EVALUATION OF MONOAMMONIUM PHOSPHATE AND BACTERIAL STRAINS TO INCREASE TREE GROWTH AND FRUIT YIELD IN APPLE REPLANT PROBLEM SOIL

The long-term effects of biological agents alone and in combination wi th monoammonium phosphate on tree growth and fruit production of apple trees planted on apple replant soil was studied for five years. Appli cation of monoammonium phosphate (MAP) in the year of planting increas ed shoot growth, cross-sectional trunk area and fruit yield of McIntos h on M.26 rootstock for the first two years. The application of bacter ial agents alone were not effective in increasing young tree growth ex cept BACT-1 in 1987. None of the bacterial agents increased fruit yiel d when applied alone. The addition of certain bacterial agents to MAP application increased young tree growth in various years. The combinat ion of bacterial agent B-10 and MAP reduced young tree growth and yiel d compared with the MAP treatment alone. These results suggest that th e application of MAP alone may be sufficient to alleviate the replant problem and the addition of BACT-1, EBW-4 or B8 bacterial agents to th is treatment may be beneficial to increase tree growth in some years.