Management Of Acid Sulfate Soils Research Articles

Coastal Acid-Sulfate Soils of Kalimantan, Indonesia, for Food Security: Characteristics, Management, and Future Directions

Coastal acid-sulfate soils are crucial for producing crops and thus, for food security. However, over time, these soil resources experience degradation, leading to higher agro-input, lower yields, and environmental hazards that finally threaten food security. The optimal use of this fragile resource is only attained by implementing vigorous integrated water–soil–crop management technologies amid the climate change impact. This study aimed to review the distribution, properties, use, and management of acid-sulfate soils in Kalimantan, Indonesia. Acid-sulfate soils cover about 3.5 Mha of the coastal area in Kalimantan and have high acidity, high-risk iron and aluminum toxicity, and low fertility, requiring precise water management, amelioration and fertilizer application, crop variety selection, and rice cultivation technologies. Lime, biochar, organic fertilizer, compost, ash, and fly ash are ameliorants that raise pH, reduce iron and aluminum toxicity, and improve crop yield. Rice cultivation has developed from traditional to modern but needs re-designing to fit local conditions. Depending on the soil nutrient status, rice cultivation requires 80–200 kg ha−1 of urea, 50–150 kg ha−1 of SP36, 50–150 kg ha−1 of KCl, and 125–400 kg ha−1 of NPK compound fertilizer, but is affected by CH4 and CO2 emissions. Good water management impacts the effective implementation of amelioration and fertilizer application technologies. The remaining challenges and future directions for water management, amelioration, fertilizer application, crop varieties, cultivation techniques, land use optimization, climate change adaptation and mitigation, technology adoption and implementation, and resource conservation are outlined. Acid-sulfate soils remain a resource capital that supports food security regionally and nationally in Indonesia.

Management of acid sulfate soils under aerobic and anaerobic soil conditions revolves around organic matter and live plant macrophytes

In acid sulfate soils (ASS), it is well established that sulfuric soil acidity is managed by application of a neutralising agent and sulfidic soil oxidation is prevented by water table management. This review summarizes recent studies using organic matter in amelioration of sulfuric soil acidity and curtailing of sulfidic soil oxidation by discussing the changes induced on soil pH, Eh and sulfatecontents under varying soil moisture regimes. Increase in low pH, low Eh values and reduction in sulfate content have been observed in sulfuric and sulfidic soil following organic matter amendment under aerobic and anaerobic soil conditions. When organic matter co-existed with live plants, pH decreased with correspondingly high Eh values and high sulfate contents in almost all cases, even under anaerobic soil conditions. Practical consideration shows that application of organic matter by incorporation and spot application as surface mulch followed by establishment of plants under general soil use and management conditions create microniches conducive for root growth and negate the mechanisms that lead to severe acidification associated with live plants.

The role of organic matter in ameliorating acid sulfate soils with sulfuric horizons

Acid sulfate soils with sulfuric horizons (pH<4) can exert a range of negative impacts on the ecology and productivity of soils. The primary treatment for these soils is to raise the pH of the sulfuric horizons using lime. Although often effective, this treatment can be expensive and not well suited to large areas. In this laboratory study, we have investigated the possible use of plant organic matter (OM) to ameliorate: (i) “sulfuric soils” [produced by the oxidization of clayey sulfidic material (pH>4) samples to form “sulfuric horizon material” (pH<4)] and (ii) “neutralized sulfuric soils” [produced by the neutralization of peaty sulfuric horizon material (pH<4) with alkaline sandy loam]. The advantage of this approach is that organic matter is readily available and inexpensive. The experimental treatments used leaf material from Phragmites australis as the source of organic matter, which was either incorporated into the two manufactured soils or applied to the surface. After 6months of incubation under either aerobic or anaerobic soil conditions, pH, Eh and sulfate content were measured. The results showed that incorporation of OM into the sulfuric soil significantly increased soil pH, the extent depending on the moisture level. Changes in pH and sulfate content were correlated with Eh. Application of OM to the “neutralized sulfuric soil” was only partially effective in preventing acidification. It was concluded that the decomposition of OM by aerobic bacteria results in oxygen depletion, which then favors metabolic conversion of sulfates to sulfides by anaerobic bacteria. The results of this study have important implications for the broad scale management of acid sulfate soils.

Groundwater management of acid sulfate soils using controlled drainage, by-pass flow prevention, and subsurface irrigation on a boreal farmland

Sulfide-bearing anoxic sediments are found in coastal regions around the world including Australia and the Baltic. Upon lowering of the groundwater by drainage, they are oxidized and form acid sulfate soils (pH < 4) that mobilize plenty of potentially toxic metals into watercourses with serious environmental consequences. Being highly valued for their excellent crop yields, there is an urgent need to find management solutions that minimize the oxidation. In this study, possibilities to manage the groundwater with controlled subsurface drainage (CD) and subsurface irrigation (CDI), which included a vertical plastic sheet to prevent by-pass flow into the main drain, was examined on a Boreal farmland in Western Finland. During a 3-year study, the groundwater in the reference field (Ref) with conventional subsurface drainage pipes at 1.1–1.4 m depth typically dropped down to almost 2 m in the end of summers (September) due to evapotranspiration exceeding precipitation. CD delayed the groundwater drop, shortening the time of oxidation. In CDI system, the groundwater could be kept at c. 1 m or shallower throughout the summers, thereby preventing oxidation of critical sulfide horizons in the lower subsoil. Differences in total discharge and soil geochemistry features were small during the course of the study period. Salt accumulation seemed to be a small risk for crop growth but the capillary rise of acidity to the surface horizon may be increased in CDI, possibly increasing the need for surface liming. A “floating groundwater antenna,” indicating groundwater fluctuations, proved to be an easy and reliable tool to farmers for proper management of controlled drainage.

A review of acid sulfate soil impacts, actions and policies that impact on water quality in Great Barrier Reef catchments, including a case study on remediation at East Trinity

An estimated 666 000 ha of acid sulfate soils (ASS) occur within the Great Barrier Reef (GBR) catchments of Queensland, Australia. Extensive areas have been drained causing acidification, metal contamination, deoxygenation and iron precipitation in reef receiving waters. The close proximity of ASS to reef waters makes them a substantial threat to water quality. Another important issue linked with ASS is their release of soluble iron, which is known to stimulate nuisance marine algal blooms, in particular Lyngbya majuscula. Known blooms of the cyanobacteria in reef waters have been confirmed at Shoalwater Bay, Corio Bay, the Whitsunday area and Hinchinbrook Channel. Acid sulfate soils are intimately related to coastal wetland landscapes. Where landscapes containing ASS have been disturbed (such as for agriculture, aquaculture, marinas, etc.) the biodiversity of adjacent wetlands can be adversely affected. However, there is no clear knowledge of the real extent of the so-called “hotspot” ASS areas that occur within the GBR catchments. Management of ASS in reef catchments has benefited from the implementation of the Queensland Acid Sulfate Soils Management Strategy through policy development, mapping, training programs, an advisory service, research and community participation. However, major gaps remain in mapping the extent and nature of ASS. Areas of significant acidification (i.e. hotspots) need to be identified and policies developed for their remediation. Research has a critical role to play in understanding ASS risk and finding solutions, to prevent the adverse impacts that may be caused by ASS disturbance. A case study is presented of the East Trinity site near Cairns, a failed sugar cane development that episodically discharges large amounts of acid into Trinity Inlet, resulting in periodic fish kills. Details are presented of scientific investigations, and a lime-assisted tidal exchange strategy that are being undertaken to remediate a serious ASS problem.

Improvements to peroxide oxidation methods for analysing sulfur in acid sulfate soils

Improvements to peroxide oxidation methods for analysing acid sulfate soils (ASS) are introduced. The soil solution ratio has been increased to 1 : 40, titrations are performed in suspension, and the duration of the peroxide digest stage is substantially shortened. For 9 acid sulfate soils, the peroxide oxidisable sulfur value obtained using the improved method was compared with the reduced inorganic sulfur result obtained using the chromium reducible sulfur method. Their regression was highly significant, the slope of the regression line was not significantly different (P = 0.05) from unity, and the intercept not significantly different from zero. A complete sulfur budget for the improved method showed there was no loss of sulfur as has been reported for earlier peroxide oxidation techniques. When soils were very finely ground, efficient oxidation of sulfides was achieved, despite the milder digestion conditions. Highly sulfidic and organic soils were shown to be the most difficult to analyse using either the improved method or the chromium method. No single analytical method can be universally applied to all ASS, rather a suite of methods is necessary for a thorough understanding of many ASS. The improved peroxide method, in combination with the chromium method and the 4 M HCl extraction, form a sound platform for informed decision making on the management of acid sulfate soils.

Evaluation of surface and groundwater management strategies for drained sulfidic soil using numerical simulation models

The effective management of acid sulfate soils is a major issue for many coastal regions in Australia. Simulations were conducted to evaluate 4 different water management strategies that could be applied to agricultural land on the south coast of New South Wales, Australia, to minimise acid generation from acid sulfate soils. The water management strategies are compared with the existing extensively drained situation which generates and discharges large quantities of acidic pyrite oxidation products. The 4 water management strategies include elevated drain water levels using a weir, 25 mm irrigation on a 7- or 14-day cycle, and elevated drain water levels with irrigation. All of these strategies were designed to minimise the generation of acid by reducing the transport of oxygen to the sulfidic soil. Simulations were conducted for weather and site conditions experienced during a 12-month period starting in July 1997. Model simulations showed that maintenance of elevated drain water levels using a weir in the drain significantly reduced the amount of acid generated by 75% and 57%, at 10 and 90 m distance from the drain, respectively, by comparison with the existing drained state. The addition of 25 mm irrigation on a 14-day cycle to the weir simulation reduced the oxidation of pyrite by a further 1–2%. Application of irrigation only on a 7-day cycle also reduced the acid generated by 89% and 94% at 10 and 90 m distance from the drain, respectively, by comparison with the existing drained state. Irrigation on a 14-day cycle was not as successful in reducing pyrite oxidation as either the 7-day irrigation or weir strategies. Evaluation of the 4 water management options showed that significant improvements can be made with respect to the amount of acid generated by relatively simple and cost-effective land management practices.

Comparison of peroxide-oxidisable sulfur and chromium- reducible sulfur methods for determination of reduced inorganic sulfur in soil

The rational management of acid sulfate soils requires analytical methods that provide reliable and accurate data on the content of reduced inorganic sulfur; it is this fraction that produces acid during oxidation. This study compared the utility of the chromium-reducible sulfur method for determining the reduced inorganic sulfur content of soil materials with methods based on oxidation using hydrogen peroxide. The results presented here indicate that methods involving oxidation by hydrogen peroxide for the determination of reduced inorganic sulfur are subject to significant interference by even minor amounts of sulfate minerals and organic matter, resulting in inaccurate determinations of reduced inorganic sulfur contents. In the presence of even minor amounts of gypsum, methods involving oxidation using hydrogen peroxide underestimated reduced inorganic sulfur contents by up to 0·167% sulfur, whereas in the presence of organic matter these methods overestimated reduced inorganic sulfur contents by up to 0·077% sulfur per cent organic carbon. The resulting errors in the determinations of reduced inorganic sulfur by hydrogen peroxide methods were often larger than the action criteria that are currently used to identify acid sulfate soils. Consequently, there is a risk of misidentification of acid sulfate soils (either false positive or false negative) for soils with low reduced inorganic sulfur contents when hydrogen peroxide methods are used. In contrast, the results from the chromium-reducible sulfur method do not appear to be affected by interferences from either gypsum or organic matter and this method appears to be more suitable for the determination of reduced inorganic sulfur in soils than methods based on oxidation using hydrogen peroxide.