Preplant soil-incorporated compost, mycorrhyzal innoculation (MI) at planting, and the combination of the two were tested for growth and yield increase of `Honeycrisp' apple trees on two rootstocks, M.26 and G.16. Compost was added at a rate of 0.51 m3 per tree. Within each main plot of compost or no compost were planted four trees with two on each rootstock. Noncompost plots were fertilized with N in year 1 and N, K, and Mg in year 4. The MI had no effect on growth until the third and fourth years after planting when annual trunk growth and tree height were greater than the untreated control. Compost increased trunk growth in the third and fourth years, but decreased growth in the fourth year when combined with MI. G.16 had greater trunk growth and tree height than M.26 in years 3 and 4. Fruiting was delayed by pruning at planting, so trees fruited for the first time in the fourth year. Bloom and yield were not increased by MI. There was more bloom and yield on G.16 than on M.26. Yield of G.16 was increased by compost from 0.08 to 1.2 kg/tree. The combination of MI and compost increased bloom compared to the control, but not yield, which was 0.3 kg/tree. Compost increased bloom but not yield of M.26, since this rootstock had low yield when planted in compost, 0.2 kg/tree, and none when planted without compost.
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