Submitted to: Acta horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/10/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Apple orchards under organic management have a very different regimen of fertilizer types than conventional orchards. Very little work has been done to understand how new apple rootstocks that are more efficient at absorbing essential plant nutrients like nitrogen, potassium, phosphorous and calcium behave under organic management. This research focused on how well several new apple rootstocks absorbed major nutrients and micro-nutrients like iron, manganese, zinc and copper by monitoring levels of those nutrients in fruit and leaves of mature trees. A few rootstocks like G.890 and G.484 were superior in their ability to uptake essential nutrients and promote growth and productivity in the organic orchards tested. These features, when combined with the added disease resistance (replant and fire blight) make them a reasonable choice for new organic apple orchards.

Technical Abstract: A substantial percentage of apple orchards in the U.S. are being managed according to the USDA Certified Organic standards which precludes the use of synthetically derived chemical fertilizers and pesticides. One of the major challenges faced by organic orchardists is to provide proper nutrition to apple trees to achieve high productivity, particularly with greater weed competition and the use of organic fertilizers. Apple rootstocks have been shown to influence the mineral nutrient composition of leaf and fruit tissue in orchards under conventional management; however, there is little information about their nutrient use efficiency under organic management. We monitored the content of phosphorous (P), potassium (K), calcium (Ca), sulfur (S), iron (Fe), manganese (Mn), and copper (Cu) in leaves and fruit of three experimental orchards using Energy-Dispersive X-ray Fluorescence (XRF) for two seasons (2022-2023). Two of the plantings (Geneva and Ithaca, NY) are part of the 2015 organic NC-140 trial and feature 11 commercial rootstocks grafted with the scab resistant scion cultivar ‘Modi®’, whereas the third trial established in 2013 in Albion, NY features 18 commercial and experimental rootstocks grafted with ‘Crimson Crisp’. In Geneva, the 2022 and 2023 XRF data showed that Geneva®(G) 969, G.41, G.935, and G.222 contained greater leaf S which has been shown to have a strong correlation with leaf N concentration. In Ithaca, the 2022 and 2023 XRF data showed that G.890 had consistently higher S, P, and K levels. Rootstocks G.11 and G.214 displayed lower levels of S in both locations and both years. Other nutrient levels were somewhat inconsistent between locations and years in the NC-140 trials. In the Albion organic trial rootstocks, G.484, G.890, G.222, and CG.5030 displayed higher levels of leaf P and S (measured by ICP in 2014 and 2016). Rootstock CG.4003 displayed consistently higher levels of Ca in leaves and fruit in the XRF data, as well as the ICP data. Multivariate analysis using mean ICP and XRF leaf nutrient data found significant similarities for Ca and K perhaps validating the usefulness of the XRF instrument to calculate rootstock influenced K/Ca ratios. While seven rootstocks were common at all experimental locations, the interaction of different scion cultivars, ground floor management, soil type, and fertilizer applications may have contributed to the low levels of correlation among other nutrients. Due to their overall nutrient use efficiency, G.890, G.484, G.222, and perhaps G.935 are well suited for organically managed orchards.