Appropriate Technology Research
hydroxide in distilled water, adjusting the pH to 8.00 ± 0.01, and diluting to 1,000 ml (Boyd and Tucker, 1992). A pH change of 0.10 unit in 40 ml of this buffer equals 0.08 meq of exchangeable acidity.
Total carbon concentration was measured with a Leco Mod
el EC 12 induction furnace carbon analyzer (Leco Corporation, St. Joseph, Michigan). Organic carbon was measured by the Walkley-Black sulfuric acid-potassium dichromate oxidation procedure (Boyd and Tucker, 1992).
Sulfur was analyzed by incinerating samples in a Leco Sulfur Furnace HP10 and titrating the liberated sulfur with standard KIO3 using a Leco Sulfur Titrator (Leco Corporation, St. Joseph, Michigan). Total nitrogen concentrations were determined with a Leco Carbon-Hydrogen-Nitrogen Analyzer CHN 600. Phosphorus was extracted from soil samples by the Lancaster (Mississippi) method for calcareous soils (Hue and Evans, 1986). The extractant is made as follows: add 900 ml glacial acetic acid, 65 g of malonic acid [CH2(CO2H)2], 120 g of malic acid [CH2CHOH(CO2H2)2], and 13.8 g of ammonium fluoride to 7,500 ml of deionized H2O; mix well to dissolve reagents; add 30 g of aluminum chloride and mix; adjust pH to 4.0 with ammonium hydroxide; dilute to 10 l with deionized water. Extraction consisted of placing 5 g soil in 20 ml extracting solution and shaking at 180 oscillations min-1 for 5 min. Phosphorus in filtered extracts (Whatman No. 1 filter paper) was determined with a Jarrel-Ash ICAP 9000 Plasma Spectrophotometer. Water-soluble phosphorus was measured by shaking 2 g soil samples with 100 ml of distilled water for 24 h and measuring phosphorus concentrations in extracts by the ascorbic acid method.
The phosphorus adsorption capacity was determined as described by Boyd and Munsiri (1996).
Cation exchange capacity (CEC) was determined as the summation of cation concentrations (meq 100 g-1) measured in neutral, 1.00 N ammonium acetate extracts of soils plus the exchangeable acidity.
The technique used to measure soil respiration was modified from a procedure of Anderson (1982).
Water samples were analyzed for total alkalinity by titration to pH 4.5 with 0.020 N hydrochloric acid and for total hardness by titration to the eriochrome black-T endpoint with 0.01
Methylenediaminetetraacetic acid (Boyd and Tucker, 1992).
Table 1. Comparison of the S-horizon thickness and total sediment depth between ponds with and without sediment removal at Samut prakarn, Thailand.
Figure 1. Map of Thailand with location of sampling area.