Low Soil pH Research Articles

Vertical Distribution of Mercury in Forest Soils and Its Transfer to Edible Mushrooms in Relation to Tree Species

Soil pollution by mercury (Hg) is a global problem that poses risks to natural ecosystems and to human health. Forests represent an important recipient of Hg deposition, however, so far, very little is known about the tree species identity effects on the distribution of Hg in forest soils and its accumulation in edible mushrooms. To clarify the effect on the two main Central-European commercial forest tree species, soil samples were collected from organic F+H horizons and from mineral soil depths of 0–2, 2–10, 10–20, and 20–30 cm in mature Norway spruce (Picea abies (L.) H. Karst.) and European beech (Fagus sylvatica L.) dominated stands. Mushroom samples of the Boletaceae family were also collected at each sampling site. The highest Hg contents were found in the F+H layer and were significantly higher in spruce- (mean 0.46 ± 0.03 mg/kg) than in beech- (mean 0.29 ± 0.10 mg/kg) dominated stands. The variation in Hg contents in F+H was best predicted by pH, the overall lower soil pH in strongly acidic spruce stands might induce Hg immobilization in the F+H layer to cause a decrease in the bioavailability of Hg for Xerocomellus chrysenteron (Bull.) Šutara. In mineral soil, the Hg contents did not differ significantly between the spruce- and beech-dominated stands. The Hg content strongly correlated with the S, N, and C contents only in mineral soil; at the depths of 2–10, 10–20, and 20–30 cm, significantly also with the silt vs. sand, Alo, and Feo contents. Studied mushroom species were not Hg-contaminated and, therefore, their consumption does not pose serious health risks regardless of the forest type. The results suggest that species-related soil chemistry and mineral associations, rather than different atmospheric Hg interception by spruce vs. beech, drive the vertical distribution and accumulation of Hg in forest soils.

Study on the new dynamics and driving factors of soil pH in the red soil, hilly region of South China.

Soil acidification has always been a substantial eco-environmental problem restricting agricultural development in the red soil region of southern China. It is necessary to determine the dynamic change in soil pH in this area to formulate regional agricultural and environmental management measures. Yujiang County, a typical county with red soil acidification in southern China, was selected as the study area. Based on soil data from 1982, 2007, and 2018, the spatiotemporal variation characteristics and the latest changes in soil pH in the county were analyzed. The results show that the soil pH in Yujiang County decreased from 5.66 to 4.74 and then increased to 4.96 from 1982 to 2018, showing a trend of first decreasing and then increasing. According to the spatial distribution characteristics of soil pH, the low soil pH values in the three periods were mainly distributed in the northern mountainous areas with more forestland and dry land area and some southern hilly areas, while the paddy soil pH values in the middle low hilly areas were relatively higher. The soil pH decreased rapidly from 1982 to 2007, showing a large area of acidification. In 2007, the proportions of acidic (4.5 < pH < 5.5) and strongly acidic (pH < 4.5) soils increased by 67.37% and 10.6%, respectively, compared with that in 1982. However, from 2007 to 2018, the soil pH of the whole county increased, and the acidification trend was alleviated, which is of great significance to the regional red soil ecological environment. Through the analysis of the main factors affecting the change in soil pH, it was found that the sharp decline in soil pH in Yujiang County during 1982-2007 was mainly caused by acid rain and excessive nitrogen application. From 2007 to 2018, no significant reduction in nitrogen fertilizer in this area occurred, and although the increase in soil organic matter contributed to alleviating soil acidification, the analysis showed that the decrease in acid rain was the main reason for the rise in soil pH in Yujiang County. At the same time, notably, there is a large area of soil in the area that is still acidic, and effective control of soil acidification is still an important ecological and environmental issue in this area. In order to further improve the pH value of soil in red soil region, it is suggested that on the basis of continuous improvement of acid rain, in addition to increasing soil organic matter by returning straw to field and other measures, appropriate amount of lime or alkaline biochar can be applied to better improve the soil ecological environment in red soil hilly region.

Diversity and functional structure of soil animal communities suggest soil animal food webs to be buffered against changes in forest land use

Forest soil and litter is inhabited by a diverse community of animals, which directly and indirectly rely on dead organic matter as habitat and food resource. However, community composition may be driven by biotic or abiotic forces, and these vary with changes in habitat structure and resource supply associated with forest land use. To evaluate these changes, we compiled comprehensive data on the species composition of soil animal communities and environmental factors in forest types varying in land-use intensity in each of three regions in Germany, i.e., coniferous, young managed, old managed, and unmanaged beech forests. Coniferous forests featured high amounts of leaf litter and low microbial biomass concentrations contrasting in particular unmanaged beech forests. However, soil animal diversity and functional community composition differed little between forest types, indicating resilience against disturbance and forest land use. Structural equation modelling suggested that despite a significant influence of forest management on resource abundance and quality, the biomass of most soil fauna functional groups was not directly affected by forest management or resource abundance/quality, potentially because microorganisms hamper the propagation of nutrients to higher trophic levels. Instead, detritivore biomass depended heavily on soil pH. Macrofauna decomposers thrived at high pH, whereas mesofauna decomposers benefitted from low soil pH, but also from low biomass of macrofauna decomposers, potentially due to habitat modification by macrofauna decomposers. The strong influence of soil pH shows that decomposer communities are structured predominantly by regional abiotic factors exceeding the role of local biotic factors such as forest type.

Soil fungal communities in abandoned agricultural land has not yet moved towards the seminatural forest

The increasing trend in the abandonment of agricultural land provides a unique opportunity for the restoration of forests. However, not only vegetation but also belowground microbial communities are vital for the development of stable forest stands. To assess whether soil fungi can affect the succession of abandoned agricultural lands, we analyzed soil fungal communities, including total and arbuscular mycorrhizal (AM) fungi in agricultural lands (AG), short- and long-term abandoned agricultural lands (SA and LA), and short- and long-term regenerating seminatural forests (SR and LR). Vegetation analysis showed that the abandoned lands were gradually converting to seminatural forests. However, significantly lower soil pH values and higher C and N concentrations were found in the LR forests than in the other land use types. Although there were no significant differences observed in the total and AM fungal diversity among land use types, the species compositions of seminatural forests (LR and SR), abandoned lands (SA and LA), and agricultural land (AG) were clearly differentiated in the ordination analysis. Significant differences were observed between AG and other land use types and between LR and abandoned land in the case of total fungal communities. The ECM fungi associated with Alnus occurred on the LA plots, whereas the LR plots were characterized by different ECM fungi (Russula, Lactifluus) and a high abundance of ericoid fungi along with hygrocyboid and clavarioid taxa. These results indicate that fungal succession is not as straightforward as vegetation changes. AM fungi will probably not constrain the abandoned land succession towards seminatural forests, but total fungal communities could be hindered by soil properties and absence of host trees.

A Medium-Term Field Experiment to Study the Effect of Managing Soil Chemical Properties on Fusarium Wilt in Banana (Musa AAA)

Fusarium oxysporum f. sp. cubense (Foc) is a soil-borne fungus causing Fusarium wilt (FW) in banana. It is practically impossible to eradicate Foc in soils. Our understanding of soil–Foc–banana interactions is hampered by inconsistent research results caused by agro-ecological variability and the complexity of the soil system. This study aimed to evaluate the options to manage soil chemical properties to reduce disease expression and maintain banana production. The expression of FW (Foc Race 1) and the agronomic performance of the Gros Michel (Musa AAA) banana were evaluated in two medium-term factorial field experiments at representative locations in the Costa Rican banana region. In the experiments, five soil chemical properties (pH, N, Ca, Mg, and Mn) were managed to achieve a low and a high level. Plant mortality caused by FW, soil fertility, plant nutrition, and agronomic performance were monitored during four crop cycles. After the first crop cycle, the treatments started to present differences in plant mortality. There was a significant rise of plant mortality after the second crop cycle resulting in a cumulative plant mortality exceeding 60% in both experiments. A lower soil pH consistently resulted in significantly higher plant mortality. The interactions between soil properties (pH-N, pH-CaMg, pH-Mn, N-Mn, and CaMg-Mn) also influenced plant mortality. Soil N was the most significant treatment affecting leaf nutrient concentrations, bunch weight, and clusters per bunch. The experiments confirmed the potential role of soil management in FW expression in banana. Our results suggest that the management of soil chemical properties in the conditions here studied may help to reduce the expression rate of FW, but not to control the disease in the long run.

Effects of mosaic biological soil crusts on vascular plant establishment in a coastal saline land of the Yellow River Delta, China

Abstract Aims The effects of biocrusts on vascular plants are rarely evaluated in coastal saline lands. Our aim was to examine whether and how a mosaic of biocrusts affect seed germination of two typical herbaceous plants in a coastal saline land of the Yellow River Delta, to enhance our understanding by which substrate heterogeneity influences plant community dynamics. Methods We conducted growth chamber experiments to investigate the effects of biocrusts and uncrusted soil from bare patch-, Phragmites australis-, Suaeda glauca- and Tamarix chinensis-dominated habitats on seed germination percentage and mean germination time of two herbaceous plants: the perennial P. australis and the annual S. glauca. We also explored the mechanisms underlying the effects of substrate on seed germination. Important Findings Compared with uncrusted soil, biocrusts increased water content, nutrient accumulation and concentration of most salt ions, but they reduced soil pH value. Biocrusts with mosses directly decreased soil pH value and concentration of Mg2+, resulting in an indirect increase in seed germination percentage of S. glaucas. The low soil pH value also resulted in an indirect decrease in seed germination speed of P. australis in their own habitats. Bare patch directly increased accumulation of Cl−, resulting in an indirect decrease in seed germination speed of P. australis. These results suggest that biocrusts with mosses in P. australis habitats offer a window of opportunity for germination of S. glaucas. Biocrusts combined with habitat type have the potential to influence plant community structure through an effect on seed germination and establishment.

Resprouting of the woody plant Pyrus calleryana influences soil ecology during invasion of grasslands in the American Midwest

Biological invasion of woody plants into grasslands is a widespread phenomenon that threatens the cultural value, biodiversity, and ecosystem function of these unique systems. In the American Midwest, grasslands are increasingly threatened by invasion of the tree Pyrus calleryana (Callery pear) which is particularly challenging to manage and has strong potential to alter ecosystem function. Mowing is a standard practice for maintaining Midwestern grasslands; however, P. calleryana exhibits an aggressive sprout response to cutting and the ecological implications of this behavior are not well understood. We measured the response of soil moisture and pH, and soil enzyme activities representing labile carbon cycling (β-glucosidase), recalcitrant carbon cycling (peroxidase and phenol oxidase), nitrogen cycling (leucine aminopeptidase) and phosphorus cycling (phosphatase) to determine how P. calleryana trees that are untreated and single stemmed alter nutrient cycling compared to their cut and resprouting counterparts. We found lower β-glucosidase activity and higher peroxidase activity underneath single stemmed trees than underneath those which had resprouted, indicating that there may be lower nutrient availability underneath untreated trees accounting for differences in enzyme activity. Generally, invasive species leaf litter has faster decay rates than native species, which results in higher activities of enzymes that degrade labile materials in soil underneath the plants. Because soils underneath P. calleryana do not follow this pattern, it is possible that its leaf material is not as labile as other common invaders. We also found that increasing P. calleryana basal diameter was associated with reductions in soil pH, which indirectly increased peroxidase and phenol oxidase activities, enzymes which are indicative of recalcitrant C sources such as lignin. This demonstrates that P. calleryana may alter carbon cycling by altering the C inputs to the soil system from its leaf litter. Taken together, P. calleryana may reduce plant richness and promote further invasion by lowering the availability of labile carbon and lowering soil pH, indicating that this invasion may be soil-mediated and self-reinforcing. Further, we recommend continued mowing as a treatment for P. calleryana invasion to ameliorate the impacts of its invasion even though there will likely be a sprout response to treatment.

Arbuscular Mycorrhizal Fungi Alleviate Drought Stress in Trifoliate Orange by Regulating H+-ATPase Activity and Gene Expression.

A feature of arbuscular mycorrhiza is enhanced drought tolerance of host plants, although it is unclear whether host H+-ATPase activity and gene expression are involved in the physiological process. The present study aimed to investigate the effects of an arbuscular mycorrhizal fungus (AMF), Funneliformis mosseae, on H+-ATPase activity, and gene expression of trifoliate orange (Poncirus trifoliata) seedlings subjected to well-watered (WW) and drought stress (DS), together with the changes in leaf gas exchange, root morphology, soil pH value, and ammonium content. Soil drought treatment dramatically increased H+-ATPase activity of leaf and root, and AMF inoculation further strengthened the increased effect. A plasma membrane (PM) H+-ATPase gene of trifoliate orange, PtAHA2 (MW239123), was cloned. The PtAHA2 expression was induced by mycorrhization in leaves and roots and also up-regulated by drought treatment in leaves of AMF-inoculated seedlings and in roots of AMF- and non-AMF-inoculated seedlings. And, the induced expression of PtAHA2 under mycorrhization was more prominent under DS than under WW. Mycorrhizal plants also showed greater photosynthetic rate, stomatal conductance, intercellular CO2 concentration, and transpiration rate and better root volume and diameter than non-mycorrhizal plants under DS. AMF inoculation significantly increased leaf and root ammonium content, especially under DS, whereas it dramatically reduced soil pH value. In addition, H+-ATPase activity was significantly positively correlated with ammonium contents in leaves and roots, and root H+-ATPase activity was significantly negatively correlated with soil pH value. Our results concluded that AMF stimulated H+-ATPase activity and PtAHA2 gene expression in response to DS, which resulted in great nutrient (e.g., ammonium) uptake and root growth, as well as low soil pH microenvironment.

Contrasting pathways of carbon sequestration in paddy and upland soils.

Paddy soils make up the largest anthropogenic wetlands on earth, and are characterized by a prominent potential for organic carbon (C) sequestration. By quantifying the plant‐ and microbial‐derived C in soils across four climate zones, we identified that organic C accrual is achieved via contrasting pathways in paddy and upland soils. Paddies are 39%–127% more efficient in soil organic C (SOC) sequestration than their adjacent upland counterparts, with greater differences in warmer than cooler climates. Upland soils are more replenished by microbial‐derived C, whereas paddy soils are enriched with a greater proportion of plant‐derived C, because of the retarded microbial decomposition under anaerobic conditions induced by the flooding of paddies. Under both land‐use types, the maximal contribution of plant residues to SOC is at intermediate mean annual temperature (15–20°C), neutral soil (pH~7.3), and low clay/sand ratio. By contrast, high temperature (~24°C), low soil pH (~5), and large clay/sand ratio are favorable for strengthening the contribution of microbial necromass. The greater contribution of microbial necromass to SOC in waterlogged paddies in warmer climates is likely due to the fast anabolism from bacteria, whereas fungi are unlikely to be involved as they are aerobic. In the scenario of land‐use conversion from paddy to upland, a total of 504 Tg C may be lost as CO2 from paddy soils (0–15 cm) solely in eastern China, with 90% released from the less protected plant‐derived C. Hence, preserving paddy systems and other anthropogenic wetlands and increasing their C storage through sustainable management are critical for maintaining global soil C stock and mitigating climate change.

Trifolium repens and T. subterraneum modify their nodule microbiome in response to soil pH.

The influence of soil edaphic factors on recruitment and composition of bacteria in the legume nodule is unknown. Typically, low (acidic) pH soils have a negative effect on the plant-rhizobia symbiosis and thereby reduce clover growth. However, the specific relationship between soil pH and the ecology of rhizobia is unknown, in either their free-living or nodule-inhabiting states. We used New Zealand pasture systems with soils of different pH, and white (WC) and subterranean (SC) clovers, to examine the relationship between soil pH and the diversity of bacteria that inhabit the nodules. Amplicon sequencing (16S rRNA) assessed the bacterial community in 5299 nodules recovered from both legume species grown in 47 soils of different edaphic (including pH) properties. Fewer nodules were formed on both clovers at low soil pH. As expected, rhizobia comprised ∼ 92% of the total reads in both clovers, however 28 non-rhizobia genera were also present. Soil pH influenced the community structure of bacteria within the nodule, and this was more evident in non-Rhizobium taxa than Rhizobium. Host strongly influenced the diversity of bacteria in the nodules. The alpha diversity of nodule microbiome in SC nodules was higher than in WC nodules and SC nodules also harbored a higher relative abundance of non-Rhizobium bacteria than WC. Beta diversity of Rhizobium and non-Rhizobium bacteria was influenced more by clover species rather than edaphic factors. The results indicate that these clover species modified their nodule biomes in response to pH-stress. The non-Rhizobium bacteria may have some functional significance (such as improved clover persistence in low pH soils) in legume nodules.

Soil fertility, enzyme activity, and microbial community structure diversity among different soil textures under different land use types in coastal saline soil

This investigation assessed the responses of soil fertility, enzyme activity, and microbial community diversity to soil texture and land use type. The tested soils included five soil textures (sandy loam, medium loam, heavy loam, light clay, and medium clay soils) with two land use types (uncultivated and paddy soils) in the coastal zone of Zhejiang Province, China. Soil texture had a significant effect on soil pH, electrical conductivity (EC), organic carbon (OC), total nitrogen (TN), available nitrogen (AN), phosphorus (AP) and potassium (AK), catalase and protease activities, total phospholipid fatty acids (PLFAs), bacterial and actinomycetes PLFAs, and microbial diversity (MD). The clay content was significantly positively correlated to soil EC, OC, TN, AN, AP, AK, catalase activity, total PLFAs, bacterial and actinomycetes PLFAs, and MD but significantly negatively associated with soil pH and protease activity. Land use type also had significantly influenced soil pH, EC, OC, TN, AN, AP, AK, catalase, protease and urease activities, total PLFAs, bacterial, actinomycetes, and fungal PLFAs, and MD. The paddy soil had higher OC, TN, AN, AP, catalase, protease and urease activities, total PLFAs, bacterial and actinomycetes PLFAs, and MD but lower soil pH, EC, and AK than the uncultivated soil. The interaction with soil texture and land use type had significantly affected soil pH, EC, OC, TN, AN, AP, AK, catalase and protease activities, total PLFAs, bacterial and actinomycetes PLFAs, and MD. Soil texture and land use type could be considered important factors in improving soil fertility, enzyme activity, and microbial diversity in coastal saline soils.

Optimizing the growth of forage and grain legumes on low pH soils through the application of superior Rhizobium leguminosarum biovar viciae strains

AbstractClimate variability and current farming practices have led to declining soil fertility and pH, with a heavy reliance on fertilizers and herbicides. The addition of forage and grain legumes to farming systems not only improves soil health but also increases farm profitability through nitrogen (N) fertilizer cost offsets. However, the formation of effective symbioses between legumes and rhizobia can be unreliable and is considered at risk when combined with dry sowing practices such as those that have been designed to obviate effects of climate change. This research was initiated to improve the robustness of the legume/rhizobia symbiosis in low pH, infertile and dry soils. Production from two cultivars of field pea (Pisum sativum) and two species of vetch (Vicia spp.), and symbiotic outcomes when inoculated with a range of experimental rhizobial strains (Rhizobium leguminosarum biovar viciae), was assessed in broad acre field trials which simulated farmer practice. New rhizobia strains increased nodulation, N fixation, produced more biomass and higher seed yield than comparator commercial strains. Strain WSM4643 also demonstrated superior survival when desiccated compared to current commercial strains in the laboratory and on seed when delivered as inoculant in peat carriers. WSM4643 is a suitable prospect for a commercial inoculant in Australia and other agricultural areas of the world where growing peas and vetch on soils generally considered problematic for this legume/rhizobia symbiosis. A particular advantage of WSM4643 may be that it potentiates sowing inoculated legumes into dry soil, which is a contemporary response by farmers to climate variation.

Improved Alfalfa Phosphate Utilization Using Zeolite Amendments in Low pH Soil

Soil amendments are used to increase the solubility of phosphate rocks (PRs) such that they can supply phosphorus (P) to high P-demanding crops. Zeolites are naturally occurring aluminosilicate minerals that can solubilize PRs and increase P nutrient supply. This study sought to evaluate the effects of zeolite addition in PR mixtures in dry matter yield (DMY), nutrient accumulation, and alfalfa’s agronomic efficiency. The experiment was conducted in a greenhouse where treatments comprised of two zeolites types (clinoptilolite and stilbite), three P sources (triple superphosphate-TSP, Morocco PR, and Cajati PR), five P levels (0, 22, 44, 87, and 131 mg kg−1), and five zeolites ratios (w/w) based on P2O5 levels (0, 25, 50, 100, and 200%). Eleven cuts of alfalfa were taken to quantify DMY and P accumulation. Alfalfa dry matter yield and P accumulation increased due to P fertilization. Reactive PR (Morocco) was more effective than TSP to increase alfalfa DMY and P accumulation. Phosphorus levels in soil did not increase with reactive PR (Morocco) fertilization and zeolite amendment. Zeolite stilbite just increased P solubilization and accumulation by alfalfa plants in a 150–200% ratio (zeolite/PR) with the low-reactive PR (Cajati). Under this experiment’s conditions, zeolite was not an efficient amendment combined with P soluble and reactive PR sources to increase alfalfa DM yield and P accumulation. Large amounts of zeolite were necessary to provide the low-efficiency PR source solubilization to satiate alfalfa P demand.

Quantitative Proteomics Analysis of Sugarcane Ratoon Crop Chlorosis

Sugarcane is the most important sugar and bioenergy crop. Sugarcane ratoon crop chlorosis, caused by deficiencies of Fe, Ca and Mg because of low soil pH and excessive absorption of Mn, is a major crop production constraint in China and reduces cane yield as much as 40%. The molecular basis of the ratoon crop chlorosis is little understood. In this study, we employed TMT-labeling quantitative proteomics approach to study the proteins associated with sugarcane ratoon crop chlorosis using chlorotic leaves collected from the field. An in-house transcriptome database for sugarcane leaf was also constructed. From the proteome database, 7480 sugarcane proteins were identified; among them, 199 and 80 were found to be up- and down-regulated by the chlorosis. By functional characterization and protein–protein interaction studies, we were able to identify the components and pathways that might play a role in sugarcane chlorosis response. In addition to genes associated with photosynthesis, drought-responsive and jasmonic acid biosynthesis genes were also found to be associated with ratoon crop chlorosis in sugarcane. Data obtained in the presented study provide the molecular details of sugarcane ratoon crop proteome response during chlorosis.

Effects of different carbon inputs on soil nematode abundance and community composition

Plants provide carbon (C) input to the soil and energy resources for soil food webs through litter and roots. However, it remains uncertain which C input pathway is more important and how different C inputs affect the community composition of the soil fauna. A long-term (9 years) field C input manipulation experiment was conducted to investigate the effects of C inputs on soil nematodes. Plant removal, litter addition, and litter removal were carried out to simulate changes in below- and aboveground C inputs. Results showed that plant removal significantly decreased soil resource availability (i.e., the soil organic C and total nitrogen). Plant removal also decreased nematode abundance (73.09%) and genus richness (17.98%). The relative abundance of bacterivores was enhanced but plant parasites and omnivores-predators were reduced by plant removal. The significantly lower soil pH and higher NO3−-N concentrations under the plant removal treatment are probably responsible for changing the community structure. Litter addition increased nematode abundance by 37.88%, but litter removal decreased the genus richness by 9.39%. There were significant interactive effects of plant removal and litter manipulation on the total nematode abundance and genus richness. Our observations suggest that belowground C input has greater impacts on soil nematodes than the above-ground C input, and that the impacts of litter on the soil nematode community could be mediated by living plants.

Soil fertility evaluation and quality of gambier (Uncaria gambir Roxb) in Kundur, Kepulauan Riau

Gambier is the main export commodity of Kepulauan Riau and its quality is highly affected by soil and climate characteristics. The research aim was to study potency of gambier crop based on the soil fertility evaluation and the quality of gambier products in Kundur, Kepulauan Riau. Study was conducted in Kundur Island, Kepulauan Riau from June to October 2018. The study method was a survey to characterize the land, identify the performance of gambier crop, and collect secondary data and gambier product samples. Results revealed that low to moderate soil fertility of the study area was indicated by low soil pH, total-N, P2O5, and K2O, low to moderate soil organic C and low to very low Ca2+, Mg2+, K+, and CEC, sandy loam to sand clay loam soil texture. Evapotranspiration of productive gambier crop is moderately high causing water deficit in January, February, and March. Based on SNI, catechin content of gambier product from West and North Kundur (52.98 and 50.14%) meet the Quality Standard 2, while from Kundur (13.19%) does not meet both Quality Standard 1 and 2. The study areas have a potency for developing gambier crop by providing fertilizer and ameliorant, and applying technology of water supplement.

Dynamics of acidity and electrical conductivity due to seawater amelioration in total reclaimed acid sulphate soils, South Kalimantan

The objective of our research was to determine the effect of inundation using seawater on the pH and EC of acid sulphate soils This research consisted of 2 stages, an incubation experiment carried out in the greenhouse, Indonesian Swampland Agricultural Research Institute (ISARI), Banjarbaru South Kalimantan and in the field of Handil, Maluka village, Bumi Makmur District, Tanah Laut Regency, South Kalimantan. The incubation experiment used several seawater concentrations of 0, 12.5, 25, 37.5 and 50%, with randomized complete design with 3 replications. The field experiment used a raise bed system with two treatment applications: (i) without brackish water and (ii) with brackish water. The results of the incubation experiment showed that the longer the incubation period and the higher seawater concentration caused a decrease in the soil pH while increasing EC values. Conversely, incubation of potential acid sulphate soils using well water (0% seawater) resulted in increasing soil pH and EC values. Field experiments showed that the application of brackish water on acid sulphate soil gave lower soil pH than that without brackish water. Contrary, EC values of acid sulphate soil applied with brackish water were higher than those without brackish water application.

Ecosystem properties in urban areas vary with habitat type and settlement age

Urban ecosystems comprise a range of habitats that support key ecosystem processes that are fundamental for the functioning of their soils. Relatively little is known about how different types of urban greenspaces and settlement ages influence the functioning of these important environments. We evaluated how four types of urban greenspaces (habitat types: natural areas, parks, gardens, roadside verges) and three settlement ages (5 to 150 years) influence multiple plant and soil ecosystem properties at 60 sites in two seasons in urban areas in eastern Australia. The type of urban greenspace and the age of the settlement influenced their ecosystem properties. In particular, habitat type had a greater effect on nutrient pools and plant biomass than settlement age, with greater nutrient pools in household gardens, but lower plant cover and plant height on roadside verges. Natural areas supported richer plant communities. We found that soil pH and soil moisture (particularly in summer) explained the contrasting effects of urban environments and settlement age on fundamental ecosystem properties. Older settlements tended to have lower soil pH, which was generally associated with greater enzyme concentrations. Soil pH effects varied depending on functions and season. Our work highlights the importance of considering settlement age and urban greenspace type for understanding the complexity of urban ecosystems, and the functions that they provide to humanity. Understanding the links between urban habitats, settlement age and ecological functions is a first step to promoting practices that sustain healthy and productive urban environments.

Reclamation of a calcareous sodic soil with combined amendments: interactive effects of chemical and organic materials on soil chemical properties

Concerns about population growth and producing adequate and nutritious food from the limited available resources have made soil conservation a top priority worldwide. This study assessed the effects of alfalfa residue (AR), sugarcane-bagasse biochar (SBB), and walnut-shell biochar (WSB) with or without gypsum (G), aluminum sulfate (AlS), and mixture of both chemical amendments on the chemical properties of a carbonated sodic soil. The organic and chemical ameliorants were added to the soil at rate of 2.5% (w/w) and the soil gypsum requirement, respectively. After a 4-month incubation, amended soils were measured for pH, electrical conductivity of saturated extract (ECe), sodium adsorption ratio (SAR), and exchangeable potassium (K) and available phosphorus (P) concentrations. Both chemical and organic amendments significantly lowered soil pH through enhancing CO2 partial pressure and/or dissolution of native soil calcites. The combined chemical and organic amendments performed more effectively than organics alone to increasing soil EC; the highest EC value was obtained by the application of G+AR (11.0 dS m−1). A synergistic effect of organic and chemical ameliorants on the replacement of exchangeable sodium by calcium was observed, which was reflected by the increased SAR values in treated soils compared with the control. Of the applied amendments, AR-alone has the best efficacy to improve soil available P by enhancing soil P concentration from 4.05 mg kg−1 in the control to 11.87 mg kg−1. Irrespective of chemical amendments, the most increase in soil exchangeable K concentration (from 45.16 mg kg−1 in the control to 274.00 mg kg−1) was obtained by applying WSB-alone to the soil. These results suggest that the partly degraded sodic soils could evolve for agricultural use by amending soils with specific kind of biochars and combined with best soil management practices.

Differential effects of various reclamation treatments on soil characteristics: an experimental study of newly reclaimed tidal mudflats on the east China coast

Reclamation of coastal land is increasingly being used as a means of raising agricultural productivity and improving food security in China. Applications of organic and inorganic supplements on reclaimed soils can significantly adjust a range of soil properties, C, N, P content and stoichiometry, and extracellular enzyme activities. However, the linkages between soil C꞉N꞉P stoichiometry and extracellular enzyme activities following reclamation of coastal saline soil remain largely unclear. In this experimental study, treatments included control (CK), chicken manure (OM), polyacrylamide plus chicken manure (PAM+OM), straw mulching plus chicken manure (SM + OM), buried straw plus chicken manure (BS + OM), and bio-organic manure plus chicken manure (BM + OM) were conducted to explore the linkages between soil physicochemical characteristics in reclaimed soils under different treatments and to evaluate their impact on oat yield. Soils under all reclamation treatments exhibited higher moisture content and, with the exception of SM + OM, lower soil pH compared to the control. The reclamation treatments also significantly decreased soil bulk density (BD) and soil salt content (SSC), and increased soil organic carbon (SOC), total nitrogen (TN) and organic phosphorus (OP). Our study of soil C꞉N꞉P stoichiometry revealed that newly reclaimed soils in the study area are N limited. Additionally, soil invertase (INV), urease (URE) and alkaline phosphatase (ALP) activity under different reclamation treatments were significantly enhanced compared with CK in surface soil, while soil catalase (CAT) activity was observed to be much higher in BM + OM than in other treatments. Mean oat yields for each of the treatments were ranked as follows: BM + OM > SM + OM > PAM + OM > BS + OM > OM > CK treatment. Our results also indicate that TN (12.1% and 12.4%) was the main factor affecting URE and ALP, whereas BD (13.5%) and pH (8.5) were key factors affecting INV and CAT activity, respectively.