Evaluating soil health in a Minnesota apple orchard: The effects of apple tree rootstock and cultivars
Ann Rogers
The Minnesota Department of Agriculture estimated that Minnesota (MN) alone has about 117 apple orchards producing around 9100 metric tons of apples every year. To increase the yield potential of our orchards, we need to improve our understanding of soil physical, chemical, and biological properties (aka. soil health). However, apple tree rootstocks and cultivars may alter soil health and aboveground traits. Therefore, we investigated the impact of two commercially successful apple cultivars (Honeycrisp® and Zestar®) and two rootstock sizes (semi-dwarf and dwarf) and their interactions on soil health in a local apple orchard located in Lake Crystal, MN. Soils were collected from five randomly selected apple trees in each cultivar with similar rootstock and, thus, 20 trees (5 replications × two cultivars × two rootstocks × one soil depth). Six soil cores were composited from the 0–15 cm depth under each selected apple tree at a radius of 0.6 m from the base of the trunk. Soils were measured for several physical, chemical, and biological soil health indicators following standard procedures. Although rootstocks had significant main effects, cultivars did not show a significant effect on inorganic N, total Ca, Mg, S, Mn, microbial activity, and microbial biomass C. However, cultivars had significant main effects on total K, available Fe, and Na. The interactions between cultivars and rootstocks were significant on total C, N, K, available Al, and Na. Out of all soil health indicators, slake test and available Na showed the most promise as the sensitive soil physical and chemical health indicators. Both interactions and main effects with rootstock and cultivars on slake test and available Na was significant. Apple rootstock–cultivar interactions should be further investigated in different locations/farms in MN to improve soil health and increase our apple orchards' yield potential.
Dr. Mriganka De
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