Soil Exchangeable Base Cations Research Articles

Effects of Exponential N Application on Soil Exchangeable Base Cations and the Growth and Nutrient Contents of Clonal Chinese Fir Seedlings.

Nitrogen (N) is an essential macronutrient for plant function and growth and a key component of amino acids, which form the building blocks of plant proteins and enzymes. However, misuse and overuse of N can have many negative impacts on the ecosystem, such as reducing soil exchangeable base cations (BCs) and causing soil acidification. In this research, we evaluated clonal Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) seedlings grown with exponentially increasing N fertilization (0, 0.5, 1, 2 g N seedling-1) for a 100-day trial in a greenhouse. The growth of seedlings, their nutrient contents, and soil exchangeable cations were measured. We found that N addition significantly increased plant growth and N content but decreased phosphorous (P) and potassium (K) contents in plant seedlings. The high nitrogen (2 g N seedling-1) treated seedlings showed a negative effect on growth, indicating that excessive nitrogen application caused damage to the seedlings. Soil pH, soil exchangeable base cations (BCs), soil total exchangeable bases (TEB), soil cation exchange capacity (CEC), and soil base saturation (BS) significantly decreased following N application. Our results implied that exponential fertilization resulted in soil acidification and degradation of soil capacity for supplying nutrient cations to the soil solution for plant uptake. In addition, the analysis of plants and BCs revealed that Na+ is an important base cation for BCs and for plant growth in nitrogen-induced acidified soils. Our results provide scientific insights for nitrogen application in seedling cultivation in soils and for further studies on the relationship between BCs and plant growth to result in high-quality seedlings while minimizing fertilizer input and mitigating potential soil pollution.

Plant diversity and species turnover co-regulate soil nitrogen and phosphorus availability in Dinghushan forests, southern China

The interaction between plants and soil is an important internal driver of ecosystem evolution. Many studies have reported the unidirectional effects of soil nutrients on plant diversity and species turnover. However, there are still many gaps in our knowledge about how plant diversity and species turnover feedback to soil nutrients. In the present study, three forest plots with different species composition and diversity were created through artificial disturbance in the same stand origin forest, and their long-term dynamics were observed. We identified underlying mechanisms of how plant diversity (Shannon-Wiener index) and species turnover (Bray-Curtis dissimilarity) affect soil total nitrogen (TN), total phosphorus (TP), available nitrogen (AN), and available phosphorus (AP). Plant diversity was associated with soil TN, TP, AN, and AP concentrations (P < 0.01). Species turnover was negatively correlated with the log-response ratio of TP (LRR TP) (P < 0.001), but not correlated with LRR AP. Species turnover had significant positive correlations with LRR TN and LRR AN (P < 0.001). The structural equation model supports hypotheses that plant diversity and species turnover influenced soil N and P availability by affecting forest community growth (total tree basal area, TBA), litter quantity and quality, and soil physical and chemical properties (soil organic carbon, SOC; soil exchangeable base cations). Collectively, our results highlighted the co-regulation of plant diversity and species turnover on soil N and P availability by “complementary” and “mass” effects during the long-term dynamics of forest ecosystems.

Contribution of different proton sources to the acidification of red soil with maize cropping in subtropical China

Increasing acid deposition and intense nitrogen (N) fertilization have resulted in severe soil acidification in many regions of the world. However, the soil acidification rate, especially quantitative contributions of different proton (H+) sources remain unclear in various cropping systems. In this study, a two-year field lysimeter experiment was conducted with a set of different N fertilization treatments (0, 100, 200 and 400 kg N ha−1 yr−1) for maize crop in typical red soil in subtropical China. The pathways and budgets of different H+ sources were quantified by calculating the input–output balance of major elements. Results showed that fertilization significantly accelerated soil acidification by increasing the leaching of NO3– and base cations (K+, Ca2+, Na+, and Mg2+) as well as increasing the cation removals by plant uptake and harvest. Unbalanced plant uptake of anions and cations was the primary H+ source (64.4–80.5%) to soils. Plants have an important effect on soil acidification by redistributing cations in soils. Due to cation removals by plant uptake and harvest, there were significant decreases of soil exchangeable base cations under high urea-N treatments (200 and 400 kg N ha−1 yr−1) and significant increases of soil exchangeable H+ and Al3+ under three fertilization treatments. Of course, N transformation also plays an important role (12.1% to 38.8%). However, the effect of direct H+ deposition is minor in this area comparatively (5.78% to 7.34%). Quantification of acidification contribution of different sources is useful for the establishment of further soil remediation practices. The field management is considered very important to alleviate soil acidification, including increasing straw return and controlling fertilizer application.

Availability of soil base cations and micronutrients along soil profile after 13-year nitrogen and water addition in a semi-arid grassland

Alteration in the availability of soil base cations and micronutrients is critical to maintain stable ecosystem functioning under the predicted global change scenarios. However, changes in these soil cations and their relationships with soil physiochemical properties along soil profile remain unclear under the combined increasing N deposition and precipitation changes. In this study, the concentrations of soil exchangeable base cations (Ca, Mg, K and Na) and available micronutrients (Fe, Mn, Cu and Zn) were determined along an 80-cm soil profile after 13-year continuous N and water manipulation in a semi-arid grassland. Our results showed that N addition significantly decreased exchangeable Ca (− 25.4%, averaging across the three N addition rates) and Mg (− 7.8%) at the depth of 10 cm while increased available Fe (+ 70.5%), Mn (+ 64.7%), and Cu (+ 26.0%). Besides, the magnitude of the increase or decrease escalated with the rates of additional N. Such pattern was also true for the concentrations of available Fe, Mn and Cu in the 10–20 cm soil layer, but the magnitude of changes was much smaller than in the top 10-cm soil layer. Nevertheless, N addition increased the concentrations of the three available micronutrients across the entire profile, indicating that Fe, Mn and Cu were more sensitive to N addition in subsoils than surface soils. Nitrogen addition significantly reduced soil cation exchange capacity (CEC) in the top 10-cm and soil base saturation (BS) ratio in the top 20-cm soil, while water addition significantly increased soil CEC and BS ratio in the top 20-cm soil. Water addition significantly increased Na (+ 75.1%) in the entire soil profile and increased Ca (+ 14.8%), Mg (+ 12.7%) at the 0–10, 10–20 and 40–60 cm soil layers. Soil pH positively correlated with soil exchangeable Ca, Mg and Na, but negatively with available Fe, Mn and Cu in the upper 20 cm. Soil base cations and CEC positively correlated with clay and silt contents, but negatively with sand content along the profile. These results can extend our understandings on soil cation dynamics to deep soil profile under long-term N and water addition and suggest that precipitation effects should be considered when assessing N deposition effects on these soil cations.

Interaction of liming and long-term fertilization increased crop yield and phosphorus use efficiency (PUE) through mediating exchangeable cations in acidic soil under wheat\u2013maize cropping system

Low phosphorus use efficiency (PUE) is one of the main problems of acidic soil that limit the crop growth. Therefore, in the present study, we investigated the response of crop yield and PUE to the long-term application of fertilizers and quicklime (CaO) in the acidic soil under wheat–maize rotation system. Treatments included, CK (no fertilization), NP (inorganic nitrogen and P fertilization), NPK (inorganic N, P and potassium fertilization), NPKS (NPK + straw return), NPCa (NP + lime), NPKCa (NPK + lime) and NPKSCa (NPKS + lime). Results showed that, fertilizer without lime treatments, significantly (p ≤ 0.05) decreased soil pH and crop yield, compared to the fertilizer with lime treatments during the period of 2012–2018. Average among years, compared to the CK treatment, wheat grain yield increased by 138%, 213%, 198%, 547%, 688% and 626%, respectively and maize yield increased by 687%, 1887%, 1651%, 2605%, 5047% and 5077%, respectively, under the NP, NPK, NPKS, NPCa, NPKCa and NPKSCa treatments. Lime application significantly increased soil exchangeable base cations (Ca2+ and Mg2+) and decreased Al3+ cation. Compared to the NP treatment, phosphorus use efficiency (PUE) increased by 220%, 212%, 409%, 807% and 795%, respectively, under the NPK, NPKS, NPCa, NPKCa and NPKSCa treatments. Soil pH showed significant negative relationship with exchangeable Al3+ and soil total N. While, soil pH showed significant (p ≤ 0.05) positive relationship with exchangeable Ca2+, PUE and annual crop yield. PUE was highly negatively correlated with soil exchangeable Al3+. In addition, soil exchangeable Ca2+, pH, exchangeable Al3+ and available N were the most influencing factors of crop yield. Therefore, we concluded that lime application is an effective strategy to mitigate soil acidification and to increase PUE through increasing exchangeable base cations and reducing the acidic cations for high crop yield in acidic soil.

Higher soil acidification risk in southeastern Tibetan Plateau

Stable soil pH is a key property in maintaining an ecosystem's structure, function, and sustainability. Increasing atmospheric deposition and grassland use on the Tibetan Plateau (TP) may increase the soil acidification risk, but we lack such information to date. Here, we evaluated the soil acidification risk in the TP, by comparing it with that in the Mongolia Plateau (MP) and applying the acid–base balance principles on atmospheric inputs, soils, and plants from 1980 to 2019. Cumulative acid input was lower in the TP than in the MP. Sulfur contributed more to acidity than nitrogen and atmospheric deposition contributed more to acidity than grassland use. Acid input was mainly influenced by local industry, animal husbandry and transportation in the MP, while in the TP it was also affected by the long-distance transportation of pollutants from South Asia and southern China. Overall, the TP was less acid-sensitive than the MP because of higher inorganic carbon content. However, soils in the southeastern TP, covering 21% of the total area, were acid-sensitive due to low levels of soil exchangeable base cation (EBCs) and lack of calcium carbonate. Coincidentally, the southeastern region has the highest concentration of acid input in the TP due to more rapid development and stronger influence of adjacent high acid deposition regions than others. Therefore, the acidification risk to the southeastern region is much higher than to other regions of the TP and the MP; in this region, the EBCs are likely to be depleted approximately 95 years earlier than in the MP. The findings of this study provide insights into the response of the TP to global change. For the ecosystem sustainability of southeastern TP, control of atmospheric acid deposition, especially sulfur deposition, in both local and adjacent regions and nations is required.

Striking a balance between N sources: Mitigating soil acidification and accumulation of phosphorous and heavy metals from manure

Manure amendment has been shown to effectively prevent red soil (Ferralic Cambisol) acidification from chemical nitrogen (N) fertilization. However, information is lacking on how much manure is needed to mitigate acidification and maintain soil productivity while preventing accumulation of other nutrients and heavy metals from long-term inputs. This study determined the effects of various combinations of manure with urea-N on acidification and changes in soil P, K, and heavy metals in a 9-year maize field experiment in southern China. Treatments included chemical N, P and K fertilization only (NPKM0), and NPK plus swine manure, which supplied 20% (NPKM20), 40% (NPKM40), and 60% (NPKM60) of total N at 225 kg N ha−1 year−1. Soil pH, exchangeable acidity, available P and K, and maize yield were determined annually from 2009 to 2018. Soil exchangeable base cations, total and phytoavailable Cr, Pb, As, Ni, Cd, Cu, and Zn were measured in 2018. A significant decrease in soil pH occurred under NPKM0 and NPKM20 from initial 4.93 to 4.46 and 4.71, respectively. Whereas, under NPKM40 and NPKM60 no change or a significant increase in soil pH (to 5.47) occurred, as well as increased exchangeable base cations, and increased yields. Manure application markedly increased soil available P (but not K) to 67.6–182.6 mg kg−1 and significantly increased total Pb, Cu, and Zn and available Cu and Zn in soil. The results indicate sourcing 40% or greater of total N from manure can prevent or reverse acidification of red soil, and provide all P required, however, additional K inputs are required for balanced plant nutrient supply. An integrated approach of increasing N use efficiency, reducing chemical input, and reducing heavy metal concentrations in animal feed are all necessary for sustainable use of manure in soil acidity and nutrient management as well as minimizing environmental risks.

Liming effects of poultry litter derived biochar on soil acidity amelioration and maize growth

Crop production in acid soils is facing enormous challenges due to low soil quality associated with an increase in the acidification rate and aluminum toxicity. Despite comprehensive prior work with biochar application on nutrient availability and crop productivity in acid soils, little information is available about the recommendation or standardization of biochar application rates that are more suitable for soil fertility improvement under different soil environments (physico-chemical properties) for maximizing the benefits of biochar applications and minimizing the potential environmental risk. Thus, the objective of this study was to investigate the effectiveness of poultry litter (PL) and poultry litter biochar (PLB) in ameliorating the fertility of acid soils through incubation and pot experiments. The soil was amended with different materials as follows; lime (1 g kg−1), PL (5, 10 and 15 g kg−1) and PLB (5, 10 and 15 g kg−1) along with control (non-amended). A pot experiment was also conducted using similar treatments to observe the responses of maize crop to the different amendments. The results indicated an increase in the pH and a decrease in exchangeable acidity in lime, PL and PLB amended soils. Lower soil pH, base cations and soil available phosphorus (P), and higher exchangeable acidity were found in control than the amended soils. Compared to PL and lime, PLB achieved greater increase rate in soil pH and reduction rate in soil exchangeable acidity with increased soil exchangeable base cations. An increase in soil available calcium (Ca) was observed in the lime treatment, while in PL and PLB treatments, there was an increase in soil available Ca, magnesium (Mg), potassium (K) and P. Application of the amendments increased availability of nitrogen (N), P, K, Ca and Mg relative to the control for maize in the pot experiment. When PL and PLB amendments were compared, it was found that the PLB was the best choice for the amelioration of acid soils as well as nutrient uptake by maize plants. It is suggested that application of PLB at the rate of 15 g kg−1 is suitable for maize growth in acid soils.

Soil aggregation and aggregate-related exchangeable base cations under different aged tea (Camellia sinensis L.) plantations in the hilly regions of southern Guangxi, China

ABSTRACT As the secondary nutrients in soils, exchangeable base cations can form cationic bridges with clay particles and organic matters to promote the formation of soil aggregates, and to protect soil organic carbon (Corg) and nutrients from loss. To have a comprehensive understanding toward the dynamics of soil exchangeable base cations in the tea planting process, it requires to evaluate these cations’ distribution in soil aggregates at various sizes. In this study, soil samples (0–20 cm) from the tea plantations at various ages (8, 17, 25, and 43 yr.) in the hilly regions of southern Guangxi, China were divided into >2, 1–2, 0.25–1, and <0.25 mm aggregate fractions through a dry-sieving procedure. Then, the cation exchange capacity (CEC), total exchangeable bases (TEB), and different individual cations, such as exchangeable potassium (K+), sodium (Na+), calcium (Ca2+), and magnesium (Mg2+), in soil aggregates were detected. Our results suggested that the mean weight diameter (MWD), that is an indicator evaluating the stability of soil aggregates, in the 17-yr. tea plantations appeared to be the highest among all the tea plantations, indicating that more stable soil aggregates could be formed in the 17-yr. tea plantations in comparison with the rest plantations. During tea planting of 35 yr. (from 8 to 43 yr.), the increasing rate of soil CEC stock was 33.42 cmol m−2 yr.−1, while the loss rates of soil exchangeable K+, Na+, Ca2+, Mg2+, and TEB were 0.89, 0.52, 3.86, 1.23, and 6.51 cmol m−2 yr.−1, respectively. Interestingly, the loss rates of soil exchangeable base cations in the middle phase (from 17 to 25 yr.) were greater than those in other phases. Therefore, it is of critical importance to implement a sustainable management scheme to maintain soil aggregate stability and to minimize the loss of soil exchangeable base cations in the tea planting process, especially after 17 yr., in the hilly regions of southern Guangxi, China.

Effects of fertilizer of calcium silicon magnesium potassium on the dynamics of soil acidity and exchangeable base cation in paddy field of southern China

Soil acidification of large areas of paddy fields in southern China has become an important problem in rice production. Therefore, how to ameliorate or remedy the acidifying paddy soil and to exposit its mechanism has important theoretical and practical significance for rebuilding healthy soils and guaranteeing national food security. Although lime has already been extensively used to remedy acidified soils, long-term application of a large amount of lime would not only cause the soil to harden, but also disturb the balance between calcium, potassium and magnesium in the soil. Given the advantages of lower solubility and comprehensive nutrient supply, fertilizer of calcium silicon magnesium potassium (CSMP) may be used as an alternative. The aim of this study was to clarify the functions of CSMP and its effects on soil acidification in paddy fields. A four-year field experiment was conducted to investigate the dynamics of soil pH, exchangeable acidi-ty, exchangeable base cation and available silicon, as well as 0~30 cm pH buffer capacity (pHBC), net base production under CSMP fertilization in the paddy soil. There were five treatments, i.e. CK (traditional fertilization practice of the local farmers), treatment I (CK plus 750 kg·hm-2 CSMP); treatment II (CK plus 1125 kg·hm-2 CSMP), treatment III (CK plus 1500 kg·hm-2 CSMP), and treatment IV (CK plus 1875 kg·hm-2 CSMP). The results showed that the traditional fertilization practice of the local farmers resulted in a decline of soil pH, soil exchangeable base cation and base saturation year by year, but soil exchangeable acid was increased with year. Conversely, CSPM fertlization significantly raised soil pH, with the magnitude of increases positively depending on the number of application times or application rate. Continuous and repeated application of CSMP effectively promoted the accumulation of exchangeable base cation and the consumption of soil exchangeable acid in paddy soil, especially for the accumulation of soil exchangeable Ca2+, Mg2+ and the consumption of soil exchangeable Al3+. Furthermore, the more amount of CSPM application resulted in the more accumulation or consumption, but with relatively slower rate. The exchangeable base cation and alkali released by CSMP contributed 108.8% to the total reduction of soil exchangeable acid, suggesting that it was the main path to reduce soil exchangeable acid. Meanwhile, CSMP application improved soil acidity in paddy field, with the content of available silicon increased year by year and the increase amplitude became larger with the more amount of CSMP application. The traditional fertilization of local farmers resulted in soil acidification, with a acidification rate was 2.86 kmol H+·hm-2·a-1. CSMP application could effectively control soil acidification, producing a lot of alkalinity with net alkalinity production of 9.93-13.82 kmol OH-·hm-2·a-1. CSPM could release Ca2+, Mg2+ and alkali, which would mitigate soil acidification in paddy fields.

Mechanisms for increasing soil resistance to acidification by long-term manure application

Soil pH buffering capacity (pHBC) plays a crucial role in determining soil acidification rates and the amount of lime required to ameliorate soil acidity. However, it remains poorly understood how soil organic matter affects soil pHBC. Here, Alfisol and Ultisol samples from long-term fertilization experiments (control, chemical N, P, and K (NPK), manure only (M), 1/2 NPK plus 1/2 M (1/2NPKM), and NPK plus M (NPKM)) were used to investigate the effects and underlying mechanisms of manure application on the pHBC and soil resistance to acidification through simulated acidification experiments. The results indicated that the application of manure increased pHBC and the resistance of soils to acidification in both the Alfisol and Ultisol. The pHBC of the Alfisol in the M and NPKM treatments was increased by 81 and 60% compared with the control, respectively. Similarly, the pHBC of the Ultisol in the NPKM treatment was 66% higher than that of the control. The extent of protons consumption by the Alfisol followed the order: M > NPKM > 1/2NPKM > NPK ≈ control during stimulated acidification, which was consistent with their pHBC. These results suggested that manure application increased the resistance of the Alfisol to acidification by increasing soil pHBC. The protonation of organic anions from the dissociation of weakly acidic functional groups on soil organic matter to form neutral molecules was the main mechanism responsible for the increase in pHBC and soil resistance to acidification induced by manure application. During this process, some exchangebale base cations were released from negatively charged sites on organic matter into soil solution. This mechanism was confirmed by the experimental observations: the release of base cations from soils increased, while soil exchangeable base cations and effective CEC decreased as soil pH decreased. The results are of fundamental significance for understanding the role of organic matter in retarding soil acidification through long-term manure application.

Ameliorating Effects of Fungus Chaff and Its Biochar on Soil Acidity

A biochar was generated from fungus chaff at 300 °C, and the ameliorating effects of fungus chaff and its biochar on an acidic Ultisol were compared using incubation experiments. Incorporation of fungus chaff and its biochar significantly increased soil pH and soil exchangeable base cations but decreased soil exchangeable acidity. The ameliorating effect was greater for the biochar than the fungus chaff, and thus the biochar was a better amendment for acidic soil than its feedstock of fungus chaff. The biochar ameliorated soil acidity mainly through the release of its contained alkaline substances, while fungus chaff increased pH of acidic soils through two mechanisms: release of alkaline substances and inhibition of soil nitrification. The incorporation of fungus chaff increased soil-available organic carbon and thus accelerated the microbial assimilation of inorganic nitrogen, while incorporation of fungus chaff biochar enhanced nitrification due to increased soil pH.

Initial effects of thinning on soil carbon storage and base cations in a naturally regenerated Quercus spp. forest in Hongcheon, Korea

Thinning can affect soil carbon (C) and base cation balances by reducing tree density and altering microclimate and organic matter budget; however, the subsequent changes in soil C and base cation contents after thinning are not well elucidated. Thus, this study investigated the effects of thinning on C storages in soil (at 0–10 cm, 10–20 cm, and 20–30 cm depths) and forest floor and concentrations of soil exchangeable base cations (Ca2+, Mg2+, K+, and Na+). Thinning treatments of different intensities based on the removed basal area (no thinning: control, 15% thinning: T15, and 30% thinning: T30) were applied to a naturally regenerated 31 to 40-year-old Quercus spp. forest. Soil C concentrations at 10–20 cm and 20–30 cm depths were significantly higher in T15 and T30 than in the control after 39 months, but not after 4 months. T15 and T30 treatments seemed to increase soil C storage at 0–30 cm after 39 months, but did not significantly change forest floor C storage after 4 and 39 months. Concentrations of exchangeable K+ of T15 and exchangeable base cations except for Ca2+ of T30 depth were significantly lower than those of the control at 0–10 cm after 4 months, but not after 39 months. This study shows that thinning treatments on a naturally regenerated Quercus spp. forest could increase soil C concentration after a few years but temporally decrease concentrations of soil exchangeable base cations.

Sheep manure application increases soil exchangeable base cations in a semi-arid steppe of Inner Mongolia

The long-term productivity of a soil is greatly influenced by cation exchange capacity (CEC). Moreover, interactions between dominant base cations and other nutrients are important for the health and stability of grassland ecosystems. Soil exchangeable base cations and cation ratios were examined in a 11-year experiment with sheep manure application rates 0–1,500 g/(m2·a) in a semi-arid steppe in Inner Mongolia of China, aiming to clarify the relationships of base cations with soil pH, buffer capacity and fertility. Results showed that CEC and contents of exchangeable calcium (Ca2+), magnesium (Mg2+), potassium (K+) and sodium (Na+) were significantly increased, and Ca2+ saturation tended to decrease, while K+ saturation tended to increase with the increases of sheep manure application rates. The Ca2+/Mg2+ and Ca2+/K+ ratios decreased, while Mg2+, K+ and Na+ saturations increased with increasing manure application rates. Both base cations and CEC were significantly and positively correlated with soil organic carbon (SOC) and soil pH. The increases of SOC and soil pH would be the dominant factors that contribute to the increase of cations in soil. On a comparison with the initial soil pH before the experiment, we deduced that sheep manure application could partly buffer soil pH decrease potentially induced by atmospheric deposition of nitrogen and sulfur. Our results indicate that sheep manure application is beneficial to the maintenance of base cations and the buffering of soil acidification, and therefore can improve soil fertility in the semi-arid steppes of northeastern China.

Amelioration of an Ultisol profile acidity using crop straws combined with alkaline slag.

The acidity of Ultisols (pH <5) is detrimental to crop production. Technologies should be explored to promote base saturation and liming effect for amelioration of Ultisol pH. Column leaching experiments were conducted to investigate the amelioration effects of canola straw (CS) and peanut straw (PS) in single treatment and in combination whether with alkaline slag (AS) or with lime on Ultisol profile acidity. The treatment without liming materials was set as control, and the AS and lime in single treatment are set for comparison. Results indicated that all the liming materials increase soil profile pH and soil exchangeable base cations at the 0-40-cm depth, except that the lime had amelioration effect just on 0 to 15-cm profile. The amelioration effect of the liming materials on surface soil acidity was mainly dependent on the ash alkalinity in organic materials or acid neutralization capacity of inorganic materials. Specific adsorption of sulfate (SO4(2-)) or organic anions, decarboxylation of organic acids/anions, and the association of H(+) with organic anions induced a "liming effect" of crop residues and AS on subsoil acidity. Moreover, SO4(2-) and chloride (Cl(-)) in PS, CS, and AS primarily induced base cations to move downward to subsoil and exchange with exchangeable aluminum (Al(3+)) and protons (H(+)). These anions also promoted the exchangeable Al to leach out of the soil profile. The CS was more effective than PS in decreasing soil acidity in the subsoil, which mainly resulted from higher sulfur (S) and Cl content in CS compared to PS. The CS combined with AS was the better amendment choice in practical agricultural systems.

Effects of aged and fresh biochars on soil acidity under different incubation conditions

Biochar has positive effects as a soil acidity amendment which is a global concern. However, few studies have been reported on the effect of aged biochar on soil acidity. Incubation methods with different ventilation conditions may induce different effects on soil acidity amendment using biochar. This study analyzed the effects of fresh and aged biochars on soil acidity amendment with different incubation methods. Samples of typical acidic soil (plinthudults) and fresh Pinus massoniana bark were collected from the hilly red soil region of southern China and used to create biochar (PB) with the oxygen-limited pyrolysis method at 450°C. A 4-month-aged PB (PBa) which was produced by a natural forest fire was collected from the same area as that of biochar PB. A 69 days incubation experiment was conducted using an improved incubation method. The treatments comprised 100g soil+2g PBa (PBA), 100g soil+2g PB (ventilated incubation, PBV), 100g soil+2g PB (sealed incubation, PBS) and 100g soil only incubated under ventilated (CKV) and sealed (CKS) conditions. Soil pH was measured periodically. Soil exchangeable base cations, exchangeable acidity, exchangeable aluminum (Al3+) and cation exchange capacity (CEC) were measured after incubation. Throughout the incubation period, PB and PBa positively enhanced soil pH (P<0.05), with PB exhibiting more remarkable effects. A similar effect was also observed for soil exchangeable Al3+ and exchangeable acidity. After incubation, soil pH values of PBV (5.05±0.02) and PBS (4.99±0.03) were than the value of PBA (4.98±0.03), with nonsignificant differences (P>0.05) between values in PBV and PBS. PB addition improved soil exchangeable base cations and base saturation compared to PBa addition. Soil CEC levels in PBA, PBV, and PBS were not significantly different from those in CKV and CKS, but CEC in PBV and PBS were significantly higher than the CEC in PBA. All parameters in PBV were not significantly different from the parameters in PBS. Biochar PB can be used to amend soil acidity, but the efficiency declines to a certain extent if biochar PB has undergone a short-term aging before being added to soils. The different ventilation conditions had little influence on soil acidity amendment using biochar.

Use of Alkaline Slag and Crop Residue Biochars to Promote Base Saturation and Reduce Acidity of an Acidic Ultisol

This investigation was conducted by using alkaline slag and crop straw biochars to reduce acidity of an acidic Ultisol through incubation and pot experiments with lime as a comparison. The soil was amended with different liming materials: lime (1 g kg−1), alkaline slag (2 and 4 g kg−1), peanut straw biochar (10 and 20 g kg−1), canola straw biochar (10 and 20 g kg−1) and combinations of alkaline slag (2 g kg−1) and biochars (10 g kg−1) in the incubation study. A pot experiment was also conducted to observe the soybean growth responses to the above treatments. The results showed that all the liming materials increased soil pH and decreased soil exchangeable acidity. The higher the rates of alkaline slag, biochars, and alkaline slag combined with biochars, the greater the increase in soil pH and the reduction in soil exchangeable acidity. All the amendments increased the levels of one or more soil exchangeable base cations. The lime treatment increased soil exchangeable Ca2+, the alkaline slag treatment increased exchangeable Ca2+ and Mg2+ levels, and the biochars and combined applications of alkaline slag with biochars increased soil exchangeable Ca2+, Mg2+ and K+ and soil available P. The amendments enhanced the uptake of one or more nutrients of N, P, K, Ca and Mg by soybean in the pot experiment. Of the different amendments, the combined application of alkaline slag with crop straw biochars was the best choice for increasing base saturation and reducing soil acidity of the acidic Ultisol. The combined application of alkaline slag with biochars led to the greatest reduction in soil acidity, increased soil Ca, Mg, K and P levels, and enhanced the uptake of Ca, Mg, K and P by soybean plants.

Pyrolysis temperature influences ameliorating effects of biochars on acidic soil

The biochars were prepared from straws of canola, corn, soybean, and peanut at different temperatures of 300, 500, and 700 °C by means of oxygen-limited pyrolysis.Amelioration effects of these biochars on an acidic Ultisol were investigated with incubation experiments, and application rate of biochars was 10 g/kg. The incorporation of these biochars induced the increase in soil pH, soil exchangeable base cations, base saturation, and cation exchange capacity and the decrease in soil exchangeable acidity and exchangeable Al. The ameliorating effects of biochars on acidic soil increased with increase in their pyrolysis temperature. The contribution of oxygen-containing functional groups on the biochars to their ameliorating effects on the acidic soil decreased with the rise in pyrolysis temperature, while the contribution from carbonates in the biochars changed oppositely. The incorporation of the biochars led to the decrease in soil reactive Al extracted by 0.5mol/L CuCl2, and the content of reactive Al was decreased with the increase in pyrolysis temperature of incorporated biochars. The biochars generated at 300 °C increased soil organically complexed Al due to ample quantity of oxygen-containing functional groups such as carboxylic and phenolic groups on the biochars, while the biochars generated at 500 and 700 °C accelerated the transformation of soil exchangeable Al to hydroxyl-Al polymers due to hydrolysis of Al at higher pH. Therefore, the crop straw-derived biochars can be used as amendments for acidic soils and the biochars generated at relatively high temperature have great ameliorating effects on the soils.

Assessing forest soil base cation status and availability using lake and stream sediment geochemistry: A case study in Quebec (Canada)

Spatial information about forest soil base cations is important because of its implications for forest health and resilience to disturbance and management.The relevance of using geochemical data from lake and stream sediments collected for mining prospection purposes was evaluated to assess on a relative basis the forest soil base cation status and availability across the Quebec (Canada) forest landbase, an area for which information on soil properties is scarce.The relevance of the acid extraction of the fine fraction (<177μm) method, used to determine element composition of sediments, was tested as an indicator of forest soil fertility and exchangeable base cation status.Values of element concentrations of sediments were then extrapolated spatially from their sampling points to the whole of the Quebec forest landbase, based on their geographical location and on the topographical features of their position using the k-nearest neighbour imputation method. The acid extraction used to determine the geochemical composition of sediments yielded concentrations of Ca, Mg and K that were well correlated with the observed exchangeable base cation concentrations, effective cationic exchange capacity and presence of clay-sized particles of soil samples. Also, spatial imputation of the geochemical signature of sediments to the forest landbase produced values that successfully represented variations in acid-extractable K and Mg in forest soils, as validated with two independent forest soil datasets, but it failed to capture variations in acid-extractable Ca concentrations. Nevertheless, the spatialized values broadly illustrated the gradient of forest soil exchangeable base cation reserves, soil clay content and site richness at a coarse scale across landscapes.

Resilience of upland soils to long term environmental changes

The effect of long-term changes in land-use, pollution deposition and climate change on upland soils was evaluated by resurveying a large set of sites in a mountain landscape in the UK, which were initially sampled forty years ago. Unexpectedly, despite the length of time between sampling dates, no significant changes in pH, soil exchangeable base cations or C and N percentage content by weight were observed across a range of soil type and parent material. This suggests that the soils have been relatively resistant to the large changes in the environmental pressures experienced in the past forty years, which include a 1.5°C increase in mean temperature; the peak of UK sulphur deposition in around 1970, followed by ~90% deposition reduction; long-term increases in nitrogen deposition; and major changes in grazing intensity. These results suggest that upland soils may be considerably more resilient to the future environmental changes than many previous assessments have suggested.