Double-cropping Rice Field Research Articles

Effects of tillage management on soil organic carbon mineralization under double cropping rice system of southern China

Soil organic carbon (SOC) plays a vital role in maintaining or enhancing soil fertility and quality of paddy field, but there is still limited information about how SOC mineralization responds to different tillage managements under the double-cropping rice (Oryza sativa L.) system in southern of China. Therefore, this study was designed to explore the changes in SOC content, soil enzyme activities (invertase, cellulose and urease), SOC mineralization at 0–10 cm and 10–20 cm layers and its relationship with 7-years tillage management under the double-cropping rice system of southern China. The experiment included four tillage managements: rotary tillage with all residues removed as a control (RTO), conventional tillage with residue incorporation (CT), rotary tillage with residue incorporation (RT), and no-tillage with residue retention (NT). The results indicated that SOC and soil labile organic carbon contents at 0–10 cm and 10–20 cm layers in paddy field with CT and RT treatments were significantly higher than the RTO treatment. Compared to the RTO treatment, SOC mineralization and accumulation at 0–10 cm and 10–20 cm layers in paddy field with CT, RT and NT treatments were increased. SOC accumulation and potential mineralization at 0–10 cm layer with NT treatment were significantly higher than the CT, RT and RTO treatments. Soil mineralization constant at 10–20 cm layer with CT treatment was significantly higher than those of RT, NT and RTO treatments. This result indicated SOC mineralization rate and accumulation at 10–20 cm layer of CT, RT, NT and RTO treatments were lower than those of treatments at 0–10 cm layer. Compared to RTO treatment, soil invertase, cellulose and urease activities with CT and RT treatments were significantly increased. Compared to RTO treatment, soil invertase, cellulose and urease activities at 0–20 cm layer of CT treatment increased by 22.6%, 46.2% and 89.0%, respectively. There was significantly positive correlation between SOC accumulation and SOC content, soil invertase, cellulose, urease activities, but SOC accumulation was significantly negative correlated with soil pH, bulk density. Therefore, CT and RT treatments were beneficial managements to improve SOC content and SOC mineralization in the double-cropping rice field of southern China.

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, β-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.

Effects of Long-Term Fertilizer Managements on Soil Organic Carbon Mineralization Under the Double-Cropping Rice System in Southern China

ABSTRACT Soil organic carbon (SOC) plays an important role in maintaining or increasing soil fertility and quality in paddy field, but there is limited information about how SOC mineralization responds to different fertilizer managements under the double-cropping rice system in southern China. Therefore, this study was designed to explore changes in SOC content, soil enzyme activities, SOC mineralization at 0–10 cm and 10–20 cm layers, and its relationship with long-term fertilizer managements in a double-cropping rice system of southern China. The experiment included four fertilizer treatments: chemical fertilizer alone (CF), rice straw and chemical fertilizer (RS+F), 30% organic manure and 70% chemical fertilizer (OM+F), and without fertilizer input as a control (Con). These results showed that SOC and labile organic carbon contents at 0–10 cm and 10–20 cm layers in paddy field with RS+F and OM+F treatments were increased, compared to CF and Con treatments. Compared with Con treatment, SOC mineralization rate and accumulation with CF, RS+F, and OM+F treatments were increased. SOC accumulation and potential mineralization at 0–10 cm and 10–20 cm layers with RS+F and OM+F treatments were increased, compared with CF and Con treatments. SOC mineralization rate and accumulation at 0–10 cm layer with CF, RS+F, OM+F, and Con treatments were higher than that of 10–20 cm layer. These results indicated that soil invertase, cellulose and urease activities in paddy field with RS+F and OM+F treatments were significantly higher than that of CF and Con treatments. There was a significant positive relationship between SOC accumulation and SOC content, soil invertase, cellulose, urease activities but were significant negative correlated with soil pH, bulk density. As a result, these were beneficial practices for improving SOC content and SOC mineralization in a double-cropping rice field of southern China by combined application of rice residue or organic matter with chemical fertilizer managements.

Effects of different long-term fertilization on rhizosphere soil nitrogen mineralization and microbial community composition under the double-cropping rice field

ABSTRACT Soil extracellular enzymes play an important role in regulating nitrogen (N) mineralization processes in paddy fields. Therefore, in this work, we determine the influence of a long-term fertilizer regime on rhizosphere soil N fertilization rates, soil enzymes, soil microbial community (bacterial ureolytic community (ureC), bacterial chitinolytic community (chiA)) under the double-cropping rice field in southern of China. The field experiment included the following fertilizer regimes: inorganic fertilizer alone (IF), rice straw and inorganic fertilizer (RF), 30% organic manure and 70% inorganic fertilizer (OM), without any fertilizer input as a control (CK). The results showed that rhizosphere soil N transformation rates in the paddy fields with OM and RF treatments were increased, compared with IF and CK treatments. Soil urease, β-glucosaminidase and arginase activities were significantly increased under OM and RF treatments. This result indicated that functional gene abundances of sub, npr and chiA were significantly greater under RF and OM treatments compared to IF and CK treatments. Soil bacterial ureolytic and chitinolytic communities were significantly changed by the different fertilization strategies. The practice of applying rice straw and organic manure seems beneficial for increasing rhizosphere soil N mineralization rates and microbial community diversity in the double-cropping rice fields.

Tillage with Crop Residue Returning Management Increases Soil Microbial Biomass Turnover in the Double-Cropping Rice Fields of Southern China

The variety of soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN) content, and the flux turnover rate of SMBC and SMBN for 0–10 cm and 10–20 cm layers in a paddy field in southern China with different tillage practices were studied. The tillage experiment included conventional tillage and crop residue returning (CT), rotary tillage and crop residue returning (RT), no–tillage and crop residue returning (NT), and rotary tillage with all crop residues removed from the paddy field as a control (RTO). The result showed that the SMBC and SMBN contents at 0–10 cm and 10–20 cm layers in the paddy field with CT, RT, and NT treatments were significantly increased. This result indicates that the flux turnover rate of SMBC and SMBN for 0–10 cm and 10–20 cm layers in the paddy field with CT treatment were increased by 65.49%, 39.61%, and 114.91%, 119.35%, compared with the RTO treatment, respectively. SMBC and SMBN contents and the flux turnover rate of SMBC and SMBN for the 0–10 cm layer were higher than that of the 10–20 cm layer in paddy fields under the same tillage condition. Therefore, applying rotary tillage or conventional tillage and crop residue returning produced beneficial management for increasing soil microbial biomass content and its turnover under a double–cropping rice system in southern China.

Long-Term Organic Manure Retarding Soil Acidity in the Double-Cropping Rice Field of Southern China

ABSTRACT This paper investigates the effects of different long-term (36 years) fertilizer treatments on soil pH, exchangeable acids, exchangeable base cation and cation exchange capacity (CEC) at 0–10 cm and 10–20 cm soil layers in a double-cropping rice field. The following fertilizer treatments were included: chemical fertilizer (MF), rice straw and chemical fertilizer (RF), 30% organic manure and 70% chemical fertilizer (OM), and without any fertilizer input as a control (CK). This result indicated that soil pH at 0–10 cm layer with RF and OM treatments was higher than that of MF and CK treatments. Soil exchangeable acidity content at 0–10 cm and 10–20 cm layers with RF and OM treatments were decreased by 48.4%, 51.6% and 49.2%, 54.2%, compared with CK treatment, respectively. Soil exchangeable calcium (Ca2+), magnesium (Mg2+) and potassium (K+) contents at 0–10 cm and 10–20 cm layers in paddy field with OM and RF treatments were higher than that of CK treatment. Moreover, compared with CK treatment, soil exchangeable base ion content at 0–10 cm and 10–20 cm layers in paddy field with OM treatment were increased by 54.1% and 42.6%, respectively. Soil CEC and effective cation exchange capacity (ECEC) at 0–10 cm and 10–20 cm layers with OM and RF treatments were significantly higher than that of MF and CK treatments. In conclusion, our results indicated that long-term application of crop residue or organic manure can improve soil exchangeable base ion and exchangeable capacity contents, alleviate soil acidity in a double-cropping paddy field.

An appropriate amount of straw replaced chemical fertilizers returning reduced net greenhouse gas emissions and improved net ecological economic benefits

With the increasing application of crop straw, the greenhouse gas emissions caused due to crop straw have received increasing attention. However, the current studies have not explored the greenhouse gas emissions from on-farmland consumption of returned straw. Based on a long-term positioning experiment, three treatments were set up in double-cropping rice fields: chemical fertilizer (CF), straw replacing 1/3 nitrogen fertilizer (MS), and straw replacing 2/3 nitrogen fertilizer (HS). We measured the biomass, soil properties, and greenhouse gas emissions of double-cropping rice and then comprehensively evaluated the global warming potential, carbon footprint, and net ecological and economic benefits. The straw treatments (MS and HS) increased the cumulative annual emissions of CH4 (98.44% and 261.23%), CO2 (30.85% and 122.29%), and N2O (7.37% and 52.50%), the cumulative annual global warming potential (74.15% and 206.12%), average GHG intensity (43.26% and 138.07%), and the annual cumulative net ecosystem carbon budget (52.96% and 100.97%) in the early and late rice growing seasons, respectively. We observed that the real-time greenhouse gas emissions were significantly correlated to the soil microbial functional genes and total carbon, NH4+-N, and NO3−-N. The results of the random forest model showed that total carbon (13.87%) and nirK abundance (9.80%) were the highest predictors of global warming potential at the booting and maturity stages, respectively during rice growing season. Combining the resource inputs for agricultural production and the greenhouse gas emission potential of the returned straw on its own, MS showed the lowest net greenhouse gas emission, and MS and HS showed significantly increased annual cumulative net ecological economic benefits (38.08% and 34.30%). Overall, MS showed the lowest net greenhouse gas emission and the highest net ecological economic benefits, which is a straw-returning measure with low environmental impact and high economic returns.

CH4 emissions from a double-cropping rice field in subtropical China over seven years

Rice paddies are important sources of the greenhouse gas methane (CH4). However, it is difficult to precisely quantify CH4 emissions using the static chamber method because of their discontinuous measurements as well as the spatial and temporal variability of CH4 emissions. To precisely quantify CH4 emissions from rice paddies and gain deep insight into the emission rhythm and environmental effects, a seven-yearlong CH4 flux measurement was carried out continuously using the eddy covariance method in a double cropping rice paddy in subtropical China. The annual CH4 emissions were 42 ± 2 g C m−2. The half hourly CH4 flux was highly correlated with gross primary production (GPP) and environmental factors, such as soil temperature (Ts), and latent heat flux (LE), which explain 47–91% of the CH4 diurnal variation. However, the peak of CH4 generally appeared at dusk during the vigorous growth period, which was quite different from the GPP peak around noon. CH4 flux seasonal dynamic were more complex, with double peaks during the growing season and lower values during the fallow season. Interestingly, in contrast to previous studies of linear or exponential relationships with short-term datasets, daily CH4 and GPP showed a logarithmic relationship at the vegetative stage in this study with seven-year data, this is crucial in improving the model accuracy in estimating annual CH4 emissions. The result implies that long-term observation is necessary to accurately assess CH4 emissions from rice paddy.

Impacts of Different Long-Term Fertilizer Management Regimes on Soil Nitrogen Mineralization and Its Enzyme Activities under a Double-Cropping Rice System in Southern China

Soil extracellular enzyme activities play an important role in regulating the soil nitrogen (N) mineralization process in paddy fields. However, there is still a need to further study how N mineralization responds to different fertilizer management techniques and the soil extracellular enzyme activities for N mineralization in paddy fields. Therefore, the influence of different long-term (35 years) fertilizer regimes on soil N mineralization, hydrolysable N fractions—such as hydrolyzed unknown nitrogen (HUN), amino acid nitrogen (AAN), amino sugar nitrogen (ASN), ammonia nitrogen (AN), and total acid-hydrolyzed nitrogen (TAN)—and their extracellular enzyme activities (soil urease, L-glutaminase, β-glucosidase, arylamidase, and β-glucosaminidase) in a double-cropping rice field in southern China were investigated in this study. The field experiment included the following fertilizer regimes: rice straw and inorganic fertilizer (RF), 30% organic manure and 70% inorganic fertilizer (OM), inorganic fertilizer alone (MF), and no application of inorganic fertilizer as a control (CK). The results show that the soil ammonium N, amino sugar N, hydrolysable unidentified N, and amino acid N contents in the paddy field with RF treatment increased by 30.56%, 5.51%, and 62.74% compared with the CK treatment. The results show that the soil aerobic and anaerobic N mineralization rates in the paddy fields with OM and RF treatments increased by 22.92% and 18.27% compared with those with MF treatment. Moreover, soil extracellular enzyme activities under RF and OM treatments significantly increased, which indicated that the main substrate of microbial activity was effective. Correlation analysis indicated that the soil L-glutaminase activity, amino sugar N, amino acid N, and total acid-hydrolysable N contents were positively correlated with soil aerobic and anaerobic N mineralization rates in paddy fields. However, there was a negative correlation between the soil N mineralization rate and soil β-glucosaminidase activity in paddy fields. This finding shows that the yields of early rice and late rice under the RF and OM treatments were significantly higher than those under the MF and CK treatments. Compared with the MF treatment, the yields of double-cropping rice with RF and OM treatments increased by 9.84% and 11.37%, respectively. As a result, the application of straw or organic manure and inorganic fertilizer was effective for improving soil N mineralization, the soil acid-hydrolyzed N content, and extracellular enzyme activities in double-cropping rice fields.

Effects of organic fertilizers produced using different techniques on rice grain yield and ammonia volatilization in double-cropping rice fields

Ammonia (NH3) volatilization from rice fields contributes to poor air quality and indicates low nitrogen use efficiency. Although organic fertilizers can meet the nitrogen requirement for rice growth, the simultaneous effects of organic fertilizers on NH3 volatilization and rice yield in paddy fields are poorly understood and quantified. To address this gap in our knowledge, experimental field plots were established in a conventional double-cropping paddy field in the Pearl River Delta region, southern China. Five fertilizer treatments were used besides the control with no fertilizer: fresh organic fertilizer, successively composted organic fertilizer, chemically composted organic fertilizer, mixture of chemically composted organic fertilizer with inorganic fertilizer, and chemical fertilizer. Ammonia volatilization was measured using a batch-type airflow enclosure method. No significant differences in grain yield were observed among organic and chemical fertilizer treatments. However, compared with chemical fertilizer, chemically composted organic fertilizer and successively composted organic fertilizer significantly decreased total NH3 volatilization by 70% and 68%, respectively. The ammonium-nitrogen concentration in field surface water correlated strongly (P < 0.01) and positively with NH3 volatilization across fertilization treatments. Our findings demonstrate that chemically composted organic fertilizer can sustain rice yield while reducing NH3 volatilization. An important future step is to promote these field measurements to similar rice cultivation areas to quantify the regional- and national-scale impact on air quality and nitrogen deposition in sensitive areas, and to design and implement better fertilizer management practices

Predicting the Nitrogen Quota Application Rate in a Double Rice Cropping System Based on Rice–Soil Nitrogen Balance and 15N Labelling Analysis

Excessive nitrogen (N) fertilization, low use efficiency, and heavy pollution are the dominant issues that exist in intensively cultivated double rice cropping systems in China. Two-year field and 15N microregion experiments were conducted to evaluate the N fate in a soil-rice system under a series of different N rate treatments from 2020 to 2021. The economic N application rate that simultaneously improved rice yield and N use efficiency in the rotation system was also investigated. Results demonstrated that soil residues and mineralized N accounted for more than 58.0% and 53.2% of the total N input in the early and late rice seasons, respectively. Similarly, most of the total N input was absorbed by rice, ranging from 43.7% to 55.6% in early rice and from 36.8% to 54.7% in late rice. Rice N use efficiency significantly decreased with increasing N application, while rice grain yield and its N uptake increased when the N application rate was below 150 kg ha−1 in early rice and 200 kg ha−1 in late rice. Exceeding this point limited rice N uptake and yield formation. The apparent N recovery rate, N residual rate, and N loss rate were 23.5–34.4%, 17.0–47.1%, and 26.0–47.8% for the early rice, and 32.8–37.3%, 74.2–87.0%, and 71.5–92.1% for the late rice. The linear plateau analysis further indicated that the recommended N application rate (118.5–152.8 kg ha−1 for early rice and 169.9–186.2 kg ha−1 for late rice) can not only maintain a relatively higher rice yield and N utilization but also significantly reduce soil N residue. Our results provide theoretical guidance for improving N management in double-cropping rice fields in southern China.

Effects of long-term fertilizer practices on rhizosphere soil nitrogen mineralization in the double-cropping rice field.

Nitrogen (N) was an important indictor in change of soil fertility, which was closely related with N mineralization process. However, there is still need to further study on how rhizosphere soil N mineralization in paddy field response to different fertilizer management. Therefore, the influence of long-term (37-years) fertilizer regime on rhizosphere soil N mineralization, ammonification and nitrification rates, and its relationship under the double-cropping paddy field in southern of China were investigated in this study. The field experiment included following fertilizer regimes: inorganic fertilizer alone (MF), rice straw and inorganic fertilizer (RF), 30% organic manure and 70% inorganic fertilizer (OM), and no application of any fertilizer as a control (CK). The result indicated that rhizosphere soil organic carbon (SOC), total N, NO3 -N, and NH4 -N contents in paddy field with OM and RF treatments were increased. The result showed that rhizosphere soil NO2 - -N and mineral N contents with OM and RF treatments were increased, and the order of soil NO2 - -N and mineral N contents with all fertilizer treatments was showed as OM > RF > MF > CK. This result proved that soil aerobic and anaerobic N mineralization rates in paddy field with OM and RF treatments were higher than that of CK and MF treatments. Compared with MF treatment, soil ammonification rate with RF and OM treatments increased by 45.16% and 67.74%, soil nitrification rate with RF and OM treatments increased by 45.71% and 77.14%, respectively. There had significantly positively correlation between soil net mineralization, nitrification rate and SOC, total N contents. As a result, applied with rice straw and organic manure was a good measure to improve soil N mineralization in the double-cropping rice field.

Impacts of long-term different fertilization managements on soil acid hydrolysable organic nitrogen fractions in double-cropping rice field

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 Fertilizer Management Systems on Soil Microbial Biomass Turnover in a Double-Cropping Rice Field in Southern China

Soil microbial biomass content is usually regarded as an early indicator of changes in soil quality and soil fertility in paddy fields. Soil microbial biomass turnover is mainly influenced by the application of different fertilizer management systems. However, there is still a need to further investigate the effects of different long-term fertilizer management systems on soil microbial biomass turnover in paddy fields under the double-cropping rice (Oryza sativa L.) system. Therefore, the effects of different long-term (36 years) fertilizer practices on soil microbial biomass carbon (SMBC) and soil microbial biomass nitrogen (SMBN) contents, and the flux turnover rates of SMBC and SMBN at the 0–10 cm and 10–20 cm layers in a double-cropping rice field in southern China were investigated in the present paper. The field experiment included four different fertilizer treatments: MF, RF, OM, and CK. The results showed that SMBC and SMBN contents at the 0–10 cm and 10–20 cm soil layers with RF and OM treatments were increased compared with the MF and CK treatments. Compared with the CK treatment, SMBC contents at the 0–10 cm and 10–20 cm soil layers with RF and OM treatments increased by 35.72% and 50.28%, and 32.29% and 42.77%, respectively. SMBN contents at the 0–10 cm and 10–20 cm soil layers with RF and OM treatments increased by 15.52% and 22.70%, and 16.32% and 21.49%, respectively. The fluxes of SMBC and SMBN at the 0–10 cm and 10–20 cm soil layers with RF and OM treatments were significantly higher than those of the CK treatment. This result indicated that the flux turnover rates of SMBC and SMBN at the 0–10 cm and 10–20 cm soil layers with the MF, RF, and OM treatments were significantly higher than those of the CK treatment. Compared with the CK treatment, the flux turnover rates of SMBC and SMBN at the 0–10 cm and 10–20 cm soil layers with OM treatment increased by 46.10% and 48.59%, and 73.39% and 116.67%, respectively. SMBC and SMBN contents, and the flux turnover rates of SMBC and SMBN at the 0–10 cm layer were higher than those of the 10–20 cm layer under the same fertilizer treatment condition. Early rice and later rice yields with RF and OM treatments were significantly higher than those of the MF and CK treatments. As a result, the combined application of crop residue and organic manure with inorganic fertilizer management is a beneficial practice for increasing soil nutrients and rice yield under the double-cropping rice system in southern Chin.

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.

Effects of long-term fertilization with different substitution ratios of organic fertilizer on paddy soil

In recent years, the abuse of chemical fertilizers has caused numerous environmental problems, such as soil acidification and compaction. Replacing chemical fertilizers with organic fertilizers can effectively alleviate these problems. However, the effects of alternative organic fertilizers remain unclear. To explore the effects of organic fertilizer substitution on rice yield and paddy soil physicochemical properties and bacterial community structure, we conducted a 5-year experiment using different proportions of organic fertilizer substitution in a double-cropping rice field in Jiangxi, China. Our results showed that replacing chemical fertilizers with organic fertilizers can reduce soil acidification, increase soil organic matter content, nutrient contents, and enzyme activities, improve soil physicochemical properties and microbial community, and enhance soil metabolism. Appropriate organic substitution also had positive effects on rice production. These findings enhance our understanding of the effects of different alternative organic fertilization methods and have important theoretical significance for the promotion of the use of organic fertilizers in the future.

Effects of Short-Term Tillage Managements on CH4 and N2O Emissions from a Double-Cropping Rice Field in Southern of China

Soil carbon (C) content plays an important role in maintaining or increasing soil quality and soil fertility. However, the impacts of different tillage and crop residue incorporation managements on greenhouse gas (GHG) emissions from paddy fields under the double-cropping rice (Oryza sativa L.) system in southern China still need further study. Therefore, a field experiment was conducted to determine the impacts of different short-term (5-years) tillage and crop residue incorporation managements on soil organic carbon (SOC) content, SOC stock, and GHG emissions from paddy fields under the double-cropping rice system in southern China. The field experiment included four tillage treatments: rotary tillage with all crop residues 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). These results indicated that SOC stock in paddy fields with CT, RT, and NT treatments increased by 4.64, 3.60, 3.50 Mg ha−1 and 4.68, 4.21, and 4.04 Mg ha−1 in 2019 and 2020, respectively, compared with RTO treatment. The results showed that early rice and late rice yield with CT treatment increased by 7.22% and 19.99% in 2019 and 6.19% and 6.40% in 2020, respectively, compared with RTO treatment. A two-year (2019–2020) investigation of GHG results indicated that methane emissions from paddy fields with NT treatment were decreased, but nitrous oxide emissions from paddy fields were increased. The lowest mean global warming potential (GWP) and per yield GWP carbon dioxide were found with NT treatment, compared to RT and CT treatments. Therefore, it was a beneficial practice for maintaining SOC stock and decreasing GHG mitigation under the double-cropping rice system in southern China by applying no-tillage with crop residue retention 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.

Effects of short-term soil tillage practice on activity and community structure of ammonia-oxidizing bacteria and archaea under the double-cropping rice field.

The potential nitrification activity (PNA), population size and community composition of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) in paddy soil from a short-term (5years) tillage field experiment conducted at tillering stage of late rice were investigated using the shaken slurry method and quantitative real-time polymerase chain reaction. 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 returning (NT) and rotary tillage with all crop residues removed as a control (RTO). The results showed that PNA in paddy soil of CT, RT and NT treatments was higher than that of RTO treatment, and the abundance of AOA and AOB was much higher in paddy soil of CT, RT and NT treatments than RTO treatment. Meanwhile, PNA and the abundance of AOB and AOA in paddy soil were greatly enhanced by combined application of tillage and crop residue, whereas PNA and the abundance of AOB and AOA in paddy soil were decreased by combined application of no-tillage and crop residue. Moreover, PNA was closely correlated with the abundance and community structure of AOB rather than AOA. The results also showed that PNA and the population sizes of AOB and AOA in crop incorporation treatments were higher than that of crop residue removed treatment. Cluster and redundancy analyses indicated that crop residue effect played a more important role in shaping AOA community structure compared to short-term tillage management. The results indicated that AOB rather than AOA functionally dominated ammonia oxidation in the double-cropping rice paddy soil, the activities of AOB and AOA were increased and the community structure was also changed under the combination of conventional tillage, rotary tillage and crop residue condition. The activity and community structure of AOB and AOA, which were affected by the combination of tillage and crop residue managements, play an important role in cycling of nitrogen.

Effects of Coconut Chaff Biochar Amendment on Methane and Nitrous Oxide Emissions from Paddy Fields in Hot Areas

Based on the rice-vegetable crop rotation model, in-situ measurements of nitrous oxide (N2O) and methane (CH4) emissions were conducted in double-cropping rice fields in Hainan to determine the impact of coconut chaff biochar on greenhouse gas emissions. The experiment involved four treatments:conventional farming fertilization (CON), nitrogen fertilizer combined with 20 t ·hm-2 biochar (B1), nitrogen fertilizer combined with 40 t ·hm-2 biochar (B2), and no nitrogen fertilizer, as the control (CK). The N2O and CH4 emissions were measured using static chamber-gas chromatography during the two paddy seasons, and the global warming potential (GWP) and greenhouse gas intensity (GHGI) were also estimated. The results show that N2O emission dynamics during the early rice season are closely related to the mineral nitrogen content of the soil. The N2O is emitted at the rice seedling and tillering stages after fertilization. The cumulative N2O emission during the early rice season was 0.18-0.76 kg ·hm-2. Compared with the CON treatment, the biochar treatments reduced N2O by 18%-43%, and the B2 treatment resulted in a significant reduction. The addition of biochar may promote the reduction of N2O at the early rice seedling stage and increase N2O emissions by improving the soil NO3--N content at the early rice tillering stage. During the late rice season, N2O is emitted during the heading and maturity stages, and the cumulative N2O emission was 0.17-0.34 kg ·hm-2. The B1 treatment reduced emissions by 37%, and B2 increased emission by only 3%, which is not a significant difference. The peak of CH4 emissions from rice fields appeared in the late phase of the early rice season and prophase of the late rice season. The cumulative emission of CH4 in the early rice season was 3.11-14.87 kg ·hm-2. Compared with CON, the CK treatment increased emission by 39%. The biochar treatment may increase soil aeration and limit the ability of CH4 production in the early rice season, as B1 and B2 treatments reduced CH4 emissions by 28% and 71%. The cumulative CH4 emission in late rice season was 53.1-146.3 kg ·hm-2, and the emission dynamics were significantly positively correlated with NH4+-N content. CK and B1 treatments increased CH4 emissions by 52% and 99%, respectively compared with CON, and the B2 treatment significantly increased CH4 emissions by 176%. Compared with CON, the B1 and B2 treatments increased the yield by 12.0% and 14.3% when applied in the early rice season and by 7.6% and 0.4% when applied in the late rice season, respectively. Due to the increased methane emissions in the late rice season, biochar amendment increased the GWP of the double-cropping rice field, in which the high amount of biochar reached a significant level; different amounts of biochar had no significant effect on the GHGI of the double-cropping rice field. Thus, the application of coconut chaff biochar for the reduction of greenhouse gas emission, from rice fields in hot areas, requires further research.