Exchangeable Ca Content Research Articles

An Assessment of the Physico-Chemical Parameters of Mangrove Soils that Support Nypa fruticans and Other Mangrove Species Establishment in the Cameroon Estuary

Invasion of Nypa palm into mangroves is a problem in the Cameroon Estuary. Soil variability is one of the dominant features that support Nypa palm establishment. The objective was to characterize the soil under the different mangrove stands; Purely Nypa palm stands (A), mixed stands i.e Nypa palm and other mangrove species (B) and other mangrove species i.e Nypa palm free (C), determine the principal soil characteristic critical for Nypa spread. 9 plots of 20 x 20 m were laid in each of the sites. 27 soil samples were collected in the North, West, South East and Center at a depth of 30 cm in these three sites using a soil auger. The results in the three sites indicated that; soils were acidic (3.87- 4.39), pH values did not significantly differ (alpha >0.05), organic matter was low in A (12.32%) and B (16.35%).Soil Organic Carbon ranged from (4.52 to 7.06%). High percentage of organic carbon content was recorded in C (7.06%). Low percentage of organic carbon was found in A (4.52%). Total nitrogen varied from 1.04 g/kg, 1.70g/kg, 1.80 g/kg in sites C, A and B. In all the mangrove stands, the values of Exchangeable Ca content were below 4.0 cmolkg-1. Soil texture in the three sites were; sandy, clay and silt. Power test showed no significant different in soil types between the three sites (p>0.05). According to the component matrix the factor is positively loaded by soil EC, moisture content, organic matter, organic carbon, N, C/N, CEC, Ca, Mg, K, Na, Clay, Silt, and negatively loaded by the percent sand. This study therefore, suggests that since soil plays key role in Nypa palm establishment, there should be constant monitoring of soil quality to forestall drastic changes that will jeopardize the survival of the mangroves. Nypa palm seedlings should also be physically removed from mangrove forest to prevent colonization. In addition, more mangrove seeds should be planted in deforested mangrove areas to close the window of opportunity for the palms.

Soil carbon accumulation with increasing temperature under both managed and natural vegetation restoration in calcareous soils

Vegetation restoration has been proposed as an effective strategy for increasing soil organic carbon (SOC) sequestration. However, the responses of SOC to managed and natural vegetation restoration strategies at a large scale are poorly understood due to the varying SOC components and changing climatic conditions. Here, we measured bulk SOC, particulate organic carbon (POC), and mineral-associated organic carbon (MOC) after 15 years of vegetation restoration along an elevation gradient with a corresponding temperature gradient in the calcareous soils of karst region, Southwest China. We compared managed plantation forest and naturally recovered shrubland vegetation restoration strategies, using cropland and mature forest as references. Overall, we found that the SOC and POC densities in both plantation forest and shrubland were significantly higher than in the cropland but lower than in the mature forest. There were no significant differences in the SOC pool between the plantation forest and shrubland. Furthermore, the relative changes in the SOC and POC densities increased with increasing mean annual temperature in the plantation forest and shrubland. Our results showed that both vegetation restoration strategies, characterized by higher soil microbial abundance and exchangeable Ca concentration, were beneficial to POC but not MOC accumulation, and sufficiently compensated SOC decomposition at lower elevation with higher MAT. Our results highlight the potential of both vegetation restoration strategies for promoting SOC accumulation in warmer karst regions and emphasize the necessity to understand soil carbon stabilization mechanisms in calcareous soils.

Оптимізація живлення сільськогосподарських культур за фізико-хімічної деградації кислих ґрунтів

Goal. To study and to identify features of optimization of crop nutrition during physicochemical degradation of acid soils. Methods. Field, laboratory, computational, mathematical, and statistical. Results. Results are given of researches in the influence of agrochemical load on gray forest soil with increasing doses of fertilizers (in combination with measures of radical chemical reclamation and without them) received during 2016–2019. It is established that the use of intensive fertilizer systems without radical chemical reclamation leads to the deterioration of the physicochemical properties of gray forest soil. On the background of reducing the aftereffects of radical chemical reclamation for 10–13 years, the annual application of a dose of alkaline earth elements, taking into account the physiological characteristics of the culture (average 11.4 and 4.6 kg/ha of calcium and magnesium, respectively) ensures for 10–12 years close to neutral reaction, and on the 13th year of application — the slightly acidic reaction of the soil solution. Besides, the content of exchangeable Ca and Mg in GVK increases slightly, it increases to 6.71–7.00 mg·eq/100 g of soil. Conclusions. The use of a dose of mineral fertilizers on gray forest soil, which is calculated according to the species genotypic ratio (SGR) of elements in the biomass of the culture on the background of application of lime, optimizes crop nutrition, physicochemical properties of the soil, reduces the dose of phosphorus and potassium and toxic action of H+ and Al3+. The optimal combination of N, P, K, Ca and Mg (216 kg/ha in the ratio of 1:0.4:0.5:0.3:0.1) in combination with seed inoculation with nitrogen-fixing and phosphorus-mobilizing bacteria provides an increase of productivity of the grain crop rotation to 5.45 t/ha g.p., and payback of 1 kg act. mat. of fertilizer applied to 15.6 kg g.p. Physicochemical degradation of acid soils at the application of high doses of nitrogen fertilizers can be partially prevented by saturation of the soil absorption complex with exchange cations of alkaline earth metals, supplementing the fertilization system with small doses of Ca and Mg, which are calculated according to the recommended dose of nitrogen, limited on acidic soils.

Soil quality and proposal for fertility improvement of arable soil in Rasina District

During the regular control of soil fertility in the Rasina District, it was established that the plots of land were distributed across Vertisol, Eutric Cambisol and Fluvisol types of soils, and to a lesser extent on Pseudogley and Ranker. The tested samples had different textures - sandy loam and loam, clay-sandy loam and clay loam, and clay. Plots of land that were of very acidic and acidic reactions were predominant, with medium amounts of humus, very low amounts of available phosphorus, and high amounts of available potassium. High or very high cation absorption capacity was found in about half of the examined fields; a deficient content of exchangeable Ca was recorded in 22% of plots and that of exchangeable Mg in 16% of plots, while an unfavorable Ca/Mg ratio was measured in 44% of plots. The overall sensitivity to acidification was mainly moderate (50.6% of plots) and strong (20.2% of plots). Very high concentrations of mobile Al, which could be toxic to plants, were found in 5 field plots.

Status of macro- and micro-nutrients in soils of Chamoli district of Uttarakhand

A GPS based soil survey was conducted in nine blocks of Chamoli district of Uttarakhand (n=300) to evaluate the status of extractable macro- and micro-nutrients and to relate them with general soil properties. Soil texture ranged from sandy loam to clay loam, pH from 4.8 to 8.29, electrical conductivity from 0.170 to 5.431 dSm 1 and organic carbon content from 3.14 to 30.72 g kg 1 soil. Among the macro-nutrients, Olsen’s and Bray’s extractable P varied from 1.41 to 47.20 mg kg 1 soil, neutral normal ammonium acetate extractable K content from 24.82 to 269.1 mg kg 1 soil. Exchangeable Ca and Mg content varied from 20 to 1620 mg kg 1 and 12 to 288 mg kg 1 soil, respectively. The content of 0.15% CaCl2 extractable S content varied from 1.23 to 26.64 mg kg 1 soil. The DTPA extractable Zn, Cu, Fe, Mn content varied from 0.09 to 15.41, 0.08 to 9.03, 3.13 to 84.22 and 1.93 to 54.96 mg kg 1 soil, respectively. Hot water-soluble B content varied from 0.23 to 2.61 mg kg 1 soil while ammonium oxalate (pH 3.3) extractable Mo content varied from 0.18 to 1.36 mg kg 1 soil. Simple correlation showed that soil pH had a significant and positive correlation with soil extractable P, Ca, S, B and Mo but a negative one with extractable Cu, Fe and Mn. Soil EC had a significant and positive correlation with extractable P, K, Mg, S, Fe, B and Mo. Soil organic carbon had a significant and positive correlation with extractable K. On the basis of calculated nutrient indices (N.I.), the soils of Chamoli district were low in soil extractable S, medium in extractable K and Zn, high in organic carbon content, extractable P, Ca, Mg, Cu, Fe, Mn, B and Mo with sporadic cases of Zn, Cu and B deficiency.

Growth and flowering of young cocoa plants is promoted by organic and nitrate-based fertiliser amendments

SummaryCocoa (Theobroma cacao) farmers in Sulawesi, Indonesia typically use subsidised, ammonium-based rice fertilisers that in combination with poor agricultural practices have resulted in soil acidification, loss of organic matter, aluminium toxicity and lower soil fertility. As a result, these soils are only marginally appropriate for replanting cocoa to boost production. A field experiment was performed to test alternative soil amendments for successful replanting of cocoa on these deficient soils. In a trial with a randomised block design, 6-month old seedlings, top-grafted with the local MCC02 clone, were planted under light Gliricidia sepium shade and after 3 months treated quarterly with two options of mineral fertilisers: either a customised fertiliser, consisting of Nitrabor (a combination of calcium nitrate and boron), dolomite, rock phosphate and KCl or a NPK/urea mix used by farmers, each supplied with or without ‘micronutrient’ rock salt, organic fertiliser and beneficial microorganisms or their culture medium, a mixture of chitin and amino acids (a total of 20 treatments). Over a 4-year period, the marginal mean rates of stem diameter increment and flowering score were higher in customised fertiliser than NPK/urea treatments. The average growth rate was highest in the first year and was increased by supplying organic fertiliser. A significant correlation (r = 0.22, p < 0.05) occurred between growth and available P, but concentrations of available P were higher in the NPK/urea plots, which also had lower mean growth rates. Combined supply of organic fertiliser and microbes increased available P, as well as growth rates, in both the customised and NPK/urea treatments. In contrast, NPK/urea-treated plots without these amendments demonstrated very low growth rates. The customised formulation was more effective with or without added organic fertiliser or inoculated microbes. Micronutrient supply stimulated flowering. Growth rates in trees supplied with NPK/urea were also promoted by micronutrients. Leaf flush production occurred in regular cycles and was unaffected by the nutrient amendments. After 3 years, the customised and organic fertiliser application increased soil pH and exchangeable Ca and Mg concentrations, although they remained below recommended levels for cocoa production. These treatments had little impact on soil C content (about 1.3%) which was also deficient. Exchangeable Al and total Zn concentrations were higher in soils amended with NPK/urea. The results of the trial provide evidence that utilisation of organic fertiliser in combination with customised nitrate-based formulations improves cocoa establishment, growth and soil properties and should be recommended as a replacement for the NPK/urea fertilisers traditionally used by farmers.

Divergent controls on carbon concentration and persistence between forests and grasslands of the conterminous US

Variation in soil organic C (%OC) concentration has been associated with the concentration of reactive Fe- and Al-oxyhydroxide phases and exchangeable Ca, with the relative importance of these two stabilizing components shifting as soil pH moves from acid to alkaline. However, it is currently unknown if this pattern is similar or different with regard to measures of soil C persistence. We sampled soils from 3 horizons (uppermost A, uppermost B, C or lowest B horizons) across a pH gradient of 11 grass-dominated and 13 deciduous/mixed forest-dominated NEON sites to examine similarities and differences in the drivers of C concentration and persistence. Variation in C concentrations in all soils could be linked to abundances of Fe, Al and Ca, but were not significantly linked to variation in soil C persistence. Though pH was related to variation in Δ14OC, higher persistence was associated with more alkaline pH values. In forested soils, depth explained 75% of the variation in Δ14OC (p < 0.0001), with no significant additional correlations with extractable metal phases. In grasslands, soil organic C persistence was not associated with exchangeable Ca concentrations, but instead was explained by depth and inorganic C concentrations (R2 = 0.76, p < 0.0001), implying stabilization of organic C through association with carbonate precipitation. In grasslands, measures of substrate quality suggested greater persistence is also associated with a more advanced degree of decomposition. Results suggest that explanatory variables associated with C concentrations differ from those associated with persistence, and that reactive Fe- and Al-oxyhydroxide phases may not be present in high enough concentrations in most soils to offer any significant protective capacity. These results have significant implications for our understanding of how to model the soil C cycle and may suggest previously unrecognized stabilization mechanisms associated with carbonates and forms of extractable Si.

Mid-term (30 years) changes of soil properties under chestnut stands due to organic residues management: An integrated study

Chestnut plantations are worldwide distributed and they are often subjected to intensive management practices such as the removal of the organic residues from the soil surface. The present study aimed to investigate the effect of such practices on soil properties at different depths and on nutrient contents in chestnut leaves. To reach our goal, 6 pits down to 30 cm soil depth were dug in European chestnut (Castanea sativa Mill.) stands where the organic residues such as burrs, leaves and pruned materials are yearly removed (REM), and 9 pits in stands where the organic residues are chopped and left on soil surface (CONS). Both practices began about 30 years ago. The nutrient contents in leaves were assessed on chestnut trees close to each pit. Our findings showed a more intense soil development in CONS than in REM. At soil surface, CONS had thicker mineral horizon than in REM probably due to the protection acted by the organic residues against erosion. In subsoil, organic residues conservation promoted the organic C (soil organic C, water–extractable organic C, fulvic–like C and soil organic C stock) accumulation which further promoted horizon development. Since the role of soil organic matter (SOM) as source of nutrients, the subsoil of CONS study sites had a greater stock of Ca, P and S and a higher exchangeable Ca content than REM. Furthermore, the higher SOM and nutrient contents in CONS subsoil compared to REM promoted the microbial respiration. The organic residues conservation effects on the surface soil horizon properties were, instead, negligible. Despite the generally better soil conditions in CONS than in REM, no differences were observed for the leaf nutrient contents likely due to the chestnut trees adaptability also to the scarcely fertile soils. Overall, our findings highlighted the importance of organic residues conservation for the improvement in deeper soil horizons of the chemical and biological fertility in chestnut plantations. Furthermore, this research pointed out to pay more attention on subsoil since it is a good indicator of the changes caused by external factors.

The Impact of Nickel Mining on Soil Properties and Growth of Two Fast-Growing Tropical Trees Species

Opencast nickel mining is common in natural forests of Indonesia. However, rehabilitation of postmining degraded land is difficult. We investigated the effect of opencast nickel mining on soil chemical properties and the growth of two fast-growing tropical tree species, Falcataria moluccana and Albizia saman. Soil was collected from post-nickel mining land and a nearby natural forest. Soil pH, available phosphorus (P) concentration, total carbon (TC) and total nitrogen (TN) concentration, C/N ratio, cation exchange capacity (CEC), and exchangeable K, Na, Mg, Ca, Fe, and Ni concentrations were determined. Falcataria moluccana and A. saman were then grown in the collected soils for 15 weeks in a greenhouse. Shoot height and shoot and root dry weights of the seedlings were measured. The post--nickel mining soils TN, TC, available P, CEC, and exchangeable Ca and Na concentrations decreased by 98%, 93%, 11%, 62%, 85%, and 74%, respectively, in comparison with the natural forest soils. The pH of postmining soil was higher than natural forest soil. Shoot dry weight of F. moluccana seedlings grown in postmining soil was significantly (P&lt;0.05) lower than that of seedlings grown in natural forest soil. However, there was no difference in shoot dry weight between A. saman seedlings grown in natural forest soil and postmining soil, as well as root dry weights of both species. The results indicate that opencast nickel mining decreased soil fertility, which subsequently inhibited the growth of F. moluccana and A. saman seedlings.

Application of earthworm cast improves soil aggregation and aggregate-associated carbon stability in typical soils from Loess Plateau

Earthworm casts exhibit remarkable fertility and have been widely used as an organic fertilizer. This study focused on the effects of earthworm cast application on soil aggregates and aggregate-associated carbon in typical soils from the Loess Plateau (China). Soil column experiments were conducted in the laboratory using cultivated loessial soil (CS), dark loessial soil (DS), and aeolian soil (AS). Application of earthworm casts significantly reduced the content of aggregates sized <0.5 mm but increased the content of water-stable aggregates. Compared to without-cast treatment, earthworm cast application increased the organic carbon content by 13.4–58.3%, 14.4–51.1%, 17.9–45.3%, 16.7–62.4%, 18.4–43.3%, and 19.8–62.9% in soil aggregate fractions of sizes <0.25, 0.25–0.5, 0.5–1, 1–2, 2–5, and >5 mm, respectively. The application of earthworm casts significantly increased heavy fraction organic carbon (HFOC), CaCO3, and exchangeable Ca contents in soil by 14.5–69.4%, 12.8–51.9%, and 33.3–63.2%, respectively. Compared with macroaggregates, microaggregates had higher CaCO3 contents but smaller light-fraction organic carbon (LFOC) to HFOC ratios, indicating that earthworm cast application improved the organic carbon stability more in microaggregates than macroaggregates. Comparison analysis of the three soils showed AS performed better in aggregation and aggregate-associated carbon stability than CS and DS after applying earthworm casts. The findings improve our understanding of the effects of earthworm cast application on soil aggregate distribution and aggregate-associated carbon stability, which will help improve the application efficiency of earthworm casts as an organic fertilizer in the Loess Plateau area.

The application of calcium containing tannery sludge for amelioration of alkali soils

Tannery industry is one of the major industries in India. Solid waste from these industries contains high amount of calcium (17.2%) alongside considerable amount of essential nutrients and organic matter. The effects of sludge along with organic manures were assessed in comparison with gypsum on biometric observations and physicochemical properties of soil by conducting incubation and pot culture experiments had been assessed. A pot culture experiment was conducted during between 2015 and 2016 at Anbil Dharmalingam Agricultural College and Research Institute, Trichy in Tamil Nadu with marigold as test crop. our results indicated that the applications of tannery sludge along with organic amendments significantly improved the soil chemical properties by reducing the pH and ESP (Exchangeable Sodium Percentage) of soil and increasing the exchangeable calcium (Ca) content, coupled with decreasing exchangeable sodium (Na) levels. Such reclamation effect was much pronounced when tannery sludge was combined with press mud and vermicompost. Thus the treatment, T6 (TS @ 100% GR+Pressmud @ 10 t ha-1) recorded the highest exchangeable Ca and lowest exchangeable Na content of soil with considerable decrease in pH.

Chemical pattern of vegetation and topsoil of rangeland fertilized over 21 years with phosphorus sources and limestone

The Pampa’s rangeland in South America is underused or replaced by annual crops or forest cultivation with higher economic returns. Our goal was to test the long term effects of phosphorus fertilizer and limestone applications on P availability, aluminum neutralization in deep soil layer and rangeland productivity. For this, three rates of three phosphorus sources combined with limestone were applied in a 21 year field trial. The dry matter (between 2016 and 2019) and nutrient accumulation in plant shoot were measured. The topsoil was divided in four layers (0–2.5, 2.5–5.0, 5.0–7.5, and 7.5–10.0 cm), and chemical properties were determined. Rock phosphate application at rate 249 kg ha−1 of P increased the soil P content along the soil profile down to 7.5 cm. After 21 years of liming, the neutralizing front reached depths greater than 10 cm and the reacidification was not significant. In these conditions, the contents of exchangeable Ca, Mg and Al and pH are greater than, and Al saturation is lower than without limestone. The effect of fertilization and limestone amendments are however limited in time and there was no response of rangeland dry matter production after more than four years after the last fertilization.

Alum split applications strengthened phosphorus fixation and phosphate sorption in high legacy phosphorus calcareous soil

High phosphorus (P) saturation arising from historic P inputs to protected vegetable fields (PVFs) drives high P mobilisation to waterbodies. Amendment of soils with alum has shown potential in terms of fixing labile P and protecting water quality. The present 15 month pot experiment investigated P stabilisation across single alum application (Alum-1 treatment, 20 g alum/kg soil incorporated into soil before the maize was sown), alum split applications (Alum-4 treatment, 5 g alum/kg soil incorporated into soil before each crop was sown i.e. 4 × 5 g/kg) and soil only treatment (Control). Results showed that the Alum-1 treatment caused the strongest stabilisation of soil labile P after maize plant removal, whereas the P stabilisation effect was gradually weakened due to the transformation of soil non-labile P to labile P and the reduced active Al3+ in soil solution. For the Alum-4 treatment, soil labile P decreased gradually with each crop planting and was lower than the Alum-1 treatment at the end of the final crop removal, without any impairment on plant growth. The better P stabilisation at the end of Alum-4 treatment was closely correlated with a progressive supply of Al3+ and a gradual decrease of pH, which resulted in higher contents of poorly-crystalline Al, Fe and exchangeable Ca. These aspects were conducive to increasing the soil P stabilisation and phosphate sorption. In terms of management, growers in continuous cropping systems could utilise split alum applications as a strategy to alleviate P losses in high-P enriched calcareous soil.

Land use and management effects on volcanic soils in West Sumatra, Indonesia

In this study, we aimed to assess the influence of land use and management on the fertility characteristics and pedogenic indicators of volcanic soils. Our study area was a mountainous area located in West Sumatra, Indonesia, where local farmers intensively cultivate vegetables by applying high amounts of chemical fertilizers and agrochemicals. Some negative impacts of conventional management were observed in the vegetable fields: soil acidification and loss of organic matter, with descended soil pH and increased acidity as well as decreased contents of exchangeable bases and with decreased amount of organic C. These impacts were not effectively mitigated by positive factors such as increased P availability and decreased capacity for P fixation. Continued cultivation over the years compounded the effects of these changes. Organic farming was advantageous in terms of soil fertility maintenance as it alleviated negative impacts compared to conventional farming. Natural fallow was effective in replenishing soil fertility as indicated by a significant increase in organic C, total N, and exchangeable Ca and Mg contents compared to the vegetable fields. The degree of replenishment was enhanced with a longer period under fallow; however, the natural fallow decreased P availability and increased P fixation capacity. Calliandra calothyrsus fallow further accelerated soil acidification, regardless of the rapid increase in the organic C and exchangeable bases contents. The adverse effects of Calliandra fallow were associated with the formation of humus–aluminum complexes to an extent that it changed from Sil-andic to Alu-andic Andosols.

Post Bauxite Mining Land Soil Characteristics and Its Effects on the Growth of Falcataria moluccana (Miq.) Barneby &amp; J. W. Grimes and Albizia saman (Jacq.) Merr.

The remediation of opencast bauxite mines in the natural forests of Indonesia is difficult. We have investigated and contrasted the chemical characteristics of soils from natural forests and mining sites and their effects on plant growth. The soil pH, total carbon (C), nitrogen (N) and available phosphorus (P) concentrations, cation exchange capacity, C/N ratio, and exchangeable K, Na, Mg, Ca, Fe, and Ni concentrations were determined. Falcataria moluccana and Albizia saman were then grown in these soils for 15 weeks, and their shoot heights, shoot dry weights, and root dry weights determined. The post bauxite mining soils’ N, C, and available P concentrations and exchangeable Ca, Mg, and Na concentrations decreased by 75, 75.7, 15.7, 92, 100, and 52%, respectively, in comparison with the natural forest soils. The shoot and root dry weights of F. moluccana when grown in the post bauxite mining soils were also lower than those from the natural forest soils. However, there was no difference in the shoot and root dry weights of A. saman when grown in the two soil types. The results suggest that opencast mining decreases the soil fertility, which in turn inhibits the initial growth of tree seedlings, and reduces the carbon stock in the land.

Variations in Soil Chemical Parameters of Long Term Sugarcane Growing Alfisols under Contrasting Cropping Conditions at Sevanagala, Sri Lanka

This study was conducted to determine the variability of soil pH, macronutrients and Na contents in long term sugarcanegrowing Alfisols at Sevanagala, South-East of Sri Lanka. The study site included the entire sugarcane-growing area covering its contrasting cropping systems namely, irrigated and rain-fed cultivation on low humic gley (LHG) and reddish brown earth (RBE) soils, and adjacent undisturbed soils. The mean pH of the two soil types was significantly different and ranged from 4.5 to 9.3. Except some soils under rain-fed cultivation with a pH less than 5.5 in RBE soil and a pH greater than 7.5 in LHG soils, pH in all other soils favoured sugarcane growth. Plant available P content of soils were not significantly different among cropping conditions due to its wide variation. In both cropping systems and soil types there were areas with very low to nondetectable P levels. Exchangeable K content was significantly different between LHG and RBE soils with the latter having a mean concentration of 257 mg/ kg that is favourable for sugarcane cultivation. Though, the mean values are higher than the optimum range, there were K deficient patches in the studied area. Soil exchangeable Ca, Mg and Na contents were low in the study area but were significantly higher in LHG soils than in RBE soils contributing to alkalinity in the former soils especially under rain-fed conditions. The sugarcane-growing soils except LHG under rain-fed conditions showed chemical properties similar to undisturbed soils in the area highlighting their buffered nature despite long-term sugarcane cultivation. This study also emphasised the need for site-specific soil fertility management strategies for the Sevanagala sugarcane growing areas.

Variation on leaching behavior of caustic compounds in bauxite residue during dealkalization process

Bauxite residue, a byproduct of alumina manufacture, is a serious environmental pollutant due to its high leaching contents of metals and caustic compounds. Four typical anions of CO32−, HCO3−, Al(OH)4− and OH− (represented caustic compounds) and metal ions (As, B, Mo and V) were selected to assess their leaching behavior under dealkalization process with different conditions including liquid/solid ratio (L/S ratio), temperature and leaching time. The results revealed that washing process could remove the soluble composition in bauxite residue effectively. The leaching concentrations of typical anions in bauxite residue decreased as follows: c(CO32−) > c(HCO3−) > c[Al(OH)4−] > c(OH−). L/S ratio had a more significant effect on leaching behavior of OH−, whilst the leaching concentration of Al(OH)4− varied larger underleaching temperature and time treatment. Under the optimal leaching, the total alkaline, soluble Na concentrations, exchangeable Ca concentrations were 79.52, 68.93, and 136.0 mmol/L, respectively, whilst the soluble and exchangeable content of As, B, Mo and V in bauxite residue changed slightly. However, it should be noted that water leaching has released metal ions such as As, B, Mo and V in bauxite residue to the surrounding environment. The semiquantitative analysis of XRD revealed that water leaching increased the content of gismondine from 2.4% to 6.4%. The SEM images demonstrated the dissolution of caustic compounds on bauxite residue surface. The correlation analysis indicated that CO32− and HCO3− could effectively reflect the alkalinity of bauxite residue, and may be regarded as critical dealkalization indicators to evaluate alkalinity removal in bauxite residue.

Biochar applied to consolidated land increased the quality of an acid surface soil and tobacco crop in Southern China

Soil needs to be ameliorated after land consolidation because this process might decrease soil fertility, soil physical properties, and the growth of microbes, and the application of biochar is one of the soil amelioration methods. However, up to date, no relevant study has been conducted by any field experiment. The objective of this study was to investigate the biochar effect on soil improvement and crop quality. A field experiment with 5 corn stover biochar application rates (0, 1, 5, 10, 20 Mg ha−1) was conducted in an acid soil (Kandiudult soil in US taxonomy) with flue-cured tobacco as representative crop. The results showed that in comparison with 0 Mg ha−1 biochar treatment, the application of biochar decreased the soil bulk density by 13.22%, increased the > 2-mm water-stable soil aggregates by 27.38%, and the 0.25 to 2.00-mm soil aggregates by 45.57% at most. The soil pH, organic carbon, labile organic carbon, and exchangeable Ca and Mg contents increased with increasing biochar application rate. The application of biochar was also beneficial for soil microbial activities. For example, the abundance of actinomyces increased with the biochar application rate, and the maximum increase of 342.28% was recorded at the biochar application rate of 20 Mg ha−1. The application of biochar decreased the total sugar and reducing sugar contents and increased the leaf K content, thus greatly improving the leaf quality of flue-cured tobacco. Biochar applied to consolidated acid soil can play a positive role in flue-cured tobacco production and soil amelioration with regard to soil physical properties and soil nutrient supply capacity. On consolidated land, this is the first study about the effect of biochar application on quality of acid soil and crop, which strengthens the understanding about the role of biochar in soil improvement on consolidated land.

Sowing maize as a rotation crop in irrigated cotton cropping systems in a Vertosol: effects on soil properties, greenhouse gas emissions, black root rot incidence, cotton lint yield and fibre quality

Although sowing winter cereal crops in rotation with irrigated cotton (Gossypium hirsutum L.) is practised by many Australian cotton growers, summer cereals such as maize (Zea mays L.) are sown more frequently than previously. Our objective was to quantify the impact of sowing maize rotation crops on soil properties, greenhouse gas emissions, incidence of black root rot (BRR) disease and crop yields in an ongoing long-term experiment located in a Vertosol in north-western New South Wales. The historical treatments were cotton monoculture (sown after either conventional or minimum tillage) and a minimum-tilled cotton–wheat (Triticum aestivum L.) rotation. The experiment was redesigned in 2011 by splitting all plots and sowing either maize during summer following the previous year’s cotton or retaining the historical cropping system as a control. pH and exchangeable cation concentrations were highest, and electrical conductivity (EC1:5) lowest during 2012, the season following a flood event, but were unaffected by sowing maize. In subsequent seasons, with the onset of dry conditions, pH and cation concentrations decreased, and EC1:5 increased. The upper horizons (0–0.3 m) of plots where maize was sown had higher concentrations of exchangeable Ca and Mg during 2012, and 0.45–1.20 m had higher concentrations of exchangeable Na and exchangeable sodium percentage, but these differences disappeared in subsequent years. Soil organic carbon (SOC) in the surface 0.15 m was higher with maize, with differences becoming evident three years after maize was first sown but without any increases in SOC storage. Soil under maize was less resilient to structural degradation. BRR incidence was lower in maize-sown plots only during 2012. Stepwise linear regression suggested that high concentrations of exchangeable Ca and Mg in the surface 0.15 m played a role in reducing BRR incidence during 2012. Maize rotation introduced into cotton monocultures improved lint yields and reduced greenhouse gas emissions but had little impact in a minimum-tilled cotton–wheat rotation. Maize is a suitable rotation crop for irrigated cotton in a two-crop sequence but is of little advantage in a cotton–wheat–maize sequence.

Environmental Impact of Exceptional Quality Biosolids Use in Urban Agriculture

Exceptional quality (EQ) biosolids may be used to rehabilitate anthropogenic soils for urban agriculture, but research on the environmental ramifications of applying biosolids at rates to improve such degraded urban soils is scarce. The objective of our study was to compare the impacts of EQ biosolids and inorganic fertilizer applied for rehabilitating anthropogenic soils on potential nitrogen (N) and phosphorus (P) water quality impairment risk. Three EQ biosolids (composted, air‐dried, and blended with woody mulch) were applied at agronomic N rates twice per year, and once per year at a disturbed land reclamation rate (5× agronomic N rate) for vegetable production to an anthropogenic, low‐fertility subsoil. A heat‐dried EQ biosolids and inorganic fertilizer control were applied at agronomic N rates only. Leachate P was below detection, and soil water‐extractable P concentrations were low. After 2 yr, reclamation rates resulted in soil P saturation ratios greater than the recommended 30% but lower than the 65% limit. The high Fe in biosolids, low soil initial P, and high pH, exchangeable Ca, and clay content, contributed to lower soluble P. Although nitrate N (NO3–N) posed the greatest nutrient leaching risk, lysimeter‐collected mass loading of NO3–N from reclamation rates was not greater than for the inorganic fertilizer. Relatively low NO3–N losses with reclamation rates could be due to denitrification or physical protection of organic N in the high‐clay soil. Our results indicate that reclamation rates of our EQ biosolids to anthropogenic, low‐fertility, clayey subsoils have low potential for N and P water quality impairment.Core Ideas Risk of phosphorus (P) loss was low even after high P biosolids applications. Cumulative nitrate loads were similar between reclamation rates and inorganic fertilizer. Dissolved organic carbon concentrations increased after biosolids reclamation rates. Large amounts of soil nitrogen accumulated 2 yr after treatment additions.