Effects of long-term organic matter application on soil carbon accumulation and nitrogen use efficiency in a double-cropping rice field.

Increasing soil carbon (C) sequestration in paddy field and improving rice nitrogen use efficiency (NUE) are vital for sustainable agriculture and environmental protection. It was a benefit practice for achieving these goals by taken rice straw and organic manure managements. However, there is still need to further investigate the effects of different long-term fertilizer managements on soil C sequestration and NUE under the double-cropping rice system in southern of China. Therefore, the effects of different long-term (36-years) fertilizer practices on soil C sequestration and NUE under the double-cropping rice system in southern of China were investigated in the present paper. The field experiment was included four different fertilizer treatments: chemical fertilizer alone (MF), rice straw residue and chemical fertilizer (RF), 30% organic manure and 70% chemical fertilizer (OM), and without fertilizer input as a control (CK). This result indicated that soil C content at plough layer in paddy field with RF and OM treatments were increased, compared with MF and CK treatments. Besides input C directly into paddy field, soil original organic C accumulation with RF and OM treatments were increased by 1.54% and 3.01%, compared with MF treatment. This result indicated that soil TOC content increase rate and annual topsoil organic C sequestration rate in paddy field with RF and OM treatments increased by 55.56%, 88.89% and 48.05%, 76.62%, compared with MF treatment, respectively. Compared with MF treatment, NUE with RF and OM treatments increased by 10.43% and 22.61%, respectively, mainly due to increasing soil organic C. Grain yield of double-cropping rice with RF and OM treatments increased by 1009.5 and 1166.5 kg ha-1, compared with MF treatment, respectively. This result indicated that there was significantly correlation between NUE/NUENPK and TOC content with RF and OM treatments, at early rice and late rice growth seasons. Therefore, it was benefit practice for increasing soil carbon sequestration and improving rice NUE in the double-cropping rice system with long-term application of rice straw and organic manure managements.

Effect of different short-term tillage management on nitrogen-fixing bacteria community in a double-cropping paddy field of southern China.

Soil nitrogen (N)-fixing bacteria community plays an important role in the N cycling process in soil, but there is still limited information about how the soil microbes that drive this process to respond to combined application of tillage and crop residue management under the double-cropping rice (Oryza sativa L.) paddy field in southern of China. Therefore, the effects of 6-years short-term tillage treatment on soil N-fixing bacteria community under the double-cropping rice paddy field in southern China were studied by using the polymerase chain reaction-denaturing gradient gel electrophoresis method. The field experiment included four tillage treatments: conventional tillage with crop residue incorporation (CT), rotary tillage with crop residue incorporation (RT), no-tillage with crop residue retention (NT), rotary tillage with crop residue removed as control (RTO). The results showed that the diversity index and richness index of cbbLR and nifH genes with CT, RT, and NT treatments were increased, compared with RTO treatment. Compared with RTO treatment, the abundance of cbbLR gene with CT, RT, and NT treatments were increased by 6.54, 4.73, and 2.78 times, respectively. Meanwhile, the abundance of nifH gene with CT, RT, and NT treatments were 5.32, 3.71, and 2.45 times higher than that of RTO treatment. The results also indicated that soil autotrophic Azotobacter and nitrogenase activity with CT and RT treatments were significantly higher (p < .05) than that of RTO treatment. There was an obvious difference in characteristic of soil N-fixing bacteria community between the application of crop residue and without crop residue input treatments. In summary, the results indicated that the abundance of N-fixing bacteria community in the double-cropping rice paddy field increased with conventional tillage and rotary tillage practice.

Microbial carbon source utilization in rice rhizosphere and non-rhizosphere soils in a 34-year fertilized paddy field.

Carbon (C) is playing an important role in regulating soil nutrient cycling, maintaining soil fertility and crop yield, but there is still need to further study on how C source utilization characteristic respond to soil physical and chemical properties change with different fertilizer treatments under a double-cropping rice (Oryza sativa L.) field in southern China. Therefore, the effects of 34-year long-term fertilizer regime on C source utilization characteristic in rice rhizosphere and non-rhizosphere soils under a double-cropping rice field in southern China were studied by using 18 O-H2 O method in the present paper. The field experiments were included four fertilizer treatments: mineral fertilizer alone (MF), rice straw and mineral fertilizer (RF), 30% organic manure and 70% mineral fertilizer (OM), and without fertilizer input as control (CK). The results showed that microbial biomass C content, basal respiration of soil microorganism and microbial growth rate in rice rhizosphere and non-rhizosphere soils with OM and RF treatments were significantly higher (p < .05) than that of CK treatment. The microbial C utilization efficiency (CUE) in rhizosphere soil with MF and CK treatments were significantly higher (p < .05) than that of OM treatment, but there was no significantly difference (p > .05) in microbial CUE in non-rhizosphere soil between MF, RF, OM, and CK treatments. In the different parts of soil, the microbial biomass C content and basal respiration of soil microorganism in rhizosphere soil were higher than that of non-rhizosphere soil, but the microbial growth rate and microbial CUE in non-rhizosphere soil were higher than that of rhizosphere soil. Compared with CK and MF treatments, the metabolic capacity of soil microorganism to exogenic C source with RF and OM treatments were significantly higher (p < .05) than that of MF and CK treatments. The largest type of exogenic C source used by soil microorganism was carboxylic acids, followed by amino acid and carbohydrate, and complex compounds was the smallest. In the different parts of soil, the metabolic capacity of soil microorganism to the types of exogenic C source in non-rhizosphere soil was higher than that of rhizosphere soil. The redundancy analysis results indicated that there had obvious difference in utilization characteristic of soil microorganism to exogenic C source among different fertilizer treatments. In conclusion, this results indicated that characteristic of soil C source utilization were significantly changed under different long-term fertilizer condition.

Utilization of carbon sources in the rice rhizosphere and nonrhizosphere soils with different long-term fertilization management.

Carbon (C) plays an important role in the interaction between plant and rhizosphere microbial communities, but there is still limited information about how C source utilization soil microbial structure responds to soil fertility changes under the double-cropping rice (Oryza sativa L.) system in Southern China paddy fields. Therefore, the effects of long-term (33 years) fertilizer regimes on the characteristics of C utilization in both rhizosphere and nonrhizosphere soils under double-cropping rice fields in Southern China were investigated by using the metagenome sequencing technology. The experiment began in 1986, and included five fertilizer treatments: without fertilizer input (CK), chemical fertilizer alone (MF), rice straw residue and chemical fertilizer (RF), 30% organic matter, and 70% chemical fertilizer (LOM), and 60% organic matter and 40% chemical fertilizer (HOM). The results showed that the relative abundance of Gemmatimonadetes and Planctomycetia in both the rhizosphere and nonrhizosphere soils was increased by application of rice straw residue and organic manure, whereas the relative abundance of Gammaproteobacteria and Nitrospira was promoted by application of inorganic fertilizers. The largest group of clusters of orthologous groups of proteins categories was "amino acid transport and metabolism" with 16.46% unigenes, followed by "general function prediction only" (12.23%). Regarding the gene ontology categories, biological process were the largest category (174 949, 46.40%), followed by cellular component (126 766, 33.62%), and molecular function (110 353, 29.26%). The principal coordinate analysis indicated that different parts of the root zone were the most important factors affecting the variation of C source utilization bacteria community, and the different fertilizer treatments were the second important factor affecting the variation of C source utilization bacteria community. As a result, the application of fertilization practices had significant effects on the abundance and community composition of C source utilization microbes in paddy soils. The results showed that the combined application of rice straw residue or organic manure with chemical fertilizer practices significantly increases the C source utilization of soil microorganisms in double-cropping rice fields.

Effects of Short-Term Tillage on Rhizosphere Soil Nitrogen Mineralization and Microbial Community Composition in Double-Cropping Rice Field.

Soil extracellular enzyme plays a vital role in changing soil nitrogen (N) mineralization of rice field. However, the effects of soil extracellular enzyme activities (EEA) and microbial community composition response to N mineralization of rice field under short-term tillage treatment needed to be further explored. In this study, we investigated the impact of short-term (8-year) tillage practices on rhizosphere soil N transformation rate, soil enzyme activities, soil microbial community structure, and the N mineralization function gene abundances in double-cropping rice field in southern China. The experiment consisted of four tillage treatments: rotary tillage with crop straw input (RT), conventional tillage with crop straw input (CT), no-tillage with crop straw retention (NT), and rotary tillage with all crop straw removed as a control (RTO). The results indicated that the rhizosphere soil N transformation rate in paddy field under the NT and RTO treatments was significantly decreased compared to RT and CT treatments. In comparison to the NT and RTO treatments, soil protease, urease, ß-glucosaminidase, and arginase activities were significantly improved by the CT treatment, as were abundances of soil sub, npr, and chiA with CT and RT treatments. Moreover, the overall diversity of soil bacterial communities in NT and RTO treatments was significantly lower than that in RT and CT treatments. Soil chitinolytic and bacterial ureolytic communities were also obviously changed under a combination of tillage and crop straw input practices.

Influence of load partial factors adjustment on reliability design of RC frame structures in China.

The partial factor method has been widely used in building design and the partial factors to ensure the safety of structures are specified in the adopted codes. The load partial factors in the design expressions have been increased in the lasted code in China, which leads to theoretically increment in reliability and a growth in the consumption of construction materials. However, the influence of load partial factors adjustment on design of building structures arises different points among scholars. Some believe that it has a great impact on the design, some think the influence is small. This makes designers have doubts in the safety of structures and investors are also confused about the cost. In order to illustrate the influence of load partial factor adjustment on safety level and material consumption of RC (Reinforced Concrete) frame structures, reliability analysis and material consumption analysis are performed using First Order Reliability Method (FORM). The approach is carried out according to the load partial factors in Chinese codes of (GB50153-2008) and (GB50068-2018), respectively. Then, the influence of load partial factors adjustment is demonstrated with a case design of RC frame structures with different load partial factors in codes. The results show that the partial factor has a noticeable influence on the reliability index. The adjustment of load partial factors in design leads to an increase of the reliability index, which is about 8-16%. The increase of material consumption used in RC structures is about 0.75-6.29%. And the case indicated that the adjustment of load partial factors mainly result in the increase of reinforcement consumption, while have little effect on the concrete consumption. This study provides an analytical and conclusive insight into the influence of load partial factor adjustment on safety level and material consumption, which is can be applied to a wide range of structures.

Effects of Long-Term Fertilizer Practices on Rhizosphere Soil Autotrophic CO2-Fixing Bacteria under Double Rice Ecosystem in Southern China.

Soil autotrophic bacterial communities play a significant role in the soil carbon (C) cycle in paddy fields, but little is known about how rhizosphere soil microorganisms respond to different long-term (35 years) fertilization practices under double rice cropping ecosystems in southern China. Here, we investigated the variation characteristics of rhizosphere soil RubisCO gene cbbL in the double rice ecosystems of in southern China where such fertilization practices are used. For this experiment we set up the following fertilizer regime: without any fertilizer input as a control (CK), inorganic fertilizer (MF), straw returning (RF), and organic and inorganic fertilizer (OM). We found that abundances of cbbL, 16S rRNA genes and RubisCO activity in rhizosphere soil with OM, RF and MF treatments were significantly higher than that of CK treatment. The abundances of cbbL and 16S rRNA genes in rhizosphere soil with OM treatment were 5.46 and 3.64 times higher than that of CK treatment, respectively. Rhizosphere soil RubisCO activity with OM and RF treatments increased by 50.56 and 45.22%, compared to CK treatment. Shannon and Chao1 indices for rhizosphere soil cbbL libraries with RF and OM treatments increased by 44.28, 28.56, 29.60, and 23.13% compared to CK treatment. Rhizosphere soil cbbL sequences with MF, RF and OM treatments mainly belonged to Variovorax paradoxus, uncultured proteobacterium, Ralstonia pickettii, Thermononospora curvata, and Azoarcus sp.KH33C. Meanwhile, cbbL-carrying bacterial composition was obviously influenced by soil bulk density, rhizosphere soil dissolved organic C, soil organic C, and microbial biomass C contents. Fertilizer practices were the principal factor influencing rhizosphere soil cbbL-carrying bacterial communities. These results showed that rhizosphere soil autotrophic bacterial communities were significantly changed under conditions of different long-term fertilization practices Therefore, increasing rhizosphere soil autotrophic bacteria community with crop residue and organic manure practices was found to be beneficial for management of double rice ecosystems in southern China.

Impact of long-term tillage management on utilization of microbial carbon sources in rhizosphere and non-rhizosphere soils under a double-cropping rice paddy field.

In order to reveal the mechanism of microbial carbon (C) sequestration in paddy soil under different tillage management and to provide an important theoretical basis for perfecting the mechanism of C sequestration in paddy soil. C can indicate changes of soil nutrient content and soil microbial community, but more research is needed to study how C sources utilization characteristics respond to different tillage management under a double-cropping rice (Oryza sativa L.) paddy field in southern China. Hence, the impact of long-term (2005-2018) tillage management on utilization of microbial carbon sources in rhizosphere and non-rhizosphere soils under a double-cropping rice paddy field was studied by using 18O-H2O method in this study. The tillage treatments were included: (1) moldboard plow with all crop residue removed as a control (CT), (2) moldboard plow with all crop residue incorporated (CTS), (3) no-tillage with all crop residue retained on the soil surface (NTS), and (4) rotary tillage with all crop residue incorporated (RTS). The results indicated that Richness, Shannon, and McIntosh indices were increased by application of crop residue management, compared with treatment without crop residue, and soil microbial growth rate, soil microbial biomass C content, and soil microbial basal respiration with CT treatment were significantly lower (p < 0.05) than that of NTS, RTS, and CTS treatments. And the soil C utilization efficiency in rhizosphere soil with NTS, RTS, and CTS treatments was significantly lower (p < 0.05) than that of CT treatment. Compared with CT and CTS treatments, the metabolic capacity of soil microorganisms to exogenous C sources with NTS and RTS treatments was increased, and the different types of exogenous C sources were showed as following: complex compounds < carbohydrate < amino acid < carboxylic acids. The redundancy analysis results showed that utilization characteristics of soil microorganisms to exogenous C sources were significantly changed under tillage and crop residue incorporated conditions. Hence, this result indicated that characteristics of soil C sources utilization were significantly increased combined applied with tillage and crop residue incorporated management.

Impacts of short-term tillage and crop residue incorporation managements on soil microbial community in a double-cropping rice field.

Soil microbial community were usually reconsidered as a sensitive indicator in soil quality and soil environment change of paddy field. However, the effects of different tillage and crop residue incorporation managements on soil bacterial community under the double-cropping rice cropping system were still need to further investigated. Therefore, the impacts of different tillage and crop residue incorporation managements on soil bacterial community under the double-cropping rice cropping system in southern of China were studied by using phospholipid fatty acids (PLFAs) profile method in the present paper. The experiment included four different tillage treatments: rotary tillage without crop residue input as a control (RTO), no-tillage with crop residue retention (NT), rotary tillage with crop residue incorporation (RT), and conventional tillage with crop residue incorporation (CT). Compared with RTO treatment, grain yield of rice with NT, RT and CT treatments increased by 1.21%, 3.13% and 6.40%, respectively. This results showed that soil aC15:0, C16:0, iC17:0, C19:0c9, 10 fatty acids with CT and RT treatments were higher than that of RTO treatment, while soil C16:1ω6c and C18:1ω9t fatty acids with NT treatment were higher than that of RTO treatment, respectively. Soil G+ and G- bacteria PLFAs contents with CT treatment were higher than that of NT, RT and RTO treatments, while the value of soil G+/G- bacteria PLFAs with NT treatment were higher than that of CT, RT and RTO treatments. This results indicated that Richness and McIntosh indices with CT treatment were significantly higher than that of RTO treatment. Principal component analysis (PCA) results showed that the first and second principal components (PC1 and PC2) were explained 93.2% of total variance with all tillage treatments. Except C12:0, C14:0 2OH and C18:2ω6, all unsaturated and cyclopropyl PLFAs contents were belong to PC1. PC1 and PC2 were explained 88.4% of total variance with all tillage treatments. There had significantly positive correlation between soil Richness, Shannon indices and soil PLFAs, G+ bacteria, G- bacteria, fungi contents. As a result, it were benefit practices for increasing soil bacterial community structure in the double-cropping rice field of southern China by combined application of rotary, conventional tillage with crop residue incorporation managements.

[Impacts of long-term different fertilization managements on soil acid hydrolysable organic nitrogen fractions in double-cropping rice field]. / é•¿æœŸä¸åŒæ–½è‚¥æ¨¡å¼å¯¹åŒå­£ç¨»ç”°åœŸå£¤é ¸è§£æœ‰æœºæ°®ç»„åˆ†çš„å½±å“.

To clarify the impacts of long-term different fertilization modes on the soil acid hydrolysable organic nitrogen and its components in the double-cropping rice field of southern China, a long-term (36-year) location field experiment was used as a platform to systematically analyze the variations of soil acid hydrolysable organic nitrogen and its components (amino acid nitrogen, amino sugar nitrogen, ammonium nitrogen, unidentified hydrolysable nitrogen) at 0-10 cm and 10-20 cm soil layers under four fertilization treatments, including chemical fertilizer alone (CF), rice straw and chemical fertilizer (RF), 30% organic manure and 70% chemical fertilizer (OM), and control (CK). The relationships of soil acid hydrolysable organic nitrogen content and soil total nitrogen, soil organic carbon content were also analyzed. The results showed that compared with CK, OM and RF treatments significantly increased the contents of total nitrogen, available nitrogen, and organic carbon at both soil layers. The contents of soil acid hydrolysable organic nitrogen at 0-10 cm and 10-20 cm layers of OM, RF and CF treatments were 10.7%-42.6% and 12.2% -51.5% higher than that of CK, respectively. Compared with CF and CK treatments, OM and RF treatments significantly increased the contents of amino acid nitrogen, ammonium nitrogen, unidentified hydrolysable nitrogen and amino sugar nitrogen contents atboth soil layers. The soil acid hydrolysable organic nitrogen and non-hydrolysable nitrogen contents at 0-10 cm and 10-20 cm paddy soils under different fertilization treatments decreased in an order of OM>RF>CF>CK. The contents of soil amino acid nitrogen, ammonium nitrogen, amino sugar nitrogen and non-hydrolysable nitrogen at 0-10 cm soil layer of each fertilization treatment were higher than those at 10-20 cm soil layer. In addition, the contents of soil acid hydrolyzed organic nitrogen were positively correated with the contents of soil total nitrogen and soil organic carbon. In conclusion, RF and OM treatments were beneficial to increase organic nitrogen content at 0-10 and 10-20 cm soil layers of double cropping paddy fields, with postive consequences on nitrogen supply capacity and soil fertility.

[Effects of different long-term fertilization patterns on net carbon sink effect and economic benefits in double cropping rice paddy ecosystem in southern China]. / 长期不同施肥模式对南方双季稻田生态系统净碳汇效应和经济收益的影响.

There is close relationship between fertilizer managements and net carbon (C) sink effect, economic benefits in rice paddy ecosystem. Based on a long-term (35-year) field experiment, we analyzed the effects of different fertilization patterns on soil C sequestration rate, C density of topsoil, annual C balance, and economic benefits in the double cropping rice paddy in southern China. There were four fertilization treatments, chemical fertilizer alone (MF), rice straw and chemical fertilizer (RF), 30% organic manure and 70% chemical fertilizer (OM), and without any fertilizer input as a control (CK). The results showed that soil C pool in the double cropping rice paddy field under different fertilization treatments changed from 216.02 to 866.74 kg·hm-2·a-1, and soil C pool under OM treatment were significantly higher than that of MF, RF and CK. The soil C sequestration rates in the double cropping rice paddy field under different fertilization treatments ranged from 51.5 to 650.7 kg·hm-2·a-1, and that of C density of topsoil was from 55.64 to 78.42 t·hm-2. The order of soil C sequestration rates and C density of topsoil was OM>RF>MF>CK. The change range of C adsorption in the double cropping rice paddy field ecosystem was from 4.42 to 9.32 t C·hm-2·a-1, with an order of OM>RF>MF>CK. Compared with the MF treatment, soil net C sink under OM and RF treatments increased by 27.6% and 13.6%, respectively. The change range of C cost material input ranged from 1.49 to 2.17 t C·hm-2·a-1, and that of annual economic benefits was from 1.30×103 to 7.83×103 yuan·hm-2·a-1 with an order of RF>OM>MF>CK. The net income of economic benefits of OM, RF and MF treatments were significantly higher than that of CK. Generally, soil C sequestration rate, C sink effect and annual economic benefits were increased by the long-term application of organic manure and rice straw returning together with chemical fertilizer, which could increase soil organic carbon storage in the double cropping rice paddy field of southern China.

Functional soil organic matter fraction in response to short-term tillage management under the double-cropping rice paddy field in southern of China.

Soil organic matter (SOM) and its fraction play an important role in maintaining and improving soil fertility of paddy field. However, there is still limited information about how SOM fraction response to carbon (C) sequestration with different short-term tillage practices under the double-cropping rice paddy field in southern of China. Therefore, the effects of 5-year short-term tillage treatments on different SOM fractions (physically protected, physico-chemically protected, physico-biochemically protected, chemically protected, biochemically protected, and unprotected) under the double-cropping rice paddy field in southern of China were studied in this paper. The field experiment included four different tillage treatments: rotary tillage with crop residue removed as a control (RTO), conventional tillage with crop residue incorporation (CT), rotary tillage with crop residue incorporation (RT), and no-tillage with crop residue retention (NT). The results showed that soil unprotected (cPOM), biochemically (NH-dSilt), physically-biochemically (NH-µSilt), and chemically protected (H-dSilt) fractions with different tillage treatments were the mainly C storage fraction in paddy field. The soil organic carbon (SOC) content in unprotected (cPOM and fPOM), physically protected (iPOM), and physico-chemically protected (H-µClay) fractions with CT treatment was increased by 1.45, 2.13, 1.91, and 1.42 times higher than that of RTO treatment, respectively. The results showed that largest proportion of fraction to SOC content was biochemically protected, followed by unprotected and physically-biochemically protected, and physically protected was the lowest. These results indicated that soil physically protected, physically-chemically protected, and physically-biochemically protected fractions with CT and RT treatments were higher than that of NT and RTO treatments. In summary, it was a benefit practice for increasing SOM fraction under the double-cropping rice paddy field in southern of China by combined application of conventional tillage and rotary tillage with crop residue incorporation management.

Effect of different long-term fertilizer managements on soil nitrogen fixing bacteria community in a double-cropping rice paddy field of southern China.

Soil microorganism plays an important role in nitrogen (N) fixation process of paddy field, but the related information about how soil microorganism that drive N fixation process response to change of soil phy-chemical characteristics under the double-cropping rice (Oryza sativa L.) paddy field in southern of China is need to further study. Therefore, the impacts of 34-years different long-term fertilization system on soil N-fixing bacteria community under the double-cropping rice paddy field in southern of China were investigated by taken chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) method in this paper. The field experiment were set up four different fertilizer treatments: chemical fertilizer alone (MF), rice straw and chemical fertilizer (RF), 30% organic manure and 70% chemical fertilizer (OM), and unfertilized as a control (CK). This results showed that compared with CK treatment, the diversity index of cbbLR and nifH genes with OM and RF treatments were significantly increased (p<0.05), respectively. Meanwhile, the abundance of cbbLR gene with OM, RF and MF treatments were increased by 23.94, 12.19 and 6.70×107 copies g-1 compared to CK treatment, respectively. Compared with CK treatment, the abundance of nifH gene with OM, RF and MF treatments were increased by 23.90, 8.82 and 5.40×109 copies g-1, respectively. This results indicated that compared with CK treatment, the soil autotrophic azotobacter and nitrogenase activities with OM and RF treatments were also significantly increased (p<0.05), respectively. There were an obvious difference in features of soil N-fixing bacteria community between application of inorganic fertilizer and organic manure treatments. Therefore, this results demonstrated that abundance of soil N-fixing bacteria community in the double-cropping rice paddy field were increased by long-term applied with organic manure and crop residue managements.

Effects of fertilizer practice on fungal and actinobacterial cellulolytic community with different humified particle-size fractions in double-cropping field.

Cellulose plays an important role in maintaining or improving soil carbon (C) cycling and soil fertility of paddy field. There had close relationship between functional cellulose genes (cbhI and GH48) with characterize of soil organic matter chemical components (fulvic acid and humic acid) and soil physical fractions. However, there is still limited information about how functional cellulose degradation response to long-term fertilizer management and their relative importance for C sequestration under the double-cropping rice paddy field in southern of China. Therefore, the objective of this study were investigated the effects of 34-years long-term fertilizer regime on community abundance of cbhI and GH48 genes in five soil particle-size fractions (> 2000 µm, 2000-200 µm, 200-50 µm, 50-2 µm and 2-0.1 µm) by using polarization magic angle spinning 13C nuclear magnetic resonance spectroscopy. The field experiment was included four different fertilizer treatments: chemical fertilizer alone (MF), rice straw and chemical fertilizer (RF), 30% organic manure and 70% chemical fertilizer (OM), and without fertilizer input as a control (CK). The results showed that distribution of soil humus and cellulolytic microbial community abundance was significant increased under long-term application of crop residue and organic manure condition. And the FA, HA and HM C contents in > 2000 µm and 2000-50 µm fractions with MF, RF and OM treatments were significant higher than that of CK treatment. Meanwhile, the alkyl C and Oalkyl C groups of FA and HA in > 2000 µm fraction with MF, RF, OM and CK treatments were higher than that of the other fractions. There had higher AL% and lower ARO% of FA and HA in different particle-size fractions with MF, RF, OM and CK treatments. The results indicated that abundance of cbhI and GH48 genes in different particle-size fractions with RF and OM treatments were significant increased, compared with CK treatment. There had significant positive correlation between soil humus C components (FA and HA) with abundance of cbhI and GH48 genes, and the o-alkyl C and AL% of FA were positively correlated with abundance of cbhI and GH48 genes. As a result, the community abundance of cbhI and GH48 genes were significant increased under combined application of crop residue and organic manure with chemical fertilizer condition.

Effects of long-term fertilizer management on soil labile organic carbon fractions and hydrolytic enzyme activity under a double-cropping rice system of southern China.

Fertilization is an effective way to improve soil quality, increase soil fertility and soil microbial diversity in paddy soil. To explore the changes of soil labile organic carbon (C) fractions and hydrolytic enzyme activity after 34 years fertilization treatments in a field experiment in double-cropping rice system of southern China. There were four treatments, including chemical fertilizer alone (MF), rice residue and chemical fertilizer (RF), 30% organic matter and 70% chemical fertilizer (OM), and the control without fertilizer input (CK). We measured soil organic carbon (SOC) content, soil labile organic C fractions, SOC related hydrolytic enzyme activity, correlation coefficients of soil enzyme activity with SOC content and its labile organic C fractions. The results showed that MF, RF and OM increased SOC content by 4.5%, 22.4% and 53.5%, respectively. Compared with MF and CK, RF and OM increased soil labile organic C fractions [cumulative C mineralization (Cmin), permanganate oxidizable C (KMnO4-C), particulate organic C (POC), dissolved organic C (DOC), light fraction organic C (LFOC), microbial biomass C (MBC)] and the proportion of each labile organic C fractions to total organic C. The contents of Cmin, KMnO4-C, POC, DOC, LFOC and MBC under OM treatment were 3.5, 3.1, 3.7, 1.9, 1.2 and 1.9 times higher than CK treatment, respectively. The proportion of labile organic C fractions to total organic C of RF and OM treatments was significantly higher than that in CK. The order of soil hydrolytic enzyme activity [α-glucosidase (αG), ß-glucosidase (ßG), ß-xylosidase (ßX), cellobiohydrolase (GBH), and N-acetyl-ß-glucosaminidase (NAG)] was OM>RF>MF>CK. The soil hydrolytic enzyme activity under OM treatment increased by 111.8%, 14.1%, 127.3%, 285.6% and 91.4% compared with CK, respectively. Furthermore, RF and OM treatments were beneficial to soil peroxidase (POD) activity. MF treatment was beneficial to soil polyphenol oxidase (PPO) activity. There was a significant positive correlation between soil hydrolytic enzyme activity and SOC content and its labile organic C fractions. In conclusion, the combined application of organic manure, rice straw returning and chemical fertilizer is an effective method to improve soil labile organic C fractions and hydrolytic enzyme activity in a double-cropping rice paddy field of southern China.

Microbial carbon source utilization in rice rhizosphere soil with different tillage practice in a double cropping rice field.

Carbon (C) plays an important role in maintaining soil fertility and increasing soil microbial community, but there is still limited information about how source utilization characteristics respond to soil fertility changes under double-cropping rice (Oryza sativa L.) system in southern China paddy field. Therefore, the effects of different short-term (5-years) tillage management on characteristics of C utilization in rice rhizosphere and non-rhizosphere soils under double-cropping rice field in southern China were investigated by using 18O incorporation into DNA. Therefore, a field experiment were included four tillage treatments: conventional tillage with crop residue incorporation (CT), rotary tillage with crop residue incorporation (RT), no-tillage with crop residue retention (NT), rotary tillage with crop residue removed as control (RTO). The results showed that soil microbial biomass C content with CT, RT, NT treatments were increased by 29.71-47.27% and 3.77-21.30% in rhizosphere and non-rhizosphere soils, compared with RTO treatment, respectively. Compared with RTO treatment, soil microbial basal respiration and microbial growth rate with CT treatment were increased 30.56%, 30.94% and 11.91%, 12.34% in rhizosphere and non-rhizosphere soils, respectively. The soil microbial C utilization efficiency were promoted with NT treatment. Compared with RTO treatment, the metabolic capacity of soil microorganism to exogenous C source with CT, RT and NT treatments were increased. The largest type of exogenous C source was saccharides, followed by amino acid and polymers, and complex compounds was the smallest. The redundancy analysis results indicated that tillage treatments significantly changed the utilization characteristics of soil microorganism to exogenous C source. Compared with RTO treatment, the grain yield of early rice and late rice with CT treatment were increased by 409.5 kg ha-1 and 387.0 kg ha-1, respectively. Therefore, the CT and RT treatments could significantly increase soil microbial biomass C content, but the NT treatment promote microbial C utilization efficiency in the double-cropping paddy field of southern China.

Effects of short-term manure nitrogen input on soil microbial community structure and diversity in a double-cropping paddy field of southern China.

The soil physicochemical properties and soil microbial communities were affected by different fertilizer management. Fertilizer regime were closely relative to the soil texture and nutrient status in a double-cropping paddy field of southern China. However, there was limited information about the influence of different manure nitrogen (N) input on soil microbial communities in a double-cropping rice (Oryza sativa L.) field. Therefore, the short-term different manure N input rate management on soil bacterial and fungal diversity in a double-cropping paddy field of southern China were studied by using Illumina sequencing and quantitative real-time polymerase chain reaction technology in the present paper. The filed experiment were including 100% N of chemical fertilizer (M0), 30% N of organic manure and 70% N of chemical fertilizer (M30), 50% N of organic manure and 50% N of chemical fertilizer (M50), 100% N of organic manure (M100), and without N fertilizer input as control (CK). The results showed that diversity indices of soil microbial communities with application of organic manure and chemical N fertilizer treatments were higher than that of CK treatment. Application of organic manure and chemical N fertilizer management increase soil bacterial abundance of the phylum Actinobacteria, Proteobacteria and Gammaproteobacteria, and soil fungi abundance of the phylum Basidiomycota and Zygomycota were also increased. Compared with CK treatment, the value of Richness, Shannon and McIntosh indices, and taxonomic diversity were increased with M30, M50 and M100 treatments. This finding demonstrated that M30, M50 and M100 treatments modify soil bacterial and fungal diversity. Therefore, the combined application of organic manure and chemical fertilizer N management could significantly increase the abundance of profitable functional bacteria and fungi species in a double-cropping rice field of southern China.

Functional diversity of rhizosphere soil microbial communities in response to different tillage and crop residue retention in a double-cropping rice field.

Microbial community functional diversity is a sensitive indicator of soil quality, soil management such as tillage and crop residue which can affect the microbial community functional diversity of paddy field. However, there is still limited information about the influence of different tillage and crop residue management on rhizosphere soil microbial community functional diversity in a double-cropping rice (Oryza sativa L.) field. Therefore, four tillage treatments were set up in paddy field, tillage treatments were included: conventional tillage with residue incorporation (CT), rotary tillage with residue incorporation (RT), no-tillage with residue retention (NT), and rotary tillage with residue removed as control (RTO). And the effects of CT, RT, NT, and RTO treatments on the average well color development (AWCD), genetic diversity indices and carbon source utilization of rhizosphere soil were studied in the present paper. The results showed that the values of AWCD with CT, RT and NT treatments were higher than that of RTO treatment. It was implied that application of crop residue management resulted in the variation of the carbon utilization efficiency of rhizosphere soil microbial communities. At maturity stages of early and late rice, the Richness indices, Shannon indices and McIntosh indices with CT treatment were significantly higher than that of RTO treatment, and with the order as CT>RT>NT>RTO. Principal component analysis (PCA) results indicated that there were significant differences in carbon substrate utilization patterns among different tillage treatments. Carbohydrates and amino acids were the main carbon resources utilized by rhizosphere soil microbes. Therefore, the combined application of tillage with crop residue management could significantly increase the rhizosphere soil microbial community functional diversity in the double-cropping paddy field of southern China.

Effects of Short-Term Soil Tillage Management on Activity and Community Structure of Denitrifiers under Double- Cropping Rice Field.

Soil physical and chemical characteristics, soil potential denitrification rates (PDR), community composition and nirK-, nirS- and nosZ-encoding denitrifiers were studied by using MiSeq sequencing, quantitative polymerase chain reaction (qPCR), and terminal restriction fragment polymorphism (T-RFLP) technologies base on short-term (5-year) tillage field experiment. The experiment included four tillage treatments: conventional tillage with crop residue incorporation (CT), rotary tillage with crop residue incorporation (RT), no-tillage with crop residue retention (NT), and rotary tillage with crop residue removed as control (RTO). The results indicated that soil organic carbon, total nitrogen and NH4+-N contents were increased with CT, RT and NT treatments. Compared with RTO treatment, the copies number of nirK, nirS and nosZ in paddy soil with CT, RT and NT treatments were significantly increased. The principal coordinate analysis indicated that tillage management and crop residue returning management were the most and the second important factors for the change of denitrifying bacteria community, respectively. Meanwhile, this study indicated that activity and community composition of denitrifiers with CT, RT and NT treatments were increased, compared with RTO treatment. This result showed that nirK, nirS and nosZ-type denitrifiers communities in crop residue applied soil had higher species diversity compared with crop residue removed soil, and denitrifying bacteria community composition were dominated by Gammaproteobacteria, Deltaproteobacteria, and Betaproteobacteria. Therefore, it is a beneficial practice to increase soil PDR level, abundance and community composition of nitrogen-functional soil microorganism by combined application of tillage with crop residue management.

Impact of long-term fertilization practices on the soil aggregation and humic substances under double-cropped rice fields.

Soil organic matter (SOM) content and soil aggregation are essential components of soil structure, which plays an important role in soil quality and fertility. Also, the SOM content, aggregation, and humus substances in paddy field were affected by application of fertilization practices. However, there is still limited information about the effects of long-term different fertilization practices on soil aggregation and carbon content in the humic acid (C-HAF), fulvic acid (C-FAF), and humin (C-HUM) fractions under double-cropping rice (Oryza sativa L.) system in Southern China paddy fields. Therefore, the effects of long-term fertilizer application on soil aggregation and C-HUM, C-HAF, and C-FAF contents in 0-5-, 5-10-, and 10-20-cm soil depth under double-cropped rice fields in Southern China were investigated. The experiment located at NingXiang County in Hunan Province, China begins in 1986 and the experiment includes five treatments: without fertilizer input (CK), mineral fertilizer alone (MF), rice straw residues and mineral fertilizer (RF), 30% organic matter and 70% mineral fertilizer (LOM), and 60% organic matter and 40% mineral fertilizer (HOM). The results showed that the soil total organic carbon content in paddy soils with RF, LOM, and HOM treatments was significant higher (P < 0.05) than that of the CK treatment at early and late rice maturity stages. The different sizes of soil aggregates with different fertilization treatments were decreased as HOM > LOM > RF > MF > CK. The HOM treatment had the highest percentage of soil aggregates in each size class and the CK treatment had the lowest percentage of soil aggregates in each size class in 0-5-, 5-10-, and 10-20-cm soil depth at early and late rice maturity stages. The soil C-HAF, C-FAF, and C-HUM contents were increased by long-term combined application of manure with mineral fertilizer practices. Meanwhile, the results indicated that the soil C-HAF, C-FAF, and C-HUM contents with RF, LOM, and HOM treatments were significantly higher (P < 0.05) than that of the CK treatment at early and late rice maturity stages. As a result, the soil total organic carbon content, each size class of soil aggregates, and soil C-HAF, C-FAF, and C-HUM contents were increased by long-term combined application of manure with mineral fertilizer in double-cropped rice fields.