Involvement of soluble organic matter in increased plant growth in solarized soils

Although soil solarization is used to control soil-borne pests, it also res ults in increased growth response (IGR) of plants, beyond the effect of pes t control. IGR is attributed to various abiotic factors (e.g. increased min eral nutrient concentrations) and biotic factors. In this work, we studied the role played by dissolved organic matter (DOM) in soil extracts in the I GR. DOM concentrations were about twice as high in solarized soil than in u ntreated soil. In two out of three soils, solarization appeared to increase amino acid synthesis, indicating that it had a favorable effect on microbi al activity. Elemental composition, carbohydrate levels, E-4:E-6 ratios and FTIR spectra did not differentiate between DOM extracted from solarized so ils and DOM extracted from untreated soils. Growth of corn plants increased with increasing concentrations of DOM. Addition to the soil of DOM extract ed from leonardite increased populations of fluorescent pseudomonads, known as beneficial bacteria, and reduced fungal populations. We conclude that t he increase in DOM concentration following soil solarization is a potential ly positive plant-growth-enhancement factor.