SOIL CONDITIONS ASSOCIATED WITH ABSENCE OR SPARSE DEVELOPMENT OF APPLE ROOTS

Abstract

Within orchards or groups of similar samples, the abundance of apple roots [Formula: see text] diameter was related to total soil porosity (Sta). Below a boundary soil porosity, roots were sparse or absent, and above this porosity, maximum root abundance tended to increase with increase in soil porosity. Depending upon soil texture, this boundary porosity varied from 29 to 39%. A previously derived model, which estimates boundary soil porosity (Stc) as a function of texture, accounted for most of these differences. If the model was correct, all boundary Sta – Stc values should have been zero and in four of six groups of samples the derived values were zero, + 1 or − 1. The greater departures from the expected in the remaining two groups (− 2 and + 4) may have been due to a tolerance of M. 12 rootstock to poor aeration and incomplete exploitation of potential rooting depth, respectively. With the exception of M. 12, apple roots were sparse or absent in samples with less than 10% air porosity at a tension of 100 cm (S100 cm). Poor development of roots in these samples was predicted by the model. In many samples with S100 cm > 10% there were few or no roots. Soil strength of many samples was within the range known to interfere with root development. For the purpose of recognizing a soil condition that will prevent apple root growth, Sta – Stc appears to be superior to the other criteria examined, i.e. Sta, S100 cm or soil strength.