Soil Cation Exchange Research Articles

Gradient variations in rhizospheric soil exchangeable cations across a forest-steppe transect

The forest-steppe ecotone (FSE) is vulnerable to climate change and valuable to predict ecosystem succession. Although species diversity covaries with climatic factors and changes gradually across FSE transects, aligning with “Whittaker’s hierarchy theory”, whether soil nutrients follow a similar distribution pattern remains unclear. We studied the ecological gradient changes in effective cation-exchange capacity (ECEC, sum of exchangeable Ca2+, Mg2+, K+ and Na+) in the near-neutral-pH rhizosphere and bulk soils along the north–south zonal transect of the Hulunbuir FSE, China. The 230-km transect includes hierarchical transitions from two closed forests through two FSE to four meadow steppes. For both rhizosphere and bulk soils, soil ECEC were the highest in meadow steppes followed by closed forests and FSE area. ECEC were inversely correlated with soil water content but positively with soil pH. Therefore, the distribution of ECEC along the forest-steppe transect did not conform to a hierarchical distribution and decoupled from vegetation transitions, possibly due to the fact that the distribution of soil pH, plant uptake and leaching break the uniformity of ECEC variation along the gradient. In closed forests and FSE ecosystems, the ECEC and exchangeable Ca2+ in rhizosphere soils were higher than those in bulk soil, indicating that rhizosphere processes may alleviate cation limitation in these ecosystems. The study substantially improves our understanding of soil nutrient mobilization and soil fertility across forest-steppe ecotones which helps projecting ecosystem succession. It further highlights the critical role of rhizosphere processes in modulating hierarchical vegetation transition along environmental gradients and provides avenues for future research opportunities.

Soil Nutrient, Enzyme Activity, and Microbial Community Characteristics of E. urophylla × E. grandis Plantations in a Chronosequence

The effects of continuous Eucalyptus cropping on soil properties and microbial characteristics and the specific factors influencing tree species growth remain elusive. In this study, three Eucalyptus stands of three different ages were selected, and soil nutrients, microbial biomass, enzyme activity, microbial community composition, and diversity were quantified for each. The findings indicated a significant decline in soil pH, soil cation exchange, soil organic matter, and available phosphorus content with the plantation age. Simultaneously, there was an observed increase in soil alkaline hydrolyzed nitrogen content. In addition, urease and acid phosphatase activities did not show a significant difference with age. In spite of this, catalase activity exhibited a decline corresponding to the advancement in plantation age. The carbon and nitrogen content of the soil microbial biomass increased with the progression of Eucalyptus planting time. The high-throughput sequencing data demonstrated a reduction in microbial diversity in Eucalyptus soils as the planting age increased. Interestingly, the microbial community structure exhibited minimal alterations, and did not exhibit a predominantly oligotrophic state overall. In conclusion, the study results showed that short-term successive Eucalyptus cropping exerts a significant negative impact on the soil system.

Nitrogen Addition Promotes the Accumulation of Soil Particulate Organic Carbon in a Subtropical Forest

Nitrogen (N) deposition rates of terrestrial ecosystems have gradually declined but are still high in some areas. Previous studies have reported that N addition elicits diverse impacts on soil organic carbon (SOC) pools. SOC can be divided into different functional fractions, namely, particulate organic carbon (POC) and mineral-associated organic carbon (MAOC). The responses of these fractions to N addition should be elucidated to better understand the changes in SOC pools. Here, we conducted a N addition experiment (0, 40, and 80 kg N ha−1 yr−1) in a subtropical Castanopsis fabri forest to simulate N deposition. The surface (0−10 cm) SOC fractions, aboveground litter product, fine root (diameter < 2 mm) biomass, soil exchangeable cation content, and soil enzyme activity under different N addition treatments were measured. The results showed the following: (1) N addition showed a positive effect on POC and SOC contents but did not significantly affect MAOC content; (2) POC content was negatively correlated with pH and soil enzyme activity and positively correlated with aboveground litter product, suggesting that POC accumulation was influenced by aboveground litter input and microbial decomposition; (3) a close negative relationship was observed between exchangeable Al3+ and Ca2+ or K+ contents, indicating that there is likely to be a trade-off between the mineral sorption and desorption, thus resulting in an insignificant reaction of MAOC to N addition. Overall, the accumulation of SOC under short-term N addition was found to be primarily driven by POC, and the response of different SOC functional fractions to N addition was inconsistent. By incorporating these nuances into ecosystem models, it is possible to predict SOC dynamics more accurately in response to global change.

Revitalizing the Biochemical Soil Properties of Degraded Coastal Soil Using Prosopis juliflora Biochar.

Biochar is an effective soil amendment with capabilities of boosting carbon sequestration and enhancing soil fertility, thus enhancing plant growth and productivity. While numerous studies have documented the positive effects of biochar on improving soil properties, a number of studies have reported conflicting results. Therefore, the current study was conducted to evaluate the impact of Prosopis juliflora biochar (0, 2.5, 5.0, and 7.5 t ha-1) on soil biochemical properties in Coastal Kenya to ascertain biochar's potential for soil fertility improvement. A randomized complete block design was used for setting up the experiment with three replicates, while Casuarina equisetifolia L. was planted as the test crop. Soil sampling for nutrient analysis was conducted quarterly for 12 months to assess nutrient dynamics under different biochar rates in the current study. Compared to soil untreated with Prosopis juliflora biochar, the results showed that there was a significant increase in soil pH by 21% following biochar utilization at the rate of 7.5 t ha-1. Total nitrogen was increased by 32% after the biochar application, whereas the total organic carbon was increased by four folds in comparison to biochar-untreated soil. Available phosphorus was increased by 264% following biochar application in comparison to the control treatment. In addition, the application of biochar resulted in an increment in the soil exchangeable cations (Ca2+, K+, Mg2+) across the assessment periods. Soil cation exchange capacity (CEC), bacteria and fungi were enhanced by 95, 33 and 48%, respectively, following biochar application at 7.5 t ha-1 in comparison to untreated soil. In conclusion, these results strongly suggest improvement of soil biochemical properties following Prosopis juliflora biochar application, thus providing potential for soil fertility improvement in regions such as the one in the study.

Effects of the age of raised beds on the physicochemical characteristics of fruit orchard soil in the Vietnamese Mekong Delta.

To grow fruit plants, farmers in the Vietnamese Mekong Delta (VMD) must use raised bed constructions to avoid waterlogging during the rainy season. This study aimed to evaluate the effects of the age of the raised beds on the soil physicochemical properties of longan orchards located in the VMD. Two raised bed systems were evaluated: a young bed constructed 10 years ago and an old bed constructed 42 years ago. Soil samples were collected from five different soil layers (0-20, 20-40, 40-60, 60-80, and 80-100 cm) with four replicates per layer. Soil samples were tested for pH, electrical conductivity (EC), available phosphorus (AP), total nitrogen (TN), soil organic matter (SOM), exchangeable cations (Ca2+, K+, Mg2+, and Na+), cation exchange capacity (CEC), bulk density (BD), soil porosity, available water-holding capacity (AWC), particle composition (sand, silt, and clay), and size. The soil pH was approximately 1.0 units lower in the old bed compared to the young bed at depths of 0-20 and 20-40 cm. The BD was higher in the old bed (0.15 g cm-3) than in the young bed at a soil depth of 0.4 m. SOM, AP, exchangeable cations (Ca2+, Na+, and Mg2+), AWC, and soil porosity were significantly lower in both the topsoil (0-20 cm) and subsoil (20-40 cm) layers in the old bed than in the young bed. In particular, the SOM, AP, AWC, and soil porosity contents in the old bed decreased by 18%, 20%, 15%, and 17%, respectively, compared with those in the young bed at soil depths of 0-40 cm. Therefore, cultivating raised bed soil for a longer period significantly reduced the soil exchangeable cations, porosity, and fertility of the surface and subsurface soils. Based on these results, farmers should use soil conservation practices, such as cover crops, rice straw mulching, and soil amendments in their orchards to mitigate topsoil degradation.

Exploración de los cationes intercambiables del suelo y auditoría del potencial de Phoenix dactylifera y Mangifera indica en el secuestro de CO2 en la biomasa del suelo en una parcela arbóroles de origen natural

Antecedentes: El experimento investigó los cationes intercambiables (EC) del suelo y auditó el potencial de Phoenix dactylifera y Mangifera indica en el secuestro de CO2 en la biomasa del suelo y en otros actos como factor de remediación para la sostenibilidad de la agricultura. Metodología: El estudio utilizó un diseño de investigación de muestreo estratificado en el que se utilizó el analizador de gas infrarrojo (IRGA) para muestrear ubicaciones estandarizadas dentro de la masa terrestre experimental para detectar el CO2 capturado en la biomasa del suelo en un período de cinco (5) meses. El índice de similitud de especies de Sorensen se aplicó en el estudio para obtener una radiografía y validar el rendimiento de las dos especies de árboles para el rendimiento de similitud potencial de secuestro de CO2. Resultados: Los resultados indicaron que existe un potencial de las dos especies de árboles para secuestrar CO2 atmosférico en un valor de 1.25± 0.13 y 0.47±0.19 para Phoenix dactylifera y Mangifera indica respectivamente en un intervalo de cinco (5) meses. Conclusiones: La distribución de cationes intercambiables de Ca2+, Mg2+, K+, Na+ indicó que existe incremento de los cationes intercambiables en la solución del suelo al final de los cinco (5) meses con un Coeficiente de Variación (CV=101%). Se observó un aumento en la capacidad de intercambio de cationes (CEC) del suelo de 7,3 cmolkg-1 al comienzo del experimento a 7,47 cmolkg-1 al final del experimento, lo que indicó un aumento en el estado de fertilidad de los suelos.

Estimation of Soil Cations Based on Visible and Near-Infrared Spectroscopy and Machine Learning

Soil exchange cations are a basic indicator of soil quality and environmental clean-up potential. The accurate and efficient acquisition of information on soil cation content is of great importance for the monitoring of soil quality and pollution prevention. At present, few scholars focus on soil exchangeable cations using remote sensing technology. This study proposes a new method for estimating soil cation content using hyperspectral data. In particular, we introduce Boruta and successive projection (SPA) algorithms to screen feature variables, and we use Guangdong Province, China, as the study area. The backpropagation neural network (BPNN), genetic algorithm–based back propagation neural network (GABP) and random forest (RF) algorithms with 10-fold cross-validation are implemented to determine the most accurate model for soil cation (Ca2+, K+, Mg2+, and Na+) content estimations. The model and hyperspectral images are combined to perform the spatial mapping of soil Mg2+ and to obtain the spatial distribution information of images. The results show that Boruta was the optimal algorithm for determining the characteristic bands of soil Ca2+ and Na+, and SPA was the optimal algorithm for determining the characteristic bands of soil K+ and Mg2+. The most accurate estimation models for soil Ca2+, K+, Mg2+, and Na+ contents were Boruta-RF, SPA-GABP, SPA-RF and Boruta-RF, respectively. The estimation effect of soil Mg2+ (R2 = 0.90, ratio of performance to interquartile range (RPIQ) = 3.84) was significantly better than the other three elements (Ca2+: R2 = 0.83, RPIQ = 2.47; K+: R2 = 0.83, RPIQ = 2.58; Na+: R2 = 0.85, RPIQ = 2.63). Moreover, the SPA-RF method combined with HJ-1A HSI images was selected for the spatial mapping of soil Mg2+ content with an R2 of 0.71 and RPIQ of 2.05. This indicates the ability of the SPA-RF method to retrieve soil Mg2+ content at the regional scale.

Effects of several superabsorbent polymers on soil exchangeable cations and crop growth

Owing to their excellent water absorption and water retention properties, superabsorbent polymers have become an important technology for realizing agricultural water savings. To explore the exchange pathways of exchangeable cations in soil caused by different superabsorbent polymers and their effects on crop nutrient uptake and growth, three types of superabsorbent polymers, sodium acrylate, potassium acrylate and acrylamide–sodium acrylate, were used in this project to study the effects of different dosages on crop growth, root morphology and the distributions of Na+, K+, Ca2＋ and Mg2+ in the root tips. The results were as follows: among all the treatments, the inhibition effect of the sodium acrylate superabsorbent polymer was the most obvious. Compared with CK, the biomass decreased by 70.3% (AN2), the root length and root surface area decreased by 62.7% and 61.1% respectively, plant K+ and Na+ increased by 18.5% and 2423% respectively, and Ca2+ and Mg2+ decreased by 27.6% and 18.7% respectively. Adsorption experiments with Ca2＋ and Mg2+ further proved that the superabsorbent polymers adsorbed more than 95% of the Ca2＋ and Mg2+ in the soil while releasing Na+ and K+ into the soil after swelling.

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.

Reinforced soil salinization with distance along the river: A case study of the Yellow River Basin

Clarifying the relationship between salt-affected soils and their adjacent river systems is critical to address the challenges posed by soil salinization on agricultural production. Among the various biophysical and land management factors linked to soil salinization, few studies have investigated the importance of the distance along the river. Based on the Hetao Irrigation District of the Yellow River Basin, we collected 5314 soil samples and analyzed 17 soil parameters to explore the relationship between salt-affected soils and their distance along the river. Soil salinization was reinforced by the distance along the river, as a trade-off between soil ion accumulation and nutrient regulation. Soil total water-soluble salt content increased by 16.4 mg kg−1 every kilometer, likely due to ions leaching from the soils upstream and partially accumulating in the soils downstream, especially for Cl-, SO42-, and Na+. Greater input and less solubility of Ca2+ based soil amendments, phosphorus fertilizers, and organic materials on the less salt-affected soils upstream may explain the declines in soil Ca2+, available phosphorus, and soil organic matter with distance along the river. With every kilometer along the river, soil exchangeable sodium and cation exchange capacity increased by 8.89 × 10−4 and 1.26 × 10−2 cmol kg−1, respectively, which led to an increase in soil exchangeable sodium percentage by 9.59 × 10−5. The increase in soil exchangeable sodium along the river was mainly due to Na+ accumulation, while soil cation exchange capacity was regulated by soil organic matter and total nitrogen. Soil pH increased by 1.21 × 10−3 per kilometer along the river, associated with the decrease of soil organic matter. Future saline soil amelioration and reutilization initiatives at regional scales may be improved by accounting for the changes in soil physicochemical properties resulting from the distance along the river.

Influence of the temperature on soil's exchangeable cations and cation exchange capacity, Derna district, Libya: A field and Laboratory study

This study conducted in Aljabal alakhdar (Green Mountain), Derna, Libya. It is the only wet region in Libya. Like other Mediterranean forests, it is exposed to the risk of fires. To assist in this, two different geographical units from the region (coastal and mountain), which been burned at different times; to identify whether these soils are regaining their pre-burn status over time. The studied properties were: the soil clay content, the soil organic matter (O M), the soil exchangeable cations and soil cation exchange capacity (CEC). It is obvious from the results that there is a relatively low clay content, compared to the contents of silt and sand, in both study sites and their burned and unburned areas. Soils of both study sites characterized by low organic matter content. The results indicated that, the basic exchangeable cations ranking was: Ca++ > Mg++ > Na+ > K+, in both study sites, for burned and unburned areas and at all depths. The rank order of these four cations did not change with depth in the four study areas except that sometimes-exchangeable potassium was more abundant than exchangeable sodium. The exchangeable calcium and magnesium account for about 80% of the CEC results so, the patterns of behaviour of the soil CEC are similar to the patterns of behaviour of these two elements.

Evaluation of the Effects of Returning Apple Shoots In Situ on Soil Quality in an Apple Orchard

Fruit tree shoots are potential useful resources that are rich in carbohydrates and inorganic nutrients but that are not typically utilized in sustainable agriculture. Our objective was to evaluate the soil properties and soil quality of an orchard after returning apple shoots in situ and to investigate the contribution rate of apple shoots as an exogenous source of organic carbon for fertility amendment of the apple root domain. One-year-old apple shoots were pruned in spring before budding, chopped into 10 cm sections and placed on the soil surface. Soil samples were collected in the first year and third year after returning the shoots. Principal component analysis, Pearson correlation analysis and soil quality index (SQI) comprehensive analysis methods, combined with fuzzy mathematics, were adopted to evaluate the effects of returning apple shoots on comprehensive soil quality, including the soil fertility indicators, soil exchangeable cations, soil neutral sugar and amino acids. Increases in soil organic carbon (SOC), available potassium (K), and available phosphorus (P) were observed in different layers of the orchard soil with returned shoots over time. The total nitrogen (N) content decreased by 18.75% and 13.79% in the 0–20 cm and 20–40 cm soil layers, respectively, in the first year, but increased significantly in the third year. Significant increases in exchangeable cations (Na+, Ca2+, Mg2+) in the 0–20 cm soil layer were also observed in the third year after returning shoots, compared to the control. In addition, obvious accumulation of glucose and xylose was observed in the 0–20 cm soil layer compared to the controls in the third year after returning shoots. The total water-soluble free amino acid contents in the third year after returning shoots were 1.08- and 1.16-times higher, respectively, than those of the controls in the 0–20 cm and 20–40 cm soil layers. The SQI in the third year was higher than that of the other treatments in the 0–20 cm soil layer. This study suggests that abandoned apple shoots used as a supplementary carbon source for orchards enhanced the soil fertility of different soil layers, regulated the soil micro environment, and improved the overall soil quality.

Karakteristik Fisik, Kimia dan Mineral Tanah Di Lokasi Kampus IAIN- Ambon Kecamatan Sirimau Kota Ambon

The aims of this study was to identify morphological characteristics, clay mineral composition and soil similarity index between two soil profiles at the IAIN campus. The results showed that soil color characteristics of soil layers of both soils are different. Both soil profiles have deep solums with loam to sandy loam texture distribution. The increasing of clay content in the B horizon of both soil profiles is still weak as indicated by the present of a Bw (kambik) horizon. Soil structure is a subangular blocky with fine to coarse sizes and weak to strong structural development. Soil consistency is slightly sticky to sticky. Cation exchange capacity is very low as indicated by low Ca dan Na, medium to high Mg and high Na soil exchangeable cations. The dominant clay mineral in both soil profiles is kaolonit, which is formed by unwell-consolidated weathering materials mixed with weathering-resistant quartz. The silt/clay ratio and CEC values shows similarity between layers between both profiles, however, the Ca/Mg ratio shows dissimilarity. The soil type in both soil profiles is district Kambisol (Typic distrudepts) categorized as a developed soil

Karakteristik Fisik, Kimia dan Mineral Tanah Di Lokasi Kampus IAIN- Ambon Kecamatan Sirimau Kota Ambon

The aims of this study was to identify morphological characteristics, clay mineral composition and soil similarity index between two soil profiles at the IAIN campus. The results showed that soil color characteristics of soil layers of both soils are different. Both soil profiles have deep solums with loam to sandy loam texture distribution. The increasing of clay content in the B horizon of both soil profiles is still weak as indicated by the present of a Bw (kambik) horizon. Soil structure is a subangular blocky with fine to coarse sizes and weak to strong structural development. Soil consistency is slightly sticky to sticky. Cation exchange capacity is very low as indicated by low Ca dan Na, medium to high Mg and high Na soil exchangeable cations. The dominant clay mineral in both soil profiles is kaolonit, which is formed by unwell-consolidated weathering materials mixed with weathering-resistant quartz. The silt/clay ratio and CEC values shows similarity between layers between both profiles, however, the Ca/Mg ratio shows dissimilarity. The soil type in both soil profiles is district Kambisol (Typic distrudepts) categorized as a developed soil

Remediation Effect and Mechanism of Inorganic Passivators on Cadmium Contaminated Acidic Paddy Soil

Cadmium (Cd) is one of the main pollutants in acidic paddy fields, and its accumulation in rice (Oryza sativa L.) and subsequent transfer to the food chain is an important environmental issue in China. In our field study, three types of inorganic passivators (silicon-calcium-magnesium-potassium fertilizer (SCMK), calcium magnesium phosphate fertilizer (CMP), and lime (L) at the rate of 750, 1500, and 2250 kg·hm-2, respectively) were applied to acidic paddy soils polluted by the heavy metal Cd in southern Zhejiang province. The objective of this study was to reveal the effects and chemical mechanisms of passivators on soil acidification and Cd accumulation in rice. The field experimental results showed that the three passivators could effectively improve soil acidification and reduce Cd accumulation in rice grains. The application of 2250 kg·hm-2 SCMK, CMP, and L increased soil pH by 0.62, 0.65, and 0.86 units; decreased exchangeable acidity by 67%, 69%, and 78%; and reduced the content of Cd in brown rice by 73%, 68%, and 77%, respectively. The application of 2250 kg·hm-2 SCMK, CMP, and L reduced the content of Cd in brown rice planted on polluted paddy rice fields to lower than 0.2 mg·kg-1, which reached the national food safety standard. Compared with the control, the application of SCMK, CMP, and L significantly (P<0.05) decreased the content of available Cd extracted by DTPA; decreased the contents of weak acid-extractable (F1) and reducible (F2) Cd; and increased the content of residual (F4) Cd. Correlation analyses indicated that Cd content in brown rice was significantly negatively correlated with soil pH and exchangeable cation content and significantly positively correlated with DTPA-Cd, weak acid-extractable (F1) and reducible (F2) Cd, and exchangeable Al contents. The partial least squares path model (PLS-PM) was used to analyze the relationship between the Cd content of brown rice, DTPA-Cd, and various chemical forms of Cd and soil properties. The direct path coefficients of soil exchangeable cations on Cd content in brown rice, available cadmium, and rice yield were -0.566, -0.866, and 0.873, respectively. Soil pH indirectly affected Cd content of brown rice mainly by directly affecting available Cd in soil. Field experiments demonstrated that the three passivators SCMK, CMP, and L were effective technologies for the safe production of rice in acidic paddy soils polluted by Cd. The possible mechanism for passivators reducing the bioavailability of Cd in soil and its accumulation in brown rice contributed to increased exchangeable cations in the soils. These findings could provide a scientific basis for the safe production of rice in acidic paddy soil polluted by heavy metals.

Fire, Herbivores, and Vegetation Type Shape Soil Biochemistry in Sodic Patches of a Semi-Arid Savanna Ecosystem

In the Kruger National Park (KNP), the lower slopes of catenas have open patches referred to as sodic patches. Fire and herbivores are dominant mediators of vegetation in sodic patches. The effect of fire and herbivores on soil properties of sodic patches remains largely understudied. Moreover, the co-existence of trees and grasses and how they influence savanna soils is an important but poorly understood phenomenon in ecology. Therefore, the present study aimed to determine the influence of 20 years of fire, herbivores, vegetation type, and their interaction on soil biochemistry of sodic patches on the Nkuhlu exclosures in the Kruger National Park, South Africa. We found a higher main effect of fire on available phosphorus, cation exchange capacity, and soil organic matter. The presence of herbivores caused an increase in soil exchangeable cations (K+, Ca2+, Na+, and Mg2+), organic matter, cation exchange capacity, and microbial activity. Tree canopies had a higher effect on total nitrogen, exchangeable Ca and Mg, soil organic matter, and cation exchange capacity than open grassland zones. Our results indicate that changes in vegetation structure due to fire and herbivores and their secondary impact on soil properties should be taken into consideration in managing savannas. Moreover, fire and herbivores play an important role in the maintenance of vegetation type (trees and grasses) in sodic patches.

Effect of shifting cultivation and fallow on soil quality index in Mokokchung district, Nagaland, India

BackgroundShifting cultivation is a major agriculture practice in the Nagaland state of India. This study examines the effect of shifting cultivation and the length of the fallow period on soil quality index (SQI). Four sites were selected for the study, viz., a shifting cultivation site (SCS), a 3-year-old fallow land (FL-3), a 7-year-old fallow land (FL-7), and a 12-year-old fallow land (FL-12). Soil parameters were recorded seasonally and SQI was calculated from the minimum data set.ResultsWith the increase in the fallow period, the values of conductivity, soil organic carbon, available nitrogen, available phosphorus, exchangeable potassium, moisture, clay, and cation exchange capacity of soil increased. Meanwhile, soil pH and bulk density decreased with fallow duration. The additive SQIa values were in the order SCS < FL-3 < FL-12 < FL-7; meanwhile, the weighted SQIw values were in the order SCS < FL-3 < FL-7 < FL-12. It is also observed that the SQI value decreases with the increase in soil depth under both the weighted and additive indexes. SCS with the lowest SQI value reflects the reduced soil organic carbon (SOC) and macronutrients. Increased SOC levels in site FL-12 (2.88–3.94%) may be one reason for its higher SQI value.ConclusionsOur study highlights that unsustainable practices of shifting cultivation and reduction in the fallow period negatively affect soil quality. Furthermore, the study also recommends the use of the weighted method of SQI as it agrees with the reports of land use causing alteration in the soil quality. Our findings may be utilized to quickly access and disseminate information to the stakeholders and aid in constructing local soil quality index maps of the region. There is an urgent need for a rapid, cost and resource-efficient soil quality assessment and SQI may be one tool that achieves this goal.

Remediation and Micro-Ecological Regulation of Cadmium and Arsenic Co-Contaminated Soils by Rotation of High-Biomass Crops and Sedum alfredii Hance: A Field Study

Rotation of high-biomass crops and hyperaccumulators is considered to be an effective, safe and economical method for the remediation of medium-mild heavy metal contaminated soil, but the present studies pay more attention to the removal efficiency rather than changes in soil micro-ecology. In order to explore the remediation effect of hyperaccumulators rotated with high-biomass crops on Cd and As co-contaminated soil, Cd hyperaccumulator ecotype (HE) Sedum alfredii Hance and crops were selected to construct a field experiment, five rotation modes including Sedum alfredii Hance-Oryza sativa L. (SP), Sedum alfredii Hance-Sorghum bicolor (L.) Moench (SS), Sedum alfredii Hance-Zea mays L. (SM), Sedum alfredii Hance-Hibiscus cannabinus L. (SK), Sedum alfredii Hance-Trichosanthes kirilowii Maxim. (ST), and investigated the effects of these modes on the removal efficiency, soil physiochemical properties and micro-ecological effects (soil nutrients, enzyme activities and microbial diversity) through a field experiment. The results showed that total soil Cd from the five rotation modes (SP, SS, SM, SK and ST) decreased by 25.1%, 20.3%, 34.5%, 6.3% and 74.3%, respectively, and total soil As decreased by 42.9%, 19.8%, 39.7%, 39.7% and 45.7%, respectively. The rotation significantly increased soil organic matter by 47.39–82.28%, effectively regulated soil pH value and cation exchange capacity. The rotation modes also significantly increased soil alkali-hydrolysable nitrogen by 9.09–50.91%, but decreased soil available phosphorus and rapidly available potassium. Except for urease, the soil enzyme activities increased overall. The Alpha diversity increased, and soil microbial structure optimized after rotation. ST mode was the most effective remediation mode, which not only reduces the content of Cd and As in the soil, but also effectively regulates the soil micro-ecology. The results from this study have shown that it is feasible to apply Sedum alfredii Hance and the high-biomass rotation method for the remediation of Cd and As co-contaminated soil.

Effect of LDPE microplastics on chemical properties and microbial communities in soil

AbstractThe accumulation of plastics in the soil ecosystem poses an increasing environmental concern worldwide. However, little is known about the effect of plastic concentrations on soil properties and soil biota. In this study, we investigated the effect of low‐density polyethylene (LDPE) microplastics (MPs) on the chemical and microbial properties of agricultural soil using a set of microcosm experiments. The soil was incubated for 100 days with LDPE at concentrations of 0%, 0.1%, 1%, 3%, 5%, and 7% at 25°C with 70% water‐holding capacity. Along with soil chemical analysis, we conducted an analysis of soil microbial properties on the first day and again after 100 days of incubation. LDPE concentrations of ≥1% significantly (p &lt; .05) decreased the pH but increased the electrical conductivity of the soil in comparison with the control (0% LDPE at 100 days). Increasing the LDPE concentration did not affect the soil exchangeable cation content or the available Pb concentration. Firmicutes were the most abundant phyla in the soil on the first day, whereas Proteobacteria, Firmicutes and Actinobacteria became dominant in all treatments after 100 days. An increasing LDPE concentration increased the abundance of Actinobacteria and decreased Proteobacteria. Principal component analysis demonstrated that only 7% LDPE was positively correlated with Actinobacteria, indicating that higher concentrations of LDPE contributed to the growth of this phylum. The findings of this study imply that MP contamination could affect soil chemical properties and microbial activity and that these effects primarily depend on MP concentrations in soil.

Long Term Trends of Base Cation Budgets of Forests in the UK to Inform Sustainable Harvesting Practices

There is growing concern in the UK that available base cation pools in soil are declining due to the combined effects of acid deposition and forest harvesting. To help inform the issue, elemental mass balances for calcium (Ca), magnesium (Mg) and potassium (K) were calculated using more than 10-years (10–24 years) of data from the UK’s ICP Forest Intensive Monitoring Network (Level II) of plots, covering a range of soil types and three tree species—oak, Scots pine and Sitka spruce. Out of the ten sites investigated, small negative Ca balances were observed at three sites and negative K balances on two sites, all on acid geology and nutrient poor soils, which were previously heavily acidified due to acid deposition. There is sufficient Ca and K in the soil exchangeable pool to sustain forest growth on these sites, however, if the present rate of Ca and K loss continues forest health and productivity are likely to be threatened within a few forest rotations. Magnesium showed a positive balance at all but one site, partly sustained by marine deposition. Base cation budgets were significantly (p &lt; 0.01) positively related to soil exchangeable cations and soil base saturation status. Six of the sites showed an increasingly statistically significant positive cation balance with time, attributed to a decline in leaching linked to recovery from acidification. This included the three sites with negative Ca balance, although Ca remained in deficit. One site (Alice Holt) exhibited a decreasing cation balance, driven by a continued significant decline in base cation deposition thought to be related to pollutant emission control. The results were used to simulate the impact of different forest biomass harvesting scenarios involving the removal of brown (extracted after needle drop) or green (extracted before needle drop) brash. Podzols and deep peats were found to be the most vulnerable to brash harvesting causing Ca and K imbalance, but problems also occurred on brown earths. Impacts were greatest for the extraction of green brash from higher productivity stands. Base cation balance calculations remain highly uncertain due to the restricted nature of available measurements and wide variation of some estimates, particularly inputs from mineral weathering. More data are required to check and improve model predictions to better guide forest harvesting practice and ensure sustainable forest management.