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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]

• Liming has been recognized to be beneficial for soil physical properties. • The physical resilience of a soil is related to its structural stability. • It may take several years to develop a sustainable structure system. Liming is a well-established practice to ameliorate acidic soils worldwide. However, the role of liming in soil structure formation and its relation to the nitrogen cycling is only little explored. We hypothesized that improved physical and mechanical soil properties, which are directly linked to soil structure, lead to lower nitrogen losses in an agricultural system. Water holding capacity, total pore volume, bulk density, hydraulic conductivity, shear stress and pre-compression stress were quantified in the topsoil of three surveys located in Germany on different soil types: Eutric Gleyic Cambisol (Loamic) (Magdeburg, Saxony-Anhalt), Haplic Luvisol (Neubrandenburg, Mecklenburg-Western Pomerania) and Eutric Cambisol (Loamic) (Puch, Bavaria). The field experiments were arranged in a Randomized Complete Block Design and treated with two different rates of lime (calcium carbonate). Furthermore, three rates of nitrogen in form of urea or calcium ammonium nitrate were applied every year. Liming significantly increased the pH, plant available water capacity, total pore volume and decreased bulk density in the soils six months after application, but twelve months after lime application the soil structure collapsed again causes by ploughing and chiseling. We, therefore, assume a positive influence of lime application on soil physical parameters, if tillage is excluded at least initially. On the other hand, our results from the shear stress parameters and the pre-compression stress values indicate that their changes need time and we assume that it may take several years to develop a sustainable structure system. [ABSTRACT FROM AUTHOR]

The rate and method of lime application modify soil chemical attributes, but the re-acidification process after liming remains poorly understood in the long-term. This study aimed to assess the long-term effect of surface and incorporated liming on shifting soil use from native grassland of South Brazilian Campos to no-tillage system (NTS) for grain production in a highly acidic sandy-loam Ultisol. In 1994, an experiment in a randomized block with split plot design and four replications was installed in Southern Brazil. The main plot consisted of lime application method (surface or incorporation by soil tillage), while the subplots were lime rates (0.0, 2.0, 8.5 and 17.0 Mg ha −1 ), corresponding, approximately, to 0, 1/8, 1/2, and 1 fold the recommended dose to rise soil pH to 6.0 in the 0–20 cm soil layer. The 2 Mg ha ‒1 treatment had reapplication every two years until soil accumulated 8 Mg ha ‒1 of lime. In October 2006 and 2012 (i.e., 12 and 18 years after lime application), soil samples were collected at every centimeter from 1 to 10 cm depth, every 2.5 cm from 10 to 25 cm, every 5 cm from 25 to 50 cm and 50 to 60 cm. The chemical attributes related to soil acidity were evaluated. Even after 18 years of lime application, the re-acidification process recovered only 50% of the exchangeable Al and 30% of the potential acidity compared to native soil. Lime incorporation before NTS adoption proved to be more rapid and efficient to mitigate soil acidity than surface liming, and it is suitable for correction of deep-layered soil acidity in the soil profile. Surface lime application induced a lower alkalinization front in the soil profile, and even after 18 years there was no neutralization of total exchangeable Al in the 10–20 cm layer. [ABSTRACT FROM AUTHOR]

Lime slotting is a strategy for the amelioration of acidic soil profiles, whereby vertical seams of lime-amended soil traverse the acidic horizon. Two experiments characterized the above-ground and below-ground response of wheat to the lime amendment of 4 cm or 8 cm wide slots traversing the 7–40 cm deep acidic (pH = 3.9), Al-toxic subsoil horizon in an 80 cm deep constructed acidic soil profile. The growth of wheat rows responded to the proximity, but not the width of the limed slots. Wheat rows positioned above or adjacent (0–4 cm) to limed slots had greater shoot growth than those in the non-amended soil profile, whereas rows positioned 4 cm or more away from a limed slot were not significantly different (at α = 0.05) to those in the non-amended profile, regardless of the width of the 4 cm or 8 cm wide limed slots. Growth responses to the limed slots were realized at the early stages of plant growth and sustained until anthesis: rows positioned above the limed slots had 83% more tillers at 28 days after sowing, 58% greater green canopy area 35 days after sowing and 13% more spikelets per ear at anthesis compared to those in the non-amended profile. A rubidium tracer within the limed slots revealed that the proximity of wheat rows to the limed slots strongly influenced the timing at which the wheat roots exploited them. Wheat rows positioned above or adjacent (0–4 cm) to a limed slot accumulated the rubidium tracer within 21 days after sowing, whereas wheat rows positioned 4, 9 or 11 cm away from the limed slot did not access it until 35, 42 or 49 days after sowing, respectively. The uptake of a rubidium tracer from acidic or lime amended soil sections was strongly correlated with the length of roots within the respective soil sections. The limed slots traversing the acidic subsoil horizon functioned in two ways. Firstly, as discrete sanctuaries for root proliferation within the acidic layer, root length density was 3–7-fold greater than in non-amended soil sections, primarily due to the proliferation of fine (≤ 2 mm diameter) roots that were inhibited in the acidic soil sections. Greater root proliferation within the limed slots enabled greater uptake of nutrients and, to a lesser extent, water from the 7–40 cm deep acidic subsoil horizon. Secondly, the limed slots acted as conduits for roots to traverse the acidic, Al-toxic horizon. Uptake of water and a strontium tracer from the 40–80 cm deep subsoil horizon (beneath the 7–40 cm deep acidic layer) demonstrated that the limed slots enabled plant rows positioned above them to acquire water and nutrients from the 40–80 cm deep horizon 1–2 weeks earlier and in greater quantities than in the non-amended profile. However, for plant rows positioned 4 cm or more away from the limed slots, root activity in the 40–80 cm deep horizon was not significantly different (at α = 0.05) to those in the non-amended profile. Therefore, responses to lime slotting amendments are likely to be greatest where limed slots are positioned beneath wheat rows, and least where they are positioned in the interrow. • Lime slotting in an acidic soil profile increased wheat growth. • Wheat growth responded to the proximity, but not the width of limed slots. • Proximity to a limed slot influenced the timing at which roots intercepted it. [ABSTRACT FROM AUTHOR]

Highlights: [•] Combining no-tillage with a Ca-amendment was the best practice in acid degraded soils. [•] In some cases tillage suppressed the positive effects of liming. [•] Carbon and glomalin-related soil proteins seem to play a role in the alleviation of Al toxicity. [Copyright &y& Elsevier]

• Liming increases the amount of biological nitrogen fixation. • Liming provides higher soybean yields and a more positive N-balance. • Soil pH and Al saturation are key factors in biological nitrogen fixation. Soil acidity can impair biological N 2 fixation (BNF) and increase soybean (Glycine max L.) reliance on soil N to satisfy its plant N demand. This study aimed to evaluate the effect of liming, fertilization strategy, and grazing on: i) the N supplied via BNF process, ii) partial N-balance, and iii) soybean yield, in an integrated crop-livestock system under a non-tilled sandy and acidic Acrisol. Initial soil conditions were soil pH of 4.0 and Al saturation of 50%. Limestone was applied to rise soil pH to 6.0 and a control area was kept with the initial soil conditions. Soybean was grown in the summer and Italian ryegrass (as a cover crop or grazed by sheep) in the winter. Fertilization strategies consisted in applying P and K prior to soybean or ryegrass. Partial N-balance was calculated by the difference between N derived from BNF and N removed in soybean seeds. Contribution of N from the atmosphere to soybeans was on average 62 and 66% in plots without and with liming, respectively. The fixed-N was 27% greater under low soil acidity due to lime. Partial N-balance was positive in both treatments, but 57% greater in the limed- relative to the non-limed (+58 kg ha−1) soils, resulting in 11% soybean yield increase when lime was added. The most relevant soil chemical properties influencing N fixation were soil pH and Al saturation. Grazing and fertilization strategies had no effect on soil acidity properties, N supply, and soybean evaluations. Further research should explore the long-term effect of grazing, fertilization strategies, and liming. [ABSTRACT FROM AUTHOR]

• Liming increased gross N mineralization and nitrification during the summer fallow. • No-tillage enhanced the liming effect on gross N mineralization. • N immobilization was higher in traditional tillage. • The gross N transformations and microbial indicators decreased during the summer period. • During the fallow period, NH 4 +, DOC and DON accumulated in all the treatments. In the Mediterranean rainfed agriculture, a summer fallow is necessary because of the severe drought and high temperatures. Due to suppressed plant nitrogen (N) uptake during this period, an accumulation of inorganic N in the soil may occur, which could be lost from the system during the first autumn rains. Both mineralization and nitrification rates can be affected by agricultural practices, such as tillage or liming, influencing the amount of available N present in the soil during the fallow period. In this study, we investigated the effects of two common agricultural practices, no-tillage (instead of traditional tillage) and liming, on soil gross N transformations during the summer fallow. Liming increased gross N mineralization (from 1.21 to 1.78 mg N kg−1 day−1) and gross nitrification (from 0.44 to 0.76 mg N kg−1 day−1) while traditional tillage increased N immobilization. Tillage did not affect gross nitrification but the effect of liming on gross N mineralization was enhanced in no-tillage plots. The total bacteria abundance was enhanced by liming and no-tillage and seemed to be responsible for gross N mineralization and immobilization. The gross mineralization, nitrification and microbial immobilization decreased during the summer fallow with an overall reduction by 40%, 56%, 74% and 54% in gross N mineralization, gross nitrification, ammonium immobilization and nitrate immobilization, respectively. The accumulation of ammonium could be interpreted as a consequence of the decoupling between ammonium production and consumption rates. The increase of gross N mineralization and nitrification caused by liming application could result in augmented risks of N losses via nitrate leaching and gaseous losses in autumn, especially under no-tillage. However further studies are required to elucidate the nitrate fate of the in Mediterranean agricultural soils under those management practices. [ABSTRACT FROM AUTHOR]