Search

Modelling the lime requirement (LR) is a fast and efficient way to determine the amount of lime required to obtain a pH that can overcome the adverse effects caused by soil acidification. This study aimed to model the LR based on the properties of soil and lime. A total of 17 acidic soils and 39 lime samples underwent soil–lime incubation in the laboratory. The predictive equations for the LR (t ha−1) were modelled using ∆pH (the difference between the target pH and initial pH), the neutralizing value (NV, mmol kg−1) of lime, soil pH, soil clay content (%), soil bulk density (BD, g cm−3), and the depth of soil (h, cm) as the factors in an exponential equation. The generic predictive equation, L R = ∆ p H × e − 3.88 − 0.069 × N V + 0.51 × p H + 0.025 × C l a y × B D × h , was validated as the most reliable model under field conditions. Simplified predictive equations for different soil textures when limed with quicklime and limestone are also provided. Furthermore, the LR proportions provided by hydrated lime, quicklime, limestone, and dolomite in commercially available lime can be expressed as 0.58:0.64:0.97:1.00. This study provides a novel and robust model for predicting the amount of lime product containing components with different neutralizing abilities that are required to neutralize soils with a wide range of properties. It is of great significance to agronomic activities and soil remediation projects. [ABSTRACT FROM AUTHOR]

Detailed knowledge of a soil's lime requirement (LR) is a prerequisite for a demand-based lime fertilization to achieve the optimum soil pH and thus sustainably increasing soil fertility and crop yields. LR can be directly determined by the base neutralizing capacity (BNC) obtained by soil-base titration. For a site-specific soil acidity management, detailed information on the within-field variation of BNC is required. However, soil-base titrations for BNC determination are too laborious to be extensively applied in routine soil testing. In contrast, visible and near-infrared spectroscopy (visNIRS) is a time and cost-effective alternative that can analyze several soil characteristics within a single spectrum. VisNIRS was tested in the laboratory on 170 air-dried and sieved soil samples of nine agricultural fields of a quaternary landscape in North-east Germany predicting the soil's BNC and the corresponding lime requirement (LRBNC) at a target pH of 6.5. Seven spectral pre-processing methods were tested including a new technique based on normalized differences (ND). Furthermore, six multivariate regression methods were conducted including a new method combining a forward stagewise subset selection algorithm with PLSR (FS-PLSR). The models were validated using an independent sample set. The best regression model for most target variables was FS-PLSR combined with the second Savitzky-Golay derivation as pre-processing method achieving R2s from 0.68 to 0.82. Finally, the performance of the direct prediction of LRBNC (R2 = 0.68) was compared with an indirect prediction that was calculated by the predicted BNC parameters. This resulted in slightly higher correlation coefficients for the indirect method with R2 = 0.75. [ABSTRACT FROM AUTHOR]

The soils of four citrus orchards in western Zhejiang were studied in this research. In order to explore the effects of lime on soil chemical properties and bacterial communities, the incubation experiment was conducted with six different dosages of lime addition, 0, 0.6, 1.2, 2.4, 4.8, 7.2 g/kg, respectively. The results showed that soil pH increased significantly (p < 0.05) and the contents of exchangeable acid decreased significantly (p < 0.05) at the early stage of lime application. As time went by, the reacidification existed in the soil of each treatment, mainly reflected in a significant (p < 0.05) decrease in soil pH. Liming increased the nitrate nitrogen content and decreased the ammonium nitrogen content in the four soils. However, the responses of other nutrient indexes to lime varied in different soils, which might be due to the different degrees of soil acidification. In general, the addition of lime increased the soil integrated fertility index (IFI) and improved the soil nutrient status. The application of lime under 2.4 g/kg significantly improved the structure of bacterial community and increased the relative abundance of soil bacterial community species, while the application of lime above 4.8 g/kg might inhibit the growth and activity of microorganisms, resulting in the reduction of soil microbial biomass and diversity. Redundancy analysis (RDA) showed that lime affected the bacterial community mainly by reducing the content of soil active acid and exchangeable acid. At the same time, network analysis showed that the bacterial community had a stronger buffer capacity against external disturbances after lime application. In conclusion, the addition of lime with appropriate amount (2.4~4.8 g/kg, corresponding to a field application rate of 5.8~11.5 t/ha) in acid orchard soil could improve soil properties, soil integrated fertility, and the diversity and stability of the bacterial community. [ABSTRACT FROM AUTHOR]

Soil acidification is a major and growing concern in many cropping regions globally. Whilst spatial variability in acidification is a common consideration in the management of soil health and fertility at sub-paddock scale, insufficient focus has been directed toward the identification of this variability. Suitability of portable visible near infrared reflectance (vis–NIR) spectroscopy was assessed in this study as a potential technique to achieve rapid, precise, inexpensive and spatially specific quantification of key soil parameters to inform lime requirements. Spectral fingerprints were taken using a 1 ha grid sampling approach, with four sampling protocols investigated as follows, scans: (i) directly on cleared soil surfaces; (ii) on 0–100 mm undisturbed cores; (iii) on dried 0–100 mm cores; and finally (iv) on dried, ground, sieved and mixed cores. Data was analysed using a partial least squares regression (PLSR) model to identify the strength of linear relationship between reference chemistry data and predictions derived from spectral readings. Lime requirement maps using vis–NIR predictions were then theoretically compared against traditional aggregated sampling patterns while considering the trade-offs between accuracy, economics and agronomy associated with the identification of spatial variability. The vis–NIR measurements demonstrated moderate predictive capabilities in field for determining pH (R2 = 0.3–0.5) and liming requirements (R2 = 0.5–0.6) rapidly at high spatial resolution. Vis–NIR in field mapping techniques, which enable the use of site specific management of soil resources, were found to positively redirect lime resources from alkaline areas toward acidic areas of the paddock, resulting in minimal difference to overall expenditure on lime purchase and potential for increased agronomic benefits over the long-term. Further spectral library development, calibration, and research on in-field sampling methods is recommended. [ABSTRACT FROM AUTHOR]

Soil acidification is a natural phenomenon that human activity can accelerate or manage. Acid soils limit plant growth by reducing nutrient availability and causing aluminum toxicity, significantly reducing crop production. Liming has proven efficient for increasing crop yield on acidic soils. Knowledge is required on the effect of liming on the soil pH dynamics to find the suitable material, application rate, timing, and method. The objective of this study was to develop a prediction model of soil pH temporal variations after lime application using data from the literature. A database was built from research results extracted from 16 scientific papers that provided data on soil acidity changes over time under different liming treatments. Machine learning (ML) was used to predict soil pH dynamics from eight predictive parameters: rate of application, time since application, neutralizing value (CCE), grind fineness (D50), pH measurement depth, soil acidity (pH prior to liming), the type of solution used for pH measurement (water or CaCl 2) and the soil:solution ratio used to measure pH. Since soil pH fluctuates with seasons, all pH values were expressed as difference between the actual pH value and that of an unlimed control (ΔpH). The Random Forest (RF) algorithm was tested to predict ΔpH over time. On testing, we obtained an R2 between measured and predicted ΔpH values of 0.881 and an RMSE of 0.230. These results are excellent, considering the heterogeneity in soils, liming materials, and pedoclimatic conditions found in the 16 papers. The primary factors influencing ΔpH, ranked by their impact are application rate, time elapsed post-application, and lime characteristics including its grind fineness and neutralizing value. • Random Forest robustly predicts soil pH change over time following lime application. • The predictors are: rate, neutralizing value, particle size, depth, and initial pH. • The model predicts that, on average, lime increases soil pH for 82 weeks. • Machine learning models are promising tools in managing liming practices. [ABSTRACT FROM AUTHOR]

Plant functional traits can serve as indicators of plant resource-use strategies in response to environmental changes. Plants growing in acidified soil exhibit conservative traits and limit growth, but there is still little known about changes in above- and belowground functional traits and their coordination under alleviation of soil acidification. Here, we conducted a pot experiment on raising soil pH by liming in Chinese fir (Cunninghamia lanceolata) saplings in southern China. The experiment involved in two degrees of acidified soil (Mild, pH = 4.3; Severe, pH = 3.6) and three liming treatments: Control (CK, 0), low liming treatment (L, 1000 kg CaO hm−2) and high liming treatment (H, 4000 kg CaO hm−2). We measured 22 above- and belowground functional traits of Chinese fir including allocation, morphological, photosynthetic, and chemical traits to assess their response to liming. The results show that liming enhanced aboveground mass fraction and total leaf area (TLA), and reduced construction cost (lower C concentration). However, specific leaf area (SLA), nutrient concentrations of N and P, and photosynthetic rate (Pn) remained unchanged. These results suggest that aboveground components exhibited acquisitive strategies in response to liming with greater TLA and lower construction cost. Moreover, liming reduced root mass fraction (RMF), increased specific root length (SRL), specific root area (SRA), and root N and Ca nutrient concentrations. These results suggest that belowground components also exhibited acquisitive strategies through constructing longer and thinner roots with greater metabolic rates. Our findings show that liming shifts above- and belowground resource-use strategies of Chinese fir from conservative to acquisitive. These changes in functional traits support the ability of Chinese fir to grow rapidly in response to alleviation of soil acidification. Our research not only contributes to a deeper understanding of plant adaptation mechanisms in the face of environment changes but also provides valuable insights for improving carbon sequestration of plantations in subtropical China. • 22 functional traits of Chinese fir were measured to assess their response to liming. • Liming elevated total leaf area and reduced leaf construction cost. • Liming elevated specific root length, specific root area and root N concentration. • Liming shifts resource-use strategies of Chinese fir towards acquisitive. [ABSTRACT FROM AUTHOR]

Globally, about 50% of all arable soils are classified as acidic. As crop and plant growth are significantly hampered under acidic soil conditions, many farmers, but increasingly as well forest managers, apply lime to raise the soil pH. Besides its direct effect on soil pH, liming also affects soil C and nutrient cycles and associated greenhouse gas (GHG) fluxes. In this meta‐analysis, we reviewed 1570 observations reported in 121 field‐based studies worldwide, to assess liming effects on soil GHG fluxes and plant productivity. We found that liming significantly increases crop yield by 36.3%. Also, soil organic C (SOC) stocks were found to increase by 4.51% annually, though soil respiration is stimulated too (7.57%). Moreover, liming was found to reduce soil N2O emission by 21.3%, yield‐scaled N2O emission by 21.5%, and CH4 emission and yield‐scaled CH4 emission from rice paddies by 19.0% and 12.4%, respectively. Assuming that all acid agricultural soils are limed periodically, liming results in a total GHG balance benefit of 633−749 Tg CO2‐eq year−1 due to reductions in soil N2O emissions (0.60−0.67 Tg N2O‐N year−1) and paddy soil CH4 emissions (1.75−2.21 Tg CH4 year−1) and increases in SOC stocks (65.7–110 Tg C year−1). However, this comes at the cost of an additional CO2 release (c. 624–656 Tg CO2 year−1) deriving from lime mining, transport and application, and lime dissolution, so that the overall GHG balance is likely neutral. Nevertheless, liming of acid agricultural soils will increase yields by at least 6.64 × 108 Mg year−1, covering the food supply of 876 million people. Overall, our study shows for the first time that a general strategy of liming of acid agricultural soils is likely to result in an increasing sustainability of global agricultural production, indicating the potential benefit of liming acid soils for climate change mitigation and food security. [ABSTRACT FROM AUTHOR]

Liming can counteract acidification in forest soils, but the effects on soil C and N pools and fluxes over long periods are less well understood. Replicated plots in an acidic and N-rich 40-year-old Norway spruce (Picea abies) forest in SW Sweden (Hasslöv) were treated with 0, 3.45 and 8.75 Mg ha−1 of dolomitic lime (D0, D2 and D3) in 1984. Between 1984 and 2016, soil organic C to 30 cm depth increased by 28 Mg ha−1 (30% increase) in D0 and decreased by 9 Mg ha−1 (9.4% decrease) in D3. The change in D2 was not significant (+ 2 Mg ha−1). Soil N pools changed proportionally to those in soil C pools. The C and N changes occurred almost exclusively in the top organic layer. Non-burrowing earthworms responded positively to liming and stimulated heterotrophic respiration in this layer in both D2 and D3. Burrowing earthworms in D3 further accelerated C and N turnover and loss of soil. The high soil C and N loss at our relatively N-rich site differs from studies of N-poor sites showing no C and N loss. Earthworms need both high pH and N-rich food to reach high abundance and biomass. This can explain why liming of N-rich soils often results in decreasing C and N pools, whereas liming of N-poor soils with few earthworms will not show any change in soil C and N. Extractable nitrate N was always higher in D3 than in D2 and D0. After 6 years (1990), potential nitrification was much higher in D3 (197 kg N ha−1) than in D0 (36 kg N ha−1), but this difference decreased during the following years, when also the unlimed organic layers showed high nitrification potential. Our experiment finds that high-dose liming of acidic N-rich forest soils produces an initial pulse of soil heterotrophic respiration and increases in earthworm biomass, which together cause long-term declines in soil C and N pools. [ABSTRACT FROM AUTHOR]

Liming materials are widely applied to alleviate soil acidification and increase rice yield in acidic soils, but their effects on nitrogen (N) use efficiency are still unclear. Here, we conducted a field-, pot-, and micro-plot experiment to investigate how the application of slaked lime (i.e., Ca(OH) 2) affects the fate of chemical fertilizer-N and straw-N in a double rice cropping system. In the field experiment, liming increased grain yield and N uptake by an average of 9.0% and 10.6%, respectively. In contrast, CaCl 2 application did not affect rice yield and N uptake, suggesting that the effects of lime application were not related to the addition of Ca2+. Results from a 15N tracer experiment (i.e., 15N-labeled urea and straw) indicated that liming reduced N uptake from fertilizer (−5.7%), but increased N uptake from straw (+31.3%). Liming also reduced soil retention of both urea- and straw-N and increased their loss rates. Taken together, our results indicate that although liming increases rice yield and N uptake, it lowers the use efficiency of fertilizer N and facilitates N losses. In addition, our results emphasize the need for long-term studies on the impact of liming on soil N dynamics in paddy soils. • Liming of an acidic rice paddy soil increased both rice yield and N uptake. • Addition of Ca2+ did not affect rice yield and N uptake. • Liming reduced N uptake from fertilizer but increased that from straw. • Liming reduced soil retention of both urea- and straw-N and increased their loss rates. [ABSTRACT FROM AUTHOR]

• Lime input significantly decreased topsoil exchangeable potassium (EK) content. • The initial EK and acidic degrees were the key factors of effect on EK decrease. • Liming enhances the excavate and uptake of subsoil EK by crop roots in Ultisol. • Soil Ca, Al, and initial EK jointly regulate the Ultisol K availability after liming. Potassium (K) is the most commonly neglected macronutrient in global change, especially in acidified areas. Lime is a typical management to eliminate soil acidification in agroecosystem soils; however, its impact on soil K dynamics remains inconsistent under different acidic environments. Here, we combine a meta-analysis based on 407 observations from 89 papers and a long-term experiment to investigate the effect and main driving factors of liming on soil K change. The meta-analysis showed that lime application significantly reduced topsoil exchangeable K (EK) content by an average of 4.8% globally. The decrease in topsoil EK content due to liming depended on various soil properties, crop types, fertilizer regimes, and experiment types. Boosted regression tree analysis showed that initial soil exchangeable K (IEK) and pH were the main factors affecting soil EK change under the lime application. The field experiment results further evidence that the decrease of soil EK after the lime application was mainly due to increased K uptake by the crop, and EK transformed to non-exchangeable K (NEK). The application of lime has a greater impact on reducing subsoil EK content at a higher IEK thresholds. Soil EK showed a significant negative relationship with exchangeable calcium (Ca) and a significant positive relationship with exchangeable aluminum (Al). Redundancy analysis revealed that K input (KI), IEK, lime, Ca, Al, pH, and exchangeable magnesium significantly affected the K in soil and crops. The partial least squares path model showed that lime application and IEK levels combined indirectly influence soil K (EK and NEK) by directly affecting soil Ca and Al, K uptake, and K balances. The findings highlight the importance of the lime effect on K management in globally adverse environmental agroecosystems and indicate the key role of initial soil EK levels and acidification degree for regulating crops to excavate the subsoil potassium when subjected to liming. [ABSTRACT FROM AUTHOR]

Low phosphorus (P) constrains productivity of many of the permanent pastures of south-eastern Australia where wool and meat production are important. Whereas the need for fertilisation with P is indisputable for many soils, the benefits of liming to ameliorate soil acidification are not always clear in terms of forage production or quality. This experiment, by measuring botanical composition and groundcover over 10 years, aimed to address the issue of forage composition and groundcover. Merino wethers were continuously grazed on a permanent pasture under two stocking rates (low and high) following treatments with three rates of surface-applied lime and two rates of P. The lime rates were: nil, and sufficient to raise the pHCaCl2 of the 0–10 cm soil layer to 5.0 and to 5.5. Phosphorus was added as two rates of single superphosphate: 125 kg ha–1 every 2–3 years, and 250 kg ha–1 every year. Two hypotheses were proposed: (i) as lime application rate increased, it would lead to the pasture swards having a higher percentage of species favourable for grazing animal production, and a higher level of sward groundcover would be maintained; and (ii) legume presence would be favoured by a higher level of applied P over the long term. The Millennium Drought (1997–2008), which coincided with this experiment (1998–2008), tended to mask or reduce lime effects; nevertheless, the higher legume content in the sward, as well as the superior groundcover found in the high lime–high P treatments at various times throughout the experiment and at its completion compared with the nil-lime control, indicated positive forage effects of lime application. Moreover, by the termination of the experiment in 2008, groundcover generally tended to be lower under nil lime than in treatments that had received lime. The higher proportion of legume in the sward was closely linked to greater applied P, although this did not occur at the low stocking rate in the absence of lime. By contrast, similar high P–low stocking rate treatments but with applied lime had the highest clover contents. It is proposed that the poor persistence of the treatment without lime may be due to a combination of poor legume seedset, because of excessive competition from accompanying grasses, and aluminium toxicity adversely affecting legume growth. Soil acidity is a serious problem reducing the production of crops and grazing animals, and although lime can reduce acidity, it is expensive because high rates are required. This research follows the effect of lime on the pasture composition of desirable legumes and perennial grasses. The higher legume content in the sward found in high lime–high phosphorus treatments at times throughout the experiment and at its completion compared with the nil-lime control indicated the value of lime application. [ABSTRACT FROM AUTHOR]

Many agricultural soils are naturally acidic, and agricultural production can acidify soil through processes such as nitrogen (N) fixation by legumes and application of N fertiliser. This means that decisions about mitigation of soil acidity (e.g. through application of lime), crop rotation and N fertiliser application are interdependent. This paper presents a dynamic model to determine jointly the optimal lime application strategies and N application rates in a rainfed cropping system in Western Australia. The model accounts for two crop rotations (with and without a legume break crop), for the acid tolerance of different crop types, and for differences in the acidifying effect of different N fertilisers. Results show that liming is a profitable strategy to treat acidic soils in the study region, but that there are interactions between N and acidity management. Choice of fertiliser affects optimal lime rates substantially, with the use of a more acidifying ammonium-based fertiliser leading to higher lime rates. The optimal liming strategy is also sensitive to inclusion of a legume crop in the rotation, because its fixed N can be less acidifying than fertiliser, and it allows a reduction in fertiliser rates. Higher rainfall zones have greater N leaching, which contributes to a higher optimal rate of lime. We find that injection of lime into the subsoil increases profit. Optimal lime rates in the absence of subsoil incorporation are higher than usual current practice, although the economic gains from increasing rates are small. [ABSTRACT FROM AUTHOR]

Mid‐infrared spectroscopy (MIRS) has proven to be a cost‐effective, high throughput measurement technique for soil analysis. After multivariate calibration mid‐infrared spectra can be used to predict various soil properties, some of which are related to lime requirement (LR). The objective of this study was to test the performance of MIRS for recommending variable rate liming on typical Central European soils in view of precision agriculture applications. In Germany, LR of arable topsoils is commonly derived from the parameters organic matter content (SOM), clay content, and soil pH (CaCl2) as recommended by the Association of German Agricultural Analytical and Research Institutes (VDLUFA). We analysed a total of 458 samples from six locations across Germany, which all revealed large within‐field soil heterogeneity. Calcareous topsoils were observed at some positions of three locations (79 samples). To exclude such samples from LR determination, peak height at 2513 cm−1 of the MIR spectrum was used for identification. Spectra‐based identification was accurate for carbonate contents > 0.5%. Subsequent LR derivation (LRSPP) from MIRS‐PLSR predictions of SOM, clay, and pH (CaCl2) for non‐calcareous soil samples using the VDLUFA look‐up tables was successful for all locations (R2 = 0.54–0.82; RMSE = 857–1414 kg CaO ha−1). Alternatively, we tested direct LR prediction (LRDP) by MIRS‐PLSR and also achieved satisfactory performance (R2 = 0.52–0.77; RMSE = 811–1420 kg CaO ha−1; RPD = 1.44–2.08). Further improvement was achieved by refining the VDLUFA tables towards a stepless algorithm. It can be concluded that MIRS provides a promising approach for precise LR estimation on heterogeneous arable fields. Large sample numbers can be processed with low effort which is an essential prerequisite for variable rate liming in precision agriculture. [ABSTRACT FROM AUTHOR]

The dual role of biochar for inhibiting soil acidification induced by nitrification was determined through two-step incubation experiments in this study. Ca(OH) 2 or biochar was added respectively to adjust soil pH to the same values (pH 5.15 and 5.85), and then the amended soils were incubated in the presence of urea for 70 days. The results showed that compared with Ca(OH) 2 treatment, both rice straw biochar and peanut straw biochar inhibited the decrease in soil pH and the increase in exchangeable acidity during the incubation. The application of biochars suppressed soil nitrification during the incubation, and thus reduced 7.5 mmol kg−1 and 1.4 mmol kg−1 protons released from nitrification compared to Ca(OH) 2 treatments. Compared with Ca(OH) 2 treatment, the ammonia-oxidizing bacteria population size was decreased by 8% and 12% in rice straw biochar and peanut straw biochar treatments respectively, which was the main responsibility for the inhibited nitrification after biochar application. In addition, the application of rice straw biochar and peanut straw biochar increased soil pH buffering capacity (pHBC) respectively by 22% and 32%. The increased pHBC played the main role (75%) in inhibiting the acidification of the soil amended with peanut straw biochar, while the rice straw biochar inhibited soil acidification mainly through suppressing nitrification during the incubation. Overall, compared with lime application, biochars can inhibit soil acidification caused by urea application through suppressing the nitrification process and improving the resistance of soils to acidification. The crop residue biochars presented a longer-lasting effect on ameliorating acidic soils than mineral lime. Image 1 • Biochar played a dual role in inhibiting soil acidification from nitrification. • Biochar decreased proton release through suppressing soil nitrification. • Biochar increased soil pH buffering capacity and the resistance to acidification. • Biochar would be a better option to ameliorate acidic soils than liming. [ABSTRACT FROM AUTHOR]

Acidification of soils is one of the most important soil degradation processes and this type of soils can be provisionally remediated towards increasing soil fertility by liming practices. However, Ca / Mg containing liming materials cannot be used in areas where perennial calcifuge plants are present. The aim of this study is to determine the ability of materials such as milled fine-grained forms of zeolite and feldspar with alkaline character to neutralize acid ions in soil environment. The ability to buffer H ions was determined by equilibrating HCl solution at varying concentrations with zeolite samples having a particle size of 1-0.5 mm, 0.5-0.25 mm and 0.1 mm and feldspar with a particle size <0.1 mm. The titration curves of the zeolite samples were found to vary significantly depending on the particle size and all zeolite sizes had better buffering ability than the feldspar. As a result, it has been concluded that zeolite and feldspar can be used as an alternative liming material for calcifuge plants both in remediating the acidity and in improving the chemical properties of soils. [ABSTRACT FROM AUTHOR]

Abstract An 18-year field experiment was conducted on a highly acidic soil in the mixed farming zone of south-eastern Australia. The experiment was a fully phased design with three major treatment contrasts: perennial systems versus annual systems; unlimed versus limed treatments; and permanent pasture versus pasture-crop rotations. The hypotheses tested in this study were that a) perennial systems would be less acidifying than annual systems, and b) surface liming would lead to amelioration of subsurface soil acidity over time. Results showed that there was no significant difference in soil pH in terms of acidification rate and amelioration rate between perennial and annual systems, thus we rejected the first hypothesis. However, both perennial and annual systems did acidify or re-acidify soil. The re-acidification rate was at least 0.09 pH units per year in the 0–0.10 m depth under the limed treatment. The acidification rate was 0.005 pH units per year in the 0.10–0.20 m depth under the unlimed treatment. The vigorous lime regime of maintaining pH ≥5.5 (measured in 0.01 M CaCl 2) in the 0–0.10 m depth increased soil pH in the 0.10–0.20 m depth at a rate of the 0.04 pH units per year, hence we accepted the second hypothesis. There was clear evidence of alkali movement vertically over time, but it was confined within the top 0.30 m depth over the 18-year period of experiment. It is recommended that soil should be limed regularly to maintain pH ≥5.5 to keep the system productive and sustainable. Highlights • Both perennial and annual systems acidify soil in depths at a similar rate. • Surface liming can alleviate subsurface (below 0.10 m) soil acidity. • Soil re-acidification rate is 0.09 pH units per year in the 0–0.10 m depth. • Soil acidity amelioration rate is 0.04 pH unit per year in the 0.10–0.20 m depth. • Soil should be limed regularly to maintain pH ≥5.5 to keep the system productive and sustainable. [ABSTRACT FROM AUTHOR]

Chemical fertilizer application is a common agronomic practice to improve crop productivity and liming is often used to counteract the soil acidification caused by long-term fertilization; however, it is unclear whether liming will counteract the effect of long-term fertilization on soil bacterial community structure and its co-occurrence pattern. Here, we examined the influence of long-term fertilization (NPKS) and liming (L) on soil bacterial community structure and its co-occurrence networks by sequencing 16S rRNA gene amplicons. Our results showed that liming counteracted the influence of long-term fertilization on soil pH, but not on soluble organic carbon (SOC) and electrical conductivity (EC). Long-term fertilization affected the abundance of Acidobacteriia, Deltaproteobacteria and Gammaproteobacteria in the 0–10 cm soil, and that of Deltaproteobacteria, Gammaproteobacteria and Gemmatimonadetes in the 10–20 cm soil; whereas liming affected the abundance of Acidobacteriia, Gammaproteobacteria, and Chloracidobacteria in the 0–10 cm soil and that of Deltaproteobacteria in the 10–20 cm soil. The bacterial community structure in soils with the NPKS-L treatment was different from that with other treatments, and was mainly affected by SOC, EC, and NO 3 − concentration. The link numbers in bacterial co-occurrence networks were decreased by long-term fertilization or liming alone, but were increased by the NPKS-L treatment. Notwithstanding the fact that liming alleviates fertilization-induced soil acidification, this study indicates that liming did not counteract the effect of long-term fertilization on soil bacterial community structure and its co-occurrence pattern, hence cannot recuperate the soil microbial functionality that is changed by long-term fertilization. [ABSTRACT FROM AUTHOR]

• Liming and labile C addition interacted to affect N 2 O emission. • Liming reduced N 2 O emission by 13–28% compared to unlimed soil following labile C addition. • Liming reduced the Q 10 of N 2 O following labile C addition. • Labile C addition facilitated denitrification. • N 2 O emission was positively related to (nirK + nirS)/(nosZI + nosZII) ratio and NO 3 − consumption. Lime has been widely applied for ameliorating soil acidification, potentially improving soil fertility and crop production. However, the long-term effects of liming and its interaction with carbon (C) availability on the emission and temperature sensitivity (Q 10) of greenhouse gas nitrous oxide (N 2 O) from acidic arable soil are not well understood. Here, the limed and unlimed acidic soils collected from a long-term field trial, amended with and without glucose as labile C, were incubated at 15℃ and 25℃ to investigate the responses of the emission and Q 10 of N 2 O and the underlying mechanisms. Results showed that liming had no effect on N 2 O emission without labile C addition. While after labile C addition, N 2 O emissions were 13–28% lower in the limed relative to unlimed soils, indicating that the mitigation effect of liming on N 2 O emission can mainly be seen when labile C (e.g., from rhizodeposition) is highly available in soils. High temperature did not affect N 2 O emissions from soil without labile C addition, but greatly increased N 2 O emissions after labile C addition with significantly lower Q 10 of N 2 O in the limed (1.23) relative to unlimed soils (1.48). These results suggested that liming could decrease the Q 10 of N 2 O emission in the presence of labile C. Elevated soil pH by liming caused increases in the abundances of N 2 O reductase genes (nosZI and nosZII) over nitrite reductase genes (nirK and nirS), thus significantly lowering (nirK + nirS)/(nosZI + nosZII) ratio compared to the unlimed soil, particularly after labile C addition. Soil N 2 O emissions were strongly positively related to the nirK abundance, (nirK + nirS)/(nosZI + nosZII) ratio, and NO 3 − consumption after labile C addition, indicating that denitrification was mostly responsible for N 2 O emission. Concluding, long-term liming could potentially reduce N 2 O emission and its Q 10 via decreased (nirK + nirS)/(nosZI + nosZII) ratio in acidic soils in the presence of labile C. [ABSTRACT FROM AUTHOR]

• Accurate and rapid method to measure low concentrations (>0.5%) of inorganic carbon established. • Detection and prediction of inorganic carbon can be used to measure agricultural lime in soils. • Various lime sources can be detected and measured in different soil types and depths. • This method can be used to monitor lime movement and assist with management of acidic soils. • Infrared Spectroscopy approach is a viable alternative to traditional laboratory methods. Globally, surface and subsurface soil acidity pose a serious threat to crop production and require effective management to prevent yield losses. The application of lime (calcium carbonate, CaCO 3) is a well-recognised remediation technique for surface soil acidity. However, for subsurface acidity, improved application and detection methods are required to manage acidity due to the stratification of acidic layers. Mid infrared (MIR) spectroscopy has potential as a rapid, cost effective and accurate method of CaCO 3 detection in soils. However, for this technology to be valuable in an agricultural context, there is a need to develop MIR spectroscopy methods for the detection of CaCO 3 at agriculturally relevant concentrations of <1%, which was the aim of this study. MIR Partial Least Square Regression (PLSR) carbonate prediction models were developed using carbonate-specific spectral regions to predict CaCO 3 concentrations in soil. Prediction models were initially developed using a single soil type spiked with reagent grade CaCO 3 and were tested further with soils collected from field trials that had been treated with various rates and sources of lime. Prediction models using specific carbonate peak regions were established and compared with models using the entire MIR spectrum to assess the model performance. Models built using a single peak range at 2560–2460 cm−1 gave the best results (highest R2 values and lowest RMSE values) followed by the single peak range at 1840–1760 cm−1. Specifically, model performance was improved when developed with a single soil type and reagent grade CaCO 3 in the 2560–2460 cm−1 spectral region, with PLSR R2 of 0.834 and RMSE of 0.030. Performance was reduced but still satisfactory (R2 of 0.735 and RMSE of 0.069) when applied to field trial soils using a range of different lime sources, including dolomitic lime. The MIR method enabled accurate prediction of carbonate concentrations and had a detection limit of 0.05% CaCO 3 , similar to what can be achieved using a pressure calcimeter. Findings suggest that MIR spectroscopy measurements of agriculturally applied CaCO 3 in soils may provide valuable insights into monitoring the movement and efficacy of lime treatments and will enable more informed lime applications in the future. The method may also be used to detect naturally-occurring carbonates at low concentrations and may be useful for rapid isolation of inorganic carbon from organic carbon in soil carbon measurements and carbon accounting. [ABSTRACT FROM AUTHOR]

In the last decades, the Masson pine (Pinus massoniana) forests in Chongqing, southwest China, have increasingly declined. Soil acidification was believed to be an important cause. Liming is widely used as a measure to alleviate soil acidification and its damage to trees, but little is known about long-term effects of liming on the health and growth of declining Masson pine forests. Soil chemical properties, health condition (defoliation and discoloration), and growth were evaluated following application of limestone powder (0 (unlimed control), 1, 2, 3, and 4 t ha−1) in an acidified and declining Masson pine stand at Tieshanping (TSP) of Chongqing. Eight years after liming, in the 0–20 cm and 20–40 cm mineral soil layers, soil pH values, exchangeable calcium (Ca) contents, and Ca/Al molar ratios increased, but exchangeable aluminum (Al) levels decreased, and as a result, length densities of living fine roots of Masson pine increased, with increasing dose. Mean crown defoliation of Masson pines (dominant, codominant and subdominant pines, according to Kraft classes 1–3) decreased with increasing dose, and it linearly decreased with length densities of living fine roots. However, Masson pines (Kraft classes 1–3) in all treatments showed no symptoms of discoloration. Mean current-year twig length, twig dry weight, needle number per twig, needle length per twig, and needle dry weight per twig increased with increasing dose. Over 8 years, mean height increment of Masson pines (Kraft classes 1–3) increased from 5.5 m in the control to 5.8, 6.9, 8.3, and 9.5 m in the 1, 2, 3, and 4 t ha−1 lime treatments, and their mean DBH (diameter at breast height) increment increased from 3.1 to 3.2, 3.8, 4.9, and 6.2 cm, respectively. The values of all aboveground growth parameters linearly increased with length densities of living fine roots. Our results show that liming improved tree health and growth, and these effects increased with increasing dose. [ABSTRACT FROM AUTHOR]

Soil acidification is a global issue that significantly reduces crop productivity. Lime application is a viable agricultural strategy to ameliorate soil acidification. However, the knowledge of the impact of lime application on the soil microbiome is still limited. Therefore, the objective of this study was to investigate the diversity, structure, and compositions of the soil bacterial community after liming on wheat fields. We established winter wheat plots in two precipitation zones, Pendleton and Moro in Oregon, facing soil acidity stress, and conducted bacterial microbiome analysis after lime application using Illumina MiSeq. Soil pH increased with increasing rates of lime amendments in the surface soil (0–7.5 cm) but did not significantly change in deeper soil (7.5–15 and 15–22.5 cm). High-throughput sequencing results revealed that liming had marginally effects on soil bacterial communities. A few bacterial families, including Cytophagaceae, Flavobacteriaceae, Intrasporangiaceae, Phyllobacteriaceae, Propionibacteriaceae, Pseudomonadaceae, and Sphingobacteriaceae, were correlated with lime application. In contrast, location and soil depth had a strong effect on soil bacterial communities. In addition, the impacts of liming on soil bacterial diversity and taxa were inconsistent and location- and soil depth-dependent. Furthermore, four nitrifiers were quantitated from all samples by qPCR assay. Ammonium oxidizing bacteria (AOB) and Nitrobacter were most abundant in the topsoil, while ammonia oxidizing archaea (AOA) and Nitrospira were more abundant in deeper soil. Only Nitrospira was significantly influenced by soil pH. Overall, these results suggest that location, soil depth, lime amendments, and their interactions have significant impacts on the soil bacterial community that may influence plant health and crop yields. [ABSTRACT FROM AUTHOR]

An 8-year field study measured soil pH changes annually at various depth increments. Limestone was applied to tilled and untilled field strips annually for 8 years at either a 2.0 Mg/ha rate (100% calcium carbonate efficiency) and once every 4 years at the 8.0 Mg/ha rate (100% calcium carbonate efficiency), or as a water-treatment-plant limestone by-product in two replicated field trials. Liming materials increased soil pH in the 0- to 5-cm and 5- to 10-cm depths with time in untilled soils. Incorporated liming materials increased soil pH faster at the 5- to 10-cm depth and increased soil pH at the 10- to 15-cm depth. Mean maize and soybean grain yields increased for all liming materials, and maize ear leaf P and soybean shoot P and Ca increased after liming at the last year of the study. Consistent surface applications of liming materials without incorporation can mitigate acidification and improve crop yields in highly buffered soils. [ABSTRACT FROM AUTHOR]

Abstract: Nitrous oxide (N2O) is a potent greenhouse gas contributing to global radiative forcing. Grazed legume pasture is one of the major agricultural land uses in southern Australia and no N2O emission studies have been undertaken previously on this system. A study over 1 year has been undertaken measuring N2O emissions from legume pasture at Wagga Wagga, Australia. The study was embedded within a larger on-farm study of the management of acid soils. Sampling involved simultaneous N2O emission measurements on two paddocks each of: acidic soil with pH 4.0; limed soil with soil pH 5.5, and limed soil with addition of 20gNm−2 of animal urine. The average emission of N2O from the acidic legume pasture was 0.35kgNha−1 y−1 with a standard error of 0.03kgNha−1 y−1. Isotope measurements indicated that in aerobic conditions the ratio of N2O emissions to gross mineralisation was 0.01–0.05%. Liming did not make a significant change to the average N2O emissions. The average of daily N2O emissions are: for the acidic plots 0.96±0.07mgNm−2 d−1 and for the limed plots 0.88±0.04mgNm−2 d−1. We conclude that under the conditions experienced at Wagga Wagga, which are typical of many Australian pastures, liming does not change the N2O emissions. Measurements from the urine-treated soil showed that between 0.1 and 0.2% of the nitrogen in the urine was released as N2O. These and a compilation of other emission factors for N2O emissions from urine addition to pasture give a median emission factor of 0.7%, significantly smaller than the two default values of 2% and 1% recommended by the Revised 1996 and the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. [Copyright &y& Elsevier]

Arbuscular mycorrhizal fungi (AMF) are important in plant nutrient uptake, but their function is prone to environmental constraints including soil factors that may suppress AMF transfer of phosphorus (P) from the soil to the plant. The objective of this study was to disentangle the biotic and abiotic components of AMF-suppressive soils. Suppression was measured in terms of AMF-mediated plant uptake of 33P mixed into a patch of soil and treatments included soil sterilization, soil mixing, pH manipulation and inoculation with isolated soil fungi. The degree of suppression was compared to volatile organic compound (VOC) production by isolated fungi and to multi-element analysis of soils. For a selected suppressive soil, sterilization and soil mixing experiments confirmed a biotic component of suppression. A Fusarium isolate from that soil suppressed the AMF activity and produced greater amounts than other fungal isolates of the antimicrobial VOC trichodiene (a trichothecene toxin precursor), beta-chamigrene, alpha-cuprenene and p-xylene. These metabolites deserve further attention when unravelling the chemical background behind the suppression of AMF activity by soil microorganisms. For the abiotic component of suppression, soil liming and acidification experiments confirmed that suppression was strongest at low pH. The pH effect might be associated with changed availability of specific suppressive elements. Indeed 33P uptake from the soil patches correlated negatively to Al levels and Al toxicity seems to play a major role in the AMF suppressiveness at pH below 5.0–5.2. However, the documentation of a biotic component of suppression for both low and high pH soils leads to the conclusion that biotic and abiotic components of suppression may act in parallel in some soils. The current insight into the components of soil suppressiveness of the AMF activity aids to develop management practices that allow for optimization of AMF functionality. • In some soils, suppression of AMF activity had a biotic component. • A Fusarium isolate from a suppressive soil inhibited the AMF activity. • This isolate produced greater amounts of antimicrobial VOCs than other isolates. • AMF suppression increased at low pH across several soils. • For these soils, Al toxicity played a major role in suppressiveness at pH ≤ 5.0 [ABSTRACT FROM AUTHOR]

The potential effect of acidification of contaminated sandy soils on Cd transport in the unsaturated zone was assessed. Forty-eight soil profiles were sampled at five depths in a polluted field that was set aside in 1992. The Cd concentration in the top 30 cm of this field was, on average, 10 mg kg−1. A column experiment was carried out with one of the topsoil samples. Homogeneously packed columns were leached with 0.001m CaCl2, adjusted to pH 3 or pH 5.7, at a pore water velocity of 6 cm day−1. The Cd and proton transport was predicted with coupled transport equations. The Cd transport was modelled by assuming local equilibrium and by using sorption parameters derived from batch experiments, while acidification was modelled with a kinetic approach, on the assumption that proton buffering was due to cation exchange and mineral weathering. Organic matter was the main contributor to the cation exchange capacity of these soils. Observed and predicted pH and Cd profiles in the columns agreed well. With the same model, the proton and Cd transport at field scale was calculated for each of the 48 profiles sampled (‘grid model’). It was predicted that the field-averaged Cd concentration in the seepage water will increase from 6 μg litre−1 at present to 200 μg litre−1 over 260 years, which greatly exceeds the maximum permissible concentration (MPC) in groundwater of 5 μg litre−1. Predictions of Cd transport using field-averaged soil properties yielded a later breakthrough time and a larger peak Cd concentration than predicted with the grid model, which illustrates the impact of spatial variability on solute transport. Continuation of liming practices is a possible solution to prevent breakthrough of Cd at concentrations far in excess of the MPC. [ABSTRACT FROM AUTHOR]

Discusses the influence of liming on soil acidification and other processes. Process of acid generation in soils; Effect of soil acidity on nutrient and heavy metal transformation in soils; Amelioration of soil acidity through liming; Interactions among lime, nutrient and heavy metal in soil.

Liming is widely used to ameliorate acidic soils. However, few studies have addressed the effects of different lime application rates on soil microbial communities. Specifically, the effects of liming on fungal communities remain largely unknown. Here, we set up a gradient of increasing lime application rates, 0, 450, 900, 1350, 1800, 2250, 3000, and 3750 kg ha−1, to investigate the effects of lime inputs on soil properties and community diversity and composition of prokaryotes and fungi in paddy soils. Our results showed that the effect of liming on soil pH improvement become insignificant when the application rate exceeded 1800 kg ha−1. Prokaryotic diversity and community composition were both significantly influenced by liming, whereas fungal communities were less responsive. Nonetheless, the promotive effects of liming on soil prokaryotic diversity declined when lime application rates exceeded 900 kg ha−1 (or pH > 6.5). Soil pH was the key factor shaping the prokaryotic community, while pH and SOM were both important in explaining the observed variation in fungal communities. Distinct responses of ammonia oxidizing archaea (AOA) lineages were also observed as pH increased. Our results provide insights into the complex responses of both prokaryotic and fungal communities to lime application in paddy soils, and suggest that the amount of lime applied is also important for maintaining a healthy and sustainable soil environment. • Prokaryotes were more responsive to liming than fungi. • Liming effects on prokaryotes vanished when application rates exceeded 900 kg ha−1. • AOA lineages showed distinct responses to increasing lime inputs. • pH was the key factor shaping the prokaryotic community. • Fungal community diversity and composition were linked to both pH and SOM. [ABSTRACT FROM AUTHOR]

Soil acidification affects crop yields which can diminish farmers' incomes. Whilst soil pH can easily be increased by application of lime, in practice application must be economically viable with yield benefits offering an acceptable return on investments. Liming is a long-term investment with benefits becoming apparent over multiple years. Long-term economic strategies can be problematic for farmers who lack investment capital and who may have short-term decision time frames, such as most smallholder farmers in sub-Saharan Africa. In addition, application of lime causes substantial greenhouse gas (GHG) emissions (especially CO 2). It is currently unclear how liming affects GHG emissions per tonne of maize, in cases where liming increases crop yields. In this study, we assessed if liming acid soils is economically and environmentally viable at different levels of intensification for maize cultivation in Western Kenya. First, a meta-analysis using a regression analysis was conducted to quantify effects of lime application on soil pH and maize yields based on 26 field experiments. Related effects on farm profit and and returns on investment were estimated for a period of five years for soils with varying levels of initial soil pH and fertiliser application. Finally, synergies and trade-offs were assessed between maize yields, economic benefits and GHG emissions. Liming consistently increased maize yields on soils with an initial soil pH between 4.0 and 5.7 in Western Kenya, with or without fertiliser use. For a soil pH of 5, applying 2 t ha−1 lime resulted in a significant increase in maize yields of 57% (from 2.3 to 3.6 t ha −1) in the first year after application. Despite these positive effects on yield, associated profits – when including costs of labour - were only positive when liming was combined with fertiliser (N,P) application. While liming causes substantial GHG emissions per tonne lime applied, these were offset when expressing GHG emissions per tonne of grain maize, due to the observed yield increases. The pay-back period for lime investments was at least two years. Our analysis shows that liming has potential co-benefits for food security and the environment in tropical acid soils, but we expect uptake by farmers to be unlikely without external incentives, at least in Western Kenya. [Display omitted] • Liming consistently increased maize yields for soil pH values between 4.0 and 5.7. • Average observed increase in maize yields was 57% (with 2 t ha −1 lime). • Associated profits were only positive with fertiliser (N,P) application. • Returns on liming investments payed off only after at least two years. • Yield increases prevented an increase in greenhouse gas emissions per tonne maize. [ABSTRACT FROM AUTHOR]

Plots in a beech-forest in southern Sweden were artificially limed with 2, 5 and 10 tonnes of dolomite lime ha-&sup-1;. Snail populations were sampled. The population increases correlated with lime dosages. In plots treated with 10t ha-¹, mean densities increased 4–40 times, depending on the species (5 years after liming). There were highly significant correlations between snail density and pH, Ca concentration, base cation concentration and base saturation; however, the correlations between nitrogen, phosphorus and potassium were very low. The results indicate that liming positively effects land snail population densities in relatively nutrient-poor deciduous forests. [ABSTRACT FROM AUTHOR]

Despite being a natural soil-forming process, soil acidification is a major agronomic challenge under humid climate conditions, as soil acidity influences several yield-relevant soil properties. It can be counterbalanced by the regular application of agricultural lime to maintain or re-establish soil fertility and to optimize plant growth and yield. To avoid underdose as well as overdose, lime rates need to be calculated carefully. The lime rate should be determined by the optimum soil pH (target pH) and the response of the soil to lime, which is described by the base neutralizing capacity (BNC). Several methods exist to determine the lime requirement (LR) to raise the soil pH to its optimum. They range from extremely time-consuming equilibration methods, which mimic the natural processes in the soil, to quick tests, which rely on some approximations and are designed to provide farmers with timely and cost-efficient data. Due to the higher analytical efforts, only limited information is available on the real BNC of particular soils. In the present paper, we report the BNC of 420 topsoil samples from Central Europe (north-east Germany), developed on sediments from the last ice age 10,000 years ago under Holocene conditions. These soils are predominantly sandy and low in humus, but they exhibit a huge spatial variability in soil properties on a small scale. The BNC was determined by adding various concentrations of Ca(OH)2 and fitting an exponential model to derive a titration curve for each sample. The coefficients of the BNC titration curve were well correlated with soil properties affecting soil acidity and pH buffer capacity, i.e., pH, soil texture and soil organic matter (SOM). From the BNC model, the LRs (LRBNC) were derived and compared with LRVDLUFA based on the standard protocol in Germany as established by the Association of German Agricultural Analytic and Research Institutes (VDLUFA). The LRBNC and LRVDLUFA correlated well but the LRVDLUFA were generally by approximately one order of magnitude higher. This is partly due to the VDLUFA concept to recommend a maintenance or conservation liming, even though the pH value is in the optimum range, to keep it there until the next lime application during the following rotation. Furthermore, the VDLUFA method was primarily developed from field experiments where natural soil acidification and management practices depressed the effect of lime treatment. The BNC method, on the other hand, is solely based on laboratory analysis with standardized soil samples. This indicates the demand for further research to develop a sound scientific algorithm that complements LRBNC with realistic values of annual Ca2+ removal and acidification by natural processes and N fertilization. [ABSTRACT FROM AUTHOR]

Soil acidification is one of the major global drivers of soil degradations this negative effect cause that soils becoming less useful for food production. Soil acidification leads to loss of base cations, increase of toxic heavy metals, unavailability of nutrients, structural deterioration of soil, and reduction of soil biological activity. The solution to the problem of soil acidification may be limning. It is a long established practice, and its effectiveness depends on the composition, reactivity and fragmentation of the lime material added. Although the effect of limning have been known for centuries, agriculture continues to develop and change this method. The aim of the study was to investigate the influence of very fine-powdered lime on soil properties such as: pHKCl, dehydrogenases activity (DHA) and sorption properties.Soil samples were taken from the 0-20 cm depth. Samples, during incubation, were analysed for soil pH, DHA and sorption properties. Incubation experiment were conducted on three soils of different texture (silty loam, sandy loam and clay loam). Limning treatment consisted of very fine-powdered CaCO3 (below 0.08 mm), applied with dose calculated for 0.5 hydrolytic acidity of soil; a no-lime treatment served as control. Soil samples were stored in polyethene boxes and kept in the laboratory at 24±2°C for 150 days; while maintaining moisture at the level of 60% of the water holding capacity. Soil properties were measured after 3, 5, 7, 15, 30, 60, 90, 120, 150 days of incubation. The average increase of pH after application of lime was 0.5, 0.6, 0.3 units for silty loam, sandy loam and clay loam soils respectively. On the sandy loam soil was observed significantly decrease pHKCl value after 30 days of incubation. The same relation was noted for silty loam and clay loam soils, but this effect was observed after 60 days of incubation. On the all types of soils greater DHA was found in lime-treated than in no-limed soils, however DHA decreased over time. Liming significantly improved sorption properties of soils, especially sandy loam soil, in which base saturation increased on average form 57.6% to 92.2%. These studies show that use very fine-powdered lime is effective and fast way of decreasing soil acidity, increasing dehydrogenases activity and sorption properties of soil.This research was financed by the Ministry of Science and Higher Education of the Republic of Poland, No. BM – 2128/18 and Czatkowice Mine BZ – 4118/18. [ABSTRACT FROM AUTHOR]

Nitrogen (N) fertilization is a worldwide indispensable agricultural practice serving the survival of half of global population. Nitrogen transformation in soil as well as plant N uptake leads to release of protons and enhances soil acidification. Neutralization of this acidity in carbonate-containing soils (7.94 109 ha; ca. 54% of global land surface area) results in CO2 release corresponding to 0.21 kg C per kg applied N. Based on the global N fertilization map and the distribution of soils containing CaCO3, we calculated the annual amount of CO2 released from carbonates as 7.48 1012 g C y-1. These baseline levels of continuous CO2 release will remain until N fertilization occurs. In the second half of the study, we estimated that about 273 1012 g C are released annually in the same process of CaCO3 neutralization by liming of acidic soils, a common agricultural practice to revitalize over-fertilized fields. These two CO2 sources correspond to 3% of global CO2 emissions by fossil fuel combustion or 30% of CO2 by land use changes. However, the duration of CO2 release after land use changes usually takes only 1-3 decades before a new C equilibrium is reached in soil. In contrast, the CO2 released by CaCO3 acidification cannot reach equilibrium until it is completely neutralized, which will take centuries or even millennia. This promotes limiting soil acidification as an effective strategy for inhibiting millennial CO2 efflux to the atmosphere. Hence, N fertilization should be plant demand-specific to prevent over fertilization, not only because of its role in local eutrophication, but also this newfound role of continuous CO2 release by global acidification.Key words: CO2 efflux, global acidification assessment, global warming, mitigation policy, nitrogen fertilization, soil acidification mechanisms, soil inorganic carbon [ABSTRACT FROM AUTHOR]