Microbial Regulation of Nitrogen Retention Under Contrasting Straw‐Derived Carbon Amendments in Red Paddy Soils

Red paddy soils in southern China originate from various parent materials; however, the respective characteristics of C sequestration efficiency (CSE) are unclear. Here, three cultivated land monitoring sites in Jiangxi province were examined, with soils originating from argillaceous rock, quaternary red clay, and granite. We assessed crop yield and soil physicochemical properties over several years and measured soil organic C (SOC) storage, SOC fractions, and chemical structure in 2019 to test differences in CSE characteristics, SOC structure stability, and factors affecting red paddy soils. The change in SOC storage under long‐term fertilization showed the following descending order: red paddy soils derived from argillaceous rock (1.10 t ha −1 yr −1 ) > granite (0.75 t ha −1 yr −1 ) > quaternary red clay (0.12 t ha −1 yr −1 ); the order of CSE was granite (0.24) > argillaceous rock (0.22) > quaternary red clay (0.08). Red paddy soil from argillaceous rock had the highest proportion of recalcitrant organic C (ROC) and SOC stability (aromaticity 0.45). Red paddy soil originating from granite had the lowest ROC proportion (54%) and SOC stability (aromaticity 0.35). Soil properties, organic C input, and amount of N fertilizer explained 53.6% of the total CSE variation. SOC, pH, and organic C input were the main factors affecting CSE, with relative contribution rates of 36.4, 6.2, and 6.3%, respectively. pH (30.4%) was the main factor affecting CSE variation in argillaceous rock paddy soil. Soil organic C (52.2%) was the main factor explain CSE variation in quaternary red clay‐derived red paddy soil. Soil organic C and organic C input explained 39.4 and 21.3% of the variation in CSE in granite‐derived paddy soils. The parent material can directly or indirectly affect CSE through soil texture.

Ammonia-oxidizing archaea are more sensitive than ammonia-oxidizing bacteria to long-term application of green manure in red paddy soil

Paddy soils show significant potential of carbon sequestration. The soil organic carbon( SOC) content of red paddy soils have been reported to be steady after 30 years' cultivation and it varies with different fertilization practice. In this study,three red paddy soils,which cultivated under different organic fertilization treatments in a 30 years fertilizer experiment in Changsha, China, was adjusted to the following seven treatments without compromising the original experiment: the original high organic fertilization treatment( HOM),the high organic fertilization treatment changed from the original normal organic fertilization treatment( N-H),the original normal organic fertilization treatment( NOM),the normal organic fertilization treatment changed from chemical fertilization( C-N),the chemical fertilization treatment changed from high organic fertilization treatment( H-C),the chemical fertilization treatment changed from normal organic fertilization treatment( N-C),the original chemical fertilization treatment( CF). CO2 flux of the three original and fourchanged treatments was measured to study the effects of the following-up fertilization reforming on the CO2 flux in red paddy soils with different fertilities in 2012—2013. The results clearly showed that the following-up changing of fertilization had obvious impacts on the dynamics of CO2 flux. The CO2 flux in the soils under long-term organic fertilization treatments decreased after the adjustment from organic fertilization to chemical fertilization. However,the CO2 flux in the soils under long-term chemical fertilization treatments increased remarkably after the adjustment from chemical fertilization to organic fertilization. The results also indicated that both organic fertilizer and soil organic carbon( SOC) had important impacts on CO2 flux. The amount of organic carbon inputted by organic fertilizers had a significantly positive relationship with the total amount of annual CO2-C flux( r = 0.9015**,n = 21),and the inherent SOC content( x) also had a positive relationship with the total amount of annual CO2-C( y)( y = 10. 962x- 68. 86,R2= 0. 7507,n = 9,P 0. 01) in the paddy soils received chemical in 2012. The fertilization reforming from organic fertilization to chemical fertilization would lead to the loss of SOC in paddy soils due to its mineralization,and the SOC loss increased with the rising of inherent SOC content. The SOC content in the paddy soils under long-term organic fertilization would be consistent with that in the paddy soils under long-term chemical fertilization after the fertilization reforming from organic to chemical fertilization for a certain time. The fertilization reforming from chemical to organic fertilization,or from low organic to high organic fertilization would lead to the SOC accumulation in paddy soils,and the accumulating rate of SOC had a positive relationship with the amount of the inputted organic material. Under same organic fertilization treatment,the apparent decomposition rate of organic material applied in the soils with high SOC content was larger than that in the soils with low SOC content,which would result in lower SOC accumulation. So,the paddy soils with different SOC content would have the same SOC level when they received same organic fertilization management for a certain time. As a conclusion,the sustained organic fertilization in red paddy soils with high or low SOC content is essential to maintain or improve the soil organic carbon content in Southern China.

Iron reduction plays an important role in the reductive transformation of organochlorine pesticides in red paddy soils. This interaction between iron reduction and organochlorine pesticides (OCPs) in red soils in south China is particularly important because of the high abundance and reactivity of iron within unique man-made paddy ecosystems. However, the relationships between iron reduction and reductive dechlorination and the geochemical constraints of these relationships are not fully understood. In this comprehensive review, we summarized current understanding of iron reduction, reductive dechlorination, the relationships between them, and their interactions with the reduction of nitrate, sulfate, Cu(II), and humic substances in red soils. Recent studies showed that iron reduction and dechlorination occur simultaneously in soils and that iron reduction could either stimulate or inhibit dechlorination. Meanwhile, sulfate and Cu(II) reduction can stimulate or inhibit iron reduction and dechlorination. Nitrate reduction can be coupled to iron reduction, but it inhibits dechlorination. Increasing evidence showed that humic substances can enhance the rates of both iron reduction and dechlorination by accelerating electron transfer. However, there is insufficient information in the literature for delineating the effects of several rising environmental problems (e.g., heavy metal pollution, deficiencies in phosphorus and aluminum) on iron reduction, OCP transformation, and the related microbial activities. Future studies are necessary because such information may be key for sustainable development of agriculture and pollution control in red soils.

Balanced fertilization over four decades has sustained soil microbial communities and improved soil fertility and rice productivity in red paddy soil

Effects of long-term green manure application on the content and structure of dissolved organic matter in red paddy soil

Soil phosphorus (P) adsorption and desorption occur in an important endogenous cycle linked with soil fertility problems and relevant to the environmental risk assessment of P. In our study, the effect of long-term inorganic and organic fertilization on P adsorption and desorption characteristics in relation to changes in soil properties was evaluated by selecting three long-term experimental sites in southern China. The selected treatments at each site were CK (unfertilized), NPK (synthetic nitrogen, phosphorus and potassium) and NPKM (synthetic NPK plus manure). The adsorption and desorption characteristics of P were evaluated using Langmuir and Freundlich isotherms. The results showed that long-term application of NPK plus manure significantly increased soil organic carbon (SOC), total P and available P at all three sites compared with the NPK and CK treatments. All three treatments fit these equations well. The maximum adsorption capacity (Qm) of P increased with NPKM treatment, and the binding energy of P (K) and the maximum buffering capacity (MBC) showed increasing trends. NPKM showed the highest Qm (2346.13 mg kg-1) at the Jinxian site, followed by Nanchang (221.16 mg kg-1) and Ningxiang (2219.36 mg kg-1). Compared to CK and NPK, the NPKM treatment showed a higher MBC as 66.64, 46.93 and 44.39 L kg-1 at all three sites. The maximum desorption capacity (Dm) of P in soil was highest with the NPKM treatment (157.58, 166.76, 143.13 mg kg-1), showing a better ability to release P in soil. The correlation matrix showed a significant positive correlation of SOC, total and available P with Qm, Dm and MBC. In conclusion, it is suggested that manure addition is crucial to improve P utilization in red paddy soils within the recommended range to avoid the risk of environmental pollution.

Biochar (BC) application is widely recognized as a promising strategy for enhancing soil fertility; however, its lasting effects on microbial communities in aeolian sandy soils of semi-arid regions remain poorly understood. To fill this knowledge gap, we conducted a field experiment to evaluate long-term changes in soil properties and microbial community structure in a buckwheat cropping system, 4 years after a single application of biochar (BC) at rates of 0 (BC0), 20 (BC1), 40 (BC2), and 60 (BC3) Mg ha-1 in aeolian sandy soils of Inner Mongolia, China. Results revealed significant improvements in soil pH, moisture content, organic carbon (SOC), and available nutrients, as well as microbial biomass and enzyme activity, particularly at higher BC application rates (BC2 and BC3). SOC increased by 9.42% (BC2) and 14.13% (BC3). BC application altered microbial community composition, with minimal effects on bacterial diversity but reduced fungal diversity. Enhanced soil C and N cycling was linked to shifts in key microbial genera, while relative abundances of potential pathogens such as Fusarium and Nothophoma declined by up to 58 and 77%, respectively. Mantel tests confirmed significant correlations between shifts in microbial diversity and community composition and changes in soil properties, with particularly strong associations for fungal diversity related to SOC (r = 0.50, p < 0.001) and microbial biomass carbon (SMC; r = 0.43, p < 0.001). Redundancy analysis further revealed that bacterial communities were significantly associated (p < 0.05) with pH, microbial biomass nitrogen (SMN), and invertase activity, while fungal communities were linked to pH, microbial biomass phosphorus (SMP), and urease activity. This study underscores the potential of biochar to enhance soil health by improving soil fertility, reshaping microbial community composition, and suppressing soil-borne pathogens, particularly at higher application rates. These findings provide valuable insights for the reclamation of degraded sandy soils in semi-arid regions on a global scale.

The aims of this study were to ascertain the difference of nitrogen uptake and verify the absorption law of the nitrogen from soil and fertilizer for tobacco grown in southwest China with red soil, yellow soil, and paddy soil by 15N tracer. The results showed a significant positive correlation between N accumulation amount and yield in flue-cured tobacco, and a suitable nitrogen demand of 60–100 kg ha-1 for tobacco in southwest zone. Absorption dynamics of nitrogen were different for flue-cured tobacco planted in various types of soil. For rate of nitrogen absorption before topping, the highest was for the tobacco planted in red soil, followed by that in paddy soil and the lowest was for that in yellow soil. N uptake peaks of tobacco planted in red soil, paddy soil and yellow soil were peaked in 7 weeks, 9 weeks, and 11 weeks after transplanting respectively. The absorption changes of soil nitrogen and fertilizer nitrogen in tobacco all showed a single peak curve, and the peak of the absorption curves of fertilizer nitrogen was earlier than soil nitrogen. Uptake rate of soil nitrogen in flue-cured tobacco was gradually higher than fertilizer nitrogen after starting prosperous growth and transferred to the stage of soil nitrogen-dominated absorption. The accumulation ratios of soil nitrogen and fertilizer nitrogen in tobacco before topping accounted 59.8% and 72.1% respectively. The proportions of N accumulation before topping were 87.8%, 47.3%, and 49.2% for tobacco grown in red soil, yellow soil and paddy soil respectively. In conclusion, the fertilizer N demand for tobacco should be estimated with N requirement and soil N supply before topping under proper N demand according to nitrogen absorption law.

Mechanisms behind the inhibition of autotrophic nitrification following rice-straw incorporation in a subtropical acid soil

Hematite enhances the immobilization of copper, cadmium and phosphorus in soil amended with hydroxyapatite under flooded conditions

Biochar and its coupling with microbial inoculants for suppressing plant diseases: A review

The combined effects of cover crops and symbiotic microbes on phosphatase gene and organic phosphorus hydrolysis in subtropical orchard soils

Archaea are the predominant and responsive ammonia oxidizing prokaryotes in a red paddy soil receiving green manures

The accelerated accumulation of phthalate esters (PAEs) in paddy soils poses a serious threat to human health. However, related studies mainly focus on facility vegetable fields, drylands, and orchards, and little is known about paddy soils. In this study, 125 samples were collected from typical red paddy fields to investigate the pollution characteristics, sources, health risks, and main drivers of PAEs. Soil physicochemical properties, enzyme activity, and bacterial community composition were also measured simultaneously. The results showed that eight PAE congeners were detected ranging from 0.17 to 1.97 mg kg-1. Di-n-butyl phthalate (DBP), di-(2-ethylhexyl) phthalate (DEHP), and di-isobutyl phthalate (DIBP) were the most abundant PAE congeners, accounting for 81% of the total PAEs. DEHP exhibited a potential carcinogenic risk to humans through the intake route. The main PAEs were positively correlated with soil organic matter (SOM) and soil water content (SWC) contents. Low levels of PAEs increased bacterial abundance. Furthermore, most PAE congeners were positively correlated with hydrolase activity. Soil acidity and nutrient dynamics played a dominant role in the bacterial community composition, with PAE congeners playing a secondary role. These findings suggest that there may be a threshold response between PAEs and organic matter and nutrient transformation in red paddy soils, and that microbial community should be the key driver. Overall, this study deepens the understanding of ecological risks and microbial mechanisms of PAEs in red paddy soils.