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.

The partial substitution of chemical fertilizer with organic fertilizer has been regarded as an effective strategy for enhancing crop yield and soil quality. Nevertheless, its effects on soil properties and microbes remain contentious. In this study, we examined the effects of four different fertilization strategies (including without fertilizer (CK), 100% chemical fertilizer (NPK), 30% organic fertilizer + 70% chemical fertilizer (LOM) and 60% organic fertilizer + 40% chemical fertilizer (HOM)) on soil nutrients and microbial communities through metagenomic sequencing in a Camellia oleifera field experiment. Compared to CK and NPK, HOM significantly increased SOC, TN, TP, AK and AN contents. The substitution of organic fertilizer notably increased Camellia oleifera yield, with the highest increase of 93.35% observed in HOM relative to NPK. Soil bacterial and fungal communities responded inconsistently to fertilization patterns. Bacteria predominated as the main soil microorganisms, and higher rates of organic fertilizer substitution facilitated a shift from bacterial to fungal communities. Organic fertilizer substitution significantly increased soil bacteria diversity and fungal richness, particularly in the HOM. Soil bacterial community structure was more sensitive to fertilization regimes than soil fungi. High rates of organic fertilizer substitution substantially suppressed oligotrophic and increased copiotrophic bacterial communities. Mucoromycota emerged as the dominant fungal group, with a considerable increment in HOM soils. SOC and TN were the main factors affecting Camellia oleifera yield and shaping soil bacteria and fungal diversity and composition. This study provided crucial insights into the ecological implications of organic fertilizer application and the potential of managing soil microorganisms for sustainable Camellia oleifera productivity.

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.

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.

Unreasonable soil tillage measures have caused a sharp decline in the soil carbon (C) pool capacity of rice (Oryza sativa L.) paddy fields, have reduced soil fertility, and have threatened the safe production of rice. Based on long-term position–location experiments started in 2005, this paper systematically studied the effects of different soil tillage treatments (CT: no return of plowing straw to the field as control; CTS: return of plowing straw to the field; NTS: return of no-tillage straw to the field; RTS: return of rotary plowing straw to the field) on soil physical and chemical properties and soil organic carbon (SOC) accumulation characteristics in rice paddy fields, in order to clarify the impact of different long-term soil tillage measures on soil carbon cycle microecology in double-cropped rice paddy fields and provide a theoretical basis for soil SOC sequestration and the sustainable utilization of rice paddy fields in double-cropped rice paddy fields in southern China. The results were as follows: A total of 30.7–40.7% of the SOC stored in rice paddy fields was residue C derived from microorganisms, and 45.7–54.2% of SOC accumulation came from plant residue-derived C. Straw return treatments (CTS, RTS, and NTS) significantly increased soil lignin phenol content and promoted the accumulation of plant-derived SOC. Soil lignin phenol content in the RTS treatment was significantly higher than that in the CTS treatment (p < 0.05). Amino sugar content in rhizosphere soil was higher than that in non-rhizosphere soil. The measure of returning straw to the field increased amino sugar content in the rhizosphere and non-rhizosphere. C derived from plants was greater than that from microbial residues in double-cropped rice paddy fields in southern China. Hence, no-till/rotary tillage and straw return can improve the sequestration of soil SOC, which is of great significance for achieving “C neutrality” and alleviating the pressure on food security.

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.