Effects Of Soil Acidification Research Articles

Impact of Soil Acidity Influenced by Long-term Integrated Use of Enriched Compost, Biofertilizers, and Fertilizer on Soil Microbial Activity and Biomass in Rice Under Acidic Soil

To elucidate the effects of soil acidity influenced by 10 years of application of enriched compost (ECM), biofertilizers, and chemical fertilizers in integration on soil microbial activity and biomass in rice crop under acidic condition of soil. A field experiment was performed with five treatments, namely, T1, absolute control; T2, 100% recommended doses of nitrogen (N), phosphorus (P), and potassium (K); T3, 50% NP + 100% K + biofertilizers; T4, 50% NP + 100% K + 1 t ECM ha−1; and T5, 25% NP + 100% K + 2 t ECM ha−1, in a randomized block design. And each treatment was repeated four times. Experimental findings revealed that pH-dependent acidity, exchangeable acidity, and total potential acidity increased with soil depth; however, the application of ECM effectively controlled various forms of soil acidity by 31, 31, and 35%, respectively, in surface soil layer (0–5 cm). Soil acidity is greatly influenced by nutrient management practices; thus, the ECM application recorded significantly higher soil microbial biomass and soil functional diversity within all layers of soil over the 100% recommended dose of fertilizer (RDF) (T2). In comparison to 100% RDF, integrated nutrient management (INM) practices enhanced the microbial activities, viz., β-glucosidase, β-galactosidases, β-glucosaminidase, phenol oxidase, and peroxidase activities, by 18, 19, 20, 21, and 8%, respectively, at the surface soil layer. The use of ECM and chemical fertilizers in integration increases enzymatic activity and microbial density in the soil by controlling various forms of soil acidity.

Agrogenic transformation (degradation) of chernozems of the Central Chernozem Region

Modern agriculture is impossible without the use of high balanced doses of mineral fertilizers. Mineral fertilizers in the modern volumes of their application are a powerful anthropogenic factor that increases the level of supply of agricultural crops with nutrients, but did not ensure the stability of yields. The long-term use of high doses of fertilizers does not allow to reach a deficit-free balance of fertilizer elements in agriculture and crop production. Studies of many scientists have shown that the long-term use of mineral fertilizers, in addition to the direct effect, causes a number of side effects, and contributes to the development of pronounced acidification of soils. This effect is observed in all agricultural zones, regardless of soil types. It is more pronounced on initially genetically acidic sod-podzolic and gray forest soils, but also on chernozems, which were considered resistant to acidification development. The consequences of soil acidification are manifested in the mobility and, as a result, the availability of fertilizer elements. Nevertheless, the main effect of soil acidification when using fertilizers is the lack of absorbed bases, which causes their progressive degradation. The acidification effect can be compensated by regular (once per rotation) liming.

Evaluation of incorporated phosphorus fertilizer recommendations on no‐till managed winter wheat

AbstractThe current Oklahoma State University Soil, Water, and Forage Analytical Laboratory (OSU) phosphorus (P) recommendations were developed for conventional tillage systems with P fertilizer incorporated in the soil. The rate recommendations were based on a sufficiency approach, and included a pH adjustment factor. Increased adoption of no‐till (NT) management across the region has resulted in more surface application of fertilizer, without concomitant changes in OSU recommendations. In the 2014–2015 and 2015–2016 growing seasons, nine on‐farm trials were conducted in north‐central Oklahoma to evaluate current winter wheat (Triticum aestivum L.) P recommendations, and grain yield responses to fertilizer in both P‐sufficient and P‐deficient soils, and acidic or non‐acidic conditions. Phosphorus fertilizer was recommended for eight of the nine locations, while responses were recorded at only five of those eight locations. The results indicate that OSU P recommendations, with a soil acidity adjustment factor, did not limit winter wheat grain yields in NT management. In addition, the application of 30 lb acre–1 P2O5 offset the effects of soil acidity on P uptake regardless of the degree of acidity. Finally, OSU recommended P on some locations where there was no response, suggesting more work is needed to understand crop response dynamics and build recommendations with increased location specificity.

Effects of gypsum on growth and nutrient status of forage grasses cultivated between the rows of organically grown Satsuma mandarin in an Oxisol from subtropical Brazil

Gypsum (CaSO4.2H2O) decreases the harmful effect of soil acidity on plants and provides calcium (Ca) and sulfur (S) for plant nutrition. Setaria grass (Setaria anceps Stapf) and black oat (Avena strigosa Schreb.) are forage grasses that are tolerant of low soil fertility and may be suitable as inter-row crops for Satsuma mandarin (Citrus unshiu Marc.) grown organically on Oxisol soils, which may suffer low native fertility and high acidity. We evaluated the effect of gypsum application to a low fertility soil from subtropical Brazil on soil chemical fertility, growth and plant nutrition of Satsuma mandarin, and plant biomass yield and soil nutrient extraction of setaria grass and black oat cultivated between the orchard rows, in the absence of soluble industrial (NPK) fertilisers. The entire experimental field was limed, and ground natural phosphate rock was applied. During planting of the Satsuma mandarin, organic manure and ground natural phosphate rock were mixed with soil and placed in each planting hole. Two agricultural gypsum treatments were applied: one without gypsum (control), and the other with gypsum at 6 t ha−1. After 12 months, gypsum reduced the level of aluminium (Al3+) and increased Ca2+ at soil depth 0–40 cm, and increased S-SO42− at soil depth 0–60 cm. Other soil chemical components (pH, phosphorus, potassium, magnesium and micronutrients) were not affected by gypsum application. Gypsum did not affect growth of Satsuma mandarin, but increased leaf S concentration. Between the rows, gypsum decreased nitrogen extraction by setaria grass and increased Ca and S extractions by black oat. Biomass yield and nutrient extraction by the studied forage grasses were satisfactory, considering the poor soil fertility conditions. Setaria grass exhibited higher efficiency in recycling nutrients from the chemically poor soils than black oat. In general, setaria grass and black oat can be used as inter-row forage grasses for organic orchards of Satsuma mandarin, where there are restrictions on use of soluble industrial fertilisers.

Responses of Acidic Soil to Lime and Vermicompost Application at Lalo Asabi District, Western Ethiopia

Soil acidity is one of the major yield-limiting factors for crop production worldwide, particularly on highly weathered and leached tropical soils. Different reports have indicated that there is significant soil acidity coverage in Ethiopia, particularly in the western part of the country; soil acidity is a well-known problem limiting crop production and productivity. As part of the solution to such problem in soils, combined application of lime and VC on maize has not been investigated in the area, in which maize was one of the potential cereal crops in the area. Field experiment was conducted at Lalo Asabi district in western Wollega during 2019/20 cropping season to evaluate the responses of acidic soil to the combined application of lime and vermicompost (VC). The experimental treatments were five rates of lime (CaCO₃) (0, 25, 50, 75, and 100% of lime requirement (LR)) and three levels of vermicompost (0, 2.5 and 5 t ha^-1). The treatments were arranged in factorial combinations in randomized complete block design with three replications. One composite surface soil samples from a depth of (0-15 cm) were collected from the experimental field before commencement of the experiment. A total of fifteen composited soil samples were also collected from each plot and then composited by replication to obtain one representative sample per treatments for determination of selected soil physicochemical properties. The soil analysis results revealed that soil pH increased from 5.1 (strongly acidic) to 5.8 (moderately acidic) while exchangeable acidity decreased from 2.44 to 0.31 cmol_c kg^-1 under combined application of lime at 75% LR+2.5 t VC ha^-1, which resulted in improvement of others selected soil physicochemical properties. This study indicates combined use of lime and VC could ameliorate the adverse effect of soil acidity at Lalo Assabi district.

Response of soybean (Glycine max L.) to application of lime and phosphate fertilizer in an acid soil of western Kenya

The effect of combining lime and phosphate fertilizer on the performance of soybean (Glycine max L.) was investigated in a pot experiment consisting of nine treatments of three rates of lime (0, 4 and 8 t ha−1) in a factorial combination with three rates of phosphorus (0, 15, and 30 kg P ha−1) at Maseno University in western Kenya. There was a significant interaction between the lime and phosphorus rate on the biomass dry weight of soybean. At the rates of 0 and 4 t ha-1 of lime, the biomass dry weight of soybean increased with increasing rates of phosphorus but at 8 t ha-1 of lime, the dry weight of soybean increased from 0 to 15 kg P ha-1 but declined at 30 kg P ha-1. There was however no significant interaction between lime and P rates on grain weight but the effects of both P and lime rate were significant. When applied without lime, 30 kg P ha-1 gave significantly higher grain (5.3 g pot-1) weight than 15 kg P ha-1 (1.6 g pot-1) of soybean, which was also significantly better than the control (0.0 g pot-1). When applied without phosphorus, both lime rates at 4 and 8 t ha−1 significantly increased grain weights of soybean compared to the control, but the grain weights of soybean between the two lime rates did not differ significantly. The highest yields of soybean were obtained when 4 t ha−1 of lime was applied with 30 kg P ha−1 (19 g pot-1). Therefore, this study demonstrates that the ameliorating deleterious effects of soil acidity through liming should simultaneous be accompanied by application of P fertilizer at appropriate rates.

Foliar application of magnesium mitigates soil acidity stress in wheat

AbstractSoil acidity is one of the most important soil constraints for wheat growth, and magnesium (Mg) can play a critical role in mitigating the adverse effects of soil acidity on plants. There is, however, limited information available about the influence of Mg nutrition, especially foliar application, on wheat (Triticum aestivum) growth in acidic soil. In a series of glasshouse experiments, Al‐sensitive wheat genotype (ES8) was grown to vegetative stage (Zadoks 23) with or without foliar Mg application at different rates (0, 50, 200 and 1,000 mg Mg/L), and acidic soil was used as the growth medium with or without lime and Mg amendment. The effects of these treatments on plant growth, physiological responses, tissue concentration of Mg, dry biomass accumulation and root length were characterized. Magnesium application to foliage significantly increased (by around 14%) both shoot and root dry biomass compared to the control (0 foliar Mg). No significant variation was observed in response to different Mg salts (sulphate or chloride) applied to either soil or foliage in relation to wheat growth and physiological responses. Other than liming, foliar Mg application (200 mg Mg/L) coupled with Mg application to soil (20 mg/kg soil) provided optimum conditions for wheat growth in an acid soil. Leaf extension rate, chlorophyll content and root length of wheat treated with 200 mg Mg/L foliar application were increased significantly (by 12%, 10% and 23%, respectively) in comparison to plants treated with 0 foliar Mg. Physiological parameters such as net photosynthetic rate, transpiration rate and stomatal conductance were 4‐fold higher in foliar Mg‐treated plants compared with those receiving no foliar Mg. Therefore, applying 200 mg Mg/L to the foliage may assist in minimizing the negative impact of soil acidity on wheat growth.

Study of the Effects of Soil Acidity and Salinity on Aluminium Mobility in Selected Soil Samples in Sri Lanka

Aluminium is the most abundant metal in the earth’s crust. In soil, aluminum is mainly found in the mineral form as aluminosilicates and aluminum oxides and this aluminium is in stable inactive form. In addition, Al can be found as precipitates or in very minute quantities appear in soluble forms such as conjugated organic and inorganic, and molecular ions. Aluminium mobility and as a consequence aluminium toxicity, is mainly restricted to acid environments. Depending on the soil pH these mobile forms are capable of influencing biological systems. Aluminium has low mobility under most environmental conditions. However, below a pH of 4.0 its solubility increases and aluminium is released from silicate rocks under such acidic conditions. The levels of dissolved aluminium in natural groundwater samples are generally low, probably due to its low solubility at neutral pH values. Release of acids by anthropogenic activities influence the soil acidity levels. Therefore, elevated levels of aluminium have been found in acidified soil solutions and surface waters causing harmful effects to living organisms. The present study was aimed at proving the above theoretical hypothesis and existence of a possible relationship between soil salinity and soil acidity on the concentration of mobile aluminium ions in samples obtained during the location surveys. Samples were collected from selected locations in Ratnapura, Rathupaswala, Marawila, Mabima and Muthurajawela to get different soil types and the survey results were used to test the hypothetical relationship between the presence of the stated factors, and the existence of a high concentration of mobile aluminium in the soil water samples. The analysis covered basic parameters such as soil pH, soil cation exchange capacity (CEC), soil organic matter, soil electrical conductivity and the influence of the concentration of mobile aluminium at different pH and Na+ concentration levels. The total aluminium concentration in the soil was assayed by digesting samples with strong acid. Concentration of mobile aluminium in soil samples were analyzed using the flame atomic absorption spectrophotometry. The results indicated that there is no clear relationship between mobile aluminium and total aluminium in the soil. It was also found that the concentration of mobile aluminium released increased with decrease in soil pH and that the increase was marked when the pH of soil water was less than 4.0. Highest mobile aluminium release to the soil solution was found from Mabima sites [at pH 5.00 was 0.54 (±0.06) mg kg-1 of dry soil, at pH 0.00 was 90.12 (±7.01) mg kg-1] and least in samples from Marawila sites [at pH 5.00 was 0.48 (±0.03) mg kg-1, at pH 0.00 was 4.52 (±0.36) mg kg-1]. This result confirmed that there is an effect of soil acidity on the concentration of mobile aluminium in the soil but with no direct correlation. Results also showed that the concentration of mobile aluminium released increased with increasing soil salinity and that the increase was rapid when the Na+ ion concentration was higher than 2.0 %. Highest mobile aluminium release to the soil solution was found from Muthurajawela sites [Na+ 1.0% = lower than detection limit, Na+ 5.0% = 9.87 (±0.67) mg kg-1] and least found from Marawila sites [Na+1.0% = lower than detection limit, Na+ 5.0% = 2.24 (±0.23) mg kg-1] confirming the effect of soil salinity on the concentration of mobile aluminium in the soil. The study also points towards the future opportunities for research to confirm these findings using wider samples and employing more vigorous research methodologies.

Effects of synthetic nitrogen fertilizer and manure on fungal and bacterial contributions to N2O production along a soil acidity gradient

Reactive nitrogen (Nr) input often induces soil acidification, which may in turn affect bacterial and fungal nitrogen (N) transformations in soil and nitrous oxide (N2O) emissions. However, the interactive effects of soil acidity and Nr on the contributions of bacteria and fungi to N2O emissions remain unclear. We conducted a field experiment to assess the effects of anthropogenic Nr forms (i.e., synthetic N fertilizer and manure) on bacterial and fungal N2O emissions along a soil acidity gradient (soil pH = 6.8, 6.1, 5.2, and 4.2). The abundances and structure of bacterial and fungal communities were analyzed by real-time polymerase chain reaction and high-throughput sequencing techniques, respectively. Soil acidification reduced bacterial but increased fungal contributions to N2O production, corresponding respectively to changes in bacterial and fungal abundance. It also altered bacterial and fungal community structures and soil chemical properties, such as dissolved organic carbon and ammonia concentrations. Structural equation modeling (SEM) analyses showed that the soil properties and fungal community were the most important factors determining bacterial and fungal contributions to N2O emissions, respectively. The fertilizer form markedly affected N2O emissions from bacteria but not from fungi. Compared with synthetic N fertilizer, manure significantly lowered the bacterial contribution to N2O emissions in the soils with pH of 5.2 and 4.2. The manure application significantly increased soil pH but reduced nitrate concentration. The fertilizer form did not significantly alter the bacterial and fungal community structures. The SEM revealed that the fertilizer form affected the bacterial contribution to N2O production by changing the soil chemical properties. Together, these results indicated that soil acidification enhanced fungal dominance for N2O emission, and manure application has limited effects on fungal N2O emission, highlighting the challenges for mitigation of soil N2O emissions under future acid deposition and N enrichment scenarios.

The effect of soil acidity on some growth-related traits of soybean genotypes

The effect of soil acidity on some growth-related traits of soybean genotypes

Soil acidification alters root morphology, increases root biomass but reduces root decomposition in an alpine grassland

Soil acidification has been expanding in many areas of Asia due to increasing reactive nitrogen (N) inputs and industrial activities. While the detrimental effects of acidification on forests have been extensively studied, less attention has been paid to grasslands, particularly alpine grasslands. In a soil pH manipulation experiment in the Qinghai-Tibet Plateau, we examined the effects of soil acidification on plant roots, which account for the major part of alpine plants.After three years of manipulation, soil pH decreased from 6.0 to 4.7 with the acid-addition gradient, accompanied by significant changes in the availability of soil nitrogen, phosphorus and cations. Plant composition shifted with the soil acidity, with graminoids replacing forbs. Differing from findings in forests, soil acidification in the alpine grassland increased root biomass by increasing the fraction of coarse roots and the production of fine roots, corresponding to enhanced sedge and grass biomass, respectively. In addition, litter decomposability decreased with altered root morphological and chemical traits, and soil acidification slowed root decomposition by reducing soil microbial activity and litter quality.Our results showed that acidification effect on root dynamics in our alpine grassland was significantly different from that in forests, and supported similar results obtained in limited studies in other grassland ecosystems. These results suggest an important role of root morphology in mediating root dynamics, and imply that soil acidification may lead to transient increase in soil carbon stock as root standing biomass and undecomposed root litter. These changes may reduce nutrient cycling and further constrain ecosystem productivity in nutrient-limiting alpine systems.

Maize second-crop intercropped with forages and soil correction depths: grain yield and forages root distribution

Correction of soils is a required practice that aims to reduce the harmful effects of soil acidity, promote better development of the plants and ensure the productive potential of agriculture. In this sense, the objective of this work was to evaluate the maize yield in monoculture and / or intercropped and to study the development of Urochloa spp roots according to different combinations of chemical correction of the soil in rainfed conditions. The experiment was developed in an experimental area, Selvíria, MS, Brazil in dystrophic Oxisol. The experimental design used was the randomized blocks with subplots, with three replications. The soil correction treatments were arranged in the plots (control, gypsum, lime (0 - 0.2 m); lime and gypsum (0 - 0.2 m); lime (0 - 0.4 m); lime and gypsum (0 - 0.4 m)), and the subplots were occupied with maize, maize intercropped with U. ruziziensis or with Mulato II hybrid (Convert HD 364) The two intercrop with forages produced sufficient amounts of straw to start and/or maintain no-tillage system in the Cerrado region and the presence of forage in maize crop did not influence grain yield. The Mulato II hybrid had a larger root diameter, being more indicated for compacted soils, however longest root lengths were obtained by U. ruziziensis.

High Aluminium Concentration and Soil Acid Saturation Reduce Germination, Emergence and Seedling Establishment of Groundnut

Studies on crop responses to soil acidity have largely neglected the germination and seedling establishment stages. The objective of this study was to determine the effect of soil acidity, including aluminium per se and acid saturation, on germination, emergence and establishment of groundnut seeds. Germination was carried out on groundnut cultivars Harts, Jasper and Rambo under 0, 50, 100 and 200 μM Al applied as Al2 (SO4)3.18H2O at pH between 4.2 and 4.5. Seedling emergence and establishment were examined in 0, 3 and 6 g of dolomitic lime per kg of soil, representing control, 50% lime requirement and 100% lime requirement, respectively. High Al concentration of 200 μM reduced germination, germination velocity index and seminal root length but had no influence on mean germination time of all groundnut cultivars. There were highly significant differences (P<0.001) in seedling emergence between non-limed and limed soils. Root length and mass were significantly (P<0.05) reduced at high soil acidity but the cultivar Rambo was least susceptible. We conclude that the germination, emergence and establishment stages were negatively affected by high Al levels and acid saturation but the cultivars showed different tolerance levels to high acid saturation, and proper liming can ameliorate the problems associated with these growth stages.
 Key words: acid saturation, aluminium, establishment, peanuts, tolerance

Effects of biochar particle size and concomitant nitrogen fertilization on soil microbial community structure during the maize seedling stage.

Biochar is widely used as a soil amendment, either alone or in association with fertilizer. However, the effects of biochar particle size on the soil microbial community are largely unclear. Biochar was divided into two groups according to diameter sizes: < 1mm and 2.5-5mm (labeled as CB1 and CB5, respectively). A pot experiment was established in which maize (Zea maize L.) was treated with CB1, CB5, and/or external nitrogen (N, NH4NO3). At the end of the seedling period (45days), analyses of soil microbial community structure and other soil and crop properties were conducted. The biochar (regardless of N addition) enhanced microbial biomass and activity. CB1 had a stronger capacity than CB5 to modify soil microbial community structure by promoting soil microbial groups (e.g., fungi, Gram-negative bacteria), which is likely due to CB1 undergoing a series of more intense processes (e.g., nutrient release, mineralization) than CB5. However, this difference was diminished or disappeared when N was added, mainly due to the masking effect of soil acidification that was induced by N fertilization. Collectively, fine biochar has a stronger effect on soil microbial community than coarse biochar. Particle size only affects soil microbial community structure when biochar is applied alone; it has no effect when biochar is applied in association with chemical N fertilizer, at least during the seedling period. The relationship between particle size and soil microbial community needs to be considered when using biochar for soil amendment.

Identification of acid-tolerant coffee genotypes in a coffee germplasm collection of Colombia

One of the limitations of coffee production in many regions of Colombia is the soil acidity. According to historical soil chemical analysis records, more than 50% of coffee farms have pH values below 5.0. Because acid-tolerant coffee varieties are not available, farmers use calcareous additives to correct the problem, which incurs associated labor and input costs. The objective of this work was to identify acid-tolerant genotypes of Coffea arabica. For two contrasting soils in the coffee-growing area of Colombia (Andisol and Entisol), the effect of soil acidity on the growth of 20 genotypes of Coffea arabica during the seedling stage was evaluated. The genotypes were wild accessions that make up the Colombian Coffee Germplasm Collection and the Castillo® Naranjal Variety, used as commercial material. Six months after the seedlings were transplanted into soils treated with or without acidity correction additives, the weight of the dry matter of the roots, stems and leaves was recorded. Later, the acid-tolerant genotypes were identified by means of the quadrant method and the tolerance index. The Timor Hybrid and Rume Sudan genotypes were identified as tolerant of the acidity of the two soil types. These genotypes could be used as progenitors in a coffee breeding program leading to a commercial coffee variety tolerant to soil acidity. Key words: Andisol; entisol; Coffea arabica L.; timor hybrid; rume sudan.

Alleviating Soil Acidity: Optimization of Lime and Zinc Use in Maize (Zea mays L.) Grown on Alfisols

ABSTRACTSoil acidity, one of the causes of soil degradation, adversely affects phytoavailability of soil nutrients and crop growth in 50% of arable land of the world. There is a persistent need for alleviating the effect of soil acidity for adequate nutrient availability and proper crop growth. Addition of ameliorants like farmyard manure (FYM) and lime to acid soils affects the crop growth and nutrient availability, especially zinc (Zn) availability, by moderating soil acidity. However, the information regarding optimum quantities of lime and zinc requirement for alleviating soil acidity, proper crop growth, and Zn nutrition in acid soil is limited. Therefore, the present greenhouse pot experiments were carried out at ICAR-Indian Institute of Soil Science, Bhopal, India, in kharif season of 2015 using two acid soils (representing Alfisol order) to optimize lime and Zn application and to understand the impact of FYM and lime application on soil properties, phytoavailable Zn, biomass yield of maize, and Zn uptake, for better growth and Zn nutrition of maize. Maize was raised for 60 days with two levels of FYM (0 and 4,500 mg kg−1), five levels of lime requirement (LR) (0, 1/10th, 1/3rd, 2/3rd, and 1.0), and three Zn levels (0, 2.5, and 5.0 mg kg−1). Results revealed that FYM and lime addition significantly influenced soil properties, biomass yield, and postharvest soil extractable Zn. Lime addition at 1/3rd LR was found optimum as biomass yield enhanced up to this level of liming. FYM addition augmented biomass yield. A higher amount of lime (2/3rd and 1.0 LR) led to a reduction in crop Zn concentration and its uptake. The phytoavailable Zn extracted by different extractants in soils declined with increasing lime rates. Zn addition enhanced biomass yield and crop Zn concentration. The lowest and the highest amount of Zn were extracted from the soil at all levels of lime addition by diethylenetriaminepentaaceticacid (DTPA) and 0.1 M HCl, respectively. The extractable Zn was correlated significantly with biomass yield, crop Zn concentration, and its uptake. Ammonium bicarbonate DTPA (ABDTPA) proved promising extractant for estimation of Zn availability in these acid soils. This knowledge will be of use for alleviation of acid soils by the addition of the required quantity of lime and effective Zn management in acid soils for proper Zn nutrition and crop growth.

Effect of soil acidification on the growth and nitrogen use efficiency of maize in Ultisols

To examine the effect of soil acidification on growth and nitrogen (N) uptake by maize in Ultisols. A clay Ultisol derived from Quaternary red earth and a sandy Ultisol derived from tertiary red sandstone were used in this study. A pot experiment was conducted with maize growing in the two Ultisols acidified to different pH values. Urea with 15N abundance of 10.11% was used to investigate the distribution of N fertilizer between soil and plant. Total N content and 15N abundance in plant and soil samples were determined by elemental analysis-isotope mass spectrometry. Critical soil pHs of 4.8 and 5.0 were observed for maize growing in the clay and sandy Ultisols, respectively. Below the critical soil pH, increasing soil pH significantly increased maize height and the yield of maize shoots and roots (both P < 0.05), but changes in soil pH showed no significant effect on maize growth above the critical soil pH in both Ultisols. Maize growing in the sandy Ultisol was more sensitive to changes in soil pH than in the clay Ultisol. Increase in the pH in both Ultisols also increased N accumulation in maize, the N derived from fertilizer in maize, physiological N use efficiency, and N use efficiency (NUE) by maize. Changes in soil pH had a greater effect on these parameters below the critical soil pH, compared to above. The change in soil pH had a greater effect on N accumulation in maize, the N derived from fertilizer in maize, and NUE in the sandy Ultisol than in the clay Ultisol. The NUE increased by 24.4% at pH 6.0, compared with pH 4.0 in the clay Ultisol, while the NUE at pH 5.0 was 4.8 times that at pH 4.0 in the sandy Ultisol. The increase in soil pH increased the ratio of N accumulation in maize/soil residue N and decreased the potential loss of fertilizer N from both Ultisols. Soil acidification inhibited maize growth, reduced N uptake by maize, and thus, decreased NUE. To maintain soil pH of acidic soils above the critical values for crops is of practical importance for sustainable food production in acidic soils.

Restoring effect of soil acidity and Cu on N2O emissions from an acidic soil

Heavy metals are believed to impact soil processes by influencing microbial communities, nutrient cycling or exchanging for essential plant nutrients. Soil pH adjustment highly influences the bio-availability of nutrients and microbial processes. We examined the effect of soil pH manipulation and copper (Cu as CuCl2.2H2O) application on nitrogen (N) cycling and nitrous oxide (N2O) emissions from an acid soil. Increasing amounts of Cu (0, 250, 500 and 1000 mg kg−1) were added to an acidic soil (pH = 5.44) that was further amended with increasing amounts of dolomite [CaMg(CO3)2] to increase soil pH. Dolomite increased soil pH values, which reached a maximum without Cu application (-Cu) at day 42 of the experiment. The soil pH values decreased with increasing dose of Cu, and remained low as compared with both control and dolomite amended soil. Ammonium (NH4+-N) concentrations were higher in Cu contaminated soil as compared with the control and dolomite treated soil. Nitrate (NO3−-N) concentrations increased in dolomite treated soil when compared with the +Cu alone treatments and control. Microbial biomass carbon (MBC) and nitrogen (MBN) contents were higher in dolomite treated soil as compared with the +Cu treatments and control. The application of increasing amounts of Cu progressively decreased soil MBC and MBN. Nitrous oxide emissions were higher (p ≤ 0.01) in +Cu soil as compared with the control, and increased with increasing Cu concentration in soil. Application of dolomite highly suppressed soil N2O emissions in both +Cu and –Cu soils. The results indicate that the effects of heavy metal contamination (specifically Cu contamination) can increase N2O emissions, but this can be effectively mitigated through increasing soil pH, also decreasing potential toxic effects on soil microorganisms.

Litter quality and the law of the most limiting: Opportunities for restoring nutrient cycles in acidified forest soils

The adverse effects of soil acidification are extensive and may result in hampered ecosystem functioning. Admixture of tree species with nutrient rich litter has been proposed to restore acidified forest soils and improve forest vitality, productivity and resilience. However, it is common belief that litter effects are insufficiently functional for restoration of poorly buffered sandy soils. Therefore we examined the effect of leaf litter on the forest floor, soil chemistry and soil biota in temperate forest stands along a range of sandy soil types in Belgium, the Netherlands and Germany. Specifically, we address: i) Which tree litter properties contribute most to the mitigation of soil acidification effects and ii) Do rich litter species have the potential to improve the belowground nutrient status of poorly buffered, sandy soils? Our analysis using structural equation modelling shows that litter base cation concentration is the decisive trait for the dominating soil buffering mechanism in forests that are heavily influenced by atmospheric nitrogen (N) deposition. This is in contrast with studies in which leaf litter quality is summarized by C/N ratio. We suggest that the concept of rich litter is context dependent and should consider Liebig's law of the most limiting: if N is not limiting in the ecosystem, litter C/N becomes of low importance, while base cations (calcium, magnesium, potassium) become determining. We further find that on poorly buffered soils, tree species with rich litter induce fast nutrient cycling, sustain higher earthworm biomass and keep topsoil base saturation above a threshold of 30%. Hence, rich litter can trigger a regime shift to the exchange buffer domain in sandy soils. This highlights that admixing tree species with litter rich in base cations is a promising measure to remediate soil properties on acidified sandy soils that receive, or have received, high inputs of N via deposition.

Biogeochemical responses of soil ecosystems to raw coal pollution in Xuanhua, China

China is the world’s largest coal producer and consumer. Despite extensive studies on coal-burning pollution, the effect of raw coal pollutants caused by transportation and turnover on soil along the road received little attention. The main purpose of the study was to clarify the biogeochemical response of soil ecosystems to raw coal pollution. The raw coal and unpolluted soil from the coal distribution area in Xuanhua, China were collected for the incubation experiments. Combined with the determination of soil physicochemical properties, including pH, electric conductivity, soluble ions, dissolved organic carbon, and available heavy metals, the biogeochemical responses of soil to raw coal pollution, such as soil enzyme activities (β-glucosidase, alkaline phosphatase, and Urease), microbial community composition, and soil respiration, were systematically studied. In addition, a q-PCR analysis of the urease was performed to clarify the inhibitory mechanism of urease by coal pollution. Furthermore, a simple field investigation was carried out to confirm the incubation results. Raw coal pollution not only changed the soil physicochemical properties but also made the available Zn, Ni, and Co accumulate significantly. A positive priming effect in soil with the low-dose raw coal addition was trigged, but soil respiration rate and soil enzyme activity, such as β-glucosidase and alkaline phosphatase, were inhibited to different degrees with the increased pollution. Urease activity also decreased under the higher coal contamination, which was due to inhibition of ureC gene expression. In addition to the slight soil acidification caused by coal pollution, microbial communities and diversity was also found to be affected. The relative abundances of the microorganisms related to urease, alkaline phosphatase, and β-glucosidase changed accordingly. The incubation results are in good agreement with the field survey results. Low-dose raw coal pollution can trigger the soil positive priming effect. However, as the coal pollution increased, the β-glucosidase, alkaline phosphatase, and urease in the soil were inhibited to varying degrees. The compounding effects of soil acidification, increased electric conductivity, and the accumulation of available heavy metals such as Zn, Ni, and Co are the key causes for the biogeochemical response of soil to coal pollution.