Low Soil pH Research Articles

Groundwater Contamination by Heavy Metals in Malaysia: Sources, Transport, and Remediation Strategies

Groundwater contamination by heavy metals is a pressing environmental concern, particularly in regions highly dependent on groundwater as a freshwater source. While Malaysia primarily relies on river water, certain states and islands depend on groundwater for their supply. Research on heavy metal contamination in Malaysia’s groundwater remains limited, making it crucial to study the distribution and mobility of contaminants to develop appropriate remediation strategies. In addition to natural sources, anthropogenic activities such as landfills, mining, and the use of fertilizers contribute significantly to heavy metal pollution in groundwater. Factors like rainfall, fluctuating groundwater levels, and low soil pH can exacerbate heavy metal leaching into aquifers. Various models and techniques, including 2D resistivity imaging and MODFLOW, are used to assess groundwater flow and contaminant transport. These models suggest that contaminant concentrations decrease with increased depth and radial distance from pollution sources such as landfills and mining areas. The health risks associated with heavy metal exposure through groundwater consumption are significant, necessitating effective remediation strategies. Phytoremediation is an economical solution for groundwater containing low concentrations of heavy metals, while permeable reactive barriers may be suitable for more complex cases, pending detailed site investigation. This review aims to examine the current state of knowledge on heavy metal contamination in Malaysia’s groundwater, focusing on sources, distribution patterns, and movement of pollutants. It also seeks to evaluate existing remediation methods, including phytoremediation and permeable reactive barriers, while identifying gaps in research, particularly concerning risk assessments and heavy metal speciation.

Sewage sludge as soil amendment in arid soils - A trace metal, nutrient and trace organics perspective

Sewage sludge management has emerged as a critical environmental challenge due to the large volumes generated globally. Valorization techniques, including energy production and agricultural applications, offer sustainable solutions, particularly in regions with low soil fertility. The sewage sludge utilization in the Middle East region is low. This paper presents a pragmatic risk-based assessment using the risk-based corrective action approach to evaluate sludge application in desert soils. This methodology focuses on the source-pathway-receptor interaction and assesses the likelihood of contaminants posing a real threat. In arid desert regions like Kuwait, where soil organic content and moisture are extremely low, the application of sewage sludge presents a feasible option to enhance soil quality and valorize unutilized sludge dumps which pose significant environmental concerns but are left to desiccate in the absence of any environmental regulation towards its utilization and due to religious apprehensions. Since the sludge characterization is not well detailed a brief review of the available data was included to establish the bounds of various organic, metal and nutrients that were used for generating the model. This study examines the changes in the physico-chemical properties of desert soils following sludge application, focusing on the likely fate of trace metals and organic contaminants. The alkaline desert soils of Kuwait, with a pH range of 7.7–8.9, are particularly suitable for sludge application due to the low mobility of metals in alkaline conditions. Additionally, sludge application lowers soil pH, improving conditions for plant growth. The region's deeper water table and scant annual precipitation (<0.15 m) further reduce the risk of groundwater contamination and deeper soil profile contamination. The presence of organic content, nitrates, Zn, and Cu in sludge can promote native vegetation growth. However, trace organic contaminants, including PAHs, PCBs, and pharmaceuticals, pose a potential risk to soil contamination, but since the geological section shows intervening impervious layers the contamination is going to be localized, even if there is sufficient leachable fraction. Given the minimal risk of contamination under the unique conditions of arid regions, this approach highlights the potential for eco-friendly sludge valorization, that will improve vegetation cover and arrest the suspended particulate suspension. However, before the large-scale implementation of this modelled concept, a detailed experimental study on the pilot scale or lysimeters is recommended to assess the long-term impacts of sludge application and to obtain data that can inform policy guidelines for sustainable sludge management in desert environments.

Land use effects on soil microbiome composition and traits with consequences for soil carbon cycling

Abstract The soil microbiome determines the fate of plant-fixed carbon. The shifts in soil properties caused by land use change leads to modifications in microbiome function, resulting in either loss or gain of soil organic carbon (SOC). Soil pH is the primary factor regulating microbiome characteristics leading to distinct pathways of microbial carbon cycling, but the underlying mechanisms remain understudied. Here, the taxa-trait relationships behind the variable fate of SOC were investigated using metaproteomics, metabarcoding and a 13C labelled litter decomposition experiment across two temperate sites with differing soil pH each with a paired land use intensity contrast. 13C incorporation into microbial biomass increased with land use intensification in low pH soil but decreased in high pH soil, with potential impact on carbon use efficiency (CUE) in opposing directions. Reduction in biosynthesis traits was due to increased abundance of proteins linked to resource acquisition and stress tolerance. These trait trade-offs were underpinned by land use intensification-induced changes in dominant taxa with distinct traits. We observed divergent pH-controlled pathways of SOC cycling. In low-pH soil, land use intensification alleviates microbial abiotic stress resulting in increased biomass production but promotes decomposition and SOC loss. In contrast, in high-pH soil, land use intensification increases microbial physiological constraints and decreases biomass production, leading to reduced necromass build-up and SOC stabilisation. We demonstrate how microbial biomass production and respiration dynamics and therefore CUE can be decoupled from SOC highlighting the need for its careful consideration in managing SOC storage for soil health and climate change mitigation.

Improving Sunflower Yield through Liming and Phosphorus Fertilizer Application in the South-Central Coastal Region of Bangladesh

Along with salinity, low soil pH is the major constraint for growing winter crops in the south central coastal region of Bangladesh. Extensive research has been done to manage soil salinity, where managing low soil pH for crop production is scarce. The aim of the experiment was to improve sunflower (Helianthus annuus L. cv. Hybrid Unisun) yield through liming and phosphorus fertilizer application in the acidic saline soil of Amtali upazila of Barguna district, Bangladesh. During the winter season of 2024 a field experiment was carried out comprising two rates of lime 0 and 2 t ha-1 and four levels of phosphorus (P) having 0, 12, 24 and 36 kg P ha-1 using RCBD design. Lime application at 2 t ha-1 rate significantly increased stem girth, head diameter, number of seeds per head, 1000-seed weight, and seed, stover and root yields of sunflower. The application of P up to the highest level (36 kg P ha-1) significantly increased the growth and yield of sunflower. Lime application increased the soil pH by 0.72 unit compared to non-liming plot. The application of lime (2 t ha-1) along with 36 kg P ha-1 recorded the highest sunflower seed yield of 3.21 t ha-1 in the soil of Amtali upazila of Barguna district, Bangladesh. The benefit cost ratio (BCR) of different rates of P application without liming ranged from 5.28-10.09 but it decreased drastically while P was applied with lime having the BCR between 0.15-1.82. J Bangladesh Agril Univ 22(3):352-359, 2024

Low soil pH enhances fruit acidity by inhibiting citric acid degradation in lemon (Citrus lemon L.)

Fruit acidity significantly influences fruit flavor, but the specific impact of soil pH on fruit acidity remains unclear. This study investigated the effects of various soil pH levels on fruit acidity and citric acid (CA) metabolism in lemon (Citrus limon L.). High soil pH (pH 8) decreased total soluble solids concentrations in lemon fruits, while low soil pH (pH 4) increased titratable acid and CA concentrations. Although low soil pH reduced the synthesis of CA due to the decreased citrate synthase and phosphoenolpyruvate carboxylase activities, the elevated fruit acidity under low soil pH conditions is not directly related to CA synthesis. Instead, low soil pH was found to suppress the activity of cytosolic aconitase (Cyt-ACO), an iron-dependent enzyme, indicating a potential role for CA degradation inhibition in low soil pH-induced CA accumulation. Furthermore, low soil pH significantly reduced cytosolic iron (Cyt-Fe) concentration, which was positively correlated with Cyt-ACO activity. In conclusion, low soil pH contributes to increasing fruit acidity in lemon, partially by inhibiting CA degradation due to the reduced Cyt-Fe concentrations. Our work unravels the influence of soil pH on CA accumulation and provides important clues for modulating CA levels through microelement fertilization in citrus.

Effect of Biostimulants and Nutrient Management on Soil Nutrients Level in Onion (Allium cepa L.)

During rabi season of 2021, a field experiment was conducted by embracing different organic manures, inorganic fertilizers and biostimulants (Pseudomonas fluorescens and Bacillus subtilis) over growth, yield, quality and persisting soil fertility of onion in the mineralized soils of Himachal Pradesh. The study was organized in thirteen treatments. The analysis revealed that lowest soil pH (6.94), electrical conductivity (0.186 dSm-1), highest soil organic carbon (0.85%), available nitrogen (257.79 kg/ha) and available phosphorus (26.14 kg/ha) were recorded with treatment T7 [75% RDF + 40 kg S/ha + Bacillus subtilis + FYM (250 q/ha)]. The highest available potassium was recorded in treatment T12 [100% RDF (125:75:60 kg/ha)] and highest available sulphur was recorded in treatment in T11 [100% RDF + 40 kg S/ha].

Effects of Varied Tillage Practices on Soil Quality in the Experimental Field of Red-Soil Sloping Farmland in Southern China

Red-soil sloping farmland in southern China plays a crucial role in the local economy and food production. However, improper tillage practices have resulted in topsoil degradation and deteriorating soil quality. This study investigated changes in soil physico-chemical properties under four tillage methods—cross-slope ridge tillage (RT), down-slope ridge tillage (DT), plastic mulching (PM), and conventional tillage (CT)—on red-soil sloping farmland. The study applied the Soil Management Assessment Framework (SMAF) to assess the influence of these tillage practices on soil quality. Results indicated that PM can increase the total porosity of the soil, reduce soil bulk density, and simultaneously decrease soil surface-water evaporation, significantly improving the soil’s water-retention capacity. RT improved soil aggregate formation and stability, leading to increased macro-aggregate content, mean weight diameter, and soil water-stable aggregate stability rates. PM and RT effectively preserved soil nutrients like total nitrogen and organic matter, although PM lowered soil pH, potentially causing acidification. RT demonstrated the highest soil quality, with PM following. Crop growth positively impacted soil macro-aggregate content and stability, showing continuous improvement in soil structure and quality (p &lt; 0.05). Priority should be given to RT in red-soil sloping farmland, followed by PM and CT, while avoiding DT if possible. This research furnishes valuable scientific substantiation for the selection of optimal tillage practices in the preservation of soil quality on red-soil slopes.

Application of Magnetized Ionized Water and Bacillus subtilis Improved Saline Soil Quality and Cotton Productivity.

Soil salinization, a significant global challenge, threatens sustainable development. This study explores the potential of magnetized ionized water irrigation and Bacillus subtilis application to mitigate this issue. The former method is hypothesized to enhance soil salt leaching, while the latter is expected to improve soil nutrient availability, thereby increasing microbial diversity. To address the unclear impact of these interventions on soil quality and cotton productivity, this study employs four different experimental methods: magnetized ionized water irrigation (M), application of 45 kg ha-1B. subtilis (B), a combination of 45 kg ha-1B. subtilis with magnetized ionized water irrigation (MB), and a control treatment with no intervention (CK). This study aims to clarify the effects of these treatments on soil bulk density (BD), field capacity (FC), salinity and alkalinity, nutrient content, microbial activity, and cotton crop yield and quality. Additionally, it aims to evaluate the efficacy of these methods in improving saline soil conditions by developing a soil quality index. The results showed that using magnetized ionized water for irrigation and applying B. subtilis, either alone or together, can effectively lower soil pH and salt levels, enhance microbial diversity and abundance, and improve the yield and quality of cotton. Notably, B. subtilis application significantly decreased BD and enhanced FC and nutrient content (p < 0.05). A correlation was found where soil nutrient content decreased as pH and salt content increased. Furthermore, a strong correlation was observed between the major soil bacteria and fungi with BD, FC, and salt content. Comparatively, M, B, and MB significantly boosted (p < 0.01) the soil quality index by 0.21, 0.52, and 0.69 units, respectively, and increased (p < 0.05) cotton yield by 5.7%, 14.8%, and 20.1% compared to CK. Therefore, this research offers eco-friendly and efficient methods to enhance cotton production capacity in saline soil.

Impacts of Solidago canadensis and Erigeron canadensis co‐invasion on soil microbial communities

AbstractInvasive plants disrupt the structure and function of ecosystems, causing a decline in their diversity. The coexistence of Solidago canadensis and Erigeron canadensis within shared habitats is a common phenomenon, and the frequent occurrence of co‐invasion has substantial implications for ecosystems. However, the effects of the co‐invasion of two plants on the soil ecosystem across varying degrees of invasion remain uninvestigated. Therefore, we investigated how the co‐invasion of S. canadensis and E. canadensis affects soil physiochemical properties and microorganisms across various degrees of invasion. The invaded regions exhibited significantly lower soil moisture content and pH values than those in the uninvaded areas (p &lt; .05). Additionally, co‐invasion resulted in higher soil organic matter (OM), total nitrogen (TN), total phosphorus (TP), and available phosphorus (AP) contents compared to single invasion by E. canadensis. Furthermore, the invaded regions exhibited a greater diversity of soil bacterial and fungal communities than the uninvaded regions. Under diverse invasion conditions, Actinobacteria and Ascomycota emerged as the predominant phyla of soil bacteria and fungi, respectively, leading to a shift in the soil microbial community structure. Moreover, homogenizing dispersal significantly influenced bacterial community succession, while ecological drift influenced the progression of fungal communities. Using structural equation modeling, this study established significant correlations between soil properties (pH, TN, and nitrate nitrogen) and bacterial interactions (diversity and community assembly) relative to microbial composition. This study revealed the influence of S. canadensis and E. canadensis co‐invasion on soil microbial communities, thereby contributing a theoretical framework delineating the impact of these two invasive plant species.

Field study on the integration of a hydrogen-producing microbiome in restoring Phellinus noxius-affected rhizosphere

At National Kaohsiung University of Science and Technology (NKUST), a mesophilic anaerobic bioreactor system produces a hydrogen-producing microbiome (HMb) containing beneficial bacteria such as Bacillus sp. This HMb, known for degrading cellulose and remediating soil, is being tested in Kaohsiung City, Taiwan, to treat tree root rot caused by Phellinus noxius (P. noxius). The study aims to evaluate HMb's effectiveness in restoring the rhizosphere, enhancing soil health, and increasing tree resistance by assessing soil bioactivity and microbial diversity.Field experiments showed that HMb treatment improved tree health by 24 % at the highest health level but reduced it by 20 % at the next level. Post-treatment soil organic matter (SOM) and total Kjeldahl nitrogen (TKN) levels remained stable, indicating minimal impact on soil fertility. HMb also lowered soil pH in some plots, potentially suppressing pathogens and enhancing nutrient absorption. The study found that HMb increased microbial diversity in the rhizosphere, particularly Acidobacteria and Proteobacteria, which inhibited fungal growth. However, HMb had no significant impact on P. noxius populations. Overall, HMb treatment shows promise in enhancing plant health by improving microbial diversity and soil conditions, but further research is needed to understand its full impact on pathogen suppression and soil health restoration.

Wheat varieties show consistent differences in root colonization by mycorrhiza across a European pedoclimatic gradient

AbstractArbuscular mycorrhizal (AM) fungi form mutualistic relationships with the majority of land plants and are an important part of the soil microbial community in natural and agricultural ecosystems. These fungi promote water and nutrient acquisition by their host plant and regulate the allocation of photosynthetic carbon to soil. Both crop variety and environment affect naturally occurring mycorrhizal abundance in roots, but the relative importance of those factors for mycorrhization is largely unknown. In a field study covering a large pedoclimatic gradient across four European sites, we (i) compared the abundance of AM fungi in the roots of 10 modern winter wheat (Triticum aestivum L.) varieties, (ii) evaluated the relative importance of variety and site for the variability in root colonization by AM fungi and (iii) tested the relationship between mycorrhizal abundance and grain yield. Root colonization by arbuscules and hyphae ranged from 10% to 59% and 20% to 91%, respectively, across all samples and varied by 8% and 18%, respectively, among varieties when averaged across sites. Variance decomposition analysis revealed a 10 times higher importance of site than variety for AM fungal root colonization. Specifically, we found the highest mycorrhizal abundance on the site with the most arid conditions and the lowest on the sites with low soil pH and high nutrient availability. Despite the low variability in mycorrhizal abundance among varieties, there were significant differences in both arbuscular and hyphal root colonization. However, this did not translate into an increase in yield as no significant relationships between mycorrhizal abundance at flowering and grain yield were detected. The consistent differences between wheat varieties in root colonization by AM fungi across European field sites underline that genetic drivers of mycorrhization are to some extent independent of the site. This highlights the relevance of breeding practices to shape a wheat variety's capacity for mycorrhizal symbiosis across a range of environmental conditions.

CsABCG11.2 mediates theanine uptake to alleviate cadmium toxicity in tea plants (Camellia sinensis)

Theanine (Thea) is a unique metabolite in tea plants, but its physiological functions remain elusive. A low soil pH increases cadmium (Cd) availability, affecting the quality of tea plant products. In this study, we found that Thea reversed the Cd-induced reduction in free amino acid (FAA) and caffeine (CAF) in the young tea leaves, as well as the down-regulation in the expression of nitrate transporters CsNRT1.2 and CsNRT2.5, and genes responsible for the nitrogen (N) assimilation. We demonstrated that Thea could alleviate Cd-induced oxidative stresses and enhance photosynthesis. Moreover, an ATP-binding cassette (ABC) transporter, CsABCG11.2, could uptake distinct Cd substrates and the five major amino acids in tea plants. Heterologous expression of CsABCG11.2 in yeast indicated a competitive absorption between Cd and Thea in a concentration-dependent pattern. CsABCG11.2-overexpressing Arabidopsis plants exhibited increased sensitivity to Cd due to enhanced Cd concentration, accumulation in the shoots, and reduction in the primary root length. Exogenous application of Thea at environmentally regular levels attenuated the adverse effects of Cd-induced growth inhibition and chlorosis in CsABCG11.2-overexpressing Arabidopsis plants. Knockdown of CsABCG11.2 tea plants significantly lowered Cd levels in young shoots. Our results suggest that Thea plays beneficial roles in alleviating Cd stress directly or indirectly by modulating CsABCG11.2-mediated Cd uptake and translocation within plants.

Global comparison shows that soil bacterial communities in extreme pH soils are more structured by deterministic processes

A major aim of microbial ecology is the search for basic ‘rules’ that dominate variation in microbial communities. An earlier comparison of several soil successional series showed that pH explained variation in the relative importance of stochastic versus deterministic processes in bacterial communities. In neutral pH soils, bacterial communities were more strongly influenced by stochastic processes than in low or high pH soils. Here, we took a broad level approach to attempt a more definitive answer of whether soil pH dominates bacterial community structuring using the global database of 237 samples. The beta-NTI showed that at both a global and continental scale, samples with low pH were dominated by deterministic processes, while in samples at around neutral pH, stochastic processes dominated. At high pH, stochasticity dominated on the global scale, but on several continents, the beta-NTI showed determinism predominating. Overall, it appears that bacterial community structuring is strongly and predictably affected by pH, with the most consistent difference observed between determinism at low pH and stochasticity at neutral pH. There is a need for hypothesis testing to explain why this trend exists. It is possible that at low pH, there is a greater selection for consortia to exploit resources, which leads to more predictable, deterministic combinations of species co-occurring. Additionally, the high energy demands for homeostasis and the constraints from the lack of available nutrient resources may impose greater niche-based competition, resulting in more deterministic community structuring at low pH.

Low levels of Al stimulate the aboveground growth of Davidia involucrata saplings

Davidia involucrata is a woody perennial and the only living species in the Genus Davidia. It is native to southern China where it holds cultural and scientific importance. However, D. involucrata is now an endangered species and its natural range includes low pH soils which are increasingly impacted by acid rain, nitrogen deposition and imbalanced nutrient cycling. The combination of these stresses also poses the additional risk of aluminum (Al) toxicity. Since the responses of D. involucrata to low pH and aluminum toxicity have not been investigated previously, a hydroponic experiment was conducted to examine the growth of one year old D. involucrata saplings after 50 d growth in a range of pH and Al conditions. Plant biomass, morphology, antioxidant enzyme activity, mineral concentrations and plant ecological strategy were compared at pH 5.8 and pH 4.0 without added Al (AlCl3) and in 0.1, 0.2 and 0.5 mM Al at pH 4.0. Our results showed that compared with pH 5.8, pH 4.0 (without added Al) not only inhibited root and shoot growth but also limited accumulation of nitrogen (N) and phosphorus (P) in leaves of D. involucrate. However, low Al concentrations (0.1 and 0.2 mM Al) at pH 4.0 partially restored the aboveground growth and leaf N concentrations, suggesting an alleviation of H+ toxicity by low Al concentrations. Compared with low Al concentrations, 0.5 mM Al treatment decreased plant growth and concentrations of N, P, and magnesium (Mg) in the leaves, which demonstrated the toxicity of high Al concentration. The results based on plant ecological strategy showed that D. involucrate decreased the competitiveness and favored its stress tolerance as pH changed from 5.8 to 4.0. Meanwhile, the competitiveness and stress tolerance of D. involucrata increased and decreased at low Al concentrations, respectively, and decreased and increased at high Al concentration, respectively. These trade-offs in ecological strategy were consistent with the responses of growth and antioxidant enzyme activity, reflecting a sensitive adaptation of D. involucrata to acid and Al stresses, which may aid in sustaining population dynamics. These findings are meaningful for understanding the population dynamics of D. involucrata in response to aluminum toxicity in acid soils.

Impact of Climate on Soil Organic Matter Composition in Soils of Tropical Volcanic Regions Revealed by EGA-MS and Py-GC/MS.

Soil organic matter (SOM) crucially influences the global carbon cycle, yet its molecular composition and determinants are understudied, especially for tropical volcanic regions. We investigated how SOM compounds change in response to climate, vegetation, soil horizon, and soil properties and the relationship between SOM composition and microbial decomposability in Tanzanian and Indonesian volcanic regions. We collected topsoil (0-15 cm) and subsoil (20-40 cm) horizons (n = 22; pH: 4.6-7.6; SOC: 10-152 g kg-1) with undisturbed vegetation and wide mean annual temperature and moisture ranges (14-26 °C; 800-3300 mm) across four elevational transects (340-2210 m asl.). Evolved gas analysis-mass spectrometry (EGA-MS) documented a simultaneous release of SOM compounds and clay mineral dehydroxylation. Subsequently applying double-shot pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) at 200 and 550 °C, we detailed the molecular composition of topsoil and subsoil SOM. A minor portion (2.7 ± 1.9%) of compounds desorbed at 200 °C, limiting its efficacy for investigating overall SOM characteristics. Pyrolyzed SOM closely aligns with the intermediate decomposable SOM pool, with most pyrolysates (550 °C) originating from this pool. Pyrolysates composition suggests tropical SOM is mainly microbial-derived and subsoil contains more degraded compounds. Higher litter inputs and attenuated SOM decomposition due to cooler temperatures and lower soil pH (<5.5) produce less-degraded SOM at higher elevations. Redundancy analyses revealed the crucial role of active Al/Fe (oxalate-extractable Al/Fe), abundant in low-temperature/high-moisture conditions, in stabilizing these less-degraded components. Our findings provide new insights into SOM molecular composition and its determinants, critical for understanding the carbon cycle in tropical ecosystems.

Soil Chemical Properties and Nutrient Dynamics under Different Legume-based Agroforestry Systems in Semi-arid Conditions of Haryana

Background: In order to support livelihoods, enhance food security, restore ecosystem services, and reduce pressure on forests, soil fertility can be improved by utilizing alternative land-use systems, such as agroforestry. Methods: The present study was conducted to investigate the effect of different agroforestry systems on soil chemical properties and nutrient availability (macro and micro) during different seasons in Hisar, Haryana. Different systems include Poplar (Populus deltoides), Eucalyptus (Eucalyptus tereticornis), Melia (Melia composita), Shisham (Dalbergia sissoo) based agroforestry system (Cowpea-Wheat) and sole cropping of Cowpea-Wheat (as control). Soil samples were collected from 0-15 and 15-30 cm of soil depth during five seasons i.e., winter, spring, summer, rainy and autumn. Result: Soil EC, SOC and available macronutrients and micronutrients were significantly affected by the depth of sampling, systems and seasons while soil pH was not significantly affected by seasons. Lower soil pH and EC was observed from agroforestry systems as compared to sole cropping. Soil Organic Carbon, availability of N, P, K and S was significantly higher under tree based systems as compared to control. Maximum DTPA extractable Mn, Zn and Cu was observed under poplar based system while highest DTPA extractable Fe was observed under Melia based system during both the years. Significantly higher SOC and nutrient availability was observed during autumn, rainy and spring seasons as compared to winter and summer seasons, while reverse trend was observed for soil pH and EC among the seasons. Soil Organic Carbon, availability of macro and micronutrients decreased with increase in soil depth. Overall, the soil chemical properties and nutrient status of soil were comparatively better under tree based systems than sole cropping of Cowpea-Wheat.

Partial substitution of manure increases N2O emissions in the alkaline soil but not acidic soils

The fertilization regimes of combining manure with synthetic fertilizer are benefits for crop yields and soil fertility in cropping systems as compared to sole synthetic fertilization, but the responses of nitrous oxide (N2O) emissions to these practices are inconsistent in the literatures. We hypothesized that it is caused by different proportions of nitrogen (N) applied as manure and various soil properties. Here, we conducted a microcosm experiment, and measured the N2O emissions from control (no N) and five manure substitution treatments (supplied 100 mg N kg−1 using the combination of urea with manure) with a range of proportions of N applied as manure (0, 25%, 50%, 75%, and 100%) in three different soil types (fluvo-aquic soil, black soil, and latosol) under aerobic condition. The stimulated effect on N2O emissions was more pronounced after manure application in an alkaline soil with high nitrification rate, due to relatively rapid soil DOC depletion and N mineralization of manure. N2O emissions from partial substitution of urea with manure were significantly higher than manure-only addition under high soil pH due to abundant labile C from manure. However, there was no difference between manure substitution treatments under acid soils. Nitrification inhibitor substantially decreased N2O emissions with increasing soil pH, but it was less effective in mitigating N2O emissions with larger proportion of manure. This is likely due to the slow nitrification under low soil pH, and denitrification derived N2O increased with increasing manure application rate. Collectively, our study shows that the application of manure substitution to alkaline soils requires careful consideration, which might have rapid nitrification potential and hence trigger significant N2O emissions. The knowledge gained in this work will help the decision-makers in optimizing a sound N fertilization regime interacted with soil properties for sustainable crop production and N2O mitigation.

Fertilizer Value of Nutrient-Enriched Biochar and Response of Canola Crop

Excessive use of chemical fertilizers (CFs) can result in a decrease of soil organic matter, lowering soil fertility and agricultural productivity. Biochar application could be a promising approach to reduce these issues and increase soil fertility. In this study, the effects of nutrient-enriched biochar (NEBC) on soil properties and canola (Brassica napus L.) plant growth were investigated. A pot experiment was conducted following a completely randomized design with three replications. Two contrasting Australian soils were amended with three doses (i.e., control, 1%, and 5% w/w) of three NEBCs, one biosolid biochar (BSBC), and CF. The canola plant growth experiment spanned over eight weeks assessing the effects of the amendments. Soil properties were examined after plant harvesting. NEBC and BSBC lowered soil pH (up to 1.38 units) and increased soil EC (up to 378 µS cm−1). They also increased P (up to 19-fold) and K (up to 0.67 g kg−1) availability, improving canola growth compared to CF. Biochar increased dehydrogenase enzyme activity (up to twofold), but NEBC reduced seed germination due to high nutrient content. Nutrient concentration in plant tissues increased with NEBC and BSBC application. Application of NEBC and BSBC improved soil properties, resulting in increased growth of canola. The application rate of NEBC fertilizer requires further optimization to improve soil fertility and crop productivity.

Driving mechanisms of soil bacterial α and β diversity under long-term nitrogen addition: Subtractive heterogenization based on the environment selection

Soil bacterial α and β diversity patterns under nitrogen (N) addition have been intensively examined, but γ diversity patterns remain largely unknown, especially, the mechanisms that concurrently control changes in α, β and γ diversity remain elusive. Therefore, we formulated a conceptual framework that simultaneously considers candidate drivers including ubiquitous species, rare species, and community assembly processes to elucidate the driving mechanisms of α, β and γ diversity under N addition. The conceptual framework was tested by compiling the sequence data of seven studies published from January 1997 to May 2022 and following the same analysis as our own two long-term multilevel N addition experiments. We demonstrate that subtractive heterogenization based on environment selection simultaneously predicts the changes in α, β and γ diversity under long-term N addition. That is, long-term N addition led to the decline of ubiquitous species (subtractive processes) through low soil pH, and promoted the strength of heterogeneous selection (heterogeneous processes) via enhancing environmental heterogeneity, subsequently causing lower α diversity and γ diversity but higher β diversity. These results mean that N addition may lead to a significant loss of soil bacterial diversity around the world. Together, these findings offer a way to simultaneously predict soil bacterial α, β and γ diversity responses to the ongoing atmospheric nitrogen deposition.

Effects of ecological intensification of agriculture on soil fertility and carbon and nitrogen stocks: An 8‐year study in southern Brazil

AbstractEcological intensification (EI) of agriculture aims to optimize soil conservation, crop diversity and nutrient management. Despite growing interest in EI, its impact on soil properties, compared with conventional farming practice (FP), remains poorly understood as a result of limited field evidence. This study, conducted over eight seasons in southern Brazil as part of the ‘Global Maize Project’ of the International Plant Nutrition Institute, evaluated EI compared with FP, and FP with silage (FPS) using a split‐plot design. Four nitrogen application rates (0, 70, 140 and 210 kg ha−1) were applied to subplots with four replicates. Soil properties were measured to a depth of 1 m. The trial systems consisted of a maize–soybean rotation under no‐till during summer and cover crops and fertilizer application during winter. In the FP system, black oats and wheat were cultivated, while FPS utilized white oats and ryegrass. In the EI system, peas (without N application) and wheat were cultivated. In the 4‐years preceding the trial, the area was cultivated in a no‐till system with maize–soybean during summer and black oat–wheat in winter. Our results reveal distinct differences in soil properties among the systems, with FPS demonstrating greater soil acidity (pH of 4.4 at 0–5 cm) caused by higher N application than FP and EI systems. The lower soil pH altered soil nutrient dynamics, with decreased available Ca, Mg and K and increased Cu, Fe, Mn and Zn. Furthermore, nutrient availability varied, with EI having more inorganic N and DON at 0–40 cm compared with FP, but less in deeper soil (40–100 cm). Notably, EI system had more soil carbon (175 Mg ha−1) compared with FP (161 Mg ha−1), a relative annual increase of 1.8 Mg ha−1 year−1 over 8 years. These findings underscore the potential of EI to promote soil carbon, thereby contributing to climate change mitigation and soil health improvement.