Abstract
BackgroundVermiculite 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.).MethodsTwo 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.ResultsThe 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).ConclusionsDue to its buffering capacity, vermiculite cannot be used as growth support to study the effect of acidity on nodulation and plant growth.
Highlights
Vermiculite is the most common soil-free growing substrate used for plants in horticultural and scientific studies due to its high water holding capacity
Treatment effects on nodulation and growth of soybean Nodule number was not affected by all treatments tested
At week 4, soybean watered with B & D nutrient solution had less nodule dry weight than soybean watered with Herridge medium of pH 4.0, but not a significant to other treatments (Herridge medium pH 7.0, Broughton and Dilworth (B&D) medium pH 4.0 and 7.0)
Summary
Vermiculite is the most common soil-free growing substrate used for plants in horticultural and scientific studies due to its high water holding capacity. Vermiculite is the mineralogical name given to hydrated laminar magnesium-aluminium-iron silicate ((Mg, Fe, Al) ((Al, Si)4O10)(OH)2.4H2O). It is an expandable 2:1 mineral and often forms from alteration of mica [1]. Vermiculite is the most common physical growth substrate used for plants in horticultural and scientific studies due to its high water holding, inert chemical nature, moderate level of aeration, absence of substrate for microbial growth and effective cation-exchange capacities compared to sand or gravel to promote better plant growth. Marx and Zak [5] found that vermiculite was not suitable for studying the effect of pH on mycorrhizal formation of slash pine (Pinus elliottii), as this substrate neutralised the pH of Melin-Norkrans nutrient solutions added to this medium
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