Release of phenolic compounds from apple residues decomposing in soil and the influence of temperature on their degradation

Investigations have been performed on phenolic compounds and allelochemical effect in soil from an apple orchard enriched with 1% apple leaves or roots and stored for 3 months at different temperatures (-5°C, +5°C and 20°C). As a result of the addition of apple residues to the soil its phenolic content increased 4-fold in the case of leaves and 7-fold in the case of roots. Temperature played a key role in the changes of phenolic compounds occurring in the soil. Their level did not decline at all for 3 months at -5°C, whereas at +5°C it decreased by 20% in the soil with the addition of leaves and by 40% in the soil with the addition of roots. A temperature of +20°C had a stronger influence: after 3 months the level of phenolics decreased to that observed in the control and in the soil with the addition of leaves and in this one with roots. The allelochemical effect of the soil with apple residues had mainly a stimulating activity, but it also showed its highly significant negative correlation with the content of phenolic compounds. This suggests that apple residues as a source of phenolics, when occurring locally at high concentrations, may also have an inhibitory effect. A negative allelochemical effect can be maintained by low temperature in winter, which is not conducive to phenolic degradation.