EFFECTS OF AMENDMENTS, SOIL ADDITIVES, AND IRRIGATION ON TREE SURVIVAL AND GROWTH

Journal of Arboriculture, Sep 2004 by Gilman, Edward F

Root weight in the backfill soil for all amendments and additives 2 years after planting was similar to the nontreated controls. Frequently irrigated control and Stockosorb trees generated more roots in the backfill soil than trees receiving less irrigation (Figure 5). There were no other differences in root growth.

Two-hundred and seven of the 210 trees in the study survived. All dead trees died in the first 5 months after planting and were in the portion of the plot that was infrequently irrigated after planting. One tree died m each of the following treatments: Terra-Sorb, Stockosorb, and ROOTS.

CONCLUSION

In summary, 5 cm (2 in.) caliper trees planted from containers irrigated with 7.6 L (2 gal) of water three times each week [22.8 L (6 gal) per week] were less stressed in the first few months after planting than those irrigated about once every 10 days with 7.6 L (2 gal). However, all trees irrigated less frequently survived, except for three, and once they were established (about 8 months after planting), they grew at the same rate as trees that received frequent irrigation during the establishment period. The faster growth of frequently irrigated trees appeared to be due primarily to better growth in the first 8 months after planting. The faster growth during this period of regular irrigation did not continue once irrigation ceased. This result contrasts with the more drought-sensitive red maple (Acer rubrum L.), for which regular irrigation in the 24 weeks following landscape planting provided for a doubling of root growth 5 months after landscape planting (Marshall and Gilman 1998). About half of this increased growth persisted 5 years later, and trunks were 35% larger despite no irrigation after the first 24 weeks (Gilman et al 2003).

Data presented in this study must be interpreted carefully because this study was conducted in a fairly loose, agricultural field soil. This soil can by no means be construed as an urban soil typical of a downtown street side or parking lot island. Other studies found that growth improved when a large area surrounding newly planted trees (in a compacted clay soil; Nina Bassuk, unpublished) or shrubs (Schultz and Whitcomb 1975; Beeson and Keller 1998) was broken up and amended with organic matter of various types. Combined with past findings, the results of the current study appear to support the recommendation to forego adding amendments to an individual planting hole in good, noncompacted soil. There may be merit for using amendments if a large area can be amended or if soil is compacted, but more research needs to be done to test this hypothesis.

Résumé. Durant la première et la deuxième année après la transplantation dans un sol de bonne qualité, il n'y a apparemment pas eu de bénéfices obtenus suite aux amendements faits dans le sol de remblai utilisé autour de chênes de Virginie nouvellement plantés dont le calibre de tronc était de 5 cm; il n'y en a pas eu non plus suite à l'application d'additifs liquides au-dessus de la motte de terre. La croissance de la cime ne s'est pas accrue dans les deux premières années après la plantation suite aux amendements ajoutés au sol de remblai, et ce par rapport au arbres témoins. Dans la première saison de croissance suivant la plantation, les arbres irrigués fréquemment - 3 fois par semaines durant 38 semaines - poussaient deux fois plus vite que ceux irrigués durant les trois premiers mois seulement après la plantation. Il n'y a pas eu d'effet persistant de l'irrigation sur la croissance de la cime une fois que l'irrigation eut cessée. La croissance en diamètre du tronc et en hauteur des arbres traités avec le paclobutrazol (Profile(TM) 2SC) a été moindre que celle des arbres avec tous les autres types de traitements, et ce en raison de l'effet régulateur du paclobutrazol. La croissance des racines dans le sol de remblai n'a pas été affectée par les amendements ajoutés au sol au moment de la plantation et n'a pas non plus été affectée par le régime d'irrigation après la plantation dans cinq des sept traitements effectués.