Acid Sulfate Soils Research Articles

Nutrient Dynamics in Acid Sulfate Soil Treated with Dolomite and Micronutrient Fertilizers and Their Effects on the Growth of Lowland Rice

The development of acid sulfate soils for agriculture is limited by high soil acidity, high soluble Fe, and low available P, base cation, and micronutrient contents. Therefore, the application of dolomite and micronutrient fertilizer is required to improve soil and rice productivity. This study aimed to determine the effect of dolomite and Cu and Zn fertilizer on the dynamics of nutrient availability in acid sulfate soils and their effect on the growth, nutrient uptake, and yield of rice. The study was conducted in a greenhouse and arranged in a completely randomized design with 13 treatments and 5 replications. The application of various doses of micronutrient fertilizer containing Cu and Zn oxide was compared with the control and dolomite application treatments. NPK as a basal fertilizer was applied according to the recommended dose for all treatments. The results showed that the application of micronutrient fertilizer and 3 tons ha-1 dolomite effectively increased the availability of P nutrient from 13.5 to 58.3 pp and decreased the potential for iron toxicity. Furthermore, applying 6 tons ha-1 dolomite, combined with 2 tons ha-1 organic fertilizer, and 6 ml l-1 micronutrient fertilizer resulted in the highest grain yield of 91.65 g pot-1 with an increase of 19%. Meanwhile, the application of 3 tons ha-1 dolomite and a combination of 3 tons ha-1 dolomite + 2 tons ha-1 organic matter could reduce 20-30% of iron uptake by plant roots. Application of dolomite and micronutrient fertilizers increases the productivity of soil and rice on acid sulfate soils.

Yield Characteristics of Mutiara Merah Rambutan Varieties (Nephelium lappaceum) Planted in Marginal Soil

The study was started to assess the early performance of rambutan yield characteristics planted on marginal sandy tin-tailing soil. The experiment was carried out for one year in a plot of 4-year-old rambutan cultivar at MARDI Kundang, Rawang, Selangor, Malaysia. Varieties of Mutiara Merah were used. Data from the plants as a measurement of yield characteristics was recorded. Mutiara Merah proved that it can be well-yield and cultivated on sandy tin-tailing soil. Mutiara Merah showed that it can be planted and farmed effectively on sandy tin-tailing soil, according to the results of the previous research. It can grow and be useful in boosting rambutan yield. Taking into account the fruit yield parameters as well as yield character components parameters such as fruit weight, seed weight, fruit diameter, flesh thickness, brix, and flesh weight, it can be concluded that rambutan cultivation in marginal tin-tailing soil was found promising for producing higher yields. More field studies are needed to standardize agro-techniques and establish the fertilizer requirements of chemical and organic fertilizers for higher yield in other marginal soils such as peat, bris, and acid sulphate soil, as well as create various value-added products to utilize excess produce.

Salinity and acid sulfate soils of the Vietnam Mekong Delta: Agricultural management and adaptation

Salinity and acid sulfate soils of the Vietnam Mekong Delta: Agricultural management and adaptation

Amelioration of acid sulphate soils in Nilwala river basin

Paddy tracts of Nilwala basin has been affected by the implementation of Nilwala Flood Protection and Drainage Project in 1979 due to excessive drainage, and nearly 7000 acres of land is abandoned. The water table goes down to the level of 50 cm below soil surface during dry periods and soil pH falls to 3-4 causing acid sulphate condition. Hitherto several efforts have been made to ameliorate the paddy lands but no any economical solution is obtained. The National Science Foundation project to find out the feasibility of using natural hydraulic forces to increase water table to keep the acid sulphate forming minerals at bay and to cultivate rice in these paddy lands. Water table fluctuation in relation to water level in the drainage channel was studied over one year and there was found a very high correlation (r2=0.985) indicating a possibility of increasing water table by heading up water in the channel. Simulated pot experiment showed that increasing water table to 15 cm below soil surface allows rice to grow effectively, showing plant survival of 112 (53%) compared to 28 (15%) plants in control. Recorded plant height of Bg. 357 variety was 35 cm compared to 22 cm in different treatments and control, respectively. Soil pH also increased to a value closer to 6.0 in the treatment which is conducive for rice cultivation. However, the low values of plant survival and plant heights were due to unusual extreme low rainfall in 2020/21 Maha season compared to 10 years’ average. SAARC J. Agric., 20(2): 211-221 (2022)

Optimizing a Biowaste Treatment Design for Energy and Environmental Efficiency of an Integrated Farming System in Tien Giang Province

Agricultural wastes can be converted into biofuels. To meet the requirements of biofuels, the conditions of their manufacturing process for these products must be considered. The purpose of this research is to optimize experimental designs for converting biomass into energy products like pyrolysis and pelleting process. The products were optimized in terms of their energy performance while lowering CO2 emissions. In Tien Giang province, we experimented with pyrolysis and pelleting biowastes derived from an integrated farming system in acid sulfate soil. The experimental factors influencing the energy content of products were determined using statistical analysis and optimization methods, and the potential CO2 emissions from the products were calculated. The optimization results revealed that the ideal pyrolysis parameters were 120 minutes of combustion time at 400oC and 30% moisture content of orchard pruning residues. The best pellets were obtained by combining biogas sludge and biochar from mango pruning residues. These products will store approximately 900 kilograms of CO2 emissions a year. The optimized processes would benefit the environment and bring profits to the system.

Dosis Kombinasi Bioarang Sekam Padi dan Berbagai Amandemen di Tanah Sulfat Masam

This study aims to determine the effect of various doses of rice husk biochar combined with organic amendments of cow manure and inorganic amendments of recommended fertilizer packages (urea, TSP, and KCl) on acid-sulfate soils. Over four months, the study was conducted in the Experimental Land of the Center for the Assessment of Agricultural Technology (BPTP) Pal IX, West Kalimantan Province. The study employed a randomized block design, with treatments including control soil, rice husk biochar 6 t ha-1, rice husk biochar 8 t ha-1, rice husk biochar 10 t ha-1, rice husk biochar 12 t ha-1, package of recommended inorganic fertilizer, package of recommended inorganic fertilizer + rice husk biochar 10 t ha-1, manure 10 t ha-1, and 10 t ha-1 + rice husk biochar 10 t ha-1. The findings revealed that single rice husk biochar amendments and their combination with inorganic and organic amendments had varying effects on the improvement of several physical properties of acid sulfate soils (density, total pore, moisture content, and penetration resistance). The amendment of a single biochar with a dose of 12 t ha-1 resulted in the lowest bulk density of acid sulfate soil, which decreased by 16% compared to the control soil. At a dose of 12 t ha-1, rice husk biochar produced the highest porosity and soil moisture content, 55% and 17%, respectively. The soil strength, as measured by the lowest penetration resistance, decreased by 30% in the treatment of manure 10 t ha-1 + biochar 10 t ha-1 (350 N cm-2) compared to the control soil.
 
 Keywords: biochar rice husk, soil amendment, soil properties of acid sulphate

Role of biochar amendments in improving the properties of acid sulphate soil

Acid sulfate soils have potential for agricultural development. However, this soil has various properties problems that can inhibit plant growth. One way to improve soil properties is through the application of biochar amendments. The study aimed at knowing the role of rice husk biochar combined with amendments to Chromolaena odorata, rice straw, and rice husk ash to improve the properties of acid sulphate soil. The study was conducted in a greenhouse and arranged in a complete randomized design (CRD) with three replications. Biochar amendments consisted of nine kinds, namely, without amendments (control), C. odorata (10 t/ha), rice straw (10 t/ha), rice husk biochar (10 t/ha), rice husk ash (10 t/ha), C. odorata (10 t/ha)+rice husk biochar (5 t/ha), rice straw (10 t/ha)+rice husk biochar (5 t/ha), C. odorata (10 t/ha)+rice husk ash (5 t/ha), and rice straw (10 t/ha)+rice husk ash (5 t/ha). The results showed that the amendment of rice husk biochar combined with amendments to C. odorata and rice straw, respectively, had a good effect on improving soil physical properties, namely, total soil pores, reducing soil content weight and soil strength. Its effect on soil chemical properties was that it could increase pH, C-organic, P-available, cation exchange capacity (CEC), lower Al-dd and Fe soluble. The research findings showed that applying biochar and organic amendments to Chromolaena odorata and rice straw could potentially improve the properties of acid sulphate soil. In future research, we recommend increasing the carrying capacity of acid sulphate soil against plant growth, and it can be done by improving soil properties through the organic amendments’ application of C. odorata or straw enriched with rice husk biochar.

Problems, Management, and Prospects of Acid Sulphate Soils in the Ganges Delta

Soil is a finite natural resource and is indispensable for human civilization because it is the medium for food production for the biosphere. Continued soil degradation is a forerunner of catastrophe for the living world. The protection of healthy soils and the restoration of problem soils are strongly needed in the current agricultural scenario as competition for urbanization and other human needs for land resources limits the scope for the further availability of land for agriculture. Naturally occurring degraded soils, such as acid sulphate soils, can be restored with scientific interventions and advanced management strategies. The Ganges Delta is a densely populated region, where the inhabitants’ major livelihood is agriculture. Soil acidity and salinity restrict crop performance in this coastal region, particularly the acid sulphate soils (ASSs) posing a risk to agriculture. ASSs are developed from land-use changes from mangrove forest to agricultural land in this region. There is no systematic study on these soil types covering Bangladesh and India. This paper unfolds several aspects related to the characteristics, problems, and detailed management strategies of ASSs relevant to the Gangetic Delta region where these soils continue to be used for intensive agriculture to meet the livelihood needs. Crop yields are very poor in the unmanaged ASSs due to a very low soil pH (<3.5), hampering the growth and development of crops due to nutrient deficiencies and/or toxicities, coupled with soil salinity. There is toxicity of water-soluble Fe, Al, and Mn. The phosphorus nutrition of crops in these soils is affected owing to a high soil P fixation capacity. A deficiency of micronutrients, such as Zn and Cu, was also observed; however, K availability is variable in the soil. The soil acidity is a general problem throughout the soil profile; however, extreme acidity (pH < 3.5) in particular soil horizons is a typical soil characteristic, which creates problems for its efficient management. Specific operations, such as the selective use of soil layers with good properties for crop root growth, major and minor nutrient applications, and soil amendments, including green manuring, application of biofertilizers, and soil microbes, are gradually improving the properties of these soils and bringing back the potential for good crop production. Scientific water/drainage management is needed to gain an agronomic advantage. Evidence of increased crop yields in these soils observed from green manuring, lime, basic slag, and rock phosphate application are presented.

Application of Earthworm Manure (EWM) and NPK Fertilizer to Improve the Quality of Acid Sulphate Soil (ASS) as a Sweet Corn (Zea mays L) Cultivation Land in North Sumatra, Indonesia

A field trial has been carried out in order to study the use of Earthworm Manure (EWM) and NPK fertilizer to improve the quality of Acid Sulphate Soil (ASS) as a sweet corn (Zea mays L) cultivation land in North Sumatra. The experiment was a Factorial Randomized Block Design. Factors studied were Earthworm Manure (EWM) and NPK fertilizer. The EWM treatment was arranged in 4 doses consisting of: Control (0 kg EWM / plot), 0.4 kg EWM / plot; 0.8 kg EWM / plot; and 1.2 kg EWM/plot. NPK treatment was given in 4 doses consisting of: control (0 kg NPK / plot); 5 g NPK / plot; 10 g NPK / plot; and 15 g NPK / plot. The treatment of EWM material was applied by mixing EWM with topsoil of ASS at a depth of about 5 cm evenly in each trial plot when it was 1 week before sweet corn plant was planted. While NPK fertilizer treatment was given between the rows of plants when the plants are 2 weeks old. Each treatment was given in each trial plot with a size of 100 cm x 100 cm and was repeated 3 times. The plant spacing was set at 60 cm x 70 cm, the distance between replications was 50 cm, and the distance between treatment plots was 30 cm. Variables observed include some soil properties, growth and crop yields. Soil properties were measured consisting of: pH (H₂O), total N (Kjeldahl), P (Bray II), Exchangeable-K (K-ex) (NH₄OAc pH 7.0). Growth and yield of plants were also determined including: plant height, stem diameter, and crop yield. The results obtained showed that the application of EWM could improve the quality of ASS properties shown by the increase in the total N content, available P, exchangeable-K, and ASS pH and plant growth based on stem diameter growth. NPK application increases total N content, available P, and K-ex, but does not increase growth in height, stem diameter, number of leaves, and crop yields. Application of EWM increases pH, whereas NPK has no effect on ASS pH. The effects of EWM and NPK interact positively on total N content where the application of EWM increases the effect of NPK on total N content; the effect of EWM was better in improving the chemical properties (N, P, K, and pH) of ASS and plant stem diameter growth compared with NPK application. EWM can be used to improve the quality of chemical properties (N, P, K, and pH) and partially or completely substitute NPK sweet corn plants in ASS so as to save on the use of NPK fertilizer. Therefore, EWM has the potential as an alternative agrobiotechnology product that has the opportunity to be used to overcome the problem of ASS as agricultural land.

Gallionella and Sulfuricella populations are dominant during the transition of boreal potential to actual acid sulfate soils

Acid sulfate soils release metal laden, acidic waters that affect the environment, buildings, and human health. In this study, 16S rRNA gene amplicons, metagenomes, and metatranscriptomes all demonstrated distinct microbial communities and activities in the unoxidized potential acid sulfate soil, the overlying transition zone, and uppermost oxidized actual acid sulfate soil. Assembled genomes and mRNA transcripts also suggested abundant oxidized acid sulfate soil populations that aligned within the Gammaproteobacteria and Terracidiphilus. In contrast, potentially acid tolerant or moderately acidophilic iron oxidizing Gallionella and sulfur metabolizing Sulfuricella dominated the transition zone during catalysis of metal sulfide oxidation to form acid sulfate soil. Finally, anaerobic oxidation of methane coupled to nitrate, sulfate, and ferric reduction were suggested to occur in the reduced parent sediments. In conclusion, despite comparable metal sulfide dissolution processes e.g., biomining, Gallionella and Sulfuricella dominated the community and activities during conversion of potential to actual acid sulfate soils.

Effects of Various Liming Materials on the Growth of Rice under Rainshelter Condition

A study was conducted to evaluate the effects of liming materials on the growth of rice under rainshelter conditions and MR 219 rice variety was used in this experiment. The treatments were: 1) T1, no application of lime, 2) T2, 4 t ha-1 of ground magnesium limestone (GML), 3) T3, 2 t ha-1 of hydrated lime, 4) T4, 20 L ha-1 of liquid lime. It was found that the application of 4 t ha-1 of GML had produced the highest rice yield of 8.2 t ha-1. The result showed that as panicle length increase, spikelet per panicle also increases. Relative rice yield is negatively correlated with the soil pH, and this indicates that as soil acidity increase (observed with pH between 2 to 3), the rice yield decrease and vice versa. At harvest, the soil pH exceeded 6 for all the treatment. It was also observed that as soil exchangeable Ca increase, soil pH also increases. Among the treatment, soil treated with 2 t ha-1 of hydrated lime gave the highest exchangeable Ca in the soil of 11.86 cmolc kg-1 soil with Ca concentration of 0.12% in the root. It was observed that liming increases soil pH and exchangeable cations in the soil. Therefore, liming is essential to ameliorate the acid sulfate soils for rice cultivation.

Potential of Phosphorus Solubilizing Purple Nonsulfur Bacteria Isolated from Acid Sulfate Soil in Improving Soil Property, Nutrient Uptake, and Yield of Pineapple (Ananas comosus L. Merrill) under Acidic Stress

This study aimed to (i) evaluate purple nonsulfur bacteria (PNSB) strains possessing the highest phosphorus (P) solubilizing capacity in field and (ii) determine the efficacy of PNSB biofertilizers in improving soil quality, P uptake, growth, and yield of pineapple cultivated in acid sulfate soil (ASS). A field experiment was conducted in a completely randomized block design with two factors, including the first factor as P fertilizer levels (0, 50, 75, and 100% P) based on recommended fertilizer formula (RFF) and the second factor as supplementation of biofertilizers containing P solubilizing PNSB (no inoculated PNSB, Rhodobacter sphaeroides W48, R. sphaeroides W42, and a mixture of R. sphaeroides W48 and W42). The results indicated that the supplementation of PNSB biofertilizers led to an increase of 25.3–33.9% in soluble P concentration in soil compared to control treatment. Among the selected PNSB strains, R. sphaeroides W42 and a mixture of the PNSB in biofertilizers solubilized all insoluble P fractions (Fe-P, Al-P, and Ca-P) and strain W48 in biofertilizers for Fe-P and Al-P. Furthermore, the supplementation of biofertilizers from R. sphaeroides W48 and W42 individually and their mixture raised plant height by 3.56–4.10% and available P concentration by 25.3–33.9%. Total P uptake in pineapple treatments with biofertilizers from mixed PNSB was 42.9% higher than that in the control treatment ( p < 0.05 ). Application of mixed PNSB strains can reduce 25% P of chemical fertilizer, but the pineapple yield rose over 12.1%. Both R. sphaeroides W48 and W42 are potent for use as crop yield enhancers to obtain the sustainable pineapple cultivation under acidic stress.

Improvement of Glutinous Corn and Watermelon Yield by Lime and Microbial Organic Fertilizers

Background. The characteristics of acid soil, often low pH and high toxicity, affect the growth and yield of plants. Aims. This study evaluates the effects of supplemented lime and microbial organic fertilizer on glutinous corn (Zea mays) and watermelon (Citrullus lanatus) yield, yield components, and economic efficiency on acid-sulfate soils. Materials and Methods. Two experiments were carried out in Phung Hiep District, Hau Giang Province, as a typical acid-sulfate soil area. The randomized complete block with four treatments and three replicates was designed for the experiment, in which supplemented fertilizers were 800 kg of lime/ha; 2,000 kg of microbial organic fertilizer/ha; and 800 kg of lime in combination with 2,000 kg of microbial organic fertilizer/ha, and treatment as farmer dose (FFT), without lime and microbial organic fertilizer. Results. As a result, using lime combined with microbial organic fertilizer increased the yield compared to using only lime or microbial organic fertilizer. Besides, the incomes increased to 12.0% and 13.8%, respectively, compared to farmer recommendations. Conclusion. To improve the yield of glutinous corn or watermelon and income on acid-sulfate soils, lime should be applied at 800 kg combined with 2,000 kg of microbial organic fertilizer/ha.

Acid sulfate soils: A challenge for environmental sustainability

Acid sulfate (AS) soils contain sulfidic compounds formed in anaerobic conditions. In aerobic conditions, they will oxidize to sulfuric acid, which commonly lowers the pH to 3 – 4. These soils cover approximately 10,000 km2 in Finland, mainly on the western coast, and over 170,000 km2 globally. Acidity and the metals dissolved from the soil matrix and leached out of the soil are serious threats to aquatic biota. Initially, AS soils were regarded as an exclusively agricultural problem, but since the 1970s nearly all studies of AS soils have been environmentally motivated. Awareness of these soils has also risen in forestry, peat mining, and in engineering projects. Liming and water management are the key methods toward the sustainable use of these soils.

Improving Soil Properties and Rice Yield on Saline-affected Acid Sulfate Soil by Controlled-release Fertilizer

Background: To determine the effectiveness of controlled slow-dissolving NPK fertilizers with NPK 19-16-18 to improve soil nutrients on rice (Oryza sativa L.). Methods: The field experiment was on saline-affected acid sulfate soil in Hau Giang province, Viet Nam, in the Winter-Spring rice crop 2018-2019. The experiment consisted of 2 treatments, corresponding to 2 formulas and 2 types of fertilizers, including new generation fertilizer application with the formula 50N-40P205 -30K20 kg/ha; and conventional fertilizers of 126N-88 P205-23K20. Each formula with 3 replications and each repetition is 1,000 m2. Result: The NPK-CFR fertilizers and urea humate help improve proper soil nutrients and total micro-organisms. In which; (i) when compared to the farmer’s control field, the rice growth and yield were comparable and did not differ significantly (5.68 tons/ha in the farmer’s control field and 5.85 tons/ha in the experimental field). (ii) However, when compared to the farmer’s field, the amount of fertilizer in the experimental field is reduced by more than 50%. Besides, the economic efficiency of NPK-CFR and Urea humate is higher than in farmers’ fields, from 1 to 8.6%. The total profit is higher than farmers’ fields. The NPK-CFR fertilizers and urea humate can be used to replace traditional fertilizers.

One-way flow system for improvement of the acid sulfate soil reclamation process in the Belanti II tidal swamp irrigation network, Central Kalimantan, Indonesia.

Belanti II tidal irrigation network was developed in 1980 on acid sulphate soil with an area of approximately 3976 ha. Belanti II has one primary channel and several secondary channels, without any water structures that regulate the direction of flow. Two-way flow occurs in the channel, supplying fresh water from the river at high tide and flowing back into the river at low tide. This two-way flow system inhibits the leaching process of acid sulphate soil. Up to now, acid sulfate soils are still found at a depth of 50-75 cm with a pH of 2.5 ~ 3.5. A one-way flow system is expected to improve water circulation, assisted by channel rehabilitation, collector channels and water control structures. The spillway structure at the secondary channel regulates the freshwater supply at high tide and the flap gate at the end regulates the flow of water to the collector channel at low tide. Hydraulic analysis was carried out using HEC-RAS modelling. The results showed the ability of the system to supply fresh water, flushing/leaching acid sulfate water and drainage the toxic water. The effectiveness of the system is evaluated regarding the direction and the volume of freshwater flowing into the secondary channel.

Backswamp Development’s Effects on Water Management System of Tidal Swamp Irrigation Palingkau SP1 SP2 SP3, Kalimantan, Indonesia

The Palingkau SP1 SP2 SP3 swamp irrigation is an expansion of handil’s agricultural area, which is influenced by tides from the Kapuas River on the left and the Kapuas Murung river on the right. The new area that exploits backswamp and the buffer zone upstream of Handil, gives an additional burden of dispersion of toxic materials resulting from the oxidation of acid sulfate soils and the loss of fresh water supply from backswamp. The actual leaching process is indicated by the water pH value in the collector and primary channels ranging from 2.58 ~ 3.6. Meanwhile, the water quality of Handil, Kapuas and Kapuas Murung rivers is better, ranging from 3.7 ~ 5.34. The confluence of tidal from two opposite sides has resulted in the disruption of pollutant discharge. Instead of discharged into rivers, its flow to Handil’s agricultural area and reduce agricultural productivity. The HEC RAS software simulation model is used to evaluate the optimal water management system. One-way flow system is introduced hydraulic structures for regulating the flow of freshwater water at high tide from the left handil into the new irrigation area and regulating the drainage at low tide through the right handil.

Norms Establishment of the Diagnosis and Recommendation Integrated System at Preflowering in Pineapple (Ananas comosus L.) and Its Verification in Case of Nutrient Omission Trial by Two Consecutive Crops

ABSTRACT This study was conducted to (i) establish the diagnosis and recommendation integrated system (DRIS) for the macronutrient and micronutrient status of pineapple at the preflowering stage and (ii) verify the reliability of the established norms for macronutrients. We collected 86 pineapple leaves at sites +1 and +3 from 86 fields of pineapples grown in acid sulfate soil (ASS) and analyzed their nutrient content. Findings revealed the establishment of 12 and 20 nutrient ratios for DRIS norms at pineapple leaf sites +1 and +3. Based on omission fertilization of N, P, K, Ca, and Mg at the first crop, the DRIS index of N, P, K, and Mg was inadequate in treatments lacking the corresponding nutrients, whereas the DRIS index in the treatment fully fertilized with N, P, K, Ca, and Mg was negative and lower at the +3 leaf position. In the second crop, the DRIS norms were highly reliable via the negative DRIS index when fertilizing without N, P, K, Ca, and Mg. By contrast, when fertilizing with N, P, K, Ca, and Mg, the DRIS index was positive or less negative. The DRIS norms established that position +3 is robust and suitable for evaluating the pineapple macronutrient status.

Effects of liming on oxic and anoxic N2O and CO2 production in different horizons of boreal acid sulfate soil and non-acid soil under controlled conditions

In acid sulfate (AS) soils, organic rich topsoil and subsoil horizons with highly variable acidity and moisture conditions and interconnected reactions of sulfur and nitrogen make them potential sources of greenhouse gases (GHGs). Subsoil liming can reduce the acidification of sulfidic subsoils in the field. However, the mitigation of GHG production in AS subsoils by liming, and the mechanisms involved, are still poorly known. We limed samples from different horizons of AS and non-AS soils to study the effects of liming on the N2O and CO2 production during a 56-day oxic and subsequent 72-h anoxic incubation. Liming to pH ≥ 7 decreased oxic N2O production by 97–98 % in the Ap1 horizon, 38–50 % in the Bg1 horizon, and 34–36 % in the BC horizon, but increased it by 136–208 % in the C horizon, respectively. Liming decreased anoxic N2O production by 86–94 % and 78–91 % in Ap1 and Bg1 horizons, but increased it by 100–500 % and 50–162 % in BC and C horizons, respectively. Liming decreased N2O/(N2O + N2) in anoxic denitrification in most horizons of both AS and non-AS soils. Liming significantly increased the cumulative oxic and anoxic CO2 production in AS soil, but less so in non-AS soil due to the initial high soil pH. Higher carbon and nitrogen contents in AS soil compared to non-AS soil agreed with the respectively higher cumulative oxic N2O production in all horizons, and the higher CO2 production in the subsoil horizons of all lime treatments. Overall, liming reduced the proportion of N2O in the GHGs produced in most soil horizons under oxic and anoxic conditions but reduced the total GHG production (as CO2 equivalents) only in the Ap1 horizon of both soils. The results suggest that liming of subsoils may not always effectively mitigate GHG emissions due to concurrently increased CO2 production and denitrification.

Land Use and Soil Type Exert Strongly Interactive Impacts on the pH Buffering Capacity of Acidic Soils in South China

Soil acidification is a severe environmental problem around the world. Soil pH buffering capacity (pHBC) is the intrinsic factor affecting the soil acidification rate and is intensively impacted by anthropogenic and natural conditions. However, composite assessments of the effects of land use and soil type on soil pHBC are still limited. Therefore, we collected samples of five soil types (red soil, lateritic red soil, latosol, paddy soil and acid sulphate soil) from two land use patterns of agricultural and adjacent forest fields at different depths (0–10 cm, 10–20 cm and 20–30 cm) in South China, aiming to investigate the effects of land use and soil type on soil pHBC in this region. The results show that land use, soil type and their interactions greatly influence soil pHBC and physico-chemical properties. Forest soils have a significantly higher pHBC (11.40–49.50 mmol·kg−1 soil·unit−1 pH), cation exchange capacity (CEC), exchangeable Al3+ (EAl3+) and clay content than agricultural soils. Acid sulphate soil has the highest pHBC (49.27–117.83 mmol·kg−1 soil·unit−1 pH) values and exchangeable acid (EA) content among all investigated soil types, whereas lateritic red soil has the lowest pHBC (10.56–31.71 mmol·kg−1 soil·unit−1 pH). In agricultural fields, soil pHBC is positively related to CEC, soil organic carbon (SOC) and EA, indicating that agricultural soils may be in a cation exchange buffering stage. The soil pHBC of forest fields is positively correlated with SOC and EAl3+, implying that forest soils may be in the Al buffering stage. In conclusion, soil pHBC would vary with different land use forms and soil types, in which a series of key complex physico-chemical processes and interactions would occur to regulate soil pH buffering capacity.