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Modulation of rock phosphate fertilizer dose in soybean cultivation is crucial for maximizing plant growth and grain yield while ensuring efficient use of resources and environmental sustainability. This study evaluated rock phosphate (RP) dose to produce soybean on Leptic Andosol in Foumbot and Acrisol in Mbalmayo, respectively in the West and Centre regions of Cameroon. This split-plot experiment consisted of five fertilizer rates (control-no input and four Phosphorus (P) rates of 0, 30, 60 and 90 kg P/ha respectively) and two soybean varieties (TGX 1910-14 F and TGX 2001-24 DM) laid out in randomized complete block design with each treatment replicated three times. Plots containing the different P rates also had N (25 kg / ha) and K (40 kg / ha) straight fertilizers. Analysis of variance showed that fertilizer application significantly increased (P < 0.01) the number of pods and seeds, aboveground dry weight, and grain yield of the soybean varieties at both locations. There was an outright grain yield and economic benefit because of fertilizer application which increased with addition of phosphorus in the fertilizer mixtures. The grain yield response to phosphorus fertilizer was fitted to quadratic and square root models. The two models predicted maximum yields which were close to the experimental maximums recorded at P rates of 30 kg / ha (TGX 2001-24 DM: 5.04 and 4.89 t / ha) and 60 kg / ha (TGX 1910-14 F: 4.72 and 4.38 t / ha) at Foumbot and Mbalmayo respectively. The average optimum P fertilizer recommendations for soybean estimated by square root model (29.41 kg P/ha) was considerably lower than that given by the quadratic equation (45.61 kg P/ha) for both sites but only slightly lower the experimental dose of 30 kg P/ha. Taking into account the yield and cost benefit analysis of the soybean seeds, fertilization with 30 kg P/ha can be recommended. [ABSTRACT FROM AUTHOR]

The present study was conducted to investigate the vertical diversity of soil dehydrogenase and phosphatase activity under coconut (Cocosnucifera L.,) and arecanut (Arecacatechu L.,) plantations within four soil depths (0–30, 30–60, 60–90, and 90–120 cm) and to determine the factors controlling the distribution across the different agro-climatic zones of Karnataka. A total of 176 soil samples from 30 soil profiles were collected from coconut and arecanut plantations representing 5 different agroclimatic zones (ACZ) and three soil types (Lixisols, Сambisols, and Acrisols) and analyzed for three major soil enzymes viz. dehydrogenase (DHA), acid phosphatase (ACP) and alkaline phosphatase (ALP). The results revealed that the pooled mean of DHA activity was higher in arecanut (7.44 µg TPF g–1 h–1) than coconut (5.75 µg TPF g–1 h–1) and the same pattern has been noticed in both ACP (84.041 and 48.19 µg PnP g–1 h–1 for arecanut and coconut plantations) and ALP (63.57 and 32.14 µg PnP g–1 h–1 for arecanut and coconut plantations). The impact of climate on soil enzyme activity showed that the southern dry zone (SDZ) was high in DHA (10.5 µg TPF g–1 h–1) and ALP (77.98 µg PnP g–1 h–1) activities followed by the eastern dry zone and the lowest was noticed in the coastal zone (CZ). However, ACP activity was higher in CZ (110.24 µg PnP g–1 h–1) and lower in SDZ (33.85 µg PnP g–1 h–1). As soil depth increases enzyme activity is decreased and nearly 50% of enzyme activities are restricted within 0–30 cm soil depth. We observed that greater activity of DHA and ALP was noticed in Lixisols than in Acrisols and Cambisols, whereas higher activity of ACP was found in Acrisols. Our analysis showed that the type of plantations, climate and soil type significantly affect the distribution of enzymes in soil. [ABSTRACT FROM AUTHOR]

The transfer of atmospheric carbon (C) in soils is a possible strategy for climate change mitigation and for restoring land productivity. While some studies have compared the ability of existing crops to allocate C into the soil, the genetic variations between crop genotypes have received less attention. The objective of this study was to compare the allocation to the soil of atmospheric C by genetically diverse wheat genotypes under different scenarios of soil water availability. The experiments were set up under open-field and greenhouse conditions with 100 wheat genotypes sourced from the International Maize and Wheat Improvement Centre and grown at 25% (drought stressed) and 75% (non-stressed) field capacity, using an alpha lattice design with 10 incomplete blocks and 10 genotypes per block. The genotypes were analyzed for grain yield (GY), plant shoot and root biomass (SB and RB, respectively) and C content, and stocks in plant parts. Additionally, 13C pulse labeling was performed during the crop growth period of 10 selected genotypes for assessing soil C inputs. The average GY varied from 75 to 4696 g m−2 and total plant biomass (PB) from 1967 to 13,528 g m−2. The plant C stocks ranged from 592 to 1109 g C m−2 (i.e., an 87% difference) under drought condition and between 1324 and 2881 g C m−2 (i.e., 117%) under well-watered conditions. Atmospheric C transfer to the soil only occurred under well-drained conditions and increased with the increase in the root to shoot ratio for C stocks (r = 0.71). Interestingly, the highest transfer to the soil was found for LM-26 and LM-47 (13C/12C of 7.6 and 6.5 per mille, respectively) as compared to LM-70 and BW-162 (0.75; 0.85). More is to be done to estimate the differences in C fluxes to the soil over entire growing seasons and to assess the long-term stabilization of the newly allocated C. Future research studies also need to identify genomic regions associated with GY and soil C transfer to enable the breeding of “carbon-superior” cultivars.

The study estimates the soil organic carbon stock under various cropping systems to assess their sequestration potential in a tropical monsoon region, namely the Chulliyar-Ikshumathi sub-watershed of Bharathapuzha in Kerala, India. The cropping systems selected are the paddy, vegetables, coconut-arecanut groves, homestead farms, and mango plantations. The standard soil analyzing procedures to collect and analyze 129 soil samples from 43 locations were followed. The carbon stock (CS) of 0–10, 10–20, and 20–30 cm depth layers at each sampling location was estimated following the Walkley-Black method. The sequestration potential of soil under each cropping system is estimated to suggest an optimal cropping system for the region. The CS decreased with depth, irrespective of cropping systems. Among the cropping systems, the mango plantations, which practiced zero/no-tillage, have stability in the distribution of CS, while paddy fields showed higher variability in the CS. Even though mango plantations have more carbon sequestration potential (CSP), the coconut-arecanut grove is a better candidate for carbon sequestration (CSeq) in this region owing to its wider areal extent and acceptability. This analysis reveals the importance of assessing CS at the watershed level for sustainable land use planning to achieve better sequestration of atmospheric carbon. [ABSTRACT FROM AUTHOR]

Understanding the factors controlling soil total N (TN) is helpful in simulating N cycling at local and regional scales. This study was conducted with the aim to; (i) understand the distribution of TN in specific soil horizons (A and B horizons) of three reference soil groups: Acrisols, Cambisols and Ferralsols, common in humid tropical environments, and (ii) to identify factors controlling TN variations among the various soil groups. Twenty-eight Acrisols, 21 Cambisols and 8 Ferralsols profiles spanning a wide range of precipitation gradients, vegetation type/land use and parent materials, from the Northwestern Highlands (NWH) of Cameroon were considered. Soil properties were analyzed following standard procedures. TN had very high coefficients of variation (>35%) in all the reference soil groups (RSGs), with highest mean TN (0.31 ± 0.03%) observed in the A horizons of Acrisols and the lowest (0.05 ± 0.01%) in B horizons of Ferralsols. Variations in TN content were significantly (p < 0.05) influenced by parent material, land use type, precipitation and slope gradient. In surface (A) horizons of all the RSGs, TN correlated positively and significantly with clay (p < 0.05), silt (p < 0.01) and soil organic carbon (SOC) (p < 0.01), and negatively with sand (p < 0.01). This observation was slightly different in subsurface (B) horizons. This study provides data which contributes to a better understanding of soil fertility in tropical highlands. [ABSTRACT FROM AUTHOR]

The transfer of atmospheric carbon (C) in soils is a possible strategy for climate change mitigation and for restoring land productivity. While some studies have compared the ability of existing crops to allocate C into the soil, the genetic variations between crop genotypes have received less attention. The objective of this study was to compare the allocation to the soil of atmospheric C by genetically diverse wheat genotypes under different scenarios of soil water availability. The experiments were set up under open-field and greenhouse conditions with 100 wheat genotypes sourced from the International Maize and Wheat Improvement Centre and grown at 25% (drought stressed) and 75% (non-stressed) field capacity, using an alpha lattice design with 10 incomplete blocks and 10 genotypes per block. The genotypes were analyzed for grain yield (GY), plant shoot and root biomass (SB and RB, respectively) and C content, and stocks in plant parts. Additionally, 13C pulse labeling was performed during the crop growth period of 10 selected genotypes for assessing soil C inputs. The average GY varied from 75 to 4696 g m−2 and total plant biomass (PB) from 1967 to 13,528 g m−2. The plant C stocks ranged from 592 to 1109 g C m−2 (i.e., an 87% difference) under drought condition and between 1324 and 2881 g C m−2 (i.e., 117%) under well-watered conditions. Atmospheric C transfer to the soil only occurred under well-drained conditions and increased with the increase in the root to shoot ratio for C stocks (r = 0.71). Interestingly, the highest transfer to the soil was found for LM-26 and LM-47 (13C/12C of 7.6 and 6.5 per mille, respectively) as compared to LM-70 and BW-162 (0.75; 0.85). More is to be done to estimate the differences in C fluxes to the soil over entire growing seasons and to assess the long-term stabilization of the newly allocated C. Future research studies also need to identify genomic regions associated with GY and soil C transfer to enable the breeding of "carbon-superior" cultivars. [ABSTRACT FROM AUTHOR]

Increasing interest in farmers' local soil knowledge (LSK) and soil management practice as a way to promote sustainable agriculture and soil conservation needs a reliable means to connect to it. This study sought to examine if Visual Soil Assessment (VSA) and farmer workshops were suitable means to engage, communicate and preserve farmers' LSK in two mountainous communes of Central Vietnam. Twenty-four farmers with reasonable or comprehensive LSK from previously studied communes were selected for the efficacy of VSA and farmer workshops for integrating LSK into a well-accepted soil assessment tool (VSA). In field sites chosen by the farmers, VSA was independently executed by both farmers and scientists at the same time. Close congruence of VSA scores between the two groups highlighted that farmers could competently undertake VSA. Farmers' VSA score was compared with their perception of field's soil quality. For the majority of farmers' perception of soil quality was consistent to their VSA score (62.5%), while the remainder perceived their soil quality was lower than their VSA score. For most farmers their assessment of soil quality using VSA valued their LSK, and the two measures were well aligned. Soil colour and presence or vulnerability to erosion were common soil characteristics mentioned by farmers and affected the final VSA score. Farmers' participation in VSA and workshops strengthen farmers' confidence in their LSK and provided guidance on the impact of their soil management on soil improvement and conservation. [ABSTRACT FROM AUTHOR]

ABSTRACT High acidity and low soil P availability in the soils from the Pampa natural grasslands generally limit the forage growth and economic return. Thus, to increase the economic return and avoid environmental degradation and biodiversity loss due to replacement by intensive cropping systems, it is essential to improve the soil P availability. This study aimed to diagnose the nutritional status of the pluri-specific natural grasslands amended with different history of P sources. Additionally, we also try to indicate the most appropriate range of soil P availability for maximizing forage growth. The experiment started in 1997 in an area of Pampa natural grasslands in the state of Rio Grande do Sul, Brazil. The treatments evaluated the application of Gafsa hyperphosphate (HP) and triple superphosphate (SP) for four years (1997, 1998, 2002, and 2010). Soil and aboveground biomass sampling were performed five times from October 2010 to March 2011 to access aboveground biomass production, botanical composition, soil available P, and N and P nutrition index. Greater P availability in the soil amended with SP produced more forage and resulted in a higher P accumulation than in the soil amended with HP. The ideal range of soil P availability in the soils of natural grasslands ranged from 14 to 20 mg kg˗1, varying for different plant species. The species Paspalum plicatulum and Aristida laevis produce less aboveground biomass and accumulate less P in their tissue than Dichantelium sabulorum and Eustachys uliginosa, and P. notatum. Therefore, areas of natural grasslands dominated by D. sabulorum, E. uliginosa and P. notatum demand higher soil P availability to maintain high forage production. Soil P fertilization of pluri-specific natural grasslands in the Brazilian Pampa biome must consider the dominant forage species in the area and the soil P availability.

The study has investigated the individual and combined effects of nitrogen and potassium on the growth, grain yield, and quality of quinoa in ferralsols and acrisols. The experiments were conducted during the dry season under rainfed conditions in Central Highland, Vietnam. The factorial design was a randomized complete block design with three replications. The results revealed the positive impacts of nitrogen and potassium on the growth and yield of quinoa. However, after the application of an optimum dose of nitrogen, growth, and yield were not significantly changed and even decreased when the dose continued increasing. Higher levels of nitrogen and potassium application resulted in greater protein and fat content, but lower starch and fiber contents, compared to lower levels. The fertilizer practice has to rely on soil fertility. The study shows that the application of 150 kg N and 105 kg K2O ha-1 could be the optimum rate of nitrogen and potassium for quinoa production in ferralsols and acrisols in Central Highland. [ABSTRACT FROM AUTHOR]

Soil in the tropics is high in diversity, and despite the diversity of Borneo's forest-soil associations, there is a paucity of data on its soil properties. We investigated the differences between three soil types in the Kabili-Sepilok Forest Reserve, Sabah, Malaysia, encompassing the contrasting alluvial, sandstone and heath forest typologies. We examined the distribution of nutrients between soil types and through soil depths, and assessed the extent of spatial autocorrelation in the three soil types. We confirmed the fertility gradient from alluvial to heath forest soil found by others. Soil elemental concentrations declined in deeper horizons with the exception of exchangeable sodium and aluminium that remained constant through alluvial and sandstone soil profiles. Spatial autocorrelation was present in all three soil types and strongest in the sandstone soil. Overall, we show how bedrock, erosion, leaching and topography influence soil properties across this mosaic of soil types and note their importance in influencing tree communities and their ecological functioning. [ABSTRACT FROM AUTHOR]

The main aim was to conduct a pilot study of diagnostic characteristics of soils on the territory of the Strandzha mountain and their classification according to WRB requirements (2006, 2007), including microbiological activity in stands with different tree composition. A total of seven soil profiles were studied. Soil and litter samples were collected from territories where it was previously known that the soils were with a clay - enriched subsoil (defined as Luvisols, Alisols and Zheltozem-podzolic soils). Soil classification indicators have been investigated according to the requirements of World Reference Base for soil resources. Five of the soil profiles were classified as Lixisols and two as Acrisols. On the second taxonomy level for Lixisols applied prefix qualifier - haplic and suffix qualifier - hypereutric. For Acrisols applied prefix qualifier haplic. Lixisols and Acrisols were established on the territory of Strandzha Mountain for the first time in oak and beech stands. Analysis of the heterotrophic microflora's total number and the structure of the microbial communities of two soil profiles was carried out. The different tree species and the period of litterfall affect the number of microbocenosis and the distribution of microbial groups in it. In the beech stand (Fagus orientalis Lipsky), the processes of enhanced transformation of easily degradable soil organic matter (SOM) predominated, compared to oak stand (Quercus frainetto Ten. and Quercus petraea Liebl,) where more advanced processes of transformation of SOM were observed. [ABSTRACT FROM AUTHOR]

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Depletion of nitrogen and phosphorus in terraced hilly areas of Rwanda has lowered maize (Zea mays L.) production. Trials were carried out in 2017 and 2018 in four-year-old-terraced Lixisols and Acrisols of medium and high altitudes to determine effect of nitrogen and phosphorus fertilizer application rates on maize yields. A factorial arrangement of four levels of nitrogen (0, 60, 120 and 180 kg N ha-1) and phosphorus (0, 40, 80 and 120 kg P2O5 ha-1) in a randomized complete block design with 3 replications, was used. Results showed that combinations of 120 - 180 kg N ha-1 and 80 - 120 kg P2O5 ha-1 resulted in significantly (P < 0.05) higher increases in plant height (45 - 60% and 56 - 70% over the control), stem collar diameter (63 - 74% and 43% over the control) and grain yields (3 times over the control; i.e. 6.40 - 6.46 t ha-1 and 6.02 - 6.12 t ha-1) in medium and high altitude sites. The optimum fertilizer rates are 176.6 kg N ha-1 and 96.2 kg P2O5 ha-1 in terraced Lixisols of medium altitude area. Land use needs to adjust fertilizer application to these optimum rates for enhanced maize yields in this area and other regions with similar agro-ecological characteristics. Further studies on integrated effects of N and P fertilizers are recommended. [ABSTRACT FROM AUTHOR]

Among the greatest challenges of Sub-Saharan Africa is the need for more crop production for supplying the increasing demand of its growing population. For this purpose, knowledge on soil resources and their agricultural potentials is important for defining proper and appropriate land use and management. We thus investigated on the status of soil fertility in Tombel area, in order to produce such knowledge through understanding and monitoring the impact of physicochemical properties of soil. Diverse analyses performed on various datasets demonstrated the direct impact of physicochemical properties of soil and derived soil fertility parameters on major constraints for plant growth and optimal crop production such as water retention capacity, roots development, soils aeration, nutrients availability, nutrients abundance and cations balance. Based on physicochemical soil properties, fertility parameters and Soil Quality Index (SQI), four soil fertility classes were identified in the area: (i) very good fertility soils (66 km2) that corresponds to Dystric Vitric Andosols (Melanic) above 500m asl; (ii) good fertility soils (506 km2), grouping Dystric Vitric Andosols (Melanic) below 500m asl and Leptic Fragic Umbrisols; (iii) fairly good fertile soils (787 km2) including Dystric Fragic Cambisols (Humic), Rhodic Acrisols (Cutanic Humic), Fragic Umbrisols (Arenic), and Mollic Ferralsols (Eutric Humic); (iv) poorly fertile soils (375 km2) including Umbric Andosols (Fragic) and Umbric Pisoplinthic Plinthosols (Haplic Dystric). The principal indicators controlling soil quality in the Tombel area as derived from ANOVA and PCA analyses, are: Ca, Mg, pH water, organic matter (OM), available P, total Nitrogen and CEC. Four of the seven indicators (Ca, pH, OM, P) were also identified as important indicators for assessing the fertility status of the different soils groups in the Tombel area.

The aim of the study was to analyze the diagnostic properties of soils on territory of Training and Experimental Forest Range (TEFR) "Petrohan" in order to classify them according to the modern requirements of World Reference Base for soil resources. Seven soil profiles were studied. Soil samples were collected from territories in which it was known that the soils are with a clay - enriched subsoil (Luvisols). Soil classification indicators have been investigated according to the requirements of World Reference Base for soil resources. Five soil profiles were classified as Acrisols and two as Lixisols. On the second taxonomy level for Acrisols apply Vetic prefix qualifier. Lixisols were identified as Vetic and Haplic. Acrisols and Lixisols were established on the territory of the TEFR „Petrohan" in beech forests of the temperate climate zone. We assume that specific weathering processes and acidifying effect of beech forests have been playing a key role for Acrisols and Lixisols formation. [ABSTRACT FROM AUTHOR]

This paper examined the contribution of various soil components to pH buffering capacity (pHBC) of haplic Acrisols in an upland area of Southeastern Vietnam. Sampling was conducted in 2016 in Tan Bien district, Tay Ninh province at seven sites from the surface to 60-cm depth. Soils were very acidic (pHH2O 4.53 ± 0.05). The pHBC were very low, 0.46 ± 0.04 and 0.44 ± 0.05 cmol H+ kg−1 pH−1, respectively, for original samples and those from which soil organic carbon (SOC, 0.52 ± 0.09%) were removed. The contribution of Al3+ to pHBC was remarkable while that of SOC was of little significance. The contribution of clay minerals to pHBC was unclear due to the low (9.37 ± 0.76%) and kaolinite-dominated clay content. The current soil conditions indicated a potential for further soil acidification. Liming would be one of the measures to remediate soil acidity in the research area. [ABSTRACT FROM AUTHOR]

Soil specific maize response to N and P may provide guidelines for improving nutrient management. Three replicates of N and P fertilizer combinations (N0P0, N0P90, N120P0, and N120P90) were arranged in randomized complete block design on Plinthic Acrisol (PA) and Gleyic Plinthic Acrisol (GPA) in Ghana. Treatment effects on maize plant height and yield parameters were assessed. Plant height differed consistently with N120P90 > N0P90 > N120P0/N0P0 from 3 to 7 weeks after planting on the GPA. On the GPA, grain yield ranged from 1.20 to 2.40 t ha−1 and increased by 10, 77 and 95% in the N120P0, N0P90 and N120P90, respectively. Residual effect of N0P90 and N120P90 increased maize yields on the GPA than on the PA. Rather than N, P was more critical to maize performance and should be externally supplied not exceeding the critical level of N0P60 (Plinthic Acrisol) and N0P90 (Gleyic Plinthic Acrisol) for optimum maize yield. [ABSTRACT FROM AUTHOR]

Abstract Pedogenic iron rich soils are prevalent worldwide covering approximately 1000 million hectares. These soils are fragile and prone to severe degradation, in many cases resulting in high erosion rates and formation of gullies. Restoration and revegetation practices face many barriers in degraded Acrisols, including low nutrient availability exacerbated by high iron concentrations. The objective of this work was to evaluate the performance of two tree species, Pinus pseudotrobus , and Fraxinus uhdei , growing in Acrisol soils in the presence of endo, ecto or both types of mycorrhizic fungi, in order to assess the effect of the interaction for management of degraded lands. The largest Fraxinus plants, those inoculated with both types of mycorrhizic fungi, accumulated three times more biomass than the smallest, and for Pinus the largest plants, those growing in soil with both types of fungi, had 1.5 times more biomass. Iron content in tissues of the Fraxinua uhdei plants was within that reported for plants in general (0.014%), and for Pinus pseudostrobus our values were higher for all treatments but within the same order of magnitude. For ecological restoration and other management purposes these results strongly suggest that dual inoculation or planting species that allow for both types of mycorrhizic fungi to be present in the soil can improve tree species performance and therefore facilitate the recovery process of heavily degraded sites. Highlights • Fraxinus in Acrisols inoculated with endo- and ectomycorrhiza, had the best growth. • Pinus growing in soil with both types of mycorrhizic fungi, grew the tallest. • Acrisol revegetation benefits from the presence of both endo- and ectomycorrhiza. [ABSTRACT FROM AUTHOR]

This study examined the pH buffering capacity (pHBC) of haplic Acrisols under intensive cassava production in an upland area of Southeastern Vietnam where accelerated soil acidification has occurred. Soil samples (0–20, 20–40 and 40–60 cm) were taken at 12 sites under cassava and three sites under secondary dipterocarp forest as reference. The pH buffer curves were linear in the pHH2O range from 3.97 to 5.24, corresponding to a pHCaCl2 range from 3.74 to 5.20. Soil pHBC were low (1.16 ± 0.13 cmol/kg/pH) and correlated significantly with pH, Aluminium (Al) and Al‐related components. The results suggested that exchange acidity contributes significantly to soil's buffering capacity in acidic soils with low organic carbon. It also pointed to the possibility of using indicators of acidity to estimate soil pHBC. The low pHBC indicated a high risk for further acidification and also pointed to the possibility of using lime to remediate soils. Either acid buffering capacity or lime buffering capacity not pHBC in general should be considered, respectively, in acidification and liming studies. Factors and processes involved in soil acidification and liming need to be addressed as a background for soil remediation in the study area. [ABSTRACT FROM AUTHOR]

Biochar is a carbon-rich porous material intensively studied for its agronomic benefits, such as decrease of greenhouse gases emission and nutrient losses via leaching, increased crop production and improved soil physical and chemical properties. We investigated the effect of holm oak biochar produced at 600 °C on mineral nitrogen (N) leaching from two contrasting soils (Acrisol and Calcisol). Biochar was applied at three rates (0%, 1% and 2% w/w) with (B0-F, B1-F and B2-F, respectively) and without (B0, B1 and B2, respectively) ammonium-based fertilizer. Soil columns were leached with deionized water and mineral N in leachate was monitored during ten weeks after each fertilization. Sorption behavior of biochar-amended soils was assessed in batch experiments before and after leaching. Biochar increased ammonium (NH 4 + -N) sorption in sandy Acrisol but had no effect on nitrate (NO 3 − -N) sorption. Furthermore, sorption properties of soil decreased by up to 25% during the study. In Acrisol, biochar affected NH 4 + -N leaching, which was increased by both doses of biochar without fertilization, but decreased by the lower biochar application rate when fertilizer was added. The leaching of NO 3 − -N was not affected by biochar in Acrisol. The ability of Calcisol to adsorb NH 4 + -N was high and was not further increased by biochar, which corresponds to no NH 4 + -N leaching from Calcisol regardless the biochar application rate. Moreover, biochar had no effect on NO 3 − -N leaching from Calcisol. Our results demonstrate that biochar effect on leaching of inorganic N forms is inconsistent, evolves in time and is highly dependent on soil properties. Alleviation of soil acidity by biochar application to Acrisol resulted in short-term stimulation organic N mineralization, which resulted in enhanced amount of NH 4 + -N being leached. Furthermore, the fact that biochar lost its effect on N leaching already after the second fertilizer application could cast a doubt on the efficiency of biochar application to soil in order to increase N retention and decrease N leaching. [ABSTRACT FROM AUTHOR]

The present study aims to determine fertilizer (N-P-K) recommendations for maize (Zea mays L.) on Acrisols (south Benin) and Ferric and Plintic Luvisols (centre Benin). Two years (2011 and 2012) experiment was conducted at Dogbo and Allada districts (southern) and Dassa (centre Benin). Six on-farm experiments were carried out to validate fertilizer rates simulated by the DSSAT model. The experimental design in each field was a completely randomized bloc with four replications and ten N-P-K rates: 0-0-0 (control), 44-15-17.5 (standard fertilizer recommendation for maize), 80-30-40, 80-15-40, 80-30-25, 80-30-0, 69-30-40, 92-30-40, 69-15-25 and 46-15-25 kg ha−1. Treatments 44-15-17.5 and 46-15-25 showed the lowest grain and stover yields. The observed maize grain yields were highly correlated with the estimated grain yields (R2 values varied between 80 and 91% for growing season 2011 and between 68 and 94% for growing season of 2012). The NRSME values varied between 12.54 and 22.56% (for growing season of 2011) and between 13.09 and 24.13% (for growing season of 2012). The economic analysis for the past 32 years (1980-2012) including the current experiment showed that N-P-K rates 80-30-25 (at Dogbo), 80-15-40 (at Allada) and 80-30-0 (at Dassa) were the best fertilizer recommendations as they presented the highest grain yields and the best return to investment per hectare. Nevertheless, 80-30-25 is advised for Dassa considering that sustainable maize production will require regular inputs of potassium. The 2 years of field experiments were not sufficient to derive biophysically optimal fertilizer recommendation rates for each site. [ABSTRACT FROM AUTHOR]

To quantify the relationship between the soil organic matter and color parameters using the CIE-Lab system, 62 soil samples (0-10 cm, Ferralic Acrisols) from tea plantations were collected from southern China. After air-drying and sieving, numerical color information and reflectance spectra of soil samples were measured under laboratory conditions using an UltraScan VIS (HunterLab) spectrophotometer equipped with CIE-Lab color models. We found that soil total organic carbon (TOC) and nitrogen (TN) contents were negatively correlated with the L* value (lightness) (r = -0.84 and -0.80, respectively), a* value (correlation coefficient r=- 0.51 and -0.46, respectively) and b* value (r = -0.76 and -0.70, respectively). There were also linear regressions between TOC and TN contents with the L* value and b* value. Results showed that color parameters from a spectrophotometer equipped with CIE-Lab color models can predict TOC contents well for soils in tea plantations. The linear regression model between color values and soil organic carbon contents showed it can be used as a rapid, cost-effective method to evaluate content of soil organic matter in Chinese tea plantations. [ABSTRACT FROM AUTHOR]

Soil compaction is a problem recently identified as one of the main constraints on the maize surface of the municipality of Villaflores in the region of The Frailesca, Chiapas, due to this, it needs to be studied with greater precision. The objective of this study was to characterize the problem of compaction on the mechanized surface cultivated with corn in the New Mexico commn. We studied 177 plots, in which the apparent density, organic matter and texture were determined at the depths of 0-20 and 20-40 cm. The owners of the properties were interviewed to obtain information about their cultivation practices and corn productivity levels. The results show that 83.3% of the studied area presented superficial compaction and 94.6% compaction in the subsoil (plow floor). The producers pointed out that in years with critical periods of drought the yields are reduced by 58%, which is correlated with the decrease of the porosity as a result of the compaction. The main causes of the compaction were the intensive tillage with machinery 100% of the sites, the very low content of 100% organic matter and the type of soil (luvisols and acrisols). The attention of the compaction problem requires a comprehensive corrective and preventive strategy that should take as a central element the elevation of the contents of organic matter, to reverse the current unsustainable management of the land. [ABSTRACT FROM AUTHOR]

Visible and near-infrared (Vis-NIR) diffuse reflectance spectroscopy with partial least squares (PLS) regression is a quick, cost-effective, and promising technology for predicting soil properties. The advantage of PLS regression is that all available wavebands can be incorporated in the model, while earlier studies indicate that PLS models include redundant wavelengths, and selecting specific wavebands can refine PLS analyses. This study evaluated the performance of PLS regression with waveband selection using Vis-NIR reflectance spectra to estimate the total carbon (TC) and total nitrogen (TN) in soils collected mainly from the surface of upland and lowland rice fields in Madagascar (n = 59; after outliers were removed). We used iterative stepwise elimination-based PLS (ISE-PLS) to estimate soil TC and TN and compared the predictive ability with standard full-spectrum PLS (FS-PLS). The predictive abilities were assessed using the coefficient of determination (R2), the root mean squared error of cross-validation (RMSECV), and the residual predictive deviation (RPD). Overall, ISE-PLS using first derivative reflectance (FDR) showed a better predictive accuracy than ISE-PLS for both TC (R2 = 0.972, RMSECV = 0.194, RPD = 5.995) and TN (R2 = 0.949, RMSECV = 0.019, RPD = 4.416) in the soil of Madagascar. The important wavebands for estimating TC (12.59% of all wavebands) and TN (3.55% of all wavebands) were selected from all 2001 wavebands over the 400–2400 nm range using ISE-PLS. These findings suggest that ISE-PLS based on Vis-NIR diffuse reflectance spectra can be used to estimate soil TC and TN contents in Madagascar with an improved predictive accuracy. [ABSTRACT FROM AUTHOR]

The Armed Forces Medical Examiner System – Armed Forces DNA Identification Laboratory (AFMES-AFDIL) and the Defense POW/MIA Accounting Agency (DPAA) are partners in the identification of missing United States service members. Skeletal materials are recovered world-wide from past military conflicts; however, this project examines the relative success of skeletal materials recovered from Southeast Asia. The soils in Southeast Asia are known to be largely acidic, with the majority being classified as acrisol or gleysol (pH4.4–7.2). Acidic soils are thought to compromise the structural integrity of buried skeletal materials leading to a degradation of the DNA found within. This study evaluates whether this idea is apocryphal or if acidic soils truly have an impact. [ABSTRACT FROM AUTHOR]

Combined Effect of Thitonia diversifolia Leaves and Inorganic Fertlizers on Maize Grain Yield and Soil Properties of a Central Cameroon Acrisol. Properties of a Central Cameroon Acrisol A study was conducted on an Acrisol in Centre Cameroon in order to evaluate the combined effects of Tithonia diversifolia (FTd) and inorganic fertilizers (NPK and Urea) on maize grain yields and soil properties. The experimental design was a randomized completed block design with three replications and six treatments: T0 (0FTd, 0NPK and 0 Urea); T1 (0FTd, 150 kg 20-10-10 and 150 kg of Urea/ha); T2 (0FTd, 75 kg 20-10-10 and 75 kg of Urea/ha); T3 (2.5 t/ha FTd, 0NPK and 0 Urea); T4 (5 t/ha FTd, 0NPK and 0 Urea); T5 (2.5 t/ha FTd, 75 kg 20-10-10 and 75 kg of Urea). Soil and Tithonia samples were collected and analyzed for nutrients contents. Tithonia leaves (FTd) were incorporated into the soil two weeks before maize sowing. Physico-chemical laboratory analyses were carried out on soil samples and Tithonia leaves. Highly significant differences (p= 0.006 and p< 0.000 respectively) were observed between treatments in the first and second cropping season for maize grain yields which varied between 1.8 to 6.4 t.ha-1; with the highest values obtained in T4 and T5 and the lowest in T0. The general trend of productivity was ranked as: T5=T4 >T1>T3>T2>T0. No significant difference was observed for all the soil properties tested. However, in the general trend, most soil properties tended to increase at the end of the experiment, excepted sand content, pH and available phosphorus. With the acceptability index (IA) of more than 2 in T4 (2.65) and T5 (2.53), the study has shown that Tithonia diversifolia has a potential for improving plant nutrient availability in these soils for the cultivation of maize without chemical fertilizers.

Despite the common use ofAcaciaspecies in Vietnam, few studies have examined changes to total soil nitrogen (TN) and total soil carbon (TC) following the planting ofAcacia mangium×Acacia auriculiformis(Acaciahybrid) plantations (AH) on formerly eroded and degraded soils. We compared the impact of AH with adjacent fallow land within a shifting cultivation system (FSC) on various soil properties, including TC, TN, pH, bulk densities and particle-size distribution in 10 cm increments down to 30 cm for 25 paired sites in northern Vietnam. The results show that TN and TC concentrations in AH were significantly higher at all 10 cm depth increments when compared with FSC. Although both TC and TN decreased significantly with depth under both land uses, the C:N ratio only decreased in AH and not the FSC. However, there was a significant decrease in soil pH in AH at all depths (pH > 0.4) and this may potentially cause acid infertility issues. While the study has shown that plantingAcaciahybrid is an excellent option for the improvement of TN and TC on degraded acidic Acrisols, mitigation of the associated acidification may be required. [ABSTRACT FROM AUTHOR]

Allanblackia stuhlmannii is a tree species currently under domestication. Potential mycorrhizal relationships of A. stuhlmannii and soil properties of native stands were investigated to determine the soil-environmental requirements of the species. Roots and soil samples were collected from five sites with A. stuhlmannii stands along an altitudinal transect in Amani Nature Reserve, Tanzania. Mycorrhizal status was investigated by combining microscopy with molecular analysis of the fungal communities. Soil adjacent to the A. stuhlmannii seedlings was analysed for physical and chemical properties and the sites were characterised. We showed that A. stuhlmannii form symbiosis with arbuscular mycorrhizal fungi, and that there was a diverse microbiome associated with the roots. The soils, classified as Ferralsol and Acrisol, were very well drained, had a pHCaCl2 generally at or below 4, high exchangeable acidity and content of sesquioxides and low effective cation exchange capacity and concentrations of most nutrients. We conclude that A. stuhlmannii is tolerant to high Al availability and possesses mechanisms for acquisition of P and other macronutrients at low soil availability, possibly through mycorrhizal symbiosis. However, being adapted to low- pH soils, it may be less efficient in acquiring Fe, Mn and/or Zn at higher soil pH. Thus, it may be most suited to introduction on farms situated on acid soils. [ABSTRACT FROM AUTHOR]

Background and aims: The southeastern part of the Amazon region is one of the largest agricultural frontiers in the world, leading to extensive land-use change. This paper provides evidence for the impacts of land-use change on soil organic carbon (OC) stocks along a large scale for Ferralsols and Acrisols including subsoil. Methods: We took soil samples to 100 cm depth for native vegetation, pasture and crop-field along a 1000 km agricultural transect in central Brazil to determine OC stocks and, by using a stable isotope approach, losses of forest-derived OC. Results: At the scale of individual plots, soil OC stocks indicate a highly heterogeneous response to land-use change (e.g. in Ferralsols in 0-30 cm from −45 % to +57 % Mg OC ha after conversion to pasture), but relatively minor responses when considering the complete transect (i.e. no significant OC changes for similar land-use type). Acrisols evidenced a slower decline of forest-derived OC and simultaneously a faster accumulation of pasture-derived OC than Ferralsols. Surprisingly, the impact of land-use change was more pronounced in the subsoil. Conclusion: Our results emphasize the role of subsoils on carbon cycling which has been previously underestimated, but may also raise doubts whether OC stocks in soil is an appropriate parameter to assess the impacts of land-use conversion on climate change. [ABSTRACT FROM AUTHOR]

It is found that the overwhelming majority of mobile forms of the chemical elements (up to 99%) that are thought to produce favorable effects when they arrive with volcanic ash to soils and supply additional elements that enhance the bioproductivity of ecosystems do not come in the form of ash particles, but in a gas-dissolved form directly from volcanic aerosol. Volcanic ash when considered independently of volcanic eruptions does not contain considerable amounts of accessible forms of chemical elements that would enable us to consider them as sources of nutrient elements for living organisms. However, the extensive range of elements that are contained in ash in ratios that are necessary for effective life activities invests these elements with catalytic properties that regulate the nutrient regime of plants and that can be used in agriculture in combination with lower amounts of traditional fertilizers to produce substantial (up to 72%) yield increases and to improve the quality of agricultural products. [ABSTRACT FROM AUTHOR]

Burkholderia pseudomallei is the bacterium that causes melioidosis in humans. While B. pseudomallei is known to be endemic in South East Asia (SEA), the occurrence of the disease in other parts of the tropics points towards a potentially large global distribution. We investigated the environmental factors that influence the presence (and absence) of B. pseudomallei in a tropical watershed in SEA. Our main objective was to determine whether there is a link between the presence of the organism in the hydrographic network and the upstream soil and land-use type. The presence of B. pseudomallei was determined using a specific quantitative real-time PCR assay following enrichment culture. Land use, soil, geomorphology, and environmental data were then analyzed using partial least squares discriminant analysis (PLSDA) to compare the B. pseudomallei positive and negative sites. Soil type in the surrounding catchment and turbidity had a strong positive influence on the presence (acrisols and luvisols) or absence (ferralsols) of B. pseudomallei. Given the strong apparent links between soil characteristics, water turbidity, and the presence/absence of B. pseudomallei, actions to raise public awareness about factors increasing the risk of exposure should be undertaken in order to reduce the incidence of melioidosis in regions of endemicity. [ABSTRACT FROM AUTHOR]

Low soil phosphorus (P) is a limiting factor for plant growth in the Brazilian savannah, where P diffuses slowly and has a high fixation rate in soil (as Al-P and Fe-P). In this study, we investigated the variation in P uptake by different cotton cultivars grown in savannah soil. We conducted a greenhouse experiment using a fully factorial 2 x 17 randomized design with two P treatments (low P = 20 mg kg-1 and high P = 120 mg kg-1) and 17 cotton cultivars. The plants were potted in Acrisol soil labeled with radioisotope 32P. There was genetic variation in the P use efficiency among the cotton cultivars. The P treatments significantly influenced the dry weight of shoots (DWS), P accumulation, the specific activity of 32P, and the L-value (both the standardized and L-values discounted the P present in the cottonseed). Hierarchical clustering analysis classified the cotton cultivars into distinct, internally homogeneous clusters. Our results suggest that cotton cultivars could be selected to maximize P absorption efficiency in conditions of low plant-available P. The cultivars FMT 523, FM 910 and CNPA GO 2043 were the most responsive to P fertilization, while Barbadense 01, FM 966LL, IPR Jataí, BRS Aroeira and BRS Buriti were most efficient at absorbing plant-available P. [ABSTRACT FROM AUTHOR]

Erosion is a major cause of soil degradation. Understanding the sources of sediment and the processes that exacerbate this problem is crucial for soil conservation. Remote and proximal sensing technologies have contributed to advance our understanding of soil erosion processes and support soil conservation research. The objective of this study is to use two proximal sensors, a portable X-ray fluorescence spectrometer (pXRF) and a magnetic susceptibilimeter, to identify the origin of sediments deposited in the lower portion of a drainage subbasin by using a fingerprinting approach. Five sediment tracing elements were selected: Fe, Si, Al, Ti, and Zr. The sediment source area is composed of gabbro, granite, and felsic orthogneiss, upon which two soil classes were formed: Rhodic Ferralsol (Dystric) (Latossolo Vermelho Distroférrico típico, LV) and Haplic Acrisol (Argissolo Vermelho-Amarelo Distrófico típico, PVA). In the source area, 35 samples were collected from the topsoil layer (0–2 cm of depth) using a regular grid of 50 × 50 m2. In the deposition area, 24 samples were collected in a regular grid of 7 × 7 m2. The source of the sediments was determined using cluster analysis with data provided by the proximal sensors and topographic attributes. Results indicated that the Haplic Acrisol, which is more susceptible to erosion, contributed most to sediment deposition. Analysis of pXRF data showed its potential to identify and differentiate sediments and their sources. Cluster models based on the abundance of Fe, Si and Al, as well as the Ti/Zr ratio, demonstrated the best results with a global accuracy of 88% and a Kappa coefficient of 0.74. The use of the susceptibilimeter data alone did not yield satisfactory results. Results indicate the usefulness of pXRF in identifying the source of sediments in drainage basins, making it a valuable tool in soil conservation and erosion assessments. • pXRF was capable of identifying the origin of sediments. • Fe, Si, Al and the Ti/Zr ratio were efficient in identifying sediment sources. • The Chromic Acrisol contributed most with sediment deposition. • Magnetic susceptibility contributed little to identify sediment sources. [ABSTRACT FROM AUTHOR]

An inventory of soil organic carbon (SOC) stocks to 100-cm depth was carried out at four pedologically comparable forest sites in the Amani Nature Reserve (Eastern Usambara Mountains, NE Tanzania). Three plots at primary tropical submontane forests and one plot at a secondary forest derived from selective cutting were sampled. The aim was to quantify the SOC stocks including the spatial variation, and to put the findings into a pedological context. At each site, a combined approach was applied with auger samples taken to 40-cm depth (topsoil) at eight points (10 cm depth intervals) surrounding a central soil pit. The subsoil was sampled at 40–100 cm depth in the soil pit, accompanied by a detailed soil description and classification according to FAO and WRB. In addition, soil analysis comprised a set of chemical and physical parameters. According to WRB, the soils belonged to the reference groups Acrisols and Alisols, depending on the method used for estimating clay-related potential cation exchange capacity. The SOC stocks to 100-cm depth ranged between 16.9 and 22.4 kg C m − 2 (mean 19.7 kg C m − 2 ). The SOC stock at the secondary forest (20.2 kg C m − 2 ) did not differ from those of the primary forest plots. In all profiles the subsoil contributed to the SOC stocks to 100-cm depth, whereas the contribution of the forest floor was small. The variation of SOC stocks between the forest sites may be explained by ‘old’ land-use and/or differences in soil chemical parameters controlling SOC stabilization. The SOC stocks appear to be related to the amounts of poorly crystallized Fe- and Al-oxides. The mechanisms and potentials for SOC sequestration are, however, unclear and merit further detailed study. Our inventory of SOC under forest represents a suitable baseline for the assessment of SOC stock changes after land-use conversion to agriculture on typical soils of the humid tropics. [ABSTRACT FROM AUTHOR]

Microbial nutrient limitation was investigated in a 53-year-old field experiment in the Central-West of Burkina Faso under sorghum-cowpea rotation, comparing three fertilization practices: mineral fertilizer (MIN), mineral fertilizer and farmyard manure (MINFYM), and a non-fertilized control (CON). We assessed microbial N and P limitation after removal of C limitation by (i) determining microbial N and P, (ii) assessing respiration kinetics in incubated soil samples amended with easily available C (glucose) alone or in combination with N and/or P, or not amended, and (iii) evaluating changes in microbial biomass and community composition at the peak of microbial respiration by microbial P and phospholipid fatty acid (PLFA) analyses. Microbial N and P were very low in all fertilization practices, but greater in MINFYM than in CON. Easily available C was the first factor limiting microorganisms in all fertilization practices. After removal of C limitation, most indicators suggested N and P co-limitation in CON. In contrast, respiration kinetics in MINFYM and MIN were only N-limited, while biomass formation in MINFYM was also P-limited. PLFA analyses indicated preferential fungal growth on the added C, and P limitation of changes in microbial community composition in MIN. Long-term application of fertilizers mostly alleviated secondary microbial nutrient limitation by P but not by N, and C always remained the primary limiting factor for microbial growth. [ABSTRACT FROM AUTHOR]

When teak (Tectona grandis L. f.) is planted on acrisols in Northeast Thailand, its growth is suppressed by low pH, infertility, and low water holding capacity. To examine materials capable of increasing water holding capacity in soil and improving teak growth, we conducted an experiment with teak seedlings. We selected bentonite, charcoal, and corncob and added these materials at a rate of 4% to sandy soil from northeast Thailand. Teak seedlings were potted on these soils and raised from July 2013 to July 2014. We compared growth, photosynthetic rates, leaf water potential, and concentrations of elements in plant organs among bentonite, charcoal, corncob, and no addition (control) treatments. Water content in the soilswas increased for the bentonite and charcoal treatments. Teak seedlings potted in these two conditions did not suffer from drought stress. Comparing the growth traits of the teak seedlings, the charcoal treatment produced larger root growth and promoted the uptake of phosphorus and potassium, whereas the bentonite treatment did not show positive effects on growth or nutrient acquisition. In contrast, the corncob treatment decreased water content in the soil, and teak seedling growth was suppressed. We concluded that charcoal was a useful material to improve teak growth in sandy soils. [ABSTRACT FROM AUTHOR]

The interactive effects between electron donor substances and iron (Fe) oxides have significant influence on electron transfer and the growth of Fe-reducing bacteria, which may affect the reductive dechlorination of 1,1,1-trichoro-2,2-bis(pchlorophenyl) ethane (DDT) in soils. To evaluate the roles of volatile fatty acids and Fe(III) oxide in accelerating the reductive dechlorination of DDT in Hydragric Acrisols, a batch anaerobic incubation experiment was conducted in a slurry system with the following seven treatments: sterile soil, control (DDTcontaminated soil), lactic acid, propionic acid, goethite, lactic acid + goethite, and propionic acid + goethite. Results showed that after 20 d of incubation, DDT residues for these treatments decreased by 34, 65, 77, 81, 77, 90, and 92% of the initial quantities, respectively, with 1,1-dichloro-2,2-bis(4-chlorophenyl)-ethane as the dominant metabolite. The application of lactic acid had no significant effect on DDT dechlorination in the first 8 d while the methanogenesis rate increased quickly but accelerated DDT dechlorination after Day 8 while the methanogenesis rate decreased and Fe(II) contents increased. The application of propionic acid enhanced DDT dechlorination rates throughout the incubation. The amendment by goethite stimulated microbial reduction of Fe(III) oxides to generate Fe(II), which was an efficient electron donor, thus accelerating DDT dechlorination significantly in the early incubation period. A synergetic interaction that accelerated DDT dechlorination, either between lactic acid and goethite or between propionic acid and goethite, was obtained. The results will be of great significance to develop efficient in situ remediation technology of DDT-contaminated soil. [ABSTRACT FROM AUTHOR]

Low soybean yields in western Kenya have been attributed to low soil fertility despite much work done on nitrogen (N) and phosphorus (P) nutrition leading to suspicion of other nutrient limitations. To investigate this, a nutrient omission trial was set up in the greenhouse at the University of Eldoret-Kenya to diagnose the nutrients limiting soybean production in Acrisols from Masaba central and Butere sub-Counties, and Ferralsols from Kakamega (Shikhulu and Khwisero sub-locations) and Butula sub-Counties and to assess the effect of liming on soil pH and soybean growth. The experiment was laid out in a completely randomized design with ten treatments viz; positive control (complete), negative control (distilled water), complete with lime, complete with N, minus macronutrients P, potassium (K), calcium (Ca), magnesium (Mg) and sulphur (S) and with, micro-nutrients boron (B), molybdenum (Mo), manganese (Mn), copper (Cu) and zinc (Zn) omitted. Visual deficiency symptoms observed included interveinal leaf yellowing in Mg omission and N addition and dark green leaves in P omission. Nutrients omission resulted in their significantly low concentration in plant tissues than the complete treatment. Significantly (P≤ 0.05) lower shoot dry weights (SDWs) than the complete treatment were obtained in different treatments; omission of K and Mg in Masaba and Shikhulu, Mg in Khwisero, K in Butere and, P, Mg and K in Butula. Nitrogen significantly improved SDWs in soils from Kakamega and Butula. Liming significantly raised soil pH by 9, 13 and 11% from 4.65, 4.91 and 4.99 in soils from Masaba, Butere and Butula respectively and soybean SDWs in soils from Butere. The results show that, poor soybean growth was due to K, Mg and P limitation and low pH in some soils. The results also signify necessity of application of small quantities of N for initial soybean use. [ABSTRACT FROM AUTHOR]

The application of electron donor and electron shuttle substances has a vital influence on electron transfer, thus may affect the reductive dechlorination of 1,1,1-trichoro-2,2-bis(p-chlorophenyl)ethane (DDT) in anaerobic reaction systems. To evaluate the roles of citric acid and anthraquinone-2,6-disulfonate (AQDS) in accelerating the reductive dechlorination of DDT in Hydragric Acrisols that contain abundant iron oxide, a batch anaerobic incubation experiment was conducted in a slurry system with four treatments of (1) control, (2) citric acid, (3) AQDS, and (4) citric acid + AQDS. Results showed that DDT residues decreased by 78.93%–92.11% of the initial quantities after 20 days of incubation, and 1,1-dichloro-2,2-bis(4-chlorophenyl)-ethane (DDD) was the dominant metabolite. The application of citric acid accelerated DDT dechlorination slightly in the first 8 days, while the methanogenesis rate increased quickly, and then the acceleration effect improved after the 8th day while the methanogenesis rate decreased. The amendment by AQDS decreased the Eh value of the reaction system and accelerated microbial reduction of Fe(III) oxides to generate Fe(II), which was an efficient electron donor, thus enhancing the reductive dechlorination rate of DDT. The addition of citric acid + AQDS was most efficient in stimulating DDT dechlorination, but no significant interaction between citric acid and AQDS on DDT dechlorination was observed. The results will be of great significance for developing an efficient in situ remediation strategy for DDT-contaminated sites. [ABSTRACT FROM AUTHOR]