Early Pinus caribaea var hondurensis root development 2. Influence of soil strength

The influence of penetration resistance (PR), an easily measured indicator of soil strength, on the growth of Pinus caribaea var. hondurensis radicles and seedlings was investigated. Negative exponential relationships between PR and both radicle and primary root elongation were observed. All root elongation ceased at PR levels of 3.25 MPa. Tip diameters of radicles and primary roots were positively correlated with PR values up to 2.4 MPa, whilst numbers of primary roots, total root lengths and lengths of longest roots were all negatively correlated with PR. Hypocotyl elongation was also reduced by increasing PR, although the reductions occurred at higher PRs than those which inhibited root development. In contrast, primary shoot development was unaffected by PR levels which were sufficient to stop root elongation, but was reduced in soil with a PR of 4.8 MPa. There were significant family x soil type and family x PR interactions for radicle, hypocotyl, primary root and primary shoot development. If these interactions are correlated with performance in the field, then they may serve as useful indicators of family suitability to both soil type and high strength soils.