Soil Cation Exchange Research Articles

Canopy responses of signal grass cv. Basilisk pastures subjected to three fertilization regimes at two stubble heights

The impacts of fertilization regimes and stubble heights in signal grass cv. Basilisk pastures were evaluated during latespring and summer in Brazil. Liming and N, P and K fertilization were applied to generate gradients in soil fertility tomaintain soil base saturations around 35%, 50% and 65%, increase soil P concentration and the proportion of K in soilcation exchange capacity, combined with two stubble heights of 10 and 15 cm. Herbage accumulation was not affectedby fertilization regimes and stubble height reaching 10 t/ha of dry matter during the growing season. Cutting at 10cm maximizes the leaf mass and leaf area index and decreases dead material mass without the need of high soil basesaturation and NPK fertilization rates to sustain plant growth. However, this stubble height required longer regrowthperiods to attain 95% of light interception (LI95%). A stubble height of 15 cm is preferred when short regrowth periods are required. The canopy height at the point of LI95% does not change with fertilization regimes, but the LI95% is reached at different canopy heights in late spring and summer in signal grass pastures. The adoption of a moderate fertilization regime is recommended as a strategy to obtain an equitable forage distribution between late spring and summer.

Chemical Response of Soils to Traditional and Industrial Byproduct Wood Biochars

ABSTRACT Soil degradation and a global focus on carbon (C) sequestration in soils have resulted in growing societal interest in soil health practices. Biochar has a high C content, porosity, pH, and cation exchange capacity that benefit soil properties. Here we described an incubation study that aims to evaluate the influences of biochar additions on representative forest organic, forest mineral, blueberry, potato, and mixed vegetable soils from Maine, USA. The experiment consisted of amendments of either a lime stabilized industrial byproduct softwood pulp biochar (SPB) or pine wood biochar (PB) at application rates equivalent to 0, 5, 10, 25, 50, and 100 t ha−1. Here we report influences of biochar addition on soil pH, loss-on-ignition (LOI), water-holding capacity (WHC), and exchangeable cations. In general, both SPB and PB increased the value of these soil properties in all mineral soils, with significant increases often being found at a rate of 100 t ha−1. Forest organic soils, however, were more variable attributable to the high organic C concentration of this substrate. Soil response to SPB amendments was strongly influenced by the lime component, although few significant differences were found between SPB and PB amended soils. Analysis of carbon dioxide (CO2) emissions from SPB amendments due to lime dissolution and acid neutralization represented less than 3% of the total carbon added in SPB treated soils, leaving SPB and PB both important potential soil amendments. This suggests that both traditional and industrial byproduct biochars have potential for soil health and C sequestration management goals.

Determining the geographical origin of lettuce with data mining applied to micronutrients and soil properties

Lettuce (Lactuca sativa) is the main leafy vegetable produced in Brazil. Since its production is widespread all over the country, lettuce traceability and quality assurance is hampered. In this study, we propose a new method to identify the geographical origin of Brazilian lettuce. The method uses a powerful data mining technique called support vector machines (SVM) applied to elemental composition and soil properties of samples analyzed. We investigated lettuce produced in São Paulo and Pernambuco, two states in the southeastern and northeastern regions in Brazil, respectively. We investigated efficiency of the SVM model by comparing its results with those achieved by traditional linear discriminant analysis (LDA). The SVM models outperformed the LDA models in the two scenarios investigated, achieving an average of 98 % prediction accuracy to discriminate lettuce from both states. A feature evaluation formula, called F–score, was used to measure the discriminative power of the variables analyzed. The soil exchangeable cation capacity, soil contents of low crystalized Al and Zn content in lettuce samples were the most relevant components for differentiation. Our results reinforce the potential of data mining and machine learning techniques to support traceability strategies and authentication of leafy vegetables.

Assessment of Capacity and Impacts of 8.5 MW Gas Fired Power Plant on Soil and Water Quality in Lekki, Lagos State Nigeria

The aim of this study is to evaluate the potential impacts of 8.5 MW thermal power plant on soil and water quality within its location, Lekki area, Lagos State. The study area was geo-referenced using the existing map and Geographical Positioning System. Auger was used to sample soil at three different locations within the power plant. The soil samples were prepared and analyzed for the following parameters using standard analytical methods. The parameters include soil texture, Exchangeable cations and anions (H+, Na+, Ca2+, Mg2+, Cl- and SO42-) Nutrients compounds (NO3-, Total Nitrogen (TN), Organic Carbon (OC) and heavy metals (Fe, Cd, As, and Mn). Surface and groundwater samples were collected within the power plant in triplicate and analyzed for true colour, turbidity, conductivity, salinity, THC and Coliform. Dissolved Oxygen (DO), BOD5, Total Organic Carbon (TOC), Organic Matter (OM) and heavy metals (As, Ag, Fe and Mn) of water samples were also analyzed. The soil from the study area is loamy-sand in texture. The average As, Ag, Fe and Mn in surface and groundwater samples were 0.055, 0.025, 3.150, 0.735 and 0.12, 0.080, 6.440 and 0.180 mg/L, respectively. The gas-fired power plant has contaminated the soil and water within its premises with petroleum and heavy metals. The engine stack should be modified to minimize the pollution effects of the power plant on the environment.

Changes in the profile properties and chemical weathering characteristics of cultivated soils affected by anthropic activities

The study of the pedogenic process in response to natural evolution, gradual anthropogenic shifts and engineering upheavals is of great significance for understanding, utilizing and transforming nature in the future. Although scholars have considered anthropic activities to be an important factor affecting pedogenesis, research on how and how much anthropic activities influence the soil-forming process is scant. This paper was conducted to analyse pedogenic characteristics dominated by anthropic activities. In this study, the parent materials and soils undergoing natural evolution (NE), tillage perturbation (TP) and engineering perturbation (EP) were selected as research objects. The genetic characteristics of soils undergoing NE, TP and EP are investigated mainly from three aspects: soil profile macromorphological characteristics, soil physical and chemical properties and chemical weathering characteristics. The results indicated that the influence of anthropic activities (TP and EP) on the process of pedogenesis is complicated. First, compared with NE, TP decreases the thickness of topsoil from 22.2 to 21.2 cm, while EP increases the thickness of topsoil from 22.2 to 23.2 cm, and EP causes the soil to have a high profile development index. Second, compared with TP, EP can improve bulk density (BD), soil organic carbon (SOC), total nitrogen (TN) and cation exchange capacity (CEC), Finally, the chemical weathering intensity differed among NE, TP and EP and followed the order of TP > NE > EP. Therefore, in the future, the genetic characteristics of soils dominated by anthropic activities should be considered. This will help us systematically understand the genesis and evolutionary characteristics of soil and lay a foundation for further perfecting the diagnostic horizon and diagnostic characteristics of the Soil Taxonomy and World Reference Base.

Are Chemical Properties of the Soil Influenced by Cover Crops in the Cerrado/Caatinga Ecotone?

ABSTRACT In Brazil, light-textured soils cover approximately 8% of the national territory. The present study assesses the effect of using cover crops, in monoculture or intercropping, and soil management systems, in different layers, on soil chemical properties in the Cerrado/Caatinga ecotone, Brazil. The study was carried out in the southwest region of Piauí State, Brazil, in an area of Andropogon grass (Andropogon gayanus Kunth) in an advanced stage of degradation. The experiment comprised cover plants in monoculture or intercropping. Cover crops improve the following soil chemical properties: pH (+15.94%), calcium (+93.54%), magnesium (+34.17%), sum of bases (+88.30%), base saturation (+198.52%), potassium (+7,767.90%), phosphorus (+673.86%), extractable aluminum (−52.67%), potential acidity (−9.15%), and aluminum saturation (−66.16%). However, soil organic matter content and cation exchange capacity decrease by 42.54% and 35.27%, respectively, in comparison to the values before the experiment. Intercroppings Urochloa brizantha + Oryza sativa and Crotalaria paulina + Zea mays have the potential to improve soil chemical properties in the medium and long term.

Long-Term Effects of Forest Plantation Species on Chemical Soil Properties in Southern Rwanda

Understanding the long-term effects of tree species on soil properties is crucial for the development of forest restoration policies in relation to the choice of species that meet both environmental and local livelihood needs. This study was performed in the Arboretum of Ruhande, Southern Rwanda, where monocultures of 148 deciduous and 56 conifer species have been established in 0.25 ha replicated plots from 1933 onwards. We investigated the effects of six exotic and two native tree species planted in monoculture plots and native species mixed within one self-regenerated plot on soil properties in two layers (0–5 cm and 5–10 cm depth). We measured general soil properties (pH, SOM, exchangeable base cations) and water-soluble C and N as a proxy for soil functioning. Changes in soil properties were observed in the upper soil layer for all tree species. Planting Eucalyptus species caused soil acidification, whereas soil exchangeable cations and pH were higher under native species (Entandrophragma excelsum and Polyschias fulva) and mixed native species. The effects of tree species were more pronounced for hot water-extractable C and N than for other soil properties. Their analyses could be used for detecting changes in soil functioning linked to vegetation types.

Changes in soil exchangeable nutrients across different land uses in steep slopes of Mizoram, North-east India

Land use change resulting from anthropogenic pressure on land has led to degraded soil quality, especially in the hilly tropical regions where ecosystems are generally fragile and susceptible to soil degradation from cultivation. Hence, sustainable land uses and management practices are crucial for agricultural production and ecological balance, particularly in these regions. The present study investigates the impact of various hill land uses (Natural forest-NAF, Jhum fallow-JF, Home garden-HG, Acacia pennata plantation-AP and Current Jhum-CJ) on soil exchangeable nutrients in steeply sloping agro-ecosystems of Mizoram, North-east India. Soil samples were collected from three different depths (0-10, 10-20 & 20-30 cm) and analyzed for pH, Pavail, Na, K, Mg, Mn and Ca. Our results indicated that land use and soil depths had a significant impact on soil pH, Pavail and soil exchangeable cations (p<0.05). Conversion of native forests for cultivation negatively affected soil properties as indicated by the reduced soil exchangeable cations in cultivated lands (AP & CJ) in relation to the natural forest (NAF) and Jhum fallow (JF). Soils under longer periods of fallow (>12 years) led to increases in soil available nutrients indicating the role of vegetation cover in conserving and enhancing soil available nutrients and vice-versa. In addition, Home garden (HG) showed moderately higher available soil nutrients signifying the role of sustainable management practices such as the addition of organic amendments and mixed cropping, leading to increased soil available nutrient content.

Improving effect of potassium in organic amendments on sodic soils

ABSTRACT Sodification is a major soil problem that limits plant productivity in arid and semi-arid regions. For ameliorating sodic soils, the application of chemical amendments that can release calcium (Ca), which expels soil exchangeable sodium (Na), is the most widely accepted approach for solving this problem. However, an alternative more economical method would be desired in developing countries that have large areas of sodic soils. The goal of the present study was to examine the effectiveness of using compost to expel soil exchangeable Na. Composts made from cattle manure, rice straw, and rapeseed pomace were added to a sodic soil (Tongliao, Inner Mongolia, China) at mass ratios of 0 − 10%, and the soil was leached with water. Soil exchangeable cations in the forms of outer sphere and inner sphere complexes were then extracted successively and their concentrations determined. Changes in the soil dispersibility resulting from the addition of compost was also examined. The concentration of Na in both the outer sphere and inner sphere complexes decreased when rice straw or rapeseed pomace compost added, but this was not observed when cattle manure compost, which is abundant in water-soluble Na, was used. The amount of K in both forms increased with increasing rate of addition of each compost, suggesting that the K in the compost replaced both the Na that is adsorbed to soil by electrostatic attraction and by chemical interactions. The largest removal of Na, 73% for outer sphere complex and 93% for inner sphere complex, was attained in the case of rapeseed pomace compost, which had the largest water-soluble K/water-soluble Na ratio, at a mass ratio of 5%. The addition of compost also neutralized soil pH and reduced soil dispersion, the latter being effective in improving the physical properties of the soil.

Liming impacts barley yield over a wide concentration range of soil exchangeable cations

Liming has widespread and significant impacts on soil processes and crop responses. The aim of this study was to describe the relationships between exchangeable cation concentrations in soil and the relative yield of spring barley. The hypothesis was that yield is restricted by the concentration of a single exchangeable cation in the soil. For simplicity, we focused on spring barley which was grown in nine years of a long-term experiment at two sites (Rothamsted and Woburn). Four liming rates were applied and in each year the relative yield (RY) and the concentrations of exchangeable cations were assessed. Liming had highly significant effects on the concentrations of most exchangeable cations, except for Cu and K. There were significant negative relationships (either linear or exponential) between the exchangeable concentrations of Mn, Cd, Cr, Al, Fe, Cu, Co, Zn and Ni in soil and soil pH. The relationships between RY and the concentrations of selected exchangeable cations (Mn, Ca and Al) were described well using log-logistic relationships. For these cations a significant site effect was probably due to fundamental differences in soil properties. At both sites the concentrations of exchangeable soil Al were excessive (> 7.5 mg kg−1) and were most likely responsible for reduced barley yields (where RY ≤ 0.5) with soil acidification. At Rothamsted barley yield was non-limited (where RY ≥ 1) at soil exchangeable Mn concentrations (up to 417 mg kg−1) greater than previously considered toxic, which requires further evaluation of critical Mn concentrations.

Modeling soil chemical changes induced by grassland afforestation in a sedimentary plain with shallow groundwater

Chemical changes produced by the establishment of tree plantations on grasslands occupying sedimentary plains could potentially impact their highly productive soils through multiple mechanisms. Some of the reported chemical changes following this vegetation shift include soil salinization, sodification, alkalization and acidification. While the associated hydrological, chemical and biological processes have been characterized in most cases, their quantitative integration remains as a complex challenge. The present work explored the simultaneous occurrence of the four mentioned soil chemical changes using reactive transport modeling and hydrological and chemical datasets (water, soil and plants) for a well described afforested grassland in the Pampas of Argentina. Processes included in the numerical model were unsaturated water flow, chemical reactions (soil cation exchange, mineral dissolution-precipitation), the intrusion of salty deep water induced by tree groundwater consumption, rhizosphere-plant processes (respiration, selective solute uptake/exclusion, root mediated electric charge compensation, and elemental recycling and uplift). Modeling results suggest that the dominant soil chemical changes depend on the interplay of all the aforementioned processes and help explain strong soil variation across very short distances (250 m) along edge-core gradients within the tree plantation. This complexity is hard to expect and explain from an isolated treatment of each of the aforementioned processes, calling for the application of numerical tools.

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.

Quantitative Relationship Between Paddy Soil Properties and Cadmium Content in Tobacco leaves.

Tobacco readily accumulates cadmium (Cd), an unnecessary and poisonous element. A total of 107 soil and tobacco leaf samples were collected from South China, to clarify the quantitative relationship between soil properties and Cd content in tobacco leaves. The results showed that 86.9% of the total sampling points had soil cadmium in excess of standard value, and the ratio of active Cd content to total soil Cd content was 24.0%. The enrichment factor of tobacco Cd was 3.43. There was a significant positive correlation between Cd concentration in tobacco leaves and soil Cd content. Soil pH, organic matter and cation exchange amount were negatively correlated with the Cd enrichment factor of tobacco. This present study has provided a regression model of tobacco Cd content based on soil factors, which could accurately predict Cd content in different parts of tobacco.

Effects of Prosopis velutina Invasion on Soil Characteristics along the Riverine System of the Molopo River in North-West Province, South Africa

Invasive alien plants are one of the major threats to ecosystems. Many invasive plant species, such as Prosopis species, have been introduced around the world and can alter the soil properties of invaded ecosystems. It is one of the most aggressive invasive plant invaders in the North-West Province of South Africa, but little information is available about their influence on soil properties. This study was conducted to investigate the effect of Prosopis velutina invasion on selected soil properties at five different sites along the riverine system of the Molopo River in North West Province. At each study site, soil characteristics were measured from soil samples taken under P. velutina canopies, between canopies and in the benchmark stands free of Prosopis species. The effect on selected soil properties of P. velutina invasion varied between the three stands and between sites. In all the sites, almost all soils collected from under the canopies had a significantly higher soil exchangeable Ca, K, Mg, and Na, organic matter (OM), total nitrogen (TN), available phosphorus (P), Electrical conductivity (EC), and cation exchange capacity (CEC) than the other sample positions, except for the pH which had the high value in intercanopies. Significantly higher (p&lt;0.05) values of almost all soil properties were found on the densely invaded sites (Tshidilamolomo I and Tshidilamolomo II) compared to lightly invaded sites (Mabule, Black Heat Farm, and Bray). However, it was difficult to generalise as the effects often appear to be site-specific. In addition, the findings also indicated that soils textural classes ranged between sand, silt, and clay in all study sites with a higher proportion of sand in the benchmark than in the soil under the canopies and intercanopies. Soil characteristics differed significantly more between sites than among positions. The site effects observed in this current study provide evidences that this species may occupy a relatively broad soil niche.

Sensors track mobilization of ‘chemical cocktails’ in streams impacted by road salts in the Chesapeake Bay watershed

Increasing trends in base cations, pH, and salinity of freshwaters have been documented in US streams over 50 years. These patterns, collectively known as freshwater salinization syndrome (FSS), are driven by multiple processes, including applications of road salt and human-accelerated weathering of impervious surfaces, reductions in acid rain, and other anthropogenic legacies of change. FSS mobilizes chemical cocktails of distinct elemental mixtures via ion exchange, and other biogeochemical processes. We analyzed impacts of FSS on streamwater chemistry across five urban watersheds in the Baltimore-Washington, USA metropolitan region. Through combined grab-sampling and high-frequency monitoring by USGS sensors, regression relationships were developed among specific conductance and major ion and trace metal concentrations. These linear relationships were statistically significant in most of the urban streams (e.g. R 2 = 0.62 and 0.43 for Mn and Cu, respectively), and showed that specific conductance could be used as a proxy to predict concentrations of major ions and trace metals. Major ions and trace metals analyzed via linear regression and principal component analysis showed co-mobilization (i.e. correlations among combinations of specific conductance (SC), Mn, Cu, Sr2+, and all base cations during certain times of year and hydrologic conditions). Co-mobilization of metals and base cations was strongest during peak snow events but could continue over 24 h after SC peaked, suggesting ongoing cation exchange in soils and stream sediments. Mn and Cu concentrations predicted from SC as a proxy indicated acceptable goodness of fit for predicted vs. observed values (Nash–Sutcliffe efficiency > 0.28). Metals concentrations remained elevated for days after SC decreased following snowstorms, suggesting lag times and continued mobilization after road salt use. High-frequency sensor monitoring and proxies associated with FSS may help better predict contaminant pulses and contaminant exceedances in response to salinization and impacts on aquatic life, infrastructure, and drinking water.

Origin of dioctahedral smectites in Lower Eocene Lulehe Formation paleosols (Qaidam Basin, China)

Smectites affecting water and soil exchangeable cations, especially potassium and ammonium related to plants, are common swelling clay minerals in sediments and paleosols that can record paleoenvironmental and paleoclimatic information. Paleoenvironmental and paleoclimatic interpretations are potentially ambiguous, because smectite minerals may have either detrital or pedogenic origins. This study analyzes smectites in Lower Eocene paleosols of the Qaidam Basin, China, with the goal of determining their origin and paleoclimatic significance. Twelve smectite-rich vertisol samples were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), inductively coupled plasma-mass spectrometry (ICP-MS), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) in the Dahonggou (DHG) section of the Lulehe Formation. The samples from DHG section contained predominant dioctahedral smectites (60–65%) in the <2 μm clay fractions. Minor dioctahedral illites, dioctahedral interstratified illite-smectite (I-Sm), kaolinite, and traces of dioctahedral chlorites and palygorskites were present. The chemical data and FTIR spectra revealed both tetrahedral substitutions (i.e., Al for Si) and octahedral substitutions (i.e., Mg and minor Fe for Al) in the dioctahedral smectites. Montmorillonite comprised the dominance of the fine-clay fractions (< 0.2 μm) with minor contributions of beidellite, as determined by the Greene-Kelly test (GK-test), geochemical and FTIR analyses. SEM observations revealed two morphological types of dioctahedral smectites, the less abundant one with typical ‘honeycomb’ structure, interpreted as neoformed, and the other occurring as thin, well-defined plates and irregular masses considered to be detrital. DSC revealed two dehydroxylation temperatures (500–550 °C and 600–700 °C), indicating the presence of trans-vacant (tv) and cis-vacant (cv) layers, respectively. The cv layers were attributed to montmorillonite originating as catchment-delivered detritus, as the study Lulehe Formation exhibited no evidence of volcanic ash layers or diagenesis that would have promoted formation of montmorillonite with high dehydroxylation temperatures. The tv layers represented pedogenic beidellite formed via solution crystallization in a floodplain pedogenic environment. The accumulation of abundant inherited montmorillonite and neoformed beidellite in paleosols of the Lulehe Formation was probably promoted by a relatively warm climate with alternating wet-dry seasons during the Early Eocene. Admixture of detrital montmorillonite makes paleoclimatic reconstructions based on bulk-smectites concentrations and isotopic compositions unreliable, showing that integrated clay mineralogical analyses of the type undertaken in this study are necessary to identify the provenance and paleoclimatic significance of smectites in sediments.

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.

Soil exchangeable cations estimation using Vis-NIR spectroscopy in different depths: Effects of multiple calibration models and spiking

Due to high rate of nutrient removal by cotton plants, the productive cotton-growing soils of Australia are becoming depleted of exchangeable (exch.) cations. For long-term development, data on exch. calcium (Ca), magnesium (Mg), potassium (K) and sodium (Na) throughout the soil profile is required. However, traditional laboratory analysis is tedious. The visible-near-infrared (Vis-NIR) spectroscopy is an alternative; whereby, spectral libraries are built which couple soil data and Vis-NIR spectra using models. While various models have been used to predict exch. cations, their performance was seldom systematically compared. Moreover, most previous studies have focused on prediction of topsoil (0–0.3 m) exch. cations while the effects of depth on applicability of topsoil spectral libraries are rarely investigated. Our first aim was to determine which model (i.e. partial least squares regression (PLSR), Cubist, random forest (RF), or support vector machine regression (SVMR)) produces the best prediction of topsoil exch. Ca, Mg, K and Na. The second aim was to evaluate if the best topsoil model can be used to predict subsurface (0.3–0.6 m) and subsoil (0.9–1.2 m) exch. cations. The third aim was to explore the effect of spiking on the prediction in subsurface and subsoil using the topsoil spectral library. The fourth aim was to see if combining all depths to build a profile spectral library improved prediction. Based on independent validation, PLSR was superior for topsoil exch. cations prediction, while Cubist outperformed PLSR in some cases when spiking was applied, and the profile spectral library was considered. Topsoil PLSR could be applied to predict exch. Ca and Mg in the subsurface and subsoil, while spiking improved prediction. Moreover, a profile spectral library achieved equivalent results with when topsoil samples coupled with spiking were considered. We, therefore, recommended to predict exch. Ca and Mg throughout the profile using topsoil spectral library coupled with spiking approach.

Application of Gliricidia sepium Tree Leaves and Nitrogen Fertilizer to Improve Tomato Production and Soil Properties

Excess use of agrochemicals for intensive cultivation affects crop quality and destroys agro-ecosystems, and eventually creates health hazards. The study aims to investigate the effect of Gliricidia sepium (GS) tree leaf as suitable green manures for supplementing nutrient supply along with nitrogen (N) fertilizer to produce quality tomato and soil fertility improvement. A field experiment was conducted at the Bangabandhu Sheikh Mujibur Rahman Agricultural University, Bangladesh, from November 2016 to March 2017. The experiment was laid out in a randomized complete block design (two factors) with three replications. There were nine treatment combinations with three levels of GS tree leaves (5, 10 and 15 t ha−1) and three doses of N (0, 50 and 100% of the recommended dose of fertilizer). The highest tomato yield was recorded in GS15×N100 treatment combination, which was 41.68% higher compared to the control treatment. Decreasing C: N ratio in increasing dose of GS and N treated plot indicated the quality of tree leaves that ensures faster decomposition and high nutrient release pattern of this species. Increasing rate of soil pH and cation exchange capacity (CEC) in different treatments as compared to initial soil showed soil fertility improvement. Overall, the results indicated that quality tomato could be grown successfully by the application of G. sepium tree leaves along with an appropriate amount of N fertilizer.&#x0D; Ann. Bangladesh Agric. (2020) 24(1) : 77-87

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.