Abstract:China’s medium-low yield fields are widely distributed and have great potential for land productivity improvement. Improving the land productivity of medium-low yield fields is of great significance for ensuring food security and achieving sustainable development goals (SDGs). Assessing the quality and spatial distribution of medium-low yield fields is the prerequisite and basis for land improvement. This paper systematically reviewed the concept, evaluation indicators, and main assessment approaches of medium-low yield fields. The main problems and development trends of the assessment of medium-low yield fields in China are also discussed. The existing concepts of medium-low yield fields focus on quantity and quality, and there are few studies on ecological indicators and sustainable development abilities. The indicators system and assessment approaches are not uniform and the temporal and spatial variation of low- and medium-yielding fields is unclear. In the future, the medium-low yield fields assessment should consider quantity, quality, and ecology indicators. The medium-low yield fields assessment should be focused on the multi-scale assessment indices system construction, multi-source data fusion, assessment methods innovation, and determining the spatial and temporal change in multi scales. It is helpful to explore ways to increase the productivity of green, high-yield, and efficient agricultural production, ensure food security and promote the realization of SDGs.

Abstract:Since the end of the 20th century, mulched drip irrigation technology has been widely promoted and applied in arid areas of northwest China, which has greatly pushed the development of oasis agriculture. However, the salt in water brought by drip irrigation cannot be discharged from the soil, which makes the sustainable development of oasis agriculture in arid areas challenging. Therefore, preventing and controlling secondary salinization of farmland to make use of the salt and alkali land resources widely distributed in the arid area of northwest China under conditions of water resource shortage is an urgent problem to be solved in order to promote sustainable development of agriculture. This article sorted literature on biological salt removal and the aspect of salt tolerance mechanism, growth and development of halophytes to salt, mutual feedback effects between salt removal of halophytes and reclamation of saline-alkali soil, and the effects of planting halophytes on soil water and salt dynamics. Also, this study points out the existing problems in the research of biological salt removal in arid areas of the northwest and suggests prospects for further research works. The study can provide decision bases for making reasonable, efficient and comprehensive salt removal systems in arid area agriculture and is of great significance for realizing salt balance in farmland, alleviating soil secondary salinization crisis and soil sustainable utilization.

Abstract:Plants roots are known as an important driving force for the change of soil structure and soil hydraulic parameters (SHP). However, there is a lack of appropriate modelling approaches to root-pore-SHP interactions with quantitative descriptions, which has led to knowledge gaps in the effects of roots on SHP at larger scales. A consequence of this gap is the bias in the simulation and prediction of hydrological processes such as infiltration, runoff and evaporation in catchments. In this paper, available literature is reviewed and used to quantify the changes and effects of plant roots on SHP. In addition, its relationships with plant and soil type are proposed. The quantitative expression of SHP and their prediction models under the dynamic growth of plant roots are summarized. This paper also analyzes problems and future research directions of the quantitative research on root-permeated soils. This study points out that the current research on SHP affecting roots focused on small-scale control experiments, ignoring the interference of soil spatial heterogeneity and environmental factors at large scales. Previous studies found contrasting root effects (on SHP) depending on which processes are dominant, including root growth (or decay) and the density and diameter of roots. Meanwhile, root-induced change of SHP was species (root characteristics), soil type, and time-dependent. Also, related studies indicated that the model’s accuracy and reliability would be improved when considering the temporal dynamics of roots induced by land cover/land use change and seasonal variations in SHP. Few efforts have been undertaken to incorporate root variables into soil function to predict SHP based on roots occupying the soil pore space, changing soil pore size distribution and soil pore network model. Neglecting root-induced change of SHP in hydrologic simulation may lead to high uncertainties. As the root-related dominant process at a larger scale is different to that in small-scale control experiments, there remain significant knowledge gaps that impede the development of quantitative guidance on root-induced change of SHP at a larger scale. It is highlighted that the importance of root effects and associated parameters related to soil structure, and it is becoming a part of hot topic about coupling hydrological and water quality models.

Abstract:The effects of iron-manganese oxidizing bacteria-induced mineralization on the environmental behavior of heavy metals were reviewed, including iron/manganese-oxidizing bacteria and biomineralization, iron/manganese- oxidizing bacteria-induced iron-manganese oxide precipitation coupled with heavy metal stabilization, and the effect of iron-manganese oxide on heavy metals in soils. The application of iron/manganese-oxidizing bacteria in the bioremediation of different heavy metals was further summarized from the aspects of the biological mineralization pattern of iron/manganese-oxidizing bacteria (direct or indirect catalytic mineralization of iron oxide protein/enzyme, dual electron transfer reaction of manganese oxidase dominated by polycopper oxidase and the mineralization induced by external factors), heavy metal stabilization mechanisms of iron/manganese-oxidizing bacteria biological mineralization in soils(precipitation/coprecipitation, adsorption/complexation and redox). The effects of extracellular polymers, temperature and pH, coexisting ions and other factors on the mineralization process were also analyzed, in order to provide theoretical references for microbial-induced mineralization to remediate heavy metal pollution. Future work should focus on the long-term stability of heavy metals generated by minerals, the regulation of different microbial species combinations on mineralization, and the application of iron/manganese-oxidizing bacteria in the remediation of soil multi-heavy metal contaminated sites.

Abstract:The evaluation and quantification of aquifer structure in the Earth Critical Zones (CZ) are of great significance to the hydrological cycle and water resources management. 【Objective】 However, the characterization of complex CZ structures at spatial scales remains a huge challenge. In this paper, research was conducted on a small karst dolomite watershed (1.20 km²) in northwest Guangxi province, China, to quantify the distribution characteristics of aquifer media in CZ and analyze its influencing factors. 【Method】 a total of 21 electrical resistivity tomography survey lines with a total length of 12, 605 meters was set up and combined with hydrological drilling at the watershed scale. 【Result】 The results show that tectonic movement and dynamic metamorphism resulted in the development of multiple fault zones in the small watershed. This provided the material and dynamic basis for the spatial distribution of karst water-bearing media (including soil, surface karst zone, and surface karst spring). The fault zone was concentrated in the depression, which has a good hydrodynamic and dissolution environment. As a result, the soil and epikarst thickness in the depression was higher than that in hillslope, and there was a significant (P < 0.05) negative linear relationship with elevation. Besides, the spatial coupling degree of soil and epikarst thickness was high, showing a significant positive linear relationship (R² = 0.63, P < 0.01) between soil and epikarst thickness. It was related to slope erosion and confluence, and special water-CO₂-rock interaction in the soil-epikarst zone system. Karst aquifer flows out of the depression or down hillslope, and its hydrological characteristics were related to the distribution and water storage features of the soil-epikarst system. 【Conclusion】 This study provides data and technical support for the characterization of the karst aquifer at the catchment scale and construction of the land surface model in future studies.

Abstract:【Objective】 The response of runoff and erosion to soil physical crust has been extensively investigated in recent decades. However, there have been few attempts to quantify the effects of the profile of soil physical crusts on erosion processes. Thus, to explore the formation mechanism of soil physical crust in microtopography, artificial simulated rainfall and stratified soil treatment method were adopted to study the distribution and characteristics of soil particle size. 【Method】 Soil plot (2.0 m long×1.0 m wide×0.5 m high) was set to a slope of 5°, filled with soil by contour tillage (20 cm ridges and 30 cm ditches). Simulated rainfall was designed for eight durations (5, 10, 12, 14, 16, 18, 20 and 30 minutes) and one intensity (100 mm h^–1). The samples were taken out by a cutting ring (diameter 10 cm) and placed in a stratified sampling device. The bottom of the device was designed with a spiral rising bottom bracket. By turning the nut, the soil sample would be rised by 1 mm after turning one circle at a time with the bottom bracket. Each tier of soil sample was stripped with a soil sampling knife. Particles of samples in each tier of soil physical crust and the collected sediment were analyzed by Mastersizer 2000. 【Result】 The results showed that: (1) During erosion, the surface sand particles of structural crust (C_st), silt-containing sedimentary crust (C_scs) and silt-free sedimentary crust (C_sfs) were dispersed, while the clay and silt particles were enriched, and the degree gradually increased with the duration of rainfall. (2) When the rainfall lasted for 30 min, from top to bottom of the profile, the content of sand and clay in C_st decreased by 4.61% and 1.73%, respectively, the content of silt increased by 1.83%. The content of sand and silt in C_scs and C_sfs increased by 29.35% and 36.59%, 4.34% and 0.39%, respectively. The content of clay decreased by 16.30% and 14.34%, respectively. (3) In the process of crust formation, the dominant factor of C_st was raindrop dispersion, the dominant factor of C_scs and C_sfs was raindrop dispersion in the early rainfall period, and sediment deposition in the late rainfall period. 【Conclusion】 Spatial location and rainfall factors were the important factors that lead to the difference in physical crust types and particle composition.

Abstract:【Objective】 Digital Soil Mapping is receiving more attention and becoming widely used. Its methods mainly include environmental correlation-based models, spatial auto-correlation based models, and a mixture of these two kinds of models. The mixed model is expected to be advantageous over the single models. A generalized linear geostatistical model (GLGM) is a kind of mixed model. Compared with the commonly used mixed model, i.e., regression kriging (RK), GLGM has advantages such as having random effects to account for the non-stationarity of soil variability. However, GLGM is seldomly used due to its major disadvantages, i.e., complicated computation. 【Method】 In this study, within a small hilly area (3.03 km²) in Gaofeng Forest of Nanning, Guangxi, generalized linear mixed model (GLMM) and its combination with ordinary kriging (OK), i.e., GLGM, were used to predict the spatial distribution of soil organic carbon (SOC), pH, clay and cation exchange capacity (CEC). Performances of the two models were then compared with commonly used models, including multivariable linear regression (MLR), geographically weighted regression (GWR), regression forest (RF), OK, RK and generalized additive model (GAM). 【Result】 The results showed that GLMM had higher accuracy in predicting clay, while GLMM and GLGM had medium accuracy in predicting CEC. Further, GLMM and GLGM had lower accuracy in predicting SOC and pH. 【Conclusion】 Based on the adjusted R²of the linear regression model, nugget effect and global Moran’s I, it is concluded that GLMM and GLGM are appropriate when there is a low adjusted R² of linear soil-landscape regression (less than 5%), weak spatial auto-correlation of soil (nugget-to-sill ratio large than 71%), and strong local spatial variability of soil (Moran’s I less than 0.09), e.g., clay in this paper. Otherwise, GLMM and GLGM are not appropriate, e.g., for SOC and pH in this paper. For the high spatial heterogeneity and multi-scale variability of soil, we think that GLMM and GLGM are promising for DSM, although more studies are needed to improve the efficiency of GLMM and GLGM modelling.

Abstract:【Objective】 Cultivated land is a special public resource and the most precious natural resource, which has a fundamental and guaranteeing role in national food security. As an important means to measure the internal basic conditions and external utilization level of cultivated land, cultivated land quality evaluation is the basis for grasping the status quo of cultivated land quality and promoting sustainable use of cultivated land resources. 【Method】 Based on the needs of the “triad” protection of cultivated land, we applied the Criteria Importance Though Intercriteria Correlation(CRITIC) method to improve the gray target evaluation model. Also, we proposed a new method for the evaluation of county-level cultivated land quality based on the triple quality dimension including soil quality, ecological quality and management quality. The Chibi City was taken as the case study. 【Result】 Results show that the organic matter content and 17 others indicators can characterize the multi-functional quality level of cultivated land under the triple quality dimensions of soil, ecology and management. The quality of cultivated land in Chibi City was at an upper-middle level, and the range of bullseye was 0.66～0.85. Furthermore, the regional spatial difference of cultivated land quality was large and the quality grade of cultivated land in Chibi City was mainly two and three, accounting for about 80.49% of the total cultivated land area. The cultivated land with a higher quality level was mainly distributed in the northwest and east of Chibi City while with a lower quality level was predominant in the central and northern urban areas and Shenshanzhen in the northeast. The difference in cultivated land management quality in Chibi City was small, soil quality and ecological quality were more restrictive to the comprehensive quality of cultivated land. 【Conclusion】 The evaluation results of this study were consistent with the existing cultivated land quality grade evaluation results. This indicate that the improved gray target evaluation model was not only more objective in the weighting and evaluation process, but also conducive to measuring the single-dimensional quality of cultivated land. The improved gray target evaluation model was an important supplement to the existing cultivated land quality evaluation methods. This research can provide theoretical and methodological references for the evaluation of cultivated land multi-functional quality, which is in line with the new perspective of cultivated land quality evaluation in the new era.

Abstract:【Objective】 With the input of acid, the lime effect of ameliorants on acidic soils is gradually weakened resulting in soil re-acidification and aluminum toxicity. As a new alternative amendment material for acid soils, the performance of biochar on alleviating aluminum toxicity during soil re-acidification is still unclear. To investigate the effect and mechanisms of biochar on alleviating aluminum toxicity during soil acidification, a comparative study between biochar and Ca(OH)₂ was conducted through a simulated soil re-acidification test.【Method】 Cyclic acid leaching with HNO₃ was used to rapidly simulate the soil acidification process. A root elongation experiment with maize was used to investigate the response of plant roots to soil acidification. The change in soil pH, soluble Al³⁺ and base cations (K⁺, Ca²⁺ and Mg²⁺) during soil acidification were also studied. 【Result】 Cyclic acid leaching effectively simulated the process of soil re-acidification. With the increase of cyclic acid leaching time, soil pH decreased and the maize root elongation was inhibited. Compared with Ca(OH)₂ treatment, biochar significantly inhibited the acidification process and alleviated adverse effects on plant roots. When acid input was simulated for 12 years, the relative elongation of maize root in biochar treatment was 18.6% higher, and the relative absorption of Evans blue was 19.6% lower than that in Ca(OH)₂ treatment. On the one hand, biochar slowed down the decrease of soil pH during re-acidification through the protonation of surface anionic functional groups, and thus inhibited the activation of soil aluminum. As a result, the soil pH and the soluble Al³⁺ concentration in biochar treatment were 0.12 units higher and 33% lower than that in Ca(OH)₂ treatment with simulated 12-year acid input, respectively. On the other hand, biochar released Mg²⁺ continuously during soil re-acidification. In the simulation of 12-year acid input, the concentration of Mg²⁺ in soil solution and uptake of Mg²⁺ by maize in biochar treatment was more than twice higher than that in Ca(OH)₂ treatment. A higher concentration of Mg²⁺ can help alleviate the symptoms of aluminum toxicity in maize by regulating the physiological response of plants to Al³⁺. 【Conclusion】 Compared with Ca(OH)₂, biochar presented more long-term potential in ameliorating acidic soils under continuous acid input. These results are of important significance for management of soil acidification.

Abstract:【Objective】 Some changes in the external environment are often observed after the remediation of heavy metal polluted soils with solidification stabilization technology. Thus, an important scientific question worth discussing is whether the inactivated heavy metals will be released again and migrate in the soil, causing pollution risk, and under what conditions.【Method】 In order to reveal the effects of different chemical factors on the activation and migration of heavy metals in contaminated soil, the desorption and migration behavior of Cu²⁺ and Cd²⁺ in soil under different ionic strength, pH and cation types (Ca²⁺, Na⁺) were studied by laboratory soil column experiments. 【Result】 In general, the peak leaching concentration of Cu²⁺ and Cd²⁺ increased with the increase in ionic strength. Using CaCl₂ as a leaching agent, the desorption capacity of Cu²⁺ and Cd²⁺ increased at 0.005, 0.01, 0.05 and 0.1 mol·L^–1 CaCl₂, and the desorption capacity of Cd²⁺ was higher than that of Cu²⁺. However, 0.5 mol·L^–1 CaCl₂ inhibited the desorption of Cd²⁺ and the desorption of Cu²⁺ was higher than that of Cd²⁺. When pH decreased, the desorption of Cu²⁺ and Cd²⁺ increased, that is, the acidic environment was conducive for the desorption of Cu²⁺ and Cd²⁺. However, the concentration peak of Cu²⁺ and Cd²⁺ at pH 3 was smaller than that at pH 4 and 5. Ca²⁺ was more favorable for the desorption of Cu²⁺ and Cd²⁺ than Na⁺, but NaCl solution was more favorable for the desorption of Cu²⁺ at 0.005 mol·L^–1. Also, the concentration of Cu²⁺ in the leaching stage with deionized water was higher than that in the leaching stage with CaCl₂. In addition, soil particles exhaled at 0.005, 0.05 and 0.5 mol·L^–1 NaCl, and the flow rate decreased at 0.05 and 0.5 mol·L^–1 NaCl.【Conclusion】 The increase in ionic strength, decrease in pH and presence of divalent cations were beneficial to the desorption and migration of heavy metals in soil. This study provides a theoretical basis for soil remediation and heavy metal release after soil remediation.

Abstract:【Objective】 Denitrification and dissimilatory nitrate reduction to ammonium (DNRA) are the two competing nitrate reduction pathways that remove the available nitrate, both of which are affected by inter-related environmental factors. Understanding how environmental factors regulate nitrate partitioning in these two competing processes is of great significance for the optimization of nitrogen management in paddy fields.【Method】 Using ¹⁵N-tracing technique in combination with membrane inlet mass spectrometer (MIMS), a series of laboratory incubation experiments were performed to investigate the effects of different environmental factors including temperature (5, 15, 20, 25, and 35 ℃), pH (5, 6, 7, 8.5, and 9.5), NO₃^– concentration (50, 100, 150, 200, and 300 µmol·L^–1), C/N (0, 2.5, 5, 12, and 30), Fe²⁺ (0, 300, 500, 800, and 1 000 µmol·L^–1), and S^2– (0, 50, 62.5, 100, and 125 µmol·L^–1) on denitrification and DNRA rates and their partitioning in nitrate reduction in three paddy soils (Wuchang, WC; Changshu, CS; Ya’an, YA). 【Result】 Denitrification was the predominant pathway (87.97% – 91.73%), whereas DNRA only contributed to 8.27% – 12.03% of the total dissimilatory nitrate reduction in all treatments. Denitrification and DNRA rates increased exponentially with increasing temperature, as well as the DNRA/(Denitrification + DNRA) (R_DNRA). The highest denitrification and DNRA rates occurred at the pH of 7 and 8.5, respectively, and R_DNRA was higher in an acidic environment (6.24%–15.56%) than under an alkaline environment (4.92%–14.67%). The response of denitrification and DNRA rates to nitrate concentrations fitted well with the Michaelis-Menten relationship, in which the V_maxand K_m of denitrification were larger than those of DNRA. In the three paddy soils, compared with the treatment without glucose addition, denitrification rates were significantly increased by 22% – 35% at the C/N ratio of 2.5. Following the C/N ratio increased to > 2.5, DNRA rates were enhanced by 74% – 199%. In terms of Fe²⁺and S^2– addition treatments, denitrification rates were the highest in the low levels of electron donors (300 – 500 µmol·L^–1 Fe²⁺ and 50 – 62.5 µmol·L^–1 S^2–), whereas more electron donors (800 – 1 000 µmol·L^–1 Fe²⁺ and 100 – 125 µmol·L^–1 S^2–) were required when DNRA reached the peak rates. 【Conclusion】 By exerting different effects on rates of denitrification and DNRA, temperature, pH, NO₃^–, C/N ratio, Fe²⁺, and S^2– concentration significantly changed the partitioning between denitrification and DNRA. Specifically, relatively high temperature, C/N, Fe²⁺, and S^2– concentration favored nitrate partitioning to DNRA, while denitrification dominated the nitrate reduction process in environments with a relatively high NO₃^– concentration. Collectively, our results provide comprehensive information in terms of regulation of environmental factors on nitrate partitioning between DNRA and denitrification in paddy soils. This deepens our understanding of nitrate reduction processes and provides a scientific basis for increasing nitrogen use efficiency by favoring the nitrate partitioning to DNRA in rice fields.

Abstract:【Objective】 The availability of soil phosphorus (P) usually limits the productivity of fluvo-aquic soil. In order to provide a scientific basis for improving P use efficiency and rational fertilization in fluvo-aquic soils, the adsorption characteristics of P and its relationship with soil properties under long-term fertilization were studied. 【Method】 We selected seven treatments: no fertilizer (CK), no P fertilizer (NK), no potassium fertilizer (NP), no nitrogen fertilizer (PK), mineral fertilizer NPK (NPK), half compost plus half mineral fertilizer NPK (1/2OM) and compost alone (OM) in a long-term fertilization experiment at Fengqiu, to determine soil properties and P adsorption capacity. The Langmuir and Freundlich equations were used to fit the isothermal adsorption curves. Furthermore, the maximum adsorption capacity (Q_m), adsorption constant (K), maximum buffer capacity (MBC), P adsorption saturation (DPS), Freundlich adsorption constant (a) and adsorption index (b) were calculated. Correlation analysis and redundancy analysis (RDA) were used to explore the vital factors affecting the soil P adsorption characteristics.【Result】 The results showed that P adsorption in fluvo-aquic soil fitted both the Langmuir (R²≥0.80) and Freundlich (R²≥0.89) isotherms. With the increase of P concentration in the equilibrium solution, P adsorption capacity rapidly increased at first and then slowly afterwards. Compared with CK and NK, Q_m and MBC of NP, PK and NPK increased by 15.62%～23.60% and 2.94%～23.46%, respectively, however, K and MBC of 1/2OM and OM reduced by 39.60%～49.57% and 36.09%～56.15%, respectively. Correlation analysis and RDA results showed that organic matter (SOM), pH, free Al oxides (Al_d) and C/P were the main factors affecting P adsorption characteristics of fluvo-aquic soil. In addition, the DPS of 1/2OM was 30.92% lower than that of OM.【Conclusion】 Long-term combined NPK fertilizer with compost can increase the content of SOM, reduce P adsorption capacity and reduce the risk of P loss compared with OM.

Abstract:【Objective】 The main forms of soil erosion are water, wind and freeze-thaw erosion in the black soil area of Northeast China, and slope farmland is the main source of soil erosion. Human factors such as long-term plowing and straw burning or leaving the field untended and heavy use of light farming or other factors have led to the loss of surface soil, shallow cultivated layer, soil infiltration and erosion resistance of sloping farmland. This would aggravate surface runoff and soil water erosion in summer during severe rainfall. To improve the straw return rate in sloping farmland, a suitable farming method based on planting and cultivating land was proposed. 【Method】 Field experiments were used to study the effects of straw mulching and rotation tillage technology (including this season straw mulching and fallow, last season straw mulching and rotary tillage) and conventional farming (straw removal and rotary tillage) on soil water and heat changes and carbon and nitrogen accumulation.【Result】 The results showed that: water content in the 20-40 cm soil layer in the early stage of planting could significantly be increased with straw mulching, and the mulching fallow and mulching rotary tillage treatments increased by 26.02% and37.49%, respectively, compared with conventional tillage. At the same time, the 20-40 cm soil bulk density in mulching rotary tillage treatment was higher than that of conventional tillage and mulching fallow, which were reduced by 6.52% and 13.04%, respectively. Compared with mulching and rotary tillage, mulching and fallow could reduce the soil temperature of 0-20 cm and 20-40 cm in the early stage of crop growth by 1.57℃-1.63℃, while the soil moisture content increased by 15.25%-24.41%, which provided conditions for crop emergence and early growth. Combining straw mulching fallow tillage and mulching rotary tillage technologies increased the carbon and nitrogen content of 0-20 cm soil layer, and the organic carbon and total nitrogen reserves were increased by 11.36% and 20.51% compared with conventional tillage.【Conclusion】 All of this provide a scientific basis for the implementation of protective farming techniques on slope farmland in the low mountain and hilly areas. In the future, the optimized combination of crop varieties and dwarfing and maturity promotion would promote the increase of productivity in slope farmland when implementing conservation tillage technology.

Abstract:【Objective】 Winter multiple cropping of green manures such as Chinese milk vetch and rapeseed is a traditional system for improving soil fertility and crop yield in the rice field in southern China. Thus, it is of great importance to analyze the soil carbon (C) cycle and the ecological functions of green manure by exploring the distribution of photosynthetic C in a rice-soil system under long-term winter cropping of green manure. 【Method】 In this study, based on a 38-year rice-rice-green manure cropping experiment, the ¹³C-CO₂ pulsing labeling technology was used to study the distribution characteristics of photosynthetic C in a rice-soil system at the tillering stage of early rice season under long-term green manure (Chinese milk vetch, rapeseed and winter fallow). At the same time, the stability of ¹³C-photosynthetic C in soil was studied by measuring the content and distribution ratio of ¹³C in particulate organic carbon (POC) and mineral associated-organic carbon (MAOC). 【Result】 The results showed that the biomass of rice at the tillering stage was not significantly changed but the root/shoot ratio was decreased by 12.6%-19.4% with the long-term multiple cropping of green manure. Compared with winter fallow treatment, the cropping of green manure promoted the distribution of ¹³C-photosynthetic C in the shoot of early rice, and the accumulation of ¹³C-photosynthetic C was increased by 19.9 mg·plant^–1 and 80.6 mg·plant^–1 in cropping of Chinese milk vetch and rapeseed treatments, respectively. The ¹³C-photosynthetic C accumulation in the root of early rice was decreased by 2.7 mg·plant^–1 under Chinese milk vetch treatment, while it was not significantly affected by rapeseed treatment. This result infers that long-term multiple cropping of green manure increased soil nutrient supply and reduced the ratio of root to shoot of early rice, which allows the rice to distribute more biomass to the shoot. Meanwhile, the cropping of Chinese milk vetch and rapeseed treatments reduced the distribution of ¹³C-photosynthetic C in the soil by 7.6 mg·plant^–1 and 7.8 mg·plant^–1respectively. The proportions of rice ¹³C-photosynthetic C to POC and MAOC were not significantly affected by the cropping of Chinese milk vetch, but the proportion of ¹³C-photosynthetic C in POC was increased by 35.3% with multiple cropping of rapeseed. 【Conclusion】 The long-term multiple cropping of green manure promoted the accumulation of rice photosynthetic C in the plant-soil system. Compared with winter fallow treatment, the accumulation of photosynthetic C in the rice-soil system increased by 3.7%-28.0% in cropping of Chinese milk vetch and rapeseed treatments. On the other hand, the long-term multiple cropping of green manure increased the distribution of photosynthetic C to the shoot of rice and reduced the proportion of photosynthetic C to the root of rice and soil. Moreover, the stability of rice photosynthetic C in soil was weakened by multiple cropping of rapeseed treatments. From the perspective of increasing the total organic carbon and the stability of photosynthetic carbon, the cropping of Chinese milk vetch treatment is a better system for winter multiple cropping of green manures.

Abstract:【Objective】 Due to the differences in carbon chemical components among maize residue s(root, stem and leaf), their return to cropland soils with different fertility levels will induce differences in soil respiration and priming.【Method】 In order to explore these differences in the field, a 540-day in-situ field experiment with eight treatments of low fertilizer soil(LF+CK), low fertilizer soil + root (LF + R), low fertilizer soil + stem (LF + S), low fertilizer soil + leaf (LF + L), high fertilizer soil (HF+CK), high fertilizer soil + root (HF + R), high fertilizer soil + stem (HF + S) and high fertilizer soil + leaf (HF + L), was carried out at a long-term positioning station of brown earth in Shenyang Agricultural University using ¹³C labeled maize straw tracing method.【Result】 Results showed that (1) the contribution rates of soil respiration flux and straw carbon to soil CO₂-C emission showed downward trends over the in-situ incubation period. (2) Compared to the treatment without straw, the cumulative CO₂-C released from low fertility soil with root, stem and leaf increased by 134%, 126% and 95%, respectively, while that from high fertility soil increased by 157%, 189% and 96%, respectively. (3) The contributions of root and stem to soil CO₂-C emission in high fertility soil were significantly greater than that of leaf, but there was no difference in low fertility soil. (4) Different parts of maize straw returning to the field could cause the positive priming effects in both high and low fertility soils. Meanwhile, the priming effects of adding root and stem were significantly stronger than that of adding leaf, showing root and stem would cause more positive priming effects of soil CO₂-C than the leaf. Moreover, there was no significant effect on the priming effect between straw parts and soil fertility.【Conclusion】 Overall, this study enriched the theory of cropland soil respiration induced by straw returning, suggesting that the interaction of straw parts and soil fertility on soil respiration should be considered in straw returning.

Abstract:【Objective】 Nutrients addition to soil have a significant effect on soil organic carbon mineralization. However, the response of soil organic carbon priming effect(PE)to the addition of different nutrients and its mechanism is still not clear.【Method】 Urea and sodium dihydrogen phosphate were selected as exogenous nutrients and the effects of nitrogen addition, phosphorus addition and nitrogen combined phosphorus addition on soil organic carbon (SOC) mineralization, (PE), microbial function and soil physicochemical properties in a Moso bamboo plantation soil were investigated through an 80-day incubation experiment.【Result】 Nitrogen, phosphorus and their interaction significantly increased the cumulative CO₂ emissions of native SOC mineralization (by 91.33%, 19.18% and 94.88%, respectively), resulting in a cumulative positive PE. The magnitude of positive PE induced by nitrogen and nitrogen combined with phosphorus was greater than that induced by phosphorus alone. The above three nutrient addition treatments all significantly increased soil pH, labile organic carbon pool (microbial biomass carbon, dissolved organic carbon and O-alkyl C), carbon-degrading enzyme (β-glucosidase and invertase) activities and cbhI and GH48 functional gene abundance, but inhibited the activity of polyphenol oxidase and RubisCO enzymes. Also, soil inorganic nitrogen content (NH⁺₄-N and NO^-₃-N) was enhanced under nitrogen and nitrogen combined phosphorus treatments but reduced under phosphorus treatment. Results of Spearman correlation analysis showed significant positive relationships between cumulative PE and soil pH, labile organic carbon, inorganic nitrogen content, carbon-degrading enzyme activities, cbhI and GH48 functional gene abundances, whereas the activities of polyphenol oxidase and RubisCO enzyme were negatively related to cumulative PE.【Conclusion】 The addition of nitrogen and phosphorus nutrients may have enhanced the rate of native SOC mineralization by affecting soil pH, the content of labile carbon and nitrogen, and stimulating the activity and function of microorganisms.

Abstract:【Objective】 Dissolved organic matter(DOM)derived from organic fertilizers may provide new insights into the potential applications of different commercial organic fertilizers.【Method】 Herein, four different sources of organic fertilizers (biochar, WSB; sheep manure, SM; seaweed, SW; shrimp peptide, SP) with soils around the Changhua mine site were used to carry out a three-month incubation experiment. The subsequent effect of organic fertilizer amendment on molecular characteristics of soil DOM was investigated using multivariate spectral analysis. 【Result】 Compared to the control, soil DOM concentrations significantly increased in response to organic fertilizers amendment during the whole incubation period, exhibiting the lowest increment in WSB treatment and the highest increment in SW treatment, respectively. The excitation-emission matrix with parallel factor (EEM-PARAFAC) showed that WSB increased the proportion of humic-like fluorophore of soil DOM while fulvic acid-like fluorophore decreased during the whole incubation period. Also, SM, SW and SP amendments lowered the proportion of microbially-transformed humic-like fluorophore and increased the proportion of fulvic-acid like fluorophore during 0-45 days, but increased the proportion of refractory humic-like fluorophore during 45-90 days. Two-dimensional correlation spectroscopy analysis on Fourier-transform infrared (2D-FTIR-COS) spectroscopy revealed that aromatic/carboxylic acid groups of soil DOM in the control and SP treatments and alkene/polysaccharide groups in the added WSB, SW and SM treatments had the fastest responses over time, respectively. In addition, Si-O-Al signals from soil nano-minerals functional groups exhibited a distinct response over time in the added WSB and SP treatments. The carbon near-edge X-ray absorption fine structure (C 1s NEXAFS) analysis showed that compared to control, the added WSB increased the proportion of oxygenated aliphatic fractions but reduced aromatic/phenolic fractions of soil DOM after incubation. Also, SW increased the proportion of aromatic and carbonyl fractions but reduced aliphatic and oxyalkyl fractions while SM and SP increased the proportion of phenolic, aromatic and aliphatic fractions but reduced the proportion of carboxyl, oxyalkyl and carbonyl fractions. 【Conclusion】 The results of this study can enhance our understanding of how the decomposition of different sources of organic fertilisers affects the molecular characteristics of soil DOM. This is essential for assessing the ecological effects of the application of commercial organic fertilisers in soils.

Abstract:【Objective】 The development of soil texture grading and zoning is of practical significance for improving tobacco quality.【Method】 Based on the soil profile data recorded in the soil species records of Yunnan Province (prefecture and county), combined with GIS technology and geostatistics, this study carried out a high-precision division of soil texture and quality for a tobacco plantation in Yuxi City. A spatial database of soil texture at 100 m spatial resolution level was built, and the quality grade of soil texture of the key soil factors for tobacco zoning was scientifically divided. 【Result】 The results showed that the soil texture and quality suitable for tobacco planting in Yuxi varied greatly. According to soil texture and quality, the areas of grade I to grade V were 9.87%, 36.08%, 11.7%, 21.38% and 20.97%, respectively. The most suitable grade I soil for tobacco planting was mainly distributed in Eshan and Huaning counties, with an area of 26.2 km² and 25.2 km², respectively. Also, suitable second class soils were mainly distributed in Xinping, Yuanjiang and Jiangchuan, with an area of 87 km², 58.6 km² and 55.5 km², respectively. There were obvious differences in soil texture and quality for tobacco plantation soils at different altitudes. The main suitable tobacco plantation area was at the altitudes of 1600 ～ 2000 m. 【Conclusion】 The spatial distribution of soil texture at 100 m spatial resolution level in Yuxi was as detailed as village scale, which greatly improved the precision and practicability for tobacco plantation zoning. These results can provide a theoretical basis for high-quality tobacco production, long-term zoning and scientific management of soils.

Abstract:Long-term chemical fertilization (especially nitrogen fertilization) under intensive land-management practices in agriculture is of great concern globally due to its adverse influence on the environment and human health. Returning the eco-friendly crop residues to farmland is a promising way of reducing chemical fertilizer input and alleviating environmental problems.【Objective】 Protists are unicellular eukaryotes with enormous abundance and diversity, and play versatile functional roles to improve soil fertility and agricultural productivity. Thus, they comprise an integral component of soil microbiota in the agroecosystem. However, little is known about the responses of the soil protist community to nitrogen fertilization in combination with straw incorporation.【Method】 Here, a fixed field trial with 2×4 full-factor interaction was performed to examine the variations in diversity, composition, and potential function of the protistan community using Illumina high-throughput sequencing under eight different fertilization treatments (2 straw returning groups×4 nitrogen gradients), Also, the key forces driving the variation in soil protistan community were determined in combination with edaphic property analysis.【Result】 The phyla Chlorophyta, Conosa, Cercozoa and Ciliophora were dominant in the soils for all treatments. Nitrogen fertilization diminished the diversity of soil protists, whereas straw returning in general modified such impacts, with more pronounced effects under higher nitrogen application rates. Regardless of whether straw was added, the relative abundance of Chlorophyta exhibited an overall decrease with increased nitrogen gradient. Cercozoa and Ciliophora presented an increase in proportion with the amount of nitrogen fertilizer in the straw returning group. In the current study, the protistan functional community was predominated by phagotrophs in all treatments. Compared to treatments without straw addition, the implementation of straw returning enhanced the relative abundance of phagotrophs, but suppressed the proportion of phototrophs. Protistan parasites preferred a high nitrogen input under exclusive nitrogen fertilizer, with highest proportion in N300 treatment, which was significantly higher than those in all other treatments. Soil properties were important environmental factors determining the shifts in soil protist community, with soil organic matter and pH exhibiting the most intensive influences as revealed by redundancy analysis (RDA) and Pearson’s correlation analysis.【Conclusion】 This study provides experimental evidence that nitrogen fertilization coupled with straw incorporation have consequences for the soil protist community. It also shows that the phylogenetic and functional taxa of protists are responsive to such agricultural management regime alterations. Future studies should aim at deciphering the trophic associations among microorganisms, as well as constructing agricultural soil microhabitat beneficial for crops based on reasonable fertilization regimes and utilization of biotic resources like protists.

Abstract:【Objective】 This study aimed to elucidate the characteristics and correlations between Fusarium oxysporum and soil nutrients in banana orchards with Panama wilt occurring through analyzing the number of F. oxysporum and nutrient contents in soils. This can provide a certain theoretical basis for the prevention and control of banana Panama wilt.【Method】 Nine symptomatic and nine non-symptomatic banana plants in each orchard from 15 banana orchards in the main banana production areas in China and Laos were randomly selected for soil sample collection. Then real-time quantitative PCR and soil agrochemical analysis were used to explore the abundance of F. oxysporum and nutrient contents in the 270 sampled soils.【Result】 The result showed that the abundance of F. oxysporum in the soil sampled near the symptomatic banana roots was significantly higher than that collected near the non-symptomatic banana roots, with an average copy of 5.5 as lg-transformed per gram of dry soil. However, there were almost no significant differences between the nutrient contents of soils sampled from symptomatic and non-symptomatic banana plants. The distribution of various indexes of soil nutrients in the studied banana orchards was different based on each factor. Among them, only the contents of organic matter and total phosphorus were distributed normally while the soil pH, and contents of total nitrogen and zinc were skewed normal distribution. Mantel test results further displayed that the overall soil nutrients were significantly correlated to the abundance of F. oxysporum. Specifically, the soil pH, and contents of iron, manganese, and copper were significantly and negatively correlated to the abundance of F. oxysporum revealed by the Spearman correlation analysis between the abundance of F. oxysporum and each soil nutrient. In addition, the correlation analysis between F. oxysporum and nutrients in soils with different degrees of acidity and different organic matter contents showed that in the weakly acidic banana garden soil (pH > 6.0), the number of F. oxysporum in soils was significantly negatively correlated with the contents of iron, manganese and copper. Meanwhile in soils where organic matter contents were not seriously lacking (> 1%), the abundance of F. oxysporum in soils displayed a significant negative correlation with soil pH and the contents of iron, manganese, copper and zinc.【Conclusion】 In summary, banana orchards in the main banana production areas in China and Laos usually exhibit an acidification trend. Symptomatic banana soil showed an increase of F. oxysporum with a negative correlation to soil pH and the contents of trace elements, especially iron, manganese, copper and zinc.

Abstract:【Objective】 Soil methanotrophs are the only biological sink of atmospheric methane (CH₄). Grazing can regulate the methane oxidation activity of the soil by affecting the abundance and diversity of soil methanotrophs. 【Method】 In this study, we collected soil samples in winter pasture from different intensities of continuous grazing on typical grasslands in the Loess Plateau and used laboratory incubation and high-throughput sequencing to determine methane oxidation activity, composition and abundance of soil methanotrophs.【Result】 The results showed that the grassland was CH₄sink, and the medium grazing (MG) and high grazing (HG) intensity increased the rate of methane oxidation. Meanwhile, the mean abundance of methanotrophs in HG and MG also increased significantly compared with CK. The results of high-throughput sequencing showed that grazing had a significant impact on the diversity of methanotrophs, Upland soil cluster gamma (USCγ) was the dominant methanotrophic group under different grazing intensities, and a small amount of Methylocaldum and Methylocystis were also present. Pearson correlation analysis showed that methane oxidation rate (MOR) showed a significant positive correlation with soil moisture content and NO₃^--N content (P< 0.05), and significantly positively correlated with the absolute amount of USCγ (P< 0.01), which indicated that USCγ played a major role in the process of methane uptake in this grassland.【Conclusion】 This study proved that grazing can improve the methane sink function of typical grasslands in the Loess Plateau.

Abstract:【Objective】 The accumulation rate of soil organic matter directly restricts the improvement of productivity of Pinus massoniana (Masson pine) in the process of vegetation restoration in eroded red soil area. The way to solve this problem has been an inevitable development process of Masson pine in eroded red soil area. Heterotrophic respiration, an important part of soil carbon emission, is a key factor affecting soil organic carbon accumulation. Therefore, it is of great significance to study the effects of Masson pine plantation restoration on heterotrophic respiration and its temperature sensitivity in eroded red soil areas. This will enhance our understanding of the carbon output process and effectively increase soil organic matter accumulation in eroded red soil areas. 【Method】 In this study, Masson pine plantations with different restoration years (Y0, Y14, Y31) were selected as the research objects. The effects of vegetation restoration on soil heterotrophic respiration were studied by separating and measuring different respiration components and combining with soil factors such as soil organic carbon, total nitrogen, soil temperature, water content and litter. The structural equation model of heterotrophic respiration between litter, soil temperature, soil nutrients, soil microorganisms and heterotrophic respiration were established to analyze the correlation between heterotrophic respiration and environmental factors in the process of vegetation restoration, and to explore the main factors affecting heterotrophic respiration. 【Result】 The results showed that the heterotrophic respiration (R_H) of the pine forests with different recovery years differed significantly. The R_H in site Y31 was significantly higher than that in site Y14 and Y0. The R_H in site Y0 was only 0.99 μmol·m^–2·s^–1, while in sites Y14 and Y31 it was 2.20 and 2.80 μmol·m^–2·s^–1, respectively. Temperature was the main influencing factor of the seasonal variation of heterotrophic respiration, explaining 40.6%(Y0), 62.2%(Y14) and 66.6%(Y31) of the seasonal variation, respectively. During the restoration process, the temperature sensitivity(Q₁₀)of relative humidity increased significantly, which was 1.58, 1.93 and 1.82, respectively. The relative contributions of R_H to total soil respiration in different recovery years are 77.94%(Y0), 70.84%(Y14), and 77.35%(Y31). The structural equation model showed that soil organic carbon (SOC), temperature and soil microbial diversity were the main factors affecting soil R_H during the restoration of Masson pine. SOC and soil microbial abundance significantly correlated with R_H, and soil temperature varied with vegetation restoration which significantly and negatively correlated with R_H. 【Conclusion】 The results of this study indicate that the accumulation of SOC and lack of effective physical protection during Masson pine vegetation restoration increase the decomposition of SOC by microorganisms; On the other hand, the reduction of soil environmental temperature, a continuous increase of bacteria and fungi abundance, and an increase of Proteobacteria, Ascomycota and Acidobacteria in the community further aggravate the microbes to the original strength of soil organic matter decomposition. Consequently, the continuous increase of heterotrophic respiration related carbon emissions limits the improvement of carbon sequestration efficiency of Masson pine forests. Therefore, the strong soil heterotrophic respiration in the eroded and degraded red soil area may be the key factor limiting further improvement of soil organic matter.

Abstract:【Objective】 Unveiling the formation and maintenance mechanisms of fungal biodiversity is crucial to understand the biogeographic distribution pattern of soil fungi. However, knowledge of the elevational distribution pattern and its underlying mechanism of fungal communities in the deep layers of soil profile remains inadequate. 【Method】 In the present study, topsoil (0～20 cm) and subsoil(40～60 cm)samples were collected along an elevational gradient of 3 300～4 600 m from Mount Segrila, Tibet. The variations in fungal diversity and community composition with elevation in the topsoil and subsoil and the driving factors were investigated by Illumina MiSeq high-throughput pyrosequencing of the ITS rDNA. Changes in the coexistence characteristics of soil fungal communities among different elevations and between top-and subsoil were further explored based on the calculation of niche properties. 【Result】 We found that fungal communities collected from the topsoil and subsoil of Mount Segrila were dominated by Ascomycota (averaged relative abundance of 35%), Basidiomycota (46%)and Zygomycota (13%). Symbiotrophic fungi (62%) and saprotrophic fungi (33%) were identified as the major functional guilds by FUNGuild. In the topsoil, indices of fungal α-diversity (richness and Shannon diversity) decreased significantly with increasing elevation. In the subsoil, fungal richness decreased whereas Shannon diversity presented a hump-shaped pattern with increasing elevation. The dissimilarities in fungal community composition (β-diversity)increased significantly with increasing elevational distance in both topsoil and subsoil, suggesting a distance-decay pattern. The β-diversity of the fungal community was also positively correlated with environmental factors such as mean annual temperature (MAT), soil pH, the ratio of soil carbon to nitrogen, and soil moisture as suggested by the Mantel test. Results from distance-based redundancy analysis (db-RDA) suggested that pH was the driving factor for the variation in fungal community composition with elevation in the topsoil, whereas in the subsoil soil moisture was the most contributive factor. The community-level habitat niche breadth (B_com) of soil fungi was significantly higher at 3 500 m and 3 689 m, indicating an increase in environmental fitness and a more metabolically flexible fungal community at lower elevations. However, the niche breadth of soil fungi became narrow at 4 420 m and 4 590 m, implying that soil fungi at higher elevations could be more vulnerable in response to climate change in the future. A greater degree of niche overlap (O_ik > 8) between major fungal taxa was observed at lower elevations (3 356～3 689 m) and in the topsoil, whereas a lower degree of niche overlap (O_ik ≤ 6) was observed at higher elevations (4 284～4 590 m) and in the subsoil. In addition, a greater degree of niche overlap was observed between Ascomycota, Basidiomycota and Zygomycota, suggesting fierce competition for resources or habitats among these taxa. The degree of niche overlap was lower between Glomeromycota, Chytridimycota and other taxa due to their symbiotic or parasitic relationships with plants. 【Conclusion】 Overall, our study shows that the elevational distribution pattern of fungal biodiversity is distinctive between topsoil and subsoil, which is strongly related to the effect of environmental filtering and coexistence characteristics of specific taxa. These results may thus provide novel insights into the diversity and coexistence mechanisms of soil fungal communities in the alpine ecosystems of the Tibetan Plateau.

Abstract:【Objective】 This study aimed to explore the possibility of herbicide application in a drip irrigation system. To do this, the relationship between the application technology of soil closed herbicide and the control effect of weeds in the field were studied by using a drip irrigation system under film.【Method】 Under three different drip irrigation belt spacing, 40% ethyl atrazine emulsion was applied in three ways. After the drip application, the herbicide concentration in soil samples in different distribution areas was evaluated. In order to provide a scientific basis for rational application of drip irrigation weed control technology in a maize field and enrich drip irrigation application theory, the control effect was investigated in the stage of weed occurrence. 【Result】 The results showed that the distribution of herbicide in soil after it was applied was not related to the laying distance of drip irrigation belt, but was related to washing time of water after the last application. The longer the washing time, the lower the concentration of acetochlor in soil, the obvious vertical settlement, and the shorter the radial diffusion distance. Through drip application, the control effect of weed plant and fresh weight was the best after 15 min of drip irrigation, 30 min of drip irrigation and 5 min of drip irrigation. 【Conclusion】 It is feasible to apply soil sealing herbicide with drip irrigation in a mulched maize field, which can save time, labor and energy, and provide a new method for early weed control in a maize field. Nevertheless, it is necessary to carry out practical technology optimization research according to different pesticide types and properties.

Abstract:To explore the effect of different carrier materials on microbial degradation of phenanthrene, the biodegradation of phenanthrene was investigated in the liquid phase by gram-negative bacteria Sphingobium sp. PHE3 immobilized on montmorillonite, goethite and maize straw-derived biochar. The results of scanning electron microscopy showed that there was the largest number of bacteria adhered to the surface of the biochar with the best morphology. The addition of montmorillonite and biochar significantly (P<0.05) improved the degradation rate of phenanthrene by microorganisms, as well as the increase of polysaccharide and protein production in bacterial extracellular polymeric substance (EPS). Nevertheless, there was no obvious effect on phenanthrene biodegradation and EPS production with the addition of goethite. Furthermore, quorum sensing might play a role in biofilm formation. The signal molecules C₈-HSL and C₁₂-HSL secreted by PHE3 might mediate the production of EPS and phenanthrene biodegradation to some extent.