Multiple sprouting of the tap root - less soil penetration, less vigor, and less drought tolerance

    Improvement in the structural root system of citrus nursery trees. Observations since 1990 showed container-grown citrus nursery plants to develop less vigorously than expected in the field, specially when compared to field-grown plants.  In addition, container-grown trees seemed less drought tolerant in the field, even when budded on Rangpur lime, a highly resistant rootstock. Close examination revealed that poor structural root system could be involved as cause of the undesirable behavior of referred trees. Citrus plants produced in containers typically show significant curling of the main tap root and of the pioneer lateral roots. The worst situation is encountered in plants produced in plastic bags. Rigid containers usually have internal ridges which prevent curling of lateral roots. Another serious problem of container-grown citrus is the multiple branching of the main and lateral roots, as opposed to the typically unbranched structural-root extremities. Resulting reduction in depth of penetration and extent of soil exploration by the defective root systems seems to be related to the reduced  drought tolerance and vigor observed. The curling of structural roots can be somewhat reduced by the use of large containers and pruning of defective roots before transplant. However, special growing techniques were required to prevent multiple branching of structural roots. Resulting plants were established in the field in the last 3 years and have compared favorably with similar plants produced in the traditional system, showing visually more vigor and higher drought tolerance. This may be explained by the fact that unbranched tap roots penetrate more deeply in the soil, probably better exploring the more humid soil layers.   In addition, the usually high number of roots resulting from branching typically grow in a tight bundle, as seen in the pictures above. As all roots in the bundle increase in girth simultaneously, significant mutual interference is expected, delaying growth and reducing tree vigor. Trees with normal structural roots as in the pictures below, on the other hand, develop freely with no limitations in the root system, attaining maximum soil exploration. As a result, vigor is preserved and drought tolerance maximized.


Unbranched tap root - greater depth, more vigor, and drought tolerance.

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