Isotope-labelling of plant materials to study carbon, nitrogen and sulfur dynamics in soils

Issue Date

8-2005

Abstract

A labelling technique to produce large quantities of plant materials multi-labelled with¹⁴C,¹⁵N,³⁵S and¹³C,¹⁴C,¹⁵N was developed to study the fate of residue-derived C, N and S following incorporation into the soil. Flemingia (Flemingia macrophylla), medic (Medicago truncatula) and rice plants were grown in pots and labelled with¹⁵N and³⁵S by adding¹⁵N and³⁵S solutions every 4 days for 6 weeks. A labelling chamber measuring 2.5 x 1.3 x 1 meters constructed from aluminum and PVC frames and covered with ethyl-vinyl alcohol film, was used to label the plant materials with¹⁴CO₂and¹³CO₂. Labelled CO₂ was generated inside the chamber by the reaction of Na₂¹⁴CO₃ or Na₂¹³CO₃ with lactic acid and circulated by a commercial air-conditioning unit set in recycling mode. The level of CO₂ within the chamber was monitored using an infrared gas analyzer (ADC Type 225 MK3 CO₂ Analyzer). The ¹⁴C-, ¹⁵N-, ³⁵S-labelled plant materials were used in a glasshouse experiment to monitor the decomposition process and trace the fate of residue-derived C, N and S in the presence of a millet crop. The labelled residues of medic hay and Flemingia leaves were dried, cut into 2-3cm length and incorporated into a sandy loam soil at a rate of 3 tons/ha. Results showed that medic hay had a faster decomposition rate than Flemingia , with almost of its ¹⁴C disappearing after 41 days. The addition of medic hay resulted in significantly higher ¹⁵N and ³⁵S recoveries in the first millet crop and lower ¹⁵N and ³⁵S recoveries in the soil. Flemingia leaves released smaller proportions of ¹⁵N and ³⁵S that resulted in higher ¹⁵N and ³⁵S recovery in the soil and in the second crop of millet. The isotopic enrichments attained were sufficient to show major differences between medic hay and Flemingia leaves as residues with respect to their usefulness as nutrient source and to the sequestration of carbon in the soil. A plant residue with a rapid decomposition rate like medic can provide an immediate source of nutrients particularly for short-duration crops; a residue that decomposes slowly like Flemingia results in a gradual release of nutrients and hence can have longer impact on crop growth.

¹³C,¹⁴C,¹⁵N, ³⁵S, crop residue, decomposition, Flemingia, isotope-labelling, Medicago, medic hay, millet, nutrient release, nutrient tranportation, rice

Source or Periodical Title

Philippine Journal of Crop Science

ISSN

0115-463x

Volume

30

Issue

2

Page

21-28

Document Type

Article

Frequency

tri-quarterly

Physical Description

schematic diagram, tables

Language

English

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