigation.[Method] For this study, an in-door incubation experiment was carried out to explore effects of extraneous carbon on N transformation and soil acidification. Glucose was amended as model carbon source at a rate of 8 g·kg-1, and (NH4) 2SO4 or KNO3 applied as model nitrogen fertilizer at a rate of 100 mg·kg-1.[Result] Results show that in the treatments of CK, application of (NH4) 2SO4 and application of KNO3 only, net mineralization of organic N and nitrification of ammonia N dominated the process of N transformation in the soil, which is attributed mainly to the lack of usable carbon sources in Ultisol. Amendment of adequate glucose as extraneous carbon source promoted rapid microbial assimilation of almost all the NH4+-N and NO3--N native in the soil and amended in the form of fertilizer within 2 days. Within 30 days of incubation, N microbial assimilation quickly transformed 28%~50% of fertilizer N into solid organic N. However, application of glucose might trigger the risk of N loss through denitrification. Change in soil pH was closely related to chemical reaction of chemical fertilizer on the surface of the soil and transformation of C and N in the cropland. Application of (NH4) 2SO4 or KNO3alone lowered soil pH through nitrification and salt effect. Decomposition of glucose generated some mid products like organic acids, such as lactic acid, pyruvic acid, citric acid, etc., thus lowering soil pH. However, these organic acids consumed protons when decarboxylating, thus neutralizing soil acidity. Addition of glucose induced microbial assimilation or fixation of NH4+-N and NO3- , thus inhibiting NH4+-N-nitrification-triggered soil acidification, which could raise soil pH by up to 0.78.[Conclusion] Consequently, amendment of extraneous readily utilizable carbon sources, such as glucose, can promote microbial assimilation of NH4+-N and NO3--N in the soil and mitigate the soil acidification induced by N transformation in the cropland. All the findings in this study are of important significance for building up soil N retention capacity, improving N fertilizer use efficiency, and inhibiting soil acidification in croplands of acid soil.

    • Effects of Liming and Dicyandiamide(DCD)Application on Soil pH and Nitrification of Acidic Red Soil

      2021, 58(1):169-179. DOI: 10.11766/trxb201908080361

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      Abstract:[Objective] Soil acidification is one of the most important limitations on agricultural production in the red soil regions of South China, where the production of staple food crops is negatively affected by acid soil because its high contents of aluminum, manganese and acid hinder efficient use of soil nutrients such as nitrogen. Therefore, there is an urgent need for dual improvement of soil pH and N use efficiency in the red soil regions. As a conventional method for ameliorating acidic soils, liming increases soil pH, but inevitably enhances soil nitrification. The enhanced nitrification not only accelerates soil acidification, but also increases the risk of nitrate loss through leaching and runoff in the red soil regions with abundant rainfall. To prevent nitrification, dicyandiamide (DCD) is a commonly used nitrification inhibitor, which will reduce nitrate loss and soil acidification. The use of DCD coupled with lime may be an effective approach to improving red soil productivity. Previous studies only focused on the effect of liming or DCD separately on soil nitrification, and the joint effects of liming and DCD on nitrification of acid red soil are rarely reported. Thus, the objectives of this study are to investigate effects of combined application of lime and DCD on soil pH and nitrification in acid red soil and their underlying mechanisms.[Method] Soils collected from the Yingtan Red Soil Ecological Experimental Station in Jiangxi Province were cultivated for 35 days, and 200 mg ·kg-1 urea was applied as substrate for nitrification. Two factors were involved in the study, i.e. liming rate (0, 2, 4 and, 6 g·kg-1 soil) and DCD application rate (0 and 20 mg·kg-1). The soil in each treatment was sampled every 7 days for analyzing soil pH, ammonium and nitrate contents to evaluate their variations. At the end of the culture, soil DNA was extracted and amoA gene copies of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) were determined.[Result] It was found that liming at <4 g·kg-1increased soil pH and enhanced nitrification, whereas liming at >4 g·kg-1 increased soil pH a bit and did almost nothing on nitrification compared with 4 g·kg-1. A parabolic relationship curve was observed between soil pH and apparent nitrification rate. Apparent nitrification rate peaked on D7, D14, and D21 in soil 6.9 or so in pH. Soil nitrification was mainly affected by AOA and AOB, either independently or jointly. Path analysis shows that abundance of AOA had certain direct, but negative effect on apparent soil nitrification rate, and also some indirect effect reducing the rate by negatively affecting the abundance of AOB. On the contrary, abundance of AOB had certain positive effect on apparent nitrification rate, indicating that the promoted nitrification was attributed mainly to AOB as a result of liming. Application of DCD displayed a significant inhibitory effect on nitrification in red soil, regardless of soil pH. In soils high in pH (pH 7.0~7.8), DCD inhibited nitrification by reducing the abundance of AOB, while in soils lower in pH (pH<6.0), DCD inhibited the growth of both AOA and AOB, thus reducing nitrification. Furthermore, soil pH was increased significantly due to the reduced nitrification when DCD was applied.[Conclusion] Combined application of an appropriate amount of lime (2~4 g·kg-1) and DCD can not only raise pH of the acidic red soils and alleviate acidification, but also reduce nitrification, thus mitigating the potential threat of nitrate loss to the environment. All the findings in this study may serve as theoretical support to and new ideas for amelioration of acid soils. However, as the present experiment was carried out under well-controlled condition, the effects of combined application of lime and DCD on soil pH and nitrification in fields in the red soil regions need to be further studied for validation.

    • Spatio-temporal Variation of Farmland Soil pH and Associated Affecting Factors in the Past 30 Years of Shandong Province, China

      2021, 58(1):180-190. DOI: 10.11766/trxb201908300416

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      Abstract:[Objective] Soil pH is a key index for quality evaluation of cultivated lands. So this paper explored temporal and spatial changes in soil pH of farmlands in Shandong Province in the past 30 years, analyzed overall situation of and dynamic changes in soil acidification, and discussed natural and human-driven factors affecting soil acidification, so as to provide certain scientific references for prevention and control of soil acidification in Shandong Province. [Method] Based on the soil pH data cited from the "Second Provincial Soil Survey in 1984' and the "Provincial Arable Land Fertility Evaluation (PALFE) in 2015", the soils of the province were sorted into seven grades, i.e. I. Highly acidified soil (pH ≤ 4.5), II. moderately acidified soil (4.58.5), in line with the criteria for soil grading in terms of soil pH (Cultivated Land of Shandong) and in light of the reality of the province. The Kriging method and some other statistical methods commonly used in geostatistics were adopted to analyze the data with the aid of ArcGIS, Excel and some other software.[Result] According to the second provincial soil survey, the soils of the province was averaged 7.6 in soil pH, and no soils were sorted into Grade I, Grade II or Grade III. The soils of Grade IV, Grade V, Grade VI and Grade VII were 94.49×104hm2, 259.0×104hm2, 498.8×104hm2 and 1.03 ×104hm2 in area or 11.07%, 30.36%, 58.45% and 0.12%, respectively, of the total cultivated land area. The soils of Grade IV were distributed mainly in 7 cities (Weihai, Yantai, Qingdao, Rizhao, Linyi, Weifang and Tai'an). According to the Provincial Arable Land Fertility Evaluation, the soils were averaged to be 7.2 in pH, and no soils were sorted into Grade I. The soils of Grade II, Grade III, Grade IV, Grade V, Grade VI and Grade VII were 7.48×104hm2, 46.09×104hm2,155.4×104hm2, 202.8×104hm2, 347.3×104hm2 and 1.647 ×104hm2, respectively, or 0.98%, 6.06%, 20.43%, 26.66%, 45.65% and 0.22% of the total cultivated land area of the province. Soils of Grade III were found in 6 cities (Weihai, Yantai, Qingdao, Rizhao, Linyi and Zaozhuang) in the Jiaodong Peninsula and along the southeast coast, and soils of Grade IV in the 12 cities, except for Dezhou, Liaocheng, Binzhou, Heze and Dongying in the alluvial plain of the Yellow River. According to the Second Provincial Soil Survey, the main types of soils in the province were sorted, in terms of soil pH, as follows:Fluvo aquic soil > Paddy soil (Fluvo aquic type) > Cinnamon soil > Sandy black soil > Skeletal bone soil > Brown soil > Fluvo aquic soil, varying in the range from 8.0 the highest to 6.8 the lowest, and showing a difference of 1.2 units between the highest and the lowest. According to the PALFE, the soils exhibited a similar order, in terms of soil pH, i.e. Fluvo aquic soil > Cinnamon soil > Sandy black soil > Paddy soil (Fluvo aquic type) > Skeletal soil > Brown soil, ranging from 7.8 the highest to 6.0 the lowest, and showing a difference of 1.8 units. Comparison of the two datasets shows that the soils of Shandong as a whole dropped from 7.6 to 7.2 in soil pH in the past 30 years, and the area of alkaline arable land increased slightly, while that of the weakly alkaline and neutral arable lands decreased relatively, but the area of acidic arable land remained increasing significantly, and some of them even were acidified.[Conclusion] Since the Second Soil Survey of Shandong Province, the average soil pH of the cultivated lands had decreased by 0.4 units. The drop of soil pH was mostly found in regions of lands of Grade IV. Changes in soil pH of cultivated lands varied sharply from region to region and from type to type of the soil. Soil acidification occurred mainly in Weihai, Yantai, Rizhao, Qingdao, Linyi and Zaozhuang, especially, in skeletal soil and brown loam derived mainly acidic parent material. The Fluvo aquic soil and Cinnamon soil derived from Yellow River alluvial deposit and limestone were both alkaline, relatively high in pH. Natural acidification, crop harvest and improper use of chemical fertilizers are the main factors triggering decline of soil pH and even acidification in Shandong.

    • Effects of Native AMF and Intercropping Reducing Nitrogen Loss from Soil-Water Interface in Purple Soil

      2021, 58(1):191-201. DOI: 10.11766/trxb201909110290

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      Abstract:[Objective] In order to explore the reduction effects of native arbuscular mycorrhizal fungi (AMF) and intercropping reducing on the N loss from of nitrogen forms in purple soil-water interface in purple soil, a field experiment of runoff simulation under natural rainfalls was carried out in a field of purple soil, in an attempt so that to provide a theoretical basis for protecting the water environment and mitigating slowing the agricultural non-point source pollution caused by the nitrogen loss of from purple soil slope farmlands.[Method] The experiment was designed to have different planting patterns or mode[monocropping of maize (MM), maize/soybean intercropping (MSI), and monocropping of soybean (MS)] and different mycorrhizal treatments[inhibited (MI) and non-inhibited (NM)] . Samples of runoff and lateral infiltration were collected seven times during the rainy season for analysis of forms of Nitrogen (N) and their concentrations therein, and further for comparison between the treatments in effect on changes in form and translocation of Nitrogen.[Result] Results show that lateral infiltration or subsoil flow was the main path of N loss from soil-water interface in the purple soil, and nitrate N was the main form of N lost with the subsoil flow With sampling going on, the concentrations of total N and nitrate N in runoff fluctuated along a rising trend, while the concentration of ammonium N rose firstly and then declined. The concentration of total N concentration in lateral infiltration exhibited a trend of descending firstly, and then ascending and descending again, while the concentration of nitrate N did a gentle descending trend, but the concentration of ammonium N did a gentle trend of increasing first and then decreasing. Among all the composite treatments, Treatment NM+MSI was the lowest in concentration of total N and ammonium N in runoff and lateral infiltration and hence in total N loss, and significantly lower than all the other treatments. Treatment NM+MSI was 13.4% and 20.3%, respectively, lower than Treatment NM and Treatment MI in concentration of total N in runoff, 56.5% and 48.7%, respectively, lower in concentration of total N in lateral infiltration, 50.1% and 43.5%, respectively, lower in total N loss, 10.0% and 16.7%, respectively, lower in concentration of nitrate N in runoff, 51.3% and 42.9%, respectively, lower in concentration of nitrate N in total N loss with runoff, 10.5% and 26.0%, respectively, lower in concentration of ammonium N in runoff, 21.7% and 30.2%, respectively, lower in concentration of ammonium N in lateral infiltration, and 29.6% and 33.7%, respectively, lower in concentration of ammonium N in total N loss with lateral infiltration.[Conclusion] All the findings indicate that native AMF and maize/soybean intercropping has a certain potential to reduce nitrogen loss from the purple soil via soil-water interface.

    • Spatio-temporal Variation of Soil Readily Available Potassium and Partial Factor Productivity of Potassium Fertilizer in Rice Cultivation Regions of China

      2021, 58(1):202-212. DOI: 10.11766/trxb201910300311

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      Abstract:[Objective] In the past 30 years (1988-2017), rice planting patterns, potassium (K) fertilization application and crop yield all changed greatly in the rice-cropping areas of China. Therefore, it is necessary to follow spatio-temporal changes in readily available K in paddy soils in those regions, which may help provide guidance to improvement of soil K utilization efficiency use and rationalization of K fertilizer application.[Methods] Based on the data gathered from the nationwide paddy soil monitoring network, laid out in 1988~2017, spatio-temporal variation of soil readily available K, K fertilizer partial factor productivity (PFP-K) and K apparent balance (KAB) was analyzed in Northeast China, the Yangtze River Delta, Middle Reaches of the Yangtze River, South China and Southwest China, and relationships between the three also discussed.[Results] In the past 30 years, soil available K content was significantly higher Northeast China than in the other four regions. In the Middle Reaches of the Yangtze River, soil readily available K increased first and then levelled off in content, but in in the Northeast China, the Yangtze River Delta and South China soil readily available K content were steady first and then increased in content with the experiment going on, while in Southwest China little change was observed. Soil readily available K content was significantly and positively related to PFP-K. In Northeast China, the Yangtze River Delta, the Middle Reaches of the Yangtze River and South China, for the increase of each 10 mg·kg-1 of soil readily available K in paddy soil, PFP-K increased by 0.31, 1.51, 0.26 and 0.49 kg·kg-1, respectively. The paddy soils in China and all the five regions exhibited a declining trend or remained in balance in KAB during the period from 1988 to 1998, but a rising trend was observed during the period from 1998 to 2017. South China was the highest in KAB of paddy soil, followed by the Middle Reaches of the Yangtze River, Northeast China, the Yangtze River Delta and Southwest China in a decreasing order. The relationships between KAB and soil readily available K content (P<0.05) in paddy soils of the country and in the five regions could be fitted with a linear equation.[Conclusion] Therefore, for the paddy soils in China, soil readily available K content was on a rising trend during the period from 1988 to 2017, but soil readily available K content and its annual growth rate varied quite sharply from region to region. Higher soil readily available K content could significantly promote rise of PFP-K, and the K apparent surplus in paddy soils as a result of long-term rice cultivation was conducive further to increase in soil readily available K content.

    • Effect of Straw Returning Mode on Soil Organic Carbon Sequestration

      2021, 58(1):213-224. DOI: 10.11766/trxb201909020267

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      Abstract:[Objective] Aiming at overcoming the shortcomings of direct application of crushed straw into the soil under the wheat-maize rotation system, a years-long field experiment was carried out in an attempt to screen out an optimal mode for straw returning that could meet the targets of high yield, cost saving and soil fertility improvement.[Method] The nearly 10 years of field experiment on returning of wheat-maize straw was designed to have four treatments or straw returning modes, namely, (i)no return of either wheat or maize straw (WN-MN, CK1); (ii) return of wheat and maize straw, both crushed (WC-MC, CK2); (iii)leaving high wheat stubblein the field (WH-MN); and (ⅳ)leaving high wheat stubble and returning crushed maize straw (WH-MC). By comparing the treatments in the yield, gain and loss of soil organic carbon stock, carbon pool management index and other indices, advantages and disadvantages of the treatments were analyzed.[Result] Results show that Treatment of WC-MC and WH-MC was 81% and 243%, respectively, higher than the other two treatments (WH-MN, WN-MN). and 24.23% and 16.05%, respectively, higher than Treatment WN-MN in SOC stock. Compared with the SOC stock of the soil prior to the experiment, carbon sequestration of the four treatments varied in the range of -0.83~6.14 Mg·hm-2. Both sequestered C and non-sequestered C were positively related to cumulative carbon input, indicating that high-amount straw returning is more conducive to carbon sequestration. The minimum carbon input to maintain the basic organic carbon balance was 4.06 Mg·hm-2·a-1. The labile fraction of SOC (LFSOC)in each treatment decreased with the increase in soil depth. Compared with Treatment WN-MN, Treatment WC-MC, WH-MC and WH-MN increased LFSOC content in the 0~20 cm layer. Among them, the labile fraction of SOC (active organic carbon, dissolved organic carbon, microbial biomass carbon, hot water soluble carbon and particulate organic carbon)was the highest in Treatment WC-MC, and then in Treatment WH-MC, both of which were significantly higher than the other two (WH-MN and WN-MN). Treatment WH-MN was 35.7%, 21.4%, 34.1%, 24.2% and 36.8% higher than Treatment WN-MN in content of LOC, DOC, MBC, HWC and POC. The five components varied in the range of 35.5%-64.3%, 21.4%-55.3%, 34.1%-58.7%, 22.7%-42.9%, and 36.7%-60.7%, respectively, in sensitivity index (Table 3) and between the treatments, with Treatments WC-MC and WH-MC being significantly higher than Treatments WN-MN. Treatments WC-MC and WH-MC were also significantly higher in carbon management index than CK in each soil layer. In the season of 2015-2016, Treatment WC-MC and WH-MC was 34.5% and 20.1%, respectively, higher than Treatments WH-MN and WN-MN in annual crop yield, and in the season of 2016-2017, Treatmentl WH-MC wasthe highest or 11.1% higher on average than the three treatments. Moreover, in the season of 2015-2016 annual crop yield was found to be significantly and positively related to SOC and C inputs, but in the season of 2016-2017. it was not.[Conclusion] So in view of its effects SOC stock, LFSOC, CPMI, crop yield and saving cost, the mode of returning of crushed maize straw plus 25-30 cm long stubble left in the field for maize cultivation is deemed as an optimal straw-returning strategy for sustainable development of the agriculture under the intensive maize-wheat rotation system in Guanzhong Plain.

    • Effects of Application of Organic Materials on Nitrogen Mineralization and Microbial Properties in Tobacco Planting Soil

      2021, 58(1):225-234. DOI: 10.11766/trxb201907220320

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      Abstract:[Objective] The production of high-quality tobacco leaves is closely related to soil properties and nitrogen conversion. The use of different types of organic materials as soil amendment in tobacco cultivation to improve quality of its produce varies in effects with the type of organic material used, so it is necessary to explore how to apply rationally organic materials in the light of soil conditions.[Method] In this study, four types of organic materials, i.e. rice straw, rape straw, ryegrass and rapeseed cake, were amended separately at a rate equivalent to 100 mg·kg-1 nitrogen into the soil samples collected from a field under tobacco-rice rotation, high in organic matter (68.2 g·kg-1) and a tobacco field low in organic matter (17.2 g·kg-1). Then the soil samples were incubated and analyzed periodically for mineralization dynamics of inorganic nitrogen (NO3-, NH4+), soil enzyme activities and microbial functional diversity.[Result] Results show that mineralization dynamics of soil nitrogen in the tobacco soil were closely related to C/N of the organic material used. In the soil high in organic matter the addition of rice straw, rape straw or ryegrass significantly reduced the net nitrogen mineralization rate, and the concentration of inorganic nitrogen was 3.7~7.8 times, 1.1~1.3 times and 1.0~1.3 times lower than that in the control, respectively, while the addition of rapeseed cake low in C/N significantly increased the net mineralization rate and promoted accumulation of inorganic nitrogen in the soil. However, in the soil low in organic matter, the addition of organic material, regardless of type, significantly increased soil nitrification rate, but the addition of rice straw or rape straw significantly reduced the concentration of inorganic nitrogen in the soil during the early culture period. The addition of rapeseed cake significantly promoted the net mineralization rate in a short period of time (7 d), bringing the concentration of soil ammonium up to 3.3~3.7 times higher than that in the control soil, which indicates that soil ammonium came mainly from mineralization of the organic nitrogen in the organic material applied. Analysis of soil biological properties shows that the application of high C/N organic materials significantly promoted soil microbial functional diversity and soil enzyme activities. However, the soil microbial community varied in structure with the type of organic material applied, and with the type of carbon source utilized.[Conclusion] Therefore, rational application of rice straw in the soil high in organic matter is demonstrated to be an important measure to improve quality of flue-cured tobacco. And it is essential to pay high attention to rational application of high-nitrogen organic manure in upland tobacco fields in the light of soil properties, so as to realize the target of the production of high-quality tobacco leaves in different tobacco cultivation areas.

    • Spatial Distribution of Microbial Biomass Carbon, Nitrogen and Phosphorus Pools in Typical Farmland Soils in North China Plain—A Case Study of Quzhou County

      2021, 58(1):235-245. DOI: 10.11766/trxb201910310367

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      Abstract:[Objective] Soil microbial biomass (SMB) is a pool of soil available nutrients, directly participating in the transformation and biogeochemical cycling of soil carbon (C), nitrogen (N), phosphorus(P)and sulphur (S). Soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN), and soil microbial biomass phosphorus (SMBP)are main components of the SMB, which serves as a hub for material cycling in the pedosphere. Since SMB is sensitive to environmental conditions, any change in SMB will affect turnover of soil elements. Therefore, SMB is considered to be a sensitive and effective indicator of soil fertility and biological quality. The study on rules of spatial distribution of SMB pool is of important significance to grasp how soil nutrients recycle in situ and how to manage soil nutrients regionally.[Method] In the present study, to explore how SMBC, SMBN and SMBP distribute spatially and what their influential factors are in the farmland ecosystem. A soil survey was conducted in Quzhou County, a typical agricultural county in the North China Plain with 56 740 hm2 of farmlands. Using the grid sampling (2.5 km×2.5 km) method, soil samples were collected from the topsoil layer (0-30 cm) of a tract of farmland for analysis of spatial distributions of SMBC, SMBN and SMBP pool with the geostatistical method.[Result] Results show:(1) The average reserve of the SMBC, SMBN and SMBP pool was 64.14×103 t, 24.55×103 t and 2.8×103 t, respectively, in the topsoil (0-30 cm) layer of Quzhou County. SMB was distributed in patch, featuring moderate spatial variability and obvious spatial autocorrelation; (2) Crop yield was significantly and positively related to MBC and MBN; (3) The mean content of carbon, nitrogen and phosphorus in soil microbial biomass per unit weight varied sharply with planting system, being higher in the wheat/maize rotation system than in the cotton monocropping system, which indicates that rotation system is superior to monocropping system to some extent, and favorable to maintaining a large soil microbial biomass pool; (4) Size and spatial distribution of SMB pools were governed by planting systems and soil fertility. MBC, MBN and MBP were closely related to soil fertility (e.g., soil organic carbon, total nitrogen, available phosphorus, available kalium), among which soil organic carbon is the most important factor.[Conclusion] For the first time, sizes of SMBC, SMBN and SMBP pools were quantified, and spatial distribution pattern and influential factors of SMB were specified in the farmland of the North China Plain. In the farmland soil of Quzhou County, soil organic carbon is the most important factor affecting SMB pool, which suggests that soil microorganisms are limited by C. Therefore, it is advisable to strengthen application of organic manure, return straw to the field and reduce mineral fertilizer application rate so as to regulate and utilize the SMB pool in the future. All the findings in this study indicate that soil microbial biomass is a potential available nutrient pool in farmland in North China and may serve as a scientific basis for regionalized nutrient management and precise agriculture.

    • Structure and Diversity of Soil Nematode Community in Soil under Tsuga dumosa Forest in Galongla Mountain

      2021, 58(1):246-258. DOI: 10.11766/trxb201907170173

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      Abstract:[Objective] In this study, a tract of Tsuga dumosa forest typical of the Garongla Mountain, Motuo County, Southeast Tibet was taken as research object. The purpose of this study was to investigate structure and diversity of the soil nematode community in the Tsuga dumosa forest ecosystem in this region and their relationships with soil properties, and stability and succession of the ecosystem by analyzing environmental indicators and functions of the soil nematode community. This study is expected to be of important scientific significance in unveiling diversity laws of the soil nematodes in the Tsuga dumosa forest ecosystem in Southeast Tibet, discussing interactions and correlations between the evolution processes underground and aboveground, and learning roles of the soil nematode community in subalpine/alpine forest soil ecological processes.[Method] In September 2017, four sample plots were set up different in plant community and topography. Soil sampling points (at least 5 points) were specified in each sample plot randomly in distribution and soil samples were collected from 5 soil layers, 0-5 cm, 5-10 cm, 10-15 cm, 15-20 cm and 20-25 cm, at each sampling point with a soil drill 7 cm in inner diameter, and then blended together into one, separately. Nematodes in the soil samples were separated with the shallow basin method, observed under stereomicroscope for identification till the genus level and characterized by species composition, individual density, diversity index and functional index for analysis of structure and diversity of the soil nematode community. The soil samples were also analyzed for physical and chemical properties with the conventional methods, and redundancy analysis and linear correlation analysis was performed of the data for relationships with the nematode community.[Result] Results show that soil nematodes in the soil under Tsuga dumosa forest in Mt. Galongla could be sorted into 5 orders, 29 families and 34 genera, averaged to be 278 individuals·100 g-1 dry soil in density and did not vary much between soil layers. In the community Tylencholaimus and Leptonchus were the dominant genera and fungivorous nematodes were the most important nutritional group. Soil organic matter was decomposed mainly by fungi. Redundancy analysis (RDA) and linear correlation analysis shows that readily available potassium, organic matter, total nitrogen and total potassium are the major factors affecting the soil nematode community and its relationship with soil physical and chemical properties, and readily available potassium is the most important one. A significant and positive relationship was found between nematode density and soil water content. Uneven distribution of soil water may be one of the important causes for the variation of soil nematodes community in density with the habitat in the hemlock forest in Mt. Garongla.[Conclusion] Soil organic matter is decomposed mainly by fungi. The Tsuga dumosa forest ecosystem in Mt. Garongla is high in maturity and in a relatively stable state. The content of readily available potassium in the soil significantly affects number and diversity of the nematodes in the community. Organic matter, total nitrogen, hydrolyzed nitrogen and available phosphorus are also factors affecting number of the nematodes. Soil water content is one of the important environmental factors that affect species composition of the soil nematode community and number of the nematodes in the soil under Tsuga dumosa Galongla forests.

    • Effects of Earthworms and Organic Materials on Soil Structure in Tea Plantation

      2021, 58(1):259-268. DOI: 10.11766/trxb201911040281

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      Abstract:[Objective] Earthworms in the soil may help improve soil structure and fertility significantly through activities, like feeding, excreting, mucus secreting, excavating, etc. To explore the effects of earthworms as affected by application of organic materials of different kinds on the soil of a tea plantation, a pot experiment, designed to have five treatments, i.e. (i) no fertilizer input (CK), (ii) earthworms only (BE), (iii) rapeseed cake plus earthworms (CE), (iv) tea tree pruning plus earthworms (JE), and (v) biochar plus earthworms (TE), was conducted with tea trees planted in each of the pots (30 cm in diameter and 35 cm in height).[Method] Three months after the start of the experiment, soil samples were collected from each of the pots for analysis, after being air dried. Soil pH was measured using a pH meter; concentrations of soil organic carbon (SOC) and total nitrogen (TN) were quantified with a CN analyzer (Vario EL, Elementar GmbH); mineral-organic complex in soil microaggregates were characterized with the synchrotron radiation infrared micro-imaging method; intact particles (100-500 mm), varying in shape, were screened out with a 2-mm-sieve, frozen at -20℃, and then prepared with a cryomicrotome (Cyrotome E, Thermo Shandon Limited, UK) into thin sections (2 μm in thickness), which were eventually transferred into infrared-reflecting MirrIR Low-E microscope Slides (Kevley Technologies, Ohio, USA). Then distribution of SOCs of various forms and clay minerals (OH) was determined with the aid of Synchrotron radiation-based Fourier-transform infrared spectromicroscopy.[Result] Results show that Treatment BE was higher than CK in content of soil total carbon in, but lower than in Treatment CE, JE and TE in content of total carbon, total nitrogen and organic matter; and Treatment TE group was the highest. Earthworm inoculation alone (Treatment CE) increased total carbon and organic matter content in the soil, and addition of organic materials (Treatment JE and TE) enhanced the effect, and addition of tea biochar (Treatment TE) had the best effect. All the treatments showed a decreasing trend in soil pH, and the trend was especially significant in Treatment BE (from 6.81 to 5.82). Furthermore, the synchrotron radiation microzone infrared spectra demonstrated that polysaccharides, proteins, fats and clay minerals in soil aggregates were highly heterogeneous. Clay minerals and macromolecular organics in Treatment CE and JE were highly dispersed. Minerals and polysaccharides were quite similar while clay minerals, protein and fat were quite different in distribution, and their distributions were had nothing to do with any interactions between earthworms and organic materials. Correlation analysis between clay minerals and organic functional groups shows that the correlation coefficients of clay minerals and organic functional groups in the five fractions of soil aggregates followed an increasing trends:clay minerals-protein < clay minerals-polysaccharide < clay minerals-fat, which indicates that clay minerals varied in affinity with macromolecular organics and their relationships were not affected by any interactions between earthworms and organic materials.[Conclusion] In summary, soil organic amendments initialize a positive feedback loop by increasing SOC, which promotes interactions between minerals and organic components in the soil, and thereby may possibly serve as a soil management tool for enhancing carbon storage in the soil.

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