Vermiculite's strong buffer capacity renders it unsuitable for studies of acidity on soybean (Glycine max L.) nodulation and growth.
BACKGROUND
Vermiculite is the most common soil-free growing substrate used for plants in horticultural and scientific studies due to its high water holding capacity. However, some studies are not suitable to be conducted in it. The described experiments aimed to test the suitability of vermiculite to study the effect of acidity on nodulation and growth of soybean (Glycine max L.).


METHODS
Two different nutrient solutions (Broughton & Dilworth, and modified Herridge nutrient solutions) with or without MES buffer addition were used to irrigate soybean grown on vermiculite growth substrates. The pH of nutrient solutions was adjusted to either pH 4.0 or 7.0 prior its use. The nodulation and vegetative growth of soybean plants were assessed at 3 and 4 weeks after inoculation.


RESULTS
The unsuitability of presumably inert vermiculite as a physical plant growth substrate for studying the effects of acidity on soybean nodulation and plant growth was illustrated. Nodulation and growth of soybean grown in vermiculite were not affected by irrigation with pH-adjusted nutrient solution either at pH 4.0 or 7.0. This was reasonably caused by the ability of vermiculite to neutralise (buffer) the pH of the supplied nutrient solution (pH 2.0-7.0).


CONCLUSIONS
Due to its buffering capacity, vermiculite cannot be used as growth support to study the effect of acidity on nodulation and plant growth.
ARC Centre of Excellence for Integrative Legume Research, and School of Agriculture and Food Sciences, The University of Queensland, St, Lucia 4072, Australia. a.indrasumunar@uq.edu.au.
Arief
A
Indrasumunar
Peter M
PM
Gresshoff
D000538:Aluminum Silicates / Q000737:chemistry / Q000494:pharmacology*; D002021:Buffers; D006863:Hydrogen-Ion Concentration; D055170:Plant Root Nodulation / Q000187:drug effects* / Q000502:physiology; D018517:Plant Roots / Q000187:drug effects / Q000502:physiology; D018520:Plant Shoots / Q000187:drug effects / Q000502:physiology; D012987:Soil / Q000737:chemistry*; D013025:Glycine max / Q000187:drug effects* / Q000502:physiology
D000538:Aluminum Silicates; D002021:Buffers; D012987:Soil; C003760:vermiculite