THE EFFECT OF COMPOSTED MUNICIPAL WASTE AS A SOIL AMENDMENT ON THE GROWTH OF YOUNG CITRUS TREES AND PHYTOPHTHORA-NICOTIANAE

Phytophthora nicotianae attacks citrus fibrous roots, causing decay an d reduction of tree growth. One-year-old Orlando tangelo trees on Cleo patra mandarin rootstock were planted in a newly established grove at Lake Alfred, FL, which had received broadcast composted municipal wast e (CMW) 3 mo. before planting. Trees were planted by either amending w ith additional CMW incorporated into the backfill or with no amendment . Half of the trees in each nonamended and CMW-amended treatment were inoculated with P. nicotianae. Stem diameters of CMW-amended trees wer e 17% greater than for nonamended trees after 2.75 yr. At times, soil populations of P. nicotianae were significantly higher in the CMW-amen ded treatment than in non-amended soil. Root density was not significa ntly affected by CMW treatment, but was reduced by P. nicotianae. Ther e was a significant interaction between CMW and P. nicotianae with res pect to tree growth, due to the apparent increase in P. nicotianae act ivity in the presence of CMW. After 2 yr, fruit yield from compost-ame nded trees was significantly higher than yield from nonamended trees.