Soil Cation Exchange Capacity Research Articles

The Application of Melatonin and Organic Waste Derived from Vitamin C Industry Effectively Promotes Seed Germination and Seedling Growth of Cotton in Saline–Alkali Soil

Saline–alkali stress severely affects plant growth and productivity. Although melatonin can promote seed germination as a growth regulator, it cannot address the weak seedling growth caused by insufficient organic nutrients in saline–alkali soil. The RAE (residue after evaporation, an industrial waste from the industrial production of vitamin C) can enhance plant salt tolerance by stimulating vitamin C (ASA) synthesis and contains abundant small molecular organic acids. We hypothesized that the combined application of melatonin and RAE might synergistically enhance cotton germination and seedling growth. The cotton seeds used in this study were “Xin Lu Zhong No. 87”; a Petri dish simulation experiment and a pot experiment were conducted in 2023. Four treatments were set: control (CK), melatonin (MT), RAE (RAE), and the combined application of MT and RAE (MR). Compared to CK, MT significantly increased the germination rate of cotton seed (194.4%), while RAE significantly enhanced the underground biomass of cotton seedlings (40.3%) and ASA content (203.8%). Compared to MT and R, the combined application of melatonin and RAE significantly increased the ASA content (54.5%, 29.6%) in roots, superoxide dismutase (SOD) activity (220.3%, 89.6%) in roots, catalase (CAT) activity (15.8%, 97.5%) in leaves on the 15th day, soil cation exchange capacity (CEC) (57.2%, 9.7%), and total fresh weight (20.8%, 33.8%). Collectively, these findings indicate that the synergistic effect under the combined use of melatonin and RAE promotes cotton seed germination and seedling growth, offering a novel technical solution for salt–alkali soil cotton cultivation along with an innovative approach for the resource utilization of RAE.

Field‐based estimation of cation exchange capacity using induced polarization methods

AbstractThis study investigates the potential of field‐based induced polarization (IP) methods to provide in‐situ estimates of soil cation exchange capacity (CEC). CEC influences the fate of nutrients and pollutants in the subsurface. However, estimates of CEC require sampling and laboratory analysis, which can be costly, especially at large scales. Induced polarization (IP) methods offer an alternative approach for CEC estimation. The sensitivity of IP measurements to the surface properties of geological materials ought to make them more appropriate than DC resistivity and electromagnetic induction methods, that are sensitive to bulk electrical properties . Such abilities of IP are well demonstrated in the laboratory; however, applications are lacking at field scales. In this work, the ability of field‐based IP to characterize the CEC of floodplain soils is assessed by implementing a methodology that allows for direct comparison between IP and soil parameters. In one field, soil polarization and CEC exhibited the expected positive correlation; but multi‐frequency measurements showed no clear advantage over single‐frequency measurements. In another field, coarser soils (with low CEC) exhibited a high polarization. These coarser soils were characterized by anomalous magnetic susceptibility values, and hence the polarization was attributed to the presence of magnetic minerals. Although better than order‐of‐magnitude estimates of CEC were possible in soils without substantial magnetic minerals, better characterization of porosity, saturation, cementation and saturation exponents, and pore fluid conductivity would improve predictions. However, the measurement of these parameters would require similar efforts as direct CEC measurements. This study contributes to bridging the gap between laboratory‐derived relationships and their applicability in field applications. Overall, this work provides valuable insight for future studies seeking to understand polarization mechanisms in soils at the field scale.

Positive impacts of compost and biochar from orange peel waste on Phaseolus vulgaris physio-biochemistry and productivity and soil properties under salinity stress

ABSTRACT Bioconversion of organic orange peel wastes into compost (OPC) or biochar (OPB) can help overcome the effects of soil salinity and maintain agricultural productivity. Effect of 1.0% OPC or 1.0% OPB as soil amendments on soil properties and performance of Phaseolus vulgaris plants under two salinity levels [5.60 dS m−1 (S-1) and 9.60 dS m−1 (S-2)] versus control [1.60 dS m−1 (S-0)] was investigated. Compared to the control, S-1 and S-2 increased soil sodium ion (Na+) content, while reducing soil organic matter (OM), macro- and micro-nutrients, cation exchange capacity (CEC), and enzyme (urease, acid phosphatase, and alkaline phosphatase) activities, reflecting decreased plant growth and yield. Under S-1 or S-2, OPC application exceeded OPB application, but both considerably enhanced soil OM content, nutrients, CEC, and enzyme activities. These positive results reflected decreased leaf electrolyte leakage and increased leaf-relative water content, pigments, nutrients, K+/Na+ ratio, antioxidant activity, plant growth, and yield. The beneficial impacts of 1.0% OPC were more pronounced under S-2 than S-1 or S-0. In conclusion, adding 1.0% OPC to saline soil (ECe of about 5–10 dS m−1) could mitigate the influences of soil salinity to improve Phaseolus vulgaris growth, physio-biochemistry, and yield.

Analysis of Topsoil Quality Changes Across Soil Groups in Vietnam

This study systematically investigates the changes in topsoil quality across various soil groups in Vietnam over a 13-year period, spanning from 2004 to 2017. The primary objective is to evaluate key soil quality indicators, including pH, organic matter (OM), nitrogen (N), phosphorus (P2O5), potassium (K2O), and cation exchange capacity (CEC), to assess the health, fertility, and sustainability of these soils in response to agricultural practices and environmental factors. The findings reveal significant alterations in soil parameters across the diverse soil groups studied, which include alluvial, red-yellow, acid sulfate, grey and degraded, and yellow-red humus soils. Notably, the average pH levels exhibited a decline in most soil groups, indicating a trend toward increased acidity. This decline in soil pH was accompanied by a marked reduction in nitrogen and potassium concentrations, which are critical for crop growth and productivity. For instance, alluvial and degraded soils demonstrated particularly pronounced nutrient depletion, with nitrogen levels decreasing from 0.23% to 0.19% and potassium levels from 1.23% to 1.03%. In contrast, while phosphorus levels exhibited a slight increase in some soil groups, the overall variability in nutrient content suggests that certain areas may be experiencing more severe deficiencies. Interestingly, the Yellow-Red Humus soils displayed enhanced organic matter retention, with mean OM levels increasing from 4.95% to 5.10%, highlighting their potential for improved nutrient availability and soil health. Cation exchange capacity also showed variability, with a notable decline in the grey and degraded soil group.

Subsurface drainage and nitrogen management affects soil properties in upstate Missouri U.S.

Enhanced efficiency nitrogen (N) fertilizer management may reduce environmental N losses and increase grain yields. The effect of N fertilizer management practices on soil properties is uncertain. In this 5-year study, we evaluated different N fertilizer management [non-treated control (NTC), fall applied anhydrous ammonia (AA) 190 kg N ha−1 with nitrapyrin (fall AA + NI), preplant AA at 190 kg N ha−1 (spring AA), top-dressed urea (TD urea) as 42 kg N ha−1 SuperU and 126 kg N ha−1 ESN as a 25:75 % granular blend] practices in free drained (FD) and non-drained (ND) soils for their impact on soil properties. In FD soils, N fertilization significantly (P > 0.05) increased soil pH, CEC, cations, and Bray I P compared to the NTC. Improved soil aeration and increased plant growth with TD urea and spring AA fertilizer treatments in FD soils increased soil organic matter (OM) 10–13 % and total organic carbon (TOC) 27–35 % compared to the NTC. Increased clay content and reduced silt content were observed in FD soils with N fertilizer treatments compared to NTC. However, fertilizer applications in ND soils had no effect on soil properties. Increased crop production with FD and 4R N fertilizer applications can improve soil properties with increased soil OM and TOC content. This suggests that a synergetic effect of N fertilization and soil drainage can improve soil health by increasing soil cation exchange capacity (CEC), OM, and TOC content.

Spatial pattern, source apportionment, and source-oriented health risk quantifying of heavy metals in farmland soils of southern China.

The contamination of heavy metal has permeated many parts of China, especially in densely populated and industrialized southern China. This study focused on the degree of pollution in farmland soil heavy metals (HMs), and its spatial distribution characteristics and source apportionment. Meanwhile, we conducted an evaluation of the health risks attributed to soil HMs and analyzed the factors that impact them. We found that the distribution of five heavy metals is mainly concentrated in the east-central and southern parts of the study area. Specifically, Cd and Hg have high levels of pollution and present potential ecological risks. The pollution sources of five HMs were analyzed utilizing positive matrix factorization. The results revealed that the contribution of different sources keeps the following order: natural source (42.42%), agricultural activities (29.93%), industrial pollution source (20.49%), and atmospheric deposition pollution (7.16%). The non-carcinogenic risks to residents were acceptable, whereas the carcinogenic risks were relatively high. Children and the elderly are more vulnerable to the negative effects of Cr, As. Using structural equation modeling, we found soil property is a vital factor affecting soil contamination, with the soil organic matter and cation exchange capacity having a relatively greater impact on heavy metals pollution. Our study provides some data reference and guidance for soil ecological protection and restoration.

Pengaruh Pembenah Tanah Cair dan Pupuk N, P, K terhadap Pertumbuhan Serta Hasil Tanaman Bawang Merah (Allium cepa, L.)

This research aims to determine the effects of humic acid application on soil pH, organic carbon (C-Organic), cation exchange capacity (CEC), as well as the growth and yield of shallots. The study was conducted at the Ciparanje Experimental Garden, Faculty of Agriculture, Padjadjaran University, Jatinangor, Sumedang, from November 2023 to February 2024. The experimental method used was a Randomized Complete Block Design (RCBD) with six treatments and five replications. The treatments were: A; (0.5 Soil Amendment and 1 Standard N, P, K), B; (1 Soil Amendment and 1 Standard N, P, K), C; (1.5 Soil Amendment and 1 Standard N, P, K), E; Without Standard N, P, K and Soil Amendment (Control), and F; (Standard N, P, K). The results showed that the combination of soil amendments and N, P, and K fertilizers significantly affected the parameters of soil pH, C-Organic, CEC, and plant height at 14, 28, 42, and 56 days after planting (DAP); stem diameter at 14, 28, 42, and 56 DAP; number of tillers at 14, 28, 42, and 56 DAP; and shallot plant weight.

Remediation of Cd-As-Ni co-contaminated soil by extracellular polymeric substances from Bacillus subtilis: Dynamic improvements of soil properties and ecotoxicity

As the primary reservoir of heavy metals in nature, soil is highly susceptible to significant co-contamination with Cd-As-Ni. In current study, extracellular polymeric substances (EPS) from Bacillus subtilis were utilized as a novel improver to simultaneously enhance soil property and restrain ecotoxicity in Cd-As-Ni co-contaminated soil. Our findings revealed that EPS effectively bound and immobilized free Cd, As, and Ni in soil and decreased 49.73 % of soil available Cd, 79.16 % of As and 77.87 % of Ni contents by increasing soil pH, soil organic matter and cation exchange capacity. The EPS was also found to inhibit the Cd-As-Ni induced ecotoxicity in Caenorhabditis elegans by increasing the activities of antioxidant enzymes including superoxide dismutase, glutathione, and catalase. The remediation of EPS showed progressive improvement over time, and maintained a lasting effect after achieving peak efficiency. Our results might provide a new perspective on the potential of EPS in remediation of soil heavy metal pollution and the development and utilization of microbial biomass resources in a wider range.

A biochar-based amendment improved cadmium (Cd) immobilization, reduced its bioaccumulation, and increased rice yield

Cadmium (Cd) contamination of soil threatens human health, food security, and ecosystem sustainability. The in situ stabilization of Cd has been recognized as a potentially economical technology for the remediation of Cd-contaminated soil. Recently, biochar (BC) and activated carbon (AC) have received widespread attention as eco-friendly soil amendments that are more beneficial for plant growth, soil health, and remediation of contaminated soil. An experiment was performed in a paddy field to investigate the effects of two different types of BC (maize straw biochar and bamboo biochar) and AC (coconut shell activated carbon) in combination with rape organic fertilizer (R), calcium magnesium phosphate fertilizer (P), and fulvic acid (F), respectively, on soil Cd immobilization, Cd accumulation in rice, and yield. The results indicated that the BC/AC-based amendments reduced soil bioavailable Cd (DTPA-Cd) and brown rice Cd by 9.58%–27.06% and 19.30%–71.77%, respectively. The transformation of exchangeable Cd (Ex-Cd) to carbonate-bound Cd (Ca-Cd), Fe-Mn oxide bond (Ox-Cd), and residual (Re-Cd) in soil accounted for the mitigation of Cd uptake and enrichment by rice. Additionally, BC-/AC-based amendments altered soil physicochemical properties, which significantly increased the soil pH and cation exchange capacity (CEC), total nitrogen (TN), total phosphorus (TP), soil organic carbon (SOC), and dissolved organic carbon (DOC), directly promoting soil health. All BC-/AC-based amendments significantly increased FeIMP and MnIMP concentrations by 47.31%–160.34% and 25.72%–73.09% in the Fe/Mn plaque (IMP), respectively. Maize straw and bamboo biochar-based amendments significantly increased rice yield by 10.46%–20.41% and 9.94%–16.17%, respectively, while coconut shell-activated carbon severely reduced rice yield by 65.06%–77.14%. The correlation analysis revealed that leaf Cd and IMP primarily controlled Cd uptake by rice, and soil pH, Eh, CEC, SOC, IMP, and TP influenced DTPA-Cd in soil. This field study demonstrated that maize straw and bamboo biochar-based amendments not only reduced soil DTPA-Cd in paddy fields but also decreased the accumulation of Cd in brown rice, as well as improved rice yield, which has potential application in Cd-contaminated agriculture fields. Coconut shell-activated carbon severely decreased rice yields, which is not appropriate for rice production.

Variability of soil chemical properties and rice productivity in salt-affected soil in the north coastal rice field of Central Java, Indonesia

A coastal rice field is generally characterized by salt-affected soil and low soil quality for rice cultivation. Identifying soil chemical properties in these areas is necessary to determine soil management options for rice production. Therefore, soil samples were collected from 33 sampling points in the Wedung Sub-district of Demak Regency in the late dry season of 2021 to evaluate the variation among soil chemical characteristics in a coastline rice field. Soil samples were obtained beneath the topsoil (0-20 cm soil depth) and observed for electrical conductivity, exchangeable potassium, sodium, calcium, magnesium, and cation exchange capacity. Soils in the research field were categorized as slightly salty (0.75-2 dS m-1) to lightly salty (2.0-4.0 dS m-1) with very high sodium (>2 cmol(+) kg-1). Exchangeable potassium was dominated by moderate (0.3-0.7 cmol(+) kg-1) and low categories (0.2-0.3 cmol(+) kg-1). Based on soil calcium-to-magnesium ratios, around 6% of all samples were classified as calcium-deficient. The range of soil cation exchange capacity was 22-30 cmol(+) kg-1 and classified as high soil cation exchange capacity. Rice productivity in the salt-affected soil was around 4 t ha-1. Strategies for soil and controlling plants, such as soil amelioration and salt-tolerant rice cultivars, should be pursued to support plant growth and enhance rice productivity in the salt-affected soil, particularly in the coastal area.

Application of oil palm and cacao waste biochar to improve the chemical properties of an Ultisol of Langsa, Aceh

Ultisols, including those of Langsa, Aceh, are known to have low fertility due to low pH, low available nutrients, low base saturation, high pH and exchangeable Al, and low cation exchange capacity. These problems can be alleviated by applying organic amendments to the soil. One of the soil amendments is biochar. This study aimed to elucidate the potential of oil palm and cacao waste biochar for improving the chemical properties of an Ultisol of Langsa, Aceh. Biochars generated from oil palm kernel shell (PKS), oil palm empty fruit bunch (PEFB), and cacao pod husk (CPH) were applied to the soil and incubated in the laboratory for 16 weeks. At 4, 8, 12, and 16 weeks after incubation, the changes in soil chemical properties were measured. The results showed that applying different types of biochar significantly improved the chemical properties of the Ultisol of Langsa. Specifically, PEFB biochar caused significant increases in soil pH (H2O and KCl), total phosphorus, available phosphorus, organic C, and cation exchange capacity. These increases became more pronounced with longer incubation times. In addition, using PEFB biochar resulted in the lowest levels of exchangeable Al and Fe in the soil. These levels decreased further with longer incubation times. In general, PEFB biochar produced at a pyrolysis temperature of 450oC for 4 hours is the most effective biochar for improving the chemical properties of the Ultisol of Langsa.

Rice straw biochar and NPK minerals for sustainable crop production in arid soils: a case study on maize-wheat cropping system

Maize and wheat are the main cereals grown in Egypt. However, the country relies on grain imports to meet its local demands. In order to improve their production, appropriate fertilization programs are needed. The present study investigates the effects of amending a clayey soil of an arid region with rice straw biochar and NPK mineral fertilizers, individually or in combination, for increasing growth and productivity of maize and wheat crops. Additionally, impacts of these additives on soil biological activities and carbon (C) transformations in soil were a matter of concern herein. To achieve this objective, a field research of a randomized block design was conducted during the summer (maize) and winter (wheat) seasons of 2020/2021. The following treatments were considered: unmodified control (CK), 100% N inputs in the form of biochar (reference organic treatment, RSB) (T1), 100% mineral treatment (reference inorganic treatment, T2), 75% RSB + 25% NPK minerals (T3), 50% RSB + 50% NPK minerals (T4) and 25% RSB + 75% NPK minerals (T5). Additional doses of mineral fertilizers were added to treatments from T3 to T5 to maintain NPK inputs within the recommended doses. Key results showed that all additives significantly enhanced plant growth parameters and productivity. They also increased soil organic carbon level by the end of the growing season hence reduced soil bulk density, even for the treatment that received only mineral NPK applications (T2). All additives also upraised soil cation exchange capacity (CEC), soil available nitrogen (N), and soil salinity. However, sole application of biochar recorded the least increase in soil salinity. Combined mineral-organic treatments not only recorded the highest increases in soluble and microbial fractions of organic carbon and nitrogen in soil; but also noted the greatest improvements in growth and grain productivity of maize and wheat versus sole applications of mineral fertilizers or biochar. The alkaline nature of biochar was buffered by soil while no significant differences were observed in harvest index among treatments. In conclusion, combined use of biochar and mineral fertilizers, especially T5 is recommended for increasing soil fertility and wheat and maize grain productvity.

Influence of dissolved and non-aqueous phase toluene on spectral induced polarization signatures of soils

Fifty-two laboratory experiments are undertaken to analyze the sensitivity of spectral induced polarization (SIP) to the presence of toluene in soils. Among these experiments, four experiments are conducted to collect SIP responses of soils containing dissolved phase toluene within the pore water using columns. The results demonstrate that SIP is not sensitive to the presence of dissolved phase toluene in soils. The remaining forty-eight experiments are undertaken with four types of soils mixed with non-aqueous phase toluene. The experimental results prove that SIP is sensitive to toluene saturation under varying salinity conditions. These observations are well-explained by a published petrophysical model accounting for the effects of water saturation on complex conductivity. The water saturation exponent n and quadrature conductivity exponent p in this model are obtained by fitting complex conductivity data versus saturation at different saturation levels. The petrophysical model is tested where in-phase and quadrature conductivity responses are predicted from water saturation, soil cation exchange capacity (CEC), and pore water conductivity. The petrophysical model provides satisfactory predictions for non-aqueous phase toluene saturation. Overall, this study contributes to our understanding of SIP as a non-intrusive tool for characterizing toluene contamination in soils with applications to the field.

Possibility of using industrial by-product combinations to remediate cadmium and arsenic contaminated soil

It is inevitable to produce by-products in industrial and mining production, and how to deal with these by-products has become a major environmental issue. Meanwhile, many studies have shown that applying soil amendments is a feasible measure for effectively controlling soil pollution. Finding low-cost and efficient soil passivators is an effective way to safely utilize polluted soil. This article provides a method of “treating contamination with waste”. Through spinach pot experiments, different proportions and doses of granite powder (A, quarry waste), market purchased conditioner (B), “granite powder+iron sulfate mineral (titanium powder industrial waste)” (C), and “granite powder+iron sulfate mineral+market purchased conditioner” (CB) were used to treat soil co-contaminated with cadmium (Cd) and arsenic (As). The results indicate that amendments affect the available Cd and As in soil by changing soil pH and cation exchange capacity. The amendment of A, B, C, and CB all has remarkable reduction rates of soil available Cd at 65.48 %, 57.02 %, 61.37 %, and 43.15 %, respectively, compared to the control. Both A and B increase the available As content in the soil and the As content in spinach. However, both C and CB reduced the available As content in the soil by 60.32 % and 12.48 %. CB treatment could simultaneously reduce the accumulation of Cd and As in spinach, increase chlorophyll content, and promote spinach growth. It was worth noting that the 3 % CB treatment has the best effect, with Cd and As content in spinach stems and leaves decreasing by 51.13 % - 69.62 % and 35.46 % - 59.53 %, respectively, and the repair cost being as low as 76.5 $ ton−1. Therefore, the combined application of granite powder, market purchased conditioner, and iron sulfate minerals for the remediation of Cd and As co-polluted soil was a cost-effective and environmentally friendly technology. However, applying these soil composite amendments also requires attention to adjusting with the soil type and with pollution type, which we are currently studying.

Feasibility assessment of biochar amendment for mitigating phytotoxicity of polyvinyl chloride micro/nano-plastics: A study based on lettuce pot experiments

Micro/nano-plastics (M/NPs) are pervasive in agricultural soils, and their detrimental effects on crops are increasingly evident. This ultimately results in reduced crop yields and quality, posing a great threat to global food security. Therefore, the urgent need to mitigate the phytotoxicity of M/NPs has become apparent. Biochar (BC), as an environmentally friendly soil amendment, plays a crucial role in modifying soil properties and boosting agricultural production levels. Its strong adsorption capacity enables it to effectively passivate soil pollutants and reduce their phytotoxicity. However, the effect of BC on the phytotoxicity of M/NPs in soil remains unknown. In this study, the feasibility of BC amendment for mitigating phytotoxicity of polyvinyl chloride M/NPs (PVC-M/NPs) was evaluated by conducting pot experiments. The results show that the application of 0.1% (w/w) PVC-M/NPs resulted in a 48.60% reduction in lettuce yield. This reduction can be attributed to the decreased soil microbial activity and soil cation exchange capacity (CEC), as well as the direct physical damage to lettuce roots caused by PVC-M/NPs. BC amendment improved soil quality, but had insignificant effect on lettuce biomass compared to the control (p > 0.05). In contrast, BC amendment at an appropriate concentration (0.5% and 2.5%, w/w) to soils contaminated with PVC-M/NPs resulted in a significant increase in lettuce yield (p < 0.01). Furthermore, BC was found to mitigate the oxidative stress of PVC-M/NPs on lettuce roots. This indicates that the BC amendment has the potential to mitigate the toxicity of PVC-M/NPs to lettuce. Improving soil quality and enhancing PVC-M/NPs adsorption are perceived as the influencing mechanisms of BC on the phytotoxicity of PVC-M/NPs. The findings suggest that it is feasible to mitigate the phytotoxicity of M/NPs through BC amendments.

Peanut cultivar response to residual soil test potassium in North Mississippi

AbstractThe average U.S. peanut (Arachis hypogaea L.) yield has increased by approximately 25% with the adoption of peanut cultivar ‘Georgia‐06G’. Since this adoption, many new high yielding runner cultivars with similar yield potential have been released. However, current nutrient recommendations are based on soil tests that were developed prior to the release of Georgia‐06G. Particularly for potassium, current soil test potassium (STK) critical values were established on soil textures with relatively low cation exchange capacity (CEC) but were not validated on soil textures with high CEC. This study aimed to evaluate the growth and yield response of five recently released peanut cultivars to four STK levels ranging from very low to medium based on Mississippi State University Extension soil testing recommendations. The STK classification levels were also based on two soil series categorized with high CEC—Leeper (∼38.4 meq 100 g−1) and Marietta (∼15.9 meq 100 g−1) soil series. Cultivars Georgia‐06G, ‘Georgia‐16HO’, ‘Georgia‐18RU’, FloRun ‘331’, and ‘AU‐NPL‐17’ were evaluated in this study. No STK × variety interaction occurred, indicating similar K requirements across all varieties evaluated. However, a positive pod yield response occurred in both soil types when the average STK increased from 128 to 167 lbs ac−1 for all cultivars and site years. Critical STK values on both soils were greater than many current Extension recommendations, and the critical STK value of Leeper is greater than the Marietta soil series, likely due to the higher CEC value. These results demonstrate the need to adjust peanut STK sufficiency levels based on soil CEC. Further evaluation of modern peanut cultivar productivity response to STK sufficiency levels is needed for soils with moderate CEC.

Can silvopasture with arboreal legumes increase root mass at deeper soil layers and improve soil aggregation?

AbstractSilvopastoral system (SPS) is a multifunctional agroforestry practice. This study evaluate soil properties and root biomass under SPS in Pernambuco, Brazil. The experiment was established in 2011. The treatments were (1) monoculture signalgrass (MS) [Urochloa decumbens (Stapf.) R. D. Webster], (2) intercropped pasture of signalgrass with legume Gliricidia (SG) [Gliricidia sepium (Jacq.) Steud.], and (3) intercropped pasture of signalgrass with legume sabiá (SS) (Mimosa caesalpiniifolia Benth). Treatments were allocated in randomized complete block design with three replications. Samples were collected at 0‐ to 10‐, 10‐ to 20‐, 20‐ to 40‐, 40‐ to 60‐, 60‐ to 80‐, 80‐ to 100‐, and 100‐ to 120‐cm soil depths. Soil samples were also taken from the native forest (NF) considered as a reference at the same Experimental Station. Legume SPS (SG and SS) presented greater root biomass per unit area compared to MS at 60‐ to 80‐cm depth (p &lt; 0.05); however, MS had greater root biomass per hectare at the top layers. The average values of the weighted mean diameter of soil aggregates were 3.20, 3.19, 3.07, and 3.27 mm in MS, SG, SS, and NF, respectively, at 0‐ to 120‐cm depths. The SPS increased soil cation exchange capacity in deeper layers, indicating greater biological activity at greater depth. Grasslands and SPS store 235 Mg C ha−1 with 71% of that found in deeper layers (20–120 cm). SPS with signalgrass intercropped with arboreal legumes has potential to improve deep soil C storage and resilience of livestock systems in tropical regions.

Comparative assessment of soil health attributes between topsoil and subsoil influenced by long-term wastewater irrigation

The reuse of wastewater (WW) for crop irrigation is increasingly recognized as an alternative to freshwater irrigation in arid and semi-arid regions. However, there is a significant gap in knowledge regarding the soil health index (SHI) and factors influencing topsoil and subsoil in cropland under long-term WW irrigation. This study aimed to comparatively assess soil health attributes between topsoil and subsoil in smallholder farmlands that have been irrigated with WW for over 50 years. This assessment utilized a combination of soil physico-chemical and fertility attributes, along with heavy metal concentrations. The soil health index (SHI) was developed using linear (SHI - L) and nonlinear (SHI - NL) models, based on the Total Data Set (TDS) and Minimum Data Set (MDS). Statistically significant differences (P ≤ 0.05) were observed between topsoil and subsoil for the soil stability index (SSI), organic matter (SOM), calcium carbonate equivalent (CCE), electrical conductivity (EC), sodium adsorption ratio (SAR), macro- and micronutrients, and heavy metals (Zn, Cu, Cd, Pb, and Ni). In contrast, soil bulk density (BD), pH, and cation exchange capacity (CEC) did not show significant differences. The mean SHI - L and SHI - NL values ranged from 0.68 to 0.77 and 0.46–0.53 for topsoil, and from 0.66 to 0.74 and 0.45–0.51 for subsoil, respectively. The SHI values were higher in the topsoil, with increases ranging from 2.3 % to 7.1 % for SHI - L and 0.65–11.3 % for SHI - NL compared to the subsoil. The regression coefficients between SHIs and corn yield were higher in the topsoil (0.46–0.49) than in the subsoil (0.20–0.22). Furthermore, the SHI - NL model demonstrated greater precision than the SHI - L model in predicting corn yield in both soil depths. These findings highlight the effectiveness of SHI assessments, particularly the SHI - NL model, in analyzing changes in soil health indices with depth and their relationship with crop performance in long-term WW-irrigated smallholder farmlands. This research provides valuable insights into addressing soil health challenges in similar agricultural systems.

Modeling of Soil Cation Exchange Capacity Based on Chemometrics, Various Spectral Transformations, and Multivariate Approaches in Some Soils of Arid Zones

Cation exchange capacity is a crucial metric for managing soil fertility and promoting agricultural sustainability. An alternative technique for the non-destructive assessment of important soil parameters is reflectance spectroscopy. The main focus of this paper is on how to analyze and predict the content of various soil cation exchange capacities (CEC) in arid conditions (Sohag governorate, Egypt) at a low cost using laboratory analysis of CEC, visible near-infrared and shortwave infrared (Vis-NIR) spectroscopy, partial least-squares regression (PLSR), and Ordinary Kriging (OK). Utilizing reflectance spectroscopy with a spectral resolution of 10 nm and laboratory studies with a spectral range of 350 to 2500 nm, 104 surface soil samples were collected to a depth of 30 cm in the Sohag governorate, Egypt (which is part of the dry region of North Africa), in order to accomplish this goal. The association between the spectroradiometer and CEC averaged values was modeled using PLSR in order to map the predicted value using Ordinary Kriging (OK). Thirty-one soil samples were selected for validation. The predictive validity of the cross-validated models was evaluated using the coefficient of determination (R2), root mean square error (RMSE), residual prediction deviation (RPD), and ratio of performance to interquartile distance (RPIQ). The results indicate that ten transformation methods yielded calibration models that met the study’s requirements, with R2 &gt; 0.6, RPQ &gt; 2.5, and RIQP &gt; 4.05. For evaluating CEC in Vis-NIR spectra, the most efficient transformation and calibration model was the reciprocal of Log R transformation (R2 = 0.98, RMSE = 0.40, RPD = 6.99, and RIQP = 9.22). This implies that combining the reciprocal of Log R with PLSR yields the optimal model for predicting CEC values. The CEC values were best fitted by four models: spherical, exponential, Gaussian, and circular. The methodology used here does offer a “quick”, inexpensive tool that can be broadly and quickly used, and it can be readily implemented again in comparable conditions in arid regions.

Effects of Biochar-Amended Composts on Selected Enzyme Activities in Soils

This study examines the effect of biochar as an agricultural soil supplement on soil quality indicators, specifically enzyme activity in Missouri regions. While the benefits of biochar on soil bulk density, soil organic carbon, and infiltration have been established, its effect on soil enzyme activity has remained underexplored in this region. A three-year field investigation was conducted with six treatments (compost, biochar, compost + biochar, biochar + compost tea, fescue, and control) to evaluate the effects on enzymes such as β-glucosidase (BG), acid and alkaline phosphatases (ACP-ALP), arylsulfatase (ARS), dehydrogenases (DG), arylamidase (AMD), cellulase (CLS), and urease (URS). Furthermore, soil pH, organic matter (OM), and cation exchange capacity (CEC) were determined. The results showed that compost and biochar treatments considerably increased soil enzyme activity compared to other treatments, with nitrogen application further increasing enzyme activity. Soil pH, OM, and CEC were all important determinants in determining enzyme activity, with BG demonstrating strong positive associations with ACP and AMD (99.5%). This study shows that compost and biochar amendments significantly improve soil physicochemical and biological properties, thereby enhancing soil health and assisting farmers’ sustainable soil management practices.