The Effect of Roots Mixed in Soil on the Occurrence of Soil Sickness Syndrome in Japanese Pear

Abstract

It is not clear whether the remaining roots of the previous tree are the cause of soil sickness syndrome in Japanese pear. In this study, we investigated the gradual changes in soil sickness risk in soil mixed with pear roots, and the effects on the growth of the annual nursery of pear planted in soil mixed with roots. First, we prepared a mixed plot of fresh or dried pear roots in non-pear soil and used the rhizosphere soil assay method to assess the soil sickness risk. As the result, regardless of the dry conditions of the pear roots, the inhibition rate of soil did not change, suggesting the growth inhibitory substances were not released in the roots decomposition process. Next, we mixed dry roots in non-pear soil in a plot and planted the annual nursery of pear. As the result, the growth of the trees in the mixed pear roots was similar to that in the non-mixed soil, and it did not show the growth suppression noted in the continuous cropping soil. Therefore it was clarified that mixed roots in soil did not cause soil sickness syndrome in Japanese pear. Furthermore, after planting the annual nursery of pear in non-pear soil, when having measured gradually by the rhizosphere soil assay method, the soil inhibition rate increased with the growth of trees. This suggested that the accumulation of growth inhibitory substances in soil occured during the process of tree growth.