[Effects of Modified Distillers' Grains Biochar on Cadmium Forms in Purple Soil and Cadmium Uptake by Rice].

Biochar and modified biochar have been widely used as remediation materials in heavy metal-contaminated agricultural soils. In order to explore economical and effective materials for the remediation of cadmium (Cd)-contaminated acidic purple soil, distillers 'grains were converted into distillers' grains biochar (DGBC) and modified using nano-titanium dioxide (Nano-TiO2) to produce two types of modified DGBCs:TiO2/DGBC and Fe-TiO2/DGBC. A rice pot experiment was used to investigate the effects of different biochar types and application rates (1%, 3%, and 5%) on soil properties, nutrient content, Cd bioavailability, Cd forms, rice growth, and Cd accumulation. The results showed that:① DGBC application significantly increased soil pH, cation exchange capacity (CEC), and nutrient content, with TiO2/DGBC and Fe-TiO2/DGBC exhibiting better effects. ② DGBC and modified DGBCs transformed Cd from soluble to insoluble forms, increasing residual Cd by 1.22% to 18.46% compared to that in the control. Cd bioavailability in soil decreased significantly, with available cadmium being reduced by 11.81% to 23.67% for DGBC, 7.64% to 43.85% for TiO2/DGBC, and 19.75% to 55.82% for Fe-TiO2/DGBC. ③ DGBC and modified DGBCs increased rice grain yield, with the highest yields observed at a 3% application rate:30.60 g·pot-1 for DGBC, 37.85 g·pot-1 for TiO2/DGBC, and 39.10 g·pot-1 for Fe-TiO2/DGBC, representing 1.13, 1.40, and 1.44 times the control yield, respectively. Cd content in rice was significantly reduced, with grain Cd content ranging from 0.24 to 0.30 mg·kg-1 for DGBC, 0.16 to 0.26 mg·kg-1 for TiO2/DGBC, and 0.14 to 0.24 mg·kg-1 for Fe-TiO2/DGBC. Notably, Cd content in rice grains fell below the food safety limit of 0.2 mg·kg-1 (GB2762-2022) at 5% for TiO2/DGBC and 3% and 5% for Fe-TiO2/DGBC. In conclusion, Nano-TiO2 modified DGBC effectively reduced the bioavailability of soil Cd through its own adsorption and influence on soil Cd forms distribution, thus reducing the absorption of Cd by rice and simultaneously promoting rice growth and improving rice yield. It is a type of Cd-contaminated soil remediation material with a potential application prospect. The results can provide scientific basis for farmland restoration and agricultural safety production of Cd-contaminated acidic purple soil.

[Effects of Four Amendments on Fertility and Labile Organic Carbon Fractions of Acid Purple Soil].

The aim of this study was to explore the effects of four amendments on soil fertility and labile carbon fraction characteristics of acid purple soil, so as to provide scientific basis for nutrient management and carbon storage stability in purple soil. Field experiments were carried out, and six treatments were set up:no fertilization (CK), only chemical fertilizer (F), lime + chemical fertilizer (SF), organic fertilizer + chemical fertilizer (OM), biochar + chemical fertilizer (BF), and vinasse biomass ash + chemical fertilizer (JZ). The contents of soil organic matter, pH, available nutrients, soil integrated fertility index (IFI), dissolved organic carbon (DOC), microbial biomass carbon (MBC), particulate organic carbon (POC), their effective rates, and soil carbon pool management index (CPMI) under different treatments were studied to clarify their relationships. The results showed that:① the application of amendments significantly increased soil pH and the contents of organic matter, alkali-hydrolyzed nitrogen, available phosphorus, and available potassium (P<0.05). The OM and JZ treatments had the most significant increase in soil comprehensive fertility index (P<0.05), with increases of 1.96 and 0.77 and 170.43% and 66.96%, respectively. ② Compared with those in the control treatment, the contents of POC, MBC, and DOC in JZ and OM increased by 110.30% and 84.81%, 61.08% and 46.56%, and 195.87% and 141.67%, respectively. The application of amendments significantly increased the soil carbon pool index (CPI) and CMPI (P<0.05), in which the OM treatment showed the most significant increase, with soil CPI and CMPI values increasing by 107.34% and 90.75% compared with those of the control, respectively. ③ Soil organic carbon and its labile fractions were positively correlated with IFI (P<0.05), and redundancy analysis showed that there were significant differences among different treatments. The interpretation rates of soil IFI, pH, and available potassium to organic carbon and its components reached significant levels, and the order of interpretation rates was IFI(74.6%)>pH (11.7%)>AK(6.5%). The application of vinasse biomass ash and organic fertilizer to acid purple soil had the most significant effect on improving soil fertility and soil quality and was conducive to promoting the accumulation and activation of soil carbon fractions.

[Effects of Different Modifiers on Aggregates and Organic Carbon in Acidic Purple Soil].

The aim of this study was to examine the effects of different modifiers on the changes in aggregates and organic carbon in acidic purple soil， providing a scientific basis for the remediation of acidic purple soil. Using purple soil as the research object， a total of six treatments were set up， including no fertilization （CK）， single fertilization （F）， fertilization with lime （SF）， fertilization with organic fertilizer （OM）， fertilization with biochar （BF）， and fertilization with distiller's grains ash （JZ）. We compared the composition of aggregates in acidic purple soil under the application of different modifiers， as well as the distribution pattern of organic carbon in aggregates of different particle sizes. Combined with the stability indicators of aggregates， we sought to clarify the impact of different modifiers on the structure of aggregates in acidic purple soil. The results showed that fertilization significantly increased the soil pH， with the JZ treatment being the most effective. Fertilization significantly increased soil organic matter content， with the OM treatment showing the largest increase. The BF and OM treatments significantly reduced soil bulk density， whereas the SF and BF treatments significantly increased soil moisture content （P < 0.05）. All treatments used < 0.25 mm aggregates as the dominant particle size. Fertilization could significantly increase the content of large aggregates （aggregate structure units with diameter > 0.25 mm）. At the same time， fertilization treatments significantly increased the soil geometric mean diameter （GMD）， average weight diameter （MWD）， and R0.25 value （ > 0.25 mm aggregate content） and reduced the fractal cone number （D） and aggregate destruction rate （PAD） values （P < 0.05）. Fertilization also promoted the aggregation and stability of soil aggregates， with the OM treatment having the greatest effect. Compared with that in the CK treatment， fertilization could significantly increase soil organic carbon content by 31.71%-209.67%， with the OM treatment showing the most significant change. Different treatments of soil organic carbon were mainly distributed in large aggregates. Compared with that in the CK treatment， each treatment significantly increased the contribution rate of organic carbon in large aggregates by 19.34%-47.76%， with the OM treatment having the most significant effect （P < 0.05）. In general， chemical fertilizer combined with organic fertilizer could promote the formation of large aggregates in acidic purple soil， improve the stability of soil aggregates， and increase the content of soil organic carbon， which is an effective measure to improve the soil structure and improve the quality of acidic purple soil.

[Effects of Organic Fertilizer Combined with Biochar on Denitrifying Microorganisms and Enzyme Activities in Orchard Soil].

To study the effects of organic fertilizer combined with biochar on soil denitrification and denitrifying microbial community structure, this study took lemon orchard soil as the research object and adopted a pot experiment, setting up five fertilization treatments:no fertilization(CK), conventional fertilization(F), organic fertilizer(P), fertilizer+biochar(FP), and organic fertilizer+biochar(PP). The abundance and community structure of denitrifying microorganisms were studied using real-time quantitative PCR and T-RFLP. Redundancy analysis(RDA) was used to explore the environmental factors affecting the denitrifying microbial community structure, and PLS-PM analysis was used to explore the environmental factors affecting the denitrification potential of lemon orchard soil. The results showed as follows:① compared with that under the single fertilizer treatment(F), the organic fertilizer and biochar(P, FP, and PP) treatments significantly increased the denitrification potential of the soil, ranging from 147.8% to 1445.3%. The denitrification rate of soil treated with organic fertilizer combined with biochar was 23.8% lower than that treated with organic fertilizer alone. ② Compared with that in the CK treatment, fertilization treatment significantly increased the abundance of nirS and nirK denitrification microorganisms. Fertilizer treatments(F and FP) significantly reduced the abundance of nosZ denitrifying microorganisms. Biochar treatment significantly changed the diversity and uniformity of denitrifying microorganisms, but the specific law and mechanism quality remained unclear. ③ The results of RDA analysis showed that fertilization could affect the community structure of nirS, nirK, and nosZ denitrifying microorganisms by changing C/N, WC, NO3--N, SOC, AK, and AP. ④ PLS-PM analysis showed that soil denitrification was positively correlated with pH and the abundance of nirK denitrification microorganisms, and NO3--N indirectly affected soil denitrification by affecting the abundance of nirK denitrification microorganisms. In addition, the nirK microbial community was the dominant microbial community in soil denitrification in lemon orchards. In conclusion, organic fertilizer directly affected soil denitrification by regulating soil pH, whereas regulating NO3--N content affected nirK denitrification microbial abundance, indirectly affecting soil denitrification. The application of organic fertilizer combined with biochar could slow down the improvement of soil denitrification caused by single application of organic fertilizer, which is more suitable for promotion in orchards in this region.

[Response of Nitrification Potential and Ammonia Oxidation Microbial Community in Purple Soils to the Application of Biochar Combined with Chemical Fertilizer and Manure].

The effects of manure and chemical fertilizer combined with biochar on nitrification potential and ammonia oxidation microbial change characteristics of purple soils were studied to explore the effects of fertilization measures and soil environmental factors on nitrification potential and ammonia oxidation microbial change characteristics. In this study, purple soil was taken as the research object, and five treatments were set up:no fertilizer(CK), chemical fertilizer(F), manure(P), chemical fertilizer plus biochar(FP), and manure plus biochar(PP). PCR and T-RFLP methods were used to study the characteristics of soil AOA and AOB communities, and soil nitrification potential and environmental factors were measured at the same time to determine the effect of manure combined with biochar on the nitrification potential of purple soil. The results showed that:① compared with that in the CK treatment, the FP and PP treatments significantly increased soil nitrification potential(P<0.05). ② Compared with that in the CK treatment, the F, P, FP, and PP treatments significantly increased the number of copies of the AOA amoA gene in the soil by 78.17%-162.22%(P<0.05), and the F, FP, and PP treatments significantly increased the number of copies of the AOB amoA gene by 21.56%-78.32%(P<0.05). ③ Compared with that in the CK treatment, the PP treatment significantly improved the Shannon, richness, and evenness indices of the soil AOA community(P<0.05), and the combination of biochar(FP and PP treatments) could change the community structure of the soil AOB. ④ The chemical fertilizer and manure affected the AOA and AOB community structure by changing soil properties such as pH, TP, AP, C/N, SOM, NO3--N, and NH4+-N. ⑤ Stepwise regression analysis further showed that AOB amoA gene abundance was the main factor affecting soil nitrification potential. Therefore, under the condition that chemical fertilizer and manure were applied together with biochar, the AOB community was the main driver of the ammonia oxidation process in acidic purple soil, and fertilization affected the ammonia oxidation process by regulating C/N and NO3--N.

[Effects of Modified Distiller's Lees Biochar on Nutrients and Enzyme Activities in Purple Soil].

In order to investigate the effects of distiller's lees biochar and different modified distiller's lees biochars on soil properties, pot experiments were conducted to study the effects of different soil amendments (CK:no amendment, JZ:distiller's lees biochar, TiO2/JZ:Nano-TiO2 supported by distiller's lees biochar, and Fe/TiO2/JZ:titanium dioxide supported by iron-modified distiller's lees biochar) and the application rates of different amendments (1%, 3%, and 5%) on the characteristics of soil nutrients and enzyme activities under irrigation-drought rotation. The results showed the following:①the modified distiller's lees biochar significantly increased soil pH and CEC (P<0.05). At the 5% Fe-TiO2/JZ addition level, the soil pH reached 7.95 during the rice season, an increase of 2.3 units compared with that in the CK treatment; the CEC reached 12.06 cmol·kg-1, increasing by 21.38%; the soil pH reached 5.99 during the cabbage season and increased by 1.5 units compared with that in the CK treatment; and CEC reached 8.91 cmol·kg-1 at 3% Fe-TiO2/JZ addition and increased by 13.11%. ②At the same time, the contents of soil total nitrogen and available phosphorus were significantly increased (P<0.05). Compared with that in the CK treatment, the soil total nitrogen of 5% JZ, 5% TiO2/JZ, and 5% Fe-TiO2/JZ increased by 20.56%, 85.04%, and 59.61% in the rice season and 12.39%, 22.68%, and 23.70% in the cabbage season, respectively. In the rice season, the increase in soil available P under 5% Fe-TiO2/JZ was the highest, reaching 10.49 mg·kg-1, which was 1.64 times that under CK treatment. In the cabbage season, the soil available phosphorus (P) reached 90.15 mg·kg-1 under 5% TiO2/JZ addition, which increased by 93.38% compared with that in the CK treatment. ③Modified distiller's lees biochar increased catalase and urease activities and decreased alkali-hydrolytic nitrogen content and acid phosphatase activity. At the 3% addition level, catalase activity increased by 12.19%, 48.17%, and 37.30% in the rice season and 5.95%, 8.34%, and 17.42% in the cabbage season, respectively. In the rice season, the soil urease activity reached the maximum under 5% Fe-TiO2/JZ addition, which was increased by 40.90% compared with that in the CK treatment. In the cabbage season, the soil urease activity reached the maximum under 5% TiO2/JZ addition, which was increased by 58.53% compared with that in the CK treatment. The activity of acid phosphatase decreased by 5.39%-24.66% in the rice season and by 54.46%-61.40% in the cabbage season. Distiller's lees biochar and modified distiller's lees biochar could effectively increase soil pH and soil nutrient content, thus affecting soil enzyme activities. The application of iron modified-titanium dioxide-loaded distiller's lees biochar of 3% to 5% in acidic purple soil is more suitable.

[Biochar or Straw Substituting Chemical Fertilizer Increase the Risk of Phosphorus Loss in Subsurface Runoff in Sloping Farmland].

The purple soil slope farmland is an important agricultural land in southwest China but is also one of the main sources of agricultural non-point source pollution in the Three Gorges Reservoir area. Taking reasonable measures to control the loss of soil nutrients is of great significance to the treatment of non-point source pollution in the region. Here, a three-year (2018-2020) field runoff experiment was conducted to monitor and evaluate the phosphorus (P) loss in sloping farmland via surface runoff (i.e., surface flow, 0-20 cm) and subsurface runoff (i.e., subsurface flow, 20-60 cm), with five treatments including no fertilization (CK), conventional fertilization (CF), optimal fertilization (OF), biochar combined with 85% of OF (BF), and straw combined with 85% of OF (SF). The results showed that fertilization application reduced the sediment yields and surface runoff flux but increased the subsurface runoff flux. The total loss flux of phosphate (PO3-4-P), total phosphorus (TP), and particulate phosphorus (PP) in surface flow were the highest in the BF treatment and the lowest in the SF treatment. All fertilization applications increased the P loss fluxes in subsurface flow relative to that in CK. The highest PO3-4-P and TP loss flux in subsurface flow was found in the BF (213.88 g·hm-2 and 694.54 g·hm-2, respectively) treatment, followed by that in the OF and SF treatments. Redundancy analysis (RDA) results showed that surface runoff flux and biochar application were the main factors contributing to increased P loss in surface flow, and subsurface runoff flux was the main factor contributing to increased P loss in subsurface flow. In summary, the SF treatment reduced the amount of sediment yield and surface runoff flux in sloping farmland of purple soil and was the most effective for controlling P loss, whereas the risk of subsurface runoff flux requires further attention.

[Effect of Chemical Fertilizer and Manure Combined with Biochar on Denitrification Potential and Denitrifying Bacterial Community in Rhizosphere Soil].

To clarify the effect of chemical fertilizer and manure combined with biochar on denitrifying microorganisms and denitrification potential of rhizosphere soil, a pot experiment growing lemon was conducted involving five treatments, namely no fertilization (CK), chemical fertilizer (CF), manure (M), chemical fertilizer combined with biochar (CFBC), and manure combined with biochar (MBC). We determined the characteristics of the rhizosphere soil nirS-, nirK-, and nosZ-type denitrifying bacteria populations; denitrification potential; and soil environmental factors to clarify the effects of chemical and manure combined with biochar on denitrification. Our results showed that compared with that in CK, the CF treatment reduced the rhizosphere soil denitrification potential by 47.7%, whereas the M and MBC treatments increased the denitrification potential by 2192.7% and 1989.9%, respectively. The M and MBC treatments increased the gene copy number of nirS and nosZ, the CF and CFBC treatments decreased the gene copy number of nirS and nosZ, and all four fertilization treatments increased the gene copy number of nirK. Stepwise regression analysis showed that pH was the main factor for the abundance of nirS-type denitrifying bacteria and SOM and NH+4-N were the main factors for the abundance of nirK-type denitrifying bacteria, whereas pH, NO-3-N, and N/P were main factors for the abundance of nosZ-type denitrifying bacteria. The results of partial least squares analysis indicated that the abundance of nirS-and nosZ-type denitrifying bacteria, pH, TN, and N/P were the main factors affecting rhizosphere denitrification potential. Therefore, in acidic purple soil, nirS- and nosZ-type denitrifying bacteria were the main drivers of the soil denitrification process in lemon rhizospheres under chemical fertilizer and pig manure combined with biochar, whereas fertilizer affected the rhizosphere soil denitrification process by regulating soil pH, TN, and N/P.

[Effects of Chemical Fertilizer Reduction Substitute with Organic Fertilizer on Soil Functional Microbes and Lemon Yield and Quality].

To clarify the effects of non-rhizosphere/rhizosphere soil functional microbes (nitrifiers, denitrifiers, and phosphorus-solubilizing microorganisms) on lemon yield and quality, the lemon fruit and non-rhizosphere/rhizosphere soil were selected as subjects. To explore the correlation between non-rhizosphere/rhizosphere soil functional microbes and lemon yield and quality under a chemical fertilizer reduction substitute with organic fertilizer, traditional fruit quality determination and multiple molecular techniques were used. The results showed that:① 30% chemical fertilizer reduction substitute with organic fertilizer increased the nitrification intensity and phosphatase activity but effectively controlled the denitrifying enzyme activity. ② The chemical fertilizer reduction substitute with organic fertilizer significantly decreased the abundances of nitrifiers and nirS/nirK-harboring denitrifiers and significantly increased the abundances of nosZ-harboring denitrifier and phoD-harboring microorganisms. However, the diversities of functional microbial community structure did not have clear regularity under chemical fertilizer reduction substitute with organic fertilizer. ③ Compared with that under the application of chemical fertilizer and organic fertilizer alone, lemon yield and quality were the highest under the 30% reduction of chemical fertilizer substitute with organic fertilizer. ④ Nitrogen and its related microbes significantly affected lemon yield through internal and external quality. Phosphorus and its related microbes affected lemon yield mainly through internal quality. In addition, the influence factors of non-rhizosphere soil and rhizosphere soil on lemon intrinsic quality were obviously different. Altogether, these results showed that the 30% reduction of chemical fertilizer substitute with organic fertilizer significantly affected soil nitrogen and phosphorus functional microorganisms and further improved lemon yield and quality.

[Effects of Chemical Fertilizer Reduction Combined with Organic Fertilizer Application on Bacterial Community Structure in Rhizosphere/Non-Rhizosphere Soil of Lemon].

The aim of this study was to examine the effects of different fertilization methods on the physicochemical properties and bacterial community structure of lemon rhizosphere/non-rhizosphere soil in order to provide theoretical basis for scientific and rational fertilization of orchards. A pot experiment was carried out, and six fertilization treatments were set up:control (CK), conventional fertilization (FM), organic fertilizer (P), fresh organic fertilizer (NP), 70% chemical fertilizer+30% organic fertilizer (70FP), and 50% chemical fertilizer+50% organic fertilizer (50FP). Chemical analysis, real-time fluorescence quantitative PCR, and terminal restriction fragment length polymorphism (T-RFLP) were used to study the effects of different fertilization treatments on the physicochemical properties of rhizosphere and non-rhizosphere soils, the abundance of the bacterial 16S rRNA gene, and bacterial community structure. Redundancy analysis (RDA) was used to explore the environmental factors affecting the bacterial community structure of lemon rhizosphere/non-rhizosphere soil. The results showed the following:① the pH and contents of organic matter, alkali-hydrolyzed nitrogen, available phosphorus, available potassium, and nitrate nitrogen in rhizosphere/non-rhizosphere soil were significantly increased by reducing the amount of chemical fertilizer and applying organic fertilizer (50FP and 70FP) (P<0.05). Compared with conventional fertilization (FM) and single application of organic fertilizer (P and NP), the soil available P content, available K content, and nitrate nitrogen content increased by 24.76%-97.98%, 6.87%-45.11%, and 18.42%-55.82%, respectively. ② Fertilizer reduction combined with organic fertilizer significantly increased the abundance of soil bacteria and soil respiration intensity (P<0.05), and the abundance of soil rhizosphere bacteria and soil respiration intensity under the 50FP treatment increased by 15.83%-232.98% and 8.0%-162.5% compared with that under conventional fertilization and organic fertilizer alone, respectively. The bacterial abundance of rhizosphere soil was positively correlated with the pH and contents of organic matter, total nitrogen, and total phosphorus. ③ The PCoA and RDA analysis results showed that the single organic fertilizer and organic fertilizer and chemical fertilizer de-weighting of rhizosphere bacterial community structure and not adding fertilizer had a bigger difference between processing, and the main environmental factors influencing the rhizosphere/non rhizosphere bacterial community structure were organic matter, total nitrogen, total phosphorus, total potassium, alkali solution nitrogen, nitrate nitrogen, and available potassium. Fertilizer reduction combined with organic fertilizer could significantly increase soil nutrient content, increase soil bacterial abundance, and change the bacterial community structure of rhizosphere soil, and the 50FP treatment yielded better results. Therefore, 50% Chemical fertilizer+50% organic fertilizer (50FP) was a better fertilization method to improve the physical and chemical properties of orchard soil, increase the abundance of soil bacteria, and improve the soil respiration intensity.

[Spatiotemporal Dynamic Evolution and Gravity Center Migration of Carbon Emissions in the Main Urban Area of Chongqing over the Past 20 Years].

Global warming caused by carbon emissions is an environmental issue that is of great concern to all walks of life. Dynamic monitoring of the spatiotemporal evolution of urban carbon emissions is an important part of achieving the regional double-carbon goals. Taking the main urban area of Chongqing as an example, based on the data of land use and energy consumption, this study estimated the carbon emissions of 153 townships and streets in the main urban area of Chongqing from 2000 to 2020 by using the carbon emission coefficient method. Additionally, using the ESTDA framework to pass the LISA time path, spatiotemporal transition, and the standard deviation ellipse model from the perspective of spatiotemporal interaction, the spatiotemporal dynamic evolution of carbon emissions in the main urban area and the shift in the center of gravity over the past 20 years were analyzed. The results showed that: ① in the past 20 years, the carbon emissions in the main urban and rural areas have had a significant positive spatial correlation, and the spatial convergence showed a trend of first decreasing and then increasing. ② In the past 20 years, there were 126 township streets with low and medium relative lengths (accounting for 82%), indicating that the local spatial structure of township carbon emissions in the main urban area had strong stability; the total number of township streets with low and medium curvatures was 138 (accounting for 90%), indicating that the volatility of the main urban and rural carbon emissions in the direction of spatial dependence was relatively stable; there were 113 township streets (accounting for 74%) of the synergistic growth type, indicating that the main urban and rural carbon emissions were relatively stable. The emission pattern had strong spatial integration. ③ In the past 20 years, the spatiotemporal agglomeration index was greater than 70%, indicating that the local spatial correlation pattern and agglomeration characteristics of carbon emissions in the main urban and rural areas had strong stability. 4 In the past 20 years, the center of carbon emission in the main urban area had been distributed between 106°30'43″-106°32'42″E, 29°33'34″-29°35'56″N, and the center of gravity shifted to the northeast as a whole. The spatial distribution changed from the "northwest-southeast" pattern to the "northeast-southwest" pattern. These results can provide reference for the green and low-carbon sustainable development of Chongqing and the formulation of differentiated emission reduction policies, as well as provide reference for other similar mountain cities in western China.

[Effect of Combined Application of Biochar with Chemical Fertilizer and Organic Fertilizer on Soil Phosphatase Activity and Microbial Community].

To study changes in phosphatase activity, we examined the diversity of phoC and phoD gene microbial communities in the rhizosphere and non-rhizosphere soil of plants under the treatment of chemical fertilizer and organic fertilizer combined with biochar. These results can provide a certain theoretical guidance for the conversion of insoluble phosphorus in the soil phosphorus pool to the inorganic phosphate ion that can be absorbed by plant roots and also provide a certain experimental basis for the improvement of the availability of phosphorus in the soil and the agricultural utilization of biochar. In this study, corn stalks and rice husk stalks were used as test materials, and the pot experimental method was adopted using the following treatments:set control (CK), traditional fertilization (F), chemical fertilizer+20 t·hm-2 rice husk biochar (FP), chemical fertilizer+10 t·hm-2rice husk biochar+10 t·hm-2 corn biochar (FPM), organic fertilizer+20 t·hm-2 rice husk biochar (PP), and fresh organic fertilizer+20 t·hm-2 rice husk biochar (NPP). We determined the rhizosphere and non-rhizosphere soil acid phosphatase (ACP) activity and alkaline phosphatase (ALP) activity and used T-RFLP technology to analyze the diversity of phoC and phoD genes in order to clarify the impact of biochar on the micro-ecosystem formed by the plants, soil, and microorganisms. The results showed that:① the ALP and ACP activities of each treatment in the non-rhizosphere soil were lower than that of CK. In the rhizosphere soil, the ALP activity was significantly increased after the combined application of chemical fertilizer and organic fertilizer with biochar, and the ACP activity in the rhizosphere soil was higher than that in the non-rhizosphere soil. ② The combined application of biochar with chemical fertilizers and organic fertilizers significantly increased the diversity of phoC and phoD genes communities in rhizosphere and non-rhizosphere soils (P<0.05); the diversity and richness of microbial communities in rhizosphere soil were higher than that in non-rhizosphere soils. ③ ACP activity was negatively correlated with phoC gene microbial community, and most ALP activity was positively correlated with phoD microbial community.

[Responses of Soil PhoC and PhoD Gene Microbial Communities to the Combined Application of Biochar with Chemical Fertilizers and Organic Fertilizers].

Soil microorganisms have an important influence on the transformation of soil nutrients. As functional genes encoding phosphatase, phoC and phoD provide effective means for detecting the types, abundance, and community structure of microorganisms in the environment, and studying the changes in the diversity of phoC and phoD gene microbial communities in the rhizosphere and non-rhizosphere soil of the plant rhizosphere and non-rhizosphere soil under the treatment of chemical fertilizer and organic fertilizer combined with biochar can provide a scientific basis for the agricultural utilization of biochar. In this study, corn stalks and rice husk stalks were used as test materials, and the pot experiment method was used to set the following treatments:control (CK), traditional fertilization (F), chemical fertilizer+20 t·hm-2 rice husk biochar (FP), chemical fertilizer+10 t·hm-2 rice husk biochar+10 t·hm-2 corn biochar (FPM), organic fertilizer+20 t·hm-2 rice husk biochar (PP), and fresh organic fertilizer+20 t·hm-2 rice husk biochar (NPP). The community structure of phoC and phoD genes in rhizosphere and non-rhizosphere soil was analyzed by using T-RFLP and fluorescence quantitative PCR technology to clarify the response characteristics of phoC and phoD genes to the addition of biochar. The results showed that:① In rhizosphere soil and non-rhizosphere soil, the phoD gene community structure was more complicated than that of phoC, and the number of end restriction fragments of the phoC gene increased after chemical fertilizer and organic fertilizer were combined with biochar. ② The combined application of biochar with chemical fertilizer and organic fertilizer reduced the copy number of the phoC gene in non-rhizosphere soil compared with that in the CK. Compared with that in the CK, the copy number in the FP, FPM, PP, and NPP treatments decreased by 9.18%, 11.46%, 10.97%, and 13.76%, respectively. Organic fertilizer combined with biochar increased the copy number of the phoD gene in rhizosphere soil by 2.48% and 5.16% in the PP and NPP treatments, respectively, compared with that in the CK. ③ Total phosphorus in the soil was the main factor affecting the phoC gene microbial community structure in non-rhizosphere soil (P<0.01), whereas the phoC gene microbial community structure in rhizosphere soil was regulated by a variety of environmental factors. pH was the most critical factor affecting the phoD gene copy number, and the copy number of phoD gene was significantly correlated with soil nitrate nitrogen and pH. The combined application of biochar with chemical fertilizers and organic fertilizers can promote the growth and reproduction of microorganisms that function in soil phosphorus conversion, which is of great significance for improving the utilization of phosphorus fertilizers.

[Effects of Biochar and Straw Return on Soil Aggregate and Organic Carbon on Purple Soil Dry Slope Land].

The aim of the study was to understand the impact of biochar and straw return on soil aggregates and organic carbon for soil improvement of the newly cultivated purple soil dry slope land in the Three Gorges Reservoir area. In this study, a field test was used to set five treatment pairs with regards to soil aggregate composition and organic carbon distribution:no fertilization(CK), conventional fertilization(NPK), optimized fertilization(GNPK), chemical fertilizer reduction combined with straw(RSD), and chemical fertilizer reduction combined with biochar(BC). The results showed that fertilization can improve the level of soil fertility, especially with the RSD and BC treatments. The soil aggregates of each fertilization treatment were<0.25 mm in size. Compared with the CK, each treatment significantly increased the aggregate content of 0.5-5 mm particles, and the values of MWD, GMD, and R0.25. Further, the treatments significantly reduced the value of D and PAD0.25(P<0.05), and each fertilization treatment significantly increased the soil organic carbon content, of which BC(6.73 g·kg-1) and RSD(5.45 g·kg-1) were significantly better than NPK(5.05 g·kg-1) and GNPK(3.63 g·kg-1). The<0.25 mm aggregates had the highest contribution rate of organic carbon(34.92%-59.49%), while the>5 mm aggregates had the lowest contribution rate of organic carbon(1.55%-6.01%). The BC treatment significantly increased the organic carbon contribution rate of 5-2 mm and 2-1 mm agglomerates(P<0.05), while the contribution rate of NPK, RSD, and GNPK was the most significant for 0.5-0.25 mm(P<0.05). Each fertilization treatment increased the yield of rapeseed and corn, with large inter-annual differences, but the overall difference between treatments was not significant. The stability of soil aggregates and crop yields showed an upward trend with the increase of soil organic carbon. Biochar and straw returning to the field may promote the formation of large and medium aggregates in soil, effectively improve the stability of aggregates, increase organic carbon content, and promote crop yields. It is therefore an effective measure to improve the soil structure of purple soil and improve soil quality.

[Response of Soil Organic Carbon Content in Different Slope Positions to Fertilization Management in Purple Soil Sloping Fields].

The purple soil sloping field is the main cultivated land type in the Three Gorges area, and the soil fertility directly determines crop yield. In order to explore the effects of different fertilization treatments on the soil organic carbon content at different slope positions, field experiments were carried out at the Three Gorges Reservoir Test Station of Chengdu Institute of Mountain and Disasters, Chinese Academy of Sciences. A total of five treatments were set up:no fertilization(CK), conventional fertilization(T1), optimum fertilization(T2), biochar combined with 85% of T2(T3), and straw combined with 85% of T2(T4), to study the differences in soil aggregate composition, soil total organic carbon, soluble organic carbon, and microbial carbon content at different slope positions under different fertilization treatments. The results showed that:①Fertilization increased the content of soil mass and improved the organic carbon content of soil, especially with T3 and T4 treatments. ②The sequence of distribution of soil organic carbon content with CK, T1, and T2 treatments in different slope positions was downslope position>middle slope position>upslope position, while the soil organic carbon content of T3 and T4 treatments was the highest at the middle slope position. ③With the decrease of slope, the soluble organic carbon content of CK, T1, T2, and T3 treated soil showed an increasing trend; the carbon content of CK, T1, T2, and T4 treated soil microorganisms increased; while the distribution of T3 treated soil microbial carbon on the slope was highest at the middle slope followed by the lower slope. In general, both biochar and straw treatments can significantly increase soil carbon content and delay the migration of soil carbon on slopes, which provides guidance for improving the soil quality and reducing water pollution of purple soil dry slopes in the Three Gorges reservoir area.

[Characteristics of Dissolved Organic Carbon Loss in Purple Soil Sloping Fields with Different Fertilization Treatments].

The characteristics of dissolved organic carbon loss with different fertilization treatments were examined to derive the best nutrient management method for sloping farmland in the Three Gorges Reservoir area where maintaining the soil carbon balance and reducing environmental pollution caused by carbon loss is crucial. Experimental runoff plots were set up at the Experimental Station for Soil and Water Conservation and Environmental Research in the Three Gorges Reservoir Region, Chinese Academy of Sciences, involving the following five treatments:No fertilization (CK), conventional fertilization (conventional), optimum fertilization (optimum), biochar combined with 85% optimum fertilizer (biochar), and straw combined with 85% optimum fertilizer (straw). The effects of the five treatments on runoff flux, sediment yield, and soil organic carbon flux were monitored and evaluated. Results show that:①Subsurface flow accounted for 52.84%-92.23% of the runoff (both surface and subsurface flow) and the loss flux of dissolved organic carbon (DOC) in the subsurface accounted for 43.64%-87.35% of the total loss flux. Thus, in this sloping farmland, subsurface flow was the main pathway of runoff and dominated dissolved organic carbon transport. ②Compared with the optimum treatment, straw treatment reduced the surface runoff flux, sediment yield, surface loss flux of DOC, and loss flux of organic carbon in the sediment by 30.39%, 39.41%, 28.71%, and 23.97%, respectively, but increased the subsurface runoff flux and loss flux of DOC. Compared with the optimum treatment, the biochar treatment significantly increased the surface and subsurface runoff flux, sediment yield, loss flux of DOC in the surface and subsurface, and the loss flux of organic carbon in the sediment. ③The loss flux of DOC accounted for 99.31%-99.94% of the loss flux of soil organic carbon, and DOC was the major species of organic carbon in the organic carbon loss in this type of sloping farmland. The loss flux of DOC under the different fertilization treatments was ranked biochar > optimum > straw > conventional > CK. ④Compared to the optimum treatment, the straw treatment and biochar treatment increased the soil organic carbon (SOC) content by 95.79% and 32.16%, respectively. Based on these results, straw combined with 85% of optimum fertilizer is the best nutrient management method for this sloping farmland as it can reduce surface runoff flux, sediment yield, and the loss flux of soil organic carbon while increasing the soil organic carbon content.

[Characteristics of Soil Nitrogen and Phosphorus Losses Under Different Land-use Schemes in the Shipanqiu Watershed].

In order to understand the characteristics of soil nitrogen and phosphorus loss under different land use patterns in the small watershed of the Three Gorges Reservoir area and provide a scientific basis for the prevention and control of agricultural non-point source pollution, a field test method was used to study the paddy fields and drought in the small Shipanqiu Watershed in the Three Gorges Reservoir area. The characteristics of different runoff concentrations and the fluxes of nitrogen and phosphorus in surface runoff under the five land use schemes of paddy filed, slope land, woodlands, citrus orchards, and vegetable land. The results show that the annual total nitrogen loss followed the order of paddy field[17.73 kg·(hm2·a)-1] > citrus orchards[4.86 kg·(hm2·a)-1] > dry slope land[4.33 kg·(hm2·a)-1] > vegetable field[4.00 kg·(hm2·a)-1] > woodland[2.41 kg·(hm2·a)-1]. The annual total phosphorous loss followed the order of vegetable fields[4.97 kg·(hm2·a)-1] > Citrus orchards[1.87 kg·(hm2·a)-1] > paddy fields[0.93 kg·(hm2·a)-1] > woodlands[0.27 kg·(hm2·a)-1] > dry slope land[0.19 kg·(hm2·a)-1]. The nitrogen and phosphorus losses under the five land use methods were mainly concentrated from April to May with frequent rainfall events, accounting for 53.80%-96.52% and 56.03%-87.78% of the total annual nitrogen and phosphorus losses. Nitrogen loss was mainly in the form of nitrate nitrogen (16.16%-52.70%), and the total nitrogen loss flux and runoff showed a significant positive correlation (R2=0.9826). Particulate phosphorus was the main form of phosphorus loss in vegetable fields (83.30%), but in other land use schemes it is not significant. There were significant differences in the loss of different forms of nitrogen and phosphorus under the different land use schemes. Among them, measures should be taken in vegetable fields to deal with the problem of particulate phosphorus loss under conditions of heavy rainfall. Fertilization should be avoided in paddy fields during periods of concentrated rainfall. Scientific fertilization and reasonable land use configurations are important ways to control agricultural non-point source pollution in small watersheds.

[Effect of Biochar and Chemical Fertilizer Mixture on Ammonia Volatilization and Phosphorus Fixation].

In order to explore biochar fertilizer addition, two types of industrial wastes (YM) and lees (JZ) and agricultural waste corn stover (JG) were used as the raw materials to make biochar, and the biochar was modified to make smoke-modified biochar (M-YM). The culture test method was used to study the law of ammonia volatilization and phosphorus fixation over a certain period of time with the different fertilizer ratios of the four biochars. We aimed to provide a scientific basis for the agricultural utilization of biochar. The results show that:① The cumulative volatilization and volatilization rate of ammonia of the four kinds of biochar with different fertilizer ratios were as follows:A1 > A2 > A3 (A1:2.25 g urea; A2:2.25g urea +2.25 g chlorination potassium; A3:2.25 g urea +2.25 g potassium dihydrogen phosphate). The addition of potassium chloride and potassium dihydrogen phosphate in urea reduced ammonia volatilization, and the cumulative ammonia volatilization and volatilization rate of different biochars under all chemical fertilizer ratios was JZ > M-YM > YM > JG; ② The amount of phosphorus by biochars fixation under the B1, B2, and B3 treatments (B1:0.4 g potassium dihydrogen phosphate; B2:0.4 g potassium dihydrogen phosphate +0.3 g urea; B3:0.4 g potassium dihydrogen phosphate +0.3 g potassium chloride) all increased and then decreased. Then, the fixation amount of phosphorus not significantly changed in period from 30th to 60th day. Among four biochar, the fixation rate of phosphorus was the highest under the B1 treatment.With the ratios of B1, B2, and B3 fertilizers, the order of the fixation rate of the four biochars to phosphorus was:M-YM > YM > JG > JZ. Therefore, in order to reduce the volatilization of ammonia in nitrogen fertilizers in agricultural fertilization, potassium chloride and potassium dihydrogen phosphate can be added to urea. At the same time, in the fixation of phosphorus, increasing the particle size of biochar may weaken the phosphorous fixation ability.

[Effect of Optimized Fertilization and Biochar Application on Phosphorus Loss in Purple Soil Sloping Farmland].

Phosphorus is an essential nutrient for crop growth, but the input of excess phosphorus is a significant cause of eutrophication. This study explored the relationship between fertilization methods and phosphorus loss in actual production, providing a theoretical basis for scientific fertilization and rational reduction of fertilizer application. In the experiment, a wild-type OD flow plot was used to monitor the occurrence of multiple rainfall runoff and sediment yield in purple soil sloping farmland in 2017-2018. Four different schemes of non-fertilizer treatment, conventional fertilization treatment, optimized fertilization treatment, and reduced fertilization combined with biochar were studied. The effects of soil flow, surface runoff, and sediment phosphorus loss on purple soil sloping farmland were analyzed. The results showed that:①The total yield of each treatment was optimized (20737.23 L) > conventional (18513.17 L) > CK (18134.58 L) > biochar (13594.85 L), and the total sediment yield of each treatment was CK (1998 kg·hm-2) > biochar (1884 kg·hm-2) > optimized (1681 kg·hm-2) > conventional (910 kg·hm-2). The middle stream of soil is the main type of runoff in the rainy season, accounting for 60.14%-87.34% of the total output flow. The total amount of sediment produced by each treatment was not significantly different from that of the conventional treatment (P>0.05). ②The flux of total phosphorus loss in each treatment was characterized by sediment > surface runoff > soil middle flow. Phosphorus lost through the middle stream of soil is the least, accounting for only 2.63%-12.91% of the flux of total phosphorus loss, while the flux of sediment loss of phosphorus can reach 63.74%-78.74%, and thus is the main output route of soil phosphorus loss. ③The application of biochar can effectively reduce the abortion flow in the soil of purple soil sloping land, and the loss flux of orthophosphate in the middle stream, which are 49.94% and 56.45% lower than the conventional treatment, respectively. However, the interception effect on surface runoff is not good, and there is no significant influence on the flux loss of particulate phosphorus. At the same time, the flux of total phosphorus in surface runoff and sediment is significantly increased by 73.28% and 123.53%, respectively, compared with conventional treatment (P<0.05). Therefore, to control the loss of phosphorus in purple soil sloping farmland in southwest China, we should focus on reducing the occurrence of soil sediment loss. Bio-carbon should be further optimized in the practical application of agricultural production with the phosphorus fertilizer input ratio.

[Effects of Fertilizer Reduction and Application of Organic Fertilizer on Soil Nitrogen and Phosphorus Nutrients and Crop Yield in a Purple Soil Sloping Field].

The reduction in chemical fertilizers combined with organic fertilizers is a national strategy to achieve environmental friendliness and maintain the quality of cultivated land. It is of great significance for the prevention and control of soil pollution and the sustainable development of agriculture. In this study, purple soil and sloping land in the Three Gorges Reservoir area was studied. The field experiment method was used to study the control, conventional fertilization, optimized fertilization, biochar (fertilizer combined with biochar), and straw under rapeseed/corn rotation mode. The effects of five treatments on soil nitrogen/phosphorus form, crop nitrogen and phosphorus content, fertilizer utilization rate, and crop yield were studied in the field (fertilizer reduction combined with straw returning). The results showed that the soil ammonium nitrogen content was the highest in the rapeseed season, which was 4.51 mg·kg-1. The contents of ammonium nitrogen and alkali nitrogen in the treated corn season were significantly higher than those in the rape season. The reduction in chemical fertilizers can guarantee and increase the total nitrogen content of the soil. Among them, the total nitrogen content in the rapeseed and corn seasons treated with straw was the highest (0.56 g·kg-1 and 0.60 g·kg-1, respectively). The soil treated with straw in the rapeseed season had the highest available phosphorus content (0.76 mg·kg-1). Compared with conventional treatment, the reduction of chemical fertilizers combined with organic fertilizer did not significantly reduce the total phosphorus content of soil. The reduction of fertilization combined with organic fertilizer showed a slight increase in yield but showed the highest yield of rapeseed treated by biochar (2328 kg·hm-2) and the highest yield of conventionally treated maize (5838 kg·hm-2). However, there was no significant difference in each treatment (P>0.05). Regardless of the rapeseed season or the corn season, the reduction of fertilization treatment generally improved the agronomic utilization rate of nitrogen fertilizer and phosphate fertilizer. In the purple soil area, the combination of chemical fertilizer reduction and biochar and straw returning were beneficial to improve soil nutrients, improve fertilizer utilization, and reduce the effects of nitrogen fertilizer and phosphate fertilizer application on crop yield.