Search

[Display omitted] • In soil, adsorption of FA is limited by the binding to external surfaces of nano-aggregates. • The overall adsorption of FA is pH independent and has a relatively low affinity. • In acid soils, FA prefers direct interaction with soil oxide particles, releasing phosphate. • NOM-oxide interaction can be reduced by soil liming, decreasing the solubility of oxyanions. • A dual-phase model is developed to describe the release of PO 4 upon FA addition. For more insight into the interaction of natural organic matter (NOM) with metal (hydr)oxides and oxyanions, the adsorption of added fulvic acid (FA) and the corresponding release of phosphate (PO 4) were studied for a series of agricultural soils (∼0 – 25 cm), strongly varying in soil properties. Interpretation of the data with surface complexation modeling using the NOM-CD model applied in a dual-phase mode shows that the adsorption of added FA, in contrast to PO 4 , is restricted to the external surfaces of nano-aggregates. The adsorption is relatively weak and pH-independent, due to its competition with the native NOM of the organo-mineral phase. At low pH, the functional groups of both added FA and native NOM shift in the interface towards the soil oxide surfaces, making both a good competitor for adsorbed phosphate, resulting in a higher amount of phosphate being released. With an increase in pH, the competition becomes weaker. As a result, more phosphate is bound and less is released when FA is added. Our surface complexation modeling points to the existence of organo-mineral nano-aggregates with sizes of >∼10 – 270 nm, which depends on the total reactive surface area of the soil. Our findings imply that organic amendments containing FA equilibrate with only a portion of the total reactive surface area. In acidic soils, the addition of such organic amendments will be more effective in solubilizing phosphate, which is beneficial from a plant nutrition perspective, but simultaneously it may also contribute more to environmental eutrophication. [ABSTRACT FROM AUTHOR]

[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 The hierarchical organization of aggregates in soil is responsible for the presence of inter and intra-aggregate pores. This research aimed to investigate effects of soil surface liming, considering lime rates of 0, 10 and 15 t ha−1, on the intra-aggregate porous system of soil aggregates with equivalent diameters of 2–4 and 1–2 mm, from 0 to 10 (A) and 10 to 20 cm (B) soil layers. These aggregates were selected by the wet sieving method carried out for determination of the mean weight diameter. Synchrotron-based computed microtomography (μCT) of aggregates was analyzed in terms of porosity, connectivity, tortuosity, and fractal dimension. Additionally, X-ray fluorescence was used to evaluate the elemental composition of the soil aggregates. All liming effects were concentrated at layer A, where calcium percentage was elevated in aggregates from 1–2 mm class as compared to those from 2–4 mm class. Accordingly, the physical parameters studied were generally more affected in the case of smaller aggregates (1–2 mm). Liming decreased total porosity, increased tortuosity of pores, and decreased fractal dimension for 1–2 mm aggregates, which was in line with the fact that larger pores were replaced by smaller ones in 1–2 mm aggregates, as found via both quantitative and qualitative analyses. On the other hand, liming did not affect pore connectivity under any of the circumstances. Highlights • Surface liming improved soil aggregation by increasing the mean weight diameter. • Smaller soil aggregates present higher percentage of calcium due to liming. • Liming effects on soil physical properties were stronger for smaller aggregates. • In these small aggregates, liming decreased porosity and increased tortuosity. • Liming provided a more homogeneous intra-aggregate pore space. [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]

• Silicate-containing amendments increased calcium and available silicate contents. • Silicate-containing amendments moderately increased soil fertility. • Silicate and lime co-application increased the relative change in soil fertility. • Long-term application of silicate and lime reduced C stratification. • Carbon stocks reduced in lime and silicate amended soils. Most agricultural soils are unproductive due to soil acidity which limits crop growth and yield. To ameliorate soil acidity constraints and enhance the ecosystem services the soil renders to achieve optimum crop yields, lime, and silicate are mostly used. However, there are few studies reporting the impacts of the combined application of silicate and lime on soil properties, soil fertility and carbon stocks and stratification in long-term experiments. This study evaluated the impacts of the combined application of silicate and lime on soil fertility indicators (pH, soil organic matter (SOM), available phosphorus, exchangeable potassium, magnesium, and calcium, and available SiO 2), carbon stratification and stocks in comparison to sole lime and sole silicate applied to a Fluvaquentic Eutrudepts over a 67-year period. Each treatment's rate of application was calculated to raise the soil pH to 6.5. Incorporation of the treatments increased the soil pH by 1.30, 1.22, and 1.35 folds in the sole silicate, sole lime, and combined silicate and lime-treated soils, respectively, relative to the baseline soil pH (5.5). The combined application of silicate and lime resulted in significant decreases in C stratification and C stocks. The significant reduction in the C stocks in the silicate and lime-treated soils implies that its long-term application could potentially reduce carbon sequestration and increase the carbon footprint of rice cultivation. This information is crucial to develop sustainable soil management interventions to curtail the environmental footprint in rice paddy ecosystems. Comparatively, the combined silicate and lime treatment caused an increase in the relative change of soil fertility by 65.7% and the average annual growth rate in the soil fertility improvement by 0.0115, as compared to the untreated soil. Among the soil variables, soil pH, exchangeable calcium, and available silicate contributed most to the variation the soil fertility. The obtained results could serve as a guide in revising the lime and silicate fertilization programs instituted by the Korean Government and reviewing national soil fertility management systems in temperate paddy ecosystems. [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]

In paddy soils, plant availability of phosphorus (P) increases during the flooding period due to the reductive dissolution of iron (Fe)-bearing minerals on which P is sorbed. Soil chemical properties are a determining factor of P availability and are subject to change after prolonged paddy rice cultivation. The purpose of this study was to evaluate the effects of long-term application of rice straw compost and slaked lime on changes in soil chemical properties, particularly focusing on the increase in available P under reductive conditions. The rice cultivation experiment was launched in 1926 to clarify the effects of mineral fertilizer (NPK), rice straw compost, and slaked lime application on soil properties. The amount of P solubilized under reductive conditions was evaluated by the difference in the P extracted by the Bray II method with and without reductive treatment of the soil. Continuous application of NPK mineral fertilizer without slaked lime resulted in higher amounts of aluminum extracted by acid ammonium oxalate and P extracted by the Bray II method until the 92nd cropping, while the increase in the proportion of available P under reductive conditions was low. In contrast, the amounts of Fe extracted by acid ammonium oxalate and P solubilized under reductive conditions were higher with increasing application of compost. The application of the compost caused strongly reductive conditions in the soil during the flooding period, and the dissolution of P in the Fe-bound fraction was facilitated. However, excessive application of compost led to the dissolution of high amounts of Fe-bound P, resulting in a loss of Fe and P from the cultivated soil. These results suggest that excessive application of rice straw compost and no application of slaked lime may cause a decrease in available P in paddy soils. [ABSTRACT FROM AUTHOR]

Albic material is a widespread soil diagnostic material. The genesis of albic materials is known to be very sensitive to changes in environmental conditions resulting from natural or anthropic driving forces. Common agricultural practices like liming or drainage improvement are able to change the nature or the intensity of albic material genesis. The direction and the amplitude of such changes have however remained controversial because of a lack of quantitative approaches. In this paper, the intensity of the genesis of albic material was quantified in one forested Retisol and compared to those previously quantified in two limed and cropped soils sampled respectively far from and close to a drain line. Liming practices were found to decrease the intensity of the genesis of albic material by two thirds with reference to natural soil evolution under forest. Contrastingly, artificial drainage improvement initiated the development of physically-driven albic material genesis due to translocation of soil particles but without significant implication of any reduction process. The observed increase in the intensity of albic material genesis after artificial improvement was higher in the immediate vicinity of drains than was its decrease after liming applications. It was however the reverse for the rest of the soil between the drains. As a result, the overall effect of cultivation was a slowdown of the genesis of albic horizons by comparison to the natural evolution under forest. Such changes in both the nature and the intensity of albic material genesis clearly demonstrated that i) numerous genetic pathways may be simultaneously or successively active at a particular location, and ii) anthropic driving-forces like agricultural practices may be a way to favour one particular genetic pathway at the expense of another. [ABSTRACT FROM AUTHOR]

Short-term potential carbon (C) and nitrogen (N) mineralization of soil organic matter and belowground plant litter was determined in the top soil layer of a sandy soil of a short-rotation coppice (SRC) and the effect of addition of lime, mineral nitrogen and poplar roots was determined. Lime addition was equivalent to 1.2 mg CaCO 3 g − 1 , mineral N and root litter were added corresponding to 6.8 μg N g − 1 and 13.8 mg roots g − 1 soil respectively. Partitioning of carbon dioxide (CO 2 ) derived from lime and soil organic matter (SOM) was calculated by using stable isotope analysis of the CO 2 . In addition, particulate organic matter (POM) as well as microbial biomass carbon and nitrogen were analyzed after 51 days of incubation. Addition of lime decreased CO 2 derived from organic matter in all treatments, but the level of decrease varied with N and root litter addition. Microbial biomass C and N increased with N addition in soil without root litter but decreased with root litter, nevertheless an immobilization of mineral N was especially high in soil amended with root litter. Particulate organic matter (POM) decreased by 41% of its dry weight in root litter amended soil. Liming decreased decomposition of POM in these soils, whereas no effect was observed after addition of mineral nitrogen or mineral nitrogen and lime. These results show that liming has the potential to decrease C mineralization of humified organic matter as well as plant residues and that decreased mineralization of organic matter occurred after liming, even if mineral N was added. [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]

• Lime addition impacts organic matter (OM) preservation in both top- and sub-soil. • Lime addition destabilizes N-poor OM associated with minerals in the topsoil. • The effect of lime on OM decomposition with depth depends on the OM availability. The development of effective strategies to maintain/increase soil C is hindered by the poor process-level understanding of the impact of management practices on C preservation, particularly at different soil depths. Based on the distinct biogeochemistry existing across a soil profile, a depth-dependent response of organic matter (OM) to soil amendments was hypothesized. To test this, we investigated the effect on OM preservation of lime addition to the topsoil and the subsoil of a volcanic soil classified as Andosol – the mineral soil with the largest organic C content worldwide. We incubated samples from each soil layer with (or without) lime addition, in the presence or absence of 13C- and 15N-labeled plant residue (simulating plant C inputs to the soil). The fate of OM in bulk soil and OM-mineral associations of microaggregates was measured using conventional chemical analyses and nano-scale secondary ion mass spectrometry, respectively. The results revealed contrasting geochemical properties existing within the soil profile, i.e. pH and amount of allophane increasing with soil depth. Functional complexity of OM also increased with depth, as revealed by an increase in spatial and molecular heterogeneity of OM, i.e. a larger proportion of microbial-derived OM with high spatial separation found in the subsoil. Lime addition caused OM destabilization as denoted by the increase in the amount of water-extractable C in both the topsoil and the subsoil (P < 0.05). In the topsoil, OM coverage of mineral surfaces decreased with liming from 49% to 30% whereas the opposite was observed in the subsoil, where it increased from 23% to 29%. Thus, liming caused the disruption of OM-mineral associations within microaggregates in the topsoil, but not in the subsoil. We infer that, at depth, the OM destabilization involved the mobilization of OM previously protected within macroaggregates. This pulse of labile C generated an advantageous environment for microbial OM mineralization in the subsoil, but this effect was diluted in the topsoil, richer in OM and where OM functional complexity is smaller. Depth-dependent soil geochemical properties and functional complexity determine differences in the effect of liming on the fate of soil OM in top vs. subsoils. [ABSTRACT FROM AUTHOR]

• Low-lability S contents in soil decreased with depth. • Ca-phosphate extractable S contents increased with depth after surface application of phosphogypsum. • Sulfate adsorbed to hematite was the main oxidized inorganic S-species. Sulfur (S) is present mainly in organic forms in the most superficial layers of well-drained soils, despite sulfate (SO 4 2−) being the main S-species absorbed by plants. Coupled broadcast application of lime and phosphogypsum (PG) is widely deployed as an agricultural practice to improve soil chemical properties and increase crop yields in highly weathered tropical soil areas under no-tillage system (NTS). However, the effects of large-scale application of these soil amendments to S-species distribution in soil in NTS are largely unknown. We combined S wet-chemical analysis with Synchrotron-based X-ray Absorption Near-Edge Structure Spectroscopy (XANES) to evaluate the effects of lime and PG application to S-species distribution along the soil profile (up to 150 cm). Soil samples were collected from a field-scale experiment under NTS for over 15 years. Soil was amended with lime and PG, either individually or in combination, four times during the experiment. Soil sampling was conducted 16 months after the last amendments' application, and treatments (lime, PG and lime + PG) were compared to a control (under NTS without amendments' application) and with soil samples from a native forest (reference for an undisturbed site). Broadcast PG application increased the contents of Ca-phosphate extractable S and pseudo-total S (microwave assisted acid digestion) contents in the deeper layers. Two peaks representing reduced and oxidized S species were detected in S K -edge XANES spectra of all treatments and NF soil. The oxidized S peak gets sharper with increase in depth, as reduced S peak intensity decreases, and fingerprint analysis suggested a greater contribution of reduced organic S species in the most superficial soil layer followed by an increase in highly oxidized S species as depth increased. Linear combination fitting analysis confirmed a greater contribution of highly oxidized S species to the total S-species as depth increased, especially in soil samples that received PG application. [ABSTRACT FROM AUTHOR]

• Data fusion did not significantly improve soil attributes prediction. • Clay, SOM, and CEC were better predicted than chemical soil attributes. • Even 1 sample per 0.25 ha were not sufficient to accurate map soil chemical attributes. • However, 1 sample per ha is adequate to map clay, SOM, and CEC. Precision agriculture aspires to manage the soil spatial variability within a field. However, agricultural practices can decrease the spatial autocorrelation of soil properties at a short distance, which requires an increase in sampling density to improve the reliability of interpolated surfaces. Data fusion of several soil spectrometers is a promising alternative that can increase knowledge about soil physicochemical variability. Therefore, this research aimed to evaluate whether the synergy of portable X-ray fluorescence, Vis-NIR, and Mid-Infrared spectrometers can successfully increase sampling density and improve the quality of the soil attribute maps, in a high fertilization management study area. We conducted a case study on a sugarcane field in Southeast Brazil. Our spectral data fusion approach did not increase the prediction performance for soil properties, achieving the same accuracy (α ≤ 5%) of the single spectral ranges (Vis-NIR or MIR or pXRF) individually. Thus, Vis-NIR was chosen to evaluate if spectroscopy could improve soil properties prediction and mapping. We used three dataset scenarios to build soil property maps: two were based on soil wet-chemical laboratory analysis using 1 sample per ha, and 1 sample per 0.25 ha and a third used a spectroscopy model with 0.25 samples per ha calibrated using soil wet-chemical laboratory analysis at the rate of 1 sample per ha. In a field with strong anthropic influences, due to liming and soil fertilization, Vis-NIR spectroscopy cannot predict well the amount of phosphorus and pH at a sampling density of 1 sample per 0.25 ha. Increased soil sampling enhances soil mapping accuracy only for chemical properties (e.g., potassium) that are correlated with soil texture. Nevertheless, soil spectra can classify areas of similar soil texture and help farmers with the site-specific management of crops. [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: The stabilisation of soil organic matter (SOM) is the result of the simultaneous action of three mechanisms: chemical stabilisation, biochemical stabilisation and physical protection. The objectives of this study were (i) to evaluate carbon-protection mechanisms in different SOM pools in soil aggregates and (ii) to identify the association of Ca2+ with total organic carbon (TOC) under the influence of surface liming in a medium-textured Oxisol in a long-term experiment under no-till system (NTS) in southern Brazil (25° 10′ S, 50° 05′ W). The treatments consisted of application of zero or 6tons ha−1 of dolomitic lime on the soil surface in 1993 and a reapplication of zero or 3tons ha−1 of dolomitic lime in 2000 to plots with or without previous lime application. Soil samples collected at depths of 0–2.5, 2.5–5, 5–10 and 10–20cm were separated into seven aggregate classes. In each of these classes, TOC, particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) were analysed. The 8–19mm sized aggregates from the 0–2.5cm layer were assessed by energy-dispersive X-ray spectroscopy (EDS) for the elemental analysis of carbon (C) and calcium (Ca). The liming caused an accumulation of TOC in the aggregates, mainly at a depth of 0–2.5cm. The aggregates from soils treated with lime had a higher mean weight diameter (MWD) that resulted in the accumulation of TOC, especially in the 8–19mm aggregate class, that was linear and closely related with C input (R2 =0.99). The proportion of large aggregates in the treatments with lime was closely correlated with the TOC content of the whole sample. The largest dose of lime (9tons ha−1) resulted in higher TOC, POC and MAOC values, mainly in the 8–19mm aggregate class. The elemental analyses for C and Ca revealed similar spectra between them for the surface-liming treatments in the clay fraction found in the centres of the 8–19mm aggregates. The surface application of lime to NT fields provided greater stability and protection of the intra-aggregate C, presumably due to Ca2+ acting as a cationic bridge between OC and the kaolinite in the clay fraction. [Copyright &y& Elsevier]

Abstract: Air-drying of soil samples is known to increase the exchangeable fraction of cadmium (Cd) in soil. Liming, on the other hand, reduces bioavailability of heavy metals in soil by metal hydrolysis reactions and/or coprecipitation with carbonate. However, due attention has not been paid to desorption and mobilization of Cd from air-dried and limed soils at realistic ionic strengths. We compared Cd desorption from moist and air-dried samples of two texture-contrasting soils which had been spiked with 3 or 30mg-Cd kg−1 after liming with 25mmolkg−1 of Ca(OH)2, or without prior liming. Repeated batch extraction with water and 1–10mM CaCl2 solutions was carried out, and chemical speciation of dissolved Cd performed using Visual MINTEQ. Desorption of Cd from the exchangeable pool in the soils was not exhaustive, with smaller fractions of Cd remaining after five extractions in the coarse-textured Chiba soil having lower CEC than the fine-textured Takada soil. Air-drying enhanced Cd desorption from the both soils particularly in the first extraction, with the cumulative Cd desorption after five extractions 1.5 times, on average, as large as that from the unlimed moist soils. Liming suppressed the Cd release, resulting in cumulative desorptions 0.14–0.19 times those from the unlimed counterparts. The air-drying and liming effects on Cd desorption were reflected in the apparent Cd2+/Ca2+ exchange selectivity coefficient, which was lowest in the first extraction upon air-drying, and significantly increased upon liming. Alternatively, assuming that constant Cd2+/Ca2+ exchange selectivities obtained from the moist unlimed soils apply, exchangeable Cd pools in the air-dried and limed soils were evaluated. The exchangeable pool was found to increase, on average, by 26% and 30% upon air-drying, and decrease by 79% and 86% upon liming in the Takada and Chiba soils, respectively. These results demonstrate that the size of exchangeable Cd in contaminated soils is prone to change upon drying and liming, and that the potentially desorbable Cd is only slowly mobilized under ionic strength conditions prevailing in the field. [Copyright &y& Elsevier]

Abstract: The aim of this study was to evaluate the effects of the particle size (2–4 mm, 0.5–2 mm, 0.25–0.5 mm and less than 0.25 mm) of magnesium limestone and the method of application (in a single dose or split in three yearly doses), on the forms of Al in the solid and liquid phases of an acid Galician soil destined for pasture production. Monitoring the experimental plots over a period of 3 years showed that the plots treated with a single application of the finest limestone (<0.25 mm) exhibited the highest pH and the lowest concentrations of exchangeable Al, with less than 10% Al saturation throughout the period of study. The average values of pH in water along the period of study were 5.30 in the most effective treatment and 5.06 in control plots. The average values of aluminium saturation were 6.5% in the most effective treatment and 16.9% in control plots. One year after liming, the plots treated with a single application of the finest limestone presented also the highest concentrations of weakly stable organo-aluminium complexes in the solid phase and of organically bound Al in the soil solution, as well as the lowest concentrations of labile Al, while no Al3+ (considered the most toxic Al species) was detected. Over time non-crystalline inorganic Al tended to precipitate, apparently at the expense of exchangeable Al and/or Al bound to the organic matter. The application of the finest limestone split in three doses (until completion of 3 t ha−1 in the third year of the study) was less effective than the application of a single dose. The plots treated with the coarsest limestone (between 2 and 4 mm) and the control plots provided similar results for all parameters throughout the three years of the study. In the former the exchangeable Al was higher than 20% and the concentration of labile Al was the highest of all plots. [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]

Abstract: The aim of this paper is to study changes in water-stable aggregation and void space in an upland grassland soil following a surface application of calcium carbonate intended to increase the diversity of soil fauna. Samples of the H and Ah horizons were collected at the time of the first lime application (June 1999) and 1 and 2 years thereafter. Void space in both horizons was quantified by image analysis of thin sections and the size distribution of water-stable aggregates in the Ah horizon was determined by laser granulometry. The effect of liming was largely seen in the H horizon where pH in CaCl2 increased from 3.4 to 4.1. Percentage void space and % voids >1000 μm2 increased significantly in the H horizon between 1999 and 2001, and there was a significant liming effect. In the mineral Ah horizon, only the change in void space over time was statistically significant. There were no significant differences in aggregate stability following liming or over time, despite a significant reduction in organic carbon concentration between 1999 and 2001. The change in void space with liming was consistent with reported changes in the abundance of larger enchytraeid genera such as Fridericia and with changes in earthworm abundance. Changes in void space with time may be linked to the cessation of grazing at the experimental site. [Copyright &y& Elsevier]

• Reduced tillage increased microbial biomass and abundance of P solubilizers. • Inorganic fertilisers reduced phosphorus solubilizing microbial abundance. • Residue addition increased soil microbial biomass and abundance of P solubilizers. • Intercropping increased microbial biomass and phosphorus solubilizers' abundance. • Liming reduced phosphorus solubilizing microbial species richness. Phosphorus is a critical nutrient for plant growth. Several agronomic practices have been promoted to improve soil fertility and crop productivity in Western Kenya. Yet, despite their benefits, a dearth of knowledge exists on their long-term effects on soil microbial biomass and phosphorus solubilizing microbial species (PSMs) abundance especially in this region. In a long-term (15 years) agronomic field trial, we selected 8 treatments that allowed for evaluation of 1) Effect of tillage in a maize-soybean rotation with fertilization and residue retention; 2) Effect of residue retention in a maize-soybean rotation with fertilization under conservation tillage; 3) Effect of N and P fertilization in a maize-soybean rotation with conventional tillage; 4) Effect of liming in a maize-soybean intercropping with conventional tillage; and 5) Effect of maize-soybean rotation versus intercropping under conservation tillage on microbial biomass and PSMs abundance. The study was conducted in a long-term conservation agriculture experiment (30 seasons) in a Ferralsol in Western Kenya in 2016 and 2017. Reduced tillage significantly (P < 0.05) increased microbial biomass phosphorus (MBP) and abundance of different PSMs relative to conventional tillage, though the results were not consistent for some species. Residue addition significantly increased MBP and abundance of different PSMs compared to systems without residue addition. Liming significantly reduced PSMs abundance in 2016, though this was inconsistent for 2017. In 2017, no effect of liming on soil pH was found. Fertiliser addition significantly increased PSMs abundance in 2016, but this was also inconsistent for 2017. Some PSMs strains were significantly more abundant in maize and soybean intercropping system compared to rotation, and vice versa. Our study demonstrated that not only the agronomic inputs applied but also tillage and cropping systems employed can variably affect the soil microbial populations. [ABSTRACT FROM AUTHOR]

• Structure liming modified macropore networks, but not mesopore networks. • Structure lime tended to reduce macroporosity, macropore diameters and connectivity. • Structure liming tended to reduce readily dispersible soil. • Liming effects on pore networks differed substantially between sites. • Although quantitatively different, effects generally pointed in the same direction. Structure liming aims to improve soil structure (i.e., the spatial arrangement of particles and pores) and its stability against external and internal forces. Effects of lime application on soil structure have received considerable interest, but only a few studies have investigated effects on macro- and mesopore networks. We used X-ray computed tomography to image macropore networks (ø ≥ 0.3 mm) in soil columns and mesopores (ø ≥ 0.01 mm) in soil aggregates from three field sites with (silty) clay soils after the application of structure lime (3.1 t ha−1 or 5 t ha−1 of CaO equivalent). Segmented X-ray images were used to quantify soil porosity and pore size distributions as well as to analyse pore architecture and connectivity metrics. In addition, we investigated the amount of readily dispersible soil particles. Our results demonstrate that structure liming affected both, macropore networks and amounts of readily dispersible soil to different degrees, depending on the field site. Significant changes in macropore networks and amounts of readily dispersible soil after lime application were found for one of the three field sites, while only some indications for similar changes were observed at the other two sites. Overall, structure liming tended to decrease soil macroporosity and shift pore size distribution from larger (ε >1.0 mm) and medium sized macropores (ε 0.3–1.0 mm) towards smaller macropores (ε 0.1–0.3 mm). Furthermore, liming tended to decrease the critical and average pore diameters, while increasing the surface fractal dimension and specific surface area of macropore network. Structure liming also reduced the amounts of readily dispersible soil particles. We did not find any changes in mesopore network properties within soil aggregates or biopore networks in columns and aggregates. The effects of lime on macropore networks remain elusive, but may be caused by the formation of hydrate phases and carbonates which occupy pore space. [ABSTRACT FROM AUTHOR]

Naturally dense soils have been commonly managed for coffee plantations in Vertentes Fields physiographic zone of Minas Gerais state, Brazil. Such dense soils in association with the irregular rainfall in recent years have increased risks for crop productivity. Therefore, management practices aiming at improving subsoil root exploration have been recommended for enhancing absorption of water and nutrient uptake, thus mitigating the edaphic drought process and ensuring the development, productivity, and longevity of the coffee crop. A field experiment was carried out in an area of dense Inceptisols through the planting of the coffee crop to investigate the effect of deep furrowing with additional liming on soil quality indexes and as a function of normalized pore distribution by volume [S*(h)]. The experimental design was in randomized blocks with 5 treatments: 40 (conventional soil preparation with furrows at 0.40 m of depth); 60 (soil preparation with furrow to 0.60 m of depth with conventional (60S) and complementary liming application (60C)); 80 (soil preparation with furrow to 0.80 m of depth with conventional (80S) and complementary liming application (80C)). These treatments were compared to an area under native Cerrado vegetation. Undisturbed soil samples were collected at different depths in each treatment. On these samples, water content was measured at different matrix potentials, and physical quality indicators along with the S*(h) were calculated. The results indicated that soil management practices, compared to the native condition, promoted a better distribution of water and air (P AWC , RFC, P MAC and S index) as well S*(h) up to 0.40 m. Below this depth, none of the management practices were able to promote significant improvements (p < 0.05) of these variables in relation to the soil native condition. The 80C treatment had the best air and water availability, with increased of pore size class having functions of drainage and aeration. Moreover, this treatment stood out in comparison to the conventional management (40) for all measured variables, maintaining the adequate conditions of the native area in depth. For the managed areas, the depth of 0.60 m gave the best improved growth and vegetative vigor of the coffee plants. Unlabelled Image • Soil management increases aeration and water availability in dense and shallow Inceptisols. • Optimum limits for physical quality indicators should be proposed considering soil classes. • Deep furrow in shallow and dense soils can mitigate the effects of water deficit for coffee trees. • Physical quality indicators correlate with Normalized Difference Vegetation Index and plant height of coffee trees. [ABSTRACT FROM AUTHOR]