The forms and distribution of aluminum adsorbed onto maize and soybean roots

Purpose

The Al forms on maize and soybean roots were investigated to determine the main factors affecting the distribution of Al forms and its relationship with Al plant toxicity.

Materials and methods

Solution culture experiments were conducted to obtain the fresh roots of maize and soybean. KNO₃, citric acid, and HCl were used to extract the exchangeable, complexed, and precipitated forms of Al on the roots.

Results and discussion

The complexed Al was higher than the exchangeable and precipitated Al. Root CECs of soybean and maize were 77 and 55 cmol kg^?1, and functional groups on the soybean roots (262.4 cmol kg^?1) were greater than on maize roots (210.8 cmol kg^?1), which resulted in more exchangeable and complexed Al on soybean roots than on maize roots, and was one of the reasons for the increased Al toxicity to soybean. The total and exchangeable Al were the highest on the plant root tips and decreased gradually with increasing distance from the tips. Ca²⁺, Mg²⁺, and NH₄ ⁺ cations reduced the exchangeable Al on the roots. Oxalate and malate also reduced the adsorption and absorption of Al by roots, and the effect of oxalate was greater than malate.

Conclusions

Higher exchangeable and complexed Al on plant roots led to increased Al plant toxicity. Ca²⁺, Mg²⁺, and NH₄ ⁺ and oxalate and malate can effectively alleviate Al plant toxicity.

     

Laser-based spectroscopic methods to evaluate the humification degree of soil organic matter in whole soils: a review

Purpose

The objective of this review is to survey critically the results obtained by the application of laser-induced fluorescence spectroscopy (LIFS) and laser-induced breakdown spectroscopy (LIBS) to the evaluation of the humification degree (HD) of soil organic matter (SOM) directly in untreated, intact whole soils.

Materials and methods

A large number of soils of various origin and nature, either native or under various cultivations, land use, and management, at various depths, have been studied to evaluate the HD of their SOM directly in intact whole samples. The LIFS spectra were obtained by either a bench or a portable argon laser apparatus that emits UV-VIS light of high power, whereas the LIBS spectra were obtained using a Q-switched Nd:YAG laser at 1064 nm.

Results and discussion

The close correlations found by comparing H_LIF values of whole soil samples with values of earlier proposed humification indexes confirmed the applicability of LIFS to assess the HD of SOM in whole soils. The high correlation found between HD_LIBS values and H_LIF values showed the promising potential of LIBS for the evaluation HD of SOM.

Conclusions

The LIFS technique shows to be a valuable alternative to evaluate the HD of SOM by probing directly the whole solid soil sample, thus avoiding the use of any previous chemical and/or physical treatments or separation procedures of SOM from the mineral soil matrix. The emerging application of LIBS to evaluate the HD of SOM in whole soils appears promising and appealing due to its sensitivity, selectivity, accuracy, and precision.

     

Soil pH,organic matter,and nutrient content change with the continuous cropping of <Emphasis Type="Italic">Cunninghamia lanceolata</Emphasis> plantations in South China

Purpose

Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) is an important native tree species in China. Consecutive cropping traditionally occurs in Chinese fir plantations (CFPs), but this practice has resulted in productivity declines in subsequent rotations. This study was designed to better understand the change of soil properties in the continuous cropping CFPs.

Materials and methods

We investigated soil pH, soil organic matter (SOM), and nutrient contents in different soil layers and in rhizosphere soil (RS) and non-rhizosphere soil (NRS) under CFPs of different ages and in different rotations.

Results and discussion

In the upper (0–20 cm) soil layer, soil pH decreased, while SOM increased, beneath mature CFPs with consecutive rotations. Total nitrogen (TN), available potassium, and available phosphorus contents in the upper soil layers did not differ significantly with consecutive rotations. Soil pH in RS was significantly lower than in NRS under mature plantations of the third rotation. Soil organic matter, TN, and available nitrogen did not differ between RS and NRS. Available phosphorus in RS was consistently lower than in NRS, and was highly deficient in the third rotation.

Conclusions

We conclude that no severe soil nutrient degradation occurred in the continuous cropping CFPs examined in this study, with soil acidification and phosphorus deficiency being two primary problems observed.

     

Molecular fingerprint of soil organic matter as an indicator of pedogenesis processes in Technosols

Purpose

Technosol management is one of the greatest challenges for the future, more specifically as regards supporting and/or restoring ecosystems. The understanding of natural soil organic matter (SOM) dynamic from Technosol may give important information about soil functioning and Technosol evolution.

Materials and methods

According to this, SOM from three French old mine Technosols, (an old tin mine, a lead and zinc, and a gold one which is arsenic-rich), were studied and characterized using thermochemolysis coupled with gas chromatography and mass spectrometry (GC-MS) with tetramethyl ammonium hydroxide (TMAH) as reagent and FTIR. The characterization and quantification of some specific biomacromolecules, used as biomarkers, indicate the specific level of incorporation relative to various subgroups. Global parameters of soils (pH, total organic matter, cation exchange capacity…) were also evaluated.

Results and discussion

Results on bulk samples show that lipids are the most reactive group and therefore play the most important role in young soil pedogenesis. All of the results show that the behavior of SOM of the Technosol is similar to homolog non-anthropized soil and depends on vegetation type.

Conclusions

A slight inhibition of bacterial activity is observed which underlines a protective effect of Technosols on SOM degradation due to the low pH, the high clay content, and the presence of Al³⁺ and metal(loid)s. In fine, lipid fraction of SOM may act as a well-done fingerprint of pedogenesis processes in Technosols.

     

Effect of low energy-consuming biochars in combination with nitrate fertilizer on soil acidity amelioration and maize growth

Purpose

We evaluated the ameliorative effects of crop straw biochars either alone or in combination with nitrate fertilizer on soil acidity and maize growth.

Materials and methods

Low energy-consuming biochars were prepared from canola and peanut straws at 400 °C for 2 h. Incubation experiment was conducted to determine application rate of biochars. Afterward, maize crop was grown in pots for 85 days to investigate the effects of 1 % biochars combined with nitrate fertilizer on soil pH, exchangeable acidity, and maize growth in an Ultisol collected from Guangdong Province, China.

Results and discussion

Application of 0.5, 1.0, and 1.5 % either canola straw biochar (CSB) or peanut straw biochar (PSB) increased soil pH by 0.15, 0.27, 0.34, and 0.30, 0.58, 0.83 U, respectively, after 65-day incubation. Soil pH was increased by 0.49, 0.72, 0.78, and 0.88 U when 1 % CSB or PSB was applied in combination with 100 and 200 mg N/kg of nitrate, respectively, after maize harvest in greenhouse pot experiment. These low-cost biochars when applied alone or in combination with nitrate not only reduced soil exchangeable acidity, but also increased Ca²⁺, Mg²⁺, K⁺, Na⁺, and base saturation degree of the soil. A total of 49.91 and 80.58 % decreases in exchangeable acidity were observed when 1 % CSB and PSB were incubated with the soil for 65 days, compared to pot experiment where 71.35, 78.64, 80.2, and 81.77 % reductions of exchangeable acidity were observed when 1 % CSB and PSB were applied in combination with 100 and 200 mg N/kg of nitrate, respectively. The higher contents of base cations (Ca²⁺, Mg²⁺, K⁺, Na⁺) in biochars also influenced the plant growth. The higher biomass in CSB-treated pots was attributed to the higher K content compared to PSB. The higher percent reduction in exchangeable Al³⁺ by applying 1 % CSB combined with 200 mg N/kg of nitrate consistently produced maximum biomass (129.65 g/pot) compared to 100 mg N/kg of nitrate and 1 % PSB combined with 100 and 200 mg N/kg of nitrate. The exchangeable Al³⁺ mainly responsible for exchangeable acidity was decreased with the application of biochars and nitrate fertilizer. A highly significant negative relationship was observed between soil exchangeable Al³⁺ and plant biomass (r ²?=?0.88, P?<?0.05).

Conclusions

The biochars in combination with nitrate fertilizer are cost-effective options to effectively reduce soil acidity and improve crop growth on sustainable basis.

     

The effect of biochar loading rates on soil fertility,soil biomass,potential nitrification,and soil community metabolic profiles in three different soils

Purpose

Biochar is increasingly being used as a soil amendment to both increase soil carbon storage and improve soil chemical and biological properties. To better understand the shorter-term (10 months) impacts of biochar on selected soil parameters and biological process in three different textured soils, a wide range of loading rates was applied.

Materials and methods

Biochar derived from eucalypt green waste was mixed at 0, 2.5, 5, 10 % (wt/wt) with a reactive black clay loam (BCL), a non-reactive red loam (RL) and a brown sandy loam (BSL) and placed in pots exposed to the natural elements. After 10 months of incubation, analysis was performed to determine the impacts of the biochar rates on the different soil types. Also, microbial biomass was estimated by the total viable counts (TVC) and DNA extraction. Moreover, potential nitrification rate and community metabolic profiles were assayed to evaluate microbial function and biological process in biochar-amended soils.

Results and discussion

The results showed that biochar additions had a significant impact on NH₄ and NO₃, total C and N, pH, EC, and soil moisture content in both a soil type and loading-dependent manner. In the heavier and reactive BCL, no significant impact was observed on the available P and K levels, or the total exchangeable base cations (TEB) and CEC. However, in the other lighter soils, biochar addition had a significant effect on the exchangeable Al, Ca, Mg, and Na levels and CEC. There was a relatively limited effect on microbial biomass in amended soils; however, biochar additions and its interactions with different soils reduced the potential nitrification at the higher biochar rate in the two lighter soils. Community metabolic profile results showed that the effect of biochar on carbon substrate utilization was both soil type and loading dependent. The BCL and BSL showed reduced rates of substrate utilization as biochar loading levels increased while the opposite occurred for the RL.

Conclusions

This research shows that biochar can improve soil carbon levels and raise pH but varies with soil type. High biochar loading rates may also influence nitrification and the function and activity of microbial community in lighter soils.

     

Effects of biochar and polyacrylamide on decomposition of soil organic matter and <Superscript>14</Superscript>C-labeled alfalfa residues

Purpose

Various soil conditioners, such as biochar (BC) and anionic polyacrylamide (PAM), improve soil fertility and susceptibility to erosion, and may alter microbial accessibility and decomposition of soil organic matter (SOM) and plant residues. To date, no attempts have been made to study the effects of BC in combination with PAM on the decomposition of soil SOM and plant residues. The objective of this study was to evaluate the effects of BC, PAM, and their combination on the decomposition of SOM and alfalfa residues.

Materials and methods

An 80-day incubation experiment was carried out to investigate the effects of oak wood biochar (BC; 10 Mg ha^?1), PAM (80 kg ha^?1), and their combination (BC?+?PAM) on decomposition of SOM and ¹⁴C-labeled alfalfa (Medicago sativa L.) residues by measuring CO₂ efflux, microbial biomass, and specific respiration activity.

Results and discussion

No conditioner exerted a significant effect on SOM decomposition over the 80 days of incubation. PAM increased cumulative CO₂ efflux at 55–80 days of incubation on average of 6.7 % compared to the soil with plant residue. This was confirmed by the increased MBN and MB¹⁴C at 80 days of incubation in PAM-treated soil with plant residue compared to the control. In contrast, BC and BC?+?PAM decreased plant residue decomposition compared to that in PAM-treated soil and the respective control soil during the 80 days. BC and BC?+?PAM decreased MBC in soil at 2 days of incubation indicated that BC suppressed soil microorganisms and, therefore, decreased the decomposition of plant residue.

Conclusions

The addition of oak wood BC alone or in combination with PAM to soil decreased the decomposition of plant residue.

     

Impacts of continuous excessive fertilization on soil potential nitrification activity and nitrifying microbial community dynamics in greenhouse system

Purpose

Sampling and analysis of greenhouse soils were conducted in Shouguang, China, to study continuous excessive fertilization effect on nitrifying microbial community dynamics in greenhouse environment.

Materials and methods

Potential nitrification activity (PNA), abundance, and structure of nitrifying microbial communities as well as the correlations with soil properties were investigated.

Results and discussion

Short-term excessive fertilization increased soil nutrient contents and the diversity of nitrifying microbial communities under greenhouse cultivation. However, the abundance and diversity of nitrifying communities decreased greatly due to the increase of soil acidity and salinity after 14 years of high fertilization in greenhouse. There was a significant positive correlation between soil PNA and the abundance of ammonia-oxidizing bacteria (AOB) but not that of ammonia-oxidizing archaea (AOA) in topsoil (0–20 cm) when pH ≥7. Soil PNA and AOB were strongly influenced by soil pH. The groups of Nitrososphaeraceae, Nitrosomonadaceae, and Nitrospiraceae were predominant in the AOA, AOB, and nitrite-oxidizing bacteria (NOB) communities, respectively. Nitrifying community structure was significantly correlated with soil electrical salinity (EC), organic carbon (OC), and nitrate nitrogen (NO₃ ^?–N) content by redundancy analysis (RDA).

Conclusions

Nitrification was predominated by AOB in greenhouse topsoil with high fertilizer loads. Soil salinity, OC, NO₃ ^?–N content, and pH affected by continuous excessive fertilization were the major edaphic factors in shaping nitrifying community structure in greenhouse soils.

     

Differential influence of four invasive plant species on soil physicochemical properties in a pot experiment

Purpose

This study compared the effects of four invasive plants, namely Impatiens glandulifera, Reynoutria japonica, Rudbeckia laciniata, and Solidago gigantea, as well as two native species—Artemisia vulgaris, Phalaris arundinacea, and their mixture on soil physicochemical properties in a pot experiment.

Materials and methods

Plants were planted in pots in two loamy sand soils. The soils were collected from fallows located outside (fallow soil) and within river valley (valley soil) under native plant communities. Aboveground plant biomass, cover, and soil physicochemical properties such as nutrient concentrations, pH, and water holding capacity (WHC) were measured after two growing seasons. Discriminant analysis (DA) was used to identify soil variables responsible for the discrimination between plant treatments. Identified variables were further compared between treatments using one-way ANOVA followed by Tukey’s HSD test.

Results and discussion

Plant biomass, cover, and soil parameters depended on species and soil type. DA effectively separated soils under different plant species. DA on fallow soil data separated R. laciniata from all other treatments, especially I. glandulifera, native species and bare soil, along axis 1 (related mainly to exchangeable K, N-NH₄, total P, N-NO_3, and WHC). Large differences were found between R. laciniata and S. gigantea as indicated by axis 2 (S-SO₄, exchangeable Mg, total P, exchangeable Ca, and total Mg). DA on valley soil data separated R. japonica from all other treatments, particularly S. gigantea, R. laciniata, and native mixture, along axis 1 (N-NO₃, total N, S-SO₄, total P, pH). Along axis 2 (N-NO₃, N-NH₄, Olsen P, exchangeable K, WHC), large differences were observed between I. glandulifera and all other invaders.

Conclusions

Plant influence on soil differed both among invasive species and between invasive and native species. Impatiens glandulifera had a relatively weak effect and its soil was similar to both native and bare soils. Multidirectional effects of different invaders resulted in a considerable divergence in soil characteristics. Invasion-driven changes in the soil environment may trigger feedbacks that stabilize or accelerate invasion and hinder re-colonization by native vegetation, which has implications for the restoration of invaded habitats.

     

Effectiveness of crop straws,and swine manure in ameliorating acidic red soils: a laboratory study

Purpose

Crop straws and animal manure have the potential to ameliorate acidic soils, but their effectiveness and the mechanisms involved are not fully understood. The aim of this study was to evaluate the effectiveness of two crop (maize and soybean) straws, swine manure, and their application rates on acidity changes in acidic red soils (Ferralic Cambisol) differing in initial pH.

Materials and methods

Two red soils were collected after 21 years of the (1) no fertilization history (CK soil, pH 5.46) and (2) receiving annual chemical nitrogen (N) fertilization (N soil, pH 4.18). The soils were incubated for 105 days at 25 °C after amending the crop straws or manure at 0, 5, 10, 20, and 40 g kg^?1 (w/w), and examined for changes in pH, exchangeable acidity, N mineralization, and speciation in 2 M KCl extract as ammonium (NH₄⁺) and nitrate plus nitrite (NO₃^??+?NO₂^?).

Results and discussion

All three organic materials significantly decreased soil acidity (dominated by aluminum) as the application rate increased. Soybean straw was as effective (sometimes more effective) as swine manure in raising pH in both soils. Soybean straw and swine manure both significantly reduced exchangeable acidity at amendment rate as low as 10 g kg^?1 in the highly acidic N soil, but swine manure was more effective in reducing the total acidity especially exchangeable aluminum (e.g., in the N soil from initial 5.79 to 0.50 cmol₍₊₎ kg^?1 compared to 2.82 and 4.19 cmol₍₊₎ kg^?1 by soybean straw and maize straw, respectively). Maize straw was less effective than soybean straw in affecting soil pH and the acidity. The exchangeable aluminum decreased at a rate of 4.48 cmol₍₊₎ kg^?1 per pH unit increase for both straws compared to 6.25 cmol₍₊₎ kg^?1 per pH unit from the manure. The NO₃^??+?NO₂^? concentration in soil increased significantly for swine manure amendment, but decreased markedly for straw treatments. The high C/N ratio in the straws led to N immobilization and pH increase.

Conclusions

While swine manure continues to be effective for ameliorating soil acidity, crop straw amendment has also shown a good potential to ameliorate the acidity of the red soil. Thus, after harvest, straws should preferably not be removed from the field, but mixed with the soil to decelerate acidification. The long-term effect of straw return on soil acidity management warrants further determination under field conditions.

     

Impact of fertilization on soil polyphenol dynamics and carbon accumulation in a tea plantation,Southern China

Purpose

The strong role that soil polyphenols play in soil organic matter (SOM) formation affects soil carbon sequestration. N deposition, which comes from man-made fertilizer, influences plant growth and soil biochemical properties therefore greatly regulates soil polyphenol metabolism. The objective of this experiment was to understand the effect of fertilizer form and rate on soil polyphenol dynamics as well as to understand the potential relationship between soil phenols and C accumulation.

Materials and methods

Urea, rapeseed cake, and chicken manure, respectively, referred as N, B, and F in the text, were applied at three rates (low N, medium N, and high N, referred as 1, 2, and 3 in the text, respectively); plots without fertilization were set as control (CK, for short). Seasonal dynamics of soil total polyphenol (Tp) and bound polyphenol (Bp) concentrations were monitored. Polyphenol oxidase (PPO), peroxidase (POD), and soil fluorescein diacetate (FDA) hydrolysis activities, all factors relevant to polyphenol metabolism, were measured simultaneously. The relationship between soil polyphenols and soil C concentration was also determined.

Results and discussion

N-fertilization altered the seasonal change pattern and the accumulation level of soil Tp and Bp, which possibly resulted from the enhancement of soil microbial activities and the change of soil nutrient status. Positive linear correlation was observed between soil Tp and TC (total C) contents, which means fertilization could influence C accumulation through affecting the metabolism of soil polyphenols. Soil chemical characteristics and enzyme activities that relate to soil polyphenol metabolism were influenced by fertilization as well. Mitigated TC increment was observed in most fertilization treatments mainly due to the increased SOM decomposition rate.

Conclusions

Our findings reveal the important role of soil phenols played in C accumulation in a tea plantation due to the significant, positive linear relationship between soil Tp and TC. Long-term studies, combined with soil microorganism community structure, soil humification, and tea leaf litter decomposition experiments, are necessary for fully understanding the role that polyphenols play in soil C cycle.

     

Land use change exerts a strong impact on deep soil C stabilization in subtropical forests

Purpose

It has been widely recognized that land use changes can cause significant alterations of soil organic matter (SOM) of various ecosystems. Forest conversion, a common land use change, and its effects on SOM have been a hot research topic during the past two decades. However, the mechanisms of the effects of forest conversion on SOM dynamics, particularly in deep soils, largely remain uncertain. This study aimed to examine the impacts of forest conversion on SOM stabilization through the analysis of soil aggregate and density fractionation, microbial composition, and functions in deep soils.

Materials and methods

Soil C and microbes were sampled in soil layers of 0–20 and 60–80 cm under broadleaved secondary forest and two coniferous plantations (Cunninghamia lanceolata and Pinus massoniana). Aggregate and density fractionation techniques were used to analyze C accumulation in non-protected, physically, chemically, and biochemically protected C fractions. A 90-day laboratory mineralization incubation experiment with and without 400-mg C kg^?1 soil glucose and phenol was conducted to determine the potential mineralizable C, utilization of substrate capacity, and metabolic quotient (qCO₂).

Results and discussion

Conversion of secondary forests into coniferous plantations significantly decreased bulk soil C, especially in the deep soils. Forest conversion significantly decreased non-protected, physically, and chemically protected C fractions in both topsoil and deep soil and biochemically protected C fraction in deep soils. The soil organic carbon (SOC) of topsoils was dominated by non-protected fraction while in deep soil which was dominated by protected fraction. Compared with the topsoils, soil microbes in the deep soils tend to preferentially use labile soil organic matter with lower substrate use efficiency (higher values of qCO₂), which indicates that a r-strategy dominates of microbes. The increased respiration rate in the deep soils caused by forest conversion, when normalized to soil C, indicates that deep SOM may be more prone to decomposition and destabilization than top SOM.

Conclusions

Forest conversion can cause a significant alteration of SOC stabilization through the changes of physically, chemically, and biochemically protected SOC fractions. The mechanisms for the changes in non-protected or/and protected SOC fractions may be associated with the redistribution of r-strategy- and K-strategy-dominated microbes due to changes in litter inputs and priming effects.

     

The fate of organic matter brought into soil by olive mill wastewater application at different seasons

Purpose

Application of olive mill wastewater (OMW) to soil may cause positive or negative effects. The present study aims at a better understanding of the fate of organic matter brought into soil by OMW application under different environmental conditions.

Materials and methods

Single OMW application to soil was conducted in spring, dry summer, summer with irrigation, and in winter. Two days and 18–24 months after the application, soil samples from two depths were analyzed for thermal soil organic matter (SOM) properties, total organic carbon, water-extractable dissolved soil organic carbon, and its specific ultraviolet absorbance at 254 nm.

Results and discussion

After winter and irrigated summer treatments, OMW was largely leached from the upper horizon within 2 days. Application in spring and summer dry initially increased the thermolabile fraction and the calorific value of SOM, however, in a different degree due to different transport, transformation, and immobilization mechanisms. At the long term, SOM content was still elevated after summer dry treatment. The reduction of the thermostable fraction in spring treatment indicates a priming effect of the labile OMW constituents.

Conclusions

Application in winter or with irrigation cannot be recommended for the investigated site. Under hot and dry conditions, SOM content increased most persistently due to stronger mineral-organic interactions. Favorable conditions for biodegradation during OMW application in spring reduced the effects on SOM quantity in the long term. However, a possible priming effect and the persistence of changes in thermal properties need to be further investigated for repeated applications.

     

Combined biochar and nitrogen fertilizer reduces soil acidity and promotes nutrient use efficiency by soybean crop

Purpose

Soil acidification is universal in soybean-growing fields. The aim of our research was to evaluate the effects of soil additives (N fertilizers and biochar) on crop performance and soil quality with specific emphasis on ameliorating soil acidity.

Materials and methods

Four nitrogen treatments were applied as follows: no nitrogen (N0), urea (N1), potassium nitrate (N2), and ammonium sulfate (N3), each providing 30 kg N ha^?1. Half plot area of the N1, N2, and N3 treatments was also treated with biochar (19.5 t ha^?1) to form N-biochar treatments (N1C, N2C, N3C). Both bulk and rhizosphere soils were sampled separately for the following analyses: pH, exchangeable base cations (EBC), exchangeable acidity (EA), total inorganic N (IN), total N (TN), and microbial phospholipid fatty acids (PLFAs). Soybean biomass and nutrient contents were also determined. Correlation analysis was applied to analyze the relationships between soil chemical properties and soybean plant parameters.

Results and discussion

With N-biochar additions (N1C, N2C, N3C), soil chemical properties changed as follows: pH increased by 0.6–1.2 units, EBC, IN, and TN increased by 175–419, 38.5–54.7, and 136–452 mg kg^?1, respectively, and PLFAs increased by 23.6–40.9 nmol g^?1 compared to the N0 in the rhizosphere. Microbial PLFAs had positive correlations with soil pH; EBC; exchangeable K, Ca, Na, and Mg; TN; IN; NH₄ ⁺; and NO₃ ^? (r?=?0.66–0.84, p?<?0.01). There were negative correlations between PLFAs and EA or exchangeable Al (r?=??0.64, ?0.66, p?<?0.01), which indicated that the additives increased microbial biomass by providing a suitable environment with less acid stress and more nutrients. The additives increased soil NH₄ ⁺ and NO₃ ^? by promoting soil organic N mineralization and reducing NH₄ ⁺ and NO₃ ^? leaching. Moreover, the soybean seed biomass and the nutrient contents in seeds increased with N-biochar additions, especially in the N3C treatment.

Conclusions

N-biochar additions were effective in ameliorating soil acidity, which improved the microenvironment for more microbial survival. N-biochars influenced N transformations at the plant–soil interface by increasing organic N mineralization, reducing N leaching, and promoting N uptake by soybeans. The soil additive ammonium and biochar (N3C) were best in promoting soybean growth.

     

Inorganic and organic carbon dynamics in forested soils developed on contrasting geology in Slovenia—a stable isotope approach

Purpose

Soil carbon dynamics were studied at four different forest stands developed on bedrocks with contrasting geology in Slovenia: one plot on magmatic granodiorite bedrock (IG), two plots on carbonate bedrock in the karstic-dinaric area (CC and CD), and one situated on Pleistocene coalluvial terraces (FGS).

Materials and methods

Throughfall (TF) and soil water were collected monthly at each location from June to November during 2005–2007. In soil water, the following parameters were determined: T, pH, total alkalinity, concentrations of Ca²⁺ and Mg²⁺, dissolved organic carbon (DOC), and Cl^? as well as δ¹³C_DIC. On the other hand, in TF, only the Cl^? content was measured. Soil and plant samples were also collected at forest stands, and stable isotope measurements were performed in soil and plant organic carbon and total nitrogen and in carbonate rocks. The obtained data were used to calculate the dissolved inorganic carbon (DIC) and DOC fluxes. Statistic analyses were carried out to compare sites of different lithologies, at different spatial and temporal scales.

Results and discussion

Decomposition of soil organic matter (SOM) controlled by the climate can explain the ¹³C and ¹⁵?N enrichment in SOM at CC, CD, and FGS, while the soil microbial biomass makes an important contribution to the SOM at IG. The loss of DOC at a soil depth of 5 cm was estimated at 1 mol m^?2 year^?1 and shows no significant differences among the study sites. The DOC fluxes were mainly controlled by physical factors, most notably sorption dynamics, and microbial–DOC relationships. The pH and pCO₂ of the soil solution controlled the DIC fluxes according to carbonate equilibrium reactions. An increased exchange between DIC and atmospheric air was observed for samples from non-carbonate subsoils (IG and FGS). In addition, higher δ¹³C_DIC values up to ?19.4?‰ in the shallow soil water were recorded during the summer as a consequence of isotopic fractionation induced by molecular diffusion of soil CO₂. The δ¹³C_DIC values also suggest that half of the DIC derives from soil CO₂ indicating that 2 to 5 mol m^?2 year^?1 of carbon is lost in the form of dissolved inorganic carbon at CC and CD after carbonate dissolution.

Conclusions

Major difference in soil carbon dynamics between the four forest ecosystems is a result of the combined influence of bedrock geology, soil texture, and the sources of SOM. Water flux was a critical parameter in quantifying carbon depletion rates in dissolved organic and inorganic carbon forms.

     

Qualitative and quantitative soil organic matter estimation for sustainable soil management

Purpose

The aims of this paper were to review tools and methods for qualitative and quantitative evaluation of soil organic matter (SOM) coming from diverse egzogenic sources for effective soil management, and to introduce a new approach to predict dynamics of SOM transformations, especially humification, as a key process in the formation of humic substances (HSs).

Materials and methods

A review of existing literature is presented on tools and methods for qualitative and quantitative assessment of organic matter in soil originating from various sources for reasonable soil management, attempting to provide a better understanding of the advances in organic matter transformations and new research directions for modeling. Diverse tools and methods for qualitative and quantitative evaluation of organic matter in soil coming from diverse sources have been adopted so far to express transformation processes.

Results and discussion

For the qualitative analysis of SOM and humic acids (HAs), the analytical techniques are applied, e.g., HPSEC, NMR, and ESI-FTICRMS. The quantitative analysis is done through the following parameters: humification index (HI), humification degree (HD), and humification rate (HR). These analyses indicated that because of lack of reliable data from sufficiently long-term experiments, mathematical modeling may be applied as a numerical tool for quantitative estimation and prediction of humification of SOM. The effective soil management should include soil properties as well as different functions: food production, nutrient and water cycling, storage, filtrating, buffering, biological habitat, gene pool, source of raw materials, climate regulations, heritage, platform for man-made structure. The soil utility value should be evaluated through the SOM qualitative and quantitative analysis of organic carbon and total nitrogen. Knowledge about dynamics of SOM transformations is essential, particularly in the context of stability and efficiency of different sources of organic matter applied into soil. A qualitative understanding of SOM dynamics transformations along with modeling for quantitative assessment of HS formation should be used to develop sustainable soil management. The modeling may be considered as a tool for predicting SOM humification dynamics and consequently the formation of HSs from the diverse sources. The existing archival data from a long-term experiment may be used to build and calibrate the reliable mathematical model of SOM humification.

Conclusions

Managing of SOM remains a sound basis for maintaining soil in a good condition for optimizing productivity. The development of land management strategies to optimize both the increase of soil organic carbon levels and the recycling of nutrients from SOM needs to be a priority. This should include policy makers and other users as well.

     

Effects of biomass ash,bone meal,and alkaline slag applied alone and combined on soil acidity and wheat growth

Purpose

The purpose of this study is to examine the effects of combined application of biomass ash (BA), bone meal (BM), and alkaline slag (AS) on soil acidity, nutrient contents, uptake of the nutrients by wheat, and wheat growth.

Materials and methods

A pot experiment with an Ultisol collected from Anhui province, China, was conducted to compare the effects of BA, BM, and AS applied alone and combined on soil acidity; soil nutrient contents; uptake of N, P, K, Ca, and Mg by wheat, and wheat growth.

Results and discussion

Application of BA, BM, and AS alone and combined increased soil pH and decreased soil exchangeable Al³⁺. BA + BM + AS showed the greatest ameliorating effect on soil acidity, and soil pH of the treatment increased by 1.24 units compared with control. Application of BA + BM + AS reduced soil exchangeable Al³⁺ and increased soil exchangeable calcium and magnesium to a greater extent than BA + BM and single application of the amendments. The BM-containing amendments substantially increased soil available phosphorous by 66–93% compared with control. Application of the amendments alone and combined enhanced the uptake of N, P, K, Ca, and Mg by wheat and thus promoted wheat growth and increased yield of wheat grains. Application of BA + BM + AS and BA + BM showed greater effects on nutrient uptake and wheat growth than single application of the amendments. Wheat straw weights of the two treatments were 11.1 and 10.1 times greater than that of control. The data were 2.7, 4.8, and 5.6 times for the treatments of BA, AS, and BM. The contents of Cd, Cr, Zn, and Cu in wheat grains were lower than standard limits, except for the single BA treatment.

Conclusions

BA + BM + AS is the best choice for amelioration of acid soils and promotion of crop production.

     

Pectin adsorption on amorphous Fe/Al hydroxides and its effect on surface charge properties and Cu(II) adsorption

Purpose

The purpose of this study was to elucidate the mechanisms for pectin-enhanced adsorption of heavy metal cations on variable charge minerals.

Materials and methods

Batch experiments were conducted to investigate the adsorption of pectin and copper(II) by amorphous Fe/Al hydroxides. The morphology, mineralogy, and functional groups of pectin–Fe/Al hydroxides were examined using X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy analysis.

Results and discussion

The amount of pectin adsorbed by amorphous Al(OH)₃ was much greater than that by amorphous Fe(OH)₃ at pH values between 3.5 and 6.5 due to the higher positive charge density on Al(OH)₃ and greater electrostatic attraction between the hydroxide and pectin compared with Fe(OH)₃. The addition of pectin decreased the positive surface charge on amorphous Fe and Al hydroxides. The presence of pectin enhanced the adsorption of Cu(II) by the Fe and Al hydroxides. The increase in Cu(II) adsorption on amorphous Fe hydroxide was more obvious at low pH values than at higher pH values, while an opposite changing trend was observed for amorphous Al hydroxide. At pH 3.9, 4.3, and 4.9, pectin increased Cu(II) adsorption by Fe hydroxide from 24.4, 76.6, and 177.0 mmol/kg to 61.6, 98.8, and 192.0 mmol/kg, i.e., Cu(II) adsorption was increased by 37.2, 22.2, and 15.0 mmol/kg, respectively. At pH 4.3 and 4.9, pectin increased Cu(II) adsorption by Al hydroxide from 3.7 and 27.0 mmol/kg to 17.3 and 69.4 mmol/kg, i.e., Cu(II) adsorption was increased by 13.6 and 42.4 mmol/kg, respectively. The greater adsorption of pectin by Al hydroxide was mainly responsible for the larger enhancement of pectin on Cu(II) adsorption on Al hydroxide at higher pH values compared with Fe hydroxide.

Conclusions

The adsorption of pectin on Fe and Al hydroxides decreased the positive charge on the hydroxides and thus enhanced the adsorption of Cu(II) by the hydroxides.

     

Influence of organic and inorganic passivators on Cd and Pb stabilization and microbial biomass in a contaminated paddy soil

Purpose

Soil contamination with heavy metals, such as Cd and Pb, has caused severe health and environmental risks all over the world. Possible eco-friendly solutions for Cd and Pb immobilization were required to reduce its mobility through various cost-effective amendments.

Materials and methods

A laboratory incubation study was conducted to assess the efficiency of biochar (BC), zeolite (ZE), and rock phosphate (RP) as passivators for the stabilization of Cd and Pb in paddy soil as well as soil microbial biomass. Various extraction techniques were carried out: a sequential extraction procedure, the European Community Bureau of Reference (BCR), toxicity characteristic leaching procedure (TCLP) test, and single extraction with CaCl₂. The impact of passivators on soil pH, dissolved organic carbon (DOC), and microbial biomass (carbon, nitrogen, and phosphorus) was examined in the metal contaminated soil.

Results and discussion

The results showed that the exchangeable portion of Cd in soil was significantly reduced by 34.8, 21.6, and 18.8% with ZE, RP, and BC at a 3% application rate, respectively. A similar tendency of reduction in Pb soluble portion was observed by ZE (9.6%), RP (20%), and BC (21.4%) at a 3% application rate. Moreover, the TCLP leachate of Cd and Pb was apparently reduced by 17 and 30.3% with BC at a 3% application dose, respectively, when compared to the control. Soil pH, nutrients, and microbial biomass C, N, and P were significantly increased with the addition of BC, RP, and ZE passivators.

Conclusions

The results showed that the incorporation of BC, ZE, and RP significantly reduced the Cd and Pb mobility in paddy soil as well as enhanced soil nutrients and microbial biomass. Overall, among all the amendments, rice straw derived-BC performed better for Cd and Pb immobilization in paddy soil.

     

Use of biochar-compost to improve properties and productivity of the degraded coastal soil in the Yellow River Delta,China

Purpose

Nutrient deficiency and salt stress (sodium, Na⁺) strongly limited the productivity of the degraded coastal soils in the Yellow River Delta. Biochar-based functional materials have been considered as a promising amendment to solving the problem of global soil security (e.g., erosion, fertility loss, acidification, and salinization). Therefore, this study aimed to explore the potential of using a biochar-compost amendment (BCA) to improve the coastal soil properties and productivity.

Materials and methods

The BCA was produced from composting of biochar and additives including seafood shell powder, peanut shell, commercial humate, and inorganic nutrients. Two halophytes, sesbania (Sesbania canabina (Retz.) Pers) and seashore mallow (Kosteletzkya virginica), were chosen as the tested plants in a 52-day pot experiment. BCA was added as the rates of 0, 1.5, 5, and 10 % (w/w). At the end of the incubation, the shoot height, biomass, and root morphological parameters including length, tips, and surface area were measured, as well as the properties (e.g., soil organic matter (SOM) content and cation exchange capacity (CEC)) of the rhizosphere and non-rhizosphere soils.

Results and discussion

The BCA application at 1.5 % enhanced the growth of sesbania and seashore mallow and increased their total biomass by 309 and 70.8 %, respectively, while significantly inhibited both the halophyte growths at 10 %. Similarly, both the halophyte root morphologies (e.g., length and tips) significantly increased by BCA addition at 1.5 %. The promoting growth of the both halophytes could be resulted from the improvement of soil properties such as the increased SOM and CEC, the decreased amount of the exchangeable sodium (Ex-Na) and exchangeable sodium percentage (ESP), and the rhizosphere effect (e.g., decreased soil pH). The higher rate of BCA addition (e.g., 10 %) sharply increased soil salinity, responsible for the inhibition of both the halophyte growths. Although BCA addition may directly supply much nitrogen (N) for the soils, N bioavailability for both halophytes was not largely improved.

Conclusions

The short-term laboratory pot experiments revealed that producing the biochar-compost with desired properties (e.g., BCA) could be a feasible alternative to remediate the degraded coastal soil in the Yellow River Delta. Moreover, the addition of BCA should be kept at an optimal level, which may produce expected positive results. Our results will be helpful for supporting the strategy of designing right biochar-compost for the right soil.