HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Figures Only Full Text Free Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Angeles, O. R. Articles by Buresh, R. J. Search for Related Content PubMed Articles by Angeles, O. R. Articles by Buresh, R. J. Agricola Articles by Angeles, O. R. Articles by Buresh, R. J. Related Collections Redox Processes Soil Analysis Soil Chemistry

Soil Chemistry

Soil Solution Sampling for Organic Acids in Rice Paddy Soils

International Rice Research Institute (IRRI), Crop, Soil, and Water Sciences Division, DAPO Box 7777, Metro Manila, Philippines

^* Corresponding author (sarah.johnson{at}cgiar.org)

Low molecular weight organic acids (OA), which are intermediates in the anaerobic decomposition of straw incorporated into submerged soils, have been implicated in causing toxicity to young rice (Oryza sativa L.) seedlings. The objective of this study was to develop a method for measuring OA in soil solution in field and greenhouse studies. Three methods of soil solution sampling were evaluated: zero-tension displacement (ZTD), variable-tension centrifugation (CFG), and medium-tension suction sampling through porous tubes (PT). All solution samples were analyzed for OA by high performance liquid chromatography (HPLC) using an ion exclusion column. Use of cation exchange membrane resin strips during sample collection to sorb interfering cations improved OA recovery. Comparison between sampling methods of the OA concentration in soil solution extracted from soil amended with reagent OA was as follows: PT = CFG >> ZTD. Variables between methods that could cause artifacts in OA measurement were tested systematically: solution pH after sampling, headspace gas pressure during sampling, and sorption to sand or soil layers. No artifact effects were observed, and it was concluded that the tension methods sampled a different fraction of soil solution than the zero-tension method. Since the tension methods extracted a higher concentration of OA, they are recommended for studies comparing treatment effects on OA production. However, it was beyond the scope of this study to determine which soil solution fraction is more relevant to OA toxicity studies with rice seedlings. Between the two tension methods, PT was more convenient for repeated sampling from the same location compared to the destructive nature of centrifugation.

Key Words: CEMR, cation exchange membrane resin • CFG, centrifugation • HPLC, high performance liquid chromatography • OA, organic acids • PVC, polyvinvyl chloride • PT, porous tube • PT-S, porous tube in sand • UV-VIS, ultraviolet–visible • ZTD, zero-tension displacement