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[Display omitted] • 5 RDs neutralise 500 up to 10 000 mmol H+/kg, variation in mineralogy and target pH. • Automatic titration (pH stat) estimates pH-dependent dissolution rates and slopes. • Novel soil-RD suspension estimates fast/slow pools of acid neutralising capacity. • Low and high doses (12 Mg/ha, 340 Mg/ha) for validation in 2 year soil-RD mesocosm. • Mechanistic model using pH stat and soil-RD suspension predicts mesocosm soil pH. The ongoing acidification of soil poses a significant threat to the proper functioning of various ecosystems worldwide. Silicate rock dusts (RD) are increasingly amended to acid soils to restore their pH, but the acid neutralising capacity (ANC) and dissolution rate of these products are highly variable and lack proper assessment protocols. It is expected that pH-dependent RD ANCs and dissolution rates dictate the pH increase in soils depending on the initial pH and pH buffer power of the soil. This study addressed these questions by comparing and validating three accelerated weathering tests for their capacity to predict the gradual liming effects in a two-year outdoor mesocosm. Five commercial RDs (two basalts, phonolite, foidite, and trachy-andesite) were tested in four acidified forest soils varying in initial pH, in texture and associated pH buffer power. First, RD dissolution was measured in aqueous batch renewal systems during one year at various starting pH (3.5, 4.5, and 5.5) and constant temperatures (20 °C, 37 °C, and 65 °C). These showed that the ANCs of RDs exhibit a fast fraction (half-life < 1 day) followed by a slower fraction. Second, titration tests of RDs at fixed solution pH, i.e., pH stat , performed between pH 3.5 and 4.5 revealed surface normalised dissolution rates that decreased factors 10–100 per unit pH increase, the slope depending on the RD's mineralogy. Indeed, the rate ranking of observed surface area normalised dissolution rates confirmed that of literature-based values, weighed by the XRD-derived mineralogical fractions. Third, lime-calibrated agitated soil-RD suspension tests were conducted for two months, illustrating the dependency of RD ANC on soil context, and yielding ANCs that were factor 2–5 times larger than in the batch renewal test because of pH buffering effects of soil particulates. Finally, an outdoor soil mesocosm on the four acid soils amended with RDs at 12 Mg/ha and 340 Mg/ha was established and soil pH was monitored for 2 years. The observed pH trends corresponded well for both the low dose (R2 a = 0.67) and the high dose (R2 a = 0.93) with model predictions made using the pH- and temperature-dependent RD dissolution rates (pH stat test) and the soil pH buffer power and RD slow ANC-fraction (soil-RD suspension test). This model predicts half-lives of RD dissolution ranging between <1 month to >100 years depending on the starting pH of the soil, its pH buffer power, the RD mineralogy (XRD based) and its specific surface area. This study shows that the dissolution and ANC of RD can be most pragmatically predicted with a series of lime-calibrated soil-RD suspension tests of maximally two months. [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]

Abstract Agricultural liming materials are broadly utilized in the world to ameliorate soil acidity. Crushed limestone (CaCO 3) and dolomite (MgCO 3 ·CaCO 3) are most common liming materials. The CO 2 emission coefficient was proposed as 0.12 Mg C per Mg for CaCO 3 by the Intergovernmental Panel on Climate Change (IPCC), which indicates that 100% of C in CaCO 3 is eventually released to the atmosphere in the form of CO 2. However, this assumption appears unlikely based on current knowledge of the very low solubility of CaCO 3 and carbonate transport through soil. To develop the direct CO 2 emission factor from the C-containing liming materials applied in moderately acidic soil, CaCO 3 was applied in a typical temperate upland soil at different levels (0–2 Mg ha−1 yr−1), and the CO 2 emission rates were determined using the closed chamber method for two years. The direct CO 2 emission factor from CaCO 3 was estimated using 13CO 2 fluxes from 13C-CaCO 3 applied soils. Approximately 0.026 Mg C per Mg of CaCO 3 was emitted as CO 2 from CaCO 3 in cropping lands. This value was much lower than the IPCC default value (0.12 Mg C per Mg of CaCO 3). The current CO 2 emission coefficient was comparable with the United States Environmental Protection Agency (EPA) emission factor (0.046 Mg C per Mg of CaCO 3) from the agricultural field. If the EPA emission factor from the ocean (0.013 Mg C per Mg of CaCO 3) is added to the currently developed CO 2 emission factor of the inner agricultural field, the total CO 2 emission factor from lime may be close to 0.039 Mg C per Mg of CaCO 3 in the selected upland soil. Therefore, we propose that the current IPCC guideline value of the CO 2 emission factor from lime should be revised as 0.039 Mg C per Mg of CaCO 3 for Korean upland soils. Highlights • IPCC proposed 0.12 Mg CO 2 -C per Mg CaCO 3 as the CO 2 emission factor from CaCO 3 in soil. • 0.026 Mg CO 2 -C per Mg CaCO 3 was emitted from CaCO 3 during maize cultivation. • EPA estimated 0.013 Mg CO 2 -C per Mg CaCO 3 of CO 2 emission factor released from agricultural field. • CO 2 emission factor of CaCO 3 should be revised with 0.039 Mg CO 2 -C per Mg CaCO 3 in Korean upland soil. [ABSTRACT FROM AUTHOR]

[Display omitted] • No-liming decreased approximately 30% of P use efficiency in CT and NT systems. • The use of NT increased P use efficiency by about 10–12% compared to the CT system. • NT without lime resulted in the highest P legacy but was non-accessible due to high Al3+. • Soil P forms and P use efficiency in NT and occasional tillage systems were similar. • Liming with soil incorporation effects persists for four decades, enhancing P use by crops. Liming combined with no-tillage (NT) can increase the efficiency of P use by accumulating soil P in more available forms and improving root exploration due to the absence of toxic Al3+. This study aimed to evaluate the long-term effect of different combinations of soil tillage managements and liming in a subtropical Oxisol on the accumulation of P forms, legacy P index, and P use efficiency. A long-term experiment was used, established in 1987 testing (i) conventional tillage with lime (lime-CT) and control (control-CT), (ii) NT with lime (lime-NT) and control (control-NT), and (iii) occasional tillage with lime (lime-OT). The NPK fertilization was the same for all treatments. The accumulated grain yield and P use efficiency of 56 crops between 1987 and 2019 were evaluated. In 2019, soil samples were collected in the 0–5, 5–10, and 10–20 cm layers and submitted to a sequential chemical fractionation of P, P indexes, and soil acidity parameters. The results reveal that is necessary to correct acidity to increase crop yields and P use efficiency, regardless of the soil management used. This increase is enhanced when soil acidity correction by liming is combined with the use of conservation systems such as NT. Furthermore, after liming with incorporation, liming can be done on the soil surface, without the need to repeat the operation of lime incorporation, ensuring high efficiency of P use even after more than four decades. [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]

Abstract: Soil acidity and low natural fertility are the main problems for grain production in Brazilian ‘cerrado’. Although lime has been the most applied source for soil correction, silicate may be an alternative material due to its lower solubility and Si supply, which is beneficial to several crops. This work aimed to evaluate the efficiency of superficial liming and calcium/magnesium silicate application on soil chemical attributes, plant nutrition, yield components and final yield of a soybean/white oat/maize/bean rotation under no-tillage system in a dry-winter region. The experiment was conducted under no tillage system in a deep acid clayey Rhodic Hapludox, Botucatu-SP, Brazil. The design was the completely randomized block with sixteen replications. Treatments consisted of two sources for soil acidity correction (dolomitic lime: ECC=90%, CaO=36% and MgO=12%; calcium/magnesium silicate: ECC=80%, CaO=34%, MgO=10% and SiO2 =22%) applied in October 2006 to raise base saturation up to 70% and a control, with no soil correction. Soybean and white oat were sown in 2006/2007 as the main crop and off-season, respectively. Maize and bean were cropped in the next year (2007/2008). Products from silicate dissociation reach deeper soil layers after 18months from the application, compared to liming. Additionally, silicate is more efficient than lime to increasing phosphorus availability and reducing toxic aluminum. Such benefits in soil chemical attributes were only evidenced during bean cropping, when grain yield was higher after silicate application comparatively to liming. Both correction sources were improved mineral nutrition of all the other crops, mainly Ca and Mg levels and agronomical characteristics, reflecting in higher yield. [Copyright &y& Elsevier]

Abstract: We studied soils exposed to emissions from the Ventanas copper smelter in central Chile. Values of pH, free Cu2+ activity, and total dissolved copper were determined in the saturated paste extracts and the soil solutions collected by means of perforated plastic bottles installed in situ. Soil solutions were collected based on the periodicity of the rain. The topsoils (up to 30 cm) exhibited pH values in the saturated paste extracts of 4.6–5.5 and total soil copper concentrations of 310–640 mg/kg. In contrast, subsoils exhibited pH values in the saturated paste extracts of 6.4–7.2 and total soil copper concentrations of 30–60 mg/kg. These data suggest that the anthropogenic inputs of the Ventanas smelter, with respect to increase in Cu concentrations and acidification, are restricted to the topsoil while the subsoil remains unaffected. The above observations are probably due to sandy loam texture of the topsoils that allowed rapid water infiltration that did not allow the equilibrium between the rain water and the soil constituents to be reached. Consistent with this argument, soil solutions were not as acid as saturated paste extracts. Likewise, free Cu2+ activities and total dissolved copper concentrations in the soil solutions were lower in the saturated paste extracts. Thus, saturated paste extracts were not a good proxy of soil solutions for short-duration and intense rain events. In situ soil solution sampling by simple and low-cost devices, such as perforated plastic bottles used in this study, is a better mean for assessment of metal mobility in contaminated soils than saturated paste extracts. In solutions percolating through the soil during rain events, dissolved organic carbon was the major factor controlling total dissolved copper concentrations while soil pH was the major factor controlling the free Cu2+ activity. [Copyright &y& Elsevier]