Soil organic carbon regulation by pH in acidic red soil subjected to long-term liming and straw incorporation.

The manipulation of soil pH through liming and straw incorporation plays a pivotal role in influencing soil organic carbon (SOC) dynamics in acidic red soil. This study aimed to assess the impact of these practices on SOC and elucidate the relationship between SOC and pH. Over a 31-year field experiment, seven different fertilization treatments were implemented: unfertilized (CK), nitrogen and potassium fertilizers (NK), NK with lime (NKCa), nitrogen, phosphorous, and potassium fertilizers (NPK), NPK with lime (NPKCa), NPK with straw (NPKS), and NPKS with lime (NPKSCa). Results revealed that liming and straw incorporation significantly elevated soil pH by 0.13-0.73 units. Lime application boosted SOC and mineral-associated organic carbon (MAOC) by 20.2% and 28.7%, respectively, in NK treatment, whereas its impact on SOC in NPK and NPKS treatments were negligible. SOC witnessed a 17.1% increase with NPKS and a 15.2% increase with NPKSCa compared to NPK alone. Notably, NPKS and NPKSCa led to a significant surge in particulate organic carbon (POC) by 19.7% and 37.7%, respectively, albeit NPKSCa reduced MAOC by 14.9% relative to NPK. Linear regression analysis unveiled a positive correlation between POC and soil pH, while SOC and MAOC exhibited an initial rise at lower pH levels followed by stabilization as pH continuously increasing. A partial least squares path model showed two pathways through which pH influenced SOC: firstly, by positively affecting SOC through increasing Fe and Al oxides contents and enhanced aggregate stability, and secondly, by negatively influencing SOC through altered ratios of fungi/bacteria and Gram-positive bacteria/Gram-negative bacteria. In conclusion, the long-term effects of lime and straw application on SOC and MAOC were contingent upon soil pH, with more pronounced positive effects observed at lower pH levels. These findings underscore the importance of considering soil pH when implementing lime and straw strategies to mitigate acidification and regulate SOC in acidic red soil.

Impacts of long-term chemical nitrogen fertilization on soil quality, crop yield, and greenhouse gas emissions: With insights into post-lime application responses.

The improvement in the agricultural production through continuous and heavy nutrient input like nitrogen fertilizer under the upland red soil of south China deteriorates soil quality, and this practice in the future could threaten future food production and cause serious environmental problems in China. This research is initiated with the objectives of evaluating the impacts of long-term chemical nitrogen fertilization on soil quality, crop yield, and greenhouse gas emissions, with insights into post-lime application responses. Compared to sole application of chemical nitrogen fertilization, combined application with lime increased soil indicators (pH by 6.30 %-7.76 %, Ca2+ by 90.06 %-252.77 %, Mg2+ by 184.47 %-358.05 %, available P by 5.05 %-30.04 %, and soil alkali hydrolysable N by 23.49 %-41.55 %. Combined application of chemical nitrogen fertilization with lime (NPCa (0.59), NPKCa (0.61), and NKCa (0.27) significantly improved soil quality index compared to the sole application of chemical nitrogen fertilization (NP (0.31), NPK (0.36), and NK (0.16). Compared to sole application of chemical nitrogen fertilization, combined application with lime increased grain yield by 48.36 %-61.49 %. Structural equation modeling elucidated that combined application of chemical nitrogen fertilization and lime improved wheat grain yield by improving soil quality. Exchangeable Ca2+, exchangeable Mg2+, pH, and exchangeable Al3+ were the most influential factors of wheat grain yield. Overall, the combined application of chemical nitrogen fertilization and lime decreased global warming potential (calculated from N2O and CO2) by 16.92 % emissions compared to the sole application of chemical nitrogen fertilization. Therefore, liming acidic soil in upland red soil of South China is a promising management option for improved soil quality, wheat grain yield, and mitigation of greenhouse gas emissions.

Optimizing potassium and nitrogen fertilizer strategies to mitigate greenhouse gas emissions in global agroecosystems.

The efficient management of fertilizer application in agriculture is vital for both food security and mitigating greenhouse gas (GHG) emissions. However, as potassium fertilizer (KF) is an essential soil nutrient, its impact on soil GHG emissions has received little attention. To address this knowledge gap and identify key determinants of GHG emissions, we conducted a comprehensive meta-analysis of 205 independent experiments conducted worldwide. Our results revealed that, in comparison to sole nitrogen fertilizer (NF) application, the concurrent use of KF elevated nitrous oxide (N2O) and methane (CH4) emissions by 39.5 % and 21.1 %, respectively, while concurrently reducing carbon dioxide (CO2) emissions by 8.1 %. The ratio of nitrogen and potassium fertilizer input (NF/KF) is identified as the primary factor explaining the variation in N2O emissions, whereas the type of KF plays a crucial role in determining CH4 and CO2 emissions. We observed a significant negative correlation between the NF/KF ratio and response ratios of N2O and CH4 emissions and a positive correlation with CO2 emissions response ratios. Furthermore, our findings indicate that when the NF/KF ratio surpasses 1.97, 4.61, and 3.78, respectively, the impact of KF on reducing N2O, CH4, and CO2 emissions stabilizes. Overall, our results underscore that the global integration of KF into agricultural practices significantly influences N2O and CH4 emissions, while simultaneously reducing CO2 emissions at a large scale. These findings provide a foundational framework and practical guidance for optimizing fertilizer application in the development of GHG emission reduction models.

The extreme wet and large precipitation size increase carbon uptake in Eurasian meadow steppes: Evidence from natural and manipulated precipitation experiments.

The distribution of seasonal precipitation would profoundly affect the dynamics of carbon fluxes in terrestrial ecosystems. However, little is known about the impacts of extreme precipitation and size events on ecosystem carbon cycle when compared to the effects of average precipitation amount. The study involved an analysis of carbon fluxes and water exchange using the eddy covariance and chamber based techniques during the growing seasons of 2015-2017 in Bayan, Mongolia and 2019-2021 in Hulunbuir, Inner Mongolia, respectively. The components of carbon fluxes and water exchange at each site were normalized to evaluate of relative response among carbon fluxes and water exchange. The investigation delved into the relationship between carbon fluxes and extreme precipitation over five gradients (control, dry spring, dry summer, wet spring and wet summer) in Hulunbuir meadow steppe and distinct four precipitation sizes (0.1-2, 2-5, 5-10, and 10-25 mm d-1) in Bayan meadow steppe. The wet spring and summer showed the greatest ecosystem respiration (ER) relative response values, 76.2% and 73.5%, respectively, while the dry spring (-16.7%) and dry summer (14.2%) showed the lowest values. Gross primary production (GPP) relative response improved with wet precipitation gradients, and declined with dry precipitation gradients in Hulunbuir meadow steppe. The least value in net ecosystem CO2 exchange (NEE) was found at 10-25 mm d-1 precipitation size in Bayan meadow steppe. Similarly, the ER and GPP increased with size of precipitation events. The structural equation models (SEM) satisfactorily fitted the data (χ2 = 43.03, d.f. = 11, p = 0.215), with interactive linkages among soil microclimate, water exchange and carbon fluxes components regulating NEE. Overall, this study highlighted the importance of extreme precipitation and event size in influencing ecosystem carbon exchange, which is decisive to further understand the carbon cycle in meadow steppes.

Extreme wet precipitation and mowing stimulate soil respiration in the Eurasian meadow steppe.

The imbalance of terrestrial carbon (C) inputs versus losses to extreme precipitation can have consequences for ecosystem carbon balances. However, the current understanding of how ecosystem processes will respond to predicted extreme dry and wet years is limited. The current study was conducted for three years field experiment to examine the effects of environmental variables and soil microbes on soil respiration (Rs), autotrophic respiration (Ra) and heterotrophic respiration (Rh) under extreme wet and dry conditions in mowed and unmowed grassland of Inner Mongolia. Across treatments (i.e. control, dry spring, wet spring, dry summer and wet summer), the mean of Rs was increased by 24.9 % and 24.1 % in the wet spring and wet summer precipitation treatments, respectively in mowed grassland. In other hand, the mean of Rs was decreased by -22.1 % and -3.5 % in dry spring and dry summer precipitation treatments, respectively in mowed grassland. The relative contribution of Rh and Ra to Rs showed a significant (p < 0.05) change among simulated precipitation treatments with the highest value (76.18 %) in wet summer and 26.41 % in dry summer, respectively under mowed grassland. Rs was significantly (p < 0.05) affected by the interactive effect of extreme precipitation and mowing treatments in 2020 and 2021. The effects of precipitation change via these biotic and abiotic factors explained by 52 % and 81 % in Ra and Rh, respectively in mowed grassland. The changes in microbial biomass carbon (MBC) and nitrogen (MBN) had significant (p < 0.05) direct effects on Rh in both mowed and unmowed grasslands. The influence of biotic and abiotic factors on Rs was stronger in mowed grasslands with higher standardized regression weights than in unmowed grassland (0.78 vs. 0.69). These findings highlight the importance of incorporating extreme precipitation events and mowing in regulating the responses of C cycling to global change in the semiarid Eurasian meadow steppe.

Mitigation of greenhouse gas emissions from a red acidic soil by using magnesium-modified wheat straw biochar.

To mitigate greenhouse gas (GHG) emissions, different strategies have been proposed, including application of dolomite, crop straw and biochar, thus contributing to cope with the increasing global warming affecting the planet. In the current study, pristine wheat straw biochar (WBC) and magnesium (MgCl2.6H2O) modified wheat straw biochar (MWBC) were used. Treatments included control (CK), two WBC dosages (1% and 2.5%), and two MWBC doses (1% and 2.5%). After 90 days of incubation, WBC and MWBC improved the soil physiochemical properties, being more pronounced with increasing rates of biochar. MWBC2.5 significantly decreased microbial biomass carbon (MBC), while microbial biomass nitrogen (MBN) increased when both biochar materials (WBC1 and MWBC1) were applied at low rate. Compared to control soil, Urease and Alkaline phosphatase activities increased with the increasing rate of WBC and MWBC. The activities of dehydrogenase and ß-glucosidase decreased with the WBC and MWBC application, compared to CK. The fluxes of all the three GHGs evaluated (CO2, CH4 and N2O) decreased with time for both biochar amendments, while cumulative emission of CO2 increased by 58% and 45% for WBC, and by 54% and 41% for MWBC, as compared to CK. The N2O cumulative emissions decreased by 18 and 34% for WBC, and by 25 and 41% for MWBC, compared to CK, whereas cumulative methane emission showed non-significant differences among all treatments. These findings indicate that Mg-modified wheat straw biochar would be an appropriate management strategy aiding to reduce GHG emissions and improving the physiochemical properties of affected soils, and specifically of the red dry land soil investigated in the current work.