Growth and Yield of 'Honeycrisp' Apple Trees with Preplant Inoculation with Mycorrhizae and Soil-Incorporated Compost

Abstract

Preplant soil-incorporated compost, mycorrhizal inoculation (MI) at planting and the combination of the two (compost+MI) were tested over nine years for growth, yield and foliar analysis of 'Honeycrisp' apple (Malus xdomestica)trees on two rootstocks, M.26 EMLA and G.16 planted in a site with mild replant disease. Mycorrhizal inoculation, measured in years 1, 5, 7 and 8, had no effect on foliar levels of most nutrients. Foliar Zn was increased by MI in year 5 from 14 to 17 mg-kg ^-1in G.16 rootstock, but not with M.26 compared to an untreated control. In year 7, foliar Cu was increased from 7 to 8 mg-kg ^-1by MI. Leaf N was higher with compost amended soil in years 2 and 3, lower in year 4, and similar to an untreated control in years 5 to 8. Leaf P and K were generally greater with compost until years 4 to 5 when they were similar to the untreated control. Levels of Ca, Mg, B, Mn and Fe were inconsistently affected by compost from year to year. Compost increased shoot growth in year 2, but not when combined with MI. In years 1 and 3, compost had no effect on shoot growth. MI did not affect shoot growth in years 1 or 2, but increased it in year 3 in G.16 trees, but not M.26. In the first three years, trees produced very sparse bloom. In year 4, compost increased the number of flower clusters in both rootstocks, but not in M.26 rootstock when compost was combined with MI. In year 5, compost did not increase bloom. MI did not affect bloom in years 4 and 5. MI did not affect trunk cross sectional area (TCA) of G.16 in any year when compared to the untreated control. Compost increased TCA of G.16 in years 3 and 5, but not when combined with MI, and this combined treatment reduced TCA in year 4 compared to compost alone. MI increased TCA of M.26 in years 3, 4, 5, 7, 8 and 9. Compost increased TCA of M.26 in years 3, 4, and 5, and when combined with MI, increased TCA in years 3 and 5, but not in year 4. MI did not affect yield until year 8 for G.16 when it was reduced compared to the control. MI increased yield of M.26 in year 9, but had no effect in other years. Compost and compost+MI increased yield in years 6 and 8 in both rootstocks, and had reduced yield in trees on G.16 rootstock in years 7 and 9 as a result of biennial bearing. Compost and compost+MI trees on M.26 rootstock had reduced yield in year 9. Cumulative yield from years 4 through 9 was not affected by rootstock, compost or MI. The addition of compost or MI was found to increase tree growth and yield, but these effects were inconsistent between the two rootstocks and did not occur consistently in every year.