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As the carbon (C) credit market evolves, incorporating organic matter into soils has emerged as a key strategy in C farming. Soil heterotrophic respiration (RH) plays a pivotal role in maintaining the C balance in terrestrial ecosystems, yet the contrasting impacts of fresh and pyrogenic organic matter applications on soil RH, and associated underlying mechanisms, have not been fully investigated. Through a 2-year field experiment, we investigated how applying maize straw and its derived biochar affect the physical, chemical, and microbial properties of soil in a subtropical Moso bamboo forest. Results showed that straw application increased soil RH, while biochar application suppressed it. Soil RH was correlated positively with β-glucosidase and cellobiohydrolase activities but negatively with RubisCO enzyme activity. Increased soil RH under straw application was linked to the increased β-glucosidase/cellobiohydrolase activities driven by elevated water-soluble organic C and O-alkyl C levels as well as GH48 and cbhI gene abundances, and the decreased RubisCO enzyme activity caused by reduced cbbL gene abundance. Conversely, reduced soil RH under biochar application was linked to reductions in β-glucosidase and cellobiohydrolase activities induced by increased aromatic C and decreased GH48 and cbhI gene levels, and increases in RubisCO enzyme activity driven by higher cbbL gene abundance. More importantly, changes in soil RH were clearly linked to microbial dynamics. Specifically, increases in the relative abundances of Alphaproteobacteria and Sordariomycetes and decreases in AD3 and Tremellomycetes contributed to the enhanced soil RH under straw application. With biochar application, the reverse effect occurred, ultimately contributing to the reduced soil RH. Our study demonstrates that maize straw application increases while biochar application decreases soil RH in the subtropical forest. These findings reveal that biochar reduced soil RH through changing microbial activity in subtropical forests, providing insight into complex dynamics of soil C cycling in response to diverse interventions. [ABSTRACT FROM AUTHOR]

Emergent plants have been remarkably effective in reducing phosphorus (P) discharge from ecological ditches; however, the treatment and recycling of these residues is a great challenge. In this study, magnetic biochars (MBs, i.e., MB-A, MB-C, and MB-T) were fabricated from three emergent plant residues (Acorus calamus L., Canna indica L., and Thalia dealbata Fraser, respectively) and modified with Fe(II)/Fe(III). Scanning electron microscopy-energy dispersive spectroscopy and X-ray diffraction spectra confirmed the successful loading of Fe3O4 and FeO(OH) onto the surfaces of the MBs. Batch adsorption experiments showed that MBs exhibited a higher P adsorption capacity than that of the raw biochars. Within the range of 0.8–43.0 mg L−1 in solution, the adsorption capacities of P by MB-A, MB-C, and MB-T were 304.6–5658.8, 314.9–6845.6, and 292.8–5590.0 mg kg−1, with adsorption efficiencies of 95.2–32.9%, 98.4–39.8%, and 91.5–32.5%, respectively. The primary mechanisms that caused P to adsorb onto the MBs were inner-sphere complexation and electrostatic attraction. Low pH conditions were more beneficial for the P adsorption of the MBs, while co-existing anions had a negative impact with the following order: HCO3− > SO42− > Cl−≈NO3−. The P-31 nuclear magnetic resonance results further demonstrated that the main adsorbed P species on the MBs was orthophosphate, followed by orthophosphate monoesters and DNA. Overall, MBs offer a resource utilization strategy for emergent plant residues and P-laden MBs are promising alternative P fertilizers. Highlights: Emergent plant biochar modified with Fe(II)/Fe(III) enhanced P adsorption capacity. Canna indica residue-derived MB exhibited the best P adsorption efficiency. MBs promoted P adsorption mainly via inner-sphere complexation and electrostatic attraction. P species adsorbed by MBs were mainly orthophosphate followed by orthophosphate monoesters and DNA. [ABSTRACT FROM AUTHOR]

Lime is commonly used to neutralize acidic soil in practical farmland management. This study aimed to examine the effect of soil pH change by liming in acidic soil on the mineralization and microbial assimilation of 13C-labelled maize straw-derived hydrophilic and hydrophobic fractions in a 60-d incubation experiment. Our results showed a higher cumulative mineralization of hydrophilic fraction in acidic (34.5%) than neutralized Ferralsol (22.3%), related to lower microbial substrate use efficiency under low soil pH. The cumulative mineralization of hydrophobic fraction was similar between acidic and neutralized Ferralsol. Soil pH affected substrate (hydrophilic and hydrophobic fractions) utilization by actinomycetes and bacteria, but not fungi. The utilization of hydrophilic fraction followed the order: bacteria (57–68%) > actinomycetes (10–19%) > fungi (4.2–5.5%). In contrast, utilization of hydrophobic fraction was the highest for fungi (24–38%), followed by bacteria (21–29%) and actinomycetes (3.2–15%). Actinomycetes showed a greater preference for hydrophilic fraction in neutralized than acidic Ferralsol; bacteria preferred to utilize hydrophilic fraction in both soils, while fungi favored hydrophobic fraction. Also, various substrate uses were found in specific phospholipid fatty acids, which showed that some individual species harbor particular organic C metabolization strategies. In conclusion, soil pH regulates the mineralization of hydrophilic fraction and variously determines the preferential utilization of hydrophilic and hydrophobic fractions by fungi, bacteria, and actinomycetes. Highlights: • Greater mineralization of hydrophilic than hydrophobic fraction was observed in acidic Ferralsol. • The pH sensitivity of substrate utilization followed the order of actinomycetes > bacteria > fungi. • Substrate utilization patterns differed for members of microbial communities. [ABSTRACT FROM AUTHOR]

Drying and rewetting (DRW) events cause the release of colloidal phosphorus (Pcoll, 1–1000 nm) in leachate, and biochar is considered an effective inhibitor; however, the microbial mechanism remains elusive. In this study, three successive DRW cycles were performed on the soil columns to assess the effect of biochar addition on Pcoll content and its possible associates, including phosphatase-producing microbial populations (phoD- and phoC-harboring microbial communities) and alkaline/acid phosphatase (ALP/ACP) activities. Results showed that the biochar addition significantly decreased the Pcoll by 15.5–32.1% during three DRW cycles. The structural equation model (SEM) confirmed that biochar addition increased phoD- and phoC-harboring microbial communities and ALP/ACP activities, which reduces the release of Pcoll into leachate. In addition, the manure biochar was more effective than the straw biochar in promoting competition and cooperation in the co-occurrence network (2–5% nodes increased on average), and the key taxa Proteobacteria and Cyanobacteria were identified as the dominant species of potential ALP/ACP activities and Pcoll content. Our findings provide a novel understanding of biochar reducing Pcoll loss from the phosphatase perspective by regulating the phoD- and phoC-harboring communities during DRW events. Highlights: Biochar reduced Pcoll by 15.5–32.1% in leachate during DRW cycles. Pcoll decreased with increasing phoD- and phoC-harboring microbial communities. Proteobacteria and Cyanobacteria were the key taxa driving Pcoll content. [ABSTRACT FROM AUTHOR]

Application of biochar to soil may stabilize soil organic carbon (SOC), concomitantly increasing nutrient retention. However, the interactive effect of biochar and nutrients on SOC and the underlying microbial mechanisms remain poorly understood, particularly in intensively managed forests where decarbonization is substantial after converting from natural forests. This 80-day incubation experiment aimed to quantify native SOC mineralization as affected by biochar (B) and nutrients [nitrogen (N) or phosphorus (P)], linking to the chemical composition of SOC, soil microbial community composition, and enzyme activities within a subtropical Moso bamboo (Phyllostachys edulis) forest soil. Results presented that compared to the control (nil-nutrient), nutrients (N, P, and NP) significantly destabilized native SOC [positive priming effect (PE); 20–98% increase in SOC mineralization], whereas such destabilization effect was significantly reduced by biochar (6.0–19%). The positive PE by nutrient was due to the increases in O-alkyl C, microbial biomass C, available mineral N, soil pH, β-glucosidase, and invertase activities. Meanwhile, the greater PE by N than P could be attributed to (i) decreases in diversity of bacterial and fungal communities; and (ii) increases in the relative abundances of microbial taxa such as Bacilli, Planctomycetes, and Alphaproteobacteria. Importantly, biochar's stabilization effect was because biochar not only lowered NH4+-N and NO3−-N and β-glucosidase activity, but also increased the activity of C-fixing enzyme (RubisCO) and polyphenol oxidase activity. Furthermore, biochar significantly decreased soil O-alkyl C that possibly resulted in less labile SOC mineralization, but increased aromatic C resulting in lower fungal diversity. We conclude that the biochar significantly reduces the destabilization effects of nutrients on SOC, highlighting that the biochar application is an effective approach to mitigate soil CO2 emissions within subtropical forest. [ABSTRACT FROM AUTHOR]

Purpose : Biochar application to soil has gained great interest as a land-based climate change mitigation solution. However, it lacks long-term field assessment on the effectiveness of biochar compared with other widely applied land management—such as stubble retention—on soil organic carbon (SOC) accumulation and carbon (C) distribution and persistence in the soil matrix. Materials and method: Here, we conducted a 9-year field trial in a temperate agroecosystem of North China to identify and quantify the location of C residing in the soil matrix (determined by two physical fractionation methods), as affected by land management—stubble removed (control), stubble returned at 15 t ha−1 year−1 (SR), two biochar doses at 4.5 t ha−1 year−1 (B4.5; equivalent to feedstock in SR) and 9.0 t ha−1 year−1 (B9.0). Results and discussion: The results showed that biochar application significantly increased SOC in the free and occluded particulate organic matter (POM) and mineral-associated organic matter (MAOM) fractions. Compared to B4.5 and B9.0, SR was less effective in soil C accrual in the occluded POM and MAOM, although the largest increase of C occurred in the free POM (about 10–17 g kg–1 soil). Consistent with this, biochar rather than stubble retention significantly increased C in (i) coarse POM (i.e., unprotected POM, > 250 μm) by 190–210%, (ii) microaggregates (μAgg) by 56–70%, and (iii) MAOM in silt–clay fraction (iMAOM) by 4–12%, but the biochar dose effect was statistically insignificant. Importantly, biochar significantly increased chemically recalcitrant C in soils that were further protected in the μAgg and iMAOM fractions. Conclusions: We conclude that biochar application was more beneficial for SOC accumulation and preservation than stubble management, particularly in the microaggregates and organo-mineral complexes, under the intensive cropping systems. [ABSTRACT FROM AUTHOR]

Purpose: Mangrove restoration has been suggested to have a great potential for global change mitigation due to the large carbon sequestration capacity of mangroves. However, the temporal and spatial dynamics of soil organic carbon (SOC) storage following mangrove restoration remains less examined and reported. To fill the knowledge gap, this study examined the SOC stocks and soil physicochemical properties among bare mudflats and adjacent mangroves at different stand ages. Methods: We collected soil cores from bare mudflats and adjacent 7-, 10-, 15-, and 60-year-old mangroves on Ximen Island, Zhejiang Province, China. SOC, pH, salinity, particle size, and dry bulk density were determined. The analysis of variance was used to test for significant differences in above parameters among mangroves with different ages and mudflats. Pearson's correlation was conducted to assess the relationship of SOC contents and other soil physicochemical properties. Results: Our results showed that SOC stock increased exponentially following restoration, reaching an asymptotic trend after 15-year mangrove restoration. The 60-year-old mangrove forests had significantly higher SOC stocks (94.31 ± 4.99 Mg OC ha−1) compared to the unvegetated mudflat (76.25 ± 1.65 Mg SOC ha−1) and the 7-year-old transplanted sites (79.04 ± 5.30 Mg OC ha−1). Soil salinity, pH, and bulk density increased significantly within the whole depth, except decreasing trend of salinity in lower depth (> 25 cm). Soil texture was finer in mudflats and early stages of mangrove plantations than that in other sites. Conclusion: This study indicated that mangrove transplantation can substantially enhance SOC stocks within 15 years after afforestation. These results provide key data on the effectiveness of mangrove afforestation on carbon sequestration to inform blue carbon policies. [ABSTRACT FROM AUTHOR]

Purpose: The term "charosphere" refers to the biochar-contiguous soil that is directly influenced by the physicochemical properties of the biochar, yet the dynamics of microbial composition in the charosphere in heavy metal-polluted soil remains largely unknown. Methods: Swine manure-derived biochars prepared at 300 and 700 °C were packed in a double-layer mesh bag and then buried in a Cd-contaminated paddy soil for 15 days (T1) and 95 days (T2). Bacterial community composition in the charosphere and the linked properties such as soil pH, dissolved organic carbon (DOC) contents, and total Cd and Zn concentrations were analyzed. Results: The results showed that biochar significantly shifted the beta diversity of the bacterial community in the charosphere, mainly due to increase in pH and total Zn concentrations. Further, 300 °C-prepared biochars stimulated Bacteroidetes and inhibited Acidobacteria by increasing soil pH. In the charosphere of biochars prepared at 700 °C, associated with the release of Zn and the adsorption of Cd, Chloroflexi became favorable over other microbial groups. Both biochar additions gave an increase in the putative function of energy metabolism and lipid metabolism, which might help bacteria dominant in charosphere resist stress of heavy metals. Conclusion: Taken together, these pieces of evidence suggest that bacterial community and potential functions in the charosphere differ remarkably from the control soil without biochar, which was mainly due to biochar reduced environmental stresses such as soil acidity and heavy metals. [ABSTRACT FROM AUTHOR]

Background and aims: Alkaline dispersive subsoils are characterised by multiple physicochemical constraints that limit plant water and nutrient acquisition. Subsoil amelioration through organic amendments (OAs) requires significant financial investment. Whereas large yield responses can result following amelioration, sometimes small or even negative yield responses can occur, resulting in a significant net financial loss for the farmer. For farmers to feel confident in investing in subsoil amelioration better prediction of the likely yield improvement is required and to achieve this an understanding of the underlying mechanisms such as nutritional and non-nutritional drivers, and the longevity of benefits are required. Our study aimed to ascertain the drivers of yield improvements from subsoil amelioration with OAs. Methods: In a controlled environment, wheat (Triticum aestivum L. cv. Scepter) plants were grown until maturity in a Solonetz amended with (i) poultry litter (PL; 20 t ha−1), and (ii) NPKS nutrients and (iii) model organic carbon (MOC) with equivalent amounts of nutrients and total carbon contained in the PL, and (iv) NPKS + MOC. Control (no amendments) and gypsum (5 t ha−1) were included as district practices. Before planting, amendments were applied as a vertical band at 20 – 40 cm depth and pre-incubated. Plant biomass, grain yield, root biomass, and physicochemical properties of the soil associated with the amendment band were quantified at harvest. Results: Compared to the control, wheat grain yield was increased by 30% for PL, 43% for NPKS + MOC, and 61% for NPKS, but no differences in yield were detected for MOC or gypsum. The lower yield increase by PL than NPKS with or without MOC was likely due to the readily available form of plant nutrients in the inorganic fertilisers vs slower mineralisation of nutrients from the OAs. Improvement in soil physicochemical properties following amelioration of alkaline dispersive subsoil resulted in better root proliferation and subsoil water use. Grain yield showed a positive correlation with root biomass in the subsoil layers. Conclusions: In the short-term (one crop cycle), organic amendments improved soil's non-nutritional physical and chemical properties but had no additional nutritional effect on wheat grain yield compared to inorganic fertiliser application. Longer-term studies are needed to determine the legacy effect of the nutritional contribution in conjunction with the improvement of soil structure from the OAs in alkaline dispersive subsoils. [ABSTRACT FROM AUTHOR]

Purpose: Intensive long-term management practices in forest ecosystems can markedly influence soils' physicochemical and microbial properties. However, their effects on the magnitude of nutrient pools and activities of enzymes regarding nutrient cycling in subtropical forest soils remain unclear. This study aimed to examine effects of long-term intensive management (organic mulching and chemical fertilization) on concentrations of different C, N, and P fractions and activities of enzymes involved with nutrient cycling in a subtropical Lei bamboo (Phyllostachys violascens) forest soil. Materials and methods: Soil samples were taken from a chronosequence of Lei bamboo forests with intensive management spanning 0, 5, 10, and 15 years. Concentrations of various forms of C, N, and P, as well as activities of β-glucosidase, cellobiohydrolase, urease, protease, and acid phosphatase were measured. Results and discussion: The results revealed that the concentrations of different classes of C (water-soluble organic C, hot-water-soluble organic C, and readily oxidizable C), N (NH4+-N, NO3−-N, and water-soluble organic N), and P [resin-inorganic P (Pi), NaHCO3-Pi, NaHCO3-organic P (Po), NaOH-Pi, NaOH-Po, HCl-Pi, and residual-P] were enhanced markedly with prolonged duration of intensive management. Furthermore, activities of β-glucosidase, cellobiohydrolase, urease, protease, and acid phosphatase were increased following a 5-year treatment, while they were markedly reduced from 5- to the 15-year treatments. The 15 years of intensive management significantly reduced microbial biomass C and N concentrations by 8.2% and 31.9%, respectively, compared to the control. Conclusions: We concluded that long-term intensive management led to the accumulation of C, N, and P, while it negatively impacted microbial biomass and activities of enzymes involved in nutrient cycling in subtropical Lei bamboo forest soils. Consequently, a reduction in chemical fertilizers should be considered toward the long-term sustainable development of subtropical Lei bamboo forests. [ABSTRACT FROM AUTHOR]

Purpose: China is not only a main source area of Asian dust but also a significantly affected area of dust deposition in the world. However, the influence range of Asian dust deposition and its influence on soil provenance remains unclear, particularly in subtropical regions. This study identified the substantial effect of Asian dust on soils and quantified its contribution to subtropical soils of China. Materials and methods: Three soil profiles derived from basalt in subtropical area (Shaoxing, Zhejiang, China) were selected and sampled. The pH, bulk density, and cation exchange capacity (CEC) of soils were determined. The Neodymium (Nd) and Thorium (Th) concentrations and Nd isotope of soils were determined. We used the Nd elemental and isotopic geochemistry to assess the deposition of Asian dust in soil profiles (up to 1 m depth). Results and discussion: The upper soil layers have negative ε Nd (0) values, which were close to those of Asian dust ε Nd 0 = - 3.30) , indicating the input of Asian dust to soils. Further, the high dust-derived Nd proportion in the soils (f dust Nd = 43 %) also suggested a great contribution of Asian dust on soils. A comparison of Nd in the soils from subtropics (Zhejiang province, Southeast China) and tropics (Hainan province, China's southernmost point) indicated that both regions were influenced by Asian dust but at different degrees. Conclusions: Asian dust has been identified as a vital source of Nd in subtropical soils of China. The high mass fraction of dust-derived Nd in the soil profiles indicated the important role of dust input in soil genesis. The results also suggest that Nd isotopes are powerful fingerprints in tracing the origin of soil materials. [ABSTRACT FROM AUTHOR]

A 120-day field experiment was conducted to investigate the responses of soil N2O emissions, plant biomass N content, and N cycling-related functional genes to yak (Bos grunniens) dung pat size, including full-size dung pat (FDP), 1/4FDP, 1/8FDP, and 1/16FDP (i.e., FDP split into four, eight, and sixteen equal-sized dung pat fragments) in an alpine steppe on the Qinghai-Tibetan Plateau. The yield-scaled and cumulative N2O emissions were lower in the 1/16FDP and 1/8FDP than in the FDP and 1/4FDP treatments. In addition, the 1/16FDP treatment had the smallest N2O emission factor (0.002%), possibly due to lower denitrification as shown by the lower nisS, nirK, and nosZ gene copy numbers in the first (day 30) and second (day 72) samplings, and increased aboveground plant N concentration and content, which was 23–32% and 21–36%, respectively, greater than in the other treatments. In conclusion, splitting the yak dung pat into 1/16 fragments would be an effective strategy for managing yak dung to reduce N2O emissions and improve aboveground plant biomass N content which enhances the sustainability of alpine steppe ecosystems on the Qinghai-Tibetan Plateau. The implication from this study is that long-term field experiments should be conducted to further investigate the potential antagonistic or synergistic effects of yak dung pat fragmentation combined with other amendments (e.g., nitrogen inhibitors, lime, or biochar) on reducing N2O emissions. [ABSTRACT FROM AUTHOR]

Background and aims: Incorporation of biochar into the soil sequesters C for millennia, but the concomitant effects on plant rhizodepositions and nutrient (e.g., nitrogen; N) trade-offs via interactions of heterotrophic microbiota, might offset this sequestration. Methods: Ryegrass (Lolium perenne L.) with and without biochar amendment were pulse labelled in a 13CO2 atmosphere and 15N fertilizer added. Ryegrass and soils were destructively sampled at 16 and 30 days after seedling emergence. Isotope analysis was coupled with MiSeq sequencing of bacterial (16s rRNA) and fungal (ITS) genes to identify the effect of biochar on the associated microbiota involved in 13C allocation into soil aggregates and promotion of 15N uptake by L. perenne. Results: Biochar increased root biomass and 15N uptake but decreased rhizodeposited-13C recovery from large and small macroaggregates (by 12–57% and 57–72%, respectively). These changes in 13C flow and 15N uptake were accompanied by an increase in microbial biomass, and enhanced negative correlations between bacteria and fungi. O2PLS indicated members of seventeen genera that were correlated with soil stabilization of rhizodeposits in soil and plant N-uptake. For instance, Xanthomonadales (Proteobacteria) and RB41 (Acidobacteria), previously reported to be plant growth promoting rhizobacteria, were found to be positively correlated with 15N uptake by L. perenne. Conclusions: Our research explored the genera associated with biochar-modified 15N uptake by Lolium perenne and photosynthate 13C allocation into soil aggregates. Future research with SIP is required to fully assess microbial turnover, the ubiquity of similar rhizosphere microbiota and their fundamental importance for sequestration in the plant-soil-microbe-biochar systems. [ABSTRACT FROM AUTHOR]

Crabs may elicit effects on wetland carbon (C), nitrogen (N), and phosphorus (P) concentrations and associated ecological stoichiometry. In this study, we assessed effects of crabs on carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) emissions; soil C, N, and P concentrations; and stoichiometry in upper and mid-tidal flats of an estuarine wetland in China. The results showed that averaged CO2, CH4, and N2O fluxes were greater in the upper and mid-tidal flats in the presence of crabs, being 46.4, 66.7, and 69.7% and 53.6, 143, and 73.1% greater than control, respectively. Mixed model analyses showed overall positive relationships between wetland soil CO2 CH4 and N2O emissions (F = 4.65, P = 0.033; F = 42.42, P = 0.042 and F = 10.2, P = 0.0018, respectively) in the presence of crabs, taking into account season, flooding intensity, and plot effects. This may be related to the direct effects of respiration and the indirect effects of feeding, excretion, and disturbance of soil on microorganisms and/or plant roots. There were no effects of crabs on total C or N concentrations, whereas decreased soil total P concentrations, especially in the upper-tidal flats (P = 0.04). Crab presence was positively associated with soil C/P and N/P ratios (P < 0.0001 and P < 0.0001, respectively), taking into account season, flooding intensity, and plot effects. In the upper and mid-tidal flats, soil CO2 emissions were negatively correlated with total soil C; CH4 emissions were positively correlated with ratios of C/N and C/P; and N2O emissions were positively correlated with N content. In general, global warming potential (GWP) of the upper-tidal flats in the presence of crabs increased by 138% compared with the absence of crabs, and GWP of the mid-tidal flats in the presence of crabs increased by 99.3% compared with the absence of crabs. Global warming and associated flooding rise in several coastal wetland areas are favoring benthic fauna number enhancement, and this in turn increases GWP of overall gas emissions further contributing to future warming rise. [ABSTRACT FROM AUTHOR]

Application of organic amendments (OAs) combined with inorganic fertilizers or gypsum in poorly structured soils has recently received much attention as an agricultural management practice aiming to ameliorate physicochemical constraints and improving soil carbon (C) storage. Although microbial C-use efficiency (CUE) is recognized as a critical parameter in ecological models to predict soil C cycling and storage, little is known about the effects of OAs with exogenous nutrient supply (to balance the resource nutrient stoichiometry) or gypsum on microbial biomass and CUE. Here, we examined the role of OAs (C4 vegetation-derived: δ13C – 12 to − 15‰) in altering microbial biomass, C mineralization, and CUE, i.e., microbial growth relative to microbial C uptake (microbial growth + respiration + death) over the long-term, in an alkaline sodic-subsoil (C3 vegetation-derived: δ13C – 24‰). Four different OAs (sorghum stubble, sugarcane bagasse, sugarcane mill mud, and sugarcane mill mud + sugarcane mill ash) were used at 6.2 g C kg−1 soil, with and without the exogenous supply of nutrients and/or gypsum. The nutrients were added with the aim to convert OAs to stable soil organic matter (SOM) with a C/nitrogen (N)/phosphorus (P) stoichiometric ratio of 100:8.3:2. Over 90 days, the cumulative mineralization of OA-C varied across OA types and ranged between 42 and 497 mg CO2-C g−1 OA-C. The OA-derived microbial biomass C (MBC) ranged between 20 and 350 mg C kg−1 soil across the treatments, which was highest with sorghum stubble that contained the highest dissolved (labile) organic C. The mill mud with an inherently balanced C/nutrient stoichiometry had the highest CUE, i.e., 0.3–0.8, compared to the sorghum stubble and sugarcane bagasse (with imbalanced nutrient stoichiometry), i.e., 0.1–0.6. Balancing the nutrient stoichiometry of sorghum stubble and sugarcane bagasse via nutrient inputs increased MBC but not CUE. The input of gypsum to the OA-treated soil had no impact on either MBC or CUE. In conclusion, balanced C/nutrient stoichiometry and labile C content of OAs are critical properties to control their impact on C mineralization, MBC, and CUE, with implications for soil C storage upon amendment into a poorly structured sodic-subsoil. [ABSTRACT FROM AUTHOR]