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Soil phosphorus (P) plays an essential role in rubber tree plantations that are rapidly and extensively being established in Southeast Asia. However, available information is quite limited on soil P fractions and arbuscular mycorrhizal fungi (AMF) in the tropical region. Herein, we investigated P fractions and AMF community under natural forest and rubber plantations at different ages of 5 years, 11 years, and 22 years in tropical coarse-textured soils from Thailand. The studied loamy sand soils were acidic (pH=5.0-5.7) with low available P concentrations (1.73-6.48 mg/kg). Data on the P fractions data revealed that the labile P (water-extractable Pi and NaHCO3-extractable Pi) and moderately labile P (NaOH0.1-extractable Po and HCl-extractable Pi) pools in rubbergrowing soils were higher than those in the natural forest soil. Elevated values of these properties were substantial with increasing stand ages. The rubber monocropping systems declined in the density and diversity of AMF spores compared to the natural forest site. Glomus badium, Rhizophagus fasciculatus, Acaulospora Laevis, and Ambispora appendiculata were the most dominant and tolerant AMF species across the rubber stands (>50% of the total species). The P fractions and AMF were correlated with soil labile-P forms. Soil labile and moderately P fractions were the important factors affecting the difference in AMF community. This study highlighted that long-term rubber plantations in tropical ecosystems promoted labile P fraction but demoted AMF density and diversity. [ABSTRACT FROM AUTHOR]

Oxides of silicon (Si), manganese (Mn), and zinc (Zn) have been used as soil amendments to reduce As mobility and uptake in paddy soil systems. However, these amendments are hypothesized to be affected differently depending on the soil pH and their effect on As speciation in rice paddy systems is not fully understood. Herein, we used a microcosm experiment to investigate the effects of natural Si-rich fly ash and synthetic Mn and Zn oxides on the temporal development of porewater chemistry, including aqueous As speciation (As(III), As(V), MMA, DMA, and DMMTA) and solid-phase As solubility, in a naturally calcareous soil with or without soil acidification (with sulfuric acid) during 28 days of flooding and subsequent 14 days of drainage. We found that soil acidification to pH 4.5 considerably increased the solubility of Si, Fe, Mn, and Zn compared to the non-acidified soil. Additions of Mn and Zn oxides decreased the concentrations of dissolved arsenite and arsenate in the non-acidified soil whereas additions of Zn oxide and combined Si–Zn oxides increased them in the acidified soil. The Si-rich fly ash did not increase dissolved Si and As in the acidified and non-acidified soils. Dimethylated monothioarsenate (DMMTA) was mainly observed in the acidified soil during the later stage of soil flooding. The initial 28 days of soil flooding decreased the levels of soluble and exchangeable As and increased As associated with Mn oxides, whereas the subsequent 14 days of soil drainage reversed the trend. This study highlighted that soil acidification considerably controlled the solubilization of Ca and Fe, thus influencing the soil pH-Eh buffering capacity, the solubility of Si, Mn, and Zn oxides, and the mobility of different As species in carbonate-rich and acidic soils under redox fluctuations. [Display omitted] • Solubilities of Si, Mn, and Zn oxides differed in acidified and non-acidified soils. • Soil acidification greatly impacted As, Si, Mn, and Zn solubility in paddy soils. • Mn and Zn oxides decreased arsenite and arsenate in non-acidified soil. • Zn oxide increased dissolved arsenite and arsenate in acidified soil. • Soil acidification and reaeration synergistically increased H 4 SiO 4 -to-H 3 AsO 3 ratio. [ABSTRACT FROM AUTHOR]

Exposure to arsenic (As) through rice consumption potentially threatens millions of people worldwide. Understanding is still lacking the recycling impacts of rice residues on As phytoavailability in paddy soils and is of indisputable importance in providing a sustainable and effective measure to decrease As accumulation in rice grain. Herein, we examined the effects of rice husk biochar (RHB) and rice husk ash (RHA) on As grain speciation, and As dynamics in the soil porewater and solid-phase fractions. The results corroborated that both the RHB and RHA (0.64% w/w) treatments significantly (p < 0.05) decreased inorganic As accumulation in rice grain to 0.27–0.29 mg kg−1, which was below the maximum inorganic As level in husked rice (0.35 mg kg−1) established by the Codex. The residual phase (F6 = 90% of total soil As) as quantified by the sequential extraction was the dominant As pool; the fractions were subsequently transformed into several As pools associated with soluble and exchangeable (F1), organically bound (F2), Mn oxides (F3), poorly crystalline (F4) and crystalline (F5) Fe oxides during the rice growing periods. The Si-rich amendments enhanced the residual phase formation upon soil flooding, which decreased the As availability to rice plant. The inorganic grain-As concentrations were well explained by the soil-extractable As concentrations in the F2, F3, F5, and F6 fractions. The pore-water analysis indicated that Mn oxides were important sources and sinks for As released to the soil solution. Our findings shed light on the beneficial role of RHB and RHA in alleviating inorganic As uptake in paddy rice. Unlabelled Image • Rice husk biochar and ash significantly decreased As(III) accumulation in grain. • Rice husk ash significantly decreased As(V) uptake in grain. • Biochar and ash promoted residual As phase formation and demoted rice grain As. • Oxalate-extractable As of flooded soil could explain inorganic grain As contents. • Mn oxides were the major sources and sinks for As released to soil solution. [ABSTRACT FROM AUTHOR]

Zinc (Zn) biofortification in rice improves human nutrition and contributes considerably to rice growth. However, available information on Zn extractability and quantitative knowledge of how Zn is bound in paddy soils from Southeast Asia, which is of immense importance for Zn nutrition in rice, is rather limited. Here, we identified and quantified Zn pools with different solubility in 150 paddy soil samples using single, selective, and eight-step sequential extractions. The pH conditions of the soils ranged from ultra-acidic to slightly alkaline. The amounts of Zn in the extractable pools indicated sufficient levels of potentially available Zn (median DTPA–extractable Zn = 1.5 mg kg −1 ) in most soils. Chemical speciation calculations based on CaCl 2 extraction and DTPA–extraction data suggested that Zn 2+ ion activities in these soils were relatively low and most likely controlled by release of incorporated Zn rather than by dissolution of known Zn mineral phases. Maximum Zn 2+ solubilities were furthermore related to the solubility of franklinite (ZnFe 2 O 4 ), which is controlled by the availability of Fe 3+ being limited by the pH-dependent solubility of Fe(III) (hydr–)oxides. Correspondingly, the sequential extraction results revealed that residual fraction (F8) and maximum acid-soluble fraction (F7) (contributed to 75% of the total Zn in soils) were the dominant Zn pools in the studied soils. The quantitative contribution of other fractions decreased in the following order: crystalline Fe oxides (F6) > Mn oxides (F3) ≈ organically bound (F4) > microcrystalline Fe oxides (F5) > mobile (F1) > mobilizable (F2). The acidic soils contained more Zn in the presumably highly mobile fraction (F1) than the neutral soils, whereas the neutral soils contained more mobilizable Zn fraction (F2) than the acidic soils. The correlation analysis suggested that the CaCl 2 – and DTPA–extractable Zn and Zn fractions were influenced by soil pH and soil constituents such as organic carbon, and amounts of crystalline and microcrystalline Fe/Mn oxides. [ABSTRACT FROM AUTHOR]

Vanadium (V) is increasingly recognized both as a medical trace element with essential biological functions and as a potentially toxic environmental pollutant, yet the current knowledge on V speciation in soils is limited. Here, we investigated the chemical speciation and extractability of V in highly weathered tropical soils, which are often rich in V compared to soils of temperate climatic regions. Vanadium K-edge X-ray absorption near edge structure (XANES) spectra of soil samples, along with a range of reference compounds differing in V-oxidation state and coordination chemistry, revealed the predominance of V4+/5+ in a primarily octahedral or tetrahedral coordination. The soil spectra were best fitted with linear combinations of reference spectra of V4+ in the structure of kaolinite, V5+ adsorbed to kaolinite, and other V5+-sorbed solids. Vanadate adsorbed to goethite, ferrihydrite, gibbsite, and/or Fe(III)-natural organic matter complexes and V4+ in the structure of goethite may be present, but cannot unequivocally be distinguished from each other by XANES spectroscopy. Sequential and single chemical extractions provided complementary information on the solubility of V under various conditions. The most labile V fractions, interpreted as weakly and strongly adsorbed V5+, are the most relevant to V mobility and bioavailability in the environment, and accounted for only ~2% of total soil V. Our results demonstrate that kaolinite and Fe oxides can effectively sequester V in highly weathered soils by mechanisms of adsorption and structural incorporation and are relevant to other Fe-oxide-rich environments under acidic and oxic conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Al compounds were the most dominated soil solid phase P species in acidic soils. • Ca and Al compounds dominated the soil solid phases P species in high pH soils. • Soil pH was the critical controller for P species and solubility. • Dissolvable-colloidal-Fe/Al phases might be bioavailable under acidic conditions. • DGT technique could explain soil-plant P concentration. Soil solid-phase phosphorus (P) speciation and chemical conditions exert a crucial role in both aqueous P speciation and concentration—the most available and mobile pool for biota in environments. However, the interplay between solid-phase speciation and the aqueous phase of P in soil systems is unresolved. Herein, we investigated the speciation and solubility of P in tropical agricultural soils, which are often poor in P availability. Phosphorus K -edge X-ray absorption near edge structure (XANES) spectra of acidic soils identified dominant Al-hydroxide-phosphates (∼58%: P adsorbed to gibbsite 19%, P adsorbed to kaolinite 14%, and variscite 16%), followed by Fe-hydroxide-phosphates (∼36%: P adsorbed to ferrihydrite 14% and strengite 22%), and trace organic P (∼6%). Calcium phosphates (∼52%) prevailed in the alkaline/calcareous soils with moderate and minor contributions from Al-phosphates (∼37%: P adsorbed to kaolinite 28%, P adsorbed to gibbsite 1%, and variscite 7%) and Fe phosphate (∼11%), respectively. The time-averaged P concentration in the aqueous phase using diffusive gradients in thin films (C DGT) was highly variable from 4 to 123 μg P L–1, with the highest and the lowest values observed in acidic-coarse- and alkaline-fine-textured soils, respectively. The C DGT concentration was positively related to belowground P uptake. The C DGT concentration had negative relationships with pH, Ca-P XANES, and total and extractable Ca, indicating that Ca phosphates were the primary constituents decreasing the dissolvable P concentration. This study highlighted the importance of solid-phase P species in determining P fluxes and is relevant to diverse soils rich in Fe/Al/Ca compounds under extremely acidic to alkaline conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Al phases were the most primary hosts for P in the clay fraction of sandy soils. • P solubilities of tropical sandy soils revealed a positive pH-dependent pattern. • The pH-dependent solubility of Al/Fe (hydr)oxides controlled the P solubilities. • Large particles of plant debris contributed to the largest total soil P stocks. • Small particles were the primary source and sinks for available soil P. Growing demands for crops have expanded agricultural production to sandy soils with low available phosphorus (P) content and high P mobility. Knowledge of P speciation and solubility in such soils is poorly understood. Here we investigated: i) the P speciation in the clay size fraction of sandy soils, ii) the pH-dependent solubility of soil orthophosphate (PO 4 –P), and iii) the particle size-dependent solubility of the soil P. The studied loamy sand soils were low in organic matter (2.6–7.9 g kg−1) and deficient in available P (1.5–8.5 mg kg−1), and kaolinite (21%) was the only clay mineral identified using X-ray diffraction technique in the clay-sized particles. The P K -edge X-ray absorption near edge structure analysis revealed that P associated with Al phases, 45% adsorbed to gibbsite and 35% in variscite (AlPO₄·2H₂O), dominated the P speciation in the clay-sized particles. The very low PO 4 –P solubilities in the investigated bulk soils exhibited a pronounced positive pH-dependent pattern that was consistent with the pH-dependent solubility of Al3+ and Fe3+. Geochemical modeling suggested that the maximum PO 4 –P solubilities were linked to the solubility of variscite and strengite (FePO₄·2H₂O), indicating that PO 4 –P solubilities were controlled by the solubility of Al3+ and Fe3+ as restricted by the pH-dependent solubility of Al phases and Fe (hydr)oxides. The analysis of particle size fractions revealed that the largest size fraction (1000–2000 µm), containing visible plant debris and contributing the least to total soil mass (<0.126%), contained most of the total soil P stocks (50–60%). The small size factions (<250 µm) were the key to available PO 4 –P. Our data highlighted the pivotal role of Al/Fe (hydr)oxides and kaolinite in controlling the pH-dependent solubility of PO 4 –P in these tropical sandy soils having very limited contents of total and available P and a high risk of P loss. [ABSTRACT FROM AUTHOR]

Abstract: Phosphate (P) sorption and desorption characteristics have been investigated for sixty-two representative samples of the major Thai upland agricultural soils which are Oxisols and Ultisols formed on diverse parent materials and under various climatic conditions. P sorption characteristics are well described by Langmuir and Freundlich equations. Values of Langmuir P sorption maximum (X m) and b coefficient range from 47 to 1250µgg−1 soil and 0.5 to 30mLµg−1, respectively and the Freundlich k varies between 12 and 1694µgg−1 and B coefficient 0.09 and 0.67. Soils derived from basalt have larger values of P sorption maximum than soils on other parent materials. Both P sorption maximum and Freundlich k are closely related to pH (NaF), SSA, total titanium, aluminum and iron, dithionite and oxalate extractable Fe and Al, and other soil properties that reflect specific surface area. Soil pH in NaF is highly effective in predicting the P sorption capacity of Thai upland soils explaining 79% of the variation in P sorption by these soils. P desorption curves for adsorbed P are well described by the Freundlich equation. The Freundlich k d coefficient for P desorption is highly, linearly related to the Freundlich k coefficient of P sorption indicating that the above soil factors that contribute to P sorption similarly affect P desorption. [Copyright &y& Elsevier]

Dwindling carbon (C) and nitrogen (N) levels in paddy soils decreases rice production and threaten human food security globally. The efficient maintenance of C and N fluxes in soil-rice systems is a crucial prerequisite for agricultural and environmental sustainability. Herein, we examined the C and N fluxes from 63 rainfed rice paddy fields under conventional farming (CF) and organic farming (OF) systems in Thailand. The C and N fluxes were measured based on a detailed analysis of relevant influxes (fertilizer, manure, and biomass addition) and effluxes (biomass harvest and greenhouse gas emission). The results demonstrated that the harvested grain and straw contributed to the most abundant C and N effluxes for both farming systems. The CH4 effluxes were moderate, whereas the N2O effluxes were meager relative to their total effluxes. Stubble incorporation and animal manure addition to soil were the most extensive C influxes. However, the primary N influxes were stubble incorporation and animal manure addition for the OF system, and chemical-N fertilizers for the CF system. Net C depletions were observed in both the CF and OF systems. However, net N was depleted and accumulated in the CF and OF systems, respectively. Straw incorporation to soils could restore the net C accumulations for the CF and OF systems and elevate the net N accumulation for both systems. This study highlighted that complete straw removal has exacerbated the C and N stock in soil-rice systems, inducing insecurity for the environment and the agricultural systems. Effective straw management is a simple approach for sustaining paddy rice production. [ABSTRACT FROM AUTHOR]

Spent drilling mud (DM), a co-product during horizontal directional drilling operations, needs proper disposal to comply with social and environmental sustainability awareness, with one option being its cost-effective reuse as a soil amendment. The possibility was investigated of DM applications to improve the physical quality of loamy sand soil. The soil was treated with increasing DM contents in a laboratory at volumetric DM-to-soil ratios of 0:100 (DM0, no DM), 25:75 (DM25), 50:50 (DM50), 75:25 (DM75), and 100:0 (DM100, no soil). The mixtures were analyzed for water retention, available water capacity, water storage capacity, S-index, soil aggregate stability (SAS), and chemical quality based on pH, effective electrical conductivity (ECe), sodium adsorption ratio (SAR), and exchangeable sodium percentage (ESP). The optimal ratio of DM and the control (DM0) in the batch experiment were selected for application to three species of forest plant seedlings in the field. The results showed that DM positively influenced soil physical qualities. The water retention increased (from 10 to 67%) with increasing DM, but the most suitable ratio was DM25, considering its water storage capacity deviated the least (1.4%) from the optimal value. DM25 also produced the highest S-index (0.081). The SAR data increased with the drilling mud application rate (1.1 to 10.9). However, the DM25 pH remained at 7.7, with an ECe of 2.5 dS m−1, a SAR of 7.0, and an ESP of 9.2, which were still favorable regarding soil structure, as indicated by no decrease in SAS with added drilling mud. In the field experiment, DM25 also decreased the water deficit of the three species of forest plant seedlings, suggesting a positive attribution to other relevant soil-plant systems. DM could be a feasible option to improve soil physical quality, but further long-term experiments are necessary before applying it as a soil amendment in real situations. Implications: With the demand in energy-driven economics, establishing national energy security nationwide in Thailand requires the installation capacity, transmission, and distribution pipelines. Horizontal directional drilling (HDD) operations are generally used to install underground pipelines, generating large amounts of drilling mud rich in sodium bentonite as a co-product. At present, drilling mud is becoming a more serious solid waste and has been raised in proper management. The best management practices are expected to reuse as a soil amendment, a cost-effective approach, for coarse-textured soils. Before any drilling mud application can be introduced to agriculture and the environment, we must clarify the optimal rate of drilling mud. This rate has to significantly improve soil physical quality associated with air-water capacity balance while minimizing the adverse effect of residual sodium to favor soil structure and sensitive plants. [ABSTRACT FROM AUTHOR]

Physical quality and chemical fertility of lateritic soils under different types of land use were assessed and tested for their relationship. Six land-use types that have been continuously applied to similar lateritic soils (Plinthic Paleustults) were included in this study. These types of land use are (1) dry dipterocarp forest, (2) 6-year sugarcane, (3) and (4) 6-year rotating forage/sugarcane, (5) 6-year rubber plantation, and (6) 6-year mixed legume-maize cropping. The soil water retention curves and available water capacity were determined as well as S-index, a single indicator of soil physical quality, was estimated by using the parameters of the van Genuchten equation. Relevant fertility parameters were also analyzed to evaluate the fertility level. The results showed that all selected types of land use influenced the physical status and chemical fertility of lateritic soils. Dry dipterocarp forest and rubber plantation enhanced the S-index of 0.044 and 0.047, respectively, which were higher than those soils influenced by other agricultural practices (0.034–0.039). The good physical quality, as indicated by S-index, is significantly correlated (p < 0.05) with increasing available potassium and positively correlated with available phosphorus, base saturation percentage, and available water capacity. Our results imply that S-index is a useful indicator of soil physical quality associated with chemical fertility for Thai lateritic soils. [ABSTRACT FROM AUTHOR]

Reclamation of phosphorus (P) from wastewater using metal-engineered biochar and its reuses as phosphate fertilizers could be an eco-friendly and effective technology for the sustainability of environmental and agricultural systems. Herein, we studied the P removal capacity of filter cake-engineered biochar loaded with Al and Fe and examined their available P release capability into the sand sample. The Al-biochar (63.7 mg/g) had a higher P retention capacity than the Fe-biochar (33.2 mg/g). Over 45 days of the incubation, Al- and Fe-biochar incorporation steadily or increasingly released adequate concentrations of available P to the sand sample. Furthermore, a considerable P fraction (99.4-99.8% of the total P) remained in all metal-biochar samples, suggesting that the metal biochar could be a long-term source of the available P pool. This study highlighted the potential use of Al- and Fe-biochar for providing available P availability in sandy soils. [ABSTRACT FROM AUTHOR]

Silicon (Si) is an abundant element in terrestrial ecosystems and makes essential contributions to agricultural crops, environments, and industries; however, current knowledge of Si speciation in soil systems is based primarily on crystalline mineral types with limited information about the effect of Si-adsorbed species on the most chemically reactive clay fraction. Herein, we investigated Si speciation in the clay-sized fraction of tropical soils. Silicon K-edge X-ray absorption near edge structure (XANES) spectra of clay samples, together with a wide range of reference compounds varying in clay and Fe/Al oxide mineralogy, showed the predominance of Si in a beidellite structure and of Si adsorbed to montmorillonite and to kaolinite. Unique features, including a pre-white-line feature, white-line position and intensity, and post-edge numbers and positions of Si reference spectra, could differentiate most Si reference standard spectra. Silicon adsorbed to goethite, Si-ferrihydrite-natural organic matter complexes, and Si in the structure of biotite, illite-smectite, chlorite, quartz, and Si nanoparticle, variously occurred in different samples. The CaCl 2 extraction data revealed that extracted Si was below the limits of Si deficiency in one-half of the total soil samples and accounted for only 0.02% of total soil Si. Soil extractable Si had a positive correlation with pH, organic matter, and clay. Our results present a novel application of Si K-edge XANES as a tool for identifying Si speciation in natural clays that are the most chemically reactive phase of Si retention and release in terrestrial and aquatic systems. [Display omitted] • Reference spectra of silicon sorbed to clay mineral and Fe/Al oxides are presented. • Si-ferrihydrite-natural organic matter complexes have been synthesized and proposed. • White-line and post-edge features of Si reference spectra can identify most Si standards. • Structural Si in beidellite and Si sorbed to montmorillonite/kaolinite dominated Si species. • Si nanoparticles could form in clay-sized fractions of soil systems. [ABSTRACT FROM AUTHOR]

Improving soil aggregate stability (SAS) is important for crop production and environmental protection. Here we aim to quantify the effects of potassium (K) on SAS and to examine SAS as a function of potassium adsorption ratio (PAR) and cation ratio of soil structural stability (CROSS). The soils were treated with the incremental K and analyzed for their aggregate stability, clay dispersion, PAR, and CROSS. The influence of K on SAS, therefore, was tested statistically and fitted functionally. The results showed that K decreased clay dispersion and improved SAS. Also, SAS as a function of PAR fit an inverse exponential regression. Based on the coefficients of determination (R2) of the obtained functions, SAS can be explained by PAR with the accuracy above 94%. Increasing CROSS according to K also caused higher SAS, implying that K is considered as a flocculating inducer for kaolinitic tropical soils. [ABSTRACT FROM AUTHOR]

Ubiquitous microbial communities in river sediments actively govern organic matter decomposition, nutrient recycling, and remediation of toxic compounds. In this study, prokaryotic diversity in two major rivers in central Thailand, the Chao Phraya (CP) and the Tha Chin (TC) distributary was investigated. Significant differences in sediment physicochemical properties, particularly silt content, were noted between the two rivers. Tagged 16S rRNA sequencing on a 454 platform showed that the sediment microbiomes were dominated byGammaproteobacteriaand sulfur/sulfate reducingDeltaproteobacteria, represented by ordersDesulfobacterialesandDesulfluromonadalestogether with organic degradersBetaproteobacteria(ordersBurkholderialesandRhodocyclales) together with the co-existence ofBacteroidetespredominated bySphingobacteriales. Enrichment of specific bacterial orders was found in the clayey CP and silt-rich TC sediments, including various genera with known metabolic capability on decomposition of organic matter and xenobiotic compounds. The data represent one of the pioneered works revealing heterogeneity of bacteria in river sediments in the tropics. Analysis of bacterial diversity by tagged 16S rRNA sequencing revealed enrichment of specific taxa in CP and TC rivers. [ABSTRACT FROM PUBLISHER]

[Display omitted] • Mineral weathering inadequately provided Zn influxes for cassava production. • Soil properties and plant cultivars played a pivotal role in cassava Zn accumulation. • Replenishing available Zn pools in soils with fertilizers is seriously needed. • Integrated approaches should be undertaken to confront human Zn deficiency. Interminable plant production with negligent management might lead to zinc (Zn) depletion in soils, which could induce a Zn deficit in staple foods and cause human Zn malnutrition in many of the least-developed countries. Knowledge of the Zn pool and balance in soil-cassava systems is unclear and requires a detailed investigation. Herein, we examined Zn mass inputs (weathering and manure) and output (harvest crop) from 34 locations of cassava-grown soils in Thailand. The results revealed that the median available Zn concentration (0.47 mg kg−1) of the studied soils was below the critical Zn requirement for cassava production. The total Zn stock in the soils varied considerably from 9.0 to 633 kg Zn ha−1, only 1% of which was identified as the available pool, and the rest of the fraction was considered as the reserved pool. Strong linear relationships (R2 > 0.61–0.90) of total Zn concentration with clay, organic matter, and total Fe concentration suggested that phyllosilicate, organic matter, and Fe oxyhydroxides were the primary hosts for Zn in the soils. Belowground biomass (70% of the total biomass) was the most abundant biomass fraction, whereas 88% of the total Zn uptake accumulated in the aboveground biomass. The Zn output from the biomass harvest was 61–642 g Zn ha−1 yr−1, corresponding to only 0.10% of the total soil Zn stock. Most locations (91% of the studied sites) received Zn input solely from mineral weathering (0.014–0.975 g Zn ha−1 yr−1) without Zn fertilizer and manure additions, causing net Zn depletions (–642 to –61 g Zn ha−1 yr−1). A few locations had net Zn accumulations (+123 to + 1,971 g Zn ha−1 yr−1) caused by animal manure additions. Without the manure additions, the total Zn stock was estimated to decline by only 1% of the total current Zn stock within the next 10 years, whereas the manure additions would enhance the total Zn stock by 0.26–7.68%. This study highlighted that the Zn input from weathering is meager for cassava production. Combined Zn fertilizer and organic manure are urgently required to resupply and replenish readily available Zn pools and to promote the total Zn stock for sustaining long-term crop production. [ABSTRACT FROM AUTHOR]