Soil Buffering Capacity Research Articles

Temporal changes of calcareous soil properties and their effects on cadmium uptake by wheat under wastewater irrigation for over 50 years

Calcareous soil has a strong buffering capacity for neutralizing acid and stabilizing cadmium (Cd) because of the high calcium carbonate (CaCO3) content. However, it is not clear whether the buffering capacity of calcareous soil can be maintained after long-term wastewater irrigation. We selected a typical area in western China that has been irrigated with wastewater for over 50 years to study the temporal changes of soil properties and their effects on Cd uptake by wheat. The results showed that compared with the background level before the 1960s, the soil pH and CaCO3 content in 2018 were lower by 0.80 units and 35%, respectively, while the soil organic matter (SOM) content, Olsen phosphorus (P) content, and soil total Cd content in 2018 increased by 1.54, 13.05, and 164 times, respectively. Due to the significant decrease in the soil pH and CaCO3, the high load of soil total Cd and electrical conductivity, the low soil clay content, and the coupling of SOM with soil nitrogen and P, the input Cd was activated. Furthermore, the activated Cd was effectively taken up by wheat roots and transported to grains with the assistance of dissolved organic carbon. Our results highlight that long-term wastewater irrigation caused irreversible damage to soil buffering capacity, resulting in the Cd activation and the enhancement of Cd uptake by wheat.

Effects of fertilization and water addition on soil acid neutralizing capacity in an old-field grassland

Increasing nitrogen (N) deposition results in soil acidification in grasslands. Acid buffering capacity of soil is a critical index evaluating soil acidification, the response of which to N input is regulated by precipitation and concentration of other limiting elements. To explore the responses of soil acidification to N, phosphorus (P), and water inputs, we conducted a 13-year field experiment in an old-field grassland and calculated the acid buffering capacity (ABC) and acid neutralizing capacity (ANC) at the reference of pH=5.0 (ANCpH5.0) and 4.0 (ANCpH4.0), using quadratic curve fitting model. The results showed that, without water addition, single N addition or combined with P addition significantly decreased soil pH, ANCpH5.0 and ANCpH4.0, whereas single P addition had no significant effect on soil pH, ANCpH5.0 or ANCpH4.0. With water addition, the addition of N or combined with P decreased soil pH, ANCpH5.0 and ANCpH4.0, whereas P addition decreased soil pH, increased ANCpH4.0, without effect on ANCpH5.0. In contrast with treatments without water addition, water addition had positive effects on soil pH, ANCpH5.0 and ANCpH4.0. For soils with different initial soil pH values, it was better to select ANC rather than ABC as an index to evaluate soil anti-acidification capacity.

Improving Effects of Different Calcium-Magnesium Conditioners on Latosol

At present, soil acidification seriously restricts the sustainable development of agricultural production. A common method that can be used to improve acidified soils is to apply calcareous materials (conditioners), but there is difference in the improvement effect of the conditioners on the same soil because of the conditioners containing different calcium-magnesium compounds. In order to find suitable conditioners for latosol (acidic red soil), two consecutive soil incubation experiments in laboratory have be done to study the improvement effects of different calcium-magnesium compounds on latosol. The results showed that: (1) Self-made conditioner (CM and it is composed of Mg(OH)2, Ca(OH)2, MgCl2, CaCl2,), CaO, CaCO3 and Mg(OH)2 could rapidly increase the pH and significantly reduce the content of potential acid in latosol. The soil exchangeable acid of Mg(OH)2, CaCO3, CaO and CM treatments than the treatment without conditioner (CK) were reduced by 88, 72, 66 and 34%, respectively, and the soil exchangeable aluminum decreased by 91, 80, 71 and 58%, respectively. (2) The calcium-magnesium compounds can significantly increase the contents of soluble and exchangeable calcium in soil compared with CK. CM and Mg(OH)2 significantly increased the contents of soluble and exchangeable magnesium in latosol. (3) The soil pH buffer capacity of CM is significantly higher than those of other treatments as a result of it has the highest organic matter content and significantly increases the contents of exchangeable calcium and magnesium in the soil. But the soil pH buffer capacity of CaCO3 and Mg(OH)2 are significantly less than that of CK. Because the organic matter and organic acid of CaCO3 and Mg(OH)2 treatments are reduced by the soil pH of them increasing and the functional groups with pH buffer capacity on them may also be destroyed. So the paper suggests that improve acid latosol by applying conditioners with more soluble calcium and magnesium, Mg(OH)2, which can effectively reduce acid ions in soil and improve the pH buffer capacity of soil.

Improvement of the chemical properties and buffering capacity of coastal sandy soil as affected by clays and organic by-product application

The main problem with coastal sandy soil is its low water and nutrient retention due to its low clay and organic matter content. This study was aimed at improving the chemical properties and buffering capacity of these soils by using ameliorants of clay and organic polymers. The leaching experiment was conducted with two factors and three replications. The first factor was a clay ameliorant (5% clay, whether from the soil type Inceptisol (I) and the soil type Vertisol (V)). The second factor was a natural or synthetic organic polymer (tapioca 1% and 2% (T1 and T2), tapioca dregs 1% and 2% (TD1 and TD2), polyvinyl alcohol 0.1% and 0.2% (P1 and P2)). The leaching was carried out at 1-month intervals and the leachate was collected for the analysis of the soluble Ca, Mg, K and Na. The leaching was stopped after all the treatments reached the electrical conductivity values < 100 μS/cm. The ameliorants of clay (I or V) and natural polymer (T or TD) significantly increased the cation exchange capacity, the available cations, and the buffering capacity of the coastal sandy soil. The single treatment of I was better than V in increasing the available Mg, while the combination with organic natural polymers could increase the available Ca and K. The treatment of ITD2 was able to increase the soil buffering and maintain the soluble Ca, Mg and K in the coastal sandy soil. Therefore, TD which is a by-product of the tapioca flour industry when combined with I has the potential to be a prospective ameliorant for coastal sandy soils.

Surface charge properties of variable charge soils influenced by environmental factors

The variable charge soils that have been developed in tropical and subtropical zones are unique soils compared with the constant charge soils that have been developed in Europe and North America, especially the sensitivity of the particle surface charges to environmental factors in the variable charge soils. In this study, to avoid the interference of side reactions, experiments were performed using a fast potentiometric acid-base titration under non-equilibrium condition, and simulation by the surface complexation model to investigate the effects of environmental factors, including the impact of CO2 (in nitrogen/in air), the impact of different ionic strengths, the impact of dry-wet rotation (different soil-to-liquid (S/L) ratios), and the impact of seasonal temperature variation (different reaction temperatures), on the surface acidity constants and on the protonation/deprotonation processes in a typical variable charge soil collected in southern China. The titration results demonstrate that the observed measured apparent pH when surface charge equal to zero (pHQ=0) were significantly negative shifted in air, and negative correlations were proven between the S/L ratios, the reaction temperatures and the observed pHQ=0 values. The simulation results from the fast titration prove that changing the S/L ratios modifies the surface species concentration (≡SOH, ≡SOH2+, and ≡SO−), further influencing the modification of the surface charge properties of the soil. Meanwhile, an increase in temperature not only increases the amount of the surface species concentration but also causes an enlargement of the protonation/deprotonation processing range, which may increase the acid-base buffer capacity of soils. Taken together, these results can help us to further understand the natural soil acidification processes occurring in variable charge soils, especially in the southern areas of China.

Transformation of metals migration and biogeochemical cycling under the influence of copper mining production (the Southern Urals)

This study aims to estimate the migration and accumulation of metals (Cu, Zn, Fe, Mn, Ni, Pb, Cd, Co, Cr, Zr, Ba, and Sc) in terrestrial and aquatic landscapes. The research is based on the results of a long-term study (1998–2018) in one of the copper mining centers in Russia in the vicinity of Sibay City in the Southern Urals. The metal contents in samples of water, bottom sediments, soils, plant shoots (total aboveground phytomass samples, agrobotanical group samples, and shoots of indicator terrestrial and aquatic species), and fish muscles are measured. It is found that within natural geochemical anomalies, the migration ability of chemical elements in the soil–plant system and general biogeochemical cycle is low because of the high soil buffer capacity (determined by the high humus content, high percentage of fine fractions in granulometric composition, and neutral pH) and the adaptation of local plants to ore mineralization. The ecosystems affected by low pollution maintain natural homeostasis, stabilize the flow of chemical elements, and preserve the natural features of geographic components. Metal pollution and the replacement of natural steppe vegetation with secondary herbaceous-ruderal communities in critical areas near copper–zinc mining objects can stimulate the mobilization and inclusion of chemical elements in biogeochemical cycling, as well as the disruption of bonds among landscape components. The water systems in catenae function as stabilizers through a system of geochemical barriers and low uptake of metals by hydrophytes, such as the common reed (Phragmites australis).

Barriers to restoration: Soil acidity and phosphorus limitation constrain recovery of heathland plant communities after sod cutting

AbstractQuestionsSod cutting has been used extensively as an effective measure in removing excess N and restoring dwarf shrub dominance in heathlands affected by increased nitrogen deposition. However, recovery of other plant species is often very limited. One barrier is high soil acidity following sod cutting, which results in soil aluminium (Al3+) and ammonium (NH4+) reaching toxic concentrations. Sod‐cutting management also removes most of the major nutrients from the system, so intensified nutrient limitation could be an additional barrier to the recovery of species‐rich communities. Soil phosphorus (P) is of special interest as research indicates sod‐cutting management can shift the system to P limitation.LocationHoge Veluwe National Park, The Netherlands.MethodsWe set up a full‐factorial experiment in sod‐cut heathland formerly encroached by Molinia caerulea, adding phosphate (P+) and lime (Ca+) and over the next three growing seasons, we recorded soil chemistry and plant responses.ResultsSoil inorganic N, especially soil NH4+, strongly declined after liming compared to the control situation, confirming that liming alleviates NH4+ toxicity. Addition of P resulted in a similar decline, also suggesting a role for soil phosphate availability in this process. Acid‐sensitive plant species richness increased significantly in both Ca+ and P+ treatment, whereas acid‐insensitive plant species richness only increased significantly as a result of P+ treatment. Mean vegetation relative growth rate increased significantly in both Ca+ and P+ treatments.ConclusionsExcessive P removal due to sod cutting constitutes a second barrier to restoration in addition to soil acidity. We discourage the large‐scale use of sod cutting to reduce soil N availability in heathlands and propose to use interventions that leave the soil nutrient balance intact, such as burning and grazing, mowing or litter removal, in combination with measures that restore the soil buffer capacity.

Adsorption and Desorption of Nitrogen, Phosphorus, Potassium, and Soil Buffering Capacity Following Application of Chicken Litter Biochar to an Acid Soil

Adsorption and desorption of nitrogen (N), phosphorus (P), and potassium (K) soils are controlled by pH, pH buffering capacity, organic matter, and cation exchange capacity (CEC). These factors optimized to improve timely availability of N, P, and K crop use using organic amendments such as chicken litter biochar (CLB). The objective of this study was to determine the effects of CLB on N, P, K sorption and pH buffering capacity of an acid soil. Different rates of CLB were mixed with an acid soil for N, P, and K sorption and pH buffering capacity determination. The CLB increased soil pH and pH buffering capacity, but unlike P and K adsorption, the different rates of CLB significantly increased N adsorption, suggesting that this soil amendment has high affinity for N than P and K. Also, because CLB reduced N, P, and K desorption, it suggests that N in particular will be slowly released with time. The reduced N desorption but higher N adsorption further indicates that N can be temporary fixed by CLB. This work has revealed CLB is more effective controlling soil N availability for timely crop use to avoid losses.

Plant communities are more sensitive than soil microbial communities to multiple environmental changes in the Eurasian steppe

Understanding species responsiveness to anthropogenic environmental changes benefits the guide to manage biodiversity. Microbes are traditionally thought to be more sensitive to environmental changes than plants. However, this hypothesis is supported by little empirical evidence. We compared plant and microbial responses to 13 types of simulated environmental changes (mowing (M), adding nitrogen (N), adding phosphorus (P), watering (W), warming (T) and combinations of these) in a steppe ecosystem. Contrary to our hypothesis, the microbial responses were generally smaller than the plant responses to different types of environmental changes, both at the community-abundance level and species/operational taxonomic unit (OTU)/gene level. This might be ascribed to the soil buffering capacity to environmental changes, and the rapid evolutionary adaptation for microbial communities. Furthermore, the responses at the community-abundance level were larger than at the species/OTU/gene level to 13 types of environmental changes, both in plant and microbial communities. Given that the community abundance representing the total number of all individuals of the organism within the community, the responses to environmental changes at the community-abundance level is likely to be larger than at the species/OTU/gene level. Plant biomass was more responsive to N addition, particularly in such N- limiting grassland ecosystem. Our findings highlight that plant communities are more responsive to environmental changes than microbial communities, contrary to the traditional viewpoint. Therefore, plant communities could be used as ecological indicators of anthropogenic environmental changes in grasslands.

ECOLOGICAL MONITORING OF UKRAINIAN AGROLANDSCAPE AS BASIS FOR ITS OPTIMIZATION AND EFFECTIVE USE

The article substantiates the necessity of conducting complex ecological monitoring of agrolandscapes due to the ecologically groundless use of the land, insufficient technical and technological support, implementation of ineffective investment and innovative economic and technological solutions, disturbance of the balance of agrolandscapes through their significant plowing, consolidation of the soil, deterioration of the ratio of arable land and ecology -stabilization lands and nature reserve fund, inefficient implementation of ecological and the Emerald Network, destruction of soil (soil buffering capacity decrease), growing areas of degraded land. A scientifically-based methodology for improving environmental monitoring of agro-landscapes of Ukraine’s territory, their optimization and effective use is proposed. The stages and specifics of carrying out of complex ecological monitoring of various kinds of agro-landscapes, their functional-structural elements, main directions and parameters are presented. The necessity of carrying out of the proposed integrated system of the agro-landscapes ecological monitoring on the territory and creation of regional information and consultation centers on agro-ecological issues has been proved.

Nitrogen addition effects on tree growth and soil properties mediated by soil phosphorus availability and tree species identity

Increasing evidence has suggested that nitrogen (N) deposition has great effects on forest productivity and nutrient cycling, but how these effects are mediated by soil phosphorus (P) availability and tree species identity remains unclear. Here, a two-year factorial experiment was conducted to examine the short-term effects of N addition (100 kg N ha−1 year−1), P addition (50 kg P ha−1 year−1) and their interactions on tree growth and soil nutrient cycling of a Mongolian pine (Pinus sylvestris var. mongolica) plantation and a neighboring Simon poplar (Populus simonii) plantation in Northeast China. Results showed that N addition promoted tree growth (stem increment), reduced soil microbial biomass carbon (C) and N in the Mongolian pine plantation, but did not affect those in the Simon poplar plantation, and these N addition effects were not interacted by P addition. P addition significantly increased microbial biomass C and N in the Simon poplar plantation. N addition elevated soil phosphatase activities and reduced net N mineralization rate, and these N addition effects were alleviated by simultaneous P addition in both plantations. N addition decreased soil labile inorganic P concentration in both plantations and elevated labile organic P in the Mongolian pine plantation, but only the decrease in labile inorganic P with N addition in the Mongolian pine plantation was counteracted by P addition. N addition significantly reduced soil pH, with a greater extent in the Mongolian pine plantation than in the Simon poplar plantation. Moreover, soil pH response explained most of the microbial and nutrient transformation response. Above results indicated that short-term N addition impacts on tree growth and soil microbial biomass were more strongly influenced by tree species identity than by P addition, while N addition effects on soil N and P transformations were strongly influenced by P addition. Drought resistance of trees and acid buffering capacity of soils are key traits influencing the short-term N addition impacts on the growth of trees and microorganisms in this semiarid region.

Measuring and simulating pH buffer capacity of calcareous soils using empirical and mechanistic models

ABSTRACTWe studied (i) the pH buffer capacity (pHBC) of calcareous soils varied widely in calcite and texture, (ii) the contribution of soil properties to pHBC and (iii) the significance of using a model based on calcite dissolution to estimate the pHBC of calcareous soils. The pHBC of soils was measured by adding several rates of HCl to soils (100–6500 mM H+ kg–1), in a 0.01 M CaCl2 background and an equilibration time of 24 h. The pHBC (mM H+ kg–1 pH−1) varied from 55 to 3383, with the mean of 1073. The pHBC of the soils was strongly correlated with soil CaCO3 equivalent (calcite) (r = 0.94), sand (r = −0.72), silt (r = 0.60), EC (r = 0.63), pH (r = 0.55), and weakly (r = 0.37) but significantly with clay content. The attained pHBC values indicated that calcite was probably the main buffer system in these soils. The chemical equilibrium model successfully predicted pH titration curves based on calcite dissolution, indicating buffering of acid inputs in the calcareous soils is dominated by calcite dissolution. The model can be used to simulate acidification of calcareous soils and to provide information for making environmental management decisions.

Long-term influence of different production systems on potassium buffering capacity of Typic Ustochrept soil

Imbalanced application of nutrients in the intensively cropped areas results in deterioration of soil fertility. Application of recommended dose of potassium (K) is essential for improving the use efficiency of other nutrients. To assess the buffering capacity of soil, three composite soil samples were collected from the surface soil (0–30 cm) during 2015 from 3 production systems viz., organic, inorganic and integrated which was maintained from 2004 with basmati rice–wheat–Sesbania system under Network Project on Organic Farming at ICAR-Indian Institute of Farming Systems Research, Modipuram. Fractionation of potassium (K) was achieved by sequential extraction of soil samples with distilled water, ammonium acetate and nitric acid in the same order. The relationship between the adsorbed and equilibrium potassium concentration, quantity was determined by plotting Freundlich adsorption isotherms. This was used to determine the buffering capacity and the concentration levels of potassium adsorbed on un-specific sites in the soil. The suitability of the adsorption equation was determined by applying the least square regression analysis. The results revealed that available potassium in the soils ranged from 119.51 to 135.01 mg/kg with 126.02 ± 5.24 mg/kg as mean (ammonium acetate method) while water soluble and nitric acid extracted potassium ranged from 28.51 to 29.05 mg/kg and 2594.49 ± 19.33 mg/kg (mean) in various production systems. The mean free energy of replacement was found to be −1998.01 ± 28.38 cal/mol indicating that soils have comparatively higher potassium supply under organic system. The potassium buffering capacity of the soils was found to be 0.7462 ± 0.16 mg/kg, 0.6295 ± 0.20 mg/kg and 0.6774 ± 0.09 mg/kg in organic, integrated and inorganic systems, respectively. The amount of potassium adsorbed on un-specific sites of the organic, integrated and inorganic systems was found to be 7.4730 ± 1.81, 15.11 ± 2.40 and 11.6 89 ± 3.58 mg/kg, respectively. It can be concluded that long-term organic production system improves K+ buffering capacity of Typic Ustochrept soil as compare to the integrated as well as inorganic production systems.

Zoogenic mechanisms of ecological rehabilitation of urban soils of the park zone of megapolis: Earthworms and Soil Buffer Capacity

Earthworms (Oligochaeta: Lumbricidae) are typical representatives of the funcitional group of ecosystem engineers. They actively participate in formation and stabilization of soil fertility through their effect on its buffer capacity. Buffer capacity defines in many aspects soil potential, supports immobilization and mobilization of certain elements of fertility – first of all mineral elements essential for plants, productive moisture, heat energy of soil, gas composition of soil air. Park soils within megapolises territory are their integral components and this defines conditions of growth and development for green plants. To evaluate the contribution of the earthworms’ coprolites into acidic-base (pH) buffer capacity of two categories of soil within the city – urban soils and urban grounds (urbanozems) of the park zones within the plots planted with Norway maple (Acer platanoides L.) trees on the territory of two parks – “Zeleny gai” and Pisarzhevsky Park (city Dnipro, Ukraine), soil and coprolites samples were collected. Buffer capacity of coprolites and anthropogenically transformed soils (urban soils) was evaluated according to Arrhenius method after “buffer area”. It was established that acid-base buffer capacity of coprolites (earthworms’ excretes), which are new formations of zoogenic origin in soil statistically significantly higher than for initial types soil within city parks. For urban soil with upper humified layer of calcic chernozem within the acidic diapason of external load it was 22.9% higher, which, in average, accordingly was 22.9 and 18.7 convectional units, within alkaline – 18.4% higher and was, accordingly, 24.2 and 20,4 convectional units, in sum (acidic-alkaline) – 20.6% higher and was 47.1 and 39.1 convectional units. For urban ground (urbanozem) with within the acidic diapason of external load it was 44.9% higher and acidic–alkaline buffering capacity, in average, accordingly, was 25.5 and 17.6 convectional units, in sum (acidic-alkaline) – 20.6% higher and was 42.8 and 35.4 convectional units accordingly. Thus, soil saprophagues, such as earthworms, in the conditions of magapolises in the recreation zones within the territories of city parks’ green plantations is one of the natural factors of ecological rehabilitation of urban soils. This, in general, improves ecological state of green plantations on the urban soils within park areas and recreation zone edaphotopes revitalization and support optimization of human living and recreation environment. DOI: http://dx.doi.org/10.5755/j01.erem.75.1.21121

Effects of phytolithic rice-straw biochar, soil buffering capacity and pH on silicon bioavailability

Supplying phytolith-rich biochar in agrosystems increases soil pH, CEC and nutrient availability, adding to the impact of Si uptake on plant growth. Here we studied this specific impact as influenced by soil properties, and assessed the role of phytoliths to provide plant available Si. We used a young Cambisol and a highly weathered, poorly buffered, desilicated Nitisol. The biochars were produced from rice plants respectively enriched (Si+) and depleted (Si-) in Si. They had identical pH and nutrient contents, but largely differed in Si content (51.3 g Si kg−1 in Si + vs 0.3 g Si kg−1 in Si-). We compared their effects to that of wollastonite (CaSiO3) on the biomass and mineralomass of wheat plants in a soil:solution:plant device. The contents of soil bioavailable Si and biogenic Si were assessed through an original CaCl2 kinetic extraction and the DeMaster Na2CO3 alkaline dissolution, respectively. The DeMaster technique dissolved Si from phytolith as well as from wollastonite. The soil buffering capacity (cmolc kg−1) was 31 in the Cambisol and 0.2 in the Nitisol. An identical supply of phytolithic biochar increased pH from 4.5 to 4.8 in the Cambisol, and from 4.8 to 7.4 in NI. It further increased the content of bioavailable Si (from 55 to 97 mg kg−1 in the Cambisol, and 36 to 209 mg kg−1 in the Nitisol), as well as plant Si uptake, biomass and Si mineralomass. That increase was largest in the Nitisol. The DeMaster technique did not specifically quantify the phytolith pool. This pool was the main source of plant available Si in both the Cambisol and Nitisol amended with phytolithic biochar. At identical phytolithic Si supply, however, soil pH and soil buffering capacity controlled the transfer of Si in the soil-plant system, which was largest in the poorly buffered Nitisol. The effect of phytolithic biochar on Si bioavailability was depending on soil constituents and properties, and thus on soil type.

Phosphate sorption indices as affected by the calcareousness of soils

An experiment was carried out to study the effects of calcareousness on phosphate sorption indices of soils using three representative calcareous soils, namely Sara (Aquic Eutrochrept), Gopalpur (Aquic Eutrochrept), and Ishurdi (Aeric Haplaquept) series of Bangladesh. Three non-calcareous soils, namely Belabo (Typic dystrudepts), Sonatala (Aeric Endoaquepts) and Ghatail (Aeric Haplaquept) series were also selected for comparison purposes. Phosphate sorption indices of soils were calculated using Langmuir and Freundlich isotherms. Isotherms were constructed taking one gram of air-dried sieved (< 2 mm) soil into a 50 ml centrifuge tube, and subsequently adding seven initial P concentrations, namely 0, 1, 10, 25, 50, 100 and 150 μg/ml to each centrifuge tube employing a soil/solution ratio of 1 : 20 (w/v). According to the Langmuir equation, the amount of phosphate sorbed followed the order: Sonatala > Ghatail > Sara = Gopalpur > Ishurdi > Belabo. The abundance of amorphous iron rather than the calcareousness was putatively responsible for the high phosphate sorption capacity of soils. Maximum phosphorus buffering capacity (MPBC) of the calcareous soils ranged from 33.4 - 62.8 l/kg. Langmuir and Freundlich equations produced different values for soil P requirements (SPR) at 0.2 and 1.0 mg P/l. Calcareous soils would require 27 - 44 mg P/kg soil to attain 0.2 mg P/l soil solution, which is deemed sufficient for crop growth. The soils would require 32 - 58 mg P/kg soil to reach 1.0 mg P/l soil solution, which is regarded to be safe for soils in terms of susceptibility to P losses. The calculated Langmuir constant b values were higher than the threshold value of 0.07 l/mg for two of the calcareous soils. Therefore, even though the non-calcareous soils sorbed more phosphate, higher bonding energy of P sorption for calcareous soils makes them less vulnerable to loss via surface runoff.
 Dhaka Univ. J. Biol. Sci. 28(1): 93-110, 2019 (January)

Input-Output Budgets of Nutrients in Adjacent Norway Spruce and European Beech Monocultures Recovering from Acidification

Soil acidification has constituted an important ecological threat to forests in Central Europe since the 1950s. In areas that are sensitive to acid pollution, where the soil buffering capacity is naturally low, tree species can significantly modulate the extent of soil acidification by affecting throughfall deposition and the composition of litter. A principal difference can be expected between coniferous and broadleaf tree species. The aim of our study was to compare long-term trends in element cycling in two stands representing the main types of forest ecosystem in the region (Picea abies vs. Fagus sylvatica). In the period of 2005–2017, we continually measured element concentrations and fluxes in bulk precipitation, throughfall precipitation, and soil leachates. A continuous decline of acid deposition was detected in both bulk precipitation and throughfall. Declining deposition of S and N in both forests has led to the recovery of soil solution chemistry in the mineral soil, manifested by rising pH from 4.25 to 4.47 under spruce and from 4.42 to 4.69 in the beech stand. However, soil water in the spruce stand was more acidic, with higher concentrations of SO42− and Al when compared to the beech stand. While the acidity of soil leachates from organic horizons was driven mainly by organic anions, in lower mineral horizons it was controlled by inorganic acid anions. NO3− concentrations in deeper horizons of the spruce stand have diminished since 2006; however, in the beech plot, episodically elevated NO3− concentrations in mineral horizons are a sign of seasonal processes and of nearby perturbations. Higher output of S when compared to the input of the same element indicates slow S resorption, delaying the recovery of soil chemistry. Our results indicate that, although forest ecosystems are recovering from acidification, soil S retention and the ability to immobilize N is affected by the dominant tree species.

Evaluation of Adsorption Isotherm Models for Potassium Adsorption under Different Soil Types in Wolaita of Southern Ethiopia

ABSTRACT Adsorption isotherm is essential for predicting its mechanisms, which are important for potassium (K) fertilizer application and to recommendation appropriate rates for acidic soils. Thus, the objective of this study was to evaluate K adsorption characteristic of the selected soils by comparing different adsorption models with soil properties of the soil in different districts (Sodo Zurie, Damot Gale, Damot Sore and Boloso Sore) in the Wolaita Zone of Southern Ethiopia. Four adsorption isotherms are: Langmuir, Freundlich, Temkin, and Van Huay were used to describe adsorption processes. Composite surface (0-20 cm) depth soil samples from four districts sites were collected. The results revealed that the K adsorption data coincide with both models with (r2 = 0.99). However, Freundlich model was better in describing K adsorption than the other model. The adsorption maxima(ad(max), distribution coefficient, buffer capacity (BC), and adsorption capacity(a(capacity) values of soils ranged from -333 to334.5,0.54 to78.7,159.9 to 389.3, and 327 to 417mg Kkg-1 respectively, these results showed that Sodo Zurie, Bolos Sore and Demote Sore were effective model parameters. Van Huay a(capacity) 417mg Kkg-1 while the bonding energy constant Langmuir is -0.075mg Kkg-1 in Bolos Sore soil compared to other soils, which were found to be more valuable in discriminating between high K adsorption soils. Correlation between some soil properties with ad(max) were positively a highly correlated with clay, pH, organic carbon (OC) and exchangeable potassium with r2 = 0.92**, 0.93**, 0.95** and 0.96 ** respectively, but negatively correlated with bonding energy with r2= -0.79, -0.80,-0.77 and -0.72 respectively, while calcium carbonate (CaCO3) was very highly correlated with ad(max) r2= 0.99***). The Freundlich constant, Temkin BC, and Van Hauy a(capacity) were correlated with CaCO3 content soils with r2=0.12,-0.01,and 0.12,respectively, while slope (1/n) was significantly negatively correlated with soil cation exchange capacity (CEC), CaCO3, clay contents and exchangeable K and Mg2+ with r2= 0.04, -0.67, -0.78, -0.69, and –0.69, respectively. These findings reveal the extent of K depletion in the soils of Wolaita providing a baseline for K rates required for crop production and validation of all models through real-time experiments in the field; this is recommended before the models are used on a large scale basis.

Continuum multiscale model of root water and nutrient uptake from soil with explicit consideration of the 3D root architecture and the rhizosphere gradients

Although modelling of water and nutrient uptake by root systems has advanced considerably in recent years, steep local gradients of nutrient concentration near the root-soil interface in the rhizosphere are still a central challenge for accurate simulation of water and nutrient uptake at the root system scale. Conventionally, mesh refinement is used to resolve these gradients. However, it results in excessive computational costs. The object of the study is to present a multiscale approach which resolves the steep gradient of nutrient concentrations at rhizosphere scale and simulates nutrient and water fluxes within the entire root zone at macroscale scale in a computationally efficient way. We developed a 3D water and nutrient transport model of the root-soil system with explicit consideration of the 3D root architecture. To capture the nutrient gradients at root surfaces, 1D axisymmetric soil models at rhizosphere scale were constructed and coupled to the coarse 3D root-system-scale simulations using a mass conservative approach. The multiscale model was investigated under different scenarios for water and potassium (K+) uptake of a single root, multiple roots, and whole 3D architecture of a Zea mays L. root system in conditions of dynamic soil water and different soil buffer capacity of K+. The steep gradients of K+ concentrations were efficiently resolved in the multiscale simulations thanks to the 1D model at the rhizosphere scale. In comparison with the refinement method, the multiscale model achieved a significant accuracy of K+ uptake prediction with a relative error below 5%. Meanwhile, the simulation at macroscale with coarse mesh could overestimate the K+ uptake in one order of magnitude. Moreover, the computational cost of multiscale simulations was decreased considerably by using coarse soil mesh. The newly developed model can describe the effect of the drying and nutrient transport in the root zone on nutrient uptake. It also allows to simulate processes in larger and complex root systems because of the considerable reduction in computational cost.

The pH buffering capacity of Acrisols under cassava production in Southeastern Vietnam, Chau Thanh district

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