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Assessing the sustainability of agricultural soils under acid deposition in the Northeast Region of Thailand | |
Author | Nawas, Rab |
Call Number | AIT Diss. no.EV-11-07 |
Subject(s) | Soil acidity--Thailand, Northeastern Soils--Environmental aspects--Thailand, Northeastern |
Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Environmental Engineering and Management |
Publisher | Asian Institute of Technology |
Series Statement | Dissertation ; no. EV-11-07 |
Abstract | The rapid increase in developmental activities has caused numerous atmospheric problems and acid rain is one of them, which causes a variety of damaging effects on almost all the ecosystems. This study assesses the sustainability of agricultural soils under acid deposition in the Northeast region of Thailand. It also determines the acidity ranking and vulnerability of agricultural soils to acid deposition in the study area. Three selected soil series {Korat (Kr), Pak Chong (PC) and Phon Pisai (PP)} cover a very large area and are very important from agricultural production perspective in the Northeast region. Soil samples were collected at the depth of 0-30 cm from the undisturbed agricultural fields. Soil samples were prepared for basic soil analysis and soil column leaching experiments in the ambient environmental laboratory. Soil samples were air dried, crushed, sieved (mesh size 2 mm) and mixed thoroughly to get the homogeneous samples. Laboratory experiments were carried out by leaching soil columns (having dimensions 30×15 cm2) with acid rain (AR) solutions {pH 5.0 (existing AR), 4.0 (10 times AR), 3.0 (100 times AR) and 2.0 (1000 times AR)} and non-acidic water (pH 7.0) as control treatment in three cycles, each cycle having a duration of 15 days with five days interval between cycles. Total sprinkling volume for 45 days (24.38 L) represented the average annual rainfall (1379.1 mm) in the Northeast region. Representative soil samples were characterized for basic properties (soil pH, CEC, TEB, SOM, texture, etc.) prior to leaching experiments and for soil base cations (Na+, K+, Ca2+ and Mg2+) and trace elements (Fe2+, Al3+ and Mn2+) before and after the experiments. During the sprinkling effluent (leachate) samples were collected after every five days and analyzed for base cations and trace elements immediately in the laboratory using Inductively Coupled Plasma-Atomic Emission Spectroscopy. F-test was performed for all the obtained data from leachate analysis with a statistical significance at α = 0.01. Regression analysis was also employed to correlate soil pH and soil base cation losses with acid rain pH. Results showed that leaching of base cations from the investigated soils increased significantly as pH of acid rain decreased. Severe leaching losses occurred at pH below 4.0, which has been observed in some areas of Thailand. The maximum concentrations of Na+ in effluent samples were found in acid rain with pH 2.0 i.e. 20.39, 26.11 and 30.14 mg L-1 for Kr, PC and PP soil, respectively. Acid rain with pH 2.0 caused the highest leaching concentrations of K+ in effluent e.g. 9.7, 12.43 and 20.78 mg L-1 from PC, Kr and PP soil, respectively. The maximum leaching concentrations of Ca2+ in leachate samples were also caused by acid rain with pH 2.0 i.e. 453.8, 884.3 and 928.0 mg L-1 from Kr, PP and PC soil, respectively. Highly acidic treatment (pH 2.0) caused the maximum concentrations of Mg2+ in leachate samples i.e. 101.9, 121.1 and 131.7 mg L-1 from PP, Kr and PC soil, respectively. Acid rain induced leaching of quite large amounts of base cations from the investigated soils. Leaching losses under highly acidic treatment (pH 2.0) amounted to 37.6, 56.9 and 57.0 mg Na+ per kg soil, 11.1, 18.6 and 39.8 mg K+ per kg soil, 263.1, 2215.2, 1939.8 mg Ca2+ per kg soil and 63.6, 291.9 and 219.8 mg Mg2+ per kg of soil from Kr, PC and PP soil, respectively. The leaching amounts of these cations were smaller in pH 3.0, but several times higher than those in pH 7.0. There were very good correlations between acidic levels of treatments and leaching amount of base cations. Results depict that leaching of K+ and Mg2+ from soils by acid rain was a serious agricultural problem for highly weathered soils, as K+ and Mg2+ are very important nutrients required for the growth of crop plants. Leaching of base cations by acid rain is also associated with unfavorable environmental consequences due to the contamination of groundwater resources. Highly acidic treatments (pH 3.0 and 2.0) caused a significant and profound ivleaching of toxic elements (Al3+, Fe2+ and Mn2+) from the investigated soils. Higher leaching of toxic elements out of the soil would cause contamination of groundwater, which is also associated with unfavorable ecological consequences. After the termination of leaching experiments, soil columns were removed carefully from the cylinders, cut into three layers (10 cm each) and characterized for residual base contents and extractable trace elements. Amounts of residual exchangeable base cations decreased under highly acidic treatments, particularly in the surface layer of the soils. Exchangeable base cations (particularly Ca2+ and Mg2+) were intensively depleted by acid rain with pH 2.0 and 3.0 from tropical soils. In contrary, residual soluble base cations increased under highly acidic treatments. Mobilization of aluminum, iron and manganese increased as the pH of acid rain decreased below 4.0. Extractable aluminum was found to be higher than threshold level at highly acidic treatments. Soil acidity developed in different soil layers by acidic treatments was also measured. Soil acidity was quantified by developing quadratic polynomial equations. Significant decrease in soil pH was observed with a decrease in acid rain pH. This is because of leaching of base cations from the soil layers. Maximum soil acidity development was found in the upper soils’ layers due to migration of base cations downwards. Maximum increase in acidity in the entire soil column (0-30 cm) was observed in Korat soil amounting 50.5, 34.0 and 8.4 %, followed by Phon Pisai soil reaching 47.1, 22.0 and 9.9 % and Pak Chong soil reaching 45.3, 17.8 and 4.4 % under acidic treatments with pH 2.0, 3.0 and 4.0, respectively. Highly acidic treatment (pH 2.0) changed all the investigated soils to extremely acidic soils due to profound leaching of base cations. Highly acidic treatment (pH 2.0) changed vulnerability of Korat soil series from very low vulnerability (V) to high vulnerability (II), while vulnerability of Pak Chong and Phon Pisai soil series changed to moderate vulnerability (III). GIS software (ArcMap) was used to develop soil maps which indicated soil acidity ranking and soil vulnerability to acid deposition in the Northeast region of Thailand. Leaching losses of plant nutrients for a long period of time from the root zone in the agricultural soils would decrease soil fertility and lower agricultural production. Remobilization of soil aluminum, iron and manganese to accumulate in the deeper soil layers would cause rhizotoxicity. Soil acidity developed by acid deposition in the tropical soils would reduce the availability of nutrients required for plant growth. Soil acidification is unfavorable for agricultural production due to reduced availability of plant nutrients (N, P, K, S, Mo, etc.) and decreased activity of soil microbes e.g. bacteria. Acid deposition on highly weathered soils would cause the leaching of nutrient cations and toxic elements, depletion of exchangeable base cations, mobilization of toxic elements to phytotoxicity levels and development of soil acidification. These all effects are associated with reduced soil quality, sustainability and food security, and accelerated contamination of water resources and unfavorable ecological and agricultural consequences. Improving energy efficiency can play a key role in controlling emission of acidifying gases (SO2 and NOx). Hence, there is a demand of developing effective countermeasures to reduce or at least control the emission of acid rain precursors in Asian developing countries to achieve sustainability. Energy conservation together with alternative energy sources can play a major role in energy planning in the future. Energy efficiency should also be improved to reduce atmospheric emissions. Strong economic growth in Southeast Asia is expected to increase energy requirement. There is a need of demand shift from non-renewable to renewable energy sources. This study can be very useful for environmental scientist, agricultural specialist and policy makers to make efforts in controlling emissions in the Southeast Asian region |
Year | 2011 |
Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. EV-11-07 |
Type | Dissertation |
School | School of Environment, Resources, and Development (SERD) |
Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
Academic Program/FoS | Environmental Engineering and Management (EV) |
Chairperson(s) | Preeda Parkpian |
Examination Committee(s) | Tripathi, Nitin Kumar ;Hathairatana Garivait ;Patana Anurakpongsatorn |
Scholarship Donor(s) | Higher Education Commission, Pakistan ;Asian Institute of Technology Fellowship |
Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2011 |