Exchangeable Base Cations Research Articles

Causes of Soil Acidity and Its Management Mechanisms in Ethiopia: A Review.

Soil acidity has become a serious problem to crop production in most highlands of Ethiopia. An earlier study estimated that about 41% of cultivated land in Ethiopia is affected by soil acidity where 28% of cultivated land is highly acidic. Even though this much were acidic, it its degree is varied from location to location in which highland was severely affected thereby limit crop productivity and livelihoods. In the highland of Ethiopia acidification could aggravated due to the different agents such as depletion of organic matter, soil nutrients, feature of topography and high rainfall which can to leach appreciable amounts of exchangeable basic cations. In large parts of the country application acid-forming chemical fertilizers, removal of crop residues, and parent material of the soil are the causes for soil acidification. Acidic soil adversely affects the availability of phosphorus, calcium, magnesium and other nutrients, which can in turns affect the diversity and function of soil microbes. Soil acidity can amend through application of; lime, integrate soil fertility management components, and using acid tolerant crops varieties. Liming can treat soil pH along with supplying oxides and hydroxides of calcium and magnesium to the soil. Management of acid soil is crucial issue for enhancing crop productivity and improves food security. It also provides important information on management options to amend soil acidity and improve soil fertility.

Linking Soil Acidity to P Fractions and Exchangeable Base Cations under Increased N and P Fertilization of Mono and Mixed Plantations in Northeast China

Atmospheric N deposition is increasing worldwide, especially in China, significantly affecting soil health, i.e., increasing soil acidification. The northern region of China is considered to be one of the N deposition points in Asia, ranging from 28.5 to 100.4 N ha−1yr−1. Phosphorus (P) is the limiting factor in the temperate ecosystem and an important factor that makes the ecosystem more susceptible to N-derived acidification. However, it remained poorly understood how the soil acidification process affects soil P availability and base cations in the temperate region to increased N deposition. To address this question, in May 2019, a factorial experiment was conducted under N and P additions with different plantations in Maoershan Experimental Forest Farm, Northeast China, considering species and fertilization as variables. The effective acidity (EA) increased by N and NP fertilizations but was not significantly affected by P fertilization. Similarly, the pH, base saturation percentage (BS%), calcium (Ca2+), and magnesium (Mg2+) were decreased under N addition, while the Al:Ca ratio increased, whereas NaHCO3 inorganic phosphorus (Pi) and NaOH organic phosphorus (Po) significantly decreased under N enrichments. However, NaOH Pi increased in N-enriched plots, while H2O Pi and NaHCO3 Pi increased under the P addition. Thus, the results suggest that the availability of N triggers the P dynamics by increasing the P uptake by trees. The decrease in base cations, Ca2+, and Mg2+ and increase in exchangeable Fe3+ and Al3+ ions are mainly responsible for soil acidification and lead to the depletion of soil nutrients, which, ultimately, affects the vitality and health of forests, while the P addition showed a buffering effect but could not help to mitigate the soil acidity.

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.

Physico-chemical evaluation of soil resources in different regions of Taza – Taounate, Morocco

<p>The area studied Taza-Taounate is a vast mountain range in north-central Morocco, characterized by a variation in bio-geographical factors that encourage a vibrant and diversified vegetation cover with a remarkable rate of endemism compared to Moroccan flora. Our work involves the physicochemical analysis of soils at seven stations in the study area. Three surface soil samples (0-15 cm) were collected and analyzed for physical and chemical parameters using standard laboratory techniques at each station.</p><p>The results showed the clay fraction's dominance in S2 and S3 and the silt fraction in stations S1, S4, S5, S6, and S7. The studied soils have low levels of organic carbon (0.97% to 2.29%), high levels of CaCO<sub>3 </sub>(10.1% to 24.9%), and neutral and slightly alkaline pH (7.01to 7.81). The most dominant element in all stations is calcium exchangeable, with values ranging from 51.52 to 74.91 cmol+/kg. The other exchangeable basic cations (Mg<sup>2+</sup>, Na<sup>+</sup>, K<sup>+</sup>) have relatively low levels. CEC values vary between 36.12 and 81.13 cmol+/kg, indicating that our soil type is heavy to organic.</p>

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.

Effects of straw decayed products of four crops on the amelioration of soil acidity and maize growth in two acidic Ultisols.

Variable charge soils have low agricultural productivity associated with low pH, low cation exchange capacity (CEC), and low pH buffering capacity (pHBC). As a result of rapid acidification rates, these soils are prone to infertility resulting from Al phytotoxicity and deficiency of P, Ca, Mg, and K, and thus require amendments that can ameliorate soil acidity and enhance soil CEC and pHBC. A 30-day pot experiment was carried out using a clay Ultisol and a sandy Ultisol amended with straw decayed products (SDPs) of peanut, pea, canola, and rice. The results showed that applying SDPs increased the soil CEC, organic matter content, and exchangeable base cations in the two Ultisols. The ameliorative effects of the SDPs were superior for the sandy Ultisol than for the clay Ultisol. The addition of SDPs significantly increased soil pH and pHBC of the two Ultisols, and simultaneously decreased soil exchangeable Al3+. Among them, the greatest effect was found in the treatment with pea straw decayed products (PeaSD). The soil pHs of clay Ultisol and sandy Ultisol treated with PeaSD were respectively 5.70 and 7.37 and were 1.26 and 2.63 pH units higher than those of control. Also, applying SDPs increased maize seedling biomass in both soils and the most significant effect was found in the treatment with PeaSD, which were 0.97 (clay Ultisol) and 2.5 (sandy Ultisol) times higher than in the respective controls. The results of this study demonstrated that carefully selected straws for SDP production can effectively improve soil chemical properties, enhanced soil pHBC, and thus promote agricultural sustainability.

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.

The Mineral Fertilizer-Dependent Chemical Parameters of Soil Acidification under Field Conditions

Soil acidification in agroecosystems is a natural process that could be accelerated, mainly by the inappropriate application of mineral fertilizers, or prevented, by sustainable management practices. On the basis of a three-year field study in a grassland agroecosystem, the impact of different rates of fertilization with nitrogen (N), phosphorus (P), and potassium (K) on soil chemical parameters related to soil acidity was evaluated. It was found that high-rate fertilization with ammonium nitrate accelerated the soil acidification process, which was additionally intensified by the application of superphosphate and potassium salt. The sum of exchangeable base cations, the values of base saturation and hydrolytic acidity in the soil reflected the interactions between the applied NPK-fertilizer levels. Considering chemical parameters related to soil acidity studied in this experiment, it seems that the best strategies for mitigating soil acidification in grasslands are reducing nitrate leaching, changing fertilizer types and increasing the input of base cations.

Does the enrichment of post-arable soil with organic matter stimulate forest ecosystem restoration—A view from the perspective of three decades after the afforestation of farmland

The restoration of forest ecosystems on former agricultural land faces numerous challenges resulting mainly from differences in soil properties between post-arable and continuously forested ground. We revisited a 34-year-old but very well-documented experiment with enrichment in organic matter of the arable sandy soil aiming to accelerate humus formation and soil biota regeneration in Scots pine plantation. The goal of our study was to determine whether the addition of a mixture of pine bark with sawdust or lupine cultivation would change the selected soil properties and, as a result, would shift soil microarthropods of post-agricultural plantations towards those occurring in pine monocultures on continuously forested land. The effect of tillage depth was also studied.The soil properties of the experimental plantation differed significantly from those of the forest soil with respect to the pH, nitrogen (N) content, C/N ratio, sum of exchangeable base cations and degree of soil saturation with base cations. Moreover, the diversity and taxonomic and functional structures of Collembola assemblages differed considerably from the assemblages of pine monoculture of the same age growing on continuously forested land. The expectation of the experiment was not met; however, a certain significant ameliorative effect on some soil properties was observed with some treatments. The total organic carbon content (TOC), C/N ratio and cation exchange capacity increased as a result of the addition of bark and sawdust. In plots where deep tillage was applied, the TOC and N contents were lower than those in plots with shallow soil cultivation. A significant increase in the number of hemiedaphic forms at the expense of euedaphic and atmobiotic forms was observed in plots with lupine, while a mixture of pine bark and sawdust caused an increase in the number of euedaphic forms.Soil pH was identified as a key parameter that determined the difference between forest and post-agricultural collembolan assemblages. The variability of the structure of post-agricultural assemblages depends on N and exchangeable Mg2+ contents and hydrolytic acidity. The enrichment of post-arable soil with organic matter and tillage had long-lasting effects on soil properties but did not stimulate restoration of forest collembolan assemblages on former farmland.

Effects of whole‐tree harvesting at thinning and subsequent compensatory nutrient additions on carbon sequestration and soil acidification in a boreal forest

AbstractResidues from forest harvesting operations may be utilized as a renewable energy source. However, the sustainability of this practice has been questioned due to the losses of nutrients and exchangeable base cations, which may impair the forest's carbon sequestration capacity and lead to soil acidification. We report the 18 year response of biomass growth, soil carbon stock and soil chemistry to whole‐tree harvest at thinning and associated compensatory measures in a Pinus sylvestris forest in northern Sweden. The whole‐tree harvest at thinning was combined with nutrient additions to compensate for the nutrient loss caused by extracting the residues. Four main treatments, stem‐only thinning, whole‐tree thinning, whole‐tree thinning with one‐time nitrogen fertilization and whole‐tree thinning with repeated nitrogen fertilization every third year were applied, with plots split for wood‐ash treatment. Eighteen years after the treatments, whole‐tree thinning that had removed 3.0 ± 0.2 Mg C/ha in residues had no effect on forest growth, soil carbon and nitrogen stocks or soil chemistry. Both nitrogen fertilization regimes increased biomass growth, but neither one resulted in a significant increase in soil carbon stock. Wood‐ash addition increased soil pH and exchangeable base cations, but did not affect carbon stock in biomass or soil. Our long‐term data suggest that utilizing harvesting residues for biofuel feedstocks is appropriate in this type of forest. Hence, any nitrogen and wood‐ash additions appear unnecessary as compensatory measures for the removal of harvesting residues, but nitrogen can be applied to increase forest growth following thinning.

High negative surface charge increases the acidification risk of purple soil in China

Purple soils, developing from rapid physical weathering of nutrient rich sedimentary rock and classified as Inceptisols or Entisols in United States Department of Agriculture (USDA) Taxonomy, are the most important agricultural soils in the Sichuan basin of southwestern China. A portion of purple soils has been acidified and the acidification risk of these soils need further understanding. Here, electrodialysis (ED) was used to simulate the process of natural acidification of soils. We investigated the acidification risk of purple soils by ED treatments and compared its acidification characteristics with that of variable charge soils (Oxisol and Alfisol). Our results showed that the degree of acidification of purple soils after ED treatments was much higher than that of variable charge soils, although the purple soils contained more exchangeable base cations. There was no significant correlation between the purple soil acidity before and after ED treatments, however, the pH of purple soils after the ED treatments had a significant negative correlation (r = −0.680, P < 0.01) with the soil cation exchange capacity (CEC). We concluded that CEC (i.e., effective negative surface charges) played a decisive role in determining the acidification potential of purple soils. High content of clay minerals and low content of Fe/Al oxides in the purple soils lead to the higher amount of effective negative surface charge than that of variable charge soils, which induced the rise in the amount of H+ and Al3+ absorbed on the surface of purple soils and increased the acidification degree of purple soils remarkably. Therefore, compared to the variable charge soils, the purple soils had a higher acidification risk. These findings will provide a useful reference for the understanding of the acidification characteristics of purple soils.

Seedling growth and survival responses to multiple soil properties in subtropical forests of south China

Soil properties and light availability have been long recognized as fundamental drivers of species distribution and are especially important during the regeneration phase. The role of nutrients such as exchangeable base cations is poorly understood, despite forests facing considerable changes in soil composition due to climatic change and atmospheric acid deposition, including in south China.With the aim of understanding the response of naturally regenerating seedling communities to a wide range of abiotic conditions, we quantified seedling growth and survival of over 2000 seedlings representing 166 morpho-species within four subtropical forests in south China, for two years. We assessed their responses to canopy openness, and a natural gradient of soil characteristics: moisture, pH, total nitrogen (N), total carbon (C), C:N ratio, available phosphorus (P), available potassium (K), calcium (Ca), iron (Fe), magnesium (Mg), manganese (Mn), and sulfur (S). We conducted our analyses at three levels: landscape (1), forest site (4), and species (7).We found statistically clear effects of several soil properties on seedling growth and survival, at all levels of analysis, while canopy openness showed a minimal negative effect on survival and none on growth. Seedling growth was positively affected by increasing soil Ca and Mn and negatively by increasing soil Mg at the landscape level (all four forest sites combined). Seedling survival responded positively to soil Fe and C:N ratio, but negatively to soil Ca, Mg, Mn, N, and S. The observed patterns were forest site- and species-specific. These results are especially relevant in a region experiencing severe changes in soil conditions as well as intense deforestation and land use change. Reforestation programs should consider the site specificity of soil properties with respect to a wide range of soil nutrients when planning restoration activities.

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.

Distribution of Root-Lesion and Stunt Nematodes, and Their Relationship with Soil Properties and Nematode Fauna in Sugarcane Fields in Okinawa, Japan

Sugarcane cultivation in Japan has not yet focused on suppressing plant-parasitic nematodes. For proper nematode management, it is essential to know the spatial distribution of economically important plant-parasitic nematodes and free-living nematodes that play important roles in terrestrial ecosystems. We aimed to reveal nematode fauna and soil properties in 85 sugarcane fields of three major sugarcane producing islands in Japan, and to examine their relationship by using the mixed-effect model and by visualizing the spatial distributions using the inverse distance weighting (IDW) approach. The nematode community structures were analyzed by non-metric multidimensional scaling (NMDS). Among plant-parasitic nematodes in sugarcane, the root-lesion nematodes (Pratylenchus sp.) and the stunt nematodes (Tylenchorhynchus sp.) were widely distributed in these islands, yet the abundance and the species varied geospatially. Soil pH was significantly correlated with the abundance of Pratylenchus and Tylenchorhynchus species. The abundance of Pratylenchus and Tylenchorhynchus species were significantly correlated with soil pH. The abundance of Pratylenchus was significantly correlated with the abundance of free-living nematodes, the number of free-living nematode species, and exchangeable cation K+, as were the abundance of Tylenchorhynchus to the clay content and that of non-Tylenchorhynchus. This study also revealed that the three islands had different nematode faunas, which were explained especially by soil pH, texture, and exchangeable basic cations.

Long-term response of tropical Andisol properties to conversion from rainforest to agriculture

Short-term changes in tropical rainforest soil properties and their impact on C cycling following land-use conversion to agriculture have received intensive study. However, long-term, land-use changes have not been explored for tropical Andisols, whose high carbon stocks and several distinctive properties may differ in their response to land-use conversion. Thus, the primary objective of this study was to assess changes in selected soil properties of Andisols in response to long-term (>100 years) changes of land use from tropical rainforests to agriculture. Soils were sampled by horizon to a depth of 110–140 cm in pine forests (PF), tea plantation (TP) and horticultural crops with either intensive cultivation (IH) or bare fallow (FH) cropping systems. Selected physical, chemical and biological soil properties were characterized, including microbial biomass carbon (MBC) and laboratory CO2 mineralization rates. Results showed that land-use change from rainforest to agriculture resulted in increased soil bulk density and meso/micropores that contributed to increased plant-available water retention capacity. Soil carbon and nitrogen stocks in the upper 1 m of soil were higher in agricultural soils (25–29 kg C m−2; 1.7 – 2.3 kg N m−2) than pine forest soil (17 kg C m−2; 1 kg N m−2) with a redistribution of organic matter from topsoil to subsoil horizons. Organic matter quality was also affected by land-use conversion with the horticultural soils having lower rates of carbon mineralization per unit soil carbon (PF > TP > IH > FH) and lower microbial biomass, especially in topsoil horizons. The MBC sharply decreased in the topsoil horizon due to land-use change from forest (330 mg kg−1) to agricultural production (<118 mg kg−1). The intensive horticultural soil receiving recent additions of horse manure had higher extractable mineral N (especially NO3), reduced P fixation, increased available P, higher pH, and higher concentrations of exchangeable base cations (Ca2+, Mg2+ and K+) and micronutrients (Zn, Mn and Cu). The Andisols in this study demonstrated strong resilience to long-term degradation of soil properties following conversion from rainforest to agronomic land use. Further, this study demonstrates the ability of these Andisols to sequester additional C upon conversion to selected agriculture practices, thereby providing a positive impact on C mitigation.

Termite mound soil properties in West Bengal, India

Termites are ecosystem engineers, they play a major role in the biotransformation and modification of soil physicochemical and morphological properties. This study was conducted to evaluate the explored and compared physicochemical and morphological characteristics of soil between termite mounds and surrounding surface soil. Therefore, this study, especially emphasizes the impacts of the mound soil on the surrounding surface soil properties and also to find out the difference between the mound soil properties and surrounding surface soil properties at different soil depth, and characteristic of termite mounds. This study unveils that mound soil properties are directly proportional to the surrounding surface soil properties except for porosity and dispersion ratio. But mound soil properties are not significantly affecting all surface soil properties. The termites have a significant role to change soil physicochemical and morphological properties and there is a significant difference in soil physicochemical properties between mound and surrounding surface soil. However, relatively greater bulk density, clay content, soil pH, organic carbon, nitrogen, exchangeable calcium, exchangeable magnesium, exchangeable sodium, total exchangeable base cations and cation exchange capacity in mound soil than surrounding surface soil. But the relatively lesser value of porosity, dispersion ratio, exchangeable potassium, phosphorus, exchangeable acidity, and C: N ratio is found in mound soil than surrounding surface soil. Conical shaped mounds have greater nutrient concentration than surrounding surface soil. It also highlighted that most of the termite mound consists of trees and bushes containing 8–21 hole or chamber. The termite mounds have granular structure and particle shape are rounded to subrounded, which make them different from surrounding areas. This study suggests and statistically prove that termites have a significant effect on soil properties, they produce physicochemically more quality soil and have an influence on surrounding soil properties.

Spatiotemporal variability, source apportionment, and acid-neutralizing capacity of atmospheric wet base-cation deposition in China

Atmospheric wet deposition of base cations (BCs) plays a significant role in providing plant nutrients and buffering acidification. However, the temporal dynamic of wet BC deposition in China during the past two decades remain unclear. Here, we used long-term monitoring and literature data since 2000 to assess the temporal dynamics (seasonal and inter-annual variation), spatial patterns, main influencing factors, source apportionment, and capacity to neutralize the acidity of wet BC depositions at site, regional, and national scales. The results showed that total wet deposition of BCs was, on average, 2.12 keq ha−1 yr−1, where Ca2+ accounted for 65.57% of the total deposition, followed by Na+ (13.21%), Mg2+ (13.68%), and K+ (7.55%). Qinghai-Tibet had significantly lower BC deposition fluxes than northern, southern, and central China, as well as Inner Mongolia. Exchangeable BCs in soil, PM10 in the atmosphere, energy consumption, and cement production are significantly related to wet BC deposition, which account for 79.17% of the variation in the spatial deposition of BC. Influenced by the strategies to control acid rain and particulate matter in China, interannual variations showed a stabilization trend after a continuous decline from 2000 to 2017, which can be explained by inter-annual changes in PM10, energy consumption and cement production. Statistical methods confirmed that 45.95% of wet BC deposition was derived from crustal contributions, 27.78% from sea salt sources, and 26.27% from anthropogenic sources. Furthermore, we found that wet deposition of BCs neutralized 84.85% of the acidity due to NO3− and SO42− depositions. Under the emissions reduction strategy, there has been a decrease in the deposition of BC. However, SO42− and NO3− depositions decreased faster than BC deposition, which buffered a higher proportion of acidic depositions. Our findings contribute to an improved understanding of wet BC deposition in China, an evaluation of their capacity to neutralize acidity, and important parameters for acidification models.

Characterization of Biochar Produced from Different Feed Stocks

Imprudently disposed and burning of organic wastes have been causing environmental pollution and greenhouse gas emission. The objective of this study was to characterize the biochar produced from different agricultural wastes to explore its potential use as organic soil amendments. The feedstock derived from each of Eucalyptus globules (EG), Acacia decarance (AD), farm yard manure (FYM) and rice straw (RS) were collected and biochar was produced by slow pyrolysis at 300oC in the furnace. The determination of pH, carbon, phosphorus, cation exchange capacity, electrical conductivity and exchangeable basic cations of individual biochar was performed and statistical analyses carried out to compare the means values obtained. Higher carbon content was observed in biochar produced from AD (65.00%) compared with that of biochar produced from other feedstock types included in this study. pH value of Bbiochar produced from EG and RS were moderately acidic (pH 5.94) and neutral (pH 6.6), respectively, whereas biochar produced from AD (pH 8.07 and FYM (pH 8.17) revealed moderately alkaline pH level. High and low EC values were recorded in biochar produced from FYM (4.70 DS m-1) and the low value from EG (0.68 DS m-1), respectively. The maximum concentration of exchangeable magnesium (20.95%), potassium (16.40%) and sodium (1.77%), EC and phosphorous (2288.75 ppm) were testimony in biochar produced from FYM is potential to prove phosphorus fertilizer requirement of a crop but calcium (39.50%) was from biochar produced from AD. Higher CEC (129.75 cmolc kg-1) was detected in biochar produced from EG followed by biochar produced from RS (127.5 cmolc kg-1), AD (117 cmolc kg-1) and FYM (87.25 cmolc kg-1). Generally, the current finding revealed that biochar from different feedstock’s had different chemical properties, so this difference could contribute for soil fertility improvement as the result agricultural wastes is managed without pollution. But, the current work was limited to the characterization of biochar. So, more detailed investigation on the rate and reclaiming the power of the biochar and other issues should be investigated.

The mechanism for inhibiting acidification of variable charge soils by adhered Pseudomonas fluorescens

Acidification in variable charge soils is on the rise due to increased acid deposition and use of nitrogenous fertilizers. The associated low pH and cation exchange capacity make the soils prone to depleted base cations and increased levels of Al3+. Consequently, Al toxicity to plants and soil infertility decrease crop yield. This study was designed to investigate the effect of Pseudomonas fluorescens on the acidification of two Ultisols. The simulated acidification experiment demonstrated that the pH of bacteria-treated soil was higher than that of control under similar conditions, suggesting that the adhered bacteria inhibited soil acidification. This observation was attributed to the association of organic anions (RCOO− or RO−) on bacteria with H+ to form neutral molecules (RCOOH or ROH) and reducing the activity of H+ in solution. The bacteria also inhibited the increase in soil soluble Al and exchangeable Al during soil acidification. The adhesion of bacteria on the soils increased soil effective cation exchange capacity (ECEC) and exchangeable base cations at each pH compared to control. The release of exchangeable base cations from bacteria-treated soil, and the decrease in soil ECEC and exchangeable base cations with decreasing pH confirmed that protonation of organic anions on adhered bacteria was mainly responsible for the inhibition of soil acidification. The change of zeta potential of the bacteria with pH and the ART-FTIR analysis at various pH provided more evidence for this mechanism. Therefore, the bacteria in variable charge soils played an important role in retarding soil acidification.