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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]

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 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]

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]

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]

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]

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]

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]

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]