Exchangeable Ca Content Research Articles

How do reactive aluminum and iron phases control soil organic carbon and phosphate adsorption capacity in agricultural topsoils across Japan?

ABSTRACT The growing number of studies suggests that the prediction of soil organic carbon (SOC) storage and persistence can be improved by accounting for variations in soil reactive metal phases. Nevertheless, the dataset on reactive metals is often limited at a national scale. In Japan, the phosphate adsorption coefficient (PAC) has been measured for agricultural soils nationwide. PAC is known to be strongly controlled by reactive metals, and hence, it can be used as a surrogate for reactive metal content. However, the relationships between SOC, reactive metals and PAC across a wide range of agricultural soils remain unclear. We thus examined these relationships using agricultural topsoils taken from 115 sites across Japan, covering two major soil great groups, Andosols and Lowland soils, as well as various land uses and soil temperature regimes (7.2–19.1°C). For the whole dataset, PAC was strongly correlated with oxalate-extractable metals (Alox + 0.5Feox: Metalox, r = 0.83) and moderately with pyrophosphate-extractable metals (Alp + 0.5Fep: Metalp, r = 0.68). These results suggest a stronger contribution of short-range-order (SRO) minerals to PAC as the former parameter reflects the content of both SRO minerals and organically complexed metals, while the latter reflects only that of organo-metal complexes. Moreover, Metalp was the best predictor of SOC contents in both Andosols (r = 0.79) and Lowland soils (r = 0.65). When only soils at near neutral soil pH range were considered, the exchangeable Ca content also co-varied with SOC in Lowland soils (n = 17). Of the two metallic elements, reactive Al phases better explained the variation of SOC and PAC in Andosols, whereas reactive Fe phases also showed similar explanatory power for PAC in Lowland soils. Our analyses also suggested that soil group (esp. erosion intensity) and land use likely impacted the SOC-Metalox relationship in Andosols, whereas environmental factors such as soil temperature and soil redox regime affected those relationships in Lowland soils. Overall, we showed that PAC is a useful surrogate for SRO minerals and organo-metal complexes and, with careful considerations of the environmental and pedogenic factors, it is potentially useful to estimate the amounts of SOC stabilized by reactive metal phases in agricultural soils across Japan.

Performance of coal slime-based silicon fertilizer in simulating lead-contaminated soil: Heavy metal solidification and multi-nutrient release characteristics

High-ash coal slime-based silica fertilizer (CSF) has the potential to provide mineral nutrients and passivate lead (Pb) in the soil to ensure the sustainable development of the coal industry and agriculture. This study investigated the performance and passivation mechanism of CSF, which contains potassium tobermorite and potassium silicate as the main components for soil improvement. Leaching experiments showed that low-crystalline muscovite was the only crystalline phase for CSF etching and that the silicon (Si), calcium (Ca), and potassium (K) in CSF had significant citric solubility. Soil cultivation and planting trials confirmed the ability of CSF to neutralize soil acidity, increase available soil Si and K, improve exchangeable Ca content, reduce the bioefficacy of Pb (exchangeable Pb by 19–75 % and carbonate-bound Pb by 6–18 %), and increase residual state Pb content. Compared to untreated Pb-contaminated soil, the 0.4 % CSF treatment reduced Pb in Chinese cabbage (Brassica rapa) by 25 % and increased plant biomass, Ca, and K by 37 %, 36 %, and 4 %, respectively. At the same time, soil pH increased by 0.58, and residual state Pb increased by 5 %. In CSF-treated soils, lead silicate is the dominant form of Pb present in the residual state. First-principle calculations showed that Pb3Si2O7 (cohesion energy −1.98 eV) formed by the passivation of Pb by CSF had greater stability in the soil compared to lead carbonate (PbCO3) (cohesion energy −1.38 eV) and lead sulfate (PbSO4) (cohesion energy −1.41 eV). This work shows the promising application of coal slime mineral fertilizers prepared using hydrothermal methods for soil improvement.

Wheat growth, yield, nutrient concentration and soil chemical properties influenced by liming in an acid soil

Soil acidity has negative effects on both plants and soil. Furthermore, liming is the most common and effective management practice used to neutralize the acid produced in the soil and the problems associated with soil acidification. The study evaluated whether liming impacts wheat growth, yield, nutritional status basis exchangeable, and their related soil acidity indices. A greenhouse experiment was performed under a completely randomized arrangement, with four lime application rates equivalent to (0, 4.0, 8.0, and 12.0 Mg ha−1). The results showed that all yield components significantly increased with increasing lime addition rate. The grain yield, shoot and root dry weight, and plant and spike height improved quadratically (R 2 = 0.909, 0.950, 0.976, 0.902, and 0.891, respectively). Additionally, the lime rate influenced P and Mg concentrations in the shoot, and the concentrations of Cu and Zn. With increasing lime rate, the soil exchangeable Ca and Mg concentrations increased quadratically (R 2 = 0.969 and 0.984), while the soil exchangeable K and Al concentrations decreased significantly. The pH of the soil solution increased linearly (R 2 = 0.994) with the lime addition rate. Liming significantly reduced the exchangeable Al3+ and Al + H in the soil. Finally, liming improves wheat yield in acid soil by reducing the negative effects of Al and H by increasing soil pH, Ca2+, and Mg2+ concentration, consequently improving root growth and resulting in wheat yield. Liming increased the grain yield by 188.7, 198.2, and 322.8% following the increase of lime rate, if compared to the control. Furthermore, lime enhances plant resilience by raising pH and improving soil nutrient availability and the root system.

Effects of Rosa roxburghii Pomace Biochar on Yield and Quality of Chinese Cabbage and Soil Properties

In order to explore the effect of Rosa roxburghii pomace biochar on the yield and quality of Chinese cabbage and soil properties and realize the resource utilization of R. roxburghii pomace, a pot experiment was conducted to study the effect of R. roxburghii pomace biochar on the yield and quality of Chinese cabbage and soil properties by setting five biochar application rates of 0 % (CK), 1 % (T1), 3 % (T2), 5 % (T3), and 7 % (T4). The results showed that:① The application of R. roxburghii pomace biochar could significantly improve the yield and quality of Chinese cabbage, and the effect was the best at a 5 % biochar application rate. The yield, soluble solids, soluble sugar, vitamin C, total nitrogen, total phosphorus, and total potassium content of Chinese cabbage increased by 71.51 %, 40.14 %, 33.65 %, 38.08 %, 9.03 %, 28.85 %, and 35.38 %, respectively, compared with those in CK. ② The application of biochar from R. roxburghii pomace could significantly improve soil properties and increase soil nutrient content and availability. The effect was better at a 5 % biochar application rate. The soil pH, organic matter, total nitrogen, alkali-hydrolyzable nitrogen, available phosphorus, and available potassium content increased by 41.06 %, 134.84 %, 157.48 %, 140.79 %, 341.75 %, and 627.13 %, respectively, compared with those in CK. The contents of available Fe, Mn, Cu, and Zn and exchangeable Ca and Mg increased by 37.68 %, 61.69 %, 400.00 %, 4 648.84 %, 617.17 %, and 351.42 %, respectively, compared with those in CK. ③ The application of biochar from R. roxburghii pomace could significantly enhance soil enzyme activity. Compared with those in the CK treatment, soil urease, acid phosphatase, catalase, and sucrase increased by 51.43 %-362.86 %, 90.63 %-134.14 %, 21.40 %-85.12 %, and 82.92 %-218.43 %, respectively. ④ Redundancy analysis showed that soil AK; exchangeable Ca, SOM, and AP; and available Zn were the main factors affecting the yield and quality of Chinese cabbage, and there was a significant positive correlation between them. In summary, the application of R. roxburghii pomace biochar can significantly increase the yield and quality of Chinese cabbage and improve soil properties. The preparation of R. roxburghii pomace into biochar can provide a theoretical reference for the rational utilization of R. roxburghii pomace resources.

Durum Wheat Production and Soil Chemical Properties in Response to Three Biannual Rotation Cycles with Residue Incorporation

Crop rotations incorporating residues generates benefits in productivity and a better efficiency of resources. However, the incorporation of residues in high quantities is not a common practice, given the lack of comprehension of farmers of the effects on the following crop. This experiment was carried out in an Andisol soil in south-central of Chile. Three biannual rotation cycles (canola-durum wheat and bean-durum wheat) with four levels of residue incorporation (0%, 50%, 100% and 200%) were evaluated on the evolution of grain yield and production of durum wheat residues, and on chemical properties of the soil at the end of the three cycles. The results indicated that pre-cultivation affected the grain yield and residue production of durum wheat, highlighting the positive effect of the bean. In soil, a higher concentration of available N and exchangeable Ca, Mg and K was obtained in the bean-durum wheat rotation, and a higher concentration of available S in the canola- durum wheat rotation. By increasing the dose of waste, an increase in the concentrations of exchangeable Ca, Mg and K was achieved. Finally, the chemical properties of the soil presented positive and negative correlations associated with the management of liming, fertilization and nutrients mostly present in the incorporated waste. This study helped to validate that the continuous incorporation of the residues produced within the rotations in this volcanic soil contributes to the improvement of some of its chemical properties with no effect of yield of the durum wheat crop.

PENGGUNAAN MULSA PLASTIK SEBAGAI UPAYA KONSERVASI LAHAN UNTUK MENJAGA STABILITAS SIFAT FISIKA DAN KIMIA TANAH

Low nutrient availability and high soil bulk density are caused by the loss of fertile soil particles due to the kinetic energy of rain. Land management that does not apply conservation principles such as soil covering is one of the factors causing this to happen. This research was conducted to determine the impact of using plastic mulch as one of conservation actions. This research was conducted at the experimental field University of Siliwangi, Mugarsari. Soil samples were taken from mulched and without mulch lands as treatments. Soil samples were collected at 0-10 and 10-30 cm soil depths. Soil samples were taken to analyze the chemical properties of the soils (i.e., pH H2O, organic C, total N, available P, exchangeable K, Ca, Mg, Na) and physical properties (i.e., soil bulk density, porosity, water content, and texture). The results showed that the use of mulch had a significant effect (p<0.05) on pH H2O, organic C, total N, available P, exchangeable K, exchangeable Ca, bulk density, and water content. The results of the correlation showed that increasing organic C in mulched land had an effect on decreasing BD (r = -0.739). In addition, the organic C increased soil porosity (r = 0.612). Meanwhile, soil depth had no effect (p>0.05) on soil chemical and physical properties.

Quality of Soils in Soybean Producing Areas in Caraga Region

This study aims to determine the soil quality of selected soybean producing farms in the Caraga region using soil quality index (SQI) measurements. Five sites were selected in the municipalities of San Miguel, Surigao del Sur and Trento, Agusan del Sur. Three 10×10 m soil monitoring plots were established within soybean fields in each site. Within each monitoring plot, three composite samples were collected coming from 10 subsamples using a soil probe. SQI was calculated following three general steps, (1) selection of minimum dataset (MDS) via Principal Components Analysis (PCA), (2) Scoring of MDS via linear method, and (3) Calculation of weighted overall SQI. Out of the 16-soil property indicator, a total of five soil properties (exchangeable Ca, % Sand, Electrical conductivity, available P, and Soil respiration) were extracted and used as the MDS for the calculation of SQI in each site. The main indicator properties for determining the quality of the soils in the area were Exchangeable Ca and % Sand contents offering a 68% and 26% weights over other soil properties, respectively. High SQI classification was found on four out of five sites evaluated, these were the two sites in the Municipality of Trento (Cebolin.M (61%) & Cebolin.T (54%)) and two sites in the Municipality of San Miguel (Libag-Gua (68%) & Upper Carromata (93%)). One site in San Miguel revealed a low SQI (Lower Carromata (41%)). These SQI values indicate that in these areas, soils with very high Exchangeable Ca and Sand content could have a low-quality condition, and sites with optimal Exchangeable Ca (400 - 600 ppm) contents and loamy to sandy loam texture could be classified as high quality soils. Proper drainage system could be best done to manage the very high exchangeable Ca content in these soil and thus, could improve its quality.

Can the Firmness, Weight, and Size of Blueberry Fruit Be Enhanced through the Application of Low Amounts of Calcium to the Soil?

The firmness, weight, and size of blueberries are vital for commercial success of this crop. Fertilization is a key agronomic management practice that affects fruit quality, where calcium (Ca) plays a critical role. This study aimed to assess the impact of low levels of soil-dosed Ca in carboxylic acid form on fruit size, weight, firmness, and residual soil fertility. The study focused on two varieties of blueberries, Duke and Legacy, over two consecutive growing seasons on three commercial farms located in south-central Chile. This study consisted of five treatments, ranging from 0 to 4.0 kg Ca per hectare. The highest firmness values observed for Duke were between 164 and 186 g mm-1, with size values ranging from 15.7 to 16.9 mm, and weight observations ranging from 1.60 to 1.76 g. On the other hand, Legacy showed firmness values between 163 and 173 g mm-1, with size values ranging from 16.2 to 17.2 mm, and weight observations ranging from 2.01 to 2.40 g. The application of low Ca rates to the soil did not impact the size, weight, or firmness of 'Duke' and 'Legacy' blueberries. There was a positive correlation between the Ca soil application and the concentration of exchangeable Ca.

Analysing the behaviour of 90Sr and stable Sr in highly weathered soils: Soil to plant transfer factor and geochemical partitioning

Public concerns over environmental protection have increased after Fukushima accident. The soil-plant transfer factor (Fv) is a critical parameter for environmental risk assessment. 137Cs Fv values determined in acid Brazilian soils could be two orders of magnitude higher than Fv values measured in soils affected by the Chernobyl accident. This paper studied the behaviour of 90Sr in Brazilian soils where very few 90Sr Fv data is available. All classes of studied soils (Ferralsol, Acrisol and Nitisol) showed that more than 80% of total 90Sr in soils remains potentially mobile, mainly at the bioavailable phase, more than 2 years after soil contamination in an experiment conducted in lysimeters. Higher 90Sr Fv for maize and cabbage was observed in the acid soils with low content of exchangeable Ca, lower Fv values occurred at Nitisol, the subtropical soil type. It seems that the behaviour of 90Sr in these soils are mainly controlled by ionic competition mechanisms occurring for root uptake and sorption sites, with stable Sr and major nutrients (Ca, Mg and K). The mineralogy also seems to play a relevant role, since goethite rich clay soil presented 90Sr Fv values higher one or two orders of magnitude than 90Sr Fv values observed at clayed soil goethite rich with trace of vermiculite, for all studied crops. The high rate of 90Sr migration down the soil profiles observed for the studied soils during the 2 first years after contamination suggests a high rate of transfer to groundwater, even transfer to leafy crop group can be also a relevant pathway. In the present study, maize, among other plant species, presented the lowest Fv values, even when compared with maize cultivated in temperate soil. Our results suggest that stable Sr may not be a very good analogue of 90Sr for determining plant Fv values: geometric mean of stable Sr Fv for maize was Fvmaize = 6.3E-1 ± 2.1E0 (n = 8) and for 90Sr was Fvmaize = 1.8E-2 ± 2.5E0 (n = 16), geometric mean of stable Sr Fv for cabbage was Fvcabbage = 1.4E0 ± 3.9E0 (n = 17) and for 90Sr was Fvcabbage = 7.9E-1 ± 4.4E0 (n = 18).

Assessment of Soil Fertility Status in Marori Block of Pilibhit District, Uttar Pradesh, India

This study aims to evaluate the agricultural productivity potential of soils in several villages in Marori block of Pilibhit district during 2022-23. 40 soil samples were collected using a random sampling technique, air-dried, and analyzed for physical and chemical properties. The results showed that the soil content varied significantly, with sand content ranging from 8.2-78.4% silt content from 9.2-67.3%, and clay content from 4.2-39.2%. Bulk density, particle density, porosity, pH levels, electrical conductivity, and organic carbon were also measured. The available nutrients varied, with nitrogen, phosphorus, potassium, calcium, magnesium, and sulphur ranging from 149.13-265.63 kg/ha, 13.59-49.72 kg/ha, 99.34-300.53 kg/ha, 3.3-6.9 cmol (P+)/kg, 1.53-4.20 and 11.29-19.23 kg/ha, respectively. The results showed that 99.5% of the soil samples had normal pH levels, and 0.5% was acidic. The majority of the soil samples had low organic carbon, with 72.5% having the highest available P. The majority of the soil samples were adequate in terms of exchangeable Ca and Mg content, and 60% had the greatest available sulphur. In a nutshell, the study highlights the importance of soil fertility in sustainable agricultural production.

Is Rockwool Potentially Harmful to the Soil Environment as a Nursery Substrate? Taking Eisenia fetida as an Example for Toxicological Analysis

We studied the effect of rockwool matrix on the conventional physical and chemical properties of soil and analyzed its toxicological effect on Eisenia fetida. The physical and chemical properties of rockwool were studied with characterization tests. By measuring earthworm enzymes and earthworm intestinal microorganisms, the effects of different rockwool particle sizes and additive amount on Eisenia fetida were analyzed. The results indicate that a low concentration of rockwool (<30 g/kg) had little effect on the soil physicochemical properties and the activity of Eisenia fetida, and played a positive role in improving the soil porosity. A high concentration of rockwool (>100 g/kg) reduced the exchangeable Ca and Mg content in the soil, and had a significant impact on the enzyme activity of Eisenia fetida. Mechanism studies have shown that high concentrations of rockwool (>200 g/kg) can have a significant impact on the nervous system of earthworm tissue. In addition, small particle size and low concentration of rockwool is conducive to the increase in intestinal microbial species of Eisenia fetida. This study clarifies the effects of emerging rockwool substrates on soil and soil organisms and provides theoretical support for the safe and reliable application of rockwool substrates in agricultural production.

Physical and Chemical Properties of Hidimundige (Crown Choking) Affected and Healthy Arecanut Gardens of Chitradurga District, Karnataka, India

The present investigation was undertaken at College of Agriculture, Shivamogga during 2018-2019 to delineate the causes for hidimundige syndrome in arecanut. Soil samples from two depths 0 to 30 cm and 30 to 60 cm were collected at 60 cm away from the trunk of arecanut from both healthy and affected gardens of Holalkere, Hiriyur, Chitradurga and Hosadurga taluks. The collected soil samples were analyzed for various physical and chemical properties and also for macro and micro nutrients. The results of the investigation indicated that soils coming under affected gardens showed the high mean clay content than healthy gardens. There was a significant increase in bulk density of affected gardens compared to healthy gardens in Holalkere (from 1.63-1.84 Mg m-3) and Hosadurga (from 1.84-1.96 Mg m-3) taluk at lower depth. Whereas, the drainable porosity decreased significantly in affected gardens compared to healthy gardens of Holalkere (from 33.54-25.69 %) and Hosadurga (from 25.79-21.23 %) taluk at lower depth. In all taluks, majority of the soils from both healthy and affected arecanut gardens were neutral to alkaline in reaction. The study showed that availability of N, P, K, S, Fe, Mn, Cu and B and also the content of exchangeable Ca and Mg was quite heterogeneous in both healthy and affected gardens. Whereas, available zinc status in the soil showed significant decrease in affected gardens compared to healthy gardens of Hiriyur, Chitradurga and Holalkere taluks.

Effects of Seasonal Variation on some Soil Chemical Properties under Different Land Use in Santa Barbara, Bayelsa State-Nigeria

A study was carried out to examine the effect of seasonal variation on some soil chemical properties under different land-use in Nembe, Bayelsa State-Nigeria. The objective was to evaluate changes in soil nutrient contents in both wet and dry seasons. A total of eighteen soil samples were collected at 0-30 cm depths in August, 2017 (Wet Season) and March, 2018 (dry season) in natural forest, oil palm plantation and arable land-use and analyzed for pH, soil organic carbon (SOC), total nitrogen (N), available phosphorus (P), exchangeable cations (Ca, Na, K and Mg), and cation exchange capacity (CEC) using standard analytical methods. Results showed that soil pH was highest (4.2) under oil palm plantation in the wet season, while high content of N 0.52 mg/kg was recorded during the wet season in all the thee-land use. Organic carbon was highest 1.69 mg/kg in natural forest, followed by 1.39 and 1.04 mg/kg for oil palm plantation and arable land use. Maximum value of P 0.22 mg/kg was observed under natural forest during the dry season, and the minimum was recorded under arable land use during the wet season. The concentration of exchangeable Ca was highest 0.3 mg/kg in the oil palm plantation, while Na was highest 2.19 mg/kg for natural forest, 1.26 and 1.06 mg/kg for oil palm plantation and arable land use. The CEC values of the soils in the natural forest were moderately high, followed by oil palm plantation and arable land use in the wet season; whereas low CEC values were observed across the three-land use in the dry season. The study concluded that soil nutrients were more available during the wet season than in the dry season in the various land use, probably due to adequate soil moisture availability in the wet season that facilitates soil nutrient release, this implies that chemical properties of soils were influenced by seasonal changes which could in turn affect agricultural production. It is recommended that crop production is encouraged in the wet season than in the dry season so as to utilize more availability of soil nutrients.

Transfer of 137Cs and 90Sr from soil-to-potato: Interpretation of the association from global fallout in Aomori to accidental release in Fukushima and Chornobyl

Ceasium-137 and 90Sr are major artificial radionuclides that have been released into the environment. Soil-to-plant transfer of radionuclides is an important route to food contamination. The radionuclide activity concentrations in crops must be quantitatively predicted for estimating the internal radiation doses from food ingestion. In this study, soil and potato samples were collected from three study sites contaminated with different sources of 137Cs and 90Sr: Aomori Prefecture (global fallout) and two accidental release areas (Fukushima Prefecture and the Chornobyl exclusion zone). The 137Cs activity concentrations in the soil and potato samples widely ranged from 1.0 to 250,000 and from 0.048 to 200,000 Bq kg−1 dry weight, respectively. The soil-to-potato transfer factor of 137Cs also ranged widely (0.0015–1.1) and decreased with increasing concentration of exchangeable K. Meanwhile, the activity concentrations of 90Sr in the soil and potato samples were 0.50–64,000 and 0.027–18,000 Bq kg−1 dry weight respectively, and the soil-to-potato transfer factor of 90Sr was 0.023–0.74, decreasing with increasing concentration of exchangeable Ca. The specific activity ratios of 137Cs/Cs and 90Sr/Sr in the exchangeable fraction were similar to those in potatoes, with a factor of 3 in the ±95 % confidence intervals over six orders of magnitude and a factor of 2 in the ±95 % confidence intervals over five orders of magnitude, respectively. According to the data, the accuracy of predicting the activity concentrations of 137Cs and 90Sr in potatoes can be improved by applying the specific activity ratios of 137Cs/Cs and 90Sr/Sr in the exchangeable fraction. This approach accounts for variable factors such as the effects of K and Ca fertilization and soil characteristics. It also emphasizes the benefit of determining the stable Cs and Sr concentrations in potatoes and other crops prior to possible future contamination.

Clarithromycin as soil and environmental pollutant: Adsorption-desorption processes and influence of pH

Antibiotics pollution is a growing environmental issue, as high amounts of these compounds are found in soil, water and sediments. This work studies the adsorption/desorption of the macrolide antibiotic clarithromycin (CLA) for 17 agricultural soils with different edaphic characteristics. The research was carried out using batch-type experiments, with an additional assessment of the specific influence of pH for 6 of the soils. The results show that CLA adsorption reaches between 26 and 95%. In addition, the fit of the experimental data to adsorption models provided values between 1.9 and 19.7 Ln μmol1−n kg−1 for the KF, Freundlich affinity coefficient, and between 2.5 and 10.5 L kg−1 for Kd, distribution constant of Linear model. Regarding the linearity index, n, it varied between 0.56 and 1.34. Desorption showed lower scores than adsorption, with an average of 20%, and with values of 3.1 and 93.0 Ln μmol1−n kg−1 for KF(des) and 4.4 and 95.0 L kg−1 for Kd(des). The edaphic characteristics with the highest influence on adsorption were the silt fraction content and the exchangeable Ca content, while in the case of desorption, they were the total nitrogen, organic carbon, and exchangeable Ca and Mg contents. Regarding the pH, within the range studied (between 3 and 10), its value did not decisively affect the adsorption/desorption process. Overall, the set of these results could be of help to program appropriate measures leading to the retention/elimination of this antibiotic when it reaches the environment as a pollutant.

Comparison of Soil pH and Exchangeable Cation Quantification by Various Wet Methods with Near- and Mid-Infrared Spectroscopy Prediction

ABSTRACT Rapid soil analyses can be obtained by infrared (IR) spectroscopy, but few studies have evaluated the suitability of different reference wet chemical methods to calibrate models predicting soil fertility. The aim of this study was to assess the accuracy of IR spectral-based models for the determination of soil pH measured in water, potassium chloride (KCl), and calcium chloride (CaCl2), and exchangeable basic cation content measured by the ammonium acetate (NH4OAc, 1 M and 0.02 M variations, pH = 7), Mehlich-III, Ambic-I, citric acid (1%), compulsive exchange, and Bray-II methods. Near- to mid-infrared (NIR, MIR) spectral-based models predicting soil pH and exchangeable cations measures were calibrated by partial least squares regression for a set of soils containing highly and intermediately weathered clay minerals and variable sesquioxide contents. The ratio of root mean square error of prediction (RMESP) to analyte component range was compared to a threshold value for contextual model accuracy assessment. pH measurements in CaCl2 matrices led to better calibrations and predictions of soil pH by IR spectral models compared to pH measurements in water and KCl matrices. Exchangeable calcium (Ca) and magnesium (Mg) concentrations determined by compulsive exchange and the NH4OAc (1 M, pH = 7) extraction methods, respectively, were most accurately predicted by NIR spectral-based models (RMSEP = 1.2–1.4 and 0.37 cmolc kg−1, respectively). The ratio of performance to inter-quartile distance (RPIQ) is recommended as an alternative figure of merit to traditionally reported ratio of performance to deviation (RPD) for IR spectral-based models predicting soil chemical properties. Subsetting soil samples by similarities in physiochemical properties improved the accuracy of soil pH and exchangeable Ca content predictions.

Soil quality index as a tool to assess biochars soil quality improvement in a heavy metal-contaminated soil.

The assessment of soil quality improvement provided by biochars is complex and rarely examined. In this work, soil quality indices (SQIs) were produced to evaluate coffee industry feedstock biochars improvement on soil quality samples of a heavy metal-multicontaminated soil. Therefore, a 90-day incubation experiment was carried out with the following treatments: contaminated soil (CT), contaminated soil with pH raised to 7.0 (CaCO3), contaminated soil + 5% (m/m) coffee ground biochar, and contaminated soil + 5% (m/m) coffee parchment biochar (PCM). After incubation, chemical and biological attributes were analyzed, and the data were subjected to principal component analysis and Pearson correlation to obtain a minimum dataset (MDS), which explain the majority of the variance of the data. The MDS-selected attributes were dehydrogenase and protease activity, exchangeable Ca content, phytoavailable content of Cu, and organic carbon, which composed the SQI. The resulting SQI ranged from 0.50 to 0.56, with the highest SQI obtained for the PCM treatment and the lowest for the CT. The phytoavailable content Cu was the determining factor for differentiating PCM from the other treatments, which was a biochar original attribute and helped to improve soil quality based on the SQI evaluation, further than heavy metal immobilization due to the soil sample pH increase. Longer-term experiments may illustrate clearer advantages of using biochar to improve heavy metal-contaminated soil quality, as physical attributes may also respond, and more significant contributions to biological attributes could be obtained as biochar ages.

Spatial heterogeneity of soil available medium- and micro-elements in evergreen-deciduous broadleaved forest in karst.

Understanding the spatial heterogeneity of soil available medium- and micro-elements in karst area can provide a valuable theoretical guideline for soil nutrient management of karst ecosystem. We collected soil samples at a soil depth of 0-10 cm using grid sampling (20 m×20 m) in a 25 hm2 (500 m×500 m) dynamic monitoring plot. We further analyzed the spatial variability of soil medium- and micro-elements and their drivers, with classic statistics analysis and geo-statistics analysis. The results showed that the average contents of exchangeable Ca and Mg and available Fe, Mn, Cu, Zn, and B were 7870, 1490, 30.24, 149.12, 1.77, 13.54, and 0.65 mg·kg-1, respectively. The coefficient of variation of the nutrients ranged from 34.5% to 68.8%, showing a medium degree of their spatial variation. The coefficient of determination of the best-fit semi-variogram models of each nutrient was higher than 0.90, except for available Zn (0.78), indicating a strong predictive power for the spatial variation of the nutrients. The nugget coefficients for all the nutrients were less than 50%, showing a moderate spatial correlation, and the structural factors played a pivotal role. The spatially autocorrelated variation was within the range of 60.3-485.1 m, among which available Zn showed the lowest range and the deepest fragmentation degree. The spatial distribution of exchangeable Ca, Mg, and available B were consistent, with contents in the depression being significantly lower than that in other habitats. The contents of available Fe, Mn, and Cu declined with the increases of altitude and were significantly lower on the hilltop than in other habitats. The spatial variation of soil medium- and micro-elements was closely related to topographic factors in karst forest. Elevation, slope, soil thickness, and rock exposure rate were the primary drivers of spatial variation of soil elements and need to be considered in soil nutrient management of karst forestlands.

Do the subterranean termite Odontotermes horni alter the micronutrient status of different host plants?

The study investigated the effects of O.horni foraging on various organic litters such as maize straw, finger millet straw, cattle dung, farm waste, grass, silver oak leaves, eucalyptus leaves and bark, and the replaced soils. The results show that the earthen sheetings of O.horni contained significantly less exchangeable Ca, Mg, Zn, Fe, Mn, and Cu contents than the various organic litters. Variations in the exchangeable Na, Ca, Mg, Zn, Fe, Mn, and Cu content were also observed among the earthen sheetings of the different organic litters. Additionally, these earthen sheetings contained slightly higher nutrient content than the surrounding subsoils

Comparative physico-chemical properties of earthen sheetings of Odontotermes horni (Wasmann) and surrounding soil.

Significantly lower coarse sand (24.73 to 27.44 percent), fine sand (22.06 to 24.43 percent), and higher clay (44.33 to 48.98 percent) with little variations in silt (3.65 to 3.77 percent) in the earthen sheeting from 15 to 90 cm height of the tree trunk was observed compared to the surrounding soil at 15,90 and 150 cm depth. Earthen sheetings on the tree trunk showed slightly less pH, EC, organic carbon, organic matter, total N, C: N ratio, available P2O5, and available K, Zn, and Cu compared to the earthen sheetings of the ground surface. Similarly, earthen sheetings on the ground surface had lower exchangeable Ca, Mg, Na, Fe, and Mn compared to the sheetings on the tree trunk. Electrical conductivity, organic carbon, organic matter, total N, available K, CEC, exchangeable Ca, Mg, Na, and Mn content were higher, and pH, C: N ratio, available P2O5, Zn, Fe, and Cu content were lower in the earthen sheetings on the tree trunk compared to 90 and 150 cm depth of the surrounding soil.